Battery Backup FAQ

Basics

A home battery system stores electrical energy to run electrical household devices (especially important devices) at a later time without the need of grid electricity.

There are two primary uses for a home battery system. The first is to serve as a backup power supply when the grid is down, so important appliances in the house are still powered during a blackout. The second use, which can sometimes come into play if an applicable time-of-use electrical rate program is available, is to help save money.  In certain situations, the battery can store lower-priced electricity (such as from a rooftop solar array), and then the stored energy can be used in the home when electricity rates are high.

Traditionally, lead-acid batteries had been used in the past for home applications. Modern stationary battery systems, normally storing 8 – 13 kWh of energy, use lithium-ion batteries with a lifetime of 10-20 years.  They are generally guaranteed for 10 years.  A portable power station is a smaller and less-expensive alternative to a stationary system. These portable systems generally store from .25 – 1.5 kWh and can be charged from a wall outlet and then stored in a closet for use during a power outage.  They can often be used to charge electronic devices, and if large enough, a refrigerator for a day or so. 

Batteries are normally installed where there is a rooftop solar system, but having batteries does not mean you must have solar. You can get an emergency battery backup system that is kept charged by the electrical grid. Or you can use a backup generator to charge the batteries should the grid be down for an extended period of time. Note that a solar+battery backup system qualifies for the federal income tax incentive, however, a battery-only system does not.

Stationary lithium-ion batteries are generally sized to hold about 8 – 13 kWh of energy. This is normally enough to power low-energy appliances like lights, refrigerators, fans, microwaves, and home electronics for a day or so.  For a longer duration, or for heavy-duty appliances, a system with multiple batteries is possible.

Economics

A basic stationary battery system in the range of 8 – 13 kWh will likely cost about $10,000 – $15,000 installed. However, state and federal incentives can sometimes bring the cost down substantially.  A portable power station in the range of .25 kWh – 1.5 kWh, will likely be in the range of $350 – $1,200.

Traditional back-up generators running on natural gas, diesel, propane, or gasoline are cheaper upfront, but have higher ongoing maintenance and fuel costs.  A home battery system can sometimes be more cost effective over the long run, and has the advantages of being quieter and less polluting.

Maintenance

Current lithium-ion batteries are practically maintenance free.

Environment

Yes. Lithium-ion batteries contain over 99% recyclable materials. They are warrantied for 10 years and can last much longer, with a small decrease in performance annually.

Yes. Home batteries can reduce our need for power plants and grid infrastructure improvements. For example, when deployed in sufficient numbers and with the right economic incentives, they can eventually be coordinated to reduce peak demands and avoid the need for inefficient gas peaking generating plants. Additionally, home batteries can store extra solar energy from the day to use at night, allowing us to use clean energy no matter the time of day.

Steps to use

Most stationary batteries can be installed indoors or outdoors. They are often located on an outside wall near the main electrical panel or inside on the garage wall. Portable power stations can be easily stored in a closet or garage and then moved into the house when needed.

Usually the whole process for installing a stationary battery can be finished in one or two days. A city permit is required and it is followed by an electrical inspection before being put in operation.

A stationary battery system is normally sized to power a limited number of crucial end-uses, such as lights, refrigerators, fans, microwaves, and home electronics. An electrical sub-panel is often installed at the time battery installation to separate out the specific loads to be backed up.

A battery system is normally sized to supply backup power for crucial end uses for less than a day without the benefit of any solar recharge.  When solar energy is available, it can be used to replenish the battery, extending the backup time. In any case, the duration of power availability will depend on the size of your battery, the availability of solar electricity for recharging, and the amount of energy used.

Generally not for a stationary battery project. These are high-voltage installations and require an expert, such as a licensed electrician.

This can be handled by the installer or accomplished with a smartphone app that is supplied by the manufacturer.  Most stationary battery systems are Wi-Fi connected, so communication is generally straightforward.

Yes, home batteries are quite safe with a lot of safety mechanisms already built in.

Incentives

Utilities, counties, Community Choice Aggregators, etc. sometimes offer rebates of various types on induction cooktops.