Please take a look at page 8 of a document produced by an organization called Good Energies.
The matrix shown here shows 5 solar technologies Good Energies classify as ‘concentrating technologies.’
As with many of these technologies listed above, there are a number of companies developing variations on each concentrating theme. The design of the ‘Dish Stirling’ is a parabolic dish which reflects and focuses the sun on a small area. Some of the companies working on this technology are as follows:
This company utilizes an engine technology invented in 1884 and which has been developed by Sandia National laboratories who have had operational engines since 1984.
The original dish was about 38 foot in diameter and consisted of 82 mirrors arranged in a parabolic structure. The parabolic dish is mounted on a dual axis tracking system which always keeps focus directly at the sun from the moment it rises until it sets. The engine employed by Stirling Energy Systems utilizes the concentrated heat from the sun to heat an internal gas (often helium), which expands and then contracts as it cools in turn driving a internal mechanism. This movement is able to generate electricity via a linear alternator. Wikipedia has an entry on the Stirling engine.
http://en.wikipedia.org/wiki/Stirling_cycle_engine
There is also a fairly good graphic on Stirling Energy’s technology page.
The Engine itself is capable of producing 25kW of power which is enough to power about 10 homes.
It would be able to produce this in AC or DC voltages as can Infinia’s engine which I will discuss later on.
Stirling Energy Systems have some significant contracts. Solar One - SES have signed a Power Purchasing agreement contract to build 500 Megawatts (20,000 dishes) of power up to 850MW (34,000 dishes)with Southern California Edison
Solar Two - a further 600 Megawatts (24,000 dishes) up to 900MW (36,000 dishes) for San Diego Gas and Electric. Both signed back in November of 2005.
To put this into perspective 1,100MW (500+600) is comparable in output to a coal or nuclear power station capable of supplying power for up to 540,000 households.
There is a video posted on youtube which shows Stirling Energy Systems dish in action.
The company is developing the manufacturing of this technology by teaming up with with Kockums Submarine Systems, NASA, Boeing and the Department of Energy.
Infinia – Kennewick, Washington
• 3kW, developing 30kW unit with DOE support
• Worked with SES, NREL, Sandia Nat Labs, NASA, IBM, Lockheed Martin, DOD
• Combined Heat/Power application with fuel cell/Rankine cycle turbo-alternator
This company is building smaller scale versions of the Stirling Energy System parabolic dish/engine. Infinia has a long parallel history with SES above having worked with them to develop their engine, as well as with DOE, IBM, NASA, NREL, Lockheed Martin and the US army to develop this and cryocooling technology. Infinia currently manufacture a smaller engine which produces 3kW of power in AC or DC voltage or up to 6kW in a combined thermal process.
They have also been working with Open Energy Corporation to develop the optical concentration component of the engine.
The engine itself is also being developed along with ENATAC to not only operate as a solar power generation unit, but also in buildings in a CHP arrangement (Combined heat and power).
Infinia is backed by venture capital from Idealab and Khosla investments and Paul Allen (Microsoft) as well as a number of other Venture Capital firms and has plans to hire up to 150 employees next year dependent on demand.
Heliofocus – Israel
• 100kW gas turbine
• Can run on clean air or on a combustible gas (24 hour operation)
• 1000ºC temperatures achievable – other uses include solar tower
• Patent out to use in extracting hydrogen from water
The technology this company is developing differs slightly in a couple of ways from the above two technologies. Instead of using sunlight to heat a gas in an enclosed device it utilizes the sun to heat clean air to drive a gas turbine engine. Concentrating sunlight via the use of non-imaging optics in a central solar receiver to heat the air to 1000ºC in turn driving a similar linear design to the stirling engine to create 100kW of electricity.
The size of the dish is 24 meters in diameter which equates to about 78 feet. This is just over double the dish size used by SES for triple the power output. The technology has been under development for the past 20 years by the Weizmann institute of science and currently Heliofocus has contracted with Capstone Energy to develop and supply the turbine. (page 21).
