By Chris O’Malley
ST. PAUL, Minn. — Registered wind capacity in MISO is projected to rise 50% by the end of 2019 — and that’s not even counting more turbines likely to sprout due to the Clean Power Plan.
MISO’s wind capacity has grown to about 14,000 MW, from 1,200 MW in 2005. Wind represents about 13% of MISO’s installed generation capacity — higher than the 7.5% for nuclear power but still well below that for coal and natural gas.
By 2019, based on its generation interconnection queue, MISO expects to have about 21,000 MW of wind in service.
“The growth of wind has been really, really steady, actually, over time. Projections continue to show similar growth as we experienced over the last five years,” Joe Gardner, vice president of forward markets and operations services, told the Markets Committee of the Board of Directors last week.
MISO officials said it’s too early to tell how the wind projections will change as a result of the Environmental Protection Agency’s final carbon emission rule, released last month. But “it’s going to be a lot bigger,” CEO John Bear said.
While MISO expects 25 GW of wind will be needed to meet existing state renewable portfolio standards, EPA’s modeling assumes the RTO’s wind portfolio will grow to 40 GW, said Claire Moeller, executive vice president of transmission and technology.
Forecasting Improves
Gardner told the board that staff is continuing efforts to improve its forecasting of wind availability, which he said is already “best in class.”
“On any given day we could have close to zero megawatts of wind … and on other days we can have 11 GW of wind. And from one day to the next you can have a swing of 6 or 7 GW,” Gardner said. “So it’s very important to try to get [the forecast] accurate. The more accurate the forecast is, the better our unit commitment is going to be and the lower our production cost is going to result and the more reliable we’re going to be.”
MISO staff uses an hourly forecast that looks seven days into the future in the reliability unit commitment process and to evaluate outage requests.
A five-minute forecast that extends six hours is used in real-time economic dispatch and look-ahead unit commitment. It also uses wind generators’ own forecasts in economic dispatch, although those are available for only about one-third of wind farms.
Gardner said MISO’s day-ahead wind forecasting accuracy has improved by about 2.5 percentage points since 2009, reducing the error rate to about 5%. The improvement is due in part to the incorporation of weather-prediction modeling; MISO added a fourth weather model in the second quarter.
Gardner said that’s better than the estimated error rate of other grid operators, including PJM’s 4 to 8% error rate, ERCOT (8%) and CAISO (10%).
“Does this forecasting accuracy give you comfort … that we’re not seeing drastic, unexpected shifts in the wind in a short period of time that causes impacts to reliability because of ramping capability in other units in the system?” Board Chair Judy Walsh asked Gardner.
“[It’s] not a huge amount of risk,” Gardner replied. “It’s not so much because of how accurate our forecast is. I think it’s more a result of geographic diversity and where the wind is located.”
He also said MISO plans a number of additional forecasting enhancements, including improved distribution of locational wind forecasts and replacement of vendors whose forecasts have persistent errors.
Solar Outlook Needed
Forecasting also will be needed to accommodate the rise of solar power generation. Gardner said an in-front-of-the-meter solar project is expected in MISO’s footprint in 2017. “So we’re preparing to be able to forecast that and I expect there will be some more [solar] beyond that,” he said.