photovoltaic (solar) cells
a briefing document
(solar cells) is one of a series of briefing
documents on the problems of power consumption, posed by the steady depletion
of fossil fuels and most particularly of pumpable oil.
One of a grouping of documents on global concerns at abelard.org.
|on energy||on global warming|
housing and making living systems ecological
sustainable futures briefing documents
|Tectonics: tectonic plates - floating on the surface of a cauldron|
Photovoltaic cell technology is an area that is changing technologically at an extremely high rate. There is an increasing race between the more efficient, but expensive, silicon technology and a variety of cheaper, less efficient and often lighter-weight technologies. Every week hopeful entrepreneurs and scientists attempt to hype another miraculous ‘break-through’. This is further complicated by the rapidly growing field of nanotechnology, which is already being applied to photovoltaics.
I cannot possibly review all these wonders, let alone assess their long-term commercial viability. Therefore, as usual, my aim is to provide you with enough outline to orient you and enable you to start digging around on your own.
Photovoltiac cells are also known as solar cells. They are a means of harnessing the sun’s energy and converting it into electricity. Photons from the sun are absorbed by semi-conductors, with electrons being knocked along electrical wires by the photons until the current (flow of electrons) reaches a device that can be powered by electricity.
This is known as the photovoltaic effect, and was first noticed in 1839. It works in a similar way to the current flow is handled in computer logic and memory chips.
Solar power from photovoltiac cells has been used since the 1950s, at first for devices where providing other sources of power was a problem, such as with satellites, remote small dwellings and motorway phone boxes. The technology has improved sufficiently that solar cells are now a feasible option for private and business buildings, providing an alternative power source in case of power failures.
The sun is an enormous source of energy, bombarding the Earth each minute with enough energy to supply the Earth’s power needs for a year.
Crystalline silicone-based photovoltaic cells will convert 15% of the sun’s energy to electricity, while newer, cheaper materials such as amorphous silicon and gallium arsenide convert 8% of the sun’s energy, thus being half as efficient as silicon-based cells.
Because the manufacturing costs of photovoltaic cells are still relatively high, solar power is as much as five times more expensive than power derived from fossil fuels. However, photovoltaic technology is changing rapidly.and new research could lead to significant cost reductions within a few years. These advances could be both by making cheaper versions of rigid crystalline silicon cells (which comprise 80% of the solar market), and by creating less expensive flexible photovoltaic technologies that are as reliable and as efficient as crystalline silicon, using, for instance, amorphous silicon and gallium arsenide.
Crystalline silicone comprises approximately 40% the price of photo-voltaic cells, therefore even halving the price of the silicone would improve the cost down from five times to four times that of fossil fuels. You will, therefore, see that there is still a long way to go before photo-voltaic cells will move into serious consideration for major power production.
a small way, germany starts acting for substitute energy production
There are various attempts to cut down expensive PV silicon cells by using many different concentrators.
Here is a diagram of a typical example from Japan.
Little 1mm balls, each in a reflector may give only 12% efficiency, but Clear Venture 21 claim that this conformation uses one fifth the silicon and so manufacture costs should also be one fifth as much as conventional silicon cells, while expending half the usual manufacture energy.
See also claims that solar pv makes another step forward, with theoretic possibilities up beyond 60% efficiency.
Standard silicon arrays are approaching 20% efficiency, whereas several less efficient technologies are struggling towards 10% efficiency. However, ‘optimism’ in the field is very high.
These less efficient technologies are often a great deal cheaper than silicon-based solutions. They are also often a lot cheaper and do not require heavy sub-structures. Thus it is hoped that the lower efficiency can be offset by easier usage and lower costs - for example, bonded into normal house tiles, windows or even painted onto structures. As you will see, serious generation may require considerable land use, not something to be taken lightly when blocking out the sun from productive farming or other land use. Even considering such low efficiency for a desert area could generate larger maintenance costs for the greater implied areas. Working life is also a potential economic consideration.
There is an expectation that these cells can be made in different colours and thus be applied artistically in architecture.
430 megawatts is about half a big power station. Keep in mind that photo voltaics [PV] cannot function on a 24 hour basis.
