How Many Solar Panels & Batteries Do You Need For Your Off-Grid System?

How do you figure out how many solar panels you need on your home? If you are just trying to run lights and maybe a refrigerator, it is not too hard to determine the number of panels and batteries yourself.

Understanding How Much Power You Need

So how do you figure out how many solar panels and batteries you need? The first step is to determine how much power the appliances and lights you intend to run draw. There are a couple of ways to determine this.

The wattage of a UL listed/approved appliance can usually be found near the AC power cord. This may be in amps or watts. If it is in amps, a simple formula will let you convert it to watts: Volts x Amps = Watts. In other words if your appliance draws 4 amps, the formula would be 120 x 4= 480 watts.

Another method is to use a Kill A Watt Electricity Usage Monitor. This is an inexpensive device that monitors how much power your appliance uses. If you don’t have the patience for math calculations and want quick answers, this is probably the best way to go!

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The average refrigerator use varies from as low as 200 watts for a new Energy Star refrigerator to as high as 600 watts for an older unit. At startup, your refrigerator may have a higher draw, so you want to err on the high side when you figure how many watts of power you need. Also, determine the wattage of any lights or other items you intend to run.

How much solar power do I need to run a refrigerator and lights?

Once you have determined the wattage, you need to run all your appliances. Determine how many hours each day they will run. For instance, your refrigerator can run approximately 1/3 of the time during a 24 hour cycle, or 8 hours a day. The light that draws 75 watts may run 3 hours a day. Once you have determined how many watts you use a day from each appliance, add them up to give you the daily watt-hour results.

For example

  • Refrigerator 1600 watts
  • Lights 400 watts
  • Misc 400 watts
  • ———–
  • Total 2400 watts daily watt-hours

Now, to allow for bad weather when the sun doesn’t shine, multiply the daily watt-hour result by three. This provides a buffer, in case you aren’t able to recharge the batteries on a daily basis.

Because you should not discharge the batteries below 50%, multiply this number by 2. This will give you the total battery capacity your system needs to store to run for three days. Or in this example, 14400 watts.

What size of battery bank?

Now we will calculate the size of the battery bank you will need in amp hours. Amp hours are used because this is the standard by which batteries are rated. This is determined by dividing the total battery capacity required by the voltage of your batteries.

For example, if your system requires 14400 watts, you would divide 14400 by 12, which would show that you need 1200 amp hours. Divide the total amp hours by the amp hour rating of your batteries and you will have the number of batteries you need. For example, if you have deep cycle batteries rated at 300 amp hours, you would need 4 batteries. The Vmaxtanks brand is one of the highest rated deep cycle battery brands that I have found.

Factor in the solar panels

With these calculations in hand, how many solar panels do you need? Again, this is just a matter of a math calculation.

Divide the daily watt-hours by the wattage of your solar panels, times the number of hours of sun. If you have a 75-watt panel and 5 hours of sun per day, you would produce 375 watts per day per panel. Now divide the daily watt-hours by the wattage produced by one solar panel. Using the 2400 daily watt-hour figure from the above example, you would divide the 2400 by 375 and need 6.4 panels. Always round this off to the higher number.

For this system you would need seven 75-watt solar panels and four 300-amp hour batteries. If you were using 200-watt panels, you would need only three panels and four 300-amp batteries.

If you’re intrigued with solar power and its uses, in this article I explain a simple way to turn a simple 12-volt battery pack into a small solar generator and more explanation for building a small solar system here. A portable solar system on wheels is another versatile option for solar power and in this article you can see photos and simple instructions.

I recommend learning the fundamentals of solar power on small projects like these and then using that knowledge on larger projects, such as a system to power a home or man cave.

Over the years, my family and I have used a number of small solar-powered gadgets and batteries around the house. Read this article to learn about creating a solar powered garage.

See also  The Four Core Elements You Need for Wilderness Survival

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227 thoughts on “How Many Solar Panels & Batteries Do You Need For Your Off-Grid System?”

  1. Anonymous Citizen

    Very timely, thank you. We are in the process of specifying a solar system for our ranch.

    The panel estimation seems very accurate. For example, we consume about 1500 kWh per month, which averages out to about 50 kWh per day, or 50,000 watt-hours per day. The panels we are considering are 250W, multiplied by 5 sunny hours, gives us 1,250W output per day per panel. 50,000 / 1,250 indicates 40 panels. However, assuming some DC-AC conversion loss, divide that by an expected system efficiency of 0.85 gives us 48 panels, after rounding up.

    My confusion comes in with your formula for battery bank capacity. Why 3 days worth of storage? Even on cloudy days, there will still be some energy production. We are considering the Trojan 2V – 1110Ah batteries in series to create a 48V battery bank. If we take our daily usage of 50,000 Wh * 3 days * 2 for the 50% depletion, that gives us a figure of 300,000 Wh. Divide that by the 2V batteries, each with 1110 Ah capacity, gives us 136 batteries required. Something seems off there.

    Can anyone help shed some light on this?

    1. You asked about 3 days, this is to give you a good power reserve. With a system the size of yous you may be able to make this smaller and just plan on using less power if faced with a situation in which the batteries are slow to charge. I know that there are some variables that come into play with a system this large of which I am unaware. I am glad to see that you are using the 20 amp hour figure instead of the hundred. I would also double check and see if my daily usage was really that high. Yours is well above average.

      1. admin said ” I would also double check and see if my daily usage was really that high. Yours is well above average.

        I’m right there with Anonymous Citizen as in my household we use adv of 1400kw per month over a years period. Still have 2 adult kids living with my wife and I using too much IMO.

    2. 50kwh per day really ? You should try doing some conservation before trying to live on solar. Sounds to me like you haven’t looked into enough low energy alternatives to normal electricity usage in this country. Do some research. You shouldn’t ever use electric heaters of any kind including water heaters on solar, low energy light bulbs are a must and turn those things off when you leave the room. No electric grow lights either. Solar requires a bit of a lifestyle change.

    3. Actually you have every calculation correct with the exception of the batteries. The wattage on those Trojans are 1110 ah x 2v = 2220 wh per battery. But batteries are rated on 20 hrs of use. So it’s 2220wh x 20= 44400wh per batteries. You are calculating 50% battery use so it’s 44400 x.50= 22200. So here we go!
      300,000 divided by 22200= 13.5 batteries so I would go for 16 16 batteries to be on the safe side if I was you. But I would double check those figures with a pro first.

    4. Looking into solar not tied into utility company.We want to set up solar panels just in emergency situations, ie hurricanes. Have whole house generator but that only buys you so many days. Would really only run a small refrigerator and small chest freezer, possibly a washing machine.

      1. Phyllis, your whole house generator should run on natural gas, which would continue running for a very long time, even in a power outage. Natural gas companies don’t turn off the flow of gas through their lines, even after an earthquake, because it’s more dangerous to get the gas flowing again through emptied lines. Regarding the purchase of a solar generator, research how many watts are required by the 3 appliances you list and then find a generator with that amount of power, or more. Remember that it takes more wattage in the power surge required to initially start these appliances.

        1. >I am off the grid in zip code 85936. I purchased the place in 2006. It was built in 2004. I have 12 5A/H panels. They show “fractures” and the panels are putting out 2.5 dc each according to each gauge that is connected to each panel. I have a 1000 A/H battery bank that no longer holds a charge. What would the cost be per panel to replace? Where would I find 5a/h solar panels? I need 12.

          5 a/h panels are 5 amp hour panels. That means they collect from the sun 5 amps every hour of full sunlight. I have 12 of these mounted on the roof of my pumphouse:

          5 a/h x 12 Panels = 60 a/h

          The 12 panels produce 60 amps for every hour of sunlight.

          Considering full sun for 8 hours of one day, that is 480 a/h being collected by my battery bank which is a 1000 amp battery bank. That is 20 batteries at 100 amps each.

