Green hydrogen is going down in cost, and concentrating solar power could pick up the pace by ditching electrolysis in favor of a thermochemical process.
New solar conversion efficiency records are a dime a dozen these days, and the cost of PV panels is continuing to sink like a stone. Apparently, though, we ain’t seen nothing yet. Researchers point out that PV cells only use part of the solar spectrum. The next big thing in solar power is the use of high heat in systems that put the entire spectrum to work from one end to the other.
The Concentrated Solar Power Workhorse
If you’re thinking concentrating solar power is the key, that’s right. For those of you new to the topic, concentrating solar power refers to systems that gather energy from the sun, by collecting it in a field of specialized mirrors or reflective troughs, and focusing it on a smaller point or pipe.
Concentrating solar power systems don’t generate electricity directly, but they do generate a lot of heat, which can be used to boil water for steam to run a turbine, which does generate electricity.
If that sounds like a lot of work for a few clean kilowatts, it is. Back during the Obama administration, skeptics pointed out that CSP systems were overly complex and costly. However, CSPs rely on a heat-storing medium such as molten salt or oil, which means they can potentially generate electricity 24/7 without the expense of an additional battery system.
In addition, CSPs don’t need to generate electricity to be useful. Many industrial processes rely on heat, and that’s where the new hydrogen-perovskite angle comes in.
Concentrating Solar Power Beats Fossil Energy For High-Temperature Work
CleanTechnica first caught wind that something new was afoot back in 2018, when the US Department of Energy and its research partners began talking about the potential use of concentrating solar power in high-heat applications
In particular, a high-heat CSP system could generate temperatures far beyond the capabilities of typical fossil power plants. John Shingledecker of the Electric Power Research Institute explained the allure to CleanTechnica in a phone interview:
“A lot of the developments are being taken from fossil power plant steam cycles or coal boilers, but they only go up to 620 degrees C,” he said. “Seven hundred degrees and beyond has been the subject of much study — for example advanced supercritical technology, involving supercritical CO2 power cycles based on CO2 as a working fluid.”
Supercritical CO2 (sCO2) is the fluid form of carbon dioxide. Once the kinks are worked out, sCO2 could provide the concentrating solar power field with a nonflammable, nontoxic substitute for molten salt or oil.
When used to run a turbine, sCO2 could also be the basis for a new compact, high-efficiency power cycle. Researchers note that the typical steam-powered Rankine power cycle is 33% efficient, while sCO2 would allow the deployment of a Brayton cycle surpassing 40%. The impact on the size of turbines would be significant, shrinking a typical 20-meter turbine down to just 1 meter.
The Green Hydrogen Angle
Where were we? Oh right, the new solar thermochemical hydrogen (STCH) production system proposed by the Energy Department’s National Renewable Energy Laboratory.
The Energy Department began launching a series of “Energy Earthshot” initiatives last summer, following the lead of the ambitious Sunshot affordable PV program. The very first Energy Earthshot zeroed in on clean hydrogen, which appeared to leave some wiggle room for less-than-green hydrogen.
However, the main focus of Hydrogen Shot does appear to be green hydrogen, and that is where NREL has focused its attention.
“Hydrogen has emerged as an important carrier to store energy generated by renewable resources, as a substitute for fossil fuels used for transportation, in the production of ammonia, and for other industrial applications,” NREL points out.
Natural gas and coal have been the primary sources of hydrogen for decades. The up-and-coming green alternative is electrolysis, which deploys renewable energy to generate electricity. When applied to water with a catalyst, the current pushes hydrogen gas out of water.
Now the race is on to cut the cost of electrolysis. The Energy Department has set a goal of $1.00 per kilogram for green hydrogen within the next 10 years, which is pretty ambitious considering the cost was about $5.00 just last summer.
The STCH system offers an alternative path to $1.00, by ditching electrolysis in favor of a heat-based chemical process.
“STCH relies on a two-step chemical process in which metal oxides are exposed to temperatures greater than 1,400 degrees Celsius and then re-oxidized with steam at lower temperatures to produce hydrogen,” the NREL team explains.
The Perovskite Twist
Before you get all excited, the team also explains that STCH systems are still in the early stages of development. The main obstacle is in the area of advanced materials, and the team is aiming at perovskites to provide high performance under high heat.
Interesting! Perovskite refers to a family of lab-grown synthetic crystalline materials with interesting optical properties. They have become a hot area of study in the PV field in recent years.
This is the first time we’ve seen them pop up in the solar thermal area, but if lower cost is the game, perovskite is the name.
You can get all the juicy details in the NREL study, published in the journal Renewable Energy under the title, “System and Technoeconomic Analysis of Solar Thermochemical Hydrogen Production.”
Next steps include digging deeper into the perovskite field to identify variants that can hit performance and cost targets.
Next Steps For Concentrating Solar Power
NREL’s solar powered thermochemical hydrogen production system is just one piece of a global concentrating solar power puzzle assembled under the SolarPACES organization.
SolarPACES is a program of the International Energy Agency. The name stands for Solar Power and Chemical Energy Systems, and it has been hammering away at the topic since the 1970s, which not coincidentally is the decade that gave rise to the National Renewable Energy Laboratory here in the US.
Now it looks like all that hard work is about to pay off.
“SolarPACES has played a formative role in CSP research from the very earliest days beginning in 1977, and the role has widened as the market for dispatchable solar has become more defined to today’s commercial deployment at full-scale,” SolarPACES explains.
The 28th annual SolarPACES conference is coming up this September in Albuquerque, New Mexico, so stay tuned for more on that.
Meanwhile, concentrating solar power fans are already eyeballing Mars as the next opportunity to deploy CSP, so stay tuned for more on that, too.