December 2007: The Nanosolar company is now in production on an economic scale, with all the first year’s production already sold.
The generally quoted figures for how much energy from the sun is reaching the Earth (solar flux energy) are:
Using a photovoltaic array, electrical energy is generated locally, on the south-facing roofs of buildings, or set out facing south on land that would be fed back into the national electric grid, thus in a sense using the grid as a battery.
The time of production tends to coincide with the peak usage times, thus allowing a reduction of back-up capacity and so lowering the costs to users and generators. It is very likely that photovoltaics will be market driven by end users.
As the price goes down, it is attractive to increasing parts of the energy-generating market. The capital costs of manufacturing PV arrays and for installation are decreasing rapidly, to a tenth or less in recent decades. At the same time, the efficiencies are also creeping upwards. In addition, upkeep costs are probably quite low.
The solar constant describes the amount of incoming solar radiation that falls on the outer surface of Earth’s atmosphere, in a plane perpendicular to the rays. Currently, the solar constant s = 1.37 kW / m².
In space, solar radiation (insolation) is practically constant.On Earth, it varies with
The maximum average insolation value on Earth is between 0.8 and 1.0 kW / m². This is estimated to one quarter of this value when night-time, haze or cloud cover are included. In Germany, for instance, the average annual amount of peak insolation varies between 0.95 and 1.1 kWh / m², depending on the region.
Because of all these factors, advantages will come earlier to those with better conditions, whether climate or location, and business or commercial premises, especially those built with energy efficiency in mind.
The more pressing problems are with mounting, storage and conversion equipment. However, independence from power utility companies and cleaner energy are already driving a growing percentage of the market to install photovoltaics.
A fairly humorous example suggests covering London in solar panels, and the contribution that this likely to make to the conquest of the universe.
Let’s look at this joke example in closer detail.
Next, there are all those roads and parks and rails that I do not think most people will welcome being covered in solar panels. And your garden will have to go; you won’t grow anything much without the sunlight.
Then, the efficiency drops rapidly if the photovoltaic arrays are not reasonably clean, or the angle is not optimal.
So, what do you think are reasonable figures for the amount of roof, garden, and so on you would be able to use for energy generation?
For reference, a large power station produces maybe a bit less than 9 billion kW a year. But this reduces by about 10% to allow for for servicing and other down time. The original figure for the Greater London power generation project is the equivalent of roughly 65 big power stations. However, the whole UK only has about 65 such stations equivalent at present. So this still isn’t peanuts (don’t forget we still have the whole of the Greater London area covered at this point).
Photovoltaic energy generation is not useless, but it requires sane numbers. The Sahara might find a useful industry, and then there’s Wales!
The following costing is purely speculative and, at the moment, all the figures are guesswork. I shall try to obtain and gradually substitute some figures from real installations. In this early stage of development, real prices will be highly variable, according to what the vendors think they can get away with. Doubtless, the quality, value and efficiency of equipment will vary. There are also widespread tax-funded incentives available from a wide variety of government sources. This technology is developing quickly and, therefore, judging when or if to buy will not be easy. Let the buyer beware.
Here is a good place to start looking for prices at the moment. Notice that the current prices quoted are a little under $5/Watt for installed capacity.
Instead of rather inelegant slabs of solar panelling placed on top of and above your current roof, integrate solar tiles with the current roof tiles. There is also a thermal tile option for heating water, but currently they are only available to housing developers, housing associations and registered social landlords, and not for private residential installations, wholesale customers or their installers.
Note that, because each solar tile takes the place of four normal tiles, “this particular solar application works best for 'new builds' or when a homeowner is re-roofing, because each photovoltaic tile replaces four conventional roof tiles and is attached straight to the roof battens”.
Already installed on housing in the UK,
Solarcentury is rather coy about their prices. However, recently (to September 2007), 12 C21e tiles cost £3,514, excluding delivery and installation.
PVs are starting to produce too much electricity in some areas, more than government will pay for. At the same time, battery research is creating what is likely to be the coming revolution in electricity storage.
email abelard at abelard.org
© abelard, 2007, 13 march
the address for this document is http://www.abelard.org/briefings/photovoltaics_solar_cells.php