          If therefore I do not use any energy, I could theoretically collect enough energy in two 8 hour days of sunlight to fully charge my battery bank. 480×2=960 of a 1000 amp battery bank

          The problem is that the panels are 16 years old and i think they are producing only half of this energy. So I am maybe in need of new panels. So I am looking for panels to replace these and retain the integrity of my solar system.

    5. You will need 136 48v batteries
      24*2=48v. So you will need 9792 2v batteries to acquire the 3 day KWH. Plus you will need the appropriate BMS(Battery Management System) to protect your batteries and property. Then you will need to monitor the entire system and balance at least weekly.

  2. Your Calculation, for the most part, is accurate. If you are using 50KWhrs of Energy per day and you want to have 3 days worth of back up (at 50% Depth of Discharge max) and you may want to use the 2V Trojan cells at 48V per string. you will need a total of ~300KWhrs of batteries. That’s a big battery! That would be nearly ~6 parallel strings of each 24 series-connected 2V Trojan cells (assuming 1100 Ampere Hours per cell).

    I would recommend using ONE string of 24 cells in series each at 2V and 2200Ahrs or higher which will give you approximately 1.5 days of autonomy. I would also highly recommend using Lithium Ion instead of Flooded Lead Acid. I know they are 2X or 3X the cost, but look at their cycle life performance and also usable energy curves. You will be much happier. Although, I must say if you end up using the Trojan Industrial line RE series they are very nice as well and we have had good performance with them.

    Also keep in mind that you have to size up your system considering an energy balance vs. peak power analysis throughout the day. Use and Excel sheet and write-down every appliance and power user for your building on each row. Add the hour by hour power usage (in Watts) for a 24 hour period in columns. estimate when various loads will be on etc.

    Total up horizontally and then vertically. Plot the data and see what your peak production looks like (in Watts). Multiply per hour peaks by the percent of time they are on for that hour and you will get hour by hour KWhrs (energy). Total up all the hour by hour energy numbers horizontally so you have a total energy use per day (should be around 50KWhrs as you have already figured out). Also look at what your critical loads are during the autonomy days. Also add min and max for your PV system during cloudy days and sunny days at your latitude. Also make sure you are using NOTC data from your PV not STC.

    Add other factors for your battery, besides DOD and the KWhrs you have calculated. Make sure you consider the operating temperature of the batteries. Also don’t forget that your batteries provide the current for the load at 48V and your actual usage after your inverter (assuming your building is at Split phase 120V/240V.) make sure you have the peak current in mind when you are sizing up your system. Remember that the battery and system voltages are at dangerous lethal level. be careful!

    These are all just a few guidelines. I would highly recommend getting a system designed, installed and tested by a local professional in the OFF-Grid/ Grid-Interactive with battery back up business. Hope this helps.

  3. Very informative article! Solar panels are such a great way to save money and protect the environment. In my opinion, it’s definitely an investment worth looking into. Thanks for sharing!

  4. This Article is very timing for us thank you. I do have some question,i.e. from which country better get solar panel and also the battery ?

  5. George Brechtefeld

    Please can you provide an accurate advice of how many solar panels 200 watts each and how many baterries to run a deep freezer consuming 75wats

    1. I see that they have tested and rated the new f150 EV to be able to run what they called the essentials in a home for 3 days off the battery and a full loss of power. My question is whether you can purchase those type batteries for storage of solar power to run a home. I know my current electric vehicle has a 68kwh battery and you can buy that replacement for around $8k. Can you use this type battery as a power cell for your home power?

  6. You need to know what the average electrical consumption is for a 24 hour period. Get a watt-meter and plug it in between the outlet and your freezer for 24 hours and this will tell you actual consumption. You should do this on a typical summer day and a typical Winter day to get a more accurate average. Let’s say that is 1 kWh in a 24 hour period. So then you need to size your solar for this. Determine your average solar insolation for your area. For example say you get 5 hours equivalent to full sun then one 200 watt panel would give you the equivalent of 1 kWh. BUT when you factor in losses and factor in the need to power the freezer during a cloudy day this will not be adequate. SO I would suggest you add at least 50% to cover losses incurred in charging the battery, in extracting power from the battery and inverter losses converting to AC. Then you have to factor in the likelyhood of cloudy days. Where I live it’s cloudy from September to May. Most books will tell you to have enough reserve to survive three days without sun. SO that means multiply your one 200 watt panel times 150% to cover losses and times 3 to have enough reserve for cloudy days. That gives you 900 watts, just to be on the safe side round that up to 1000 watts. Then there are the batteries. This is more complicated and depends on unknowns so I can’t give you an answer. Probably at least two good 12V deep cycle batteries but it could be 4 depending on various factors.

  7. Can an expert on solar panels give me the number of solar panels and batteries to power a house with the following.
    14 lights
    1 chest Freezer
    1 Refrigerator
    4 ceiling Fans

    1. Douglas David.

      You would need to know how many watts each uses per day or watts used total per day.
      Example on lights. You could be using 100watt bulbs or 60watt bulbs or led and each will give you different usage for the same amount of time it is on.
      Your freezer and Fridge don’t run constant they cycle so you need to know how many watts they use in a day.

      1. Thanks for answering these questions, Richard. I actually just got a job in the solar industry and hope to be able to share some of what I’ll be learning here on Preparedness Advice.

  8. following is my usage
    1 ) one 2 hp 3 ph 230 volt with drive
    2 ) 1 ph 230 volt { 1 hp }
    how huge i will require the solar panel to run the machine for 10 hrs a day { 7 am to 5 pm }

    1. shoaib hashim

      If they run 10 hours per day then you can calculate the wattage by this formula: amps x volts = watts.
      Your usage would then be watts x the 10 hours.

    1. “solar system for our ranch.” Did you see that it is not a house in town! Maybe several outbuildings to deal with and a few high watt use items that can’t be just not used or turned down? I hate it when people always assume it is a waste of energy instead of needed use of energy! Also what difference does it make maybe he just want to cover what he want to use. I have a house built in 2003 have leds for lights and in the summer I use 38 KWHs a day and am not cool all day or night! I turn off everything when not in the room or in use.
      I wish that when a question is asked and as many details given as he did everyone just answer what they can and not get on the save more band wagon!

  9. I know it’s a whole year later, but I wanted to share what we ended up putting together. Our needs were very similar to Anonymous Citizen.

    We ended up with a 12kV hybrid system that we are very happy with. We were also very happy with the subcontractor that helped with installation. I really don’t see how we could have put a system like this together without their help. See pics:

    1. Most golf cart sized deep cycle batteries eg Trojan t-105 can hold around 200-230 amps capacity at 6 volts. with a total of 1200 watts capacity, they make 12 volt batteries in the same form factor too but hold less amp hours like around 100 ah, but still with a total capacity of 1200 watts since they are higher voltage eg. volts × amps = watts. Figure for a max cycle discharge of 50% so usable energy = 600 watts Per battery. Energy required is 12000 watts so 600×20 batteries = 12000 watts not including lossses incurred with converting the power from low voltage dc to high voltage ac at about 15% loss, so stored power required would actually need to be 13800 watts ÷ 600 watts Per battery = 23 t-105 style batteries or 2300 amps at 6 volts or 1150 amps at 12 volts etc. Keep in mind 23 6 volt 200 ah batteries is including the 50% discharge value that you should not go below to maintain decent battery life.

  10. I just installed a system in Baja MX and the installer used 2 250 watt panels(good inverter and wired correctly) but I am concerned that the batteries( 2 200 amph 12 volts each) is not enough battery storage. We operate a 6 amp(120 volt 16 cubic refer and 4 lights(led 20 watts each) Plenty of sun all day and we only use the cabin for 4 days a month. Does this seem adequate?

  11. Simple formula for estimating how many solar panels and batteries you need?

    First use a kill-A-watt meter and calculate 24 hour usage. That will be your daily usage in kilowatt hours.

