APS, First Solar plan large West Valley solar power plant with giant battery

Tempe-based First Solar Inc. will build a large solar plant in the West Valley that will use a massive battery to deliver power to Arizona Public Service Co., the companies said Monday.

The project will be unique not only for the size of the battery being put to use, but for the way the plant is operated, officials said. APS recently has placed other batteries on the grid, but they are much smaller than what will come with the solar plant.

It will be about half the size of a massive battery Tesla Motors Corp. built in Australia last year, which is billed as the largest in the world.

The First Solar plant is planned to be operational in 2021 and will be build near the APS Red Hawk Power Plant on 363rd Avenue in Arlington.

The battery will be capable of delivering 50 megawatts of power, enough for 12,500 homes, for three hours. The solar panels will have a capacity of 65 megawatts, enough for about 16,250 homes, when sun is shining on the panels.

APS wanted a power plant that would deliver electricity only from 3-8 p.m., when demand on the power grid is highest in summer. Most solar panels produce the most electricity when the sun is highest in the sky around noon.

The plant will either use the power generated early in the day to charge the batteries or sell it elsewhere, delivering to APS only when demand on the grid is high.

"We had just about every technology you could think of producing during those time windows bid on this (request for proposals)," said Brad Albert, vice president of resource management for APS. "All the way from stand-alone battery storage to natural-gas fuel peaking units. This was the winning proposal."

The 'duck curve' is a problem for solar

As more solar is installed on rooftops and in large power plants, utilities face a problem known as the "duck curve," where demand on the power grid rises sharply like a duck's neck in the late afternoon.

The duck curve gets steeper with more solar on the grid because solar displaces other power sources midday, but ceases production in the afternoon as overall electricity use spikes.

Already the abundance of solar on the power grid in the Southwest has led to negative pricing, where on certain days California utilities will pay those in neighboring states to take their surplus midday power.

Albert said APS will need more battery installations and other technology to address the duck curve.

"We told everyone in this (request for proposals) we don't want that (midday) energy," he said. "Sometimes it creates bigger operational problems than it solves."

Power on the open market is more expensive during peak demand, and likewise, power from this contract will cost APS a premium. But Albert said the 15-year, fixed-price contract offers a reliable way for APS to meet peak demand. The price was not disclosed.

"Yes, it is more expensive, but it is a much more valuable product for meeting our customer needs," he said.

First Solar has plans to build additional solar facilities in the same area near Red Hawk, spokesman Steve Krum said.

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