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Saving sunbeams for a rainy day

Copyright © 2018 Albuquerque Journal

On the vast, scrubby landscape of Kirtland Air Force Base, a tall, albeit nondescript, tower rises above its surroundings.

Mechanical engineer Clifford Ho talks about the National Solar Thermal Test Facility during a celebration of the facility’s 40th anniversary on Monday. (Jim Thompson/Albuquerque Journal)

Upon closer inspection, the tower is bordered on one side by what looks to be a geometric grid of solar panels, positioned like worshippers bowed before a deity.

This is Sandia National Laboratories’ National Solar Thermal Test Facility, and it’s being used by researchers to develop a renewable energy that could fill a gap in the capabilities of photovoltaic and wind energy.

The grid at the facility is not, in fact, made up of solar panels.

Each of the 218 units, called heliostats, is made up of 25 square mirrors whose sole purpose is to optimally reflect the sun’s light.

“Rather than converting sunlight directly into electricity, we generate heat first and foremost,” said Clifford Ho, a Sandia mechanical engineer.

It’s called concentrating solar power technology, and the test facility has been at the forefront of its development since its construction 40 years ago.

“Over those 40 years, we’ve had lots of great developments in concentrating solar power research,” Ho said.

Sandia hosted a 40th anniversary celebration at the facility on Tuesday, offering tours to members of the media and solar industry, Sandia retirees and politicians.

In a view from the top of the “power tower,” people walk among the 218 heliostats at Sandia National Laboratories’ National Solar Thermal Test Facility. (Jim Thompson/Albuquerque Journal)

When the technology got off the ground in the 1970s, researchers used the mirrors to reflect the sun’s light at pipes filled with water, creating steam that could be directly used to power a turbine.

These days, the preferred medium is salt, because it doesn’t become pressurized when exposed to the heat and thus is easier to store. The salt becomes so hot – it can reach temperatures into the thousands Fahrenheit – it melts.

The liquefied salt can then be used to heat water into steam.

The heat generated by sunlight is evident in a half-inch thick slab of aluminium with a gaping hole at its center that Ho said was burned through in around 20 seconds using just half of the facility’s heliostats.

What really sets the technology apart from other renewable energy sources is the ability to store the heated liquid inside insulated containers for use when the sun isn’t shining or the wind isn’t blowing.

Ho said states like California and Hawaii are already struggling with producing too much solar energy during the day.

“Wind and solar can offset the load during the day,” he said. “The problem is the evenings.”

The 200-foot tower at the National Solar Thermal Test Facility at Sandia National Laboratories is shown through a half-inch aluminium plate that was melted at the site. The plate was on display during a 40th anniversary celebration at the facility on Tuesday. (Jim Thompson/Albuquerque Journal)

That’s where storage ability is key.

But utilities are looking for the cheapest option, and part of what Ho and others at the test facility are doing is trying to bring the price of concentrating solar power down to competitive prices.

The technology currently costs around 9 to 10 cents per kilowatt-hour; Ho said they hope to get that down to 6 cents.

“A critical part of concentrating solar power going forward is getting that cost down to competitive levels,” said Kevin Smith, CEO of SolarReserve, a developer of solar power projects.

While the National Solar Thermal Test Facility has a rich history of developing and enhancing concentrating solar power technology, the facility will continue to play a role in its future.

Sandia, along with SolarReserve and other partners, was recently awarded $10 million by the U.S. Department of Energy to develop a concentrating solar power system using what’s called high temperature falling particle technology.

The technology would concentrate sunlight onto and heat sand-like particles falling through the beam, removing the heat resistance created by pipes.

The DOE will choose between Sandia and two groups – one using a liquid and the other using a gas as a medium – after two years of research.

That group will be awarded another $25 million to build a pilot facility.

If Sandia is chosen, the pilot facility would be built at the test facility.

“We hope to see (the National Solar Thermal Test Facility) continue to serve our nation and world in advancing critical energy technologies for the next 40 years and beyond,” Ho said.

Each of the facility’s 218 heliostats is made up of 25 mirrors.
(Jim Thompson/Albuquerque Journal)


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