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Power - Photovoltaic - Residential - 0.3 kW - Off-grid / Canada
Case study assignment
You operate a small business installing photovoltaic (PV) systems. The owner of a cottage that is roughly 0.5 km to 1 km from the nearest grid connection has asked you for a quotation on the cost of a photovoltaic system. Your client requests a detailed price quote and estimate of the energy produced by the system. The client would also like to know the distance from the grid at which the PV system becomes cost-competitive with grid extension.
Site information
The site is located in Huntsville, Ontario, Canada, at 44°30' north, and the Muskoka airport is the nearest weather data location. The cottage is occupied only during weekends and only during the months of May through September. During these months the electric loads at the cottage are presented in the table:
Case study assignment
You operate a small business installing photovoltaic (PV) systems. The owner of a cottage that is roughly 0.5 km to 1 km from the nearest grid connection has asked you for a quotation on the cost of a photovoltaic system. Your client requests a detailed price quote and estimate of the energy produced by the system. The client would also like to know the distance from the grid at which the PV system becomes cost-competitive with grid extension.
Site information
The site is located in Huntsville, Ontario, Canada, at 44°30' north, and the Muskoka airport is the nearest weather data location. The cottage is occupied only during weekends and only during the months of May through September. During these months the electric loads at the cottage are presented in the table:
The client does not wish to have a back-up generator. You design the system with sufficient battery autonomy to operate the loads for the entire weekend.
Financial information
Financial figures for the analysis are inflation of 2.5%, fuel cost escalation rate of 5.0%, debt ratio of 60%, debt interest rate of 8.5%, discount rate of 9%, and a debt term of 10 years. No income tax analysis is required. Installation of poles, wires, and a transformer for the grid connection in this location costs $10,000 per km. The connection fee for the grid is $17/month. The price of electricity is $0.08/kWh. The photovoltaic system is expected to last 25 years.
Since your company has installed a number of similar systems the estimated design time is only three hours; two additional hours will be required for a site visit. In your experience installation will take about 1.5 days. You estimate that the batteries will require replacement every 10 years.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
Results
Owners of an off-grid cottage located north of Toronto, Ontario, Canada, chose to supply their electricity needs with a photovoltaic (PV) system rather than grid extension or a gasoline generator. The cottage was 8 km from the electrical grid. Solar Power Systems of Tara Ontario was commissioned to design and install the system. In 1997 a 300 watt peak PV system was installed, with the cottage owner intending to expand the system at a later date; in the summer of 1999 a further 100 watts of PV modules were added. The cottage is occupied during weekends in the summer.
System description
The electrical loads at the cottage consist of a 1.5 kW deep well pump, 1.0 kW toaster, 125 watts of lighting, and a radio. Total energy consumption per day during the weekend is about 1.9 kWh of AC power. Six 50 watt Solarex PV panels were initially installed, and with the upgrade to 8 panels in the summer of 1999, the system has a nominal capacity of 400 watts. Energy is stored in eight 220 Ah Trojan T-105 flooded lead-acid batteries. A Prostar 30M charge controller, manufactured by Morningstar, manages battery charging. The Trace DR 2412 inverter is capable of supplying the surge of power required to start the well pump. Both the controller and inverter are sophisticated devices capable of managing battery charging and discharging so as to ensure long battery life.
Lessons learned
The cottage market is significant for small- and medium-sized PV system suppliers and installers. Grid extension is often too expensive and the clients, coming to their cottages to escape noise and pollution, seek to avoid generators.
Inverters, PV panels and associated PV BOS equipment continues to become more refined, reliable and cost-effective. These improvements make PV battery systems more cost and performance competitive with grid extension. The increasing cost of grid electricity - both in terms of energy and connection charges - and falling prices for PV will lead to further growth in this market.
Many suppliers now offer packaged "cottage kits" which are sold on the basis of the amount of energy they will typically supply in the summer months of cottage use.