    Second understand batteries. I am only going to talk about the big #27 marine and 6 volt golf cart batteries. Whether 100 amps @12 volts or 225 amps @6 volts, these batteries will only give you back about one kilowatt for an hour each.
    Yes I know the math says a little bit more, but you have losses in both charger and inverter.

    To get that kilowatt hour back in your batteries, your panels have to put in 100 amp hours from the sun before it sets.
    In a perfect world that you use 1 Kwh per day. One 100 watt solar panel in 10 hours of strong sunlight every day into your battery and you are self sufficient.

    In the real world never drag your batteries below %50 charge.
    Double above number.
    Its cloudy every other day?
    Double number again.
    Only 5 hours of sun?
    Double yet again.

    Now we are at 800 watts of panels and 8 batteries for your kilowatt per day. That’s how it works in the real world,but at least you have a week of power at your place after the sun goes out.

    Quick recap:
    A battery will give you 1 kilowatt for one hour.
    A 100 watt panel in 10 hours of sunlight will fill that battery.

    your mileage wont vary much after all above caveats are applied

    Quote this message in a reply

  12. Do you have a solar panel about 42″×42″to light up 2 bulbs continuesly. Please could you let me know what is the best size of panel required thank you

    1. You would need a solar panel, batteries and controller. What size bulbs are you talking about and would they be on 24/7

      1. I have 2- 200 watt solar panels and 4- 35 amphrs batterys that power my home lighting 24-7 I use 10 watt led dc lights. I only get 5 hours of sun a day and I have never been in the dark. Its only a beginning, I do plan to add more later to run my tv and fridge.

  13. Hi Michael,

    I blew my overload relay on my refer. I plugged in 3 13 watt lights and my refer blew this overload relay so the compressor stopped working. My question is: can a bad inverter cause a surge like this?
    the inverter is brand new.



    1. There is not enough information to know the cause of failure Dave. replace the relay and retest

  14. Hi guys glad i found you,i live off grid and mainly use wind turbines and generators,i currently have 2 banks of 350ah 12v batteries,then run from turbine shed to house via inverter,im now looking into solar panels,how many panels would i need to keep them topped up?

    I use :
    4 -10w lights
    fridge freezer 95w
    charger for my spotlight=60w
    This is all i use in the day.

  15. 2 banks of 350 Ah batteries are 700 Ah.
    700 amps x 12 volts = 8400 watts for an hour or 350 watts per hour for a 24 hour period.
    Read my post above for how many batteries and how many panels I would estimate you need and multiply your usage accordingly.

  16. I am installing an off-grid solar system and am concerned about an EMP wiping out some of the components. There seems a consensus that the inverter would get fried, but I have also heard the diodes in the solar panels would fail and wonder about the charge controller. I see two ways of retaining usability after an EMP attack or CME: 1) do not use the system, keeping it only for standby use after an attack by keeping critical parts in a Faraday cage; or 2) use it but keep redundant parts like a $2000 inverter in a Faraday cage. Either way, it seems expensive. Any ideas?

    1. Nels, you have the best information currently available about CME or EMP protection. No one knows for sure the effects that another Carrington event would have on solar panels and the IC’s in controllers or inverters.

      One thing is for sure, the copper wires running to and from all electronics will function as an antennae or conduit for EMF to the electronics plugged into them. Keep non essential and spare components unplugged from long runs.

      Grounding is important for panels AND wiring in your system.
      When in doubt run a ground wire. Voltage always takes the path of least resistance. Effective grounding will lessen damages.

      Having spare components in a grounded metal box will give you some hope of resurrecting your system if such an event occurs.

  17. Hi,
    How many batteries and solar panels (200W) will i need to provide 3000W per day of consumption?


    1. The article was written pretty well explaining the math needed. Several responses were written explaining the math also.

      You need 3 kilowatt hours of electricity per day (3000 watts for an hour).
      If you have 10 hours of sunlight and 300 watts of panels into three 12volt 100 amp hour batteries you will be OK.

      This would be unusually good conditions, you should probably double that figure.

      600 watts of solar panels (3×200 watt)
      6 100amp hour batteries

      Read my comment above how solar works for me and adjust your numbers according to
      1) hours of sun into panels
      2) capacity of battery bank

  18. Hi
    I have 3 deep freezers on my shop and a fan cooling system.
    I would like to have your advice. How many solar panels and battries required to run my 3 deep freezers.


  19. In Central & South America as well as Africa, some folks will take clear 2 liter soda bottle and put them in the roof like a sky lite. Close to 40 watts of light. I can’t remember if they added clear water to the bottle or not.
    A good seal would be a caulk of some kind, but also a rubber boot like you might use for a vent pipe or sewer pipe coming thru the roof.
    Free light in the day time and maybe a little in a full moon,
    Best Regards, RangerRick

  20. I have 1450watt solar panel but I want know what size of charge controler I need? And how many bettries bank I need ? Regoudles how many watts I need per day , my power invertor is 3000 watts

    1. An estimate would be to take the total watts and divide by the battery bank voltage. So if you have a 24 volt system that would be 60 amps of charge controller you need. 4 hours at max watts of 1450 would be 5.8 kwh supplied each sunny day. 4 – L-16 – 6 v batteries in series would give you 400 ah x 24v = 9600 wh storage. If you discharge to 50% then you need 4800 wh x 1.2 (loss factor) = 5.7 kwh which would just match your supply.
      I have seen people using much higher daylight hours on this forum to determine the wattage supplied but that is just not true. You get nowhere near the maximum input on your panels throughout the day unless you use a tracker which is expensive. Best to use the 4 hour rate for a fixed system.

  21. hi I would used 1623.00 watts a day. 3 100 watts solar panel
    average sun 4.5 a day where i am confused is how many batteries and amp hours i will need thinking on 6v batteries like to have a batteries reserve of 2-3 day using on my cargo van. any help much appreciated

    1. Brad

      You would use 16 batteries worth of power everyday from fully charged to fully discharged
      Your panels would only charge 13 batteries in 4.5 hours of sunlight.
      If you add another 100 watt panel you would be able to fill 18 batteries.
      16 batteries will weigh a half ton.
      In a cargo van you are probably going to have to learn how to get by with less power. I don’t see how you will be able to store a second or third day of power unless you use a generator. A propane refrigerator would probably be your best bet and only run air conditioner while the sun is shining.
      Cut your consumption in half, use 8 batteries and add another 100 watt panel and you might have your minimum for a day, certainly not for a second day.

      1. I am sorry, I was wrong, I was thinking 16 kilowatt hours daily, you are only using 1.6 kilowatt hours. That’s about one and one half batteries.

        4 to six 6 volt golf cart batteries will last you 2 to 3 days.

        Your solar output will be 4.5 hours x 300 watts or 1350 watt hours per day, you need another 100 watt panel to get you to 1800 watts per day.

        Sorry for the confusion

  22. Good writeup, I am normal visitor of one’s site, maintain up the excellent operate, and It’s going to be a regular visitor for a long time.

  23. Thank u for that article. I have been wanting to get a solar set up that would take care of a refrigerator and several lights, probably similar to the 2400 daily watts. Could you offer any recommendations. I live in Southern California so sun power is available. I do not want to be part of the power company,s system. I have read many ads but do not feel knowledgeable to spend so much money and then not be able to use the refrigerator. Any suggestions about what to ask for and any manufacturer would be most welcome. Thank u for your time. Joan

    1. I am sorry but I don’t know anyone in southern Ca who builds off grid systems. Maybe one of our readers can offer a suggestion.

