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76 Expert Q&A

 
 
Q. What is solar electric energy?

Posted on August 2012

A. Solar electricity is energy converted directly from the sun into electricity. This conversion is done through solar cells, also known as photovoltaic or PV cells. PV modules are made up of individual PV cells and are joined together to form a PV array, which is used to generate electricity. The PV array is installed on a roof or in a sunny location to maximize the sun’s rays. When the sun shines on the array, the sun’s energy is converted into electric current that can be used to operate appliances and other household devices.

Once installed, a photovoltaic system requires little maintenance and can produce power for more than 20 years.

 
Q. What is solar thermal energy?

Posted on August 2012

A. The principle behind solar thermal technologies is the same one often used to brew tea in a jar outside on a hot summer day. The sun’s energy radiates to the earth and is captured in a jar of water. The water is warmed by this captured energy, and brews the tea. In the same manner, solar thermal energy can be used to heat water for household use.

A solar water heating system requires collectors (“the jar”) to absorb the sun’s energy and a storage system to hold the energy until it is needed. The collectors are large, flat panels that are most frequently mounted on a roof. The storage systems look and act like conventional water heaters. Pumps are also part of the system and are used to circulate the heated water.

A residential solar water heating system is usually designed to meet 50-80% of a home’s water heating requirements. Water heating typically accounts for about 14-25% of the average home’s utility bill.

 

A. The Department of Energy (DOE) estimates that by 2030, solid-state lighting (SSL), which is much more energy efficient and longer lasting, could reduce the annual U.S. electricity consumption by about 25 % (when compared to a scenario with no SSL on the market)–enough energy to illuminate 95 million U.S. homes. An emerging clean energy technology, SSL uses various forms of light-emitting diodes as illumination sources. SSL is expected to make a significant energy and environmental impact over the course of the next decade. By 2025, the DOE’s SSL Core Technology Research and Product Development SSL R&D Program hopes to have advanced solid-state lighting technologies that are much “more energy efficient, longer lasting, and cost-competitive” than conventional lighting technologies.

 

A. The most rigorous way to locate duct leaks is with a blower door or similar analysis performed by a professional. This analysis measures the magnitude of your duct leakage and identifies its location. Some companies offer ductwork sealing services with a follow-up blower door check to ensure duct leakage has been reduced to acceptable levels. A blower door is a special instrument used to measure air leakage in a building shell and its ductwork. The equipment consists of a temporary door covering which is installed in an outside doorway and a blower which forces air into or out of the building. The blower door measures how leaky the building and ductwork are, and can be used to find the location of the major leaks. Without a blower door, finding the leaks in the ductwork can be difficult since the ducts are often in hard to reach areas such as the attic or crawl space and the leaks are usually hidden from view by duct insulation.

 

A. The best way to reduce the need for cooling during the hot summer months is by keeping the sun out of the home. Begin as far away from the house as possible with shade trees, trellises covered with vines, or awnings. Pay particular attention to east and west facing windows. The sun is low in the sky as it rises and sets allowing its rays to penetrate deep inside the home and making it tricky to keep out. When allowed to enter the home through windows, this solar radiation can cause the inside temperature to rise as much as 20°F on a hot day. The most effective way to shade the home’s east and west windows and walls is to plant tall trees or plant vines on horizontal trellises. Be sure to use deciduous trees and vines because their leaves provide shade in summer, but they drop them in winter when the solar gain is appreciated. Awnings wider than the windows can provide shade, but even they are ineffective when the sun is very low in the sky and can enter the home right under the awnings. To further protect the home, whenever possible, locate porches and garages on east and west walls for additional shading. Shading large areas that can either reflect or retain and reradiate heat into the home like concrete patios and driveways is also helpful. Most homes have roof overhangs that sufficiently shade the windows. When replacing windows, it is preferable to look for high-performance windows with low-E glazing. They look perfectly clear, yet block out a large percentage of unwanted solar radiation. As you move closer to the home, measures tend to become less effective and more expensive to install. Inside the home, solar gain through windows can be reduced by installing drapes with light-colored linings or blinds that can reflect sunlight. Vertical blinds are particularly effective on east- and west-facing windows. Also, choosing lighter colors for roofs and walls to reflect sunlight will reduce heat gain.

 

A. The major difference between a furnace and a boiler is the medium used to distribute heat. Boilers use water or steam, while furnaces use warm air. Furnaces can heat the air with any number of sources, but the most common are gas, oil and electricity. There are two primary types of hot air systems: gravity and forced air. In gravity systems the air travels upward naturally because it is lighter than the surrounding cooler denser air. It travels through ducts into the home.

