On a napkin
The short version
A solar panel converts sunlight into DC electricity. An inverter converts that to AC for the grid. A battery stores excess generation for later dispatch. What makes solar + storage financially interesting is the ability to stack revenue across multiple market products simultaneously — turning a simple generation asset into a multi-service platform.
On a sunny midday in California, solar panels may produce at full capacity while wholesale LMPs are near zero or negative. A paired battery charges during this window. When the sun sets and demand ramps for the evening peak, the battery discharges into a market where prices may be $80–$200/MWh. That spread, minus round-trip efficiency losses, is energy arbitrage. Layer capacity market payments and ancillary service revenues on top, and the project economics start to work.
The IRA changed storage economics fundamentally — and the OBBBA largely preserved that change. The IRA extended the 30% 48E ITC to standalone battery storage regardless of solar co-location, with transferability that dramatically simplified project financing. The One Big Beautiful Bill Act (July 2025) retained the storage ITC essentially intact while terminating the ITC for the solar portion for facilities placed in service after December 31, 2027. Solar-plus-storage developers must now plan asymmetrically — storage long-term, solar racing to BOC before July 4, 2026.
How the revenue stack works
Energy revenue comes from selling power at the prevailing LMP. For merchant projects without a PPA, this is fully exposed to market price risk. Arbitrage revenue is earned by the battery independently — charging when prices are low, discharging when high. In CAISO, where the midday-to-evening spread routinely exceeds $50/MWh in summer, a 4-hour battery can earn $60,000–$150,000 per MW-year in arbitrage alone.
Capacity payments come from clearing capacity auctions or signing resource adequacy contracts with utilities. Ancillary services — particularly frequency regulation — are well-matched to battery capabilities. Batteries respond to AGC signals in milliseconds, outperforming thermal generators on accuracy and earning performance premiums in markets like PJM.
DC-coupled vs. AC-coupled
In a DC-coupled system, solar and battery share an inverter — solar flows directly into the battery before AC conversion, improving round-trip efficiency. In an AC-coupled system, each component has its own inverter; energy is converted AC-DC-AC, adding conversion losses. DC-coupling is preferred for new utility-scale builds; AC-coupling is simpler to retrofit onto existing solar installations.
The interconnection bottleneck
The single biggest constraint on solar + storage development is the interconnection queue. Projects must receive a study from the relevant ISO to connect to the transmission grid — a process that has grown to 3–5 years in most markets due to backlogs. FERC Order 2023 introduced a cluster study approach to reduce timelines, but the backlog remains substantial. For developers and investors, interconnection timeline is often the determining factor in project viability.
Common questions
Related reading on The Outlet
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