New 'solar reactor' could tackle renewable energy's biggest problem

A new solar energy generating technique could solve a key problem with the power source – what happens when the Sun goes down or clouds block the light.

To tackle the intermittency problem, an international group of researchers looked to concentrated solar power (CSP), a technique where mirrors focus the Sun’s rays on a central tower. However, instead of installing turbines in towers to generate electricity, the German and Greek team’s technique used collected heat to power a “solar reactor” capable of extracting hydrogen from water or methane at 850^oC.

Zero-carbon hydrogen extracted without fossil fuel-fired power stations will be a key future power source, said the engineers from the German Aerospace Centre (DLR) and the Aerosol and Particle Technology Laboratory in Greece.

Despite solar energy’s potential for extracting hydrogen, one lingering issue with the power source is its inconsistency. “Solar reactors in the past have had the problem of what you do at night when you don't have sun, or even when clouds go by,” said lead author Justin Lapp from the DLR, now a mechanical engineer at the University of Maine.

To achieve the round-the-clock energy needed, the team built two CSP-powered reactors side-by-side. One side uses heat for direct chemical processing, while the other heats air to a theoretical maximum of about 1,100^oC. In future, the hot air could then potentially melt copper, storing thermal energy in the molten metal for use in the chemical processing side when needed.

The international group built a laboratory prototype named Contisol, powered by simulated ‘Suns’ and reaching 5kW power with a temperature of 850^oC. “This scale is a scientific prototype simply for us to understand how to control it. It wouldn't be commercialised at 5kW,” said Lapp. “Commercially, 1-5MW would be about the smallest for industrial-scale reactors, and they could scale to 100MW or even larger.” The team used the reactors to reform methane, although other hydrogen sources could include water and sulphuric acid.

The research was published in Applied Thermal Engineering.

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