"The Heliogen company is a provider of “artificial intelligence enabled” solar power.
They just received an award from the Department of Energy to build a prototype plant that generates electricity.
As a student of solar energy and the author of the book Dumb Energy, my opinion is that this is another solar energy scheme designed to vacuum up government and private money.
Heliogen is promoting concentrated solar power or CSP.
CSP uses optical methods, generally mirrors, to concentrate sunlight so that high temperatures can be obtained.
If you ever used a magnifying glass to start a fire you were using CSP.
... The proposed prototype plant, for which the government is providing $39 million, will use super critical CO2 rather than steam as the turbine working fluid.
Part of the heat collected during the day will be stored in hot rocks where it can be extracted after sunset to continue electricity generation.
Turbines using super critical CO2 are a mostly theoretical technology.
The potential advantages are greater efficiency and smaller equipment size.
A general rule is that the higher the turbine inlet temperature the better the efficiency.
A 20% gain in efficiency may be possible with CO2 turbines as compared to using steam.
Existing large scale CSP plants use flat mirrors that track the sun to direct the sunlight to an energy collector atop a tower.
The average degree of concentration of energy remains constant even as the size of the field of mirrors is increased.
This is because as the mirrors become more distant from the central tower, the illuminated spot size increases, diluting the concentration of energy.
Heliogen uses focusing mirrors to make the spot size smaller.
Focusing gives an increase in the obtainable temperature but does not overcome the rule that increasing field size does not further increase the temperature as the image of the sun is larger the more distant each focusing mirror is.
The light spot on the collector is a focused image of the sun.
As the sun moves through the sky, the focusing mirrors have to track the sun to keep the focused spot aimed at the collector.
Unfortunately, the shape of the mirror has to change as the angle of the sun changes.
This requires deformable mirrors.
Actuators controlled by a computer have to warp the mirror into a constantly changing shape.
Naturally, deformable mirrors are more complicated and costly.
The further away from a collector a mirror is, the more critical is the shape of the mirror, and the more critical the accuracy with which the mirror is aimed at the collector.
The result is that the mirror fields cannot be very large and still obtain high temperatures.
Heliogen says its units are modular and spins that as an advantage.
They are modular out of necessity because the mirrors cannot be deformed with enough accuracy to get good focus on a distant collector.
Modularity is not an advantage but a problem because multiple towers and probably multiple turbines would be necessary to get increased energy output.
Concentrated solar power is not new and has never been remotely practical.
(for the former) Ivanpah CSP plant in California near the Nevada border:
The towers are illuminated by sunlight directed by thousands of motorized mirrors that track the sun and direct the sunlight to the towers.
The intensity of the sunlight on the towers is hundreds of times stronger than the sunlight falling on the ground.
Water circulating through a boiler in each tower is turned into high pressure steam used to power a turbine and electrical generator.
The electricity is only generated during the day and at a cost around 5 times as much as using natural gas.
The plant cost about $2 billion.
Another CSP plant is Crescent Dunes near Tonopah, Nevada.
This plant has a tank of molten chemical salts that are heated to a high temperature during the day.
At night the hot salts can be used to generate steam to drive a turbine and make electricity.
By storing energy as heat, electricity generation can be extended into the night.
The plant was plagued by a leaky salt tank and forced into bankruptcy.
Recently it has resumed generating overpriced electricity.
Much of the basics of CSP are described in the 2012 SunShot study:
https://www.energy.gov/sites/default/files/2014/01/f7/47927.pdf
Both Ivanpah and Crescent Dunes CSP plants were financed with huge government loans and utility contracts to purchase the power at highly inflated prices.
Most likely the government loan for Crescent Dunes was discharged in bankruptcy.
Photovoltaic solar plants use semiconductor panels to generate sunlight from electricity.
About 20% of the energy in the sunlight is converted to electricity.
As more of these plants are built it becomes necessary to add fiendishly expensive batteries to move excessive midday power to the early evening.
The result is electricity costing five or ten times more than using natural gas to generate electricity.
The entire fossil fuel generating infrastructure has to be kept, staffed and ready to operate, due to the erratic nature of sunshine.
In theory CSP plants could be more efficient than photovoltaic plants but the high cost wipes out any advantage.
Neither type of solar plant is remotely competitive with natural gas, coal or nuclear.
The motivation for solar electricity is the global warming scam, a prime example of junk science promoted by special interests.
If one takes global warming seriously, the only solution for massive CO2 emission reductions is nuclear power.
Nuclear power is blacklisted by superstitious environmentalists.
Thus, we have a massive and pointless money sink of solar and wind plants.
By reaching higher temperatures the Heliogen solar scheme could be used for the thermal production of hydrogen by decomposition of water.
Hydrogen as a common fuel has many problems.
It is difficult to store in quantity in high pressure tanks.
If it leaks it is far more explosive than natural gas.
It damages steel pipelines as well as being prone to leaking out of any attempt to confine it.
Unlike natural gas it is difficult to liquify due to the low temperature required, and because the liquid has a very low density the tanks have to be very large.
Converting hydrogen to mechanical or electrical energy involves further large losses." ...