Oversized solar farm keeps lights on until midnight

The nation’s largest approved solar and storage project has a secret. Beneath its record-break headline-size announcement is a “hidden” second power plant. And it’s driven by two of the most important clean energy trends: low cost solar panels and advancing battery technology.

This hidden power plant comprises 2.4 GW of solar modules and 7.2 GW of energy storage, all feeding into a 1.2 GW grid interconnection. In practice, this means the Sunstone Solar Project will generate significantly more electricity than a typical solar plant, store the excess in batteries, and supply it to the grid well into the evening.

pv magazine USA reached out to Pine Gate to ask how they plan to structure electricity sales and for their perspective on the project’s unique sizing but received no comment.

According to the U.S. Department of Energy’s Energy Information Administration, the average ratio of solar modules (DC capacity) to inverter sizing and grid connection (AC capacity) has been about 1.25:1 over the past few years. For this project, also known as the “DC-to-AC Ratio” or “Inverter-Load Ratio,” the figure is 2:1.

Historically, solar developers have kept the DC-to-AC ratio near 1.25:1 to avoid “clipping,” where electricity production on sunny days exceeds inverter capacity and is effectively wasted. Battery manufacturer Fluence created the animation above to illustrate how pairing batteries with a high DC-to-AC ratio solar plant can capture this otherwise clipped electricity for use in the evening.

One of the unique benefits of adding extra solar modules is that they cost less on a per-unit basis than in a standard plant. Since the inverters, interconnection and various overheads are already accounted for, the additional costs are mainly for racking, modules, conduit, copper and support gear. According to Fluence, these extra panels are estimated to cost about 40% less than a conventional installation.

To explore the Sunstone power plant’s output, pv magazine USA used the Solesca solar design tool to estimate how long it would take 2.4 GW of solar electricity to pass through a 1.2 GW interconnection. We modeled a 1.01 MW single-axis tracking solar plant located at Sunstone’s Oregon site, which would deliver about 1,743 MWh of electricity to the grid annually.

During much of spring and summer, a 1 MW model delivers more than 200 MWh per month, or about 6.5 MWh per day. Multiplying that daily figure by 2,400 (the factor by which Sunstone’s capacity exceeds the 1 MW model) gives 15,737 MWh per day—around 15.7 GWh—that must be transferred through a 1.2 GW interconnection.

Sending 15.7 GWh through that 1.2 GW connection would take about 13 hours. On the longest days in northern Oregon, a plant like this could reach peak output (1.2 GW) around 9 a.m. and continue delivering electricity until midnight.

It’s not yet known whether Pine Gate will fully implement this oversized design. Depending on the terms of the power purchase agreements, the company could still build these facilities at more standard sizes.

Either way, this project follows trends already seen in California, where solar-plus-storage has become standard and storage now supplies a major portion of evening energy demand.

An interesting aspect of this site is its proximity to multiple proposed, approved, and operating wind, solar, and transmission assets, including the Wheatridge Renewable Energy facility—the nation’s first power plant integrating wind, solar, and storage.

Because wind and solar resources tend to complement each other seasonally and daily and, because such projects undergo extensive local grid capacity analysis, you might assume the local grid can achieve a higher capacity factor than any single asset (wind, solar or storage) could on its own. In fact, the large battery systems at Sunstone could potentially charge from local surplus wind power after the finish discharging around midnight, then meet early-morning demand before sun rise.

Popular content

U.S. electricity rates rise about 5% annually – outpacing inflation

07 January 2025 While electricity generation costs have gone down thanks to technology like solar and wind, transmission and distribution costs have driven bills high...