Solar Power: Lighting up the Future
Solar energy is a free, clean and abundant source of renewable energy. However, there are a number of issues that must be overcome in order to ensure that solar power becomes a key technology in driving the low-carbon transition. Energy markets have long been dominated by fossil fuels, and today solar power cannot compete on cost. Production costs remain high and technical advancements must be made in order to drive down costs and achieve high solar energy conversion efficiencies in devices. Despite the relatively low overall contribution of solar technologies to the energy mix today, solar energy capacity has grown by a staggering 30% per annum in the last decade as a result of government policies and increased investment in these technologies.
A single statement may sum up the potential for solar energy: more solar energy reaches the surface of the earth in one hour, than that which is anthropogenically consumed in one year. If this is true, why is it that the solar contribution to the total energy consumed globally is currently a fraction of a percent1? With such a huge capacity, why does solar power not contribute more significantly to global energy production? What are the barriers to solar power becoming a key energy source of the future?
PV devices provide a free source
of electricity for up to 25 years
and require little maintenance
There are a number of alternative ways of generating energy from renewable sources, such as wind and wave power, hydroelectricity and biomass. The direct conversion of solar energy to electricity is normally performed employing photovoltaic devices (PV). Solar PV technology has the advantage that it can be installed in most environments and can be designed to blend into the surrounding architecture. Photovoltaics can be used as singular modules to produce small amounts of electricity to power specific devices or be connected to the national grid. They can also be used in to create Solar Power Plants, consisting of large arrays of modules producing electricity to power hundreds of homes. Despite high initial setup costs, due to expensive materials and manufacturing processes (land costs can also be an important factor), PV devices provide a free source of electricity for up to 25 years and require little maintenance. Wind turbines share similar advantages but are often large and unsightly, whereas the application of wave power and hydroelectricity has the disadvantage of being site specific.
More energy is produced in regions of high insolation (a measure of solar radiation energy) yet PV devices are also effective in countries that receive less sunlight. This is highlighted by the fact that currently Germany has the largest PV capacity in the world. The main disadvantage of solar PV is that electricity is not produced during the night and solar-electrical conversion efficiencies are significantly diminished in cloudy conditions, thus a complementary power source is generally required.
Solar-electrical conversion efficiency is defined as the ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device. A typical crystalline silicon device has solar-electricity conversion efficiency of approx. 15%. This may seem low but compared to the sunlight-biomass conversion efficiency in photosynthesising plants it is significantly more efficient. Although the efficiencies of the conversion of sunlight to biomass in plants can vary dramatically between species, typically they do not exceed 5%. In just a few decades humans have surpassed this, with record efficiencies of some PV devices exceeding 40%2. Australia has high levels of insolation and, if much of the landmass were covered in devices of 15% conversion efficiency, over 2000 times the country’s energy demands could be produced. It is thus evident that efficiency is not the main factor preventing solar power from becoming a viable alternative energy source.
The most significant issue encountered
when considering solar power is cost.
However, when compared to the
1990’s, solar photovoltaic systems
are now over 60% cheaper
Over 90% of solar cells currently produced worldwide are made from silicon crystals3. These provide the most economical and reliable source of solar PV power and dominate the PV market. Nevertheless, solar power is expensive when compared to energy derived from other sources. In 2006, electricity derived from solar energy cost $0.35 [kWhr]-1, whereas that from fossil fuels had significantly lower costs of $0.02-0.05 [kWhr]-1 4.
So, the most significant issue encountered when considering solar power is cost. However, when compared to the 1990’s, solar photovoltaic systems are now over 60% cheaper and the estimated average cost of solar energy in 2010 was approximately $0.29 [kWhr]-1 in northern Europe and is as low as $0.12 [kWhr]-1 in the Middle East5.
In order to enhance the potential of solar power and to enable its wider use, these costs must be further reduced. There is a global consensus that this can be achieved through extensive research and development of photovoltaic technologies. Governmental organizations, such as the United States National Renewable Energy Laboratory (NREL) and the European Renewable Energy Research Centres Agency (EUREC Agency) have been set up in order to achieve this goal.
The European Commission Mission
The European Commission stated in 2009 that it aims to increase the use of solar energy within the European renewable mix. This strategy stems from an effort not only to reduce the environmental impact of energy production and consumption but also to improve security of Europe’s energy supplies.
A key component of this strategy is to maintain a European lead in solar RD&D. Photovoltaics are a key aspect of this plan as, not only are they safe, clean, robust and efficient, but they are highly scalable and easy to introduce and implement on a large scale. Thus far, the Commission has widely supported the development of solar photovoltaic technologies in order to produce cheaper more efficient PV devices. Thin-film, organic and dye sensitised solar cells are currently undergoing extensive research and development. These devices require less semiconductor material and can be produced via cheap roll-to-roll manufacturing techniques, providing attractive less expensive alternatives to crystalline silicon based devices.