  24. my fridge is run by 500w of solar panels into 14 6v golf cart batteries via a 1500w 12 volt square wave inverter for the past 20 years. [replaced inverter 3 times][replaced 6 batteries][replaced 1 solar panel blocking diodes 1 time][replaced charge controller with 8 blocking diodes in series][just add water ~1 gal per mo.]
    im in southern ca

  25. Pls I need help I have ( 200watt)incubator which need a stable power supply and am planking to back it up with batterie pls how many amp-batterie will hold this ( 200watt) for two days.pls reply tanx

  26. i also have a big challenge in sizing solar system.
    I have 12volt 2400ah batteries bank, 20panels of 120watts and solar regulators of 60amps two of them, and an inverter of 5kva.
    I connected the solar panels in series the batteries could not charge well and when I changed the connection, the batteries were well charged but the inverter blew immediately. Now what could have gone wrong I don’t know I need a help.

  27. Thanks sir great information. About solar system. Kindly givie me information about solar pump. Specially which circuit breaker are required as compare to pump rating

  28. hi. Like this discussion page.
    We have a 90 ft yacht that would have similar fixtures and apliences to an apartment. I will do all the calculations before we buy but my rough guess is 1000 watt of solar and 2000 ah of battery will reduce how often we need our generator.
    Sunlight is provided by the Bahamas so long days.

    As a rough guess do you think this seems close to the size required.

    Thanks. Geoff

    1. Hi Geoff
      I like this website for helpful prepping advice too.
      This thread is overall good for solar discussion.
      The solar/battery questions are somewhat complicated with many variables, but not if you understand the basic math as the thread contains.
      I have been off grid for 20 years and started buying panels when they were over $10/watt.
      Prices are much lower now and the equipment is much cheaper and better quality thanks to competition.
      The best way to learn how solar works is to actually buy the components and do your own tests.
      I have been very pleased with Renogy products, prices and their tech support.
      Perhaps just trying to get one circuit at a time off the grid or generator is the best teacher.
      600 watts in panels with a 60 amp MPPT charge controller and 1500 watt pure sine wave DC-AC inverter is a realistic minimum.
      Start with at least 6 or 8 deep cycle golf cart batteries you may buy more as needed.
      The total costs of these components will be a little over $2000.
      The payback starts as soon as you get it running and to me independence is worth more than the cost.

  29. I required 2 tons refrigerator which is run by solar with daily 24 hours, (not a single second it is stopped) with temperature of -5.5 degree centigrade ),how many solar panel of 250 Watt and how many batteries I require?
    Please assume my daily amp. use.

  30. I have a small house on an island in Bahia Brazil, Climate is much like Florida. We are off the grid and have no chance to have power other then what we can provide. I use 850 kwk per month in Florida and think this would be a safe number to use in for powering the island house. my question is how many panels & batteries ( size of batteries & Panels ) money is tight we are retired.
    thank you for your help.

  31. Hi, thanks for the article. I need your help.

    I live in IRAQ and we have electricity problem since more than 10 years. So i’m thinking of the solar system. Now in our street we have a 100 KVA electricity generator has been sat up couple of years ago that supply’s power to many houses in our street but only for 8 hoers a day. my house share is only 10 amp, i pay for that 10 amp in monthly bases. for that 10 amp i can run 1 refrigerator 2 TVs, 3 fans, and all house lamps.

    My question is. what do i need to buy to generate 10 amp 24 H /7 D for my house? please kindly advise how many panels? size of each panel? battery …etc . i want to know if i will have enough space and room in my house and how much that will cost me. specially our houses roofs are not like yours, we have flat roofs that we can go walk and put stuff on it, and sometimes we put our beds on the roof and sleep at night 😀 . as there is no electricity and its too hot to sleep inside.

    Thanks in advance for the reply.


  32. We are in southern Zambia with good sunlight. How many solar panels, size of inventer and size and no. of batteries would we require for the following 4 LED tvs, 4 decorders, 40 LED bulbs, 4 fans, 4 radios and in scenario b, 2 small fridges, 2; 32 inc tvs

  33. I am interested in powering my Energy Star rated 15 cf freezer with solar energy. My Kill-a-watt indicates my 24 hour usage is 2.0 KwH. What is the minimum solar panel wattage (I am using Renogy 100 watt panels) and T105 Trojan battery requirements to have the freezer work off-grid indefinitely. BTW, southern Ohio…

  34. I want to intall grid off solar panel in my shop,my shop’s load is about
    450w details are 5 savour 1 ceiling fan 1 water dispencer 1 computer
    1 printer ,what will be its total cost,

  35. Hello ..I want to make battery 12 volt 250 amp
    How to make battery please give details about material
    And making installation. ..Thanks

  36. I have 230 amp hour batteries. 5 hours of sun a day. What size solar panel do I need to charge them fully. All appliances off

  37. hi i need work my freezer 24/7 how many splar i need and battery bank
    my freezer data
    220v in put
    240w energy consumption
    .45 current
    plz tell me how many for thes freezer

    1. Yes, the kwh on your bill are kilowatt hours.
      Multiply by 1000 to find the number of watt hours.

      For example 2.4 kilowatt hours x 1000 = 2400 watt hours.

  38. Hi guys, Im from malaysia… im using in total 480watt of light on 240volt. can u help me calculate what sizze battery should i need… for info, i have 7 120watt solat panel aand 7 12c 120amp hour battery…. tq in advance

  39. If my daily Wattage is 400Watt and the Sun in 3 Hrs Per day in Winter and 6 hours in Summary but not ensure the regularity of Sun there could be Clouds and Rain for many days …please suggest a solution ..Do we have any solution for rainy days……

    1. More batteries take you thru the non solar times. That means more solar to charge the batteries as well. Work on energy efficiency like LED lights, efficient appliances and an efficient set up to begin with. Long wire runs equal wasted power just like ghost loads in an entertainment system, computers and cell chargers.

  40. Ajitsinh varnamiya

    how can i run my 0.5 hp water pump only 3hrs a day so what can i need for whole setup like how many watts panel,battery,and inverter.

    1. Too little information, if it just needs to run 3 hours and it doesn’t matter when then just run solar to a DC pump. No battery and no inverter. If you need to use the water under pressure at non solar times then put the tank up high and use gravity.
      If that’s not an option then you need Solar and batteries for the DC pump. To run a .5 hp pump you need 372.85 watts. Divided by 12v that’s 31 amps and 93 amp hour battery for it to run for 3 hours. I don’t know the type or voltage of your pump or any inefficiencies in your set up like wire length, voltage drop etc.. but hope this gets some basics in your hands.

  41. Hi I have four 150 watt panel and two 150ah batteries. But My per hour consumption is 1000watt of ac.
    How Many Panels and battery should i have to get 15 hours of uses.

  42. Hi,
    I need a solar system to only light up a rural house using eight 2-watt solar bulbs and a single phone charger. What size panel do I need and which charge controller?

  43. Dear sir/madam i would like to ask i have a battery cycle .that need 12*4=48V each battery 100amp hr.every date 10 hours working . now i want to do make one charge by solar panel and battery back.

  44. hi my name is chuck. I am looking to setup a basic emergency backup system. currently I have a grid tied system that consists of 7x 255 watt panels. my backup system would be mainly to run my fridge, some lights and TV during a blackout. I would be switching 3 of my panels for backup for an emergency. my question is, how many batteries and at what AH rating would I need to keep my devices going from dusk till dawn? and how fast would the 3 panels charge my batteries? thanks

  45. I need help,

    I made 3 solar panel producing 40.3volt when connected in series. Can i use this with an inverter of 800-1400w, and with 12v battery connected in parallel or 24v battery connected in series.
    I want to know the right way to do this connection.

    Thank you

  46. How many 250w panel.
    How many 200amp battery.
    How many amp changer controller.,
    8hrs sun light
    600w of load
    Hours needed to work 10hrs
    Question how many Panel, Battery, and the amps of the changer controller to be used. how many KVA invater will be used


    I want to run system of 650watt equipment or 16 hours, sun hours in my area is 7 hours . How many solar panels of 150 watt and batteries do i need?

