A kWh is 1,000 watts of energy running continuously for one hour. With solar batteries, this defines the usable energy within a battery system, also referred to as the battery bank. For Example:
- 1 kWh is equivalent to ten 100 watt light bulbs being on for an hour.
- It is equivalent to a 1,000 watt microwave running for one hour.
- It is equivalent to a 2,000 watt air conditioner being on for 30 minutes.
Is the rate at which energy is used to power a device or the rate of energy produced. For a battery system, this instantaneous power is important, as the ability to provide a surge of power to turn on a pump or other high wattage appliances and systems is necessary. A battery may have the capacity to run an air conditioner non stop for 8 hours, but without strong power capability, the system could be useless for many household appliances.
The amount of energy put into the battery which can be then be expelled and used by the home. The higher the round trip efficiency, the less losses that occur during the switch from DC to AC power.
DC stands for “direct current” and AC stands for “alternating current.” They are terms used to describe the current flow in a circuit. The electricity produced by the solar panels and stored by batteries is DC, while the electricity used in a home and by the utility grid is AC.
Solar plus storage works by using the clean energy produced by a solar array to charge a battery system. In the case of grid outage, the battery system works in the same way a conventional generator would. The homeowner may select critical loads for the battery to cover during an outage. An advantage of a battery system over a gas-powered generator is that the solar array can continue to recharge batteries, allowing the system to operate indefinitely without fuel costs.
There are currently two types of battery systems, AC coupled systems, and DC coupled systems. An AC coupled system is best to be used in a retrofit situation, as the battery unit itself will have an inverter to convert the AC power coming off the solar inverter back to DC power used in the battery. A DC coupled system will offer a slightly higher efficiency than an AC coupled system. With a DC system, the power coming off the roof stays in DC all the way through the battery bank until it is ready to be used by the home.
A home battery can provide a backup source of energy in the event of an outage and in some areas can even be used as a smart energy management system providing relief from “time of day” demand charges. When coupled with a solar array, the battery can be recharged and continue to provide power to a home, even during extended outages. A conventional grid-tied solar array will be shut down during an outage, rendering the solar panels dormant. A home battery also provides independence from fossil fuels as an environmental and financial advantage.
