Clean technology series: harnessing the sun – a brief review of the solar power landscape

As we mentioned in our first of this series of articles, recognition of the need to replace fossil fuels with more sustainable energy sources is continuing to grow. To fully supplant their fossil fuel predecessors, new energy sources must have a low environmental footprint, high efficiency and economical production. Solar power is seen as one of the most promising sources in this regard, with solar power being the fastest growing renewable energy source in the world and accounting for over half of the renewable energy capacity installed in 2021.[i]

Part of this growth comes down to the relatively low cost of solar power.  There was a surge in patent application filings for solar power technology from 2008 onwards, with the number of published international patent applications peaking around 2012.[ii]  These early R&D efforts seem to have paid off, with the cost of solar power decreasing by 82% between 2010-2020[iii] as these inventions have been commercialised.

While the initial boom may be over, the number of patent application filings relating to solar power has stayed fairly steady with about 50,000 applications currently being filed worldwide each year (as shown in Figure 1).

Figure 1 the number of the solar energy technology patent applications (net addition) filed in all countries/areas, by year.  Source: https://www.irena.org/Data/View-data-by-topic/Innovation-and-Technology/Patents-Evolution

These new filings can be broadly separated into three main technology areas: photovoltaics, solar thermal energy and photovoltaic-thermal hybrid systems.  In this second article of the series, we take a look at these different technologies, considering some of the challenges and exploring some of the key areas of research and development.

Photovoltaics

Photovoltaic (PV) cells convert light directly into electricity using semiconducting materials that exhibit the photovoltaic effect. Silicon is by far the most common semiconducting material used in PV cells currently in operation, mostly due to the maturity of the technology and the relatively low cost. However, silicon based PV cells have a limited energy conversion efficiency, especially at higher temperatures, which has led researchers to pursue alternative semiconducting materials.

One such alternative is gallium arsenide. Gallium arsenide based PV cells are more efficient than silicon based PV cells as they absorb a broader spectrum of incident light. They also have a higher tolerance to radiation damage and high temperatures. Nevertheless, gallium arsenide based PV cells are significantly more expensive than silicon based cells due to higher material and manufacturing costs, limiting their use to high performance applications like in satellites and spacecraft where their resistance to radiation damage is particularly beneficial.[iv] Whilst this helps push the boundaries of space exploration, other approaches are needed to solve the energy supply problems here on Earth.

A relatively new type of PV which has seen a lot of development in recent years is based on a family of materials called perovskites. Perovskite materials are cheap to produce and simple to manufacture, which is a key benefit when looking to commercialise PV technology. Perovskite based PV cells historically struggled with low efficiency relative to silicon, but over time the efficiency of perovskite PV cells has increased to rival that of silicon based PV cells,[v] with many lab-based perovskite cells now exceeding the efficiency of silicon cells.

Perovskite PV cells also have benefits in terms of manufacturing: perovskite inks can be printed onto flexible substrates, providing a low cost, thin, lightweight and flexible PV cell.  Researchers at Oxford University are maximising this flexibility with new perovskite coatings “just over one micron thick … almost 150 times thinner than a silicon wafer”.[vi]  These coatings could be applied to a wide variety of surfaces, such as building walls and windows, or even the roofs of cars, allowing for the generation of solar power cheaply and efficiently, and without the need for solar farms or the large arrays of solar panels currently seen on roofs across the UK.

One drawback of perovskite based PV cells is poor stability, with heat, moisture and oxygen degrading the perovskite material.  Addressing this stability challenge has been another area of recent focus in the industry.  One approach, developed by researchers at Imperial College London and the University of Hong Kong, is the incorporation of a metallocene interface layer (optionally a ferrocene layer) into the PV structure.  The researchers have discovered that the use of such an interface layer improves the stability of the perovskite PV cell; moreover, the efficiency of perovskite PVs with a ferrocene interface layer can reach 25%, again rivalling the efficiency of traditional silicon devices.[vii]

Whilst research into perovskites is still ongoing, PVs containing perovskite materials are now at the commercialisation stage.  One innovation that has been particularly successful is the combination of perovskite PVs and conventional silicon PVs into “tandem solar panels”; these tandem cells incorporate a perovskite cell on top of a traditional silicon cell, the two different cells connected with an interconnect layer.[viii]  This tandem solar panel technology, developed by Oxford University spin out Oxford PV, “can produce up to 20% more energy than a standard silicon panel” and after 10 years of development is now being commercialised.[ix]

Given this long lead time between the research and development stage and the commercialisation stage, the steady flow of new patent applications for photovoltaic technology seen in Figure 1 is a promising sign for future products in this area.

