Now concentrate

Mirror, mirror on the floor…

Concentrating solar power (CSP) systems could be the energy of the future in off-grid locations, both small and large scale. Lenses or mirrors focus a large area of sunlight into a small beam. In power stations the beam shines on a vessel that contains a gas or liquid that can be heated up to around 400C (750F) enough for conventional steam turbine. Small-scale off-grid CSP power stations don’t have to be hugely expensive either.

In fact, the basic idea of concentrated solar power is the same as in solar cooking and new methods of water pasteurization – already widely used in the third world – eliminating the need for biomass as a fuel.

But what makes the plants really efficient is their recycling of energy.

German scientists Dr Gerhard Knies and Dr Franz Trieb have calculated that covering just 0.5% of the world’s hot deserts with a CSP system would provide the world’s entire electricity needs. This form of solar power is also attractive because the hot liquid can be stored in large vessels which can keep the turbines running for hours after the sun has gone down, avoiding the problems association with other forms of solar power.
The mirrors are so large that they can create shaded areas where horticulture can thrive with irrigation coming from the desalinated water generated by the plant. The cold water can also be used for air-conditioning for nearby cities. “It is this triple use of the energy which really boosts the overall energy efficiency of these kinds of plants up to 80% to 90%,” says Dr Knies.

So why is CPS hardly ever mentioned when we talk about renewables?

It’s certainly not a new technology, with the oldest plant operating in the Mojave desert in California for the past 15 years.

Consider, too, the millions of tons of firewood this would save instead of being used for fuel.

The company Solar Cookers International (SCI), a California-based nonprofit organization, has launched a number of projects all around the world since its conception in 1987, to encourage the reduction in cooking fuels and substitute them with solar cookers.

Their Sunny Solutions project in Nyakach, Kenya started in 2003 and involves the use of a small, portable device that collects energy from the sun to generate heat. Firewood is used only at night and on cloudy days. These simple cookers concentrate the sun’s heat so that a pot of food can be heated, often with a covering of some sort to stop the heat escaping. A panel cooker takes about an hour to build and costs around $5 in Kenya, with a saving of around $6 on fuel per month.

The technology has proved simple and effective, especially during humanitarian crises of the recent years. Sudanese refugee in the Iridimi camp in Chad made use of solar cookers out of necessity because leaving the camp to gather firewood is extremely dangerous.

Four humanitarian groups (Solar Cookers International, KoZon Foundation, Jewish World Watch, Refugee Foundation Netherlands and CARE International) partnered to make and distribute solar cookers those families living in the camp and to others in neighbouring camps.

On both the very large and the small scale, CSP is a demonstrably viable energy source…that is, unfortunately, getting little attention from governments.