Surely no one will accept such type of electricity, which is available only in daytime and usually on clear days only. For such situation we need electricity storage devices (batteries). But sad to say, that batteries add a lot of cost and maintenance to the PV system. Anyhow currently, it’s a necessity if you want to be completely independent. One solution to this problem is to connect your house to the utility grid, buying power when you need it and selling to them when you produce more than your need. In this way the utility acts as a practically infinite storage system. Of course in most cases the utility have to agree to buy power from you at a much lower price than their own selling price. You will need special equipment to make sure that power you sell to your utility is occurring at the same time as theirs means that it shares same sinusoidal waveform and frequency. For that safety is basic issue also, the utility has to make sure that if there’s a power outage in your neighborhood, your PV system wont try to feed electricity into line that lineman may think is dead. That is called islanding.
If you decided to use the batteries then keep in mind that batteries should be maintained and also replaced after certain number of years. Usually PV modules lost for 20 years or more while batteries don’t have such long useful life. Batteries in PV systems can be very dangerous because of the energy they store and the acidic electrolytes they contain, so for that you will need a well-ventilated, non-metallic enclosure for them.
Though there are different types of batteries are used but one common characteristic is all batteries is that they are all deep cycle batteries. While a car battery is a shallow cycle battery, deep cycle batteries can discharge more of their stored energy while still maintaining long life. While car batteries discharge a large current for a very short time only for starting up your car and they are immediately recharged also when you drive. A PV battery has to discharge a smaller current for long period (during night), and gets charged then in daytime.
The most commonly used deep cycle batteries are lead acid batteries and nickel cadmium batteries. Nickel cadmium batteries are more expensive but with long durability and can be discharged more completely without harm. Deep cycle lead acid batteries can’t be discharged 100% without seriously shortening battery life and PV systems are generally designed to discharge lead acid batteries no more than 40% or 50%.
To use the batteries another component Charge controller is required to be installed also. Proper caring can enhance batteries life, so that they aren’t over discharged or drained too much. That is the basic function of a charge controller. When the batteries will be fully charged then the charge controller wont let the current from the PV modules continue to flow into them. Same like that when the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will not allow more current to be drained from the batteries until they have been recharged. For long battery life charge controller use is so much essential.
Another problem aside from energy storage is that the electricity generated by our PV modules, and extracted by our batteries if we choose to use them, is not the form that’s used by the electrical appliances in our home. The solar system generates the direct current while the electricity supplied to our utility is alternating current. For that an inverter is needed, a device that converts DC to AC. Large inverters can automatically control how your system works.
Some PV modules that are called AC modules are having built in inverter already benefit of that AC module is that it helps to simplify wiring issues.
Now throw in the mounting hardware, wiring, junction boxes, grounding equipment, over current protection, DC and AC disconnects and other accessories and you have yourself a system. It’s highly recommended that the electrical codes must be followed and a licensed electrician who has the experience with PV systems will do the installation. After installation of a PV system it needs a very little maintenance and will provide electricity cleanly and quietly for 20 years or more.
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