Zero-energy homes are structures built with the eventual goal of producing as much energy as they consume. They incorporate the most advanced energy efficient features for heating and cooling, lighting, siding and insulation, roofing, and solar power. The attainment of zero energy involves not only the selection of the right high-efficiency components, but also the prudent use of electricity throughout the home.

From 2002 to 2005, TVA and the Oak Ridge National Laboratory built five such homes in Lenoir City, Tennessee, through the Habitat for Humanity program. As each new home was built, the lessons learned from the earlier homes were incorporated into the design to produce even greater energy savings. The goal of a fully sustainable zero-energy home has not yet been reached but should be attainable for new homes within a few years.

In 2006, power costs for the house shown above — with two occupants, 1,200 square feet, a 2.2- kilowatt photovoltaic system, and a 17 SEER air source heat pump — were only $0.41 a day.

Heating, cooling, and water heating

Through energy right, TVA offers assistance with high-efficiency air source or geothermal heat pumps. Unlike other types of systems that convert fuel to heat, heat pumps operate by moving heat from one place to another. Since they move heat rather than generate it, they are very efficient. They are more efficient than gas furnaces, and that’s good news today when gas is more expensive than electricity.

In colder weather air source heat pumps remove the heat from outdoor air and transfer it indoors; the process is reversed in summer to expel indoor heat to the outside, leaving cool air inside the home.

Geothermal heat pumps use the ground to absorb or dissipate heat through a series of pipes buried below the frost line. Because ground temperatures are much more constant year round — warmer in winter and cooler in summer than the air — a geothermal heat pump is one of the most efficient systems available. In addition, through the use of an auxiliary heat exchanger, excess heat that would normally be dispersed through the buried pipe can be used to meet water heating needs, providing virtually free hot water in the summer and significant savings on water heating throughout the rest of the year. Additional ownership benefits include no visible outdoor unit to suffer deterioration from weather or vandalism and no outdoor compressor noise. Geothermal systems are more expensive to install because of the excavating involved, but they can save as much as 60 percent on heating costs and 30 percent on cooling.

Ductwork in the zero-energy homes is placed inside the conditioned space, which prevents heat transfer from (or to) the ducts. This technique adds to the efficiency of the system and can be used in any home.

Heat-pump water heaters are another alternative for water heating. Research shows they are twice as efficient as conventional electric water heaters. They not only save on operational costs but have the added benefit of dehumidifying the air, which make them a great solution for basement areas.

Lighting

In a home, lighting typically represents 6 or 7 percent of the electric bill. With standard incandescent bulbs, almost 90 percent of the energy released is in the form of heat, not light. Compact fluorescent lamps, however, use 66 percent less energy than standard incandescents, while providing the same amount of light. Fluorescent lamps last more than 10 times longer than incandescents, give off very little heat, and cost less than a third as much to operate. With recent improvements, their light coloring more closely matches natural lighting.

Today’s compact fluorescent lamps fit into most fixtures on the market, and they do not produce the annoying hum that marked the original tube fluorescents. They cost a bit more than standard lamps, but the cost is quickly offset by lower operating costs. Some fluorescents can be used for exterior lighting and some are even dimmable.

Certain design elements in a structure can also reduce the amount of energy used for lighting. In the zero-energy homes, more windows are put on the south side to capture sunlight for natural indoor lighting. A two-foot overhang and special window glazing help reduce heat buildup in the summer.

Insulation and ventilation

Zero-energy homes feature airtight construction using structural insulated panels (SIPs), or something similar in energy efficiency. The SIPs, which consist of two pieces of wood sandwiching a foam core, are used to construct the exterior walls, roof, ceilings, and floors. The system forms a tight envelope for the interior of the house and provides superior insulation and faster installation compared with comparable wood-framed homes. Because the SIPs can insulate the home so effectively, the size of the equipment needed to heat and cool the home can be reduced. The walls, floors, ceiling joints, and openings for electrical wiring are sealed to reduce the infiltration of exterior air.

A mechanical ventilation system is required to ensure the exchange of air from outdoors. Proper ventilation of a home’s interior is important to reduce the potentially negative effects of substances inhaled from cleaning products, glues from furniture and carpets, pet dander, cooking, and other sources. Research indicates that indoor air pollution may be as much of a problem as outdoor pollution. The zero-energy home solves this difficulty with a mechanical ventilation system in the ductwork that uses the heat pump’s circulating fan (equipped with a variable-speed electronically commutated motor, or ECM) to ventilate the home. If the heat pump does not cycle on within a certain period of time, an automatic sensor activates the fan and opens a damper to an air duct that allows the system to distribute fresh air to every room.

Windows and siding

Efficient windows are critical in an energy-efficient home. Multi-pane glass is no longer the main measure of efficiency. New advanced technologies and designs have dramatically improved the performance of the most energy-efficient windows. Glass coatings, gas fills, warm edge spacers, and improved framing materials enable today’s windows to deliver more benefits than simple double-pane windows. When selecting a window, choose the best window your budget will allow. Windows are rated two ways: the U-factor and the solar heat gain coefficient (SHGC). The U-factor tells you how well the window insulates: the lower the U-factor, the better the window performs. The SHGC tells you how well the product blocks heat from sunlight. The lower the SHGC, the less solar heat the window lets in. Among the choices for siding, the more-efficient materials include brick, stone, and fiber cement that’s made of cellulose, sand additives, and water. Efficient siding can be both attractive and cost-effective.

