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Photovoltaic (PV) Solar Information
Photovoltaic System Overview

Photovoltaic (PV) systems are used to convert sunlight into electricity. They are a safe, reliable, low-maintenance source of solar electricity that produces no on-site pollution or emissions. PV systems incur few operating costs and are easy to install on most Canadian homes. PV systems fall into two main categories — off-grid and grid-connected. The "grid" refers to the local electric utility's infrastructure that supplies electricity to homes and businesses. Off-grid systems are installed in remote locations where there is no utility grid available.

PV systems have been used effectively in Canada to provide power in remote locations for transport route signaling, navigational aids, remote homes, telecommunication, and remote sensing and monitoring. Internationally, utility grid-connected PV systems represent the majority of installations, growing at a rate of over 30% annually. In Canada, as of 2009, 90% of the capacity is in off-grid applications; however, the number of grid-connected systems continues to grow because many of the barriers to interconnection have been addressed through the adoption of harmonized standards and codes. In addition, provincial policies supporting grid interconnection of PV power have encouraged a number of building-integrated PV applications throughout Canada.

With rising electricity costs, concerns with respect to the reliability of continuous service delivery and increased environmental awareness of homeowners, the demand for residential PV systems is increasing

 
PV System Components

The most critical component of any PV system is the PV module, which is composed of a number of interconnected solar cells. PV modules are connected together into panels and arrays to meet various energy needs, as shown in Figure 1. The solar array is connected to an inverter that converts the Direct Current (DC) generated by the PV array into Alternating Current (AC) compatible with the electricity supplied from the grid. AC output from the inverter is connected to the home's electrical panel. Various AC and DC disconnects are installed to ensure safety when working on the systems.

pv components

Figure 1 — Components of a PV array

 
PV Metering

BC Hydro has developed a Net Metering Tariff – rate schedule 1289, which was approved by the BC Utilities Commission (BCUC) on May 31, 2004 and assigned an effective date of March 10, 2004. The tariff has been designed for residential and commercial customers who wish to connect a small generating unit using a "BC Clean" (as defined by the B.C. government) energy source to the BC Hydro distribution system. When customers with their own generation facilities are approved to participate in Net Metering, BC Hydro installs a bi-directional meter for this program.

http://www.bchydro.com/planning_regulatory/acquiring_power/net_metering.html

The following are pictures of a grid tie system Wizards installed on the Kyoto House in Nanaimo as demonstration system. We went through the net metering process with BC Hydro and therefore we can offer assistance to other homeowners wanting to set up net metering their alternative home energy system.

pv metering_a

pv metering_b

 
PV Backup Power

With systems configured as in Figures 2, the system shuts down during power outages. In such a case, inverters are designed to sense the outage and automatically disconnect all power going to the utility meter as a safety requirement to protect utility service employees that may be working on the power lines. So even though you have a PV system, it would not be available during power outages. In order to have backup power, you need to add a battery bank. The whole domestic electrical load is too large to be entirely powered, but some inverters have the capability to continue powering an emergency sub-panel that can be used to provide power to critical loads (e.g. refrigerator, security systems, etc.) in the case of a power outage, as depicted in Figure 43. In addition to a battery bank, this configuration requires a charge controller that is able to effectively manage the batteries charging from the PV system, to ensure their optimal performance and extend their life expectancy. This system is more costly and loses some of the efficiency advantages of a battery-less system.

pv backup_a
Figure 2 — Net-metering PV system configuration

pv backup_b

Figure 3 — Net-metering PV system configuration with emergency backup

 
PV Off Grid Options

The following are pictures of an off grid system for a shed.

pv offgrid_a

pv offgrid_b

 
PV Evaluating Solar Electricity Generation Potential

The first step in evaluating the potential of solar electricity for your home is a site assessment. PV modules are extremely sensitive to shading. Cells within a PV module and PV modules within an array are often connected in series. Think of these cells as forming a long chain, and the amount of current flowing through the chain is limited by the weakest link, i.e. the shaded cell or module. The shaded cell or module will act as a resistor. For example, if one PV module in an array of 20 modules is completely shaded, it can reduce the output power of the entire array by 100%. In addition, given that the module will be acting as a resistor stopping the current flow, it will heat up to the point where it can become damaged.

Therefore, when evaluating different locations to mount a PV array, a shading analysis needs to be performed that will identify when and where shading will occur taking into consideration that during the winter months the sun is lower in the sky and tall objects, such as trees and buildings, 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. However, chimneys and other rooftop projections need to be considered in the shading analysis. Also, the future mature height of nearby trees should be used in the evaluation instead of current tree heights.

Properly aiming modules due south with an appropriate tilt will maximize the solar energy that the PV array collects; however, small variations of up to 15° in orientation or tilt will not significantly affect performance. As a general rule, a tilt angle equal to the latitude of the site will maximize yearly performance. Reducing the tilt by 15° does not affect performance significantly (see Table 1); however, a lower tilt will result in more snow accumulation in the winter. At higher angles, snow generally melts off on its own. At lower angles, snow can accumulate, reducing the power produced in the winter. However, given that most of the yearly output is produced outside winter, snow accumulation will not drastically reduce the annual performance of the system.

