Solar technologies use the sun's energy and light to provide heat, light, hot water, electricity, and even cooling, for homes, businesses, and industry.   According to the International Energy Agency, integration of solar and energy conservation in homes can reduce consumption by 75-90%.  There are already incentives for North Carolina residents to use solar energy to power their homes.  A list of tax credits and other incentives for green upgrades can be found here.  If the Town of Chapel Hill could get residents to adopt this technology, it could greatly reduce the overall carbon dioxide emissions for the town.

The following information from the U.S. Department of Energy’s website on Energy Efficiency and Renewables provides descriptions of the different kinds of solar technologies.

Solar Technologies

Photovoltaics (PV)

    Photovoltaic solar cells, which directly convert sunlight into electricity, are made of semiconducting materials. The simplest cells power watches and calculators and the like, while more complex systems can light houses and provide power to the electric grid.

Passive Solar Heating, Cooling and Daylighting

    Buildings designed for passive solar and daylighting incorporate design features such as large south-facing windows and building materials that absorb and slowly release the sun's heat. No mechanical means are employed in passive solar heating. Incorporating passive solar designs can reduce heating bills as much as 50 percent. Passive solar designs can also include natural ventilation for cooling.

*See the bottom of this page for our consolidated information on passive solar technologies.

Concentrating Solar Power

    Concentrating solar power technologies use reflective materials such as mirrors to concentrate the sun's energy. This concentrated heat energy is then converted into electricity.

Solar Hot Water and Space Heating and Cooling

    Solar hot water heaters use the sun to heat either water or a heat-transfer fluid in collectors. A typical system will reduce the need for conventional water heating by about two-thirds. High-temperature solar water heaters can provide energy-efficient hot water and hot water heat for large commercial and industrial facilities.

    Many large commercial buildings can use solar collectors to provide more than just hot water. Solar process heating systems can be used to heat these buildings. A solar ventilation system can be used in cold climates to preheat air as it enters a building. And the heat from a solar collector can even be used to provide energy for cooling a building. (See EERE solar basics)

The following information from the North Carolina Million Solar Roofs Partnership provides an explanation of why solar power makes sense for North Carolina:

Energy Independence
    The energy in sunlight that falls on NC on an average day is sufficient to provide all of our state’s energy needs for a year. Diversifying our energy supply to capture our own resources protects us from supply disruptions and price fluctuations, and enables us to be more self-sufficient.

Local Job Creation
    Since the fuel (sunlight) for solar energy systems is free, the primary costs are for labor-intensive manufacturing, installation, and maintenance. The solar industry generates about 3,000 jobs for every $100 million of module sales. Instead of sending billions of dollars out of the state for fossil fuels, why not use some of that money to create jobs in North Carolina.

Investment in a Growing Market
    Solar power has become a multi-billion dollar industry, producing 742 megawatts in 2003 and growing at a brisk 30 to 35 percent per year. Venture capital firms and institutional investors are taking note as both established solar companies and nanotechnology startups compete in a fierce effort to bring down the costs of solar energy. Manufacturers are rapidly increasing production capacity as solar products are snatched up by the Japanese and Germans.

Clean Energy
    Solar energy systems do not pollute. They silently convert sunlight to electricity and/or heat day after day without emitting any carbon dioxide, nitrogen oxides, sulfur dioxide, mercury, or any of the other toxic wastes created by coal-fired and nuclear power plants. Over 60% of North Carolina’s electricity comes from coal, causing air pollution, health problems, environmental degradation, and greenhouse gases. Virtually all the rest comes from nuclear energy, with its unresolved problem of radioactive waste storage. Solar energy can play an important role in addressing problems such as ground level air pollution, global warming, mercury poisoning, and acid rain that affect our state.

Energy Security
    The practice of locating small energy generators near end users instead of having a few huge centralized plants is known as “distributed generation.” New technologies have made it practical, and clean renewable energy sources such as solar have made it safe. Distributed systems are less likely to have widespread failures, are relatively quick and easy to repair, and are more secure.
The implementation of solar energy in Chapel Hill residences and commercial building is a important step in reaching 60% reduction of carbon emissions.
 

    The Million Solar Roofs Initiative was established in 1997 with a goal of "seeing that 1,000,000 new solar energy systems are installed in the United States by 2010.  The MSRI is overseen by the United States Department of Energy, and operates as the combined effort of approximately 50 partnerships across the country.  Technologies covered under the partnerships involve photovoltaics (PV), solar water heating, transpired solar collectors, solar space heating and cooling, and pool heating.

    While working diligently to give the solar energy market a jumpstart, MSRI is also working more and more toward offering consumers an affordable clean-energy option.  They have successfully created many new U.S. high-technology jobs, and they are playing an important role in the effort to cut back carbon emissions.

    Several households and schools in Chapel Hill have already begun taking advantage of the trend, and already derive much of their energy from solar panels.  Click here for a detailed description of the green energy changes that have been implemented by R.D. Euzelle P. Smith Middle School here in Chapel Hill.

   In passive solar design, a building itself is a heat and light collector. By carefully planning the way that sunlight will strike a building, heating and cooling effects are possible without use of mechanical means. This is because the heat produced by the sun causes air to move in predictable ways. Since passive solar energy systems require no mechanical parts, they can lead to significant reductions in the electricity required to run the home.

