Houses Off The Grid (Stand Alone)
Residential solar systems, called photovoltaic (PV) systems, are said to be stand alone if they are not connected to the local electrical grid provided by the local power company. The elements needed to convert power created by a stand alone solar system into a useable form for a house. Most households use only alternating current (AC current). Solar panels produce only DC current. A device, called an inverter, can convert DC current into AC current. A stand-alone solar system uses batteries for storage to provide electricity on cloudy days and at night. However, energy stored in a battery has losses. Only about 80% of the energy that enters a battery can be retrieved. Also, batteries are kind of messy and they need to be replaced from time to time. However, if you have a cabin in a remote area, solar power may be your only choice. Likewise, the space station and space ships depend on the conversion of solar energy to make living in space bearable.
The reliability of solar systems focuses not on cells, but on solar panels and other system components. Failures in solar systems usually originate from interconnection failures, glass breakage, or electrical insulation breakdowns. Solar systems normally have fault-tolerant circuit designs that utilize redundant features in the circuitry to allow continuous operation in spite of a partial failure somewhere in the system.
Houses on the Grid
A house is said to be “on the grid” if in addition to having solar panels installed it is also still connected to the local electricity “grid” from the local power company. Homes on the grid do not normally have battery storage, instead they draw power from the grid during evenings and very cloudy days, When they are drawing power from the grid their meters operate normally and they pay the normal price for their electrical service. If during daylight hours their solar system is generating more electricity than they are using, their meter runs backwards and they pump electricity back into the grid for others to use. When their meter runs backwards, they are selling electricity back to their local power company at the same price that they buy it for. Residential solar systems have become very popular in Arizona.