In order to assist in assessing the PV generation potential across Canada, Natural Resources Canada developed Photovoltaic potential and solar resource maps of Canada that give an estimated PV electricity production for over 3500 Canadian municipalities. The maps and tables provided present monthly and annual electricity generation per kilowatt of installed PV. As shown in Table 2, Canadian cities have a good solar potential, compared to many cities worldwide. One of our least sunny locations, St. John's, has more solar potential than cities in Germany and Japan, which are the world leading countries in solar electricity generation.

Table 1 — Yearly PV potential (kWh/kW) at varying tilts

All south facing

Yearly PV potential (kWh/kW)

Latitude tilt -15°

Latitude tilt

Latitude tilt +15°

Vertical, 90° tilt

Regina

1355

1361

1295

1055

Toronto

1173

1161

1095

801

Vancouver

1026

1009

939

717

St. John’s

946

933

879

686

 
PV System Sizing

In off-grid PV system applications, the PV array and associated battery banks must be carefully sized to be able to meet the load demands through periods with the lowest solar availability. In grid-connected applications, the presence of the grid eliminates the need to closely match the system size with the year-round electrical loads. For net-metered systems where the utility does not pay for excess electricity generation, the estimated annual solar electricity generation should be less than or equal to the annual electricity consumption as there is no financial benefit to generating more electricity than you need. For systems with a battery bank serving an emergency sub-panel, the battery bank must be sized factoring in the size of the emergency electrical loads, the PV system size, and how long emergency backup power is needed.

Sizing of grid-connected PV systems can be approached in a number of ways depending on your objectives which could include:

  • To maximize PV generation for a given budget;
  • To offset your yearly purchased electricity;
  • To offset a portion of your family's carbon footprint;
  • To completely take advantage of available unshaded south-facing roof area;
  • To take advantage of a government or utility incentive.
Table 2 — Yearly PV potential of major Canadian cities and major cities worldwide

Major Canadian cities and capitals

Yearly PV potential
(kWh/kW)

Major cities worldwide

Yearly PV potential
(kWh/kW)

Regina (Saskatchewan)

1361

Cairo, Egypt

1635

Calgary (Alberta)

1292

Capetown, South Africa

1538

Winnipeg (Manitoba)

1277

New Delhi, India

1523

Edmonton (Alberta)

1245

Los Angeles, U.S.A.

1485

Ottawa (Ontario)

1198

Mexico City, Mexico

1425

Montréal (Quebec)

1185

Regina, Canada

1361

Toronto (Ontario)

1161

Sydney, Australia

1343

Fredericton (New Brunswick)

1145

Rome, Italy

1283

Québec (Quebec)

1134

Rio de Janeiro, Brazil

1253

Charlottetown (Prince Edward Island)

1095

Beijing, China

1148

Yellowknife (Northwest Territories)

1094

Washington, D.C., U.S.A.

1133

Victoria (British Columbia)

1091

Paris, France

838

Halifax (Nova Scotia)

1074

St. John's, Canada

933

Iqaluit (Nunavut)

1059

Tokyo, Japan

885

Vancouver (British Columbia)

1009

Berlin, Germany

848

Whitehorse (Yukon)

960

Moscow, Russia

803

St. John's (Newfoundland and Labrador)

933

London, England

728

Source: Natural Resources Canada. (2007). Photovoltaic potential and solar resources maps of Canada. Retrieved February 1, 2010, from https://glfc.cfsnet.nfis.org/mapserver/pv/rank.php?NEK=e

 
PV Panels

The three most common types of solar cells are distinguished by the type of silicon used in them: monocrystalline, polycrystalline and amorphous. Monocrystalline cells produce the most electricity per unit area and amorphous cells the least. If you want to maximize solar electricity generation for a given area, then you should select the most efficient monocrystalline PV panels you can afford. If, on the other hand, your goal is to cover a given area at the lowest cost, then you may wish to buy amorphous panels. If you are concerned with maximizing your solar electricity generation for the lowest cost, then it is best to look at the cost-effectiveness of a panel regardless of its technology by examining its cost per rated production:

pv calc

For example, you want to compare the cost-effectiveness of a 160-watt PV panel from manufacturer A selling at $800, to a 60-watt PV panel from manufacturer B selling for $350. In this case, the more expensive panel from manufacturer A is more cost-effective at $5/watt compared to $5.83/watt for the other panel. Other factors should also be considered, such as the quality of the product. Good quality PV panels have 20- to 25-year warranties, have gone through testing evaluations and bear the appropriate certification labels. Also, some PV panels might be more expensive, but may also be more easily installed and thus less expensive overall. As discussed in the next section, some PV panels are designed to act as roofing tiles or shingles. Although they might be more expensive on a $/watt basis, you also need to factor in the avoided cost of shingles or other roofing material.

