Residential energy storage has the potential to be one key solution for effectively integrating distributed renewables into the future electricity mix. It is already seeing solid traction and offering respectable returns in some markets around the world. Hawaii and Australia, among others with their high electricity prices and vast solar resources, have become hotspots for residential energy storage.
Southern California has very customer friendly net metering policies that allow residential solar customers to lean on the grid as their battery, feeding excess solar power in during the day and drawing it back at night. As more residential and utility-scale solar is added to the grid, it is becoming more and more clear that this model is not sustainable and cannot scale much further. Grid-scale storage is being brought online to absorb the surplus, but more accurate pricing signals are needed to drive customers at the residential, commercial, and industrial levels to install their own electricity storage.
It was this inevitable shift that led me into numerous discussions with local Sunrun expert, Noah Crowe. We both knew there was much more to the conversation, so I reached out to Sunrun to get in touch with an expert on storage. They graciously connected me with the Sunrun VP of Grid Services, Audrey Lee, for a chat about the work they are doing in residential energy storage.
We initially discussed Sunrun’s residential solar + storage offering, which it has dubbed Brightbox. This consumer option went live in Hawaii and California last year and was recently launched in Arizona. The solution allows residential solar customers to store the electricity generated by the onsite solar system in an onsite battery, and then use electricity from that battery at night. Audrey shared that Sunrun currently has “over 2000 Brightbox orders” in California and Hawaii and is expecting a sunny reception in Arizona.
Audrey shared that Sunrun views storage as a competitive upsell and that, “long term, I could see every customer installing storage with solar.” It isn’t just good business for Sunrun that makes storage a good fit with solar, but rather, it is a technical requirement to continue with more residential solar installations: “to get a higher penetration of residential solar, we really need residential storage.”
Hawaii is a good case study for this imperative, as the local utility has already hit the cap for the number of residential solar customers that are permitted to feed excess electricity generation into the grid. That has created a ripe market for storage, as it is now essentially required to install a new residential rooftop solar system.
“With solar, they can continue to operate: charge up the battery when the sun is shining and use it from the battery when it is not.”
Back on the mainland, the value proposition in California is not as straightforward, though a compelling case can still be made for residential storage. Many users are simply looking for a battery backup solution that will allow them to keep their home running in the event of a power outage.
The system also has the ability to help customers on a time-of-use (ToU) rate plan save some cash. Rates are currently the highest during the day, when the sun is shining and air conditioners are cranking, meaning that the solar power generated has the most value to the utility. Conversely, as the sun goes down, so do rates, meaning customers can use any power needed from the utility at the lowest rates available. The battery is able to intelligently maximize these balances for the customer.
Looking toward the future, the battery system protects customers from future ToU rate changes. As more and more solar comes onto the grid, it is expected that the peak usage will shift from mid-day to the “duck curve” that is becoming more and more pronounced (PDF) due to the massive new production from solar.
The customer is able to see the battery system in the MySunrun app though it does not offer visibility of the power flows between the various components of the customer’s home energy system. The actual logic dictating how energy flows from the battery to the home and to the grid are managed by Sunrun to ensure they are optimized for the customer at all times.
“We are essentially selling storage as a service. Customers don’t want to have to manage their battery. We take care of that and manage storage to maximize savings while ensuring capacity is available for emergencies.”
Managing the storage system in house allows Sunrun to partner with utilities directly to maximize the benefits of the system to the customer and to the grid. Sunrun Chief Executive Officer Lynn Jurich spoke to this as part of the initial launch of Brightbox, noting that Sunrun is looking to “forge new relationships with utilities as we work with them to maximize the value of solar energy in modernizing America’s energy infrastructure.”
Sunrun is also leaning heavily into utilities to maximize the financial value the distributed residential storage they manage provides, aiming for maximum reasonable benefit to the grid and financially to customers. Audrey shared that Sunrun is bidding on demand response options to the CAISO market.
Getting down to the nuts and bolts of the solution, Audrey shared that Sunrun has installed Tesla Powerwalls for customers but has tapped LG Chem as its primary supplier for residential energy storage systems. Specifically, the LG Chem RESU 10, which is a part of LG’s “Energy Storage Solutions” or ESS family of products. The RESU 10 has a storage capacity of 9.8 kWh with 9.6 kWh of usable capacity, the top end of LG Chem’s RESU line.
As an existing residential customer of REC Solar (acquired by Sunrun), I am eager to get my hands on some storage for my house but have found that many installers are hesitant to add storage to an existing solar installation. This is due to their inability to leverage efficiencies of a single inverter system that can be tapped with a combined install but poses a challenge in a retrofit like mine.
Solar systems produce DC power and residential storage systems store DC power but homes use AC. Building a system with the solar and storage optimized with a single inverter is a better financial decision and allows for unique optimizations that simply are not possible with a retrofit. I prodded Audrey about this and she shared that Sunrun is looking into the matter but there is nothing official to share at this point.
Sunrun is clearly pushing forward with solar to maximize the benefits to its customers and to society. Its work in the Grid Services space represents the leading edge of that push. Audrey closed by reiterating that “Sunrun’s mission is to create a planet run by the sun,” which in this case has opened up new revenue streams and markets for Sunrun to play in.
For more about Sunrun and the Brightbox solution, head out to their site on the wild, wild web.
Images courtesy of Sunrun