Photo
Cottage - Photovoltaic - Off-grid, Ontario, Canada
References
Financial information
Financial figures for the analysis are inflation of 2.5%, fuel cost escalation rate of 5.0%, debt ratio of 60%, debt interest rate of 8.5%, discount rate of 9%, and a debt term of 10 years. No income tax analysis is required. Installation of poles, wires, and a transformer for the grid connection in this location costs $10,000 per km. The connection fee for the grid is $17/month. The price of electricity is $0.08/kWh. The photovoltaic system is expected to last 25 years.
Since your company has installed a number of similar systems the estimated design time is only three hours; two additional hours will be required for a site visit. In your experience installation will take about 1.5 days. You estimate that the batteries will require replacement every 10 years.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
- This project has an immediate simple payback period as the cost of grid extension ($10,000) that the cottage owner must pay to the local electric utility is higher than the initial cost of the PV system. Therefore, most of the financial feasibility indicators (e.g. IRR) are not required as the PV system is the least cost option on an initial cost basis.
- The inverter capacity of 2.4 kWAC has been chosen to ensure that adequate AC power is available to start the deep well pump, which requires a surge of current at start-up. It is unlikely that all loads in a cottage will operate simultaneously, and the inverter need not be sized to match the peak AC load.
- The nominal battery capacity has been sized to provide sufficient autonomy to operate the loads for the entire weekend. RETScreen's suggested nominal battery capacity is likely too low, for the reason explained in the online manual for that cell. The nominal battery capacity has been calculated using the "2/7" factor described in the user manual. This figure has been rounded to 220 AmpHrs, which happens to be the nominal capacity of a commonly available flooded battery.
Results
Owners of an off-grid cottage located north of Toronto, Ontario, Canada, chose to supply their electricity needs with a photovoltaic (PV) system rather than grid extension or a gasoline generator. The cottage was 8 km from the electrical grid. Solar Power Systems of Tara Ontario was commissioned to design and install the system. In 1997 a 300 watt peak PV system was installed, with the cottage owner intending to expand the system at a later date; in the summer of 1999 a further 100 watts of PV modules were added. The cottage is occupied during weekends in the summer.
System description
The electrical loads at the cottage consist of a 1.5 kW deep well pump, 1.0 kW toaster, 125 watts of lighting, and a radio. Total energy consumption per day during the weekend is about 1.9 kWh of AC power. Six 50 watt Solarex PV panels were initially installed, and with the upgrade to 8 panels in the summer of 1999, the system has a nominal capacity of 400 watts. Energy is stored in eight 220 Ah Trojan T-105 flooded lead-acid batteries. A Prostar 30M charge controller, manufactured by Morningstar, manages battery charging. The Trace DR 2412 inverter is capable of supplying the surge of power required to start the well pump. Both the controller and inverter are sophisticated devices capable of managing battery charging and discharging so as to ensure long battery life.
Lessons learned
- Off-grid cottages are an excellent application for PV power. Typical alternatives to photovoltaic systems are grid extension, fossil-fuelled generators, or propane-powered lights and appliances.
- Since most cottages are used only in the summer months, the PV systems can take advantage of the plentiful summer sun. Many cottages are used only on weekends, which allows for battery charging during the weekdays. Electrical loads are typically less than for homes occupied year-round since fewer appliances are used. These factors result in a much less expensive PV system than is typical for a year-round home.
- Systems should be designed such that increasing the number of PV panels does not require major changes in the balance of system (BOS) equipment. Adequate initial battery capacity for possible expansion of the PV array is also important.
The cottage market is significant for small- and medium-sized PV system suppliers and installers. Grid extension is often too expensive and the clients, coming to their cottages to escape noise and pollution, seek to avoid generators.
Inverters, PV panels and associated PV BOS equipment continues to become more refined, reliable and cost-effective. These improvements make PV battery systems more cost and performance competitive with grid extension. The increasing cost of grid electricity - both in terms of energy and connection charges - and falling prices for PV will lead to further growth in this market.
Many suppliers now offer packaged "cottage kits" which are sold on the basis of the amount of energy they will typically supply in the summer months of cottage use.
Photo
Cottage - Photovoltaic - Off-grid, Ontario, Canada
References
- Lapp, Steve, "Personal communication," SGA Energy, 2000.
- Kitto, Judy, "Personal communication," Solar Power Systems - Photovoltaic Supplies and Accessories, 2000.
