Just a bit more than a year ago, I told readers about an experimental apartment building in Hamburg, Germany, which is powered by algae.
Algae don't have a very good reputation right now because of the spread of toxic blue-green algae in Lake Erie that left the folks in Toledo, Ohio, without safe water for a few days recently.
But, algae aren't all alike. The stuff that powers the building in Hamburg is the icky green kind you and I think of as pond scum.
Algae are the world's fastest growing plants, and some strains, when dried, can be processed into fuel that is much like diesel.
In Hamburg, a five-storey, 15-unit apartment building, water and algae gathered from the nearby Elbe River are put into 29 rectangular glass tanks mounted on scaffolding so that they form a part of the building's façade.
Some carbon dioxide is pumped in, and when sunlight hits them they become "bioreactors."
Photosynthesis causes the algae to multiply and give off heat - lots of it.
The water temperature climbs to about 40°C.
To ensure maximum efficiency, small motors slowly turn the elongated tanks so they track the sun as it moves across the sky.
Part of the heat produced is used to meet the building's hot-water needs.
Surplus heat is transferred to boreholes under the building. When it's needed, a geothermal system moves it back into the building's system where it is used to generate electricity.
That's what the system designers hoped it would do. And it did.
It's been in service for just over a year now, and its performance has, if anything, exceeded expectations.
The building is called the Bio Intelligent Quotient (BIQ) House, and it was built specifically to demonstrate the ability to use algae to heat and cool larger buildings.
The energy system was created by Splitterwerk Architects, and Arup, the British-based multinational design firm. System performance is being monitored by the Colt Group, which hopes to market the system.
Jan Wurm, an architect and materials specialist at Arup, says the system reduces the building's over-all energy needs by 50 per cent, and he believes 100 per cent is achievable.
The algae grow so fast that they must be harvested occasionally and the tanks recharged with a fresh batch from the river.
The harvested algae are moved to a processing room in the building's basement, where they are converted to biogas, which can be burned to provide heat in the winter.
Add in some solar panels to power the pumps and heat exchangers, and the building could be completely energy self-sufficient.
The building's occupants have been surveyed and they all like the system. They like the idea that their building actually takes carbon dioxide out of the atmosphere, although the amounts aren't large.
Wurm says each square metre of panel reduces emissions by eight tonnes of CO2 a year.
That includes two tonnes sucked up by the algae and six tonnes that have not been produced by generating energy using dirtier alternatives. With a total of 200 square metres of panels, that's 1,600 tonnes of CO2 a year.
The down-side of all this is the cost.
Wurm estimates that installing the system and monitoring it comes to about $2,500 per square metre.
That's far more than the energy costs of a typical apartment building just about anywhere.
In the long run, the algae will significantly reduce continuing costs, maybe even getting them down to zero.
In order to achieve that long-term benefit, the building owner would need to make a substantial up-front capital expenditure. As fossil fuels wear out their welcome, more and different alternative energy sources will come into play. Simple pond scum could be one of them.
Korky Koroluk is a regular freelance contributor to the Journal of Commerce. Send comments or questions to firstname.lastname@example.org.