How Concentrating Solar Power (CSP) Works

There are predominantly two types of solar power generation methods used to create electricity on a commercial scale. Photovoltaic panels, which are the large collections of the systems that you see in small scale on house roofs. Using the heat of the sun as thermal solar power are concentrating solar power (CSP) plants.

We will take a look at the way in which concentrating solar power plants create electricity. CSP plants are capable of producing electricity at a higher maximum capacity than a photovoltaic facility of the same size. They will play an increasingly important role in the move away from fossil-fuel sourced energy to that of renewable energy.

Commercially, four types of concentrating solar power are in use: 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 further solar thermal power in progress to try to meet future demands.

Parabolic troughs use mirrors to direct sunlight onto a fluid-filled receiver positioned in directly in front of each trough. The heat generated from this process heats the fluid to high levels so that super-charged steam is generated. 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 exposure is maintained thanks to the pivoting nature of the parabolic troughs which track the sun’s movement across the sky. Thermal storage is also used to allow electricity generation to continue 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.

Power plants known as Andasol 1, Andasol 2 and Andasol 3 in Spain all use the parabolic trough design, forming a combined 150MW solar power plant. The surface area of the mirrors used to form the energy collection field of Andasol 3 alone is around 500,000m2.

Fresnel relectors are similar to parabolic troughs except they are flat mirrors that focus light onto one receiver. Costs are reduced using this method because the rows are positioned more closely together, there are fewer moving parts and less receivers are required. The receiver is stationary and it is shared by several 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. From there the energy is converted into mechanical power and electricity is generated similar to the way a mechanical engine runs. 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 that will be used in fields of thousands to form a power facility capable of generating over 500MW of electricity.

Central receiver systems are also known as power towers. Looking as though they’re honoring a higher deity, thousands of mirrors called heliostats cluster around a receiver that sits on top of a tall tower. The heat that is collected by the receiver then heats molten salt as it flows through which is then used to make steam that operates 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.

An example of a central receiver system in development is the Solar Tres power plant being built in Spain. 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.

As technological advancements continue to be made, the critical factor of the cost to produce each watt is gradually being addressed. 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.

Solar energy continues to grow and with continued support it will eventually become one of the main sources of electricity around the world. Concentrating solar power has proven to be a renewable energy source with still more untapped potential