If you’re researching home batteries, you may be overwhelmed by the amount of information out there. From the batteries size to its installation location and maintenance, there are a many factors to consider when buying a home backup battery. Our experts have compiled some of the most frequently asked questions in this home battery FAQ and answered them to help you make the right decisions when purchasing a home backup battery.
Can I add batteries to an existing rooftop solar array?
Yes. Adding batteries will make your rooftop array even more valuable since you will be able to store excess solar energy and you will be able to use solar power even if the grid goes down. You will need to decide if you want an AC coupled system or a DC coupled system.
What is the difference between an AC coupled battery system and a DC coupled battery system?
In an AC coupled system, the DC power produced by your solar panels is converted to AC power by your solar inverter so that the power is compatible with your home's AC wiring system. Your battery inverter is connected to your home wiring system and converts some of that AC power back to DC to be stored in your battery. When you need to pull energy from your battery, your battery inverter converts the stored DC power back to AC for use by your home appliances. Each time the power is converted between AC and DC there is a slight efficiency loss. In an AC coupled system, any stored energy that you use has to be converted three times. In a DC coupled system, The DC power from your solar array charges your battery directly without the need for a conversion. The power from your solar array and your battery only needs to be converted from DC to AC one time in order to be used by your home appliances, so it is more efficient.
Should I get an AC coupled battery system, or a DC coupled battery system?
If you are purchasing solar and batteries at the same time, it may be better to get a DC coupled system because it requires less electronics and it is more efficient.
If you are adding batteries to an existing solar array, the answer is more complicated. To install a DC coupled system on an existing solar array may be easy if you happened to purchase a solar inverter that is designed to have a battery system attached. If not, then you will need to remove your existing inverter and replace it with DC coupled solar & a battery inverter. The alternative is to install an AC coupled battery system which requires a separate battery inverter but is easier to install with an existing solar system, and will likely cost less. However, operating a DC coupled system over time will cost you less because of the higher efficiency. In most cases the extra cost of a DC coupled system will be recovered in 3 to 5 years.
What is an inverter?
An inverter converts Direct Current (DC) power to Alternating Current (AC) power. Since your home uses AC power and your solar panels produce DC power, a solar inverter is used to make the energy produced by solar panels compatible with your home appliances. Since batteries also discharge their stored energy in the form of DC power, an inverter is also needed to convert battery power into a form that you can use.
What is a bi-directional inverter?
A bi-directional inverter can convert AC power to DC power and it can also work in the opposite direction by converting DC power to AC power. Bi-directional inverters can be useful for batteries because it enables them to convert discharged power to AC, but it also allows them to charge from an AC power source. Standalone home batteries that charge exclusively from the grid require a bi-directional inverter.
What is a charge controller?
A charge controller controls the charging and discharging of a battery. A charge controller is required for solar panels to charge a DC coupled home battery. The charge controller will shunt the solar power to the grid once the battery has reached the desired level of charge. A charge controller enables a battery and a solar array to share a single inverter.
Does it make sense to buy a home battery if I don’t have solar?
Yes. You can charge a home battery from the grid and use it to provide backup power during power outages. It can also save you money if you are on a time-of-use utility rate plan. You can charge your battery when electricity prices are low, and you can draw power from your battery when electricity prices are high.
What is the best home battery technology?
There are a lots of options for home batteries with a variety of technologies and brands. Different types of lithium-ion technology are the most popular because they are able to store a large amount of energy in a small space and weight compared to other technologies. This is why most electric vehicles and new home battery products use some type of lithium-ion technology. Lead-acid batteries may be a more cost effective solution if you need a lot of energy storage and have a lot of space to devote to batteries. The technology that a battery product uses is not as important as how the battery product performs compared to your needs.
What should I consider when buying a home battery?
The key factors are:
The energy storage capacity, usually measured in kilowatt-hours (kWh)
The form-factor. What is the size, weight, and appearance?
The configuration. How is the system wired into the home and what functions does it perform?
What are the common configurations for a home battery?
The common home battery configurations are: battery-only, DC coupled with solar, AC coupled with solar, and battery plus generator.
