Solar Panels

Home

ICF

Heat Pumps

ECO-AIR

Tankless Water Heater

Solar Panels

Windmills

About

Solar Panels

Photovoltaics (PVs)

Photovoltaic or PV systems are devices used to convert sunlight into electricity. Photovoltaic systems are a safe, reliable, low-maintenance source of solar electricity. They have a life expectancy exceeding 40 years. They produce no pollution or emissions, incur few operating costs, and are easy to install on most Canadian homes. With rising energy costs and concerns with respect to the reliability of continuous service delivery, the demand for PV systems is increasing.

PVs can be used effectively in most homes, alone or in combination with other systems. PVs are ideal for homes or cottages which are located some distance away from utility power lines. Power line extensions typically cost $5,000 to $10,000 per kilometer. These “off-grid” applications make up the majority of solar-electric installations in Canada. However, PV systems are being increasingly used to provide electricity for homes that are connected to utility power. Internationally, utility grid-connected PV systems represent the majority of installations, growing at a rate of over 30 per cent annually.

The basic building block of a solar-energy generating system is called the solar cell built into a PV module. PV modules are connected together into panels and arrays to meet various energy needs.
Modules used for home power applications usually range between 75 to 120 watts, and measure about 0.6 m x 1.2 m (about 2 ft. x 4 ft.). Based on current module efficiencies, one square meter (10.7 ft.2) of solar modules generates about 130 watts in bright sunshine. A 100 watt PV module generates an average of about 400 watt-hours per day or 100 kWh annually in most populated regions of Canada.

House with a building-integrated photovoltaic roof (BIPV)

Off-Grid & Grid Connected PV Systems

Applications for PV systems fall into two main categories — off-grid and grid-connected. The “grid” refers to the local electric utility’s infrastructure that supplies energy to homes and businesses. Each system type is unique and often uses slightly varying equipment.

Off-Grid PV Systems

Off-grid does not necessarily mean being a great distance away from power lines. Many homeowners already use solar-powered patio and garden lights. These solar lights are miniature versions of PV systems that power off-grid or autonomous homes. In this type of system, the solar modules charge a battery, which in turn operates the electrical loads. Since PV modules generate direct current or “DC” power, a power conditioner called an “inverter” is used to operate normal household electrical equipment that requires “AC”, or alternating current power.

Components of a PV Array

Another type of off-grid PV system directly connects the solar module to an electrical load. Examples of this type of system include attic-ventilation fans, and agricultural and livestock water pumps. Solar attic fans are often a cost-effective option for homeowners when a power vent is required and when it’s costly to run a wire to the attic.

Off-grid homes rely on batteries to store the solar electricity for nighttime use and during periods of cloudy weather. In this type of application, the size of the solar array and the capacity of the battery bank are carefully sized to give optimum performance.

For homes that are off-grid, appliances that use a lot of electricity are usually taken off the PV system. House heating usually includes a combination of wood, propane and passive solar housing design, while water heating is often accomplished by using a combination of propane and solar domestic hot water heaters. High-efficiency refrigerators that can operate on solar are available; however, they tend to be expensive and many off-grid homeowners choose a propane refrigerator instead.

While a battery bank can store energy for short periods — typically three to seven days of “autonomous power” — there may be periods of cloudy weather when a back-up source is required. PV-hybrid systems combine a PV system with another power source such as an engine generator (gasoline, diesel or propane) or other renewable energy source such as a wind generator. This offers all the benefits of PV for low operation and maintenance costs, but also ensures a secure electricity supply. Hybrid systems can allow the size of the PV array and battery bank to be reduced, making the system more cost effective.

Grid-Connected PV Systems

The most popular type of grid-connected solar power is the “synchronous” system. The solar array is connected to a synchronous inverter that blends the PV generated electricity with grid power, after which the combined electricity is fed into the house to run the domestic energy loads. When the solar array generates more power than is required, the excess is fed out into the grid where other utility customers use this solar-generated electricity. The inverter in this system is very different from the one in the off grid system and must meet stringent utility guidelines.

Off-grid PV system with battery backup

Off Grid PV System

Off-grid PV system

The disadvantage of this system is that the inverter also shuts down in case of power failure, for example during a lightning or ice storm. Thus, the PV system cannot provide electricity if the power goes out. This is a utility safety requirement to protect utility service employees that may be working on the power lines.

A synchronous system with batteries allows the blending of a PV with grid power, but also offers the advantage of “islanding” in case of a power failure. A synchronous system automatically disconnects the utility power from the house and operates like an off-grid home during power failures. This system, however, is more costly and loses some of the efficiency advantages of a battery-less system.

System Design Issues

The first step in evaluating the potential of solar electricity for your home is a site assessment. PV modules are extremely sensitive to shading. Ten per cent shading of a module can reduce power output by 100 per cent. Generally, a good site will be free from shade from 9 a.m. through to 3 p.m. Year-round systems must take into consideration that during the winter months the sun is lower in the sky and tall objects, such as trees, cast longer shadows. In most cases, the ideal location for a solar array is on the roof of the house. This alleviates most shading concerns, and its large, flat surface makes mounting relatively easy. It also can reduce snow buildup in front of the modules.

Grid Syncronous

Grid-connected synchronous PV power system

Grid Battery

Grid-connected synchronous PV power system with battery backup

Properly aiming modules for direction and tilt will maximize the energy the solar array collects; however, small variations of up to 15° in direction or tilt will not significantly affect their performance. Solar modules should face true south and be tilted so that they are perpendicular to the sun during the month of highest energy demand for off-grid applications. For grid-connected systems, a solar array tilted for maximizing energy generation during the summer will tend to supply the highest annual energy output. Installations further north will have a higher tilt angle than systems in southern Canada. For example, the optimum summer tilt in Toronto is 30°, while in Edmonton it is 40°.

Once it has been determined that solar-generated electrical energy is feasible, it is necessary to estimate the home’s power and energy needs. This is a critical step for off-grid applications, as the homeowner will be relying on the solar system to provide all or most of the electricity. This step is less important for grid-connected systems as solar is being used to replace or supplement an existing source — the sizing in this case is often based on how large a system the homeowner can afford.

Energy efficiency and conservation are important measures when you generate your own electricity. It is far cheaper to save a kilowatt-hour than to produce one. Compact fluorescent lights and energy-efficient appliances will save significant sums of money when it comes to purchasing a PV system. While most homes in Canada use 20 – 30 kWh per day, energy-efficient homes often require only 8 – 12 kWh daily. A highly energy-efficient home may be able to be powered by a two-three kW solar array, while remote cottage systems typically range between 100 watts to 1.0 kW.

Adequate wall space is also required in the utility room or next to the load centre for the “solar power centre.” Small systems may only require a 0.6 m x 0.9 m (2 ft. x 3 ft.) wall area, while larger systems may require a 1.21 m x 1.21 m (4 ft. x 4 ft.) space. If the system has batteries, then a separate battery enclosure will be necessary. Batteries should be kept in an insulated enclosure where the temperature is maintained between 18° to 22°C (64° to 72°F) year around. The batteries should be kept well away from open flames or sparks as they release small quantities of hydrogen when being charged. Battery enclosures should be vented to the outside with an up-sloping vent pipe so that the hydrogen can escape. For most home-sized battery banks, a 5 cm (2 in.) diameter vent is adequate.

Grid-interconnected

Grid-interconnected PV power system with battery backup