Poor Solar Energy Performance is More Evidence the VCEA is Failing

Every solar facility in Dominion Energy Virginia’s expanding fleet of silicone panels is failing to perform up to its initial energy promises, according to a State Corporation Commission staff analysis. In many cases the shortfalls are dramatic.

A high confidence in the ability of solar power to replace Virginia’s dominant natural gas and coal electricity generators is at the heart of the Virginia Clean Economy Act, still a key plank in the Virginia Democrats’ 2025 campaign platform. This latest cold splash of reality is just one more sign that it takes closed eyes and blind faith to continue to trust that path forward. 

The performance data popped up in testimony that is part of the utility’s application for a base rate increase. There are dozens of issues in that pending case, set for a public hearing September 2. They range from the allowed profit margin to a new rate structure for the giant data centers. But one side issue is whether the company has earned a bonus on its profit margin due to good performance, and the SCC staff have recommended it not get it, in part because of the poor solar performance.

Neil Joshipura of the SCC staff wrote in his testimony:

Based on the data provided, all of the Company’s solar facilities had average actual capacity factors that were lower than their respective design capacity factors. The absolute differences between the design and actual values ranged from 1.2 to 10.3 percentage points, with an average difference of 4.3 percentage points. Piney Creek Solar had the largest absolute difference; its design capacity factor was 22.6 percent, while its actual capacity factor for 2024, the only year with available data, was 12.3 percent. This represents a 48 percent shortfall relative to the design value.

Capacity factor is a measure of how often a power plant produces electricity, and it is never 100% peak production 100% of the time. When the plant is advertised as producing 100 megawatts (MW) or 500 megawatts or more, that is the energy output at peak production. That must then be multiplied by the capacity factor, the actual output divided by the maximum possible energy output.

In the case of these utility-owned solar fields here in Virginia, that capacity factor is a very low number, usually about or below 25% in design capacity and about 20-21% in actual output. That is the average output after all the nighttime hours, all the days with little or no direct sun, and all the days down for maintenance are accounted for. Hurricane Erin, for example, has brought Virginia several low solar days due to clouds.

Joshipura’s testimony included a table that listed the “capacity factor” for 25 Dominion solar plants for 2023 and 2024, the performance period being reviewed in the rate case. It then compared that to the amount of production the utility projected when the facilities were designed and installed. The nominal discrepancy was more than four percentage points, but that is misleading. Many produced 20% less electricity over those years than what we ratepayers were promised.

The SCC staff should have taken an extra step and included the faceplate value of the plants. Then it could calculate how much actual electricity was promised but not produced, for each individual location and then for the whole fleet. That is important information. The fleet is growing. Under the mandates of the Virginia Clean Economy Act, Dominion has only started to build the thousands of megawatts and hundreds of square miles of solar fields needed to keep the lights on (and keep them on only just some of the time).

A 100 MW solar field at full capacity all the time would produce 876,000 megawatt hours of juice in one year, ideally. At a 25% capacity factor the output is only 219,000 megawatt hours per annum and at 20%, only 174,000 megawatts. Apply that example to the 13,000 MW of panels envisioned by the Virginia Clean Economy Act, and you start to see the problem. Dominion of course does see the problem and is desperately trying to get approval for natural gas plants to provide needed reliability backup.

Dominion blamed the performance shortfalls on maintenance issues, usually failures of the inverters, and “lower than expected insolation.” That means the sun didn’t shine. Funny how that works. But 20 of the 25 also had inverter failures, and inverters are what convert the direct current from the panels into alternating current for the grid. 

The company had better luck with its two existing offshore wind turbines, Joshipura reported, with their 46% reported capacity factors, meaning a bit more wind hit than expected. That bodes well for the major offshore wind project Dominion should begin operating late next year, but it still means plenty of days with low or no output. (And again, think about some future hurricane, one that doesn’t veer off.)

The next time a Dominion spokesperson in the newspaper brags about a 400 MW megawatt solar plant coming to cover a denuded forest in your county, remember that 400 MW must be discounted by the design capacity factor (suddenly it only 100-110 MW) and then further eroded by the historical production at the company’s other plants.

In the end 400 MW of panels produce only about 80-90 MW on average. For that they tore down the trees. Yes, the marginal cost for energy is low when it works. It just doesn’t work very often.

In rebuttal testimony also filed with the SCC in the case file, Dominion doesn’t dispute Joshipura’s numbers (it had provided them) and really doesn’t dispute his recommendation that there be more attention to preventive maintenance. The company’s VP for Generation merely responds that the discussion belongs in another review, not this general rate case.

Where it belongs is front of mind as Virginians vote in this election. 

Steve Haner is a Senior Fellow for Environment and Energy Policy. A previous version of this article appeared in Bacon’s Rebellion. Steve Haner can be reached at Steve@thomasjeffersoninst.org.