  48. the big flaw in this is that solar cells are rated in a lab under PERFECT SIMULATED SUN with no clouds bird shadows or other reductions….. including dust. real life instances are rare and almost exclusively in the soutwest. in addition they are pointed directly at the simulated sun. thats why they make tracking collector array mounts. if the array is stationary, even mounted ideally, you can reduce the output by 50%. then there are the batteries. while they are called deep cycle it refers to the capability without damage…. they do not furnish full voltage but approx. HALF the rating.. appliances wont run at less than 11vdc. inverters shut down at 11.5vdc. there are also numerous mistakes in the load estimates…… rule of thumb. DOUBLE the textbook design results for a reliable system.

  49. OK, so how many times are we going to say, “How many solar panels does it take to do ” or “How many batteries do I need to do “. This is why people get so confused. Somebody please make a matrix, just like load tables for joists used in the building industry. Otherwise this thread will never end!

    1. That made me laugh! I’ll see what I can do. I have a background in electrical work and have designed some solar systems myself.

    1. I’m not selling a product. Just explaining how to do a simple calculation for figuring out how many solar panels and batteries a home would need to operate the most basic necessities. I’ll work on adding additional articles in upcoming weeks.

  50. Quick question. I have a window AC (120V. 4.5amp) on 200 watt panel, Two 75AH deep cycle batteries and a 1,000 inverter. the AC compressor does not kick on. Do I need an additional 75AH battery?

  51. Hi I love I’m the Caribbean Trinidad to be excact I now ordered a 200watts panel and a 12v gel battery would that be enough and what can i run on it meaning appliance and light

  52. Hi
    I’m going to use a 1 tan ac with solar power and battery
    I want to ran 24h 1 tan ac
    So can you help me .How many battery and solar panels I need to ran 24h off grid ac

  53. Hi everyone!
    This is my situation… I try to install a 24/7 refrigerator (off grid) in a ranch where obviously energy lines don´t reach.
    The refrigerator im trying to install is an LG smart inverter compressor and it´s a 9 cu/f which the power consumption tab says its consuming 323 Kwh/year and maximum of 378 Kwh/year

    I´m really confused with the solar panels and batteries that I need to install thanks

  54. This is a great subject thread. I may have put the cart before the horse, or in this case the Solar Panels before the Batteries. I bought 10 230 watt panels for a total of 2300 Watt for my new 16×40′ detached garage (man cave) shell which i’d like to make off grid. Living in Florida, eventually this will also have a 16×10′ enclosed air conditioned room and I’ll add more panels if necessary. I also have a 3500W 12V DC to AC power inverter with up to 7500W peak power. I know I still need a charge controller, connectors, power box, switches etc.
    I’m ready to buy Batteries and build the battery bank. Any recommendations are greatly appreciated. What would you do?

    1. Any system you build, you have to determine what your actual load is going to be. This is relevant whether you’re putting a service on a house and tying it to the utility grid or building a solar array to function off grid. Make a list of what you’re going to put in your man cave and what their energy usage is going to be. If you haven’t done this yet, do it before you buy your batteries. You can always add more later, of course. The market is starting to produce more off grid devices/appliances that you can directly tie into your system without the need for inverters.

  55. Hi,

    I am planning to install a solar power system at my home. I have 3Nos. of 1/2 AC and approx 200 watts of Refrigerator and 10Nos. of 40watts of lights.

    Would anyone tell me how many solar panel (300 watts), Batteries (Which specs) and inverter (how many watts) I need ?

    I am planing to run it 18 hours a day. Is it possible?

    Thanks mate..


    I have:
    1 plasma tv 50° – max consumption 275w
    1 pc gamer(without monitor) consumption between 30w-500w-load
    2 led light bulbs (low wattage)

    Now, I bought myself a battery 12v 400a (stationary-deep cycle)
    also, 1x 315w 24v canadian solar panel

    I’ll run all this on a pure sine wave inverter 1000w(nominal),
    I intend to keep the bank 12v(even if paralel), and the controler a 60a mppt (for upgrade)…

    also I intend to run this system almost every single night for about 6 hours, and 1 hour during the morning, it remains the whole day completly turned off…

    Now down here in south Brazil, I can achieve I believe 5 to 6 hours of sun peak per day, also since I’m a glazier its very simple to me to set the painel with some sort of chain, so I can control the inclination, to maximize the performance of it, wherever, to the point…
    How many batteries will I need to be able to run this system each night for the periods decribleds above, and how much 315w panels to be able to charge those very batteries, being ready for each night? Do I need more than 1 battery and one 315w solar?

  57. Im preparing to purchase five 100 watt solar panels and already have 10 Enersys Oddyssey 12 volt 185 amp hour AGM batteries for my bank. The question is what amp hour rated solar charge controller would be appropriate? Theoretically, the panels would produce 60 a/h at 12 volts but battery charging really requires a solid 18 volts or more, correct? Should I do a combo of parallel and series panels to reduce the amperage but increase the voltage? If so, whats the best controller, regarding amperage? If not, whats the best layout? Thanks So Much.

  58. I am confused with all the calculations you explained, really is hard for me. I am in Florida, I would like to know if is possible, to tell me what I need to run a refrigerator and a freezer, both 800 Watts. I have already a 100 Watts solar panel, 2 batteries 12 volts ea.-650watts ea., 2 charges controllers 30amp and a inverter 2000watts. The charges seems that charge and discharge at the same time the juice put in the batteries. This is a project that my husband (84 years old) is doing and he is deaf and I must to make calls to try to get answers for him and he running me crazy with this, please I need HELP. I will appreciate it!

  59. Hi to all its a very nice information about solar panel..but please kindly help me to this,we consumed only 60 to 70 watts daily please kindly help me to know how how many watts of solar panel and batteries in need to buy..thanks in advance and God Bless..

    1. We have had no sun for one month. What would happen to the solar power? Would it get enough charge from thirty gloomy days to carry through until sun comes out?

  60. I am looking for advice as to how many panels and what type I need to start buying, my electric bill says current month’s KWh per day is 30, so trying to figure out how much and what type panel is best for this, message me here or at my email at [email protected],
    any help greatly appreciated,

  61. charles crabtree

    I want to run my swimming pool pump on solar..1hp what do I need in panels and batteries..should run at least 5 hours a day.

  62. If everyone just reads the math he explains over and and over you Will get it.. What a great informative arrival. This is basic math U must learn to figure Your own system. All you have to do is figure what you use Daily and monthly and use the formula he explains in detail to figure our Your system. He definitely has it right in a General term.. It All depends where U live.. Sunny and dry All the Arizona…or North West Seattle ?? Rain capital…lol. Once you look at Your first small appliance and see the watts.. How often do u use it ?? Add it All will totally understand the math and you Will have you system…

  63. hello i have the following load
    20bulbs of 2w for 6hrs
    15 bulbs of 2w for 12hrs
    TV 30wts for 6hrs
    what panels and batteries do i need?

    1. Two pcs of Solar panel @ 100 watt capacity assuming 5hrs of sun. Two pcs of Battery @12vdc 200 amp-hours.

      Based on Admin calculation. ty

  64. I have install a 600 watt Mono Solar Panel system at my home. I have 6 Nos. Ac 100 Watt Fan Ceiling Fans & 2 No’s DC 35 watt Ceiling Fan Watt , 20 Sever Blub 25 watts , and Medium Size Refrigerator.

    Would anyone tell me how many solar panel to add more , Batteries (Which specs) and inverter (how many watts) I need ?

    and full procedure about Solor Charge Contoller Which is best MPPT/ PWM
    I am planing to run it 18 hours a day. Is it possible?


  65. I have 3 250 watt panels, all i want to do is have my 500 watt window unit to run all night till i get up which without sunlight is about 12 hour’s. How many batteries do i need? What preference? Any advice helpful thanks!!

  66. Setting up my off-grid system at my hunting cabin. I want to run TV, lights, directv box and a small AC unit. I figure 1500W inverter with max surge 3000W.
    My question is this: how many batteries can I hook up to the inverter to store power and how do they connect?

