Passive Solar

Passive Solar Heating includes a series of strategies to harness the warmth provided by the sun to heat your home in the winter. These strategies also account for warm weather in the summer and can help keep you house cool as well. Passive solar design uses your windows to collect solar energy, and your walls and floors to store and distribute solar energy to your house as heat. True passive design does not involve any electrical or mechanical components, such as an HVAC system, furnace, or fans. However, there are also ways to integrate fans or pumps into a passive solar design to make it perform better. Additionally, passive solar design strategies can also be used in conjunction with an HVAC system to reduce the load on your mechanical system and lower your energy bills.

Some components of passive solar design can easily be integrated into new construction with no cost implications, such as including south facing windows that collect solar energy in the winter with over hangs that block summer sun. Other strategies require added design elements, but can also be integrated into most homes and in some cases can be taken advantage of as living spaces. Passive solar design is also possible in existing homes as a retrofit, although your options will be somewhat limited by your home's orientation and other existing conditions.

Passive solar design works by moving heat from warm objects to cooler objects and by circulating air through your home. There are three ways that heat is transferred from warm objects in a passive solar home, conduction, convection, and radiation. Conduction is the movement of heat from one object to another through direct contact. Convection is the circulation of heat through liquids or gases (such as air) – warm air is lighter than cool air, so it tends to rise to the ceiling, while cool air sinks to the floor. Radiation describes how heat moves from warm objects to cool objects that are not directly touching by passing through the air – Different objects absorb and emit warmth at different rates, depending on the color and another material property called thermal capacitance. Materials that store heat – a critical component of passive solar design – are called thermal mass. Thermally massive materials include brick, concrete, stone, tile, and even water. The reason thermal mass is so important is that by storing heat and releasing it over a long period of time, it moderates temperature swings and preserves some of the warmth collected during the daytime for cool nights. Without thermal mass, solar energy will be released inside your home as soon as it is collected, which may make your home uncomfortably hot during the daytime (even in winter), but provided inadequate heating at night.

Successful passive solar design will include five elements: Thoughtful placement and square footage of windows (called an aperture or collector); a dark masonry surface, or absorber, to absorb heat; Thermal Mass to store heat that enters as solar energy; A distribution method to transfer heat to warm rooms in your home; and elements that can be used to control the amount of solar energy entering your home – this includes insulating shades that you can draw closed during the winter at night to prevent warmth collected during the daytime escaping, and it also includes overhangs or awnings that can block the high, hot summer sun and prevent overheating.

Active Solar

Active Solar heating systems take a fluid - such as air, water or an anti-freeze solution - heated in rooftop collectors and then distribute it either directly to rooms in your house or to a storage system for later distribution. These types of heating systems can be integrated with radiant floor heating, boilers with hot water radiators, absorption heat pumps and coolers, forced air systems.

Factors such as climate, type of collectors, and how energy-efficient your house is will determine how large the system must be. It may be cost-effective to supply up to 80% of your home's heating needs with an active solar heating system. If you are considering this type of system, you should also make sure your home is well sealed and insulated to maximize the effectiveness of the heating system. In most cases, a supplementary mechanical heating system will be required, but it will be much smaller and cheaper to install and operate than a full-capacity mechanical heating system.

Active solar heating systems require advanced, complex control systems that monitor the temperatures of the solar collectors and storage unit determine when the conventional backup heating system must be activated. A differential thermostat monitors the difference in temperature between the collectors and storage unit, which determines when fluid from the collectors can be distributed. Control systems range in cost, energy use, and complexity. In some cases, photovoltaic panels can be used to generate electricity to operate pumps or blowers in an active solar heating system. This initial investment can help you save on energy use in the long-term.

Photovoltaic Panels

Photovoltaic (PV) panels are a clean, emissions-free way to convert solar radiation into electricity. By installing PVs on your home, you can reduce or eliminate your reliance on utility-supplied electricity. PV systems can be connected to the electrical grid, or they can be installed as stand-alone systems with no tie to the grid. PV systems can be implemented in a retrofit by adding them onto a roof or wall, or designed to be integrated into the building form, known as Building Integrated Photovoltaic, or BIPV. Although PV panels will be more efficient and produce more electricity in clear, sunny weather, they can also be effective in cloudy conditions. They may not operate at maximum efficiency, but it could still be an option worth exploring if you are considering options for on-site generation of electricity.

PV panels can be mounted in a variety of arrangements. The solar cells will generate the most electricity when the panels are oriented at exactly a 90 degree angle from the rays of the sun that fall on them. As a result, PV panels that are mounted on a tracking device that rotates over the course of the day and throughout the year will generate the most electricity. However, this type of device can be expensive and may not be feasible in all cases. If you are mounted fixed PV panels, there are a few guidelines to follow. The panels should be mounted facing due south, or very close. The angle at which the panels are tilted will depend on your latitude and the time of year when you electricity needs are greatest – if your electric loads are higher in summer, the angle should be your latitude minus 15 deg; if your electric loads are higher in winter, angle should be latitude plus 15 deg.

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Geothermal Systems

Geothermal Systems take advantage of stable soil temperatures year-round to trade warmth with the ground in order to both heat and cool buildings. Even in climates with extreme weather conditions – both hot and cold – soil temperatures remain fairly constant and moderate just a few feet below the ground. Ground temperatures are cooler than air temperatures during the summer and warming than air temperatures during the winter, so a heat exchange unit can use this stable condition to both heat and cool your home.

Also known as Geothermal Heat Pumps or Ground Source Heat Pumps, these systems are made up of a loop of pipes that are buried in the ground, and a heat exchange unit. Water is passed through the pipes and through the ground. During hot summer weather, the water deposits heat in the ground and drops to the temperature of the soil before returning to the heat exchange unit. This cool water is then used to provide cool air to the house. During cold winter weather, cold water passes through the pipes picking up warmth as it makes its way back to the heat exchange unit. Then, rather than using a lot of energy to warm very cold air in order to heat the house, it only needs to warm air a small amount.

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Where Can I Get More Information?

U.S. Department of Energy