There are different types of solar installation. Perhaps the most romanticized type is the completely off-grid solar system — the only choice for a house situated in a remote area. This system requires batteries, typically of lead acid; these can be messy and require ongoing maintenance by the homeowner. An off-grid solar system will need to accommodate the year-round variance of sun intensity. This type of setup is typically more expensive than grid-based solar. Some individuals, prioritizing true independence and seeking to live efficiently, may choose to go off-grid even though they don’t have to. Sometimes, people use the term “off the grid” not literally but as a metaphor for reducing overall usage and focusing on efficiency and sustainability.
The most popular type of grid-based solar is a grid-tied installation with no batteries. This system is cheaper, has no moving parts and is highly reliable — a homeowner can anticipate decades of sun power with virtually no maintenance. Such systems are eligible for generous federal and state tax credits. However, when the electric grid goes down, a grid-tied solar installation will also go down, by design. This occurs to disable backfeeding of power from the inverter into the grid — possibly shocking line workers or emergency personnel. Some homeowners may opt to have a generator ready to use during outages.
Adding batteries to a grid-tied solar installation provides a complete solution. Unfortunately, batteries are very expensive and usually require maintenance. They must be replaced eventually (within 7-10 years). For example, a battery system capable of providing load to a normal home for two days could cost nearly $25,000. Additionally, a generator may be necessary to recharge the batteries.
Some systems have an “intertie” allowing them to trade or sell back power to the local utility, lowering the homeowner’s costs. In this case, incoming power and outgoing power are measured by a bidirectional meter. The utility adds power from the homeowner to a “bank account.” Each month, this account balance is credited toward the homeowner’s bill.