FEATURE: Experts differ over how solar capacity surge is affecting ERCOT prices

The commercial startup of Duke Energy Renewables' 200-MW(AC) Rambler Solar plant adds to about 2 GW of solar brought online in Texas so far in 2020, about which industry observers differ regarding wholesale power price impacts going forward.

With its commercial operation announced July 23, Rambler Solar is in Tom Green County about 200 miles northwest of San Antonio, and is the second such facility Duke brought online this month. The 200-MW(AC) Holstein Solar site is in Nolan County, about 200 miles west of Fort Worth. In All, Duke Energy Renewables has about 500 MW(AC) of solar in Texas.

The Electric Reliability Council of Texas' June Capacity Changes by Fuel Type Charts, released July 14, shows 4.2 GW of solar generation either in commercial operation or synchronized to the grid as of June 30, up from 2.3 GW at the end of 2019. Another 1.6 GW has signed interconnection agreements and has posted financial security to start up in 2020, which would bring the overall total to 5.8 GW.

The additional solar resources, usually producing the most at peak demand hours, have coincided with significantly weaker average real-time on-peak locational marginal prices so far this summer.

Real-time prices

Between June 1 and July 21, ERCOT Hub real-time on-peak locational marginal prices averaged $19.12/MWh, down almost 44% from $34.07/MWh for the comparable period of 2019, S&P Global Platts price data shows.

Evan Caron, former head of power at an Austin, Texas, energy asset management company, said the 2-GW year-on-year solar capacity increase would "of course" have "significant implications" on power prices, especially "combined with load-related issues."

"Right now, a lot of the peak demand is served by solar," Caron said in a July 23 email. "We should see the remainder of the coal fleet priced out of the market in the near term."

Joshua Rhodes, a University of Texas Webber Energy Group research associate, said, "The deployment of solar is going to have an on-peak impact, as the sun is still shining bright in West Texas when the population centers are demanding their air-conditioning."

Peakloads for June 1-July 21 averaged 63.9 GW in 2020, up 1.9% from the comparable period of 2019, ERCOT data shows. CustomWeather reports that ERCOT's population-weighted cooling-degree days averaged 10.8% more for June 1-July 21, compared with the same period of 2019.

Price suppression effects

Mike Brasovan, founder of Thigbe, an energy consultancy near Fort Worth, Texas, indicated in a July 23 email that solar generation's impact on power prices could persist, as it "affects prices more like permanent (10 to 20 years) demand destruction."

"Most solar is developed for a fixed price or a set contract for one or more customers or suppliers," Brasovan said. "The solar output that is tied directly to customers displaces peaking generation without the price spikes associated with merchant generation. It's as if that demand doesn't exist in the market anymore because it is being offset by the new generation."

Manan Ahuja, senior director of North American power for S&P Global Platts Analytics, said this summer's lower prices, so far, are more tied to low natural gas prices than to solar expansion.

"Gas prices year to date are about 33% lower year on year at Henry Hub," Ahuja said in a July 23 email. "Yes, solar power matters too, but the penetration of solar is not that high in ERCOT to drive the prices down significantly."

Jeff Schroeter, managing director of Genova Power Advisors, a Plano, Texas, energy market consultancy, said this summer's price weakness likely owes more to factors such as "much lower natural gas prices than last year, COVID-19's effect" on how power demand is shaped during the day and high wind output on certain high-demand days.

"All suppress prices," Schroeter said in a July 23 email. "Looking ahead, although the forward prices for 2021-25 have fallen in thes last month, I am still in the 'increasing-intraday-volatility' camp as more solar is added to ERCOT."

Peter Kelly-Detwiler, principal at the NorthBridge Energy Partners consultancy, expressed uncertainty about how much solar is affecting ERCOT pricing this summer.

"That having been said, the onslaught of solar in the years to come is clearly going to have an impact," Kelly-Detwiler said in a July 23 email. "It's effectively going to rip out the soft underbelly of many of the most high-priced hours of the day."

Regarding coal plants' future in the ERCOT market, Ahuja said, "Wind generation in ERCOT and low gas prices are much bigger factors in recent years in driving coal generation and also less efficient gas generation out of the market."

Brasovan said, "I do not think [solar growth] will drive more baseload fossil-fuel generation out of Texas. "[By] and large, I expect the existing generation to be needed to serve the load at night and lower production months/times,."