Energy efficiency facts

Energy efficiency is defined as using less energy to provide the same level of energy service. Some examples of energy efficiency are better insulation of buildings, using energy saving light bulbs, buying cars with better gas mileage. Energy efficiency is achieved primarily by means of a more efficient technology or processes rather than by radical changes in individual behavior.

Energy Star is an international standard for energy efficient consumer products. It was first created as a United States government program in 1992, but Australia, Canada, Japan, New Zealand, Taiwan and the European Union have also adopted the program. Devices carrying the Energy Star logo generally use 20%–30% less energy than required by federal standards.

Regular or incandescent light bulb uses four to five times more energy than compact fluorescent light to produce same amount of light. Since lighting accounted for approximately 9% of household electricity usage in the United States in 2001, widespread use of compact fluorescent light could save as much as 7% of total US household usage.

If every US home replaced just one light with an Energy Star efficient light, saved energy would be enough to light more than 3 million homes for a year and prevent 9 billion pounds of greenhouse gas emissions per year, equivalent to the emissions of about 800,000 cars.

Energy saving light bulb.

Energy Star qualified clothes washers use about 30% less energy and use over 50% less water than regular washers. The average American family washes almost 400 loads of laundry each year. If your washer is over 10 years old then replace it with a new energy efficient washer and you could save $135 each year on your utility bills.

Average passenger car fuel consumption in the United States is 22.4 miles per US gallon (about 10.5 liters per 100 km) and the same average in European Union is a bit more than 40 miles per gallon (less than 6 liters per 100 km). That is mainly because the US citizens prefer massive SUV-like vehicles and fuel prices are considerably lower than in EU so the fuel economy is not very important in the US. If citizens in the United States would accept cars with EU fuel economy there would be savings of about 32.9 billion gallons of fuel per year (42.1 billion gallons per year instead of current 74.0 billion gallons). From ecology perspective that would be more than 300 million tons less carbon dioxide released into atmosphere per year.

US citizens prefer massive vehicles.

Although both terms are related to saving energy, the terms energy conservation and energy efficiency have two distinct definitions. Energy conservation is any behavior that results in the use of less energy – behavioral change. Energy efficiency is the use of technology that requires less energy to perform the same function – technological change.

The United States and Germany are countries with almost the same standards of living, but average US citizen uses twice as much energy than average German. Reasons for that difference are quite complex, but we will mention two main reasons. First reason is cheap energy in US that does not motivate people to invest in energy efficiency. Second big reason is inferior spread of high-tech and energy efficient technology in US comparing to Germany.

Since buildings use 40% of the total energy in the US and European Union, energy efficient houses are becoming more and more interesting. In Germany a "Low Energy House" has an energy consumption limit of 50 kWh/m² per year for space heating. In Switzerland the term is used in connection with the MINERGIE standard - no more than 42 kWh/m² per year should be used for space heating.

In the United States, a house built to the Passive House standard uses between 75 and 95% less energy for space heating and cooling than current new buildings that meet today's US energy efficiency codes. The Passivhaus in the German-language camp of Waldsee, Minnesota uses 85% less energy than a house built to Minnesota building codes. The Passivhaus standard for central Europe requires that the building must use less than 15 kWh/m² per year in heating and cooling energy.

The dark colours on this thermogram of a Passive house (right) show how little heat is escaping compared to a traditional building (left).

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Solar collector facts

Solar collectors transform solar radiation into heat and then transfer that heat to a medium (water, solar fluid, or air). The term is applied to solar hot water panels, but may also be used to denote more complex installations such as solar parabolic, solar trough and solar towers.

Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems.[

For residential use the three most common types of hot water solar collectors are the flat plate solar collector, the evacuated tube collector, and the concentrating collector. They each work a little differently to heat water.

Flat plate solar collectors are the most common for heating water and air in the home. The flat plate solar collector is an insulated box with a plastic or glass “lid” on top. Water is heated when sunlight passes through the top plastic or glass glazing of the collector, strikes a dark-colored absorber plate underneath this “lid”, which then heats the air or water inside the collector.

An evacuated (vacuum) tube solar collector is an array of tubes. The vacuum tube solar is a second generation collector and it is more expensive then flat plate solar collector. According to some tests, the evacuated tube collector is approximately 1.6 to 4 times more effective than a flat plate collector (4 times more effective in January and only 1.6 in August).

Concentrating solar collectors use mirrored surfaces to concentrate the sun's energy on an absorber called a receiver. Concentrating collectors also achieve high temperatures, but unlike evacuated-tube collectors, they can do so only when direct sunlight is available.


In China currently is installed 114 million square meters of rooftop solar collectors for heating water and they plan to increase that to 300 million by 2020. Europe goal is to reach 500 million square meters of installed solar collectors by 2020, and US goal is 300 million square meters by 2020.

With appropriate assumptions for developing countries other than China, the global total of rooftop solar collectors in 2020 could exceed 1.5 billion square meters. This would give the world a solar thermal capacity by 2020 of 1,100 thermal gigawatts, the equivalent of 690 coal-fired power plants.

Flat plate solar systems were perfected and first used on a very large scale in Israel. In the 1950s there was a fuel shortage in the new Israeli state, and the government forbade heating water between 10 p.m. and 6 a.m. Levi Yissar built the first prototype Israeli solar water heater and in 1953 he launched the NerYah Company, Israel's first commercial manufacturer of solar water heating. Despite the abundance of sunlight in Israel, solar water heaters were used by only 20% of the population by 1967. Following the energy crisis in the 1970s, in 1980 the Israeli Knesset passed a law requiring the installation of solar water heaters in all new homes.

Solar thermal collectors for nonpotable pool water use are often made of plastic. Pool water, mildly corrosive due to chlorine, is circulated through the panels using the existing pool filter or supplemental pump.

The amount of heat delivered by a solar water heating system depends primarily on the amount of heat delivered by the sun at a particular place. In tropical places the insolation can be relatively high, e.g. 7 kWh per day, whereas the insolation can be much lower in temperate areas where the days are shorter in winter, e.g. 3.2 kWh per day.

The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year.

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