Solar retrofits are solar energy applications for an existing home. The sun’s energy can provide space heating, domestic hot water, swimming pool heating and electricity for lights and appliances. Solar energy is an endless, environmentally friendly energy source. Using solar energy reduces utility bills.
How Can Solar Energy Be Used?
Knowing how we want to ue the energy will help determine the most effective manner of capturing the sun.
The first step in a solar retrofit is to list how energy is used in the home so that the most appropriate applications can be selected. The next step is to decide how much sun is available. The amount of solar energy available is dependent on time of year and location. In the winter the days are shorter and the sun is lower on the horizon, so the optimum collecting angle may vary. As one moves north the changes in the sun’s position are more pronounced, so the position of solar energy collectors will differ based on latitude and time of year for which the system is optimized.
Southeast to southwest is the prime solar orientation. Determining how much sun is available can be done by looking at what obstructions there are on the south side of the house. Trees, other buildings or natural features that cast shadows must be evaluated to figure out if or when they will cause shading at various times of the year. Local geographical conditions that affect solar availability must also be taken into account. Rural or urban location will also have some bearing on appropriate solar options to harness.
Deciding the Best Options For You
Conservation is the first step. For space heating applications that means draft-proofing the house and upgrading insulation where appropriate.
Renovations, repairs and maintenance offer opportunities to undertake significant upgrades, such as wall and ceiling insulation, extensive air sealing, and new windows. If windows are being replaced or added, the new units should be high performance windows with low-e glass, gas fill and insulating spacers.
Solar energy retrofit options may include the following means of harnessing the sun: active and passive solar, photovoltaics, wind, and geothermal.
Passive Solar Heating
Passive solar is the most cost effective approach to maximizing the use of solar energy for Canadian homes. Passive solar heating of buildings occurs when sunlight passes through a window. The term passive suggests that no additional mechanical equipment is used other than normal building elements. All passive solar applications use building elements such as walls, windows, floor and roof in addition to exterior building elements. Landscaping can be used to control overheating by proving summer shade. Landscaping can also provide windbreaks for winter winds, and surfaces that can create sun pockets and reflect and reflective surfaces for winter sun.
Once the heat is collected inside, a well-insulated airtight building envelope helps prevent heat loss and allows the sun to provide more of the heat needed by the house.
At Canadian latitudes, proper design of exterior overhangs and shading devices can be optimized to get maximum sun penetration in winter, when it is needed most, and shade for most of the walls during the summer, when it is least wanted.
When retrofitting an existing home, some significant changes to window areas may be desired. Building code regulations for fire safety may restrict the amount of south side windows that can be used if the south side is near a property line.
Solariums are one of the most common and effective approaches to gaining solar energy in an existing home. They can be an attached solarium, or integrated into the existing structure. To reduce temperature swings, and uncomfortable overheating, the solarium should include reasonable thermal mass to store heat. This can be an insulated concrete floor slab with an exposed concrete or tile finish, a masonry feature wall, and even double thickness drywall. Water tanks are an excellent heat storage medium, and they can sometimes be incorporated into the design.
To be effective as a solar collector, the solarium should be treated as an area that can be closed off from the main living area at night. Even high performance insulating glass has heat loss, so the large solarium glass area can lead to an uncomfortably cool space on a cold night.
Active solar systems use solar collectors and a pump or fan to distribute the sun’s energy. Active systems are best suited to heating water. The collector is a dark colour to absorb the sun’s energy and converts it into heat. Some collectors have glass covers, and collect solar energy year round. Unglazed collectors are typically used for seasonal applications such as swimming pools.
Domestic hot water needs can be met at least in part by active solar systems. In most cases solar energy will only provide some hot water needs in winter, but most of summertime needs. On average, it can provide 50 to 60% of annual domestic hot water needs. In most applications the solar system is used as a preheater for city or well water going to the conventional water heater
Outdoor swimming pools can be entirely heated by solar systems, thus eliminating the need for any auxiliary heater. These systems have a short payback. Plumbing can be connected directly to the pool’s filtration system, so there is minimum added equipment that has to be installed.
Photovoltaics (Solar Electricity)
Sunlight converted directly to electricity through solar cells is known as photovoltaic (PV) energy. Solar cells come in a variety of sizes and produce electricity as long as light shines on them. Solar cells used for electrical generation are a more sophisticated version of the solar cells used in calculators and other small household electronic devices.
PV cells generate direct current (DC). This means that to use PV generated electricity directly, DC appliances and lights must be used. These are used in recreational vehicles and on boats. Otherwise, to use conventional household appliances the power must be converted to alternating current (AC), which is the form supplied by utilities. This means that a solar electric system has to be designed to convert the power to AC.
Although prices have been reduced dramatically in recent years, and they are still dropping, a PV is system is expensive. They are cost effective for some special applications, especially in remote areas away from utility grids, where you have to generate your own electricity. Recreational vehicles and boats are other common applications.
Because of the higher initial cost of a PV system, a careful electrical load analysis must be done to establish required capacity. The efficiency of appliances to be supplied by the electric system must also be considered. It is usually more cost effective to reduce demand for electricity than to install a larger alternate system.
Geothermal or ground source heat pumps take advantage of the stored solar energy in the soil and natural water bodies. They rely on electricity, but provide the equivalent of 3x kW of electrical heat for every kW supplied. Because heat pumps are reversible, providing cooling and heating, they are a useful consideration in areas with substantial cooling loads.