SOLAR ELECTRIC SYSTEMS

Transcription

1 SOLAR ELECTRIC SYSTEMS Steve Clarke, OMAFRA, Engineer, Energy & Crop Engineering Specialist Don Hilborn, OMAFRA, Engineer, By-Products AUGUST 2009 This infosheet provides farmers and rural residents with options for solar electric systems, an explanation of current technology and a method to determine whether a solar electric system is right for you. Also included is information on incentive opportunities. SOLAR ELECTRIC SYSTEMS Solar electric panels, or photovoltaic (PV) panels, use semiconductors like silicon to convert sunlight directly into electricity. Unlike non-renewable sources of energy, solar energy is free, releases no emissions, and is available to everyone. PV panels have no moving parts and require little maintenance. Locating Your Solar Electric System PV panels should be located so that they have a clear southern exposure during peak sun hours, from 10 a.m. to 3 p.m. PV arrays work best when they are perpendicular to the direction of the sun s rays, tilted at an angle approximately equivalent to the latitude of the site. For southern Ontario, that is from 42º to 45º from flat. Fixed PV Systems can be mounted on the ground (Figure 1) or on any southern facing roof including barn roofs (Figure 2). Barns are typically designed for low human occupancy, and have different requirements for structural support. Adding solar panels can increase the structural load on the roof. Barns may also be structurally compromised due to animal generated Figure 2. Barn-roof mounted PV system. Courtesy of TDL Electronics. moisture and manure gases, or simply from age. If you have any doubt about the structural viability of your barn consult a structural engineer. Tracking PV Systems, mounted on the ground (Figure 3), will turn from east to west with the sun. This can increase the power production of PV modules by 25 per cent. However, for the panel to realise the benefits of the tracking system, it needs clear exposure on the eastern and western sides as well. Figure 3: Tracking unit mounted PV system. Figure 1. Fixed-tilt mounted PV system. Courtesy of Bill Kemp.

2 How Much Will it Cost? The cost of a PV system depends on a number of factors, including the surface area of panels, the type of PV cell, and how they are mounted. Installed, a fixed-tilt mounted, crystalline silicon PV system with an output of 10 kw/h typically costs $80,000. Mounting a similar system on a tracking device will increase the cost by several thousand dollars. A sunlight-concentrating system using triple junction PV cells, mounted on a tracking device, typically costs around $90,000 with installation. DESCRIPTION OF THE TECHNOLOGY from a square block of multiple crystal structures, rather than a single large crystal, minimizes waste during the production process but also results in a slight (1-2 per cent) drop in cell efficiency. Thin Film Solar Cells Thin film solar cells (Figure 5), rather than using an entire wafer of silicon, use a layer of semiconductor only micrometres thick, greatly reducing the cost of production. Currently, however, the efficiency of these cells is much less than the older crystalline varieties, yielding only 10 per cent in lab tests and 6 to 8 per cent in practice. The types of PV cells include: Single-crystal cells Poly-crystal cells Thin film cells and Triple junction cells Single-Crystal Cells Single-crystal cells (Figure 4) use a treated wafer of purified silicone, cut from one large crystal of the semiconductor. Dating back to 1955, they were the first form of photovoltaic technology. Because each wafer is cut from a single crystal, each cell is a uniform shade of dark blue. They are the most common and widely available form of photovoltaic cell, and in lab tests have converted up to 25 per cent of the sunlight they receive into electricity; in practice, however, their efficiency is closer to 16 per cent. Figure 5. Thin-film solar cell. Courtesy of the Muskegon Chronicle. Triple Junction Cells Triple junction cells (Figure 6) use layers of different semiconductors, including gallium, indium, germanium, and arsenic, to absorb a wider spectrum of the sun s light showing over 40 per cent efficiency in lab tests and over 30 per cent in practice, employed on orbiting satellites. Their relatively high cost limits their commercial application to smaller surface areas, upon which a system of mirrors may concentrate sunlight. Figure 4. Single-crystal solar cell. Courtesy of Day4 Energy. Poly-Crystal Cells Poly-crystal cells are made from the same material as mono-crystalline cells, but moulded into a square block of multiple crystal structures, rather than one large crystal. The different crystal structures in each wafer give the cell a variety of shades of blue, distinguishing them from the uniform single-crystal cells. Cutting wafers 2 Figure 6. Diagram of triple junction solar cell. Courtesy of Uni-Solar.

