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CSP (concentrated solar power)

A Short Guide to Concentrated Solar Power (CSP)

Concentrating solar power (CSP) plants, utilize mirrors or lenses to concentrate sunlight producing temperatures strong enough to trigger conventional steam turbines or engines that consecutively produces electricity. The most economical CSP plants are hundreds of megawatts (MW) in size, making them appealing as wholesale energy providers to utilities. Presently, more than 520 MW of CSP plants function in the United States and there are more than 1,950 MW of CSP projects with signed PPAs.

The Department of Energy (DOE) backs studies and development of concentrating solar power technologies as a distinctive course to attain initiative outlay targets with systems that can provide solar power on demand via the use of thermal storage.

How Does CSP Work?

CSP technology employs focused sunlight. CSP plants generate electric power by utilizing mirrors to center or focus the sun’s energy and transform it into high-temperature heat. Afterwards, the heat is channeled through a traditional generator. The plants include two parts, one that gathers solar energy and changes it to heat and the other that changes the heat energy into electricity. A short video showing how CSP works using a parabolic trough system is available from the Department of Energy Solar Energy Technologies website.

To put it briefly, CSP technologies use mirrors to reflect and focus sunlight onto receivers that gather solar energy converting it into heat. Thermal energy can then be utilized to generate electricity through a turbine or heat engine powering a generator.

In the United States, concentrating solar power plants have been working consistently for over 15 years. All CSP high-tech methods demand large areas for solar radiation collection when used to generate electricity at commercial levels.

Various CSP Systems

Though CSP systems make use of differing configurations to direct sunlight, they have comparable mechanisms such as thermal storage, power block, receivers, and collectors. DOE finances CSP research and development geared towards producing the fundamental technologies to acquire technical and financial targets. The program also finances systems probing all CSP technologies to evaluate cost, longevity, and performance. CSP technology draws on four optional high-tech approaches; trough systems, power-tower systems, dish/engine systems, and compact linear Fresnel reflector.

Trough Systems

Trough systems utilize large, U-shaped (parabolic) reflectors (concentrating mirrors) with oil-filled pipes going down the center. The mirrored reflectors are skewed toward the sun and focus sunlight onto pipes to heat the oil inside to as high as 750 Fahrenheit. Afterward, the hot oil is used to boil water, which in turn causes steam to operate traditional steam generators and turbines.

Power Tower Systems

This CPS system also known as “central receivers” employs various large, flat mirrors or heliostats to follow the sun and direct its rays onto a receiver. The receiver rests on top of a high-tower where intense sunlight heats a liquid, such as molten salt, to as high as 1050 Fahrenheit. The hot liquid can be utilized right away to create steam for generating electricity or kept for use later on.

Molten salt preserves heat effectively; therefore, it can be stored for days prior to being converted into electricity. This means electricity can be generated during times of peak demand on cloudy days or even a few hours after sunset.

Dish Engine Systems

Mirrored dishes used with Dish Engine Systems are roughly 10 times bigger than a backyard satellite dish, and focuses and concentrates sunlight onto a receiver. The receiver is mounted at the center of the dish. To capture the highest amount of solar energy, the dish assembly follows the sun across the sky. The receiver is merged into a high-efficiency exterior combustion engine.

The engine includes slender tubes consisting of hydrogen or helium gas that moves along the exterior of the engine’s four piston cylinders and opens into the cylinders. As intense sunlight falls onto the receiver, it heats the gas inside the tubes to an extreme temperature, which causes hot gas to enlarge inside the cylinders. The increasing gas drives the pistons. The pistons turn a crankshaft, which in turn powers an electric generator. The receiver, engine, and generator comprise one integrated assembly, attached at the focus of the mirrored dish.

Compact Linear Fresnel Reflector

To decrease a quantity of the upfront capital expenditures of plant construction, Compact Linear Fresnel Reflector (CLFR) developers depend on principles of curved-mirror trough systems, but utilize extended parallel rows of economical flat mirrors. The modular reflectors center the sun’s energy onto raised receivers that include a system of tubes where water flows. The intense sunlight boils the water producing high-pressure steam for direct use in power generation and industrial steam applications.

Key Requirements For Concentrating Solar Power Plants

There are nine CSP plants equaling more than 350 MW in day-to-day operations near Kramer Junction, California for more than 20 years. During the last four years, new plants have been introduced in California, Nevada, and Arizona. The plants’ locality mirror the crucial conditions needed for this type of project. CSP plants need:

Financing

The main obstacle to utility-scale solar power is project funds. The economic crisis of 2008 critically restricted the private sector capital that is normally used to finance renewable energy ventures. Today, commercial banks are simply not interested enough to tackle long-term low interest debt to finance construction of every project that comes before them.

Contiguous Parcels of Land (with unlimited cloud cover)

A CSP plant functions best and most effectively when built in dimensions of 100 MW and more. Though land requirements will differ by technology, a typical CSP plant needs 5 to 19 acres of land per MW of capacity. The bigger acreage houses thermal energy storage.

Access to Water Resources

The same as other thermal power plants such as nuclear, coal, and natural gas, some systems need access to water for cooling. All require minute quantities of water to wash collection and mirror surfaces. Concentrating solar power plants can use wet, dry, and hybrid cooling techniques to increase efficiency in electricity production and water conservation.

Available and Proximate Transmission Access

CSP plants should be placed on land fitting for power generation with sufficient access to a growing stressed and outmoded transmission grid. Availability to high-voltage transmission lines is the answer for the creation of utility-scale solar power ventures to shift electricity from the solar plant to end users. Most of the existing transmission infrastructure in the Southwest is nearly overflowing and new transmission is needed immediately.