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A Photovoltaic Plant with thermal co-generation

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Towards the world’s first hybrid photovoltaic and thermal storage plant

If renewables are to become the world’s go-to energy solution, the challenge of storing an intermittent source will have to be met. With electrical battery storage proving too costly, SPIRE developed a hybrid solution, tapping the best of photovoltaic and solar thermal energy.


Conventional concentrated solar power (CSP) tower technologies which use mirrors to harness the sun’s energy, have struggled to vie with renewable energy alternatives, largely due to their costs. Yet as the demand for photovoltaic (PV) and wind energy grows, their intermittent nature means that meeting demand will rely on energy storage. CSP technologies could play an important role. The EU-supported SPIRE project substituted the CSP-tower plants’ mirrors with PV panels which were integrated with an intelligent filter. This filter spectrally splits solar radiation, letting the radiation (mainly visible light) used by the PV panel pass through, while reflecting 40 % of the energy (mainly blue light and infrared) as thermal energy to be captured. The technology known as BlueSolar emits no CO2, is suitable for off-grid solutions, does not need a fuel supply and is scalable, and its customised filter can be adapted to every situation, particularly where there are light spectrums and dedicated applications/operation modes.

The hybrid solution

BlueSolar substitutes the silver mirrors of CSP towers with PV modules which have an integrated optical light-selective filter that splits the solar spectrum, transmitting only wavelengths useful to the PV cell semiconductors and reflecting the remaining wavelengths to the tower’s central thermal receiver. These latter wavelengths generate heat that can be stored at a fraction of the cost of electrical batteries and converted to electricity with turbines or used to produce steam for industrial processes. “While PV panels are the cheapest and the easiest way to produce electricity directly from the sun, thermal storage is easier and cheaper than storing electrons. Our unique solution was to combine both technologies,” says Jose Julio Caparros. BlueSolar plants can be integrated with current PV and wind plants, storing their electricity using electrical heating – more competitive than electrical batteries. But the electricity and heat combination can also be used for a wide range of applications including: desalination, heat for industrial processes, in agriculture and for city heating/cooling. “We tested the technology in top European Technological Centres and were pleased with the results, consistent with the engineering designs and simulations, while improving the efficiency of standalone PV and CSP systems by more than 30 %,” says Caparros.

Boosting the viability of renewables

BlueSolar helps ensure increased market penetration of renewables, offering the associated benefits of: reduced global warming; improved public health; inexhaustible, reliable and resilient energy; cheaper prices; and newly created green jobs. There are additional operational benefits such as: no dumped energy due to overloaded TES/turbine capacity, better utilisation of diffuse radiation – increasing the solar resource, less land footprint per installed plant, no mirror degradation as the filters are made of inorganic oxides and quick start turbines for a fast response to power shortages due to clouds, etc. And with more competitive prices than PV and batteries, BlueSolar offers a bankable solution for the expected 25-30 years’ lifetime of the plant.

Towards commercialisation

The team is now designing the first pilot plant, alongside a small-scale filter factory. They are also working in parallel to commercialise the technology for both energy storage and industrial process heat. “We could become the first company to sell dispatchable electricity generated from solar in the open market without the need for special tariffs to be profitable,” says Caparros.


SPIRE, electrical battery, energy, renewables, solar thermal, photovoltaic, wavelengths, storage, global warming, turbines, power

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