Roofing and solar panels

Roofing can also be designed to reduce energy use. One type uses standard metal construction but adds reflective paint or infrared reflecting pigments that allow darker colors to reflect heat in the same way lighter colors do. That keeps heat from being absorbed into the roof and conducted into the house, with the potential for a 30 percent reduction in heat gain during summer afternoons. These metal roofs can also be installed on conventional homes and are especially good for reducing air conditioning costs in the South, with its high summer temperatures.

Solar panels provide a way for homeowners to generate some of their own electricity. Solar photovoltaic (PV) panels are thin wafers of silicon that are connected within a glass panel or frame and mounted on a roof. When the sun hits the PV cells, the electricity produced can be used immediately, stored in batteries for later use, or sent to the utility power grid. Each PV system on the zero-energy homes has a power rating of about two kilowatts and produces 20 to 32 percent of the electricity used by the home.

Homeowners may receive credits on their utility bills for electricity generated through a TVA program called Green Power Switch Generation Partners. The cost of the PV systems in 2002 was $22,000, and by late 2004 that had declined to under $14,000. The price should continue to come down over time. Because the solar system requires a house with a southern exposure, many existing homes aren’t good candidates for the systems. But builders will have to begin considering energy-efficiency features if more consumers demand that they be incorporated into their new homes.

Promoting energy efficiency

TVA promotes energy efficiency through programs such as energy right®, Green Power Switch®, and Green Power Switch Generation Partners®.

Offered in cooperation with local power companies in the Valley, energy right provides information and incentives that encourage energy efficiency through quality construction, better insulation, and high-efficiency heat pumps and water heaters in new and existing homes.

Green Power Switch allows consumers to buy electricity produced by wind, solar systems, and methane gas. Homeowners pay $4 per month for each 150-kilowatt-hour block of renewable energy. Businesses buy amounts based on their monthly energy use.

GPS Generation Partners program provides incentives for the installation of solar and wind generating facilities. Consumers sell the electricity they produce to TVA.

energy right Main New Homes Heat Pumps Water Heaters

Weekend Project: How to Build Your Own Cheap, Simple Solar Oven :
Source: http://www.chelseagreen.com
We got a great response to our post “Cheap “Sun in a Box” Solar Cooker Wins Climate Change Prize” from earlier today. It seems a lot of people are into solar oven cooking!

Cindy

The sun is an incredibly powerful source of energy. That’s why TVA is using photovoltaic panels to transform solar energy into usable electricity.

When rays of sunshine strike a solar panel, they give some of the electrons inside it more energy, a process that creates an electrical current.

How much power are we generating? Check the data on daily power output at TVA’s solar generating sites. (If you don’t see yesterday’s data, reload the page while holding down the Shift key.)

Learn more here.

Wind turbines use the momentum of moving air to quietly turn large blades that are attached to the shaft of an efficient electric generator.

TVA’s wind power site is on Buffalo Mountain near Oak Ridge, Tennessee. In 2004, TVA greatly expanded its wind generating capacity when it added 15 very large turbines to the three original, smaller turbines at the site. Wind energy is now a major contributor to Green Power Switch. Learn more about the wind turbines here.

Looking at the current price of fossil fuel-based electricity, it is quite impractical to convert into solar energy system. However, with the growing concern on the state of the earth, there is really a need to find other means of energy aside from what power plants are using right now. Where do you place yourself?

Whether you are an advocate of clean energy or simply care about where your finances go, looking at the pros and cons of residential solar energy system will help you decide on whether to convert or not.

Pros

Solar energy is free. Did you know that the earth absorbs 174 pettawatts of solar radiation? This means that we have more than enough source of free energy to power every house in the world. Unfortunately, most of our energy is still drawn from oil, gas and coal. But in recent years, there is a steady increase of demand for alternative and renewable energy like solar power. It is estimated that the demand for alternative sources of energy will increase by 53% between 1999 and 2020.

Solar energy is clean, renewable and sustainable. Because the energy created from the sun’s rays does not produce byproducts like those from fossil fuel power plants (sulfur dioxide, nitrogen oxide, mercury or carbon dioxide), it does not contribute to pollution. Accordingly, the increase in the use of solar energy and other alternative forms of energy will decrease the demand for greenhouse gases-producing power plants.

The price of photovoltaic cells is steadily decreasing. The demand for solar panels has risen by 57% in the United States in 2007 and is steadily increasing on a monthly basis. The increase in demand results to the improvement of solar technology as a whole. The prices of photovoltaic cells have declined on the average of 4% every year over the past 15 years.

Solar panels can be installed on most rooftops, eliminating the problem of finding a suitable place for installation. Solar panels require little or no maintenance. The original photovoltaic cells technology is used for most satellites orbiting our earth today which are not maintained at all. Many solar panel manufacturers give 25 to 40 years warranty on their products.

Because most areas of the country receive a substantial amount of sunlight throughout the year, solar panels can be installed anywhere.

Many states in the country give tax credits and rebates to households who want to install solar energy system. Check with your state government the cost of these incentives.

Cons

While the prices of PV cells are in constant decline, the cost of installation is substantially high compared to the current electric cost. But the good thing is, after your initial cash out, you don’t have to pay every month on electric bills for the rest of your life.

On areas cities and areas with heavy pollution problem, solar energy may not work as fine. Weather can also affect the efficiency of solar energy. If it is raining, overcast weather or if there is a hurricane, the solar panels’ efficiency is decreased.

You are only producing energy during day time.

These are general pros and cons you might encounter when considering the conversion to solar energy system. It would be best if your decision is based on location, cost, budget, rebates, tax credits and practicality.