(Photo from Totally Absurd)

Large blue machines at the end of a 300-metre long tunnel in a hillside in central Oslo use fridge technology to suck heat from the sewer and transfer it to a network of hot water pipes feeding thousands of radiators and taps around the city.

Now this doesn't look anything like the picture above, but I've known stranger things from Norwegians. Actually, this isn't all that strange, but more wonderful if the price system works and it can be done cheaper than oil. Basically your endless supply of crap (renewable) can be turned into power (heat energy) in urban areas.

The heat pump, a system of compressors and condensers, cost 90 million Norwegian crowns ($13.95 million) and has an effect of 18 megawatts (MW), enough to heat 9,000 flats or save burning 6,000 tonnes of oil a year.

And experts say sewers could be exploited elsewhere.

"The technology is there, so if the infrastructure is also there, this is a feasible solution in many cities worldwide," said Monica Axell, head of the International Energy Agency's heat pump centre. The agency advises 26 industrialised nations.

She said a bigger heat pump in Sweden, with a 160 MW capacity, exploited heat from treated sewage. And in Finland, a 90 MW plant ran on waste water.

One thing this article doesn't go into enough is the cost issues. It seems Vancouver is thinking about a similar project, and one with a similar price to Oslo's. So that might be good news for social investors who are looking at similar scaled projects. Still, they are quite costly, at least up front, unless there are people willing to make a business out of raw sewage power plants. Some Chinese researchers are on to this with further inventiveness. More on all this at IHUB and the other ways raw sewage could be used for powering water treatment plants, or using microbial fuel cells in similar ways hydrogen fuel cells would be used.

And it seems more and more social investors are willing to put their bucks behind "green technology" projects, according to this report.

North American venture capitalists invested more than $1.6 billion in cleantech companies last year, a 35 percent increase over 2004, according to a report by the Cleantech Venture Network, a trade group.

"It's a strong area for venture capital," said Craig Cuddebach, the network's senior vice president, whose group expects venture capital investment in the sector to double over the next three years. "It's no longer a choice between whether you will be clean or profitable."

Also known as clean technology, the field includes technologies related to water purification, air quality, nanotechnology, alternative fuels, manufacturing, recycling and renewable energy.

As prices of more traditional energy sources continue to rise, the global market for clean energy sources such as biofuels, hydrogen fuel cells and solar and wind energy rose to $40 billion last year, according to a report released last month by Clean Edge Inc., a Bay Area marketing firm. The figure is expected to more than quadruple to $167 billion by 2015, the report said.