Alternative energy has made great advances over the past few years. The technology has evolved to the point that anyone can incorporate it into their lives if they are so inclined. The Solar Garage Project is intended as an introduction to the world of alternative energy if you plan on living off-grid or just like the idea of solar energy to offset costs. If you have a detached garage or shed that does not currently have electric power, or you would like to experiment with solar, this is the project for you.
In this article we will discuss the planning and installation of a 12 Volt Direct Current (DC) solar system. The DC current will be converted to 120 Volt Alternating Current (AC) for device operation. We will explore the required components and their purpose.
Keys To Success
Planning is the most important element when undertaking a solar project of any size. You must have a specific power production goal in mind before work begins. Any electrical system has a limit. Even a home running on grid power is limited to 100 – 200 Amp service.
If the homeowner attempts to draw over the amps provided, the fuses will blow and lights will go out. Power outages are never an enjoyable experience.
In the case of solar power, we must also take time into account. Since the system will only charge during daylight hours, we must plan for power used at night.
There are no special power tools required for most solar installations. A good assortment of typical hand tools and wiring components will do the job.
- #1 and #2 Flat and Phillips screw drivers.
- Pliers and needle nose pliers.
- Wire cutter and stripper.
- Electric Drill.
- Standard set of drill bits.
- Spade bits or hole saw set.
- Screw driving bits.
- Miscellaneous mounting hardware.
- Basic Volt-meter or Multi-meter.
- Electrical tape.
- 12 gauge ROMEX.
- Materials appropriate to accommodate any building penetrations for wire routing.
- Battery terminal connector appropriate for your batteries.
- Wire nuts for 12 gauge wire.
- Short piece 10 gauge battery interconnect cable and terminals.
- Assortment of wire terminals for connection to devices.
- UV resistant zip ties.
The Solar Garage Power Plan
Before purchasing solar components, it is necessary to determine how much power will be required. This project is intended to provide enough power for lights, a garage door opener, and an outlet to charge 18 volt hand tool batteries. The power ratings used are examples only. You will need to collect power rating for the devices you plan to use. They will be similar, but may vary significantly.
Power Requirements of Various Devices
When calculating the power required for a solar system it is necessary to research the power required by each device to be operated. Find the wattage rating of each device. Then, estimate the time each device will be used in a 24 day. With a little math we will calculate the amp hours required to satisfy the demand.
Garage Door Opener Motor
A modern 3/4 horsepower garage door opener is rated at approximately 360 watts (120 volts x 3 amps). This is the power required when opening and closing the door.
Garage Door Opener Radio
It is important to remember that a garage door opener has a radio to receive a signal from the remote. The radio receivers tend to draw about 5 watts. While that is not a lot of power, it is on 24 hours a day, so must be considered in our calculations.
For simplicity sake we will assume 100 watts of lighting. While incandescent bulbs can be used, compact fluorescent or LED bulbs provide much more light with the same power.
18 or 20 Volt Battery Charger (single)
Quick chargers for 18 – 20 volt Lithium Ion or NiCad or Ni-Mh rechargeable batteries are rated around 75 watts per battery. Standard chargers are rated at much lower power levels. We will plan for a single quick charger. In standby mode, when the battery is charged but still on the charger, the units will draw just a few watts. Some will shut off entirely. We will assume 1 watt in standby mode.
Estimating Time of Use
Garage Door Opener Motor
An opener will run for approximately 15 seconds to open or close the door. We will estimate 2 open and 2 close cycles per day.
15 seconds x 4 cycles = 1 minute
Garage Door Opener Radio
The radio receiver in an opener is on 24 hours a day.
Light usage is highly variable. For this project we will use an estimate of 4 hours.
18 Volt Battery Charger.
Modern chargers will fully charge a battery in 4 – 6 hours.
If the charger has a standby mode, it will operate 24 hours a day.
Calculating Amp Hours Required
Now that we know the watt and time requirements for each device, we can calculate the DC amp hours needed to maintain the system. For simplicity sake, we will use the adage, “Watts are Watts.” While it is not completely true that a watt of AC power is the same as a watt of DC power, it is close enough for our purposes. The ratings of the devices are specified in 120 volt AC watts. We will be converting those values to 12 volt DC watts. This value will be used to size the solar system components.
