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Solar innovations

Solar energy has been the focus of research effort for decades now, and some interesting new technologies have emerged. Most of the effort has been going into improving cell efficiency, using new materials or configurations, but there have also been some novel developments based on completely new concepts. For example, as reported in New Scientist last year (20/12/10), the US Dept of Energy’s Idaho National Lab has developed a device that works on infra-red radiation – which accounts for about half of the available energy in the solar spectrum. Moreover IR is re-emitted by the Earth’s surface after the sun has gone down, so the device can capture some energy at night. Lab tests have suggested that a complete system could have an overall efficiency of 46%; much higher than the best silicon cell at 25%. And they would not be so directionally sensitive. The new device doesn’t rely on photons liberating electrons in semi conductors, as in conventional solar cells. Instead it uses tiny nano-scale antennas which resonate when hit by light waves, generating an alternating current at very high frequency. That has to be rectified to be useful- tricky it seems at nano-scale.

There are also some other clever new technologies on the horizon. For example A US team led by a North Carolina State University researcher have developed solar cell with a water-based gel infused with light-sensitive molecules – the researchers used plant chlorophyll in one of the experiments and have shown that water-gel-based solar devices can produce electricity.

The researchers say “We do not want to over-promise at this stage, as the devices are still of relatively low efficiency and there is a long way to go before this can become a practical technology. However, we believe that the concept of biologically inspired ‘soft’ devices for generating electricity may in the future provide an alternative for the present-day solid-state technologies.”

Just as intriguing, New Energy Technologies Inc. has developed a room temp ‘spray-on’ solar PV coating for glass windows, using nano-particles 4 times smaller than a grain of rice . It’s claimed to cut solar cost/kW by a third and leaves windows translucent. www.newenergytechnologiesinc.com

Meanwhile, MIT has developed transparent organic PV cells, which can be used in windows. They only use near infra red wavelengths- the rest passes through: http://apl.aip.org/resource/1/applab/v98/i11/p113305_s1?bypassSSO=

Even more exotic, and moving beyond PV electricity production, is the prototype solar device that has been developed by researchers at CALTEC and in Switzerland which uses a quartz window and cavity to concentrate sunlight into a cylinder lined with cerium oxide, also known as ceria, which exhales oxygen as it heats up and inhales it as it cools. If, as in the prototype, hydrogen and/or water are pumped into the vessel, the ceria will rapidly strip the oxygen from them as it cools, creating hydrogen and/or carbon monoxide. The hydrogen produced could be used to fuel hydrogen fuel cells, while a combination of hydrogen and carbon monoxide can be used to create “syngas” for fuel.

The BBC web site reported that ‘the prototype is grossly inefficient, the fuel created harnessing only between 0.7% and 0.8% of the solar energy taken into the vessel. Most of the energy is lost through heat loss through the reactor’s wall or through the re-radiation of sunlight back through the device’s aperture. But the researchers are confident that efficiency rates of up to 19% can be achieved through better insulation and smaller apertures. Such efficiency rates, they say, could make for a viable commercial device’.

However, in terms of even more radical large-scale developmental concepts, University of Tokyo researchers have launched a Sahara Solar Breeder project, aiming to use desert sand to produce PV solar units and desert sun to ultimately generate 50% of the planet’s electricity, by distributing solar energy globally through a superconducting supergrid.

As I mentioned in my previous Blog, the idea is that power generated by the first wave of plants would be used to “breed” more silicon manufacturing and solar energy plants, which would in turn be used to breed yet more in a “self-replicating” system.

The initiative is funded by Japan’s Ministry of Education, Culture, Sports, Science and Technology (JST) and the Japan International Cooperation Agency (JICA) under the auspices of the International Research Project on Global Issues, which will fund the project to the tune of 100 million Yen ($1.2 million USD) annually for five years.

The aim of this initial five-year phase will be to demonstrate the possibility of manufacturing high quality silicon from desert sand and of building a high-temperature superconducting long-distance DC power supply system. But they suggest that it should be possible to generate 50% of global electricity globally with solar by 2050 .
http://www.diginfo.tv/2010/11/24/10-0135-r-en.php

Clearly many of these ideas will take some time to develop to be viable options, and some won’t succeed. But the pace of change in the solar world is quite dramatic. There is already over 40GW (peak) of conventional PV capacity in place globally and rapid growth continues, with new technologies and applications feeding in. For example over 20 MW of large-scale concentrator photovoltaics (CPV) systems are now connected to the grid, and CPV should reach GW level in the next 5 years, according to the European Photovoltaic Industry Association. Module efficiency in current power plants has reached 25-27% and is expected to grow to 30% by 2012. One of the attractions of CPV is the simple fact that, at present, mirrors, for focussing sunlight, are less expensive than PV cells.

New cheaper, light weight scratch resistant mirror materials are also emerging for use with concentrating solar (thermal) power (CSP) systems: www.mulkre.com That could make CPV, as well as CSP, more competitive. But even without that, focussed solar heat CSP seems to be booming. Some are hybrid systems with gas fired back-up/parallel generation, but with molten salt heat stores being added to some projects to allow for continued solar generation overnight.

Currently there is around 3 MW of CSP capacity in place globally and over 50 MW of new large-scale projects is being deployed around the world, mainly in Spain and the USA, but also in N Africa and the Middle East (see my last Blog). However, some say CPV will overtake CSP. Either way solar electricity generation looks likely to prosper, with much talk of price parity with conventional power sources within the next few years.

*For an interesting series of youtube videos on the many solar innovation projects in the USA, many of them seeking to copy/adapt phototsynthsis, see: http://www.energyfrontier.us/videos

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