Solar Thermal Energy

Solar thermal systems differ from photovoltaic solar cells in that they harness the sun’s energy to create heat, instead of generating electricity directly from light. This heat can be used to, for example, heat a home, fulfil heat requirements in industry or drive a heat engine to generate electricity (as is the case with concentrated solar power, or CSP). In CSP plants, large mirrors or lenses are used to concentrate sunlight from a large area into a receiver, where the concentrated sunlight heats a working fluid to a very high temperature; the high temperature working fluid is used to generate high pressure steam, which in turn drives a turbine.

Whilst PV technology has experienced huge growth over the past decade, the growth of CSP has been much slower, due in large part to the technical complexity of the technology and high initial establishment costs.[x] Nevertheless, CSP plants are becoming more widespread, particularly in countries with large, unpopulated areas of open space and long periods of sunlight, with China, the UAE, South Africa and Spain all having CSP plants in development in 2023.

One key advantage of a CSP plant is that it can incorporate energy storage.  Excess thermal energy from the receiver can be stored using e.g. molten salt, which has a high heat capacity and can retain the excess heat for many hours when stored in an insulated tank.  This enables CSP plants to continue supplying electricity whenever it is needed, day or night, in contrast to intermittent PV based solar power.  CSP plants are therefore a potential replacement for traditional power plants.

The efficiency of CSP plants is affected by factors such as: the design and shape of the solar concentrators, the solar irradiance, the choice of working fluid and the efficiency of the energy storage system.  One company that is looking to address these efficiency issues is Sunrise CSP, whose “Big Dish” technology[xii] and mirror panels can provide a solar-to-thermal efficiency of approximately 87%.[xiii]  This can reduce the amount of land required to capture the same amount of energy, making CSP plants more viable.

Hybrid Systems

Photovoltaic-thermal (PVT) panels combine PV cells with a solar thermal collector, which transfers the unused, waste, heat from the PV cells to a heat transfer fluid. The heat transfer fluid can be used for domestic water heating, but also for applications such as desalination and the drying of agricultural products.[xiv]  The ability to capture both light and heat from the sun simultaneously holds great promise, and the adoption of PVT technology within residential and industrial buildings is expected to increase as consumers look to decarbonise their energy supply and achieve energy independence.

Future Outlook

It is clear that more developments are required to address some of the problems with the different solar power technologies.  However, solar power is already a viable energy source and the commercialisation of the more established technology is already sufficient for large investments to be made in solar capacity: for example, the EU aims to increase solar energy capacity from 259.99 GW in 2023 (almost all from from PV sources) to 320 GW from PV sources by 2025, and to almost 600 GW from PV sources by 2030.[xv]

If you’re interested in learning more about patent protection for solar power inventions, whether that be protecting new materials or compositions, methods of constructing new solar panels or recycling obsolete ones, control systems or energy storage mechanisms, please get in touch with Joseph O’Leary, Alexandra Seymour-Pierce or your usual Venner Shipley adviser.

[i] https://www.solarpowereurope.org/insights/market-outlooks/global-market-outlook-for-solar-power-2022

[ii] https://www.wipo.int/wipo_magazine/en/2020/01/article_0008.html

[iii] https://energy.ec.europa.eu/topics/renewable-energy/solar-energy_en

[iv] https://www.sciencedirect.com/topics/earth-and-planetary-sciences/gallium-arsenide

[v] https://www.sciencedirect.com/science/article/pii/S2589299123000241

[vi] https://www.ox.ac.uk/news/2024-08-09-solar-energy-breakthrough-could-reduce-need-solar-farms

[vii] https://www.ipo.gov.uk/p-ipsum/Case/PublicationNumber/GB2618521

[viii] https://register.epo.org/application?number=EP18707955

[ix] https://www.oxfordpv.com/news/20-more-powerful-tandem-solar-panels-enter-commercial-use-first-time-us

[x] https://www.sciencedirect.com/science/article/abs/pii/S2213138821004446

[xii] https://register.epo.org/application?number=EP09756976

[xiii]https://sunrisecsp.com/technology/#the-big-dish

[xiv] https://www.sciencedirect.com/science/article/abs/pii/S0960148116310588

[xv] https://energy.ec.europa.eu/topics/renewable-energy/solar-energy_en