Solar Engineering Applications

The SEA solar energy conversion system is a cogeneration system, producing both electricity and valuable low-grade thermal energy (material temperatures less than roughly 50 to 60°C). Our system has multiple rows of parabolic trough reflectors that focus solar radiation onto actively cooled arrays of solar cells. The solar cells convert part of the incident radiation directly into electricity. The part that is not converted to electricity is collected as low-grade thermal energy in coolant flowing through cooling channels that support the solar cells. This low-grade thermal energy is normally discarded as waste heat, but our SEA system collects it, stores it, and makes it available for later use.

Trough reflectors used in solar energy conversion systems track the sun by rotating in one angular dimension. Sun tracking for an SEA system’s reflectors is accomplished by azimuthal-angle sun tracking; that is, the entire system—trough reflectors, solar-cell receivers, and support structure—rotate as a unit in a horizontal plane about a central vertical axis. As the system rotates, the optical planes of the reflectors are held in a fixed vertical orientation and the gravitational force acting on the reflectors is always parallel to the reflectors’ optical planes. This greatly simplifies the mechanical design of the system, reducing fabrication and installation costs while at the same time increasing system reliability. Also, whenever wind velocities reach a high level, sun tracking can be interrupted and the reflectors’ longitudinal axes can be rotated into alignment with wind direction, thereby significantly reducing the possibility of wind-induced damage.

Since the reflectors in an SEA system don’t tilt or roll as in previously deployed trough reflector systems, they don’t produce mutual shadowing at low sun angles. That’s why our system’s reflectors can be placed side by side, as shown in the animation above, thereby collecting sunlight from roughly 95% of the area covered by the reflector field. Efficient use of land area means that SEA systems can be deployed near the energy markets they serve, utilizing the solar resource locally, even in locations where available land may be expensive or in limited supply.

When irradiated by the intense sunlight (25 to 30 suns) coming from our system’s parabolic trough reflectors, the back-contact, single-crystal silicon solar cells used in our system (silicon solar cells) can produce electrical energy with an efficiency approaching 25%.   Active cooling of the cells maintains their high efficiency even when they are exposed to highly concentrated sunlight. Also, the light-concentrating power of the parabolic trough reflectors reduces—by a factor of 20 to 25—the area, and thus the cost, of the solar cells required to generate a given amount of electrical power. Just think about that. The cost of the solar cells in an SEA system is only 4 or 5% of the cost of the cells in a non-focusing system with the same output power.

In summary, SEA solar energy conversion systems are modular, scalable, mechanically simple, and they make very efficient use of both available land area and incident solar radiation. They collect sunlight from more than 95% of the land area covered by the reflector field and they convert more than 90% of incident direct solar radiation into useful output energy.