The Best of Solar Technology: Thermal or PV?

The Best of Solar Technology: Thermal or PV?

Solar energy shining at the earth surface represents a thousands of times of the current world’s electricity. Solar power has a bright future but the technology that is going to rule is still a question. Is it going to be thermal solar power or photovoltaic solar technology?

Although, solar power has an Olympian capacity it is merely supplying a percent of world’s electricity consumption. This is so because the technology is currently relatively inefficient, expensive and requires a lot of subsidies.

It is important that solar technology expands so that research and development can enhance current systems. In other words, solar power plants will be able to generate more KWh at a lower cost.

Eicke Weber who is the current director of the Fraunhofer Institute for Solar Energy Systems, says that solar power will be generated at a cost of 5 to 10 cents per KWh by 2030. This will make it as effective as fossil fuels and therefore, financial support will no longer be required.

This vision is perceptible but how to get there is still not clear.

Solar Photovoltaics

According to Weber, gradual enhancement to silicon-based-solar photovoltaic (PV) technology will become the most common use of solar technology. Now, 85 to 90 percent of the world’s solar market is represented by PV technology.

He also said “The big driver will remain crystalline silicon getting ever more efficient, with thinner wafers and cheaper silicon materials. It is a kind of Moore’s Law for solar PV,”

One potential way to enhance actual systems is to integrate laser methods in the production of solar PV. This will help to refine the efficiency, as thinner wafers can be produced, meaning less material and lower costs.

Fraunhofer institute did in 2009 create a new world record in the efficiency of converting sunlight into electricity. Concentrated photovoltaic reached an efficiency rate of 41.1 percent. Most commercial solar PV cells have only an efficiency ranging from 10 to 20 percent.

The prime weakness of conventional PV cells is that they are only able to absorb a limited bandwidth of sunlight. However, the concentrated PV increases the bandwidth potential as it uses “triple junction” solar cells. These cells are made from three particular materials being gallium indium arsenide, gallium indium phosphide and germanium. These materials are able to absorb the various colours of sunlight. Additionally, lenses are used to further amplify and intensify the energy, making the beam concentrated up to 500 times its original state.

Weber claims that various solar markets are behaving differently to the development of new technologies. In American the focus is on inventing the next generation photovoltaics while the European manufacturers are emphasising on mass production of silicon cells (high-volume and low cost).

Revolutionary technology is in the corner. In the first quarter of 2010, some members of the California Institute of Technology laboratory scrutinized the potential gain of enhancing silicon wire design. The team reported that an improvement of 85 percent efficiency was experienced on plain sunlight. There was also an increase in 95 percent on the efficiency of some wavelengths in collecting solar energy.

At “University of Texas scientists Xiaoyang Zhu” is moving from micro to nano-scale technology. It was in June 2010 proved that the use of ‘quantum dots’ or so called semiconductor nanocrystals could capture much more energy than typical solar cells. This technology could theoretically increase the efficiency by 60 percent.

Concentrated Solar Power (CSP)

It cannot be refuted the efficiency of concentrated solar power (CSP) is still far above photovoltaics. Another advantage with CSP systems is that they do usually have a natural gas turbine as back-up power whenever the weather is inappropriate for CSP.

The shortcoming related to this type of technology is the large demand for land and water footprint to install these mirrors. Moreover, these Concentrated Solar Power plants need to be erected in regions where there is intense sunshine. These areas are most commonly very far from large population centers, making transmission another issue..

The CSP and photovoltaic industry are both in an interesting technology race. We are unsure which one will be more prosperous in the future.

Currently, the best design is the parabolic mirrors that direct its concentrated sunlight to steam a synthetic fluid, heating water to stimulate turbines. Unfortunately, these transfer fluids are expensive and have a limited heat capacity of 380 degrees Celsius. Therefore, its energy and efficiency potential is restrained.

The International Energy Agency’s Concentrated Solar Power Roadmap says that the major challenge ahead is to be able to develop plants where the temperature can reach 500 degrees Celsius. The Agency recommends the replacement of the transfer fluids by water, thus inducing direct steam generation, which might both be cheaper and more effective.

There is also another way to reach superheated steam temperatures. This would be by using solar power towers surrounded by thousands of mirrors having sunlight concentrated at the tip of the tower. This would allow the heat to steam liquids in a central tank to an unanticipated superheat.

In Ivanpah CSP plant in California, researchers are already trying to bypass 530 degrees Celsius. This would meet new energy efficiency levels.

There is an undeniable benefit of CSP over typical solar PV cells. CSP plants can store solar energy even at night. An example is “Andasol solar power plant in Spain” where heat is stored in molten salt. The salts cool down during the evening, and this emits a heat enabling the generation of steam for another 7.5 hours. This is done despite that there is no sunlight.

Solar Technology Needs New Storage systems

According to Weber, if a similar storage system used for thermal would be available for solar PV then the market would expand rapidly.

A storage system is currently being examined for PV solar power during the day, where surpluses are used to drive a pump to compress air beneath the ground. The air would then be released during the night to spin a turbine.

Daniel Nocera a research at MIT has discovered a complex technique that could be used for small solar PV installations. This system uses solar-powered electrolyzers to split atoms of water into oxygen and hydrogen, and thereafter re-combining the gases in a fuel cell, in order to produce current. This is an expensive process but could within a few years become effective.

According to IEA, using electrolyzers at an industrial scale as well as for CSP could probably help to introduce hydrogen fuel to the world transport system. This would thus significantly help to decrease carbon emission.

It is necessary that solar power contributes significantly to our energy mix. Otherwise, our future generation will have to behold various climatic disasters. Evidently, the energy provided by the sun is limitless so it is simply to capture and use it. There is no reason for not exploiting the solar power for world energy requirements.

Source: Allianze

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RPN's contributed to this report.

Professional freelancer in Green Technology and Scientific Development. Educational background in the field of Human Resources Management.

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  1. Fuel Cell Efficiency Advancing To Support Personalized Energy Systems Says:

    [...] creation of a solar energy system combined with an electrolyzer would provide clean energy 7/24. So solar energy could indirectly be used to generate electricity [...]

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