FAQs

Here are answers to some of the most common questions about REhnu's technology and concentrated photovoltaic power.

How does REhnu convert sunshine into electrical energy?

REhnu’s technology uses a large mirror to focus sunlight onto many small but powerful photovoltaic cells. These cells convert sunshine energy directly into electricity, with higher efficiency than other photovoltaic and thermal methods.

What makes REhnu’s generator design unique?

REhnu’s method of concentrating sunlight onto small photovoltaic cells is unique. A large area of sunlight is first brought to a powerful focus, then the light is apportioned in a small receiver to many closely packed cells, by unique dividing optics. By contrast, in a traditional concentrator system, the light is evenly divided before concentration. This means the cells must be packaged in a large module, to make room for many identical small optical concentrator units, one above each cell.

What is REhnu doing now to advance this technology?

With the system concept proven in the second-generation prototype, work on a third-generation prototype is underway. The focus is on manufacturability, lower cost, and still higher end-to-end system efficiency, with a target of 31% or better.

Does REhnu plan to adapt its generators for residential installations?

No. REhnu’s technology is not cost-effective for small installations. REhnu’s approach is optimized for mass-produced systems where there are significant economies of scale for assembly in field factories and installation in large-scale farms.

How big will a gigawatt-scale REhnu solar farm be?

Approximately 6 square miles using present multi-junction cells, 5 square miles using future, higher efficiency cells.

What is a gigawatt?

A gigawatt (1 GW) is a unit of electrical power equal to 1000 megawatts or one million kilowatts. For reference, the peak load in the U.S. (on the hottest summer afternoons) is 800 GW. The total energy produced annually by a REhnu 1 GW solar farm is about equal to that consumed by 220,000 U.S. homes.

What happens at night?

REhnu’s system produces electricity only during the day, as do all photovoltaic systems. At levels up to tens of gigawatts, this power can be used to help meet local daytime peak loads. In the longer term, hundreds of GW of daytime solar power can be combined with other renewable energy sources (such as wind, which is strongest at night) in an upgraded grid. With the aid of long-distance transmission lines and large-scale storage, such as pumped hydro, renewable energy can largely replace fossil fuel, 24/7, and on a continental scale.

Do REhnu’s large-scale solar farms consume water?

No. REhnu’s generators use a closed-loop system for active cooling, using no water. The small amount of water needed to wash the reflectors can be obtained by using the upturned reflector dishes to collect rainwater.

What will be the impact of REhnu’s farms on the desert?

A 1 GW REhnu farm generates no CO2 and uses no water, while a 1 GW coal-fired plant every minute emits 5 tons of CO2 and consumes 10,000 gallons of water. Installation of the generator units leaves most of the land undisturbed. In operation, the generator units make almost no noise.

Can’t the waste heat from the receivers be put to use?

Perhaps, but not efficiently. To achieve highest electrical output, our system cools the cells to run only 20°C higher than ambient air temperature. At best, only a very small amount of additional energy could be extracted from coolant at such low temperature.

Can REhnu’s farms really reduce atmospheric carbon build-up?

The carbon and energy used in manufacturing and installing a REhnu farm is paid back in fewer than 2 years. For each of the next 40 years the farm spares the atmosphere 2 million metric tons of CO2 that would otherwise be emitted by a coal-fired plant. A thousand REhnu 1 GW farms operating worldwide (with a total area of 80 x 80 miles) would reduce total global CO2 emissions by 10%.

Is REhnu’s process dependent on government subsidies?

REhnu’s process is inherently cost-efficient and is designed for high-volume production, lending itself to highly automated production and installation. The projected cost at high volume is fully competitive with electricity from fossil fuels. In the initial, smaller-scale phases, REhnu will benefit from Renewable Energy Credits (RECs) and solar investment tax incentives, but these are not used in REhnu’s long-term business model.