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Power - Photovoltaic - Industrial - 0.25 kW - Off-grid / Canada
Case study assignment
You have been hired by a telecommunications services provider to prepare a photovoltaic (PV) system pre-feasibility study on their behalf. As part of its telecommunications network, the firm operates 11 repeater towers for transmitting VHF radio signals in the northwestern part of Canada. These VHF repeaters consume a relatively small amount of electricity and are all located at remote mountaintop sites, typically accessible only by helicopter. Disposable potash batteries, which are replaced every 1 to 2 years, provide electricity to the repeaters. The potash batteries have proven to be less costly to use than conventional small diesel generators because of the high cost of transporting fuel and providing maintenance at these remote sites. They are still expensive, however, they must be replaced annually and due to their caustic nature they have special disposal requirements. The firm would like you to prepare a preliminary feasibility analysis to determine whether a PV system would be more cost-effective than the existing potash battery power supply.
Site information
The 11 sites are located in northern British Columbia and southwestern Northwest Territories, Canada; the nearest weather data are from Whitehorse, Yukon Territory, Canada. The total electrical load estimated by the telecommunications firm for the VHF repeater site is approximately 100 Wh/day (all equipment run on 12VDC). The total estimated daily load is assumed to be constant year-round. Given the firm's high reliability requirement for the site, the PV system design requires 30 days of autonomous operation by the PV system (i.e., operating off the batteries only) under worst-case conditions.
Financial information
Typical financial figures for the analysis are provided by the firm (income tax rate of 43.6%, inflation at 2.5%, debt ratio of 80%, debt interest rate of 8%, discount rate of 9% and a debt term of 10 years). The PV system capital cost is assumed to be depreciated using a straight-line method over the first 5 years of system use. The PV system is assumed to last 25 years. Subsequent PV battery bank replacements are required every 10 years. For the analysis, O&M costs are not considered, as they are relatively small and similar for both technology solutions. Potash battery systems are virtually maintenance-free while PV system maintenance is limited to a bi-annual inspection which can be performed as part of other regular trips to the site. The potash batteries are typically replaced each year at a cost of $9,800. The cost breakdown for this includes battery replacement costs, helicopter travel time, battery disposal costs and labour. The 100 Wh/day load equals 36.5 kWh/year. This works out to an astronomical electricity rate of approximately $270/kWh!
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 1994, NorthwesTel requested that the CANMET Energy Diversification Research Laboratory (CEDRL) prepare a preliminary feasibility analysis study for a typical VHF repeater power supply in northern Canada. The objective of the analysis was to determine if a photovoltaic (PV) system is a more cost-effective alternative to typical potash battery power systems used within NorthwesTel's service area.
The original study prepared by CEDRL demonstrated that the conversion of the power supply at NorthwesTel's VHF telecommunication site, from disposable potash batteries to PV, would be highly cost-effective. Partly as a result of this study, during 1996 and 1997 NorthwesTel, along with supplier SOLTEK Solar Energy Ltd., converted 9 of the 11 potash battery sites to PV. The PV systems have been operating without problem ever since.
System description
The PV systems consisted of a 0.2 kWp monocrystalline PV array (4 Siemens Solar SM-50H 50 Watt PV modules); a 1,150 Ahr absorbed glass mat, maintenance-free battery bank (GNB ABSOLYTE IIP); a SOLTEK PV-5 regulator; and a SOLTEK