Petr, the problem with photovoltaic is that the way they're produced uses an absolute *stack* of really nasty acids and heavy metals. It's the same system as used for silicon chips, except in this case you've got a few square metres of silicon chips so there's a pretty significant impact. This wouldn't be such a big deal if they lasted forever. But they don't last forever - the ones on my parents' boat, for example, are about 10 years old, and only 50% of the cells still work.

Plus they're inefficient - last I heard, even the best ones are less than 15% efficient (12% IIRC?). And they're expensive. In Britain, we're still advised (by independent consumer groups) not to buy photovoltaic panels for houses, because the payback time is about 20 years and the panels simply won't last that long. They might make economic sense somewhere very sunny, but at the moment they don't. They're only a good bet for places that don't have a better way of getting power - remote cabins, boats, caravans, etc.

Where solar power's being used more seriously, it's using the solar power to heat water, and then using that heat to generate electricity and/or run your domestic hot-water system. You mount what are basically large radiators on your roof, except that they're catching heat instead of giving it out. Early versions actually did use radiators, and it's perfectly possible to put together a reasonable low-cost home-made solution from old domestic radiators (there are a zillion plans on the web, and a lot of people have done it), although more professional systems are much more efficient now (but cost more). This is not only more efficient than photovoltaic, but it's also a lot cheaper, and their lifespan is a lot better too.

There are ideas around for new photovoltaic systems. Some are trying to get better efficiencies, which might make them break even that way. Others are trying to use organic chemicals to make systems which are less efficient but are a whole lot cheaper and less polluting to produce. There's stuff in the pipeline there, but it's going to be a while yet before anything hits the shelves.

Graham.