Gas boom

APS and SRP plan to add almost twice as much capacity from natural-gas power plants as they do from solar and wind over the next 10 to 15 years to meet customer demand.

APS and its customers will add about 2,200 megawatts of capacity from renewable forms of energy by 2027, according to its resource plans. In that same time, APS will add about 3,712 megawatts of capacity from natural-gas power plants.

SRP’s resource plans call for 415 megawatts of new capacity from wind, geothermal and solar power by 2020, and once the economy rebounds, nine new gas-fired turbines with a capacity of 819 megawatts by 2023.

Both utilities will get close to 25 percent of their electricity generation from natural gas, and about half from coal and nuclear.

Because they are not adding significant new coal resources, or any nuclear, the relative proportion of their power from those sources will drop.

One megawatt of capacity is enough power to supply about 250 homes at once while a power plant is running.

Though natural gas is a potential rival to solar as a fuel for power plants, it also complements the use of solar.

Natural gas works together with solar and wind energy to keep the power grid in balance, with gas power plants firing up when clouds pass over solar plants or wind farms miss the breeze.

“They really work in complementary ways,” said Rhone Resch, president/CEO of the Solar Energy Industries Association in Washington, D.C. “They rely on natural gas in the evening after the sun has gone down and after the thermal storage (of some solar-power plants) has been exhausted.”

Wind farms might only provide their full capacity 25 to 35 percent of the time, depending where they are in the country.

Solar-power plants also only provide their full capacity about 25 to 30 percent of the time, unless they have some sort of heat storage, like the new Solana plant.

When those plants stop making power, utilities rely on natural-gas-burning power plants to take up the slack.

That’s because natural-gas plants can turn on and off, and up and down, much more quickly and cheaply than coal and nuclear plants, which utilities try to run at full power around the clock to maximize efficiency.

Though the two are potential competitors, Resch said solar power, particularly in Arizona, offers several benefits that natural gas can’t.

“We do not anticipate that the expansion of natural-gas production is going to have a significant impact on the solar industry,” he said.

For starters, solar can be installed on homes and businesses, while natural gas can only be built as a centralized power plant.

So-called “distributed” solar on rooftops benefits utilities by minimizing demand on the electrical grid and producing power where it is used, he said.

“The other point is that natural gas, while abundant in certain areas of the country, is constrained by pipeline capacity in others,” he said.

And while cleaner burning than coal, natural gas still emits carbon dioxide, a gas that contributes to climate change.