The most visible components of a photovoltaic (PV) energy-generation system are the solar panels. You usually don't see the devices that convert the energy the solar panels generate to a more useable form. Hidden out of the sun and sometimes far from the panels, these devices store the energy and make it accessible to your home's electric system. Understanding the basics of a PV system will help you choose components wisely and install them correctly so you can get the most from your system.
Things You'll Need
- Solar panels
- Mounting brackets
- 12-volt deep-cycle batteries
- Battery cables
- Charge controller
- Phillips screwdriver
- 14-gauge, plastic-coated electrical cable
- Transfer switch
Calculate the number of panels you need by determining your energy needs. These will be different if you are "off the grid" and running your house exclusively from the PV system than they will be if you are supplementing energy supplied by the power company. Each solar panel is built to output direct current (DC) electricity at a specified voltage and wattage. Each one in your array should be rated for the same voltage.
Set up your solar panels in a southerly facing direction in a shade-free location on your property. Mount the panels securely, with mountings designed for the specific panels you have. Anchor the mountings securely so the panels won't be displaced by the wind.
Construct a battery bank from deep-cycle batteries. It is most common to use 12-volt batteries specifically designed for solar systems.
Match the voltage of the bank to the output voltage of the panels. Panels commonly have an output of 24 or 48 volts. To match this voltage with 12-volt batteries, wire them in series. A unit made up of two batteries wired in series has double the voltage of either battery. To make a 24-volt unit from two 12-volt batteries, connect the positive terminal of one to the negative terminal of the other. To make a 48-volt unit, connect two more 12-volt batteries in the same way so that the four batteries are daisy-chained, with the terminals of each battery connected to the opposite terminals of the adjacent ones. There will be a free terminal on the battery on either end.
Increase the capacity of the bank, and its ability to store energy, by adding more batteries, according to your energy requirements. They should be in units that are wired together in series to match the panel output. Wire the units together in parallel by connecting all the free positive terminals to each other, and all the free negative ones. For example, if your panel has a 48-volt output, and you have 16 12-volt batteries, wire them in units of 4, connected in series, then connect the 4 free positive terminals together, and the 4 free negative ones, to make your bank.
Install a charge controller near the battery bank, and connect it to the positive and negative terminals of one of the battery units in the bank with battery cables. The purpose of the controller is three-fold. It regulates the voltage of the panels, which fluctuates with weather conditions, to create a stable input for the batteries. It also prevents the batteries from overcharging. Finally, it prevents current from flowing from the batteries to the panels and damaging them.
Connect all the panels together in parallel by following the instructions of the panel manufacturer. Some panels simply plug into one another, while others have a terminal box that you can open with a Phillips screwdriver to do the wiring. Loosen the terminal screws inside the box, wrap the wires around them, and tighten the screws. Connect a length of 14-gauge double-stranded plastic-coated wire to the terminals of one of the end panels, and run it above-ground or underground to the charge controller.
Install an inverter near the battery bank and connect it with battery cables. The inverter converts the DC voltage supplied from the batteries into 120-volt AC household current. Connect the inverter to the main current feeds in your panel. If you are installing a grid-tie system, this is best done by a licensed electrician, who will have to install a transfer switch. It will prevent your panels from energizing the power lines in the event of a power blackout, which could injure a lineman working on them. It will also allow you to use battery power when it is available, and grid power only when necessary.
Program the inverter to sell power back to the power company, if it has this capability. When it is programmed this way, your electric meter will run backward when your power consumption falls below that supplied by the PV system.
Tips & Warnings
- You can dispense with the battery bank, if you like, when you are tying into the grid. You will only have power when the sun is out, but you can use it to make your meter run backward and save on your energy bill.
- Photo Credit Solar energy image by lefebvre_jonathan from Fotolia.com
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