Is Concentrated Solar Power The Next Big Thing?

Over the years, Microsoft’s Bill Gates has been involved in many interesting projects but this one seems pretty special. He is backing a start-up which has recently made a breakthrough in concentrated solar power (CSP). This also means there could be massive potential for industrial green energy.

The company in question is Heliogen, originally set up in 2013, it’s come a long way in a short space of time. After considerable investment in research and development, including bespoke software, they’ve announced a unique capability of producing concentrated solar power. For the first time, temperatures over 1000°C are possible on a commercial scale.

What Is Concentrated Solar Power?

Concentrated solar power (CSP) is often referred to as concentrating solar power or concentrated solar thermal systems. They generate solar power by using mirrors or lenses to focus a large area of sunlight onto a receiver. This converts concentrated light into heat (solar thermal energy) which produces electricity and that powers a heat engine, often a steam turbine, connected to a generator.

Concentrated solar energy has more in common with thermal power stations such as coal, gas and even geothermal. These concentrated solar plants can incorporate thermal energy storage in the form of sensible heat or latent heat by using molten salt, for example. This enables CSPs to continuously generate electricity whenever necessary, day or night.

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More On Heliogen’s Installation

Temperatures they had previously achieved were only around 5kW using a parabolic dish. This method involves moving focus with the sun where Heliogen’s system concentrates the power on a stationery target mounted on a tower. The breakthrough was based on the use of computer vision and sophisticated software to control an array of mirrors.

According to Bill Gross: “With a dish, when you want to concentrate sunlight, all you have to do is point it at the sun. In our system, we have to align every mirror slightly differently to bisect the angle between the sun and the tower.”

Every mirror points in a slightly different direction and not focused on the sun or the tower. Instead, they are pointed halfway between or at an invisible point in the sky. Their installation at Lancaster, California, has 400 mirrors each measuring 1.5 m² spread over 1800m².

How Did They Achieve The Breakthrough?

Mirrors are often several hundred metres from the target and typically focus sunlight on a spot of around 10m in diameter, achieving a maximum temperature of 600⁰C. Whilst this is hot enough to make steam and drive a turbine, it doesn’t match the output of photovoltaic panels.

Through computer vision and bespoke software, Heliogen found a way to move their mirrors more precisely. This resulted in focusing the light on an area the size of a basketball hoop (18in or 460mm in diameter).

Cameras on the tower point at the entire mirror array capturing video at 30 frames per second. Their new software analyses the position of the mirrors’ edges and the angles of reflection from each panel. From there, it can make tiny positional adjustments of each mirror 30 times per second.

How Are CSP Panels Made?

CSP mirrors are made from ordinary glass with a silvered backing which is protected against the elements through a layer of copper and a coating of outdoor paint. The glass is only 3.2 mm thick to ensure maximum reflectance but they are thick enough to withstand a hailstorm.

Concentrated solar power mirrors don’t require special materials as they reflect the light which means they remain cool. The collector uses refractory ceramic bricks inside kilns, specifically designed to withstand high temperatures.

Related: ‘Solar Power – Our Endless Fuel Supply’

What Does Concentrated Solar Power Mean For Heavy Industries?

According to Heliogen founder and CEO Bill Gross, by “commercial” they mean that the temperature achieved was combined with sufficient power which is between 250 and 400kW. For industrial purposes, they are aiming to increase this output to between 1 MW and 10 MW.

As it stands, Heliogen claims that concentrated solar power could replace fossil fuels in critical industrial processes. This includes the manufacturing of cement, steel or aluminium; and potentially for thermally splitting water to produce hydrogen thanks to the extreme temperatures.

The next stage is integrating CSP into manufacturing processes with cement manufacturing at the top of the list. This sector accounts for over 7% of global carbon dioxide emissions. It currently uses rotary kilns and would have to adapt their process to successfully integrate concentrated solar power.

Next Steps For CSP

Heliogen’s initial focus will be on the first stage which is calcining as this process uses the most energy. Here, they heat limestone (calcium carbonate) to between 900-1000°C to drive off carbon dioxide which leaves behind calcium oxide. They plan to achieve this by carrying limestone to the top of the tower in batches using conveyor belts for heating in a form of an oven.

Another possibility is using steam heated to 1000°C and brought to ground level in insulated pipes. With only a 10-20°C temperature drop, it can be used to either heat the materials directly or through a convective heater to heat an oven.

They have ambitious plans for practical applications expecting to see the technology in use with steam customers this year. Plans for 2021 involves the integration of concentrated solar power into processes such as cement or steel production whilst aiming at 2022 for hydrogen production.

Final Thoughts

One of the important points is that Heliogen’s system allows the heating of steam to the required temperature at a low cost. Also, it can then transfer the steam to wherever the heat is needed. Installing concentrated solar power does not involve a mammoth construction project, besides the 40m tower as that requires significant construction skills.

The mirrors don’t need any special foundations and could be installed by unskilled labour. Gross believes that concentrated solar power will soon be more efficient than PV as it uses heat directly from the sun instead of converting it to electricity. An added benefit is that this process will be capable of continuing overnight.

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