    Thanks, in advance.

    1. Please check with the installation instructions. Depending on which inverter you use, there will be limitations on how much capacity the inverter will be able to handle, both input and output.

    1. Simple math. Whether you are calculating by Watt hours or Amp hours, the total load served must be calculated using the same measurement. Amps are the best for baterries since their capacity (run time) will probably be the factor you are most concerned with. I’m assuming you have them arranged for the operational volage you are wanting to use.

      60W light bulb, 5.2A (120V) refrigerator. Bulb (60W/120V) .5A + Frig 5.2A = 5.7A.
      If my batteries have a 13Ah capacity, as arranged, I could run these two items for 2.3 hours.

    1. If it is a regular (AC Volts) fridge, you will need an inverter between the DC Voltage of the solar array and the appliance.

  67. So your batteries are down to 50% and you need to run your house too. Your panels should be able to run your house and recharge your batteries in a reasonable time during a time of the year when the sun isn’t shining and maybe you are using more than normal because of the weather.
    If you’re off-grid then you have a problem.

  68. Great article. Very useful for me. Now is there a similar article about choosing the correct charge controller and choosing the correct inverter? These are still mysteries to me. Thanks.

  69. I have a 24vdc input 5000watt/20000watt psw inverter. I have 6x 160amp deep cycle 12v batteries, in 24v series/ parallel formation, meaning 3x24vx 160amp.
    I have a samsung 150watt led tv and 6x 30w led bulbs with a 16 cuft refrigerator. How long would my setup last

  70. i am having 315w solar panels 2 and 1 inverter and 180ah battery .so how much capacity change controller required.

  71. how many 200AH batteries and 250watts solar panel do i need to power an hybrid system that is comprise of 12 Air conditioners (1100watts each), 8 deep freezers (350watts each) and 6 Tv set. please can someone help me

  72. Hi There
    I want to know how manny pannels and what size and how many batterys i need please, i want to have my fridge, deepfrezer and lights X 12 and my tv and alarm running please. Can you please supply me with this info.

    Thank You

  73. Hi to all.
    I bought
    Power rated 3kva inverter/charge contoller. Power output 24vdc, 100a.
    Just a regular house electricity consumption a old fridge, led 32″ tv, 30w lights 5each
    Please advice if i can add (1hp) a/c 9hrs aday of usage…as regular usage fridge is 24hrs usage..
    How many car battery i need and how many solar panel i need…
    Any comment is very much appreciated…
    Thank you all in advance.

  74. Hi,

    Thank you for this article. I’m a bit of a newbie on solar and I appreciate your clear and organized article.

    Could you kindly elaborate on the effect of the starting current for the batteries? I’ve read some people use a multiplier of 3 or 6 for the required starting power. Will this mean, aside from the daily watt-hr requirement, you’d also need to add an allowance for the 600% requirement of each appliance to start?

    Ex. 2HP air conditioner (around 1.5-2KW running) would need about 12KW to start (using 6 as a multiplier).

    Wouldn’t this drain the batteries instantly if it is not considered?

  75. Hopefully a simple question. Is there a rule of thumb for “X watts of panel array” for “Y amp/hours of battery bank”..?

    I’m considering doing a fairly large pv system to power one level of a house we’re building; possibly as much as 6,000 watts of panel array. I’m fine with calculating my daily watt/hours of usage; I’m just completely lacking in first-hand experience with large scale pv systems. If I’m understanding the C/20 rule, it sounds like I’m looking at an absurd number on the battery amp/hours for that size of panel array.

    Curious what I’m missing, and frankly what others would use battery-wise; in terms of “amp-hours per 1,000 watts of panel” or similar.

    Thanks in advance, from an admitted noob on the subject.

  76. David A Nyberg II

    Aside from everything I’ve read on this blog, I don’t see one question answered that is maybe too complex for this venue. High capacity 12 volt sealed AGL deep cycle batteries are not only common but relatively affordable. My question is: If I have a 24V solar system and a boat load of power from them, is it necessary to stay with a 24 volt battery system or can I stand to eat a bit more conversion loss and get an MPPT charger that can handle the 12 volt batteries from a 24 volt solar system? They do make them. That way I wouldn’t have to waste one battery in order to make a 24 volt two battery string. Am I making sense here or am I too tired…

  77. What would I need to power my water well ? It’s 220 volts and I need it to run at lease 12 hours a day. Can you help me out with a list and price ?

  78. Hello
    I have a 3 bedroom house and we have 6 fans , 6 lights, 1 AC, Fridge, Boiler only used during winter, LCD TV, 2 Laptops. My question is how much watts do we need. Can we start with 1000 watt to power just the fans and lights and once in awhile ac during the summer time. Can you let me know by email. Appreciate it

  79. I find your electric math tutoring a blessing. Trying to build a teaching urban agricultural extension, off grid, for all schools.

  80. I am planning to install solar power at a hunting cabin. We are only there 2 days a week. We will only be running 4 lights, a ceiling fan, a coffee pot, charging phones and maybe a radio. We wired the cabin and have a breaker box in place. Any suggestions on what solar equipment I need?

  81. I have a question on the panel calculation used in the example. I’ll use different numbers to simplify my question.

    If my daily watt hours is 1000 and I get 5 hours of sun the calculation shows that a single 200w panel would work.

    Even assuming no loss, which isn’t realistic, shouldn’t the production of the panels be greater than the daily usage to allow for recharge of the batteries?

    If they match as in the above example and your usage remains constant, it doesn’t seem you’d ever be able to recharge the batteries if they start to become depleted.

    Am I missing something?

  82. I have a hospital in Serra Leone and need to keep some cooling equipment going 24 hours a day . they need 20 kv generator for now and the load is constant about there so am having the gen set at full

    we have on average 5.5 hours of sunlight an thinking of getting 315 wp panels . how many panels and how many batteries of what size ..the full shopping list would be good.

    1. I’m very new at this so please double check my numbers.

      You also need to know the utilization of the generator to get a more accurate number but assuming that it is 100% loaded 24 hours a day, this is what I come up with.

      20000 (watts) * 24 (hours) = 480000 (Watt hours)
      480000 * 3 (days buffer) * 2 (50% discharge) = 2880000
      2880000 / 12 (volts) = 240000
      240000 / 300 (AH for battery) = 800 (batteries)

      For panels I come up with the following.

      315 (watts) * 5.5 (peak sun) = 1732.5 (per panel with 0 loss)
      480000 (daily watt hours) / 1732 = 278 (panels).

      Again, my math or assumption may be way off but either way, it seems a system this size requires involving a professional. There would be loss that needs to be added into the calculations but I’m also sure the generator isn’t running 100% 24 hours a day.

  83. I am trying to pump water for a community in Haiti over a hill. I have a submersible pump that I am told needs 600 watts of power.
    How many panels will I need? I am thinking that we can do without storage batteries. The pump is DC. thanks for your help

  84. I am designing a solar standalone system for a rural community with a load of 365,262 Wh/day, please how many panels, charge controllers, batteries and inverters would you recommend and ratings? thank you.


  86. Chibueze Ezenduka

    You considered just the actual daily watt-hour ( 2400) when sizing your panels, and that implied dividing 2400 by 375. I wonder why you didn’t consider the “buffered” value of the battery bank (7200) or even the new 50% safety value (14400). If the solar panels are expected to charge the batteries at least, then it will require more than 2 sunny days (5hrs each as in this case) to charge those batteries by 50% without an additional burden. Please check.

