Environmental Stewardship

Environmental stewardship is especially important for production on a very large scale, and is central to REhnu’s choice of technology. The generators have been designed for manufacture with the minimum of materials, energy, and carbon released. They are installed with minimal disturbance of the land and operate with no need for cooling water.

The primary reflectors and their tracking supports, the only components that must be large in order to collect the energy, are made almost entirely of glass and steel. These are common materials made already in huge volume by processes already well developed to conserve energy and to minimize carbon emission. Our design is configured to use as little of these materials as possible, the minimum needed to survive high wind and hailstorms. The unique spaceframe design of REhnu’s generators has the highest structural efficiency of any design. While the photovoltaic cells in the receivers do use some environmentally sensitive materials, they do so in tiny quantities compared to many PV panels, because they are 1000 times smaller.

Minimum payback time for energy and carbon used in manufacture

The metric used for optimization of the 12-reflector, 30 kW generator was the mass per kilowatt of peak power output. More than half the total mass is in steel, which Including the foundation weighs 3 metric tons, i.e. 100 kg per kilowatt of power produced. The payback time for the energy used in making the steel is 5 months, while the CO2 emitted in manufacture is paid back in 3 months, assuming the electricity produced replaces that from a coal-fired plant. For the next heaviest material, the glass at 40 kg/kW, the total payback time for both energy and CO2 is 2 months.

The other material that results in major consumption of energy and carbon emission during manufacture is the aluminum needed to make the heat exchanger or radiator. By transferring heat mostly by coolant, the mass of the aluminum in the REhnu design (for cooling fins) is reduced to one tenth that of the steel. Nevertheless, because aluminum manufacture is much more energy and carbon intensive, its payback time is similar, totaling 6 months.

For all materials, manufacture, transportation, and installation of the generators, the total payback time is estimated at less than two years, less than for most other forms of renewable energy. Since the productive lifetime exceeds 20 years, the net gain is large.

Small ground footprint

The farm has a light footprint on the land. The open-structured 70' x 30' generators are mounted on single pedestals 78' apart that turn silently 8' above the ground, minimally disturbing wildlife habitat beneath. Most of the sunlight reaches the ground when the sun is high, as the harvested area is only one quarter the land area. Generators can be installed on sloping or hilly as well as flat land, with no requirement for grading or blading prior to installation. Especially sensitive habitats, such as wildlife corridors and riparian areas, will be avoided. The installation sequence involves first building the 10' access roads 135' apart, thus covering less than 10% of the land. The pedestal foundations for the generators are set off to the side of the roads, and use no concrete and a minimal amount of steel. Power from the generators will run mostly in trenches below the roads.

Water

To wash dust off the primary reflectors, rainwater will be collected by facing the dishes upward. Eight inches of rain yields 500 gallons of water per dish. From experience washing trough thermal concentrators, this is enough for a year of washing. No other water is consumed by the generators. The cells are cooled in a sealed system by recirculated antifreeze coolant.