3 Many PV cells, connected in series, form a PV module; several modules attached to a frame form a solar electric panel. A panel can power a stand-alone system, simply and cost-effectively generating electricity away from the power lines, or it can be connected to the power grid, allowing the owner to sell the electricity generated. COMPONENTS OF SOLAR ELECTRICITY GENERATION The basic components of a PV system (Figure 7) include: PV modules which are a group of cells that generate an electric field by absorbing sunlight, resulting in direct current (DC) electricity. An inverter which converts the DC electricity from the PV modules into the alternating current (AC) electricity is used in the power grid and is required by most electrical appliances. Most PV systems in operation use one centralized inverter to convert electricity from multiple panels. These large inverters involve power loss and can be noisy. Microinverters, a new technology, attach directly to each solar module in the power system. STATE OF THE INDUSTRY Since they became widely available for commercial use in the 1970 s, technological developments have lowered the cost and increased the efficiency of solar electric panels. The further development of thin-film cell technology promises to greatly reduce the cost of producing PV modules. Their lower cell efficiency, however, means that it would take twice the area of thin film cells to generate the same power as a crystalline PV system. Though the cost of PV modules has declined by an average of 10 per cent a year for the past eight years, at an average of $4.50 per watt, it remains unlikely to be cost effective as a household s main source of electricity without subsidy. IS A SOLAR ELECTRIC SYSTEM RIGHT FOR YOU? One of the most important considerations before installing a PV system is the solar resource in your area, which is the measure of the sunlight that falls upon a specific area. For a solar resource map of Ontario, showing the annual potential energy in kilowatt hours produced per kilowatt of solar panel installed, tilted at an angle equal to the latitude of the site, see Figures 8 & 9. Though currently uneconomical as a main source of power without substantial subsidy, a PV system can be useful as a source of backup electricity. If connected to the power grid, it can be used to supplement your use of utility electricity, reducing your electric bills. Ontario offers net metering, a process that calculates your utility bill by subtracting the amount of electricity you produce through a PV system (or any renewable energy source) from the amount of electricity you consume. INCENTIVES Currently, the provincial government offers a rebate of the Provincial Sales Tax incurred in the purchase of any PV system. The prospective Green Energy and Green Economy Act will establish a Feed-in Tariff (FIT) program designed to make the adoption of renewable energy more economical. Sun PV Panel Inverter Breaker Panel Meter Utility Grid Solar Photovoltaic System Net Metering Figure 7. Photovoltaic power diagram. Courtesy of Go Solar. 3

4 See Table 1 for the proposed PV electricity purchase price for different system sizes. Table 1. Proposed FIT Price Schedule Technology Rooftop and Ground Mounted PV Rooftop Mounted PV Ground Mounted PV Output (kw) Price / kwh 10 $ $ $0.653 >500 $0.539 >10 $0.443 The options for ownership of a PV system are : Sole proprietorship - owner buys the components and contracts the installation of a PV system. Lease-to-own - companies offer complete solar packages for monthly payments. Lease (land or rooftop) - specialised companies offer to build, install, and operate a PV system on a suitable rooftop or stretch of land, paying the owner of that land a set amount from the sale of electricity generated. FarmEnergyOnline.com: Sample Business Plans for PV Systems Canadian Solar Industries Association Ontario Power Authority: Feed-In Tariff Program Natural Resources Canada: Solar Maps for Canada, REFERENCES 1. Ayoub, Josef, and Dignard-Bailey, Lisa. Photovoltaic Technology Status and Prospects Canadian Annual Report Natural Resources Canada, A special thank you to Graham Juneau for all of his hard work in creating this infosheet. Note: Information contained here, especially those dealing with prices is still being developed and subject to change. For more information on FIT visit ADDITIONAL RESOURCES Ontario Ministry of Agriculture, Food and Rural Affairs Ontario Sustainable Energy Association: Solar PV Community Action Manual Clean Air Foundation s Go Solar Website Integration of Renewable Energy on Farms (IReF) OMAFRA: Energy Conservation and Generation 4

5 Figures 8 & 9. Solar Resource Maps, Northern and Southern Ontario. Data Source: Natural Resources Canada. Courtesy of OMAFRA. 5

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