Welcome to Home Energy Storage 101. Here you’ll receive an introduction to the basics of home energy storage, including:

• Components

• Benefits

• Design considerations and trade-offs

Home energy storage is a way to store energy in a battery for your home to use. The battery system can be a standalone setup or connected to a solar system. 

Why is home energy storage trending right now? There are several overarching themes emerging. 

• Some homeowners are looking to store excess solar energy produced by their panels in order to use it later, as opposed to selling it back to the power company. 

• Others are looking for resilience during power outages. 

• With rising energy costs and peak rates (or time of use rates), many homeowners are trying to save some money by using stored energy instead of the grid during peak times. 

• Lastly, it’s a way to support the grid, especially during extreme weather or peak use times.

A home energy storage system needs a battery to store energy, and an inverter to turn the stored energy into usable energy for your home.

Optional components would include solar panels or a generator.

Batteries

When shopping for batteries, you’ll come across some terms and numbers that can quickly become confusing as you compare across various brands. 

Let’s look at the main specs you’ll want to consider:

• Capacity 

  • • 1. 1. • How much energy storage the battery has, in kWh

• Usable capacity

  • • 1. 1. • Some batteries have to retain some charge to help prolong life and maintain efficiency, so usable capacity may not be equivalent to capacity

• Output power

  • • 1. 1. • How much electricity the battery can provide at once, in kW

• Round Trip Efficiency

  • • 1. 1. • How much electricity the battery provides compared to its capacity

            • Some energy can be lost between storage and use. The higher the efficiency, the less energy is lost.

Inverters

Batteries store energy in the form of DC electricity. An inverter is necessary for translating DC power into AC power for use in your home appliances. If you have an existing solar system, read on for more details on whether you can use an AC or DC coupled battery system.

As mentioned above in why home energy storage is on the rise, there are many benefits to adding a solar or storage battery to your home. Here are the key benefits - depending on your home and location, some may add more or less value to your situation.

• Backup Power - having stored power can help alleviate the stress of a power outage (link article)

• Self-consumption - allows you to generate and use solar energy from your panels, then save your excess energy to use later

• Time of Use (ToU) - If you have varying rates based on the time of day, you can use your battery to do something called rate arbitrage, which is using your stored energy during peak rate hours and avoid the surcharge

• Zero export - without storage, excess solar energy would be sent back to the grid (or exploited). With a battery, you could store and consume that energy yourself when you are not generating solar energy.

  • 1. • With net energy metering (NEM3) in California, selling excess solar energy back to the power company is financially a less attractive option than storing it for later use

• Peak-load shifting - this is more applicable in commercial or industrial contexts, but essentially it means shifting the bulk of energy use to the times of day that are low demand or off-peak hours

• Virtual Power Plant (VPP) and Grid Stabilization - this is an exciting concept of bundling multiple storage systems together to harvest energy to help support the grid when the grid is stretched too thin, or to help store excess energy from wind or solar.

AC vs DC Coupled Battery

There are a couple key differences to having either AC or DC coupled battery systems. 

Here at Mountain Microgrids, we support both systems.

DC coupled is more efficient because it requires fewer conversions (and therefore less energy loss). 

Overall, compared to AC coupled batteries, DC allows for a 15% increase in energy stored in the battery.

AC coupled batteries can be retrofitted to existing solar systems or new micro-inverters, but requires more conversions, and therefore less efficient.

Whole House vs Critical Loads panels

A large deciding factor for home energy storage is whether you want to back up your entire house (to the main panel) or set up a critical loads panel with the “must-have” appliances and outlets to keep on during a power outage. 

This will depend on your family’s needs, how much of your home is electrified, and your budget.

Whole house backup can be 2-3 times the cost for 2-3 times higher power output, and might be a better fit for those who have mostly electrified homes. If you have the budget, this provides for the most seamless and least disruptive solution for your family during power outages.

Having a battery to power just the critical loads will be less expensive overall, but more limiting during a power outage. However, this might be sufficient if you have gas heating and cooking appliances.

Mountain Microgrids is here to provide additional support designing a solution for your unique home and family.