[Battery Series] An Overview on Backups

[Battery Series] An Overview on Backups

With the recent fires on the West Coast and the ice storm in Texas that shut down electrical utilities for days, sometimes weeks at a time, backup power has become top of mind for a lot of people. Because roof top solar shuts down in the event of a power outage, adding a battery to a solar system is a great way to maintain solar power when the grid goes down.

You might be asking, why does solar not work in a power outage? This is a code requirement for all secondary sources of power like solar, batteries, and generators. The utility companies don’t want those sources of power back-feeding the electrical lines when their workers are up there trying to restore power, possibly killing someone.

So, how do we get around this requirement? This is where an automatic transfer switch (ATS) comes into play. The ATS isolates your onsite electrical system (batteries and/or generator) from the grid so power cannot be back-fed onto the power lines. When power is restored, the system senses grid power and the transfer switch puts the system back into normal operation. The homeowner never has to leave the comfort of their home to make this happen, it is all automatic.

Enphase Enpower system installed at a client's home.
Enphase Enpower battery system.

Solterra has been designing and installing battery systems since 2010, so if you are unsure where to begin, we are happy to walk you through a few different options. The first questions we will want to have you consider are as follows:

  1. What items (circuits) do I want to back up and have operational when the power goes out?
  2. How long do I want to run those items for in the event of a power outage?
  3. What is my budget?

The answers to questions one and two will directly impact the answer to number three. The more circuits you want to back up and the longer you want to back them up for will increase the size of the battery bank and therefore the overall cost. One of our battery partners, Enphase, has a great sizing tool that you can play around with to hone in on the perfect backup battery system for you.

Tesla Powerwalls installed in a client's garage.

When choosing between a whole home backup and only powering a few critical items, it becomes important to understand how fast you might drain the battery. During an outage and when living off a battery, it is not business as usual. You will want to be very aware of only using necessary electrical loads to get you through an emergency. You never know how long the power will actually be out. For an entry level battery system, we can install a critical loads panel where the battery will only energize certain circuits in the house to get you through a power outage. These will allow you to stay warm, eat hot food, read a book, stay connected to the outside world, or watch a show. Here is a list of a few items and creature comforts:

  • Refrigerator
  • WIFI Router
  • Furnace blower on a gas furnace
  • Microwave
  • LED lights in select rooms
  • Outlets in select rooms for charging devices and watching TV

These few things will consume around 5kwh of energy per day. That means if you have a 10kwh battery then your battery will last 1.5days-2 days without a recharge. During a PNW winter, a full recharge from the solar may not be possible with our short, cloudy days, but in most cases pairing solar with batteries will give you much more resilience and autonomy than with a battery alone. Some batteries also have the capability of having generator support to top them off and some don’t. We also frequently install larger battery backup solutions so that customers can back up more items in the home.

LG Batteries installed at a client's home.

I always recommend to my customers who have recently installed batteries to turn off the main breaker to their home and practice living off the battery. That way, when there is an actual power outage, they will already have a good idea of how fast their batteries will drain. It is kind of like doing a fire drill. As part of the installation, we will set you up with an app on your phone that allows you to constantly track the state of charge of your battery. If it’s draining too fast, you can shut more circuits off. If it looks like you have plenty of energy in the battery, then fire up the blender and make some margaritas!

The peace of mind knowing that you can use your solar and certain electrical loads in your house during a power outage can be a huge stress relief. Solterra has installed multiple battery systems over the years, including Enphase Encharge, Tesla Powerwall, and LG Chem Resu Prime. All are great options with their own pros and cons that will be discussed in a future blog. If you want to know more now, feel free to call or text (206) 462-1103, reach out at [email protected], or submit your info here.

Author Bio:



Kevin is a Board Certified NABCEP PV Installation Professional and Licensed WA journeyman electrician.  He is currently the Sales Manager at Solterra.  He is passionate about the outdoors and environmental health, which led him into the solar industry.  Skiing and fishing were his main activities before having kids, which now dominate his free time.  Through his work at Solterra, he hopes to help do his part so that his kids can continue to grow up in a world with clean air and water. 

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