  87. India is now focusing on use of Solar Electricity for homes.
    This is especially useful in the Rural segment of the country, which is littered with 575,000 villages, each with about 2000 population and where maintenance of steady power supply is not an easy task.
    On the other hand, there is abundance of Solar Energy in most parts of the country.
    We have our Institute of Clean Energy Technologies, where we are focusing powering the Rural areas with Clean Energy.
    For Small rural homes, 200 Watts or 400 Watts ( 2 nos. 200 Watts ) panels will meet the local needs.
    We are keen to make Charge controllers for such homes, working off 200 watts panels and carrying 20 Amps.
    We need a good design circuit for this.
    We wish to have a know-how transfer from you for this as you have an excellent reputation in this field.
    Please advise if this is possible. If so, please intimate the terms.
    Thanking you,
    yours sincerely,
    B S Murty

  88. Hi, kindly assist, I have a 200amp deep cycle new battery, 280watts panel and 2000watts inverter, the issue, after charging to full capacity during the day, at night my battery can’t last till morning with four 5 watts bulb (I.e 20watts) the whole connection is linked to the inverter. Do you think the inverter loss is responsible? Or what suggestions.

  89. how many solar panels and batteries do i need to run a 0.5hp submersible pump on solar. We have effective sunshine for a minimum of 8hrs per day.

  90. Guys I have a 100 watts harbor fright solar system controller, 750 inveter and a MARINE RV DEEP CYCLE 12V BATTERY SEARS DIEHARD 675CCA.

    I need 500 watts every hour to run my stuff, at night time only for 6 hours, can you please let me know if this will help me to achieve that.

  91. Hi
    Hi like your article a lot because I just bought a camp in the boony lol My options right now is only my generator so I have a 25 fts trailer camper with a build up roof above it and a full room build on one side of it with one light and one wall plug the rest is usual trailer accessories fridge wall plug and a few ceiling light.I think that 3 panels of 200 watts and 4 deep cycles batteries should work fine !But what do you think is it too much or not enough and how much roughly would that cost me?Thank you very much

  92. For a solar street light of 30W 12V ,what size of Solar Panel and Deep Cycle Battery should be used? And the numbers of the panels and batteries?
    And how should the panels and batteries connected-series or parallel?
    I look forward to hearing from professionals here.

  93. Hi
    Please i will like to build a 4000 w system and i will like you to help me by telling me what type of components that i will need to build it .

    Best Regards,
    Daniel .

  94. Thomas Amukeshe

    hey guys, quick question here.

    how do i decide whether to use series or parallel connections on my panel? does the input of the invertor matters? 12v or 24 v? i have two 180 watts panels, a 12v inverter, *4 12v batteries, 20 Amps regulator, and i want to power a freezer, a tv and a juke box machine(common in namibia). whats the best connection i can use?

  95. Mian Shams ul haq

    AOA… I wants to run 1 AC ceiling fan and 1 bulb light of 15 watts on 150 volt solar panel plates…! Who many plates are required to install system?and that also keeps backup for battery through UPS… Please brief me with detail

    1. You will need to know the amperage or wattage of the fan plus the wattage of the bulb. After that, calculate your needs using the information in the article to determine your needs based on the way you intend to use the devices.

  96. Hi, I hope you can help me- I want to pressurized my rain barrel with a SEAFLO 12V 3.0 GPM Water Pump and I would like to do it with a solar panel connected to a charge controller and battery. My question is how many watts of solar panel, how many AH of 12V deep cycle battery, How many Amp of charge controller to run with this pump? The pump uses 8 amp max and I only intend to use the pump daily for 1 hour during summer months. My calculation was solar panel 30 watts, 12v 35 amp battery, and 30 a charge controller. Thanks

    1. 8A for one hour is 8Ah. So, your 35A battery will handle it. What are the amp hours on the battery? That will tell you how long it can run between charges although you are going to be recharging daily. Your panels will give you about 2.5A charge/hour so 3.25-4 hours a day should get you back to full charge with the battery.

  97. Gravitating the explanation of the ratio of p v panels to batteries. Is there an app that will do this if you enter parameters like panel output and watts required plus battery capacity?
    I remember a programme put out by shell that did the balancing for you around the turn of the century.
    Thank you for your attention.


    my power requirement is 12000 watt per day
    i installed 3000 watt solar system (4 peak hours per day)
    to support 3000 watt i installed a 5.5 kva 96 volt off grid solar inverter. if i divide 12000watt by 96 volt it gives 125 amp utilization. it means i required 125 amp current need to be generate.
    if i consider 50% DoD of battery i required 250 ah battery.
    to charge 250 ah battery i required 10 % charging current it means 250/10= 25 amp.
    to charge 250 ah batter 250/25= 10 hours. but i have 4 peak hours to charge a battery.
    it is very confusing pls help to solve this issue if my calculation is correct.

  99. Will this work:
    24 volt system
    16 – 240 watt panels
    Flex max 80 CC
    Outback 3524 Inverter
    3.5 to 4.5 Sun hours
    50 % DOD
    Can 4 Trojan SIND 06 1225
    6 volt 1225 Ah @ 100 Hr
    20 – Rate

  100. Based on the calculation above, does that includes 24 hours? I’m thinking of running my computer, which takes about 400W per hour. So the figures and calculation above…covers per hour? Or how.


  101. please help me by give a number of solar panel, battery and size of inventer to power a home with the following:
    12 light 15watts
    1 television 40watts
    1 fridge freezer 95watts
    2 sports light 30watts

  102. i live in a condo that does not allow gas generators. i only want to run my refrigerator 2 hours a day so i don’t lose my frozen food. it is a 25 cuft , can i use a 100 amp solar panel and one battery to get me thru hurricane season? i only need this for emergency purposes. last year i lost power for 4 days and lost all frozen food. i assume a large amp hour battery will suffice.

  103. older post but good info. but in 2019 lithium batteries are more affordable . and one big savings are led bulbs author listed 400watts
    for lights led probably 100 watts and you can get them for 1.00
    and shut sat or cable and tv off with power strip

  104. Hi there,
    I am looking at running a 190w water fountain 12 hours a day (during the summer, less in the winter). with the calculations i make it the same as the example with 3 x 200 watt panels and 4 x 300amp batteries. Is this anywhere close to the right figures?

  105. Ok, so I’ve researched alot and like your thread. I am in process of getting my system put together for my 550sqft house. Right now I have 3 100w panels ordered, and will be running 2 12v 40ah batteries to get by for now. (Currently living without power). Outdoor and outbuilding will be on their own power system. (Smaller solar point of use for distance)
    I will be running a hydro generator from my artesian 5″ well that will be a constant (size to be determined once it’s in depending on output, but estimate 1000w constant power. The solar I will expand on as needed. The batteries will be lithium, with Boston power 24v arrangement seeming to be the best candidate.
    I will be running the whole house on 12v, cellphone, laptop,fridge, lights, tv, projector.
    Wood/coal heat, cooking, and hot water. I want to use an inverter in the kitchen for the microwave and anything else that would run on 110 as “point of use” (inverter turned on only when needed to run it).
    My questions are;
    1) what is the power consumption of a stepdown from 24v to 12v? And would it be more efficient to stay 12v with the batteries?
    2) Are there any other products or ways to reduce power draw I’m missing?
    3) what is the best way to join the well power and solar?
    4) what’s the best way to run a 180amp 220v welder for short use? (This one’s the hardest to research)

    Enjoy your thread, and Hope you can help

    1. 1. The lower the voltage, the larger the conductor needs to be to carry the same load.
      Below is a comparison of different variables to consider with the goal of trying to keep the voltage drop below 5% (approximately)

      12V, 10A (load), #12AWG, 40 feet from the source, voltage drop is 10.59% resulting in a 10.73 volts at the furthest point.
      24V, 10A (load), #12AWG, 40 feet from the source, voltage drop is 5.29% resulting in a 22.73 volts at the furthest point.

      12V, 10A (load), #8AWG, 40 feet from the source, voltage drop is 4.19% resulting in a 10.73 volts at the furthest point.
      24V, 10A (load), #12AWG, 40 feet from the source, voltage drop is 5.29% resulting in a 22.73 volts at the furthest point.

