Solar pond

A solar pond is a special pool filled with saltwater. It can collect and store energy from the sun. This works because the saltwater forms layers. Less salty water is on top and very salty water is at the bottom. These layers are called a vertical salinity gradient, or a "halocline". The water at the bottom stays warm because it does not mix with the cooler water above. This lets the pond store heat for a long time. Solar ponds can help heat buildings and other things that need warm water.

Description

When the sun shines on the bottom of a shallow pool, it warms the water there. Solar ponds stop the warm water from rising by using salty water. Salt makes the water at the bottom very heavy, so it stays there and doesn’t mix much with the lighter water above. This way, the bottom water can get very hot — up to 90 °C — while the top stays around 30 °C. The hot water can be used to make electricity or provide heat.

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Advantages and disadvantages

Solar ponds are great for places in developing countries that don't have a lot of resources. They can be big and only need a clay or plastic liner to start working.

One problem is that salt can build up and need to be cleaned out. This can cost money and take time. Solar ponds don’t need special parts to catch the sun’s heat, and they can keep making power even when it’s dark. But they don’t get very hot, so they can only change a small amount of sunlight into energy. They also lose water to evaporation, so you need to add fresh water to keep the salt levels balanced.

Efficiency

Solar ponds collect heat energy and can reach temperatures between 70 and 80 °C, while the air around them is about 20 °C. The maximum amount of useful energy a solar pond can produce is about 17%. This is lower than some power plants, but solar ponds can be built on a large scale and might cost less overall.

Development

Scientists are trying new ways to make solar ponds better. One idea is to use a special thin material called a membrane. This membrane goes between the layers of water and helps the layers stay separate without mixing the salt. It makes the pond work better.

Examples

The largest solar pond used to make electricity was at Beit HaArava in Israel. It operated until 1988 and could make 5 MW of electricity.

India was the first Asian country to build a solar pond, in Bhuj, Gujarat. It started in 1987 and finished in 1993. This solar pond could give out hot water every day. Sadly, problems happened later that stopped it from working.

In the U.S., a smaller solar pond in El Paso, Texas, powers part of Bruce Foods Corporation. It was the first solar pond of its kind in the country.