By: N. Olison - PVPower.com Contributor - August 13, 2009
- Off-Grid systems are not tied into the local utility grid
- These systems must produce enough energy to fulfill the energy needs of the home
- Batteries are a key component of any off-grid system; power is stored in rechargeable batteries
Off-grid systems take the sun’s light and turn it into a useable current that provides all of the modern conveniences you’re used to. Off-grid battery systems are a little bit more expensive than grid-tied systems because of the cost of batteries and the charge controllers. Batteries generally need to be replaced every 10 years or so. It’s difficult to measure the lifespan of a battery because it really depends on the quality of the battery, how often the battery is used, and how well the battery’s maintained. An off-grid system depends more heavily on the batteries than an on-grid system would.
Some off-grid systems use a backup generator in addition to the batteries. These backup generators are usually run by fossil fuels. With a special type of off-grid inverter, the generator can be used to power the house, as well as simultaneously charge the battery.
Off-grid batteries should be kept in a weatherproof room. It can be either inside the house or outside. This room is going to house not only the batteries, but the charger controls, an off-grid inverter, direct current (DC) fuses, an alternating current (AC) fuse box, and a dump heater. The dump heater is used to handle the overflow of energy. If the batteries are fully charged, the system sends the energy to the dump heater, which in turn heats up the house.
Off-grid systems normally use 24 to 48 volt batteries. Higher voltage saves money on wiring. The 12-volt batteries aren’t obsolete, but they’re confined to doing smaller jobs. Off-grid batteries are very big, clunky devices. They use chemical reactions to charge and discharge electricity. Sulfuric acid reacts with lead and lead dioxide to form lead sulfate. The chemical reaction is reversed when the battery charges back up again. This however, leaves a lead sulfate residue that can cause problems with battery efficiency over time. This can all be fixed with an equalizing charge. During an equalizing charge the battery is charged at a higher voltage, burning away the residue in the process. After an equalizing charge, you have to add water back into the battery solution. This is why off-grid batteries are better off if you buy them unsealed. So you can add the water yourself.
Off-grid battery systems are a little less convenient than on-grid systems. But they can also be quite rewarding, especially if you live in a more rural area, where the utility company charges extra to put you on the grid.
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