<strong>Base load Generation</strong>
The benefit of this particular technology is it can also use natural gas to keep the turbine operational. In other words it is able to operate 24 hours a day or as a base load generator. Jobs with Capstone Turbines – Chatsworth, California
Gas heating apparatus - Hydrogen
Heliofocus also have patented a means to extract hydrogen from water in a process that appears to only use sunlight and Argon. This one is not on their website, but does appear to be a technology with a lot of future potential.
Thermal operation
The company also claim high optical and thermal efficiencies utilizing the concentration of sunlight onto a central receiver tower. This particular technology belongs more in the solar tower concept which is discussed later on but what I will mention is the process flow diagram in the patent shows temperatures of 1200ºC and 100 Bar. These operational temperatures and pressures are what you would expect from a smaller fossil fuel power plant.
There are a couple of other Stirling Engine applications which rate a mention here, although they do actually rely on the use of a fuel, not sunlight. The first goes back to Infinia with its combined heat and power unit which runs a gas through a ceramic fuel cell (producing electricity) and using the heat generated (up to 800ºC) and also Heliofocus hybrid capability to run on natural gas..
Another application is in a biomass operated Stirling Engine
It is worth noting here the Stirling engine relies on the expansion and contraction of a gas (air is made of gases) to drive the linear alternator. The parabolic trough design, however is similar in operation to a how a coal fired power station generates electricity. Most coal fired stations produce heat, similar to a big kettle, which heats water to steam with the steam driving a turbine.
To understand this Rankine cycle a little better (and this is very simplified) when water is heated above boiling point, or 212ºF, 100 ºC it expands 1,700 times it volume at atmospheric pressure.
So first the water is heated above this level, all of it, and because it is contained within a confined space what happens is the steam created starts to gain pressure. This high pressure steam is then contained in pipes and fed into a turbine which has lots of blades, causing them to turn. At one or both ends of the turbine shaft is mounted what is called an alternator which generates the electricity we use.
Here is a graphic of a multi-stage turbine
Parabolic Trough
Ausra - Palo Alto, California
This company has just opened a factory in Nevada to produce the hardware for their concentrated solar technology. The Ausra design is based on multiple flat glass mirrors on a single axis tracking system, which concentrate the sunlight onto a pipe which heats water to steam. The steam then drives a turbine in the same way a coal fired or nuclear power station uses steam. The company has recently raised $60.6 Million dollars from KERN, KPCB, Starfish enterprises and Khosla ventures.
The factory will supply the concentration equipment required for the 177MW plant Ausra have been contracted to build for Pacfic Gas and Electric in San Luis Obispo County, California and the ongoing commitment to build up to 2,000MW of solar thermal plants for PG&E and Florida Light and Power. Jobs with Ausra
How Ausra’s technology works:
Compact Linear Fresnel Reflector, or CLFR, is Ausra’s solar power technology.
Mouse over the numbered dots at the end of the animation to see an explanation of how the technology works.
Skyfuel – Arvada, Colorado and Albuquerque, New Mexico (Parabolic trough Linear Fresnel tower)
• Heats Molten salt to 800ºC (potential 24 hour operation)
• 30% lighter than normal parabolic trough designs
• No on-site welded parts
• One whole 375 foot assembly fits on one flat bed truck.
Instead of using glass mirrors Skyfuel use a parabolic trough (skytrough) made of reflectively coated metal (Reflectech). This results in significant material and weight reductions (important for the installation and supporting structure design cost reductions). Sky fuel also use what is called a linear Fresnel design. This is where multiple parabolic troughs focus not on a single pipe but on a linear aligned vessel tower. The tower is designed to heat salt to 800ºC heating molten salt which acts as a storage medium and via a heat exchanger can be used to heat water to steam and in turn drive a turbine. By storing the molten salt in this way, Skyfuel have an ability to provide base load power as the molten salt is available for use when the need arises.
Skyfuel has been awarded 2 research grants by the DOE, and have capital investors Leaf Clean Energy, Shaw Capital add $17M to the development of this technology.
They have recently unveiled their design at an event in Colorado.
