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Power - Photovoltaic - 80 kW / Canada
Case study assignment
An electric utility wishes to investigate the effectiveness of using grid-connected PV for peak load shaving. To do this, they will build a photovoltaic system of 80 kW peak output. You have been hired by the utility to prepare a study of the financial viability of the proposed system. They do not expect this system to be competitive with present utility rates, but are interested in determining how the system performs and how much it will reduce summer peaking demands on the utility.
The utility wants you to determine the price that would have to be paid for the electricity generated by the photovoltaic system in order for it to achieve a 10 year simple payback period. They are also interested in the possibility of selling the greenhouse gas (GHG) offset from this installation and want you to determine the impact of credits for avoided CO2 on the simple payback.
Site information
The site, located in Toronto, Ontario, Canada, has unrestricted solar exposure; the array can be oriented due south. The array slope will be selected to maximise annual energy generation. The high-quality monocrystalline modules will feed their output onto the grid via an inverter.
Financial information
Typical financial figures for the analysis are provided by the utility: inflation of 2.5%, fuel cost escalation of 5.0%, debt ratio of 60%, debt interest rate of 8.5%, discount rate of 9%, and a debt term of 10 years. The utility does not pay income tax. Feasibility study, development and engineering costs are expected to be about 10% of the total project costs. The system is expected to last for 25 years.
Assume that the PV system will be displacing a natural gas power plant. For GHG calculation the utility assumes that the value of avoided CO2 emissions will be around $25 per tonne of CO2 equivalent.
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
In 1991, Ontario Hydro decided to build and monitor a grid-connected photovoltaic demonstration system. The project was part of a research and development partnership with the Bloorview MacMillan Centre and the provincial and federal governments. The Canadian Electrical Association later joined the project by sponsoring the performance monitoring of the system. The objectives of the demonstration were to investigate the efficiency and cost-effectiveness of PV components and to provide data on the extent to which PV can reduce the utility's summer peak electricity loads. Three 25 kW PV sub-arrays were installed on the roof of the Hugh Macmillan Rehabilitation Centre in the first year of the project; in the fourth year of the project a 5 kW PV system with its own inverter was installed on a nearby covered walkway. The grid-tied system, located in Toronto, Ontario, Canada, continues to operate year-round.
System description
The peak output of all four installations is 80 kW. Each of the three sub-arrays is composed of modules from a different manufacturer; the individual module sizes vary from 45 to 242 watts peak output. The modules are connected in strings with output voltage from 260 to 350 VDC. Each sub-array is connected to its own inverter; the three inverters, with outputs of 25 to 35 kW AC, come from three different manufacturers.
Different PV array mounting structure designs were utilised to determine their cost-effectiveness. The mounting structure for the first sub-array was installed in a way that required penetrating the roof membrane of the building. This was found to be expensive and risked roof leakage. Later designs eliminated the roof penetration by using concrete slabs to hold down the PV array. The slabs were easier to install and more cost-effective. The fourth array, of 5 kW, was built as a canopy over an entranceway and has a welded steel support structure.
Lessons learned
The electricity market across Canada is in transition, moving from regulated monopolies toward deregulated competitive markets. This provides challenges as well as opportunities for renewable energy sources. The cost of electrical power from rack-mounted PV arrays is substantially more than central grid electrical power. Architecturally integrated PV arrays, new PV technologies, green power incentives, carbon and other emission credits and environmental legislation will all improve PV's competitiveness with other forms of electricity generation. The demonstration of grid-connected PV systems is an important part of the evolution of the electricity production industry and necessary for PV product design, and regulatory and electrical code development.
Photos
Rehabilitation centre - Photovoltaic - Hugh Macmillan, Ontario, Canada Photo 1
Rehabilitation centre - Photovoltaic - Hugh Macmillan, Ontario, Canada Photo 2
References
Case study assignment
An electric utility wishes to investigate the effectiveness of using grid-connected PV for peak load shaving. To do this, they will build a photovoltaic system of 80 kW peak output. You have been hired by the utility to prepare a study of the financial viability of the proposed system. They do not expect this system to be competitive with present utility rates, but are interested in determining how the system performs and how much it will reduce summer peaking demands on the utility.
The utility wants you to determine the price that would have to be paid for the electricity generated by the photovoltaic system in order for it to achieve a 10 year simple payback period. They are also interested in the possibility of selling the greenhouse gas (GHG) offset from this installation and want you to determine the impact of credits for avoided CO2 on the simple payback.
Site information
The site, located in Toronto, Ontario, Canada, has unrestricted solar exposure; the array can be oriented due south. The array slope will be selected to maximise annual energy generation. The high-quality monocrystalline modules will feed their output onto the grid via an inverter.