The two equations we will use are:
- Watts / Volts = Amps
- Amps x Time = Amp Hours
Garage Door Opener Motor
- 360 watts / 12 volts = 30 amps
- 30 amps for 1/60th of an hour = 0.5 amp hours
Garage Door Opener Radio
- 5 watts / 12 volts = 0.42 amps
- 0.42 amps x 24 hours = 10.08 amp hours
- 100 watts / 12 volts = 8.3 amps
- 8.3 amps x 4 hours = 33.2 amp hours
18 volt Battery Charger
- 75 watts / 12 volts = 6.25 amps
- 6.25 amps x 6 hours = 37.5 amp hours.
Battery Charger Standby
- 1 watt / 12 volts = 0.08 amps
- 0.42 amps x 24 hours = 2 amp hours.
Total Amp Hours Required = 83 Amp Hours (Ah)
It is evident that prolonged power applications are the challenge. Any reduction of the time a device is used benefits the system. However, it is best to plan for the worst case scenario.
Selecting System Components
There are five specialized components in basic solar panel kit; Solar panel, charge controller, battery, inverter. The components must work in concert to supply the power required. It is vital that voltage and current ratings of each item is adequate to handle the power being fed to the system. We will use our 12 volt plan and 90 amp hour demand to select components.
Solar panels are available in various voltage ranges and silica crystal structures. The type of crystal is not particularly important. It does impact efficiency and lifetime, but only a minor amount.
Our system will require a 12 volt panel. Buyers are often confused by the voltage range of a panel. For instance, a 12 volt panel Open Circuit voltage is around 16 volts. This is normal.
Available daylight is also a factor in selecting a panel. In most areas, significant sunlight is only available for about 6 hours a day. We are trying to collect at least 83 Ah per day. The result of dividing the Ah required (83) by the number of sunlight hours available (6) will be the amp rating of the panel.
- 83 Ah / 6 hrs = 13.8 amps
Multiplying the amps required (13.8) times the volts of the system (12) will produce the watt rating of the panel required.
- 13.8 amps x 12 volts = 156 watts.
Look for a 12 volt panel rated at 150 – 160 watts .
A charge controller regulates the voltage and current from the panel as it charges the battery. Overcharging batteries can shorten their lives or even destroy them. Undercharging will leave you short on power and can shorten the life of the battery. Most charge controllers work with any style of Wet Cell Battery. Lithium Ion batteries MAY require a special charge controller. Since Li-Ion batteries are very expensive, sticking with some form of Lead Acid battery is recommended. We will look at battery selection shortly.
Types of Controllers
Two types of charge controllers are available: Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT).
PWM chargers are very simple, inexpensive devices. They sense the voltage of the battery and regulate the incoming voltage and current to charge the battery to a full state. They are essentially a smart voltage regulator. The drawback to a PWM controller is that it can only limit voltage and current.
A MPPT charger is smarter yet. It will take all the power that the panel can provide and modify it to the best voltage and current to fully charge the battery. If the battery is very low, the MPPT charger will drop the voltage and increase the current to charge the battery more quickly. As battery voltage increases, the MPPT charger will increase volts to push the battery to a full state. MPPT controller are over 25% more effective than a PWM controller.
Selecting A Charge Controller
Most Charge Controllers in this power range are designed to handle both 12 and 24 volts. The variable factor when purchasing a controller is the current. Since our panel will put out about 14 amps, we will need a controller rated at 20 amps.
There are four types of batteries used in solar applications: Flooded Lead Acid (FLA), Absorbed Glass Matt (AGM), Gel Cell and Lithium Ion. Gel Cells and Li-Ion batteries are price prohibitive, so will not be discussed in this article.
FLA and AGM batteries are two two versions of the standard Lead Acid Battery we are all familiar with. The main difference is that FLA batteries need some maintenance and AGM batteries do not. Since FLA batteries are not sealed, water evaporates from the cells and must be replaced. This needs to be done monthly. AGM batteries are sealed, so no evaporation can occur. FLA batteries also require a monthly Equalizing Charge to maintain the battery acid . This is a function of the charge controller. Most agree that FLA batteries provide the best bang for your buck, but do require some work.
Selecting a Battery
Batteries have several ratings. For solar applications, the Voltage and Amp Hour (Ah) rating are all we need to consider. We know that we have a 12 volt system and that we need to store over 83 Amp Hours. There are several ways to achieve these values. It is important to know that acid based batteries can only provide approximately half of their rated power. So, a 200 Ah battery can only provide 100 Ah of power. Discharging the battery more than 50% can shorten the life of the battery. The most effective way to achieve our 100 Ah value is to purchase two 6 Volt Deep Cycle batteries with a 200 Ah rating. These will be wired in series to achieve 12 volts.
