The concept of virtual power plants has been kicking around for decades. Coordinating a network of distributed energy resources — think solar panels, batteries, and smart appliances — to operate like a single power plant upends our notion of what grid-scale electricity generation can look like, not to mention the role individual consumers can play. But the idea only began taking slow, stuttering steps from theory to practice once homeowners started pairing rooftop solar with home batteries in the past decade.
Now, enthusiasm is accelerating as extreme weather, electricity load growth, and increased renewables penetration are straining the grid and interconnection queue. And the money is starting to pour in. Today, home battery manufacturer and VPP software company Lunar Energy announced $232 million in new funding — a $102 million Series D round, plus a previously unannounced $130 million Series C — to help deploy its integrated hardware and software systems across the U.S.
The company’s CEO, Kunal Girotra, founded Lunar Energy in the summer of 2020 after leaving his job as head of Tesla Energy, which makes the Tesla Powerwall battery for homeowners and the Megapack for grid-scale storage. As he put it, back then, “everybody was focused on either building the next best electric car or solving problems for the grid at a centralized level.” But he was more interested in what was happening with households as home battery costs were declining. “The vision was, how can we get every home a battery system and with smart software, optimize that for dual benefit for the consumer as well as the grid?”
VPPs work by linking together lots of small energy resources. Most commonly, this includes solar, home batteries, and appliances that can be programmed to adjust their energy usage based on grid conditions. These disparate resources work in concert conducted by software that coordinates when they should charge, discharge, or ramp down their electricity use based on grid needs and electricity prices. So if a network of home batteries all dispatched energy to the grid at once, that would have the same effect as firing up a fossil fuel power plant — just much cleaner.
Lunar’s artificial intelligence-enabled home energy system analyzes customers’ energy use patterns alongside grid and weather conditions. That allows Lunar’s battery to automatically charge and discharge at the most cost-effective times while retaining an adequate supply of backup power. The batteries, which started shipping in California last year, also come integrated with the company’s Gridshare software. Used by energy companies and utilities, Gridshare already manages all of Sunrun’s VPPs, including nearly 130,000 home batteries — most from non-Lunar manufacturers — that can dispatch energy when the grid needs it most.
This accords with Lunar’s broader philosophy, Girotra explained — that its batteries should be interoperable with all grid software, and its Gridshare platform interoperable with all batteries, whether they’re made by Lunar or not. “That’s another differentiator from Tesla or Enphase, who are creating these walled gardens,” he told me. “We believe an Android-like software strategy is necessary for the grid to really prosper.”That should make it easier for utilities to support VPPs in an environment where there are more and more differentiated home batteries and software systems out there.
And yet the real-world impact of VPPs remains limited today. That’s partially due to the main problem Lunar is trying to solve — the technical complexity of coordinating thousands of household-level systems. But there are also regulatory barriers and entrenched utility business models to contend with, since the grid simply wasn’t set up for households to be energy providers as well as consumers.
Girotra is well-versed in the difficulties of this space. When he first started at Tesla a decade ago, he helped kick off what’s widely considered to be the country’s first VPP with Green Mountain Power in Vermont. The forward-looking utility was keen to provide customers with utility-owned Tesla Powerwalls, networking them together to lower peak system demand. But larger VPPs that utilize customer-owned assets and seek to sell energy from residential batteries into wholesale electricity markets — as Lunar wants to do — are a different beast entirely.
Girotra thinks their time has come. “This year and the next five years are going to be big for VPPs,” he told me. The tide started to turn in California last summer, he said, after a successful test of the state’s VPP capacity had over 100,000 residential batteries dispatching more than 500 megawatts of power to the grid for two hours — enough to power about half of San Francisco. This led to a significant reduction in electricity demand during the state’s evening peak, with the VPP behaving just like a traditional power plant.
Armed with this demonstration of potential and its recent influx of cash, Lunar aims to scale its battery fleet, growing from about 2,000 deployed systems today to about 10,000 by year’s end, and “at least doubling” every year after that. Ultimately, the company aims to leverage the popularity of its Gridshare platform to become a market maker, helping to shape the structure of VPP programs — as it’s already doing with the Community Choice Aggregators that it’s partnered with so far in California.
In the meantime, Girotra said Lunar is also involved in lobbying efforts to push state governments and utilities to make it easier for VPPs to participate in the market. “VPPs were always like nuclear fusion, always for the future,” he told me. But especially after last year’s demonstration, he thinks the entire grid ecosystem, from system operators to regulators, are starting to realize that the technology is here today. ”This is not small potatoes anymore.”
