Facing Gov. Jared Polis’ mandate to eliminate coal as a source for electrical power generation by 2050, Xcel Energy is looking into repurposing its Hayden coal-fired power plant in northwestern Colorado to preserve its investment in the plant and aid the economic health of nearby communities including Hayden and Craig — and store carbon-free solar energy to generate electricity.

The plant provides nearly half the property tax base for Hayden schools and fire districts, and the threat of losing the plant left the town staring economic disaster in the face.

What U.S. government surveyor, F.V. Hayden reported in the 1870s as one of the largest coal reserves in the country, coal has been the mainstay of the region’s economy since 1887.

Peter Brixius, Craig Town Manager, told The Denver Gazette, “Anything we could do to keep some of the employees and to utilize that infrastructure will assist the tax base of both Routt County and Moffat County.”

Hayden Unit 1, built in 1965, and Hayden Unit 2, built in 1976, were originally scheduled for shutdown in 2036. Xcel accelerated the schedule to stop burning coal by 2028 as part of its current energy resource plan approved by the Public Utilities Commission in March.

Now the utility is looking at repurposing the plant to use renewable energy to spin the existing generators.

One of three renewable sources being studied is molten salt.

Molten salt energy storage works by concentrating solar power (CSP) using parabolic reflectors focused on pipes carrying molten salt that convert the light into heat in the salt. The salt is kept fluid at about 525 degrees F and is stored in tanks where it can be used to quickly generate the steam needed to produce electricity.

The need for ways to store energy for use when it’s dark or the wind isn’t blowing is the focus of major investment worldwide. Right now, utility-scale lithium batteries cost as much as 90 times as much as coal or natural gas of equivalent capacity and currently only last a few minutes to several hours.

Molten salt can store 10 to 12 hours worth of energy and storage scales up easily simply by adding more salt storage.

The Chilean government intends to shutter 30 coal-fired power plants comprising 30% of its national generating capacity by 2024, and is studying using CSP storage to keep the plants operating.

Xcel is only in phase one of its planning process and hasn’t decided on which, if any of the renewable fuel options might be used to rescue the Hayden plant, says Hollie Velasquez Horvath, senior director of state affairs and community relations for Xcel.

Speaking of CSP installations in Nevada’s Mojave Desert, Velasquez Horvath told The Denver Gazette, “There’s a lot of challenges that they’ve had with that concentrated solar and their positioning of that generation. So that is something that we’re also factoring into in trying to understand as we explore it.”

Developers of one facility thought that the sun always shines in the Mojave Desert, but discovered that from November through February clouds create overcast conditions as much as 50% of the time. Without storage, this resulted in dismal overall production of electricity.

According to the EIA, solar panels, which can still produce power even when there is cloud cover, have a 5% capacity factor advantage over non-storage CSP under the best of conditions, as well as much lower, and still declining capital costs.

The costs of building a CSP energy storage plant are high compared to solar panels. According to BloombergNEF, a strategic research company, from 2009 to 2019 the cost of utility-scale solar panels dropped from $355 per MW hour to $51 per MW hour, whereas the Crescent Dunes CEP project in Nevada, built with $737 million in U.S. Department of Energy loan guarantees, came in at $135 per MW hour and was reported in January by Greentechmedia.com as being shut down.

But, like Chile, Xcel already has the generators and distribution infrastructure in place and it doesn’t really matter how the steam to spin the generators is produced, which may produce significant cost savings.

Xcel’s plan is more than a little experimental, but House Bill 21-1234, signed into law by Polis July 6, says investor-owned utilities “should pursue opportunities to develop new energy technologies or moify existing generation resources with new technologies…”

While ratepayers will have to pay Xcel’s costs for building the storage infrastructure, and pay off any existing debt on the plant, if the CSP project is “abandoned or cancelled, in whole or in part,” and the Public Utilities Commission finds that the costs were not “prudently incurred,” the PUC can deny cost recovery.

The law also protects ratepayers somewhat by saying that Xcel cannot earn a total return on the project that exceeds what it would have earned from a “photovoltaic…or wind generation facility of equivalent capacity.”