Everything You Need to Know About Home Batteries

ProductsCalendarMay 16, 2018

Did you know you can use a battery to power your home? We’re not talking about a few emergency flashlights, but actually having some energy stored in a home battery to power what you need in case of an outage - like a breaker and an outlet for your wifi router. A home battery can store energy needed for your home and even potentially save you money on your electric bill!

Battery Benefits

There are several reasons why you might want to equip your home with an energy storage system, and more than one way to do it. You can have a battery connected to the utility for charging, but the most economical choice is to install a home battery that can be charged by solar power. Pairing a rooftop solar system with battery storage means you can charge the battery with your own panels instead of the power you buy from a utility - and the power can be replenished daily. Solar energy stored in a home battery not only gives you backup power in the case of an emergency, but the battery can also optimize savings for you. You not only have the option to choose when to use the stored energy if you live in an area that has Time-of-Use (TOU) rates, but the battery will do it for you!

If you already have a rooftop solar system and previously decided against battery storage, it’s a good time to revisit your options. Batteries have evolved significantly in recent years and they keep getting less expensive and more efficient. Net metering policies are also in flux.

With a rooftop solar system, power from your panels flows into the home to meet the household’s needs, and any excess solar energy is sent to the grid. During hours when panels don’t generate electricity (at night, for example), the home draws power from the grid. With a favorable net metering policy, this often balances out financially. Where net metering isn’t an option though, it doesn’t make financial sense to funnel your excess power to the grid, as you have to turn around and buy it from your utility later at a higher rate. This is where a battery becomes especially helpful. A battery gives you the flexibility to choose when to draw power from the grid and is likely to save you money if your utility charges TOU premiums or doesn’t offer net metering.

How They Work

A home battery or storage system allows solar customers to get the very most out of their rooftop panels by storing unused electricity for later use instead of routing it to the grid. This way, when your panels aren’t generating power, your home pulls power from the battery instead of the grid. In a power outage, your battery provides you with backup - because rooftop solar panels are tied to the grid, you’ll otherwise lose power during an area outage even if your panels are getting sunlight. Some batteries can also be charged by the grid.

The way your home battery is configured may impact which tax incentives you can claim, and when you install it may affect your net metering agreement, so you’ll want to be sure you understand all the particulars specific to your location before you have something installed.

The amount of battery backup power will depend on a variety factors including the size and capacity of your battery (or batteries) as well as the energy demands of your home. Your battery installer should be able to explain the specifics to you and help you determine what is available and necessary for your home.

The Options

Now the real question...what are the options and which one should you choose?

Lead-acid and lithium-ion batteries are the market standards for home energy storage. There are developing technologies like flow and zinc-air batteries, but the dropping price tag of lithium-ion batteries has secured them as the only major market players today.1 Lithium-ion is recommended for solar home batteries because of its longer lifespan and high depth of discharge - which is tech talk for how much of the battery’s capacity can be used before it needs to be recharged. Basically, a high depth of discharge means you get more power out of each charge.2 Lead-acid batteries are typically cheaper upfront, but they have a shorter lifespan and a lower depth of discharge.

The current market leaders for U.S. residential batteries all use lithium-ion batteries - LG Chem’s RESU, Tesla’s Powerwall, and the sonnenBatterie. Each of these options will give you the advantage of backup power when you want it, but they’re not exactly the same. Just like any other major home purchase, you’ll want to find the one that’s best for your needs. We’ll take a look at your options next. (If you’ve heard about a battery that’s not on our list, it may be because it’s not available in the U.S. yet - several are currently made only for European markets.) 

Each of the batteries listed here are compatible with rooftop solar and offers an app to view your batteries charge and discharge. Some even allow you to control your battery use from a smartphone or tablet.

LG Chem RESU10H

This is a 9.8 kWh battery and you can stack two together for up to 19.6 kWh of storage depending on your home’s needs. LG Chem guarantees its battery storage capacity with a 10-year warranty,3 which is worth taking into account when you consider your potential return on investment. The RESU design also allows you to choose where in your home to install it.

The RESU is available in most solar markets - in fact, it’s quickly becoming the industry standard for U.S. residential installations, which can give homeowners additional peace of mind about the long-term stability of the company (and its warranty). Check with your solar installer to see if the RESU is an option for you and find out exactly what the price includes. Installation costs are usually extra and you may need to buy a dedicated battery inverter. (Vivint Solar offers the LG Chem RESU, which is compatible with Vivint Solar’s inverter, so no need for a separate one here.)

Tesla Powerwall

Powerwall offers 13.5 kWh of storage and can stack up to 10 batteries. Powerwall also offers a 10-year warranty but no guarantees on retained storage capacity or performance over time.4 The Powerwall is also available in most U.S. markets and is installed only by Tesla or a Tesla-certified installer. As with the RESU, the cost to install a Powerwall varies greatly but it does have a built-in inverter.

sonnenBatterie

Sonnen’s home battery is prevalent in Europe but not in the U.S. to date. It is available in capacities from 4 kWh to 16 kWh5 and also boasts a 10-year warranty and built-in inverter. It is usually the most expensive of the U.S. options and is only available through select installers.

Installing Your Home Battery

Installing a solar battery is a lot more complex than changing the batteries in your smoke alarm and it’s best to have a professional do it. Some battery producers are partnered with rooftop solar installers to ensure flawless integration into your solar system. If you think a home battery is a good fit for your household, ask your solar provider if they offer home battery installation and which batteries they offer. 

Because battery installation is just starting to gain momentum, solar companies may only offer them in some areas. If your area is not one of them yet, ask about a waiting list so you can be first in line when it’s offered in your city! 

You can find out more about the RESU battery option and talk to an expert today.

 

Endnotes:
1. https://www.greentechmedia.com/articles/read/how-alternative-battery-makers-are-trying-to-compete-with-lithium-ion#gs.ogtBmjE
2. https://www.energysage.com/solar/solar-energy-storage/what-are-the-best-batteries-for-solar-panels/
3. https://www.energysage.com/solar/solar-energy-storage/lg-chem-resu-battery/
4. https://news.energysage.com/tesla-powerwall-vs-sonnen-eco-vs-lg-chem/
5. https://sonnenbatterie.de/en-us/sonnenbatterie

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