What are the advantages of a battery-only configuration?
Battery-only systems provide a few hours of back-up power to protect against short duration power outages. Battery-only systems can also provide a financial payback if you have any type of variable electric rate plan with your electric utility.
What are the advantages of a DC coupled battery with solar configuration?
DC coupled configurations provide the most efficient storage of your solar energy, and is the most cost effective if installed at the same time as your solar system. This configuration also gives you extended back-up power if you have a daily surplus of solar energy production.
What are the advantages of an AC coupled battery with solar configuration?
An AC coupled configuration is most cost effective if you are installing your battery as an add-on to an existing solar system. AC coupled systems can also be charged from the grid as well as your solar array, allowing you to take advantage of low variable utility rates in some situations. This configuration also gives you extended back-up power if you have a daily surplus of solar energy production.
What are the advantages of a battery plus standby generator configuration?
A battery plus a standby generator gives you back-up power for extended outages and is more cost effective to operate than a generator alone, particularly if you have frequent power outages of short duration.
Can I use the battery in my electric vehicle to power my home?
This feature is not generally available in electric vehicles being sold in North America, but this is likely to be an option in the near future.
Can I use my electric vehicle to store excess energy produced by my solar array?
Yes. By charging your vehicle during hours of excess solar production you are effectively keeping the energy for yourself rather than feeding it back onto the grid. This makes financial sense because most utilities do not compensate you for the full retail cost of any solar that you feedback to the grid.
Can a home battery power my air conditioner?
It depends on the size and number of air conditioning units that you have. For larger AC units that cannot be started by your battery, it is possible to install a “soft-start” module which buffers the in-rush current to your AC and allows a home battery to start the unit. One can also install more batteries to provide higher current output. It should be noted, however, that running air-conditioning from a home battery will deplete the battery quickly, and you may be better off saving that energy for refrigeration and lighting.
How long can a home battery power my home during a power outage?
If your home battery is paired with solar panels, you can power your home indefinitely by using solar energy during the day and storing the excess to get you through the night. At times, you would have to carefully manage your power use, unless your solar and battery installation was extremely oversized. Nevertheless, you would have some energy available virtually everyday unless you live above the arctic circle in the winter or are experiencing complete solar blockage from extreme weather. With a properly sized system, you would have enough energy to live comfortably most days. If you have a battery without solar, then a typical home battery system will provide back-up power for anywhere between 3 hours and 12 hours between charges, depending on your level of power usage and the size of the battery.
Will I still get paid for solar energy I sell to the grid through net metering?
Yes. Although a battery may help you keep more of the energy that you produce with solar, it does not impact the compensation or credit that you receive when you do send energy back to the grid.
How many years will a home battery last?
Most home batteries have a 10 year warranty, and will likely last longer than that.
Do home batteries require maintenance?
Old style lead-acid batteries traditionally used for off-grid back-up in remote applications do require some maintenance, but the new lithium-ion home batteries require no routine maintenance.
How long does it take to get a battery installed?
Some battery products require a lead time to be delivered because of product shortages. These lead times can range from no delay to a few months depending on the brand and the local market conditions. Once the installer arrives on site with the battery, installation can generally be completed in 1 day or less.
Can I save money with a home battery?
Yes. If you have solar, a home battery can help you save your excess solar production which you can then use to offset the use of costly utility power. If you do not have solar but are on a utility variable rate plan, You can save money by charging your battery when electricity prices are low, and drawing power from your battery when electricity prices are high. Discover potential savings with our home battery pricing tool.
Where are home batteries located?
Home batteries are typically installed in a garage. While this is not mandatory, the garage is usually the most practical and cost effective location for the battery.
Are home batteries safe?
Yes. Almost every product on the market is UL 9540 listed, and are equipped with safety features that make it almost impossible to short the battery and create a fire. As with any electrical equipment that does not plug into an existing outlet, a licensed electrician should do the installation to ensure a safe and reliable install.
Do I need a permit to install a home battery?
Most likely. If you are in a location that requires permits for modifications or expansions to your home electrical system, then you will need a permit. Your licensed electrician installer will usually handle obtaining the permit as part of the install service.