Forced air systems accomplish the same task, but use a fan to push the air. They also allow more flexibility than other systems. For one thing, humidifiers can be placed in the system to add moisture to the air and cooling units can be added to distribute cool air.

If you’re considering adding a cooling system to an existing forced air furnace, note that larger ducts are required for cooling than for heating. This is because there is less of a temperature difference in cold air so the system needs to move more air.

 

A. An Act to move the United States toward greater energy independence and security, to increase the production of clean renewable fuels, to protect consumers, to increase the efficiency of products, buildings, and vehicles, to promote research on and deploy greenhouse gas capture and storage options, and to improve the energy performance of the Federal Government, and for other purposes.

 

 

A. Attics should be ventilated year-round, to reduce the build-up of heat and moisture. In winter, attic ventilation expels moisture that might otherwise accumulate and deteriorate insulation or other building materials. Don’t be tempted to seal the vents to conserve energy. Sealing them could cause costly moisture damage. In summer, proper ventilation reduces roof and ceiling temperatures thereby lowering cooling costs and extending roof life. Attic heat, which would otherwise intensify, pouring unwanted heat down through the attic floor into the living area, will escape naturally if vent area is provided.

An unventilated attic can reach temperatures as high as 140°F, while allowing a path for natural ventilation lowers the temperature to a more manageable 90-100°F. Homes with poorly ventilated attics often have heat trapped in the insulation radiating into the living space late into the evening after the sun has set. Codes and practices vary, but you should plan on one square foot of free vent area for every 150 square feet of attic. A two-and-one-quarter-square-foot gable vent with louvers and screening would have one square foot of free-vent area. Free-vent area can be reduced by one-half if half of the vents are low-soffit vents and half are at least three feet off the attic floor.

One of the most effective ways to ventilate a roof is the combination of a continuous ridge vent along the top of the roof with soffit vents along the sides. This creates plenty of area for the temperature differential to form, allowing warmer air to exit at the highest point in the attic. Roof vents come in a wide variety of types, some turbine-style vents even spin. Studies show the effectiveness of passive vents is about the same whether they are stationary or moveable. Power vents will draw more air out of the attic, but any energy savings attributable to them must be tempered with the fact that they use energy to operate.

 

A. An air-to-air heat exchanger is the most common type of heat recovery ventilator. An air-to-air heat exchanger consists of two fans and a heat exchanger core enclosed in a box that is usually attached to both supply and exhaust ductwork. One fan expels indoor air while the other draws in outside air. Inside the heat exchanger both air streams pass through a lattice of small air passages made of metal, plastic, or even treated paper. The air streams do not mix, but travel through adjacent passages.

In winter, the warmth of exhausted air is transferred to the cold incoming air, while in summer, the coolness of the air conditioned exhaust air reduces the temperature of the hot incoming air. Air-to-air heat exchangers are usually found in fairly tight houses. Most are used in northern climates for heat recovery in the winter, where they recover as much as 80% of the heat from the outgoing air.

 

A. The purpose of an energy audit is to identify places in the home where energy is being wasted and prioritize the actions needed to fix them. The end result is intended to reduce the amount of energy the home needs to operate and keep occupants comfortable. Energy audits range from simple walk-throughs you can do yourself to more elaborate services performed by trained professionals. Which is right for you will depend on your situation, abilities and interest level.

If you own the home, there is a clearly defined benefit for your efforts. You’ll start saving money on your energy bills as soon as you identify and fix energy wasters. If you rent or lease, it’s a good idea to check with your landlord early on to see if the audit findings can be acted on. A landlord who pays the utility bills is more likely to invest in the process knowing that there will be savings through lower utility bills down the road.

If you are a tenant and pay the utility bills yourself, you’ll benefit immediately from no-cost and low-cost measures uncovered by an energy audit. Improvements requiring an investment in the building itself or its systems should be carefully evaluated since you don’t own them and won’t be taking them with you if you move to another property. The Internet has brought consumers many new conveniences and tools, including help evaluating your home’s energy use. Online calculators let you enter information about your home and appliances and compute your energy costs. Such calculators can be helpful as part of an overall energy plan to help you assess and analyze your best savings opportunities.

If you’d like to conduct a free in-home energy audit or online energy checkup, Georgia Power can help. Find out more.

 

76 Expert Q&A