Local Energy Production
A number of communities have begun community energy production systems. These do not literally represent energy conservation, but by their nature they tend to, and are intended to, conserve traditional energy sources. Many communities have developed or are developing so-called low head hydroelectric systems; for example, using a source that was used for power but subsequently abandoned when relatively low-cost power from central sources became available. One factor that makes such development practical is state laws that require utilities to buy power from small-scale generators and thus create a market for the output of such facilities. New England, with a large number of dams dating from the period when many mills and factories ran on waterpower, is the national center for such activity.
In many communities, solid waste, which was once disposed of in landfills or burned in incinerators, is now used as the fuel for power generation. The power is either used locally or sold back to the area utility and distributed through the utility's transmission grid. A number of municipalities have looked at the possibility of cogeneration, a system in which waste heat from one process is put to a second use rather than simply discharged into the atmosphere. For example, waste heat from a municipal power-generating facility might be converted into steam and used to supply heat for municipal or other buildings.
There is now considerable interest in recovering heat from wastewater. How does it work? Assume water in the municipal sewer system is at 60 degrees Fahrenheit (16 degrees Celsius), a typical temperature. It is 30 degrees outside and we want to maintain the air temperature in buildings at 70 degrees. A heat exchange system captures the heat of the sewer water and brings water for building heating systems up to 60 degrees. The amount of heat required to go from water at 60 degrees to a building air temperature of 70 degrees is much less than would be required in the absence of this boost from the sewer water. The sewer water thus carries most of the base load. The remainder of the load can be carried in various ways. For example, there might be roof-mounted solar heaters for daytime supplementation and natural gas heat (the most efficient fossil fuel from a greenhouse perspective) for peak loads. Viewed as a whole, the system is basically a means of capturing the waste heat from showers, dishwashers, washing machines, and all of the other household or commercial devices that use hot water.
It is not practical to pump heating water over distances greater than a few hundred yards. Therefore an energy district based on recovered heat from sewer water fits in well with some design concepts discussed earlier such as transit-oriented development that provides a large amount of residential or commercial floor space in a small area. The energy district offers advantages of cost, reduced greenhouse gas (GHG) emissions, and space savings in buildings because the building does not need to have its own heating plant. Like other systems, it is more practical to design the energy system in from the beginning rather than to retrofit it later.
On-site solar power generation has considerable potential to reduce greenhouse gas emissions and a potential which should grow as solar panel prices fall further. California has gone furthest in this direction following the passage of the Solar Roofs Bill in 2006, now the Go Solar California campaign. One big obstacle to roof-top solar was the front-end costs that confronted homeowners. The main business model that has evolved to deal with this problem is for the installing firm to put up the front-end costs and then recover its investment in either of two ways. One is for the company to sell the electricity produced to the homeowner at a price below that which the state's electric utilities charge. That works well in California where electric rates are high. The other alternative is to lease the system to the homeowner and recover the investment as a landlord recovers the cost of the property from the monthly rents.
As of 2013 California had about 2,000 megawatts (2 million kilowatts) of roof-top solar in operation and the number of installations was growing rapidly. Assuming a typical house to use an average of several kilowatts across the day, that suggests the ability to provide daytime power for perhaps half a million or more homes, not a trivial number. If you google a few words like "California roof-top solar," one item that will come up is ads for a number of solar installation firms, a clear sign of a vigorous and competitive market for the product. Roof-top solar is also growing rapidly in a number of other states, particularly in the Southwest. A local government can help that trend along through solar access zoning building codes that are friendly to solar panel installation, and requiring subdivision requirements that place houses in such a way as to facilitate solar energy systems.