Reduced Energy Consumption
- PV panels do not reduce electricity consumption but they can generate electricity from sunlight that can offset purchased electricity use or be returned to the utility grid to offset use elsewhere.
Reduced Energy Costs
- Generates electricity without energy cost, once system is installed.
- Feed-in tariffs may be available from local utilities that pay for the electricity generated. This can help can offset installation costs, depending on the regional program and provincial programs.
- Alternatively, PV electricity generation may be “credited” against your consumption on your electricity bill.
Reduced Environmental Impact
- Lowers emissions from utility electricity generation.
- Reduces consumption of non-renewable fuel resources.
- Reduces requirements for increased generating capacity.
Figure 1 — The Photovoltaic Panels on the Roof of the Now House EQuilibrium™ Demonstration Home.
Photovoltaics (PV) convert sunlight into direct current (DC) electricity. PV Collectors are made up of thin wafers or films of silicone, known as ‘cells’ that are mounted in modules, or collectors. Cells in a module can be made from a variety of semiconductor materials (see table at right).
The modules are wired together in series or parallel, depending on the system design. A set of modules or collectors is called an array.
New ‘bifacial’ modules produce electricity on both sides of a module.
In building-integrated photovoltaics (BIPV), the collectors also function as roofing or glazing.
Efficiencies range from 10% to 20% for newer technologies, but 12% efficient is a typical efficiency for a wide range of PV materials.
PV systems are made up of the array of collectors, an inverter to change the electricity generated from DC to alternating current (AC) so that the electricity can be used in the house. Additional controls and monitors specific to the system design are commonly known as the ‘balance of system’ (BOS).
PV systems are silent and pollution-free in their operation, with no moving parts to service and maintain. Reliability and performance has been well established.
There are two primary system types, ‘grid-tied’ and ‘off-grid’.
Grid-tied systems can get a credit from the local utility for the electricity they supply to the grid. Policies dealing with connecting to the grid, net-metering requirements and feed-in tariff programs vary according to province or territory. When there is a power outage on the grid, a grid-tied system must shut down as well, to ensure the safety of the utility’s repair crews. Some grid-tied systems also have battery backup in case of power outages though this adds complexity and cost.
Off-grid, or stand alone, systems, are typically used in remote locations that are far from the established electrical grid. They require batteries for energy storage and a generator for back-up power during times when there is not enough solar gain, or when there is a heavy energy drain on the battery storage.
|Type of Semiconductor Material
|Monocrystalline Silicone = $$$
||12 – 15% efficient
|Polycrystalline Silicone = $$
||11 – 14% efficient
|Amorphous Silicone = $
||6 – 8% efficient
|Cadmium Telluride = $
||7 – 10% efficient
|Copper Indium Diselinide = $
||8 – 12% efficient
Figure 2 — Diagram of Different PV Array Systems
Net-metering PV system configuration
PV generated electricity is individually measured
Net-metering PV system configuration with emergency backup
In the net-metering photovoltaic (PV) system, the energy from the sun is transferred by the solar panel through a direct current to an inverter which converts the direct current to an alternating current and feeds it into the breaker panel for use in the home or to be fed out through the meter into the power utility grid system. The breaker panel can also accept power from the grid system if the solar system is not producing sufficient power for the home.
In the second diagram, the solar panel directs the power through a direct current to the inverter which sends it by an alternating current to an export meter to the power utility grid. A separate import meter brings power from the grid into the breaker panel for use in the home.
In the net-metering PV system configured with emergency backup, the photovoltaic panel sends the energy by a direct current to a charge controller before it is transferred to a battery tank for storage. The battery tank directs the energy to an inverter for conversion to an alternating current for transmission to the breaker panel, where it can be sent for use in the home or fed out through the meter to the power utility grid. The meter can accept power from the utility grid as well. This system also includes a feed from the inverter to an emergency subpanel with a critical load connection which keeps the home powered when the solar panel is not producing electricity but does not feed the power stored in the battery tank into the utility grid.
