Solving Solar Power Issues

Having electricity during the day, and then only on clear days, is not a situation that anyone would choose to put themselves in, given a choice. There is a need for energy storage, in short, batteries. Unfortunately, batteries add a lot of cost and maintenance to the PV system. They are currently a necessity if you want to be completely independent. Some people attempt to get around the problem by connecting their house to the utility grid, buying power when they need it. They even sell the excess power when they produce more than they need. This way, the utility acts as a practically infinite storage system. The utility has to agree, of course, and in most cases will buy power from you at a much lower price than their own selling price. You will also need special equipment to make sure that the power you sell to your utility is synchronous with theirs -- that it shares the same sinusoidal waveform and frequency. Safety is an issue as well. The utility has to make sure that if there's a power outage in your neighborhood; your PV system won't try to feed electricity into lines that a lineman may think is dead. This is called islanding.

Please keep in mind that when using batteries, they will have to be maintained and then replaced after a certain number of years. The PV modules should last 20 years or more, but batteries just don't have that kind of useful life. Batteries in PV systems need to be in a well-ventilated, non-metallic enclosure for them because they can be very dangerous because of the energy they store and the acidic electrolytes they contain.

There are different kinds of batteries commonly used, but one characteristic they should all have in common is that they are deep-cycle batteries. Unlike a car battery, which is a shallow-cycle battery, deep-cycle batteries can maintain a long life but still discharge more of their stored energy. Shallow-cycle batteries discharge a large current for a very short time, for example to start your car, which are then immediately recharged as you drive. PV batteries generally have to discharge a smaller current for a longer period (such as all night), while being charged during the day.

Lead-acid batteries are the most commonly used deep-cycle batteries, which can be both sealed and vented, and nickel-cadmium batteries. Though more expensive, Nickel-cadmium batteries last longer and can be discharged more completely without harm. Even deep-cycle lead-acid batteries will have a seriously shortened life expectancy if they are discharged 100 percent. PV systems are designed to discharge lead-acid batteries no more than 40 or 50 percent.

A device called a charge controller is needed with the use of batteries. The life of the batteries last a lot longer if care is taken so that they aren't overcharged or drained too much. A charge controller does exactly that. Once the batteries are fully charged, the charge controller will not allow current from the PV modules continue to flow into them. Once the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will also not allow more current to be drained from the batteries until they have been recharged. Charge controllers are very important in maintaining a long life for a battery.

Another of the problems besides energy storage is that the electricity generated by your PV modules, and the electricity extracted from your batteries should you choose to use them, is not in the form that's used by the electrical appliances in your house. The electricity generated by a solar system is direct current. The electricity supplied by your utility as well as the kind that every appliance in your house uses is alternating current. That means you will need an inverter, a device that converts DC to AC. Some PV modules actually have an inverter already built into each module, called AC modules. These eliminate the need for a large, central inverter, and simplifying wiring issues. Most large inverters will also allow you to automatically control how your system works.
In order to have a working system, you will need mounting hardware, wiring, junction boxes, grounding equipment, over current protection, DC and AC disconnects and other accessories. You will also need an inspection to make sure that the electrical codes were followed. There is a section in the National Electrical Code just for PV, and it's highly recommended that a licensed electrician who has experience with PV systems do the installation. But once up and running, a PV system requires very little maintenance, especially if no batteries are used. It will provide electricity cleanly and quietly for 20 years or more.



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