A power inverter simply converts DC power to AC power. There are many variation of these devices on the market. For our purposes, a 750 watt (or larger) 12 Volt DC to 120 Volt AC Pure Sine Inverter will do the job. AC connections can vary on inverters. Some units supply only standard 3-prong outlets. Others have hard-wired connections available. If you are limiting yourself to bench-top systems, outlets are probably fine. If you are planning to install lights and a garage door opener, a unit with hard wire connections is preferable.
Some Notes About Purchasing Components
Most solar components are available on-line. While most home delivery services will not handle batteries, they can be ordered as Ship To Store items. Often, solar panels come as part of a kit. Such solar panel kits may include mounting hardware and an appropriate charge controller.
Looking for a 150 watt solar kit may help ease the tension when putting together your first system.
Solar Panel Installation
Installing a small solar system is a fairly simple project. Before beginning, it is wise to check on codes in your area. Most jurisdictions do not require a permit for a small 12 volt system. Once you convert to AC and hard wire some devices, it may be a different story. It may be worth a phone call to the County Building Inspector’s office just to be sure.
Location, Location, Location
Before placing any component, determine where components need to be used, where wires will be routed, where batteries can be stored, and where the solar panel will be mounted. There is no RIGHT answer. Every project is different. Make a plan and go with it. If it does not work out, items can be relocated.
Things To Consider
- The inverter should be placed close as possible to the point of use.
- The charge controller and inverter should be mounted on a wall at eye level.
- Location of the solar panel must also be considered.
- Will the panel be mounted on the garage roof, or on a pole nearby?
- Southern exposure is preferable for maximum sunlight.
- Avoid shadowy areas around other structures or trees. Direct sunlight is best.
- To minimize wire use, group the components in as small an area as possible.
- Accessible, but out of the way, is the best bet for all components.
- Batteries should be located on the floor, on a low shelf.
- Sealed batteries can be tucked out of the way.
- FLA batteries will need some attention so need to be easily accessible.
- A cover to keep the battery tops and terminals clean is recommended.
- A battery box or cabinet is good if available.
Mount The Components
Once you have decided the best location for the components, it is time to mount them. Mount the charge controller and inverter to a firm wall. Be sure to leave some space around both devices for wire routing and access to controls.
Place the batteries in their location. If two 6 volt batteries are being used, place them end to end. Terminals should be arranged in series: + – + – Using an appropriate length of battery cable, connect the middle – terminal to the middle + terminal. This will leave an open + on left and an open – terminal on the right. Voltage across these open terminals will be 12 volts.
Mount the solar panel as planned. Tape or wire nut the ends of the panel wires when working with the panel.
Use 12 gauge ROMEX for all locations. For outdoor runs, be sure to use exterior grade ROMEX. DO NOT connect anything at this time. Just route and stabilize wire in planned locations. Leave about 2 feet of extra wire at each location for connections.
- Run wire from the solar panel to the charge controller.
- Run wire from charge controller to batteries.
- Run wire from batteries to inverter input.
Make The Connections.
When making connections, be careful to watch the polarity of all components. White wire is always COM (-). Black or Red wire is always POS (+).
The sequence of connections is not particularly important, except one. The first connection must be from the batteries to the BATTERY terminals of the charge controller. This connection will let the controller know the voltage it will be working at. Depending on the type of battery terminal connectors you have, it may be a good idea to include the Battery to Inverter wires at this time. When you connect the battery to the charge controller, the unit should come on immediately. If not, check connections.
Next will be the connection from the battery to the inverter. Be sure inverter power switch is OFF. Make the connections. Once complete, switch on inverter to check power is flowing. If power comes on, turn unit back off to conserve battery power. If unit does not come on, check connections and any fuses the device may have.
The next connection will be the solar panel. Cover the panel with a tarp, cardboard, or old blanket to block the sunlight. Connect the wires to the panel leads or terminals. Use supplied connectors or wire nuts to make the connections. Use a electrical sealant if you have it. Also, secure wires to mounting hardware with zip ties.
The final connection will be from the solar panel to the charge controller SOLAR IN terminals. Once these connections are made, carefully pull cover off of the panel. The controller will indicate battery voltage, charge state, and possibly input power values.
Congratulations! You should now have a functioning solar garage. Connecting AC devices to the AC outputs on the inverter will provide power for your electrical needs. You now have a reliable source of renewable energy that will be more cost-effective in the long run than being grid-tied.
Keep moving towards total sustainability, reduce or eliminate your electric bill, and create a more energy efficient home with the use of more off grid solar projects!