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This June we paid $245.50 for the 1,298 kWh of electricity used in our Connecticut home. That’s a rate of 18.9¢/kWh. The electricity in Connecticut comes from a mix of nuclear and fossil-fueled power plants. The 18.9¢/kWh rate covered only the bill from the power company. It did not include the taxes I pay to finance the military, which is protecting our fossil energy supplies, and it did not cover the collective price we all pay for global warming.
In comparison, thermal solar power plants generate electricity at 15¢/kWh; photovoltaic plants at 20¢/kWh. Solar energy is free and inexhaustible. Furthermore, the decision to cover 10 million American homes with solar roofs would trigger the biggest economic expansion of the decade and generate energy savings exceeding the imports from the Persian Gulf.
If in the suitable areas of the country, solar roofs generated “free energy” that was stored on the grid, the energy consumption of private homes could be reduced to zero in most areas.
According to a 2007 study of the Mc.Kinsey Global Institute, the residential energy consumption in the U.S. is 21.3 quads (Q = 1015 BTUs), and it can be reduced to half by installing double windows, improving sealing, thermal insulation and the efficiency of lighting and appliances. Operating appliances consume 8.5Q; heating/cooling, 7.5Q; hot water, 3.2Q; and lighting, 2.1Q. The study concludes that efficiency improvements alone can reduce the energy consumption of American homes to 13.5Q by 2020.
In some areas, the renewable energy supplies are insufficient and have to be complemented by conventional energy supplies, while in other areas “zero-energy” homes can be built. In order to supplement the solar energy, these energy self-sufficient homes can also use geothermal and/or wind energy. According to my calculations, in most locations, the “zero-energy” home can also provide the energy needed for plug-in hybrid or electric cars.
Naturally, today we are a long way from having 10 million “zero-energy” homes, but the process of conversion has already started. Many electric power companies accept the excess electricity generated by renewable energy sources into their grid for a credit (the electric meter is running backwards). This is beneficial to both parties, because the times of excess solar generation coincides (because of the air conditioning load) with the periods of peak demand. This way, when more energy is being generated than needed, the home’s owner does not need to be concerned about energy storage, while the power company can reduce the otherwise-very-expensive peak power requirement of the system.
The “zero-energy” household (Figure 1) can later use this accumulated credit to receive free electricity when at night, or during the winter, solar or wind energy is not available. When specifying the size of the solar collectors, it is advisable to double the maximum expected requirement, so that sufficient excess electricity will be generated in the summer to “zero out” the electricity bill for the year.
Most of the private homes of Europe or the U.S. could take advantage of inexhaustible, clean and “free” forms of energy— solar, wind and/or geothermal. (Go to www.controlglobal.com/lessonslearned.html for a map showing the “free energy” potential of the U.S.) Their use could eliminate completely the emission of greenhouse gases, which today amounts to 10 metric tons (22,000 pounds) a year for the average American household. This is five times the global average.
Naturally, the initial investment needed to convert theses energy forms into electricity can be high. Many governments subsidize the use of renewable energy systems. The payback periods of alternative energy installations ranges from five to 20 years, solar hot water systems being the least expensive.
The payback period for installing a photovoltaic electricity generating system, based on a home with a monthly electricity bill of $100, an installed system cost of $50,000 and a rebate plus tax credit of $20,000 in California, is about 15 years. If the monthly electricity bill is $250, the payback period drops to about eight years, and factoring in the increase in the homes’s value, it drops to about four years. These payback periods were calculated on the basis that the electricity cost in the area is 12¢/kWh and will not rise. (This cost in my area is 18.9¢/kWh and rising.)
The generating capacity of the average solar collector system for private homes ranges from 5 kWp to 10 kWp. The yearly energy bill of an “average” household in the north central U.S.is about $4,500. (Links to energy usages sites are at http://www.controlglobal.com/lessonslearned.html.)
The technology for the “zero energy” home is readily available now.
ControlGlobal.com is exclusively dedicated to the global process automation market. We report on developing industry trends, illustrate successful industry applications, and update the basic skills and knowledge base that provide the profession's foundation.