Figure 3 — PV System Inverters and Switchgear — from Harmony House EQuilibrium™ home
Figure 4 — PV Panels Being Installed on Racks Attached to a Roof — from Harmony House EQuilibrium™ Home
Figure 5 — PV Integrated Into Roof Shingles – from Avalon Discovery 3
- Professional installation is required.
- In remote sites, off-grid PV systems may be less costly than power lines.
- Arrays are sized according to their rated peak capacity: a 2 kilowatt system, for example, produces 2 kilowatts of electricity at its peak operation, that is, when the sun is shining directly on it, there is no cloud cover and there are no obstructions shading out any of the collector area.
- Appropriate rooflines and adequate roof areas are needed for roof installations.
- For maximum performance, all installations need unobstructed southern exposure and appropriate angle to the sun.
- PV modules lose efficiency when they are overheated, or when the sun is shaded by cloud or obstructions or when snow and ice covers the collectors.
- Utility rooms need to be larger in order to accommodate BOS equipment (inverters, etc.), especially if battery storage is used.
- Battery storage requires a separate vented space.
- Preplanning (wiring/attic access/adequate mechanical room space) can be a cost-effective way of allowing for future installation.
- A height restriction variance may be required if roof-mounted arrays have to be installed at an angle that would result in the top of the array being higher than the allowable building height.
- All electrical components and installations must meet national safety and approval requirements.
- Grid connect installations must meet utility requirements for connection.
- Battery storage requires maintenance.
- PV panel surfaces may need to be routinely cleaned.
What Does it Save?
PV systems do not save energy — they simply offset the amount of energy you may have to buy from the utility or they provide you with a credit on your utility bill or a stream of revenue under a feed-in tariff (FIT) program. The energy offset associated with a PV system is based on the contribution it makes by generating electricity. The contribution is dependent upon a number of factors including the efficiency of the equipment, the cost of electricity, the extent of regional feed-in tariffs, and the amount of electricity required by the house.
Assuming that there are no feed-in tariffs in place, here are two examples of the possible contribution of a grid-tied PV system installed on the roof of 2-storey house with an unobstructed south-facing roof, built in 1973, using polycrystalline modules rated at 13% efficiency.
A house of this age and style would typically have enough roof space to carry a 2kW system, which would offset some of the electrical use. A household that was aiming for Net Zero Energy status (producing as much energy as it consumes in a year), would require a system that was 5kW system or more, given current system efficiencies and typical energy use patterns. A 5kW system would require more roof space or another unobstructed location.
The chart shows the estimated contribution potential for the two sizes of PV systems described above. The two lines on the chart show the amount of energy required in a year using 24 kWh/day (8,750 kWh/year for a typical household) or 10 kWh/day (3,650 kWh/year, for a highly energy efficient household). The 5 kW system modelled would produce between 6,400 and 8,600 kWh/year, nearly enough to cover the electricity consumption in a typical 24 kWh/day household. The 2 kW system modelled would produce between 2,500 and 3,300 kWh/year, nearly enough to cover the electricity consumption in a household with the smaller energy load of 10 kWh/day.
Annual Energy Production
|2 kW System
|5 kW System
The information contained in this publication represents current research results available to CMHC. Readers are advised to evaluate the information, materials and techniques cautiously for themselves and to consult appropriate professional resources to determine whether information, materials and techniques are suitable in their case. The text is intended as general information only and project and site-specific factors of climate, cost, aesthetics, practicality, utility and compliance with applicable building codes and standards must be taken into consideration. A number of assumptions were applied with respect to fuel prices, water rates, costs of materials, equipment and labour, planning horizons, etc. Actual reductions in energy consumption and fuel savings will vary. Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. CMHC accepts no responsibility for consequences arising from the reader’s use of the information, materials and techniques herein.
Last revised: 2013