Solar Thermal generated electricity – Future dominating technology?
Solar Thermal Technologies
What dominating technology will play the largest part in the solution of providing clean energy in the future?
Well the answer is that it stands between a handful of technologies where large scale or utility scale solar thermal generated electricity might be the winner.
A more detailed update of the companies active in the utility scale solar power area is found here
There are many estimations made that say that solar power generated electricity will see a tight competition between photovoltaics and solar thermal where the arguments for photovoltaics usually are:
- Faster getting down in cost due to faster volume ramp including China and improved production techniques
- Concentrated Photovoltaics is moving fast to lower the amount of neccesary silicon and thereby cost.
- All PV technologies are pushing performance, Silicon PV, Thin Film CIGS, CdTe, CIS and AmSi are quickly improving their performance.
- More modular and the infrastructure supports using photovoltaics from the best sub contractor.
- Easier to install and lower maintenance cost
The arguments for solar thermal is usually:
- Higher quality of the produced electricity (Less abrupt spikes from clouds blocking the sun)
- Some of the technologies can store thermal energy to be used when the sun is blocked. Lots of research here to lower cost of the storage solution.
- Ability to capture a larger part of the solar light spectrum like infra red, enables higher efficiency.
- The high temperatures that are used to produce steam for the Concentrated solar power turbines can be achieved with a secondary plant based on natural gas or other biofuels and can be used during night and in the winter as backup.
I guess we will see in 50 years but the large scale solar thermal market is expected to grow roughly by a factor of 40 between 2009 and 2014 and that is not bad.
Here are 5 different Solar Thermal Electricity generating technologies:
1. Solar Tower with updraft wind Turbine
Solar Thermal – Updraft Wind Turbine
Solar Tower functionality description
Principle of operation:
Heated air is generated below the glass shield covering the ground. The heated Air travels, by convection, up through the large chimney where wind turbines generates the electricity.
+ Low cost to cover the ground with glass.
+ The moving media (ie the upward air) is moving through a limited area where turbines can work in a very efficient way.
- Requires a very tall chimney
- How do you maintain a turbine within this tower??
Probably very robust way of large scale solar thermal generated electricity where these types of towers are allowed.
The Australia project:
Companies active in the solar updraft tower area is found here
2. CSP Solar Power Tower
BrightSource Solar Thermal Power Tower
Principle of operation:
This solution is all about maximizing the efficiency from thermal energy to electrical energy (Rankine cycle efficiency).
- Two dimensional moving mirrors, or heliostats, focuses the sunlight roughly 500 times toward a receiver, containing a working fluid, recently molten salt, located close to the top of the turbine tower.
- Water is pressurized by a pump from 0,02 Bar to 100 Bar to prepared for the boiler
- The working fluid driven boiler or evaporator generates dry 550 C steam of the high pressure water to drive the steam turbine which generates the electricity.
- The lower pressure and lower temperature steam is condensed back to water in a condenser.
- Thermal energy is stored in a molten salt(a mix of sodium and potassium nitrate) container to be used when the sun is not shining. As a reference a 9 m high and 25 m in diameter molten salt container drives a 100 MW turbine for 4 hours.
+ The medium heated during the day can be stored in vessels to keep the turbines running at night to perhaps if the storage cost is reduced, produce electricity 24/7.
+ They claimed earlier to achieve the highest Efficiency.
+ High boiling temperature and small relative receiver area together with large scale turbines enables good price/performance for large scale plants.
+ Lots of research ongoing of lower cost/ high quality mirrors that will also scale with volume.
+ Requires less water than Parabolic trough
- The mirror cost itself + 2d axis movement and syncronisation of mirrors need to get down in cost.
- There are some safety concerns with reflections from the tower and there are also some environmental concerns regarding bird life and highly concentrated light.
- Will the storage solutions ever get down in cost so that electricity can be produced 24/7?
This is already becoming a large scale technology and it has had its breakthrough. Success gives volume and then the expensive 2 axis mirrors and the storage solution could be cheap enough.
Companies active in the CSP Solar power tower area is found here
3. Parabolic trough CSP
Parabolic trough solar thermal power plant
Andasol 1: Parabolic trough power plant
Parabolic Trough Functionality Description
Principle of operation:
A parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or heat pipe, placed at the focal point, containing coolant which transfers heat from the collectors to the boilers in the power station. The world’s largest parabolic trough facilities, located in the Mojave Desert, consist of nine plants producing 354 megawatts of power at peak output.
+ Parabolic trough power plants are the only technology for utilizing solar energy in large power plants that has been commercially proven over a number of years
+ Simple & robust technology
+ Probably still the lowest price/performance of the large scale thermal solutions, especially when looking at maintenance cost and life time.
+ Can easily be combined with other sources electricity production, like natural gas, during cloudy days to produce electricity 24/7
Likely to be one of the big electricity generating technologies for the future.
Companies using the parabolic trough solution is found here
4. Concentrating Linear Fresnell reflector (CLFR)
One dimensional moving flat deflector for solar thermal electricity
Principle of Operation:
The Compact Linear Fresnel Reflector (CLFR) solar collector and steam generation system, uses linear flat reflector mirrors to focus the sun’s heat onto elevated receivers, which consist of a system of tubes containing the heated working fluid. Some solutions use water directly as the working fluid to reduce complexity and a heat exchange step.
The working fluid boils pressurized water in the boiler or evaporator, generating high-pressure steam for producing electricity by the turbine.
CLFR Optical principle
- Claims to be one of few to use water as a working fluid and that it is animal safe .
- Mirrors are said to be cheaper than parabolic trough due to the flat design.
- Easier to maintain and less efficiency reduced shading compared to Parabolic trough due to its flat construction.
- A more complex and potentially more expensive solution compared to parabolic trough
- Does the same thing as parabolic trough and parabolic trough was there first and already have volumes.
As large as the conventional parabolic trough technology.
Companies using the CLFR solution is found here
5. Two dimensional parabolic dish solar thermal collector or Stirling dish
2D parabolic dish solar thermal plant
Parabolic dish system
Principle of operation:
Parabolic dish concentrators are similar to trough concentrators, but focus the sunlight on a single point. Dishes can produce much higher temperatures and the small focal heating area reduces the thermal radiation loss, and so, in principle, should produce electricity more efficiently. This technology have not yet had its big breakthrough due to its higher complexity but recent use of the Stirling engine have increased the efficiency and perhaps lowered the price/performance.
More info of the Stirling dish system technology can be found here
- A modular solution providing very high temperatures in a small low thermal radiation area enables a high rankine cycle efficiency and solar irradiation collector efficiency.
- Requires no water which is a big advantage in the desert
- Combine the dish with a sterling engine in the focal point and you get the highest efficiency so far with a record of 32%
- Complexity and cost (At least initially)
- Same limitations as photovoltaics with uneven production and no energy storage to produce electricity during night
- Why did Tessera solar loose lately?
Companies using the Parabolic dish or Sterling solution is found here
Companies within large scale Solar Power Generation
- Concentrix Solar
Parabolic dish concentrating photovoltaics
CSP Solar Power Tower
CSP Fresnel Reflectors
CSP Parabolic Trough
CSP Sterling dish
List of current and ongoing Solar Power Plants in the world can be found