Posted Wednesday, January 23, 2013 in Sustainable Maine


Bioreactor panels on demonstration house                          (Photo courtesy

by Paul Kando

Imagine an integrated neighborhood of homes, stores and businesses, clustered around a transit stop and served by an energy system that mimics nature and uses no fossil fuel at all. Like nature, this system relies on zero-waste energy conservation and sunshine as its sole energy source. Let’s take a tour.

The most striking components are the translucent green panels that cover walls, filter light, provide shade and also serve as noise insulation.  They are actually hybrid devices -- bioreactors -- that convert sunshine to both heat and biomass. Installed about two feet from wall surfaces, rather than directly upon them, they are automatically adjusted to the incoming sunshine. In addition to a heat transfer fluid used to harvest solar heat, they separately circulate a slurry of nutrients (mostly from waste water and urine) and carbon dioxide. The slurry is alive with millions of green microalgae, microorganisms 3 to 5 micrometers in size, not much larger than bacteria. (One micrometer, or micron, is 1/1000 of a millimeter or 0.000003937”) Like green leaves, the algae combine water and carbon dioxide to plant sugars through the process of photosynthesis, essentially building and reproducing themselves. Under optimal conditions, these single cell organisms divide twice daily, i.e. increase in volume by a factor of four. By “optimal conditions” I mean the right amount of sunshine, nutrients, carbon dioxide, and optimum temperature for the photosynthesis. Excess heat removed from the bioreactors is available for space and water heating. The algal biomass itself is harvested, dehydrated, and stored daily for later use. The water is recycled

When the dehydrated biomass is fed into a digester, biogas is produced.  The gas, which is 80 percent methane, may be used as fuel, e.g. for cooking or motor vehicles. The biomass-biogas cycle produces about 4,500 kWh of energy per square meter of bioreactor surface per year. This compares favorably with the energy consumption of the average family of four living in this energy efficient neighborhood: a total of 4,000 kWh annually.

Much of the biogas is used in fuel cells that produce both heat and electric power. Carbon dioxide, a byproduct, is recycled back into the bioreactors as an important feedstock of photosynthesis. This completes the biomass part of the energy system. Additional energy sources include photovoltaic arrays that produce electricity and earth tubes that provide geothermal heat.

The energy center is the brain of the system. This is where all energy flows are managed with the aid of sophisticated computing equipment. Energy arrives here in two forms: heat (from the bioreactors, fuel cells and geothermal earth tubes) and electricity (from the fuel cells, and the photovoltaic arrays). The energy center’s heat pumps boost all low temperature energy to useful temperatures. All heat is stored, to be distributed as needed for space and water heating through a highly efficient district heating system.

On the electric side, the energy center conditions all incoming power, to make it compatible with the public power grid to which it is connected. The system sells power to the grid and purchases from it as its needs dictate. The center also stores electricity and handles all power distribution for the neighborhood. Mutual arrangements like this, increasingly common in Europe, contribute to grid stability and help reduce the frequency and duration of power failures.

Our virtual tour ends here. If you are the traveling kind, you may visit this installation real time in Wilhelmsburg, a neighborhood of the city of Hamburg, Germany. Located on an island at the confluence of two branches of the river Elbe. Wilhelmsburg is a former industrial district rehabilitated as part of the city’s long range program to become energy-self-reliant.

Imagine such 100 percent self-reliant systems scattered around Maine, starting with just one! The bad news is that there are a thousand reasons why “this could never work in Maine”. The good news is, we need only one reason why it can. We don’t have to invent anything either. We just need to adjust an existing design to our local circumstances. Then make It happen.

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