Most people think that concentrating solar thermal (CSP) power plants must be large and expensive. Systems are generally based on very large steam turbines with a high overhead cost that can only be amortized over large scale production rates (typically 50-100MW, or more). This amount of power requires thousands of reflectors spread out over a large area. That means it will most likely be sited in some remote area, far from where the power will be used, thereby subject to significant transmission losses.

Aora Solar has developed a different kind of CSP technology that breaks out of this mold.

“Our strategy,” says Zev Rosenzweig, Aora Solar’s CEO and Founder, “is to create CSP that is capable of distributed generation. We take the plant to the user, rather than taking the electricity to the user.”

He calls their system, “micro-CSP technology.”


It is based on a micro gas turbine with a capacity of 100kW, and a compact heliostat (tracking mirror) field, with the heliostats close to the tower. This field directs intensified sunlight on to the solar receiver which is located at the top of the tower. The operating fluid is compressed air, which is heated to 1000 degrees C, and then expanded through a gas turbine.

It’s a hybrid system that can be set to automatically burn biogas or other fuels to heat the air when the sun isn’t shining or if the sunlight isn’t strong enough. This results in a system that can produce renewable power around the clock, 24 hours a day and can continue to produce power even if the sun doesn’t come out for several days in a row.

Rosenzweig considers these systems more nimble than conventional CSP plants, which he refers to as «dinosaurs.» Aora’s target market is isolated, off-grid villages in developing countries.

“One small plant can easily serve the needs of an entire village on a micro-grid in a manner more cost-effective than individual household PV, without bringing in power from a distant power grid.”

The government of Ethiopia recently signed a memorandum of understanding for several plants after visiting Aora’s demonstration plant in Almeria, Spain. A typical village there, requires around 68 kW, well within the capacity of Aora’s system which seems to be a good fit. Additional units could be added fairly easily.

The compact solar field takes up only about 2,700 square meters, which is about two-thirds an acre. It consists of 45-50 heliostats using parabolic mirrors. These mirrors lose less energy because they are close to the tower. This results in a lower amount of glass per MW, compared to the larger CSP plants.

When it comes to cost, Rosenzweig calls his system a “sophisticated collection of simple parts.” The only big ticket items are the receiver and the turbine. Everything else is either steel pipe or glass.

If you compare 1 MW of this technology with 1MW of PV, you have to consider a number of factors related to storage. In essence, with PV, if you want around-the-clock power, you need 4 MW of solar to be producing power during peak hours in order to be able to store energy for the rest of the time. Then you also have to pay for the storage.

A good price for today is $1.25 million per MW. That means you need $5 million for the solar, plus another 10% to account for power lost going in and out of storage. So that’s $5.5 million for PV. Plus you’ll need 18-19 MWh of battery storage. GE has a battery cost goal of $400k in three years. At that price, you’d need about another $7.5 million for batteries that will only last around 8 years. So, for 20 years, you’re looking at a system cost in the neighborhood of $20 million.

This plant, on the other hand will cost about $6.5 million for 1 MW. That leaves $13.5 million for biogas, which will cost a lot less than that, especially if it’s locally produced. So for this type of off-grid application where power is desired around the clock, this solution is very cost effective. Biogas production could also stimulate agriculture and create local jobs in the area.

Rosenzweig estimates that his system requires 30% less area than PV for a comparable output.

They are also scoping new projects in areas like Lake Victoria, where fishermen could benefit greatly from the availability of refrigeration, and would have plenty of feedstock for biogas production. There are countless other examples like this across the developing world.

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