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Photo by Energy and Environment Ltd

The on-site generation of electrical power is increasingly popular in green building. Rapidly developing technologies have made it more feasible and affordable to generate electricity on a small scale, and legislation has required electrical utilities to accommodate customers who wish to supplement their electric power requirements with their own generation. Net-metering arrangements safely connect these customers to the power grid, and the utilities are required to purchase excess electricity that the customer generates that is fed back to the grid.

On-site electrical power generation can be environmentally beneficial in several ways. First, it can allow the substitution of renewable resources (usually solar or wind) for the fossil fuels that are relied upon for the electricity sold by most utility companies. Secondly, any power that is generated on-site, regardless the source, that replaces power supplied from elsewhere will avoid the waste of energy that is lost in transmission. On-site electricity generation can be used to reduce peak demand on the utility.

On the scale of a single small or medium-sized building, solar-electric (“photovoltaic”) panels and small wind turbines are the most popular types of electric generators. Both are dependent on climate and the weather, and the solar panels depend upon the season and time of day (solar angle), as well.

The wind turbines drive small electric generators that are mounted behind the propeller. They are usually mounted above a building where the wind is stronger than nearer to the ground. Their effectiveness depends on their location in areas where wind is steady. Coastal and mountainous regions are best.

Photo by Key Energy Solutions

Solar panels work best, of course, in areas where sunlight is plentiful. The inclination and angle of the panels relative to the sun is important to maximizing their effectiveness. Panels have usually been mounted on racks above a building roof, but are increasingly used in other configurations that are more directly integrated into the design of the building.

Buildings that are much larger, or groups of buildings such as educational or business campuses, can generate electricity with on-site power plants that burn conventional fuels like oil or natural gas, or renewables such as biomass or even trash. These plants produce steam that is used to produce electricity by driving turbines, and that can be used for other purposes (heating or cooling the building, or industrial processes) in a process known as cogeneration. On-site cogeneration plants can also capture waste heat from the combustion process and put it to good use for heating or hot water. By comparison, electricity purchased from the power grid may represent less than 30% efficient use of the fuel used at the power plant (due to waste heat and other losses at the power plant, and losses in transmission lines), while on-site cogeneration can capture and apply energy at 90% efficiency. That is a 300% improvement!