Solar power could provide
energy for more than a billion
people in 2020 and sustain 26%
of global energy needs by 2040
On the implementation side, a 2007 Commission White Paper set a target of 3,000 MW of photovoltaic capacity to be installed by 2010. This target was easily surpassed and by the end of 2010 the cumulative installed capacity of PV in the EU was over 28,000 MW6. This is an energy output level that equals the electricity consumption of around 10 million households in Europe. The European Photovoltaic Industry Association (EPIA) stated that they believe solar power could provide energy for more than a billion people in 2020 and sustain 26% of global energy needs by 2040.
Solar goes Global
Non-EU countries have a lot of potential for growth of the solar power sector in the coming years. Last year the rest of the world increased capacity by an estimated 3,000 MW, with Japan making the largest contribution of 1,000 MW. The USA and China also increased their capacities by 700-800 MW and 400-600 MW respectively. Other emerging solar enthusiasts include Canada, Australia, India and South Korea, all of which increased their PV capacity by 50 MW or more in 20105.
Despite Europe’s attempts to dominate the PV market, non-EU countries such as China and India have also invested large amounts in development of new technologies. With ready supplies of raw materials and cheaper labour costs, PV systems from these countries compete directly with those produced in the EU. Such price pressure will inevitably contribute to pushing prices down as the technology evolves.
Despite Europe’s attempts to
dominate the PV market, non-EU
countries such as China and India
have also invested large amounts
in development of new technologies.
PV technologies produce most energy when implemented in areas of high insolation. The Sahara desert is one such area that could provide energy for both North Africa and Europe, and reduce dependence of these countries on fossil fuels from Russia and the Middle East. The Desertec Industrial Initiative (DII) aims to provide 15% of Europe’s electricity by 2050 or earlier via power lines stretching across the desert and Mediterranean Sea. This project aims to use CSP technology rather than PV as generators can run overnight (see fact-box). Coastal wind power could be used to support a PV network exploiting strong North African summer winds when Europe’s winds are weak. Despite the attraction of these proposals, there are political and ethical concerns surrounding European exploitation of African resources and political instability in many North African countries.
Feed-in tariffs (FiTs) are implemented by a number of countries worldwide including Germany, the US and the UK. A feed-in tariff is a policy designed to encourage both individuals and businesses to utilise renewable energy sources. Under this scheme, regional and national electric grid utilities are obliged to take the energy produced by renewable energy sources that are privately owned and pay the owner a premium pre-arranged price for it. FiTs offer the guaranteed purchase of energy from renewable sources on long-term contracts that are typically in the range of 15-25 years. Alternative incentives for promoting the deployment of renewable energy generation include initial investment and operational support in the form of tax exemptions and reductions, grants and subsidies, which may be used in combination.
Solar at Imperial
Imperial College has a large stake in research into improving solar power generation. Groups aiming at developing and improving device efficiency and production costs can be found in a number of departments, from chemistry and physics, to materials and engineering. The new Doctoral Training Centre (DTC), established in 2009, provides an excellent platform for interdepartmental interdisciplinary research. In particular, a number of Plastic Electronic DTC positions span chemistry, physics and materials and focus on researching nanomaterial devices such as dye-sensitised, quantum dot and organic photovoltaics. These technologies use relatively small amounts of semiconductor materials and may be manufactured by roll-to-roll printable techniques that can drive down costs dramatically. The main problem currently encountered with these devices is that their solar-electrical conversion efficiencies are generally relatively low and do not rival those of silicon based devices.
PV technologies produce most energy
when implemented in areas of high
insolation. The Sahara desert is one such
area that could provide energy for both
North Africa and Europe, and reduce
dependence of these countries on fossil
fuels from Russia and the Middle East.
This article has explored the current position of solar technologies and the challenges that must be overcome if they are to play a significant role in future energy supply. Although currently more expensive than fossil fuels, research and development is decreasing the production costs of PV panels dramatically each year. With a global consensus that there is a future in solar power, both to combat climate change and to reduce reliance on fossil fuels, governments worldwide are offering incentives to stimulate innovation and deployment. Within the past decade global solar capacity has increased year on year, with 2010 being a record-breaking year in the number of new PV installations. Let’s hope this trend is set to continue.
Alice Rolandini Jensen is a postgraduate researcher Imperial College Department of Chemistry where she is investigating electrolytes in dye sensitised solar cells.
 King, R. et al (12-16 March 2000). Metamorphic Concentrator Solar Cells with Over 40% Conversion Efficiency. 4th International Conference on Solar Concentrators (ICSC-4), El Escorial, Spain.
 del Canizo, C., del Coso, C. & Sinke, W. C. (2008). Crystalline Silicon Solar Module Technology: Towards the 1 Euro Per Watt-Peak Goal.
 Lewis, N. S. & Nocera, D. G. (2006). Powering the planet: Chemical challenges in solar energy utilization. Proceedings of the National Academy of Sciences of the United States of America.
 EPIA report (2011). Solar Generation : Solar Photovoltaic electricity empowering the world.
 EPIA press release (2010). Solar Photovoltaics: 2010 a record year in all respects.