A growing share of residential solar projects now attach energy storage batteries. In part one of this new series, we consider the backup power feature of batteries.
Attaching a solar array to a home is a long-term commitment, with many considerations, and one that offers great potential for energy bill savings. A recent addition to the list of options is whether or not to attach a battery energy storage system.
A battery can often add $10,000 or more to the total cost of a residential solar system, according to EnergySage. But it comes with a range of benefits that vary depending on the home’s electricity needs and experience with the utility company. So, what are the benefits?
In part one of this two-part series, pv magazine reviews the benefit of backup power. In the next part, costs, benefits, and timing are evaluated.
Blackouts or power outages occur with varied frequency and for different reasons, depending on location. Some regions experience transmission issues on the grid, weather events can knock out power, and some regions like southern California have scheduled rolling blackouts during high energy-demand periods.
A SunPower-backed survey of 1,500 homeowners found that 40% of respondents worried about power outages on a monthly basis. And one-third of respondents said high-profile outages, like the ones caused by winter storms in Texas this past February, are the top reason for considering energy storage.
The next logical question might be: how much battery to install, and for how long should it provide backup?
Installers typically give the choice between whole-home backup, which often require the installation of multiple batteries, or a partial backup, which allows the homeowner to select specific circuits that are tied to desired appliances or outlets. When selecting specific breakers, homeowners often select the refrigerator, garage door opener, home office, or other kitchen appliances.
To understand a home’s power needs, and to evaluate what is most essential to back-up, homeowners can use the Department of Energy’s Energy Saver appliance energy calculator .
One of the most common home batteries is the Tesla Powerwall, which has a 13.5 kWh usable storage capacity. This means it can provide 13.5 kW for one hour, or 1 kW for 13.5 hours, said EnergySage. A second big energy storage brand is from LG Chem, which has 9.6 kWh and 16 kWh models.
Translated to appliances, EnergySage said 13.5 kWh is equivalent to running a 3,500 W air source heat pump for just under four hours, a 200 W refrigerator for 67.5 hours, or five 20 W light bulbs for 135 hours.
EnergySage said a PowerWall can typically back up essentials like WiFi, phone, refrigerator, and some lights for about 24 hours.
Simulations run by the Energy Department’s Lawrence Berkeley Laboratory of residential solar and storage systems operated for backup power purposes suggest that a system with a 7 kW pv array and 10 kWh of storage could support 60-80% of a customer’s average daily load over the course of a year, depending on the region.
Plus, if the sun is still shining, a battery-connected solar array will continue to produce and store electricity. Solar arrays without a battery must power down during an outage, for safety reasons. Without a battery to store the power, there is no safe place for the power to go, so the system must use a rapid shut down device (the grid is inaccessible as it’s being repaired).
Solar installers will typically work with a homeowner to determine backup needs, and will evaluate the readiness of the home’s main electrical panel to be integrated for backup. In some cases, the installer will call for a main panel upgrade to accommodate the battery, Doing this may come at an additional cost.
In part two, we look at other capabilities, consider costs/benefits, and look at the issue of retrofitting existing systems.
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More articles from Ryan Kennedy
@RYAN KENNEDY Thank You for the timely article (always timely I guess really). I would please ask that you list more than just Tesla & Panasonic/Evervolt battery systems , there are many more, such as Growatt as well which uses LFP Battery Packs. Additionally, people need to realize & understand that when using Lithium Based Battery systems, that battery packs can be added over time and does “not have to be done” at the same time.
For example, one can start out with a 7.5kWh PowerWall type Module, and then another can be added 6 months or a year later if desired. Unlike the old Lead Acid days, Lithium Based systems do not suffer the same age degradation process as old Lead.
Battery Costing as you have shown may require some updating as well.. While A Tesla PowerWall may be close to 10K USD and Evervolt may run from 12-20K there are now several at similar storage capacity using LFP for far less cash outlay.
Also, something possibly you may not be aware of. There are Server Rack Mounted Smart Battery Packs which connect directly to AIO’s (All In Ones) from Victron, Growatt, SolArk, MPPSolar and other brands of equipment. using either CanBus or RS485. Do a quick search on “LiFePower4 Battery by EG4” or check out “Volthium BATTERY RACKMOUNT 51.2V – 10.24KWH / 5.12KWH – ESS” (Made & Tested in Canada).
I live in a region (North Ontario, Canada) which suffered 19 Power Failures in 2020. There are several Large Dairies here and they are now all installing solar, biogas & more. Many residences are now also installing solar + battery, the Grid Reliability is worsening annually while prices keep climbing, people have had quite enough…
Good article thanks. Looking forward to follow on parts. What is the maximum power output of these batteries or maximum load ? In other words it can deliver 13.5 kW for 1 hour but can it deliver, for example, 27kW for 30 minutes?
The 13.5kw Tesla battery can deliver 7kw peak and 5 kw continuous so the article is misleading in it’s suggestion that 13.5k can be delivered in 1 hour.To get 13.5kw per hour continuous you would need 3 x 13.5kw power walls
The tesla battery is rated for 5kwh continuos load at a time I’m able to have oxygen concentrator ,tv and video, fridge, and ac on and it lasts to about 5am then starts to recharge the battery once the sun shines on the panels at about 7.30am it recharges the battery by lunchtime. I have no shade on my panels and so far after 10 months I have powered the house 90% of the time and built up enough credit to also pay my gas bill and very happy with the investment.
Saving money; compelling. Saving a planet; it’s already saved or it ain’t gonna be. What I put on my roof isn’t gonna do $#it in that regard.
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