Elements of passive solar design

    Passive solar designs require intimate knowledge of site-specific conditions, such as wind patterns, terrain and vegetation. The following guidelines are adapted from Edward Mazria’s The Passive Solar Energy Book (1979) and The Sustainable Building Sourcebook.

Orientation of Homes

    Because the collecting mechanisms of passive solar homes are the structures themselves, correct location, shape, and orientation are crucial.  Often, the most energy efficient shape for a passive solar building is one elongated along the east-west axis. During North Carolina summers, the sun warms the east and west sides of a building for long periods of the day. Therefore, making the east and west sides of the building shorter than the north and south sides minimizes the cooling requirements of the building. Similarly, in the winter, the sun spends much of the day warming the south side of the building (See Figure 1, below). However, buildings that face due south are at risk for collecting too much sunlight and overheating.

Figure 1. In the winter, the sun is low on the horizon, so a south-facing building will collect the most sunlight and heat. During the summer, the sun passes almost directly over the top of a building. Overhangs reduce the amount of light entering the building.
 
 
 

Recommended strategy: Orient new homes in such a way that will collect the amount of sunlight that will maximize heating in the winter and minimize heating in the summer.

Location of buildings on the site

    The south side of each building will receive the most light, heating, and cooling. The north side of each building will be the coolest and the darkest. The grounds to the north side of each building will be shaded.

Recommended strategy: Place garages, storage buildings, and other spaces that do not require ample sunlight in areas that will be shaded by the rest of the house or by elements of the terrain. Within the household structure, place bathrooms and hallways on the north side and living spaces on the south side. Kitchens placed on the west side of buildings will receive sunlight during dinnertime hours.

Windows

    The most important item to keep in mind about windows is that quite a bit of heat is lost through a window, especially when compared to a well-insulated wall. Care must be taken to avoid losing more heat through a window than is gained by letting the sunlight in; for obvious reasons, this problem is especially great at night. To reduce the percentage of heat lost, the south side of the building should have the only major window openings. The east, west, and especially the north side, which is the coldest and darkest side of the building, should only have small windows with double-glazing.
Overhangs should also be placed to block out the sun's rays during the summer.

Heat collection and distribution

    Heat in a passive solar system is stored in a thermal storage mass, which can be made of materials such as concrete, brick, adobe, and even water. The thermal mass, which can look like a large wall, is placed in a room on the south side of the building. There, the light that streams through the windows strikes the thermal mass and is stored. Throughout the day, at night, and on cloudy days, heat is slowly released from the thermal mass, into the surrounding areas. If openings are placed in the thermal mass, the heat will circulate throughout the house; the openings will also allow light into the central areas of the building

Ventilation and cooling

    One method of passive cooling in hot and humid climates is to use natural ventilation. In the Chapel Hill area, prevailing summer breezes are from the southwest.

Recommended strategy: Design houses that cool themselves as much as possible, while incorporating a back-up (mechanical) cooling system.  Operable windows are a possibility in houses that will likely contribute to resident satisfaction.

Tips for increasing the natural cooling qualities of the buildings are:

• Place operable windows on the south and west exposure to capture the Chapel Hill breezes.
• In rooms that can only have one window, place two widely-spaced windows instead of one large one.
• Design buildings with thermal chimneys, which encourage warm air to be drawn out of the buildings, pulling in cool air.

    The land surrounding the house can be integrated into the passive solar system. Although trees cannot be placed on the south side of the building, since even the bare branches of deciduous trees in winter block a significant amount of light, other trees can be useful. Not only can they block winter winds, reducing the house’s heating needs, they can serve as a conduit for summer winds, guiding them through the buildings and reducing cooling requirements.

Recommended strategy: Dense plantings on the west and northwest sides of the house will reduce the heat of the afternoon summer sun. On the north sides of buildings, evergreens will serve as a windbreak, keeping the structures warmer in the winter. Vines can give shade on walls and windows. Finally, trees that shade buildings can significantly reducing cooling costs.

Daylighting

    The use of skylights, windows, and other types of glazing can be used light rooms with the sun. Indoor light levels can be monitored automatically so that artificial lights are dimmed or brightened as needed.  Daylighting saves energy because artificial lights consume a significant portion of a building’s energy while giving off waste heat that increases cooling costs. Daylighting is already in use in several North Carolina schools.

How much energy will a passive solar design save?

    In office buildings, thirty to fifty percent energy reductions are feasible with a mix of energy conservation and passive solar design, according to the US Department of Energy.

    A study by the Federal Energy Management Program found that in 19 new and retrofitted passive-solar commercial buildings, on average, energy costs were 51 percent less than traditional buildings. The International Energy Agency’s Solar Heating and Cooling Program found that commercial passive solar buildings required only 10 to 35% of the energy of conventionally designed buildings.

    The Adam Joseph Lewis Center for Environmental Studies at Oberlin College, which incorporates a range of energy-saving measures, is projected to use 21% less than average for new construction.

    According to the Department of Energy, using passive solar designs can reduce heating bills as much as 50 percent.