      12V, 5A (load), #12AWG, 40 feet from the source, voltage drop is 5.29% resulting in a 10.73 volts at the furthest point.
      24V, 10A (load), #12AWG, 40 feet from the source, voltage drop is 5.29% resulting in a 22.73 volts at the furthest point.

      12V, 10A (load), #12AWG, 20 feet from the source, voltage drop is 5.29% resulting in a 10.73 volts at the furthest point.
      24V, 10A (load), #12AWG, 40 feet from the source, voltage drop is 5.29% resulting in a 22.73 volts at the furthest point.

      2. The best way to reduce power consumption is to turn off (and unplug) anything that uses power.
      Don’t forget about “phantom” or “vampire” loads. Most electronics that are normally powered via a receptacle draw a minute amount of electricity all the time.
      Buy and use the most efficient item you can. The most recognizable comparison is a light bulb: 75W halogen flood light, LED would be about 11W resulting in an 85% reduction in power needed.
      Use DC voltage equipment. You have some power loss through the inverter. Plus, if you lose the inverter for some reason, anything requiring the higher voltage will be useless. The cost of going all DC my outway the risk of losing the invereter. But, it is a part of the thinking process.

      3. I have no experience with combining hydroelectric power and solar power generation. I would imagine though that, for starters, you would have to decide what operational voltage and current (AC/DC) you wanted to ultimately use. Then, where and how to combine the two.

      4. Running a welder… I would suggest a small portable gas operated generator. Depending on what you are trying to weld, thickness wise, the power consumption can be upwards of 7,500W. The amount of additional (and most of the time unneeded) infrastructure cost may outweigh the investment into a gas generator.

  106. I am attempting to build a small solar generator to power my 14′ travel trailer, I have 7 x 255 watt (8.75A) 30.5V Panels. which arrangement would be more efficient, connect all my batteries in parallel creating one large 12V system or parallel and series to create a 24V system?

    1. Harry, which voltage system would be easier for you to get parts for that’s compatible with your choice of brands? Does that brand commonly have equipment for 12V or 24V? Using that information, decide if you want to power more for a short period of time or less for a longer period of time. The higher the voltage the shorter amount of time you’ll be able to run things in your travel trailer.

  107. I would like to run a medium size refrigerator up at our fishing camp for the 5 days we go up in the spring and then the fall. We presently have 2 solar panels of 100W each and the refrigerator is rated at 400W. Our batteries are rated at 154Ah and I’m trying to figure out how many batteries we need and what size inverter is required.

  108. My mother-in-law is disabled. We have an aerobic septic system in a rural area. The septic system requires an air pump to run 24 hours/7 days/week. It is 110 volt. And is rated at 1.6 Amps. I live just North of Oklahoma City. What kind of solar power would be required if we lost our power for say, 5 days to a week?

    Your help will be greatly appreciated.

    Ron Henderson

  109. This is absolutely hilarious. There’s at least 50 people here mansplaining math to each other and everyone else. And it’s always ‘simple math’ and obvious. No it isn’t. Trying to work this out is probably one of the main reasons fossil fuels are so hard to phase out. Solar is bloody hard to work out and leaves a lot of people vulnerable to con artists. Can’t wait to get off grid solar now and worry that my house will burn down because I have 100 batteries under my house ready to cook-off if I don’t ‘monitor them closely’. Sounds great. Not.

  110. Hello. My question is regarding: “Because you should not discharge the batteries below 50%, multiply this number by 2.” How do you get 2 mathematically? Or in other words, if used 50% in an equation, what is the equation with the perent?

    Could you clarify if you are referring to the Depth of Discharge rate for a battery? If so, some batteries recommend 60%. How would you multiple by? What would be the equation?

    I’m trying to understand what the formula calculation is with the % versus plugging in a number (in your example 2).

    Brand new to the game, any guidance would help me understand more.

  111. Hi what system would I need to power a LCD TV 300w and a PS5 with two remotes for 3 days straight? If SHTF I’d prob survive for 3 days since we can only survive without water for 3 days.

  112. I have a 1000w light 68w ac infinity and 10w fan I want to run 24/7 how many solar panels n battery do I need

  113. So I have a 14.5 KW panel Ray on my roof. I live in Florida and I’m getting about 10 hours of good sunlight during the day and the summer. Not quite sure what that will be in the winter. Anyway, I would like to have enough of a battery pack to power me for 24 hours because I also have a generac whole home generator with the 10-day supply of propane. I tried to work through the calculations but my head is spinning. Can you estimate how many batteries I would need and what the cost would be? I am likely going to get the lithium iron batteries. Thank you.

  114. Frederick Francis Johnson

    I have a shed 35ft longx16ftwide…I have 12 100watt solar panels. I have 4 12v 35ah Ul deep cycle batteries. Power Regulator. My Question is this enough to power 4 14kw led shop lights, a 70in deep freezer and maybe a 32 smart tv.

    Also I know, I’ll need a converter…but I was thinking can I hook it up to the separate electrical panel…that isn’t live until I turn the power on from the main house. And put in the 10amp and 15amp switches.
    Assuming, I hook up the batteries for over night power for the freezer and lights, but hooking up the solar panels powering during the day.

    My house set up for solar already…enough power to give me 116% more power than I use in a year…which is 7400kwh a year. I’ll be producing 8100kwhs.
    I also have 2 100watt panels that powers my fish pond pump…and charges the same 12v35ah up deep cycle batteries.

  115. Good day all,

    I am trying to build a greenhouse on solar and I need to verification on my numbers please.

    My 12v lights and fan run at 2,6amp, which gives me 31,2W.

    I need this to run for 14hrs, giving me 436,8Wh required. This would then calculate to a minimum of a 36,4ah 12V battery.

    I have 8hrs of sunlight, in winter, which then would calculate to a required solar panel of at least 54,6W.

    Any advise and suggestions are more than welcome.

    Thank you.

  116. when i swa question and then answere used 75 watt panels. firs there so outdated i doubt if you find them 100 is basic with up to 400 watt now very economical now, and fall 2021 lithium batteries are only about 1.3 more than sla 100ah but usable to 80% vs 50% so more capacity.
    but the first thing replace all incandescent bulbs to led. dollar tree 40 and 60 equivalent buck a piece. so from 60 watt to about 6 watt . and careful shopping new appliances . most time don’t pay just to junk and buy new rare cases does . but buy the lowest use. but the big problem computing usages. is the charts are like 30 years old made to estimate emergency generator use. not the newer things just tv way lower electric vs old tube TVs. Cable and sat boxes are high use when off. be very wary os leasing and financing systems and don’t take first quote. and grid tie make sure they include switch to disconnect from power co or if they are out your out even when sun shines i include battery for ref and lights but even no battery you still have power during sun. lastly if you roof mount you need a fairly new roof . better ground mount if possible. been doing research and experiments before i build in 2022 to me i dont want grid tie i rather run ref and freezer and part house than grid tie

  117. Hello, I have a simple question (simple for you all, not for me). The landlord showed me an electric bill of 7900 kWh of power being used in the last 30 days. so my question is, how many panels would i need and how many batteries would i need to “cover” that usage? just exploring options of moving myself totally off grid.

  118. Hi, I really need help. I am attempting to convert my pantry shed to solar. I have a 18 cft upright freezer along with a 5 cubic ft chest freezer, an 5,000 btu air conditioner and 60w light bulb that runs approx 2 hours a day. I need help in figuring out the # of panels and batteries i would need to have to power the shed. We get approx. 7-8 hours of daylight daily, I live in Florida.

  119. hey i tried to figure this out but cant get the same answer I am looking to move off grid
    I have kids who game who play games in order for them to agree they dont want to make any sacrifices as it stands now im using about 1800watts every hour (i have 5 kids 4 of which aare on their pcs 24/7)
    i was wondering what would be the most practical setup for my family

    can i figure out good wind turbine to make up for days its not alwsys sunny(i live in PNW its not real sunny but ive notice more and more houses with panels on top

    thanks in advance

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