Solar power tower

Figure 1. Two solar power towers.

A solar power tower is a system that converts energy from the Sun - in the form of sunlight - into electricity that can be used by people by using a large scale solar setup. The setup includes an array of large, sun-tracking mirrors known as heliostats that focus sunlight on a receiver at the top of a tower. In this receiver, a fluid is heated and used to generate steam. This steam then powers a conventional turbine generator to generate electricity.

Potential downsides of using towers such as this is that they involve large facilities that require large amounts of initial investment. As well, the large field of mirrors and tower that can range from 50 to more than 100 meters can be seen as an eyesore and can impact that local landscape.

Operation

As explained briefly above, a solar power tower is one of the main components of a solar power plant. This tower is placed in the center of a large array of mirrors. These mirrors can be curved or flat, but generally speaking flat mirrors that track the Sun are used as they are less expensive than curved mirrors. As these mirrors track the Sun, they "catch" the incident sunlight and reflect it back to the solar tower. A large number of these mirrors focus a large amount of solar radiation onto a small spot on the tower known as the receiver, heating up some fluid inside of it. This fluid is used to transfer the heat from the sunlight to the water. Old towers used steam as a heat transfer fluid, but newer designs use molten salts because of their increased heat transfer and energy storage abilities. When the heat is transferred to water, it turns to steam. This steam is then transported to a conventional turbine to produce electricity.

It is important to note that these solar power towers are heat engines as they take the energy from being warm in comparison to their surroundings and turn that heat into motion. More specifically, these solar power towers are external heat engines as the heat source (the Sun) is separate from the fluid that moves and does work. It is external combustion as heat from the Sun heats some fluid that is then turned to steam and used to turn a turbine.

Environmental Concerns

As is the case with other solar power technologies, solar power towers represent a type of electricity generation technology that is cleaner than generating electricity by using fossil fuels. Thus, solar power towers are one of the cleanest options for generating electricity. Despite this, there are still associated environmental effects of these towers. First, a life cycle analysis shows that there are still greenhouse gas emissions associated with the fabrication and construction of the tower and mirrors, as well as greenhouse gas emissions from dismantling and recycling once the plant is done being used. However, these emissions are significantly lower than emissions from fossil fuel combustion.

The water demand of these plants can also be seen as an issue, as solar towers can require large volumes of water to operate. To minimize the amount of water being used, alternative cooling technologies are being investigated - such as the possibility of using air cooling.

A final potential impact of the use of these towers is the harmful effect these plants have on birds. Birds that fly in the way of the focused rays of Sun can be incinerated. Some reports of bird deaths at power plants such as these amount the deaths to about one bird every two minutes.

For Further Reading

• Photovoltaic system
• Solar power
• Solar thermal power plant
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