 
PV Inverter Consideration

Once the PV array is sized, the size of the inverter is determined to maximize the performance of the system. If you plan to expand your PV system in the future, you may wish to oversize the inverter in order to be able to meet the additional demands of the larger system. Adequate wall space to mount the inverter and other associated components is also required in the utility room or next to your electrical panel. 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 1.2 m x 1.2 m (4 ft. x 4 ft.) space. Some inverters are designed to withstand harsh conditions and can be mounted on an exterior wall, therefore not requiring any interior wall space. Alternatively, each PV module can be fitted with its own micro-inverter eliminating the need for one large inverter and minimizing the impacts of shading on the performance of the overall PV array.

 
PV Battery Bank

If the system has batteries, then a battery enclosure that is vented and protected against freezing will be necessary. Car batteries are not optimal for PV systems as they are designed to deliver a high current for a short period, whereas backup batteries for household applications need to deliver a relatively continuous current over extended periods. Special deep-discharge batteries are best suited. Certain types of deep-discharge batteries release small quantities of hydrogen when being charged and should be kept in a ventilated enclosure, well away from open flames or sparks. Consult your PV or battery dealer to determine the size of battery bank you need, and the installation and venting requirements for your chosen battery system.

 
PV System Installation

When it comes to installing PV panels on your house, there are a number of mounting options available.

 
Standard PV Panels Installed on Racking System

Standard PV panels can be mounted together on racking systems that fit on a typical roof (see Figure 9). PV systems convert 5% to 20% of the incident solar energy into electricity, a small portion is reflected, and the rest gets converted into heat. Without dissipating this heat, PV panels heat up and their efficiencies start to decrease. To address this, a small air space is typically left between the PV panels and the roof to allow for air circulation to help cool the PV panels.

It is best to select a racking system designed for roofs and to follow the manufacturer's installation specifications. All roof penetrations for both the mounting hardware and electrical equipment need to be carefully sealed to avoid any water penetration in the future. PV systems can also be mounted vertically on a wall, but will produce less electricity. If you do not have sufficient south-facing roof space but have a large yard, there are a number of pole-mounting options available.

If you are installing a PV system on an existing roof, you may wish to replace the existing shingles, if they have only a few years of life remaining. You do not want to have to take off the PV system shortly after its installation in order to replace the underlying roof. If you are installing a PV system on a new roof that is covered under warranty, you should ensure that adding a racking system with roof penetrations will not void your warranty. Adding a PV system on top of an existing roof can help extend its life, as the PV system will shelter the roof from the elements.

 
Integrating PV Into New House Construction

If you are in the process of designing a new house or doing major renovations, you may want to consider installing a PV system, or at least preparing your house to be "PV ready." You have an opportunity to substantially reduce costs and increase system performance. Although you may not yet be ready to invest in a PV system, the fact is that electricity prices will continue to rise while concerns about the reliability of the utility supply and the environment, combined with the decreasing cost of PV systems, will make solar electricity much more viable in Canada in the future.

While doing this preparation work, you may also wish to consider making your home "solar ready" for both PV and solar domestic hot water systems. Preparing your house to be solar ready now costs approximately $300 to $400 but can save thousands of dollars in the future. Natural Resources Canada has identified the following five basic requirements to make a home solar ready:

  1. A roof location of suitable size, pitch and orientation;
  2. Labelled conduits from the mechanical room to the attic area below the future PV location;
  3. Extra plumbing valves and fittings on the water heater (for solar hot water systems);
  4. An electrical outlet at the planned solar tank location (for solar hot water systems); and
  5. Construction plans that indicate the future component locations.

Orienting the house on the building lot to maximize its solar exposure and installing a roof with the correct solar pitch can maximize the performance of the PV array. Alternatively, if the lot does not permit a house to be oriented south, consider a roof shape that will have a south-facing area. Landscaping features, such as trees, should be considered when preparing the site — removing trees or moving the house site slightly can make a significant difference in available solar radiation. Remember that trees can grow a couple of feet per year and mature tree heights should be considered when determining shading potential. Although trees can have a detrimental impact on PV system performance, they can offer other benefits such as summer shading, reducing heat island effect, providing a windbreak, adding privacy, improving air quality, providing wildlife habitat that must also be considered. By carefully selecting the variety of trees and their location, you can enjoy the benefits of trees without shading your PV system.

Wires should be installed before interior walls are enclosed, as this will reduce installation time and hide unsightly conduits. Conduit runs through walls, for battery enclosure cables, battery vents, etc., should be done at the time of construction. It is far less expensive to put conduit runs in place when installing the foundation walls than to have to drill holes later. As solar systems generate low-voltage DC power, the system wires are generally larger than normal house wiring. Minimizing the distances of wire runs is an effective method of reducing costs and increasing system efficiency.

 


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