Financial information
Typical financial figures for the analysis are provided by the utility: inflation of 2.5%, fuel cost escalation of 5.0%, debt ratio of 60%, debt interest rate of 8.5%, discount rate of 9%, and a debt term of 10 years. The utility does not pay income tax. Feasibility study, development and engineering costs are expected to be about 10% of the total project costs. The system is expected to last for 25 years.
Assume that the PV system will be displacing a natural gas power plant. For GHG calculation the utility assumes that the value of avoided CO2 emissions will be around $25 per tonne of CO2 equivalent.
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
- The greenhouse gas emission credit has very little effect on the financial viability of this system, largely because the system is so far from being cost-effective compared with cheap grid electricity.
- In the emission analysis, the transmission and distribution losses for the photovoltaic system are one-half those of the base case. This reflects the proximity of the building loads to the photovoltaic array; the base case electricity is generated outside of the city and thus has higher transmission and distribution losses.
Results
In 1991, Ontario Hydro decided to build and monitor a grid-connected photovoltaic demonstration system. The project was part of a research and development partnership with the Bloorview MacMillan Centre and the provincial and federal governments. The Canadian Electrical Association later joined the project by sponsoring the performance monitoring of the system. The objectives of the demonstration were to investigate the efficiency and cost-effectiveness of PV components and to provide data on the extent to which PV can reduce the utility's summer peak electricity loads. Three 25 kW PV sub-arrays were installed on the roof of the Hugh Macmillan Rehabilitation Centre in the first year of the project; in the fourth year of the project a 5 kW PV system with its own inverter was installed on a nearby covered walkway. The grid-tied system, located in Toronto, Ontario, Canada, continues to operate year-round.
System description
The peak output of all four installations is 80 kW. Each of the three sub-arrays is composed of modules from a different manufacturer; the individual module sizes vary from 45 to 242 watts peak output. The modules are connected in strings with output voltage from 260 to 350 VDC. Each sub-array is connected to its own inverter; the three inverters, with outputs of 25 to 35 kW AC, come from three different manufacturers.
Different PV array mounting structure designs were utilised to determine their cost-effectiveness. The mounting structure for the first sub-array was installed in a way that required penetrating the roof membrane of the building. This was found to be expensive and risked roof leakage. Later designs eliminated the roof penetration by using concrete slabs to hold down the PV array. The slabs were easier to install and more cost-effective. The fourth array, of 5 kW, was built as a canopy over an entranceway and has a welded steel support structure.
Lessons learned
- Reliability issues were only encountered with the inverters; all other components have been trouble-free.
- For a grid-connected system in Toronto a general rule of thumb is "one watt of peak PV power will produce one kilowatt hour of electricity per year." This is typical of a mid-latitude, non-maritime climate.
- Cost reduction in every area of design and installation is critical, but especially in the array mounting structure design.
- Integrating the PV modules such that they take the place of some building components (i.e. roofing) is an important step towards future PV system cost reduction.
- Cost-effectiveness of grid-connected PV systems in areas served by large grids requires significant PV array cost reduction, integration with building designs and/or changes in utility charges.
- One of the goals of this installation was to investigate the ability of the PV system to shave building loads and achieve a "capacity credit." Data from the installation shows that during times of peak load in the summer, the array can be credited with a peak reduction capability of about 25% of its nominal capacity. Other studies have found much higher capacity credits for PV systems installed on grids where the peak load is due to air-conditioning. Peak electrical loads, which coincide with hot days requiring air conditioning, do not always coincide with days of peak insolation; thus the peak power of the array is not necessarily available during peak summer utility conditions. In addition the array temperatures on hot days lower the array output.
The electricity market across Canada is in transition, moving from regulated monopolies toward deregulated competitive markets. This provides challenges as well as opportunities for renewable energy sources. The cost of electrical power from rack-mounted PV arrays is substantially more than central grid electrical power. Architecturally integrated PV arrays, new PV technologies, green power incentives, carbon and other emission credits and environmental legislation will all improve PV's competitiveness with other forms of electricity generation. The demonstration of grid-connected PV systems is an important part of the evolution of the electricity production industry and necessary for PV product design, and regulatory and electrical code development.
Photos
Rehabilitation centre - Photovoltaic - Hugh Macmillan, Ontario, Canada Photo 1
Rehabilitation centre - Photovoltaic - Hugh Macmillan, Ontario, Canada Photo 2
References
- Drewes, Per, "Personal communication," Sol Source Engineering, 2000.
- Drewes, Per, Hugh Macmillan Rehabilitation Centre, Sustainable Energy Systems, 1995.
- Lapp, Steve, "Personal communication," SGA Energy, 2000.
- Ontario Hydro Technologies, SED Case Study.
