Concentrated Solar Power 101

This type of solar panel comes in two variations: photovoltaics and thermal. Concentrated photovoltaics or CPV use parabolic concentrators, reflectors or lenses to focus more light onto a photocell. An influx of more photons lets properly designed cells generate more power. Reflective or mirrored surfaces can be expensive, so design efforts have been to find inexpensive reflective surfaces that can withstand normal environmental conditions such as rain.

A diagram of a parabolic trough solar farm (top), and an end view of how a parabolic collector focuses sunlight onto its focal point. -Andrew Buck

One manufacturer of solar panels produces arrays that combine silicon cells, durable reflector materials in a parabolic trough and single-access tracking into one system. The company says as the solar industry matures, customers are valuing energy yield and cost more than peak “nameplate” rating. The company’s high-gain solar is a series of system-level design features which drive lower installed cost and higher energy yield relative to traditional fixed PV arrays. The equipment, says the company, starts with high-efficiency silicon cells and tracking, which increases energy yield. It now includes reflective materials, lower-cost panels, convection cooling, string and shadow management, and streamlined installation and maintenance.

This concentrating design includes a holder for the cells used on its array so they are easily replaced. This would happen when it makes economic sense, as it will when more efficient cells become available in a few years. Such a panel will let a solar park increase its output and become more useful, a claim few other power production facilities can make.

The concentrated photovoltaics from a German PV manufacturer use lenses to focus direct sunlight onto small, efficient solar cells. This conversion of sunlight into electricity makes it possible to generate about twice the electricity per square meter of module area than traditional flat-panel photovoltaics. The cells are mounted on a structure that tracks the sun on two axes to enable a near constant power output curve. This better matches the peak power demand in arid climates. This CPV technology is intended for areas of high irradiation and a low heat reduction coefficient, making it suitable for large power plants in desert regions.

Because it scales to large plants, companies can design facilities from one to hundreds of megawatts. Other benefits, according to the manufacturer, include attractive rates of return, a design well suited to hot climates, and about double the operating efficiency of conventional PV systems. In fact, a company reported 25% AC-system efficiencies in 2009 and says it is aiming for 35% efficiency.

The modules are also said to have a low environmental impact and minimal water consumption — even a dual land use with agriculture is possible, unlike conventional PV or CPV power plants. These require using the land only for the array. This is a plus in areas where rare animals could impede a project. The equipment is also almost completely recyclable.

Parabolic troughs are also going through rapid changes. Solar concentrators using a parabolic trough on utility scale arrays can harness the sun’s energy to make steam for electricity generation. One utility-scale solar concentrator uses a lightweight mirror film in place of the fragile glass mirrors.

Thermal efficiency for any solar application is the proportion of available sunlight converted into heat to generate electricity. The proportion predicts performance of a given parabolic trough and allows comparing competing technologies. NREL tests show the thermal efficiency of one mirror-film trough in particular at a remarkable 73%. Temperature of the working fluid reaches 350°C (662°F). The efficiency figure means nearly three quarters of the solar radiation striking the trough’s surface is converted into thermal energy. The lab’s results confirm that the design’s performance is comparable to or exceeds that of the previous, proven, utility-grade trough systems at a cost that the lab says is below industry standards.

  • http://profile.yahoo.com/ESTKS5OWV7YYMJJMTICRSZAP6Y Brian

    Kathleen,

    This is almost unbelieveable efficiency. Its great that companies are moving towards products like this. Is water or some other liquid being used as the heat transfer liquid.

    Thanks,
    Brian L.