There are two main types of solar power generation methods used to generate electricity on a commercial scale. Photovoltaic panels, which are the large collections of the systems that you see in small scale on house roofs. Concentrating solar power (CSP) uses thermal solar power, the heat of the sun, to produce environmentally friendly energy.

It’s the way in which concentrating solar power plants produce electricity that we will concentrate on here. CSP plants are capable of producing electricity at a higher maximum capacity than a photovoltaic facility of the same size. Technological advancements are making affordable solar energy, particularly from CSP plants, ever closer to reality.

There are four main types of concentrating solar power systems: parabolic troughs, fresnel reflectors, dish / engine systems and central receiver systems. The technology involved with each is proven and either has been or still is in operation around the world with more concentrating solar power plants in progress to increase global capacity.

Trough systems work by making use of mirrored troughs that are used to focus the sun’s energy onto a receiver tube that is filled with fluid. The fluids are heated to very high temperatures so that super-charged steam is produced. This steam is then directed into a conventional steam generator to produce electricity.

A trough-based CSP plant typically consists of rows of mirrored troughs placed parallel to each other along a north-south axis in what is known as a collector field. Optimum heat is focused on the receiver tubes thanks to the pivoting nature of the parabolic troughs which track the sun's movement across the sky. Thermal storage continues to generate electricity either when the sun is not shining or after it has set. Technological advancements are continuing to prolong this production period in a bid to move to continuous solar electricity production.

One of the largest developments to use the parabolic trough design is the Andasol project in Spain. The surface area of the mirrors used to form the energy collection field of Andasol 3 alone is around 500,000m2.

Fresnel reflectors provide a more concentrated focus of solar energy onto centrally placed receivers. This is a simpler system to the parabolic trough system with fewer moving parts and the rows can be positioned closer together. The receiver is stationary and it is shared by multiple mirrors.

An example of a recently commissioned CSP plant using reflector technology is the Kimberlina CSP plant in California developed by Ausra. This power plant is relatively small at only 5MW capacity, but it paves the way for future large-scale developments.

Dish / engine systems are stand-alone units that contain dish-shaped parabolic mirrors that concentrate the sun’s energy onto a receiver mounted above the dish. The receiver takes the energy and converts it into heat which is then converted into mechanical power, similar to a mechanical engine. Each dish / engine unit has a capacity of around 25kW of solar power and it tracks the sun to ensure optimum power.

An example of the dish / engine technology is the Stirling Energy Systems dish called the Suncatcher. It will be used in fields of thousands to form a power facility capable of generating over 500MW of electricity.

Central receiver systems, known colloquially as power towers, is another way to produce concentrated solar power. Looking as though they're honoring a higher deity, thousands of mirrors called heliostats cluster around a receiver that sits at the top of a tall tower. As the energy is directed into the receiver it is used to super-heat nitrate salt mixtures which goes on to produce steam that runs a conventional steam generator. The molten salt can be stored for great lengths of time which means that this type of solar energy generates electricity continuously around the clock.

Solar One, Solar Two and the latest power tower, Solar Tres are all examples of central receiver systems. The Solar Tres power plant will be a 15MW facility and it follows on from the successful demonstration power plant known as Solar Two which was located in the Mojave Desert.

Opponents of solar energy cite cost as a limiting factor, but this is being overcome thanks to advancements in technology. Already, concentrating solar power plants hold a huge advantage over the traditional fossil fuelled counterparts in the lower impact to the environment. In fact, one of the only impacts that concentrating solar power plants have on the environment is land use.

There continues to be solid progress made in ways in which solar energy is used to replace traditional energy sources. Concentrating solar power has proven to be a renewable energy source with still more untapped potential