What a 100-percent renewable electricity system in Minnesota might look like on a week in January.

Monday’s post, “Could Minnesota get by on 100 percent renewables?,” has generated quite a few comments. A report released this week by the Institute for Energy and Environmental Research (IEER) claims the state could meet all its electricity needs through wind and solar, provided they were matched with the right mix of energy storage and efficiency improvements. I decided to check back in with Arjun Makhijani, IEER’s president and senior engineer, and ask him to respond to some of your questions and comments.

PwrSavy commented “As I understand it, if you’re relying on typical [compressed air energy storage]; they couple with combustion turbines when supplying energy, so this is not a ‘100% Renewable’ scenario… unless that is you’re burning some kind of biofuel.”

On this point, the reader is correct, says Makhijani. The scenario described in IEER’s report actually does rely on a small amount of natural gas for generating power from the compressed air energy storage. The amount of natural gas used in generating from compressed air storage is about one fifteenth the amount of gas used in a conventional natural gas combustion plant.

“The amount of natural gas is so small that I believe it could be replaced with biogas,” says Makhijani.

Another option that could become economical at some point is pairing compressed air storage with hydrogen powered generation.

Mary is alarmed about how expanding commercial wind farms in the state could affect bats and birds. “If we pepper this state with the turbines required to produce enough energy to provide for households alone, we will have an environmental disaster of biblical proportions down the road,” she writes.

Makhijani says improved turbine design has largely resolved the problem of bird collisions at newer facilities. He thinks the bat issue is a bigger problem and one that we need to pay attention to. He hopes that careful siting of wind farms might help reduce the impact.

“I think wind farms should be carefully sited, and I think we do have the luxury of doing that in Minnesota because the available resources are enormous,” he says.

About a third of the state’s land area is rated as having relatively high wind potential by the National Renewable Energy Laboratory. The state’s total wind generating potential, depending on turbine height, is 20 to 30 times the state’s current consumption, says Makhijani. Achieving the 12,000 to 15,000 megawatts of wind capacity called for in his report would require developing on about 5 percent of the state’s high-wind-potential land.

“It’s not huge. It’s not negligible,” Makhijani says.

Mouli Vaidyanathan comments that the data used in the report to estimate Minnesota’s solar potential is about 10 percent to 15 percent optimistic. “Such over estimates could harm our renewable energy industry in over promising and under delivery.”

While the report includes an Average Solar Radiation map for Minnesota, Makhijani says they didn’t calculate the state’s solar potential based on land area. Minnesota is unlikely to have large-scale PV or concentrated solar thermal, he says. Instead, the more likely application of solar is smaller, distributed installations on commercial rooftops, of which there are more than enough to provide the kind of solar capacity called for in the report.

“The solar generation in our scenario is not very big. It serves mostly to reduce the variability of the renewable resource rather than as a big source of supply,” Makhijani says. “Solar generation plays a role of moderating the storage requirement and the seasonal variability of your renewable resource. It improves the economy of the system.” That’s because solar generation tends to peak with demand on hot summer days when air conditioners are running.

Rolf Westgard doubts whether the state could ever build enough storage to moderate wind and solar’s variability. “There is no storage supply to compensate for the erratic nature of those sources. Imagine a warm muggy summer night when all AC’s run and there isn’t a ‘breath of air’.”

Makhijani admits building energy storage will be expensive and challenging. Under his report’s scenario, the state would need about a $9 billion investment in storage. Siting issues would undoubtedly arise, although he believes enough sites do exist. The state could shrink its storage requirements by further improving efficiency and expanding the use of demand dispatch, in which customers agree to have certain appliances or equipment powered off for short intervals when electricity demand is high, usually in exchange for a discount.

“The whole idea was to show that you can actually run a renewable system though all of the erratic supply and all of the variability in the existing demand with out doing anything to the existing demand,” says Makhijani. “You can get through all of these warm muggy nights.”

(Also, as noted previously, the IEER is a member of RE-AMP, which also funds Midwest Energy News.)

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