Energy storage combined with solar energy in behind-the-meter (BTM) applications reached around 550 MW in 2020, which, according to Lawrence Berkeley National Laboratory (LBL), corresponds to around 17% of the total US battery storage capacity installed during the year.
Berkeley Labs reports that residential complexes account for about two-thirds of total BTM solar storage capacity, in part because almost all residential storage is solar-powered.
Around 3,200 MW of storage capacity had been added in the USA by 2020. Around 1,000 MW (30%) were behind the meter, 550 MW of which with solar energy. In 80% of the projects, the residential storage system was coupled with solar energy, while the BTM storage system for non-residential buildings comprised solar energy in 40% of all projects. Around 19% of all storage capacities in the supply area / in front of the meter reading were coupled with solar energy.
80% of the batteries are coupled with solar energy at the residential level.
Image: Berkeley Labs
Battery attachment rates
Despite the national growth, the storage connection rates of BTM solar installations remain low, the report says, with 6% of residential and 2% of non-residential facilities choosing to connect batteries at installation.
Some states and coverage areas had much higher storage retention rates, particularly Hawaii. In 2020, around 80% of all PV systems in residential buildings and 40% of non-residential systems were coupled with storage.
Hawaii is an outlier in connection rates for solar and storage systems due to high energy prices and the lack of net metering.
Image: Berkeley Labs
California also showed relatively high retention rates caused by a combination of direct bar discounts on warehouse equipment and concerns related to power outages caused by forest fires, Berkeley Labs said.
Income had some correlation with residential-level storage retention rates, the report said. In California, residential PV + storage customers had median incomes 66% higher than the median income in their area, while individual PV + users had 41% higher.
Schools' share of PV + storage systems (25%) was significantly higher than that of island PV (8%). Berkeley Labs attributed this to a unique resilience score and relatively large stresses on the sector.
Retrofitting or adding batteries to an already active PV system was not a relatively common occurrence, except in California. In residential complexes, 25% of the paired systems were retrofits and 38% of the solar and storage systems for non-residential buildings were the result of retrofitting.
PV systems of all ages were fitted with storage retrofits, but they were typically installed on systems that were less than three years old. About 10% of all retrofits have added additional PV capacity, the report said.
Berkeley Labs said the private storage market was dominated by two brands in 2020, the Tesla PowerWall, a 5 kW / 13.5 kWh, 2.7 hour unit, and the LG Chem, a 5 kW / 9.3 hour unit kWh, 1.9 hour unit.
Most residential complexes consist of a single battery, although the proportion of installations with multiple batteries almost doubled from around 20% to 40% between 2017 and 2020, the middle case being around 1 kW larger.
In the non-residential segment, there was a greater variety of battery suppliers, although the Tesla Powerwall dominated about half of the segment. The storage sizing in paired applications was broad, but the median values were 100 kW and 200 kWh, and most batteries had a run time of around two hours.
PV systems in paired applications were generally much larger than stand-alone in the non-residential BTM market, with an average system size of 200 kW for paired versus 40 kW for stand-alone.
BTM installers were increasingly offering storage systems in addition to their solar systems. In 2020, 50% of all active installers reported having completed at least one paired project. According to the report, the market for solar plus storage is still significantly more concentrated than that for stand-alone solar systems.
Ten companies accounted for around 60% of all US PV and storage installations in 2020. Sunrun and Tesla each had a share of around 20%. Most of the others in the top 10 were local firms in Hawaii and California.
Installer retention rates in California varied from company to company, suggesting a variety of different business and marketing strategies.
According to the report, BTM solar plus storage systems for non-residential buildings have remained relatively specialized, with around 17% of companies having completed at least one system by 2020. Tesla stood out with more than 200 cumulative installations, although its market share has shrunk to 10% in recent years, the report said.
Berkeley Labs synthesized data from studies by the National Renewable Energy Laboratory, Tesla Online Quotes, the WoodMackenzie Monitor Report, and other sources to get typical price figures for including storage with a BTM system.
It found that the additional cost of adding batteries to PV systems averaged around $ 1,000 / kWh of storage. Depending on the source, this varied from around 700 to 1300 US dollars / kWh and was much wider for individual projects. The installed premium for residential PV was $ 1.20 / W, with sources between 1.15 and $ 1.50 / W, and individual projects also have a much wider premium range.
Berkeley Lab also analyzed the value to the customer in adding storage. It turned out that the benefit largely depended on the supply area and state in which the project was located. On average, the financial value of the storage expansion was estimated to be between 500 and 1000 US dollars / kWh.
Berkeley Labs said that result suggests that the joint rollout was likely driven by non-financial considerations, such as the value of resilience to power outages.
On the non-residential side, on the other hand, the customer economy performed better. The report estimates the present value benefits at $ 1,200 to $ 2,000 / kWh. This was partly due to the availability of accelerated depreciation and partly because these buildings were able to avoid relatively high electricity demand charges through the use of intelligent storage export techniques.
LBL also analyzed how much emergency power can be expected from a residential system. It turned out that a 7 kW system in standard configuration paired with a 5 kW / 10 kWh battery storage system could cover around 60-80% of a customer's daily consumption on an annual average. These values vary seasonally and vary even more dramatically from day to day due to cloud cover.
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