Solel have a number of projects underway including 3 x 50MW plants being built with Sacyr in Spain, they have a 553MW contract with PG&E, have been building a $140M manufacturing plant in Spain as well as well as a $9M reflector manufacturing facility in Finland. Solel have recently secured a $105M investment from Ecofin.
Acciona – Parabolic Trough
This company also uses parabolic concentration to focus the sun onto piping heating a mineral oil transfer fluid to 735ºF which in turn heats water through a heat exchanger turning it into steam.
Nevada Solar one, a 64MW nominal 75MW peak load power station, as of 2007 was generating electricity which is being sold to Nevada power company and Sierra Pacific Power to supply the city of Boulder City, Nevada.
FPL Energy – Florida
Florida Power and Light have been involved with the original Luz plants as mentioned above. Apart from Kramer Junction, they currently have ownership of the remaining assets of these original installations totaling 150MW. The parabolic trough design has been proven to be reliable and long lasting and FPL have contracted to build 250MW in addition to what they currently own and operate. There are expansion plans to build 850MW generation by 2015.
Please visit FPL website for more information and source of above process diagram
Solar Tower
Abengoa - Arizona, Texas, Colorado, California
Abengoa, employing over 17,000 people and with turnover at 3.2 Billion Euro last year, is one of the biggest solar and renewable companies in the world. As a result of this Abengoa has developed multiple solar based technologies. Aside from multiple parabolic trough plants, Abengoa has also built a number of heliostat towers. Having built a Solucar Heliostat tower in Sevilla Spain, Abengoa are now building a larger plant in Seville, Spain.
The first of these towers is capable of supplying 55MW of saturated steam at 495ºF (257ºC) to a steam turbine to generate enough power to supply around 6,000 households. Abengoa has multiple sites under development in the US including a recent 280MW trough plant project in Arizona, as well as a number of parabolic heating installations in Texas, Colorado and California.
Abengoa have a very strong research and development program investing in multiple concentrating technologies including Solar Towers, parabolic troughs and concentrating photovoltaics.
Brightsource - Oakland California
Based on a Heliostat tower design, Brightsource which is the same team of experts who developed the original Luz parabolic trough system (see Solel, FPL above), is building a 400MW plant called Ivanpah, close to Primm near the California/Nevada border. Brightsource claim their technology is capable of supplying all of the electricity for homes in a state as big as California if only 2% of the Mojave desert contained their installations. They already have some very big power station projects inked including 500MW up to 900MW with PG&E.
The application to commence construction on this plant was lodged in
September 2007.
Not surprising when you consider some very big initial investors are backing Brightsource including Morgan Stanley, JP Morgan, Chevron Technology Ventures, VantagePoint partners and Draper Fisher Jurveston. Second round investment of $115M from additional investors Google and BP alternative investment advisers.
Solar Reserve - Santa Monica
Molten Salt Smaller towers 25MW to 500MW
Backed by investors such as Good Energies, US Renewables Group, Citi, Credit Suisse and Sustainable Development Investments, this company has recently raised an additional $140M in working capital. The technology they utilize is a Heliostat tower design which heats molten salt, allowing the generation to continue even after the sun sets because of stored energy.
Hamilton sundstrand are developing the molten salt pumping technology.
There is a very good video on Solar Reserves website which explains the technology and is worth watching. Yet another technology which is relying on innovation to change the way electricity is generated.
Esolar – Pasadena
Esolar’s technology takes uses a heliostat tower design where flat reflective mirrors concentrate solar energy on a central receiver, heating water to steam. By simplifying the design to flat mirrors, and modularizing the installation in 46MW blocks, as well as reducing the height of each tower, this technology has various manufacturing and construction cost benefits which can be realized. eSolar has managed to secure enough land to build 1GW of these installations in SW California and has raised an initial <a href="">$10M from Google</a>.
as well as a follow on investment from Google, Idealab and Oak investments of $130M
The land base to build 46MW of this type of solar thermal power is currently pegged at 160 acres. This consists of 16 heliostat towers and a single air cooled condenser 46MW power block. Covering 1% of the Sahara desert with eSolar power plants would provide enough electricity to power the entire world.
