Battery Backup

A battery backup system provides electricity for crucial needs during a power outage. When coupled with solar, batteries can extend the length of time that you’re protected because you can recharge the batteries from your rooftop. Battery storage is still quite expensive, however, so it’s not a good option for everyone.

Cost Range

$13,000 – $17,000

Based on typical system size of 12.5 kWh

About the technology

Uses: A battery storage system can provide peace of mind by storing electricity that lets you run important household devices during a power blackout. Also, in certain situations , a battery can let you store cheaper solar power for later use to reduce the need for higher-priced electricity from the grid. 

Types of Systems: Stationary battery systems typically use lithium-ion batteries and range from 4 to 13 kWh of storage capacity.  A portable power station is a smaller and less-expensive option that’s suitable for renters as well as homeowners.  Generally in the range of .25 – 1.5 kWh, these can be charged from a wall outlet and then stored in a closet until needed during a power outage.

Economics: Stationary battery storage is still quite expensive, sometimes costing as much or more as a rooftop solar system alone.  Given the costs, homeowners often opt for storage only when the reliability of power supply is a significant concern or local electricity prices present a substantial benefit for the later use of stored electricity.

Maintenance: The current generation of lithium-ion batteries is virtually maintenance free. 

EV-Related Storage Options: An emerging storage option involves the use of an EV’s battery, instead of a stationary battery system.  This has the economic advantage of using one battery for both home storage and transportation. It can also result in a much larger available capacity since many EV batteries hold 50 kWh or more.

Frequently Asked Questions (FAQ)

1. What are the main uses of a home battery system?

A home battery system stores electrical energy to run household devices (especially essential devices) at a later time without the need of grid-supplied 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 electric rate 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.

2. What types of batteries are there?

Lead-acid batteries had sometimes been used in the past for home applications. However, modern storage 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 until needed during a power outage.  They can often be used to charge electronic devices, and if large enough, a refrigerator for a day or so. 

3. Is rooftop solar a must for batteries?

Stationary batteries are normally installed where there is also a rooftop solar system. This allows you to charge the battery when the grid is down and the sun is up. However, having battery storage does not mean you must have solar. You can get an emergency battery backup system that is kept charged by the electrical grid. Note that a solar+battery backup system qualifies for the federal income tax incentive, while a battery-only system does not.

4. Will one battery be enough?

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 two.  For a longer duration, or for heavy-duty appliances, a system with multiple batteries is typically used.

1. How expensive are they?

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.

2. Are back-up generators less expensive?

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.

1. What type of maintenance is needed?

Current lithium-ion batteries are practically maintenance free.

1. Can the batteries be recycled?

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.

2. Are home batteries good for the environment?

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 for load shifting, they can be coordinated to reduce peak demands and reduce the need for fossil-fired generation plants. Additionally, home batteries can store extra solar energy from the day to use at night, allowing us to use clean energy later into the evening.

1. Where are batteries typically installed?

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.

2. How difficult is the installation process?

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

3. How many appliances can a battery system power?

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 of battery installation to separate out the specific loads to be backed up.

4. How long can a home battery serve as backup in case of a power outage?

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.

5. Can it be a DIY project?

Generally not for a stationary battery project. These installations require some expertise and are typically carried out by an expert, such as a licensed electrician.

6. How is the operation of a battery system programmed and monitored?

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.

7. Are batteries safe?

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

1. What types of incentives are available for home energy storage?

A key incentive is the 30% federal tax credit which is available when storage is paired with a solar system.   In some cases other incentives are also available at the state and utility levels.  Taken together, incentives can take thousands of dollars off the price of a battery system, making them much more affordable.

2. Can I take the Federal Solar Tax Credit for a battery storage system?

It depends. If the battery is only charged by a renewable energy system located on your property, then the 30% credit can probably be taken. It may also be required that the battery be installed within one year of the renewable energy system’s installation and that it be installed at your primary residence. On 1/1/33 the credit is scheduled to drop to 26%, on 1/1/34, it will drop to 22%, and on 1/1/35, it will drop to zero. (Consult a tax expert for a definitive assessment of your ability to make use of the credit.)