Of the total energy usage in the US in 2007, 7% was renewable energy; of which just 1% came from solar power. Compare this to the fact that in one hour, the sun provides more than enough energy to supply the earth’s energy needs for one year; and in one day, it provides more energy than the world’s population could consume in 27 years.
So if we have a plentiful, universal source of energy – why aren’t we totally solar powered?
A partial answer to that lies in our, to-date, clumsy and inefficient (compared to nature at least) methods for harnessing that power. Solar cells have taken many years to improve their efficiency range from a mere 6% in 1954 to 17% in the 70s, up from 24 to 30% between 2000 and 2007. That said, the last few years have seen the introduction of potentially game-changing innovations in the shape of new materials and device structures that are allowing us to obtain solar energy from a wider range of substrates. Such developments are putting the means for energy generation in the hands of consumers rather than ‘big energy’, giving us greater control over where, from, and how we power our lives.
From the first thick crystalline silicon wafers (0.5 mm thick) which were expensive to produce and rather delicate, we now have thin film technologies using semiconducting compounds such as crystalline and amorphous silicon (c-Si and a-Si), cadmium telluride (CdTe), and copper-indium/gallium selenide (CIGS), which are deposited as layers a few micrometers thick onto glass or even flexible substrates. Silicon still makes up 95% of the world’s photovoltaics, and is still the best at gaining high efficiencies, but materials such as CdTe and CIGS are much easier to process and deposit, making them a better mass production option.
Solar Forest by Neville Mars
Indeed, a forecast by the Prometheus Institute for Sustainable Development states that by 2012 non-silicon thin-film applications will make up 40% of the market. Up till now multi-junction concentrators have been the most efficient with an efficiency of 40.7% (this is a photovoltaic consisting of different layers of thin films) compared to 19.9% for single thin film technologies.
There are a few emerging technologies that have garnered interest in this heavily contested field. Dye-sensitized solar cells (DSCs) are low-cost thin film photovoltaics; a photosensitive dye (such as a ruthenium metal-organic dye) is screen printed onto a very rough TiO2 surface. These dyes are cheaper and easier to produce, but tend to degrade over time. In spite of this, it is a popular emerging technology with some good commercial impact forecast over the next decade in paints onto exterior surfaces.
Organic/Polymer solar cells (sometimes known as photosynthetics after their similarity to the way plants synthesize energy from the sun) rely on certain organic chemicals having semiconducting properties. Conducting plastic compounds with these properties tend to have low efficiencies - the best in the last few years have been close to 7% by Solarmer of California, a spin-off from UCLA that also has academic partners at the University of Chicago – but the idea is that these are easier to deposit and can be applied like paint to achieve greater catchment areas on existing structures. Think paints and coatings on the outsides of buildings, cars, boats, apparel. Konarka, for example, is working on incorporating its photosynthetics into window films and covering tents in the film for military encampments.
Another development has been the change in the shape of photovoltaics in order to gather more rays. Domes, (Kyosemi, Japan), cylinders (California’s Solyndra) and lenses (Germany's Fraunhofer Institute for Solar Energy Systems) are all now being used as ways of capturing more of the suns rays per square inch.
In terms of where solar cells are being utilized, it may be surprising to learn that the majority are used in residential projects. In terms of billions of BTUs generated out of a total of 72,000 for photovoltaics in the US in 2006, residential made up 67000 billion, independent power producers 5,000 billion and the electric power sector less than 500 billion. No data was available for commercial usage due to such small numbers – this is expected to change in the future though (Energy Information Administration/Renewable Energy Trends 2006). With the improvements in design, performance and ease of application, we could expect to see more usage in structures until now deemed too small or complex to utilize photovoltaics. As well as the aforementioned incorporation into glazing, there are now specifically developed photovoltaics in polycarbonate bus shelters (3form), panels that are installed like roofing tiles, flexible photovoltaic cells by Semprius that can be applied to plastic films that are so thin that they can easily be wrapped around a pencil, and architectural uses such as 3form’s photovoltaic integrated in polycarbonate and cleverly integrated roofing photovoltaics like SRS Energy’s roofing tiles.
Lots of new development, with advances made and efficiencies improved. So what?
Orange Solar Concept Tent
It’s clear that this industry, without full scale backing of federal or state funding, will remain a minor fraction of the country’s energy needs due to the scale of change needed to create large power generating PV systems for industrial use. Unless of course, we begin to run out of oil or we realize that burning coal is sending our CO2 emissions dangerously high. Come to think of it, those may well be happening right now.
Solar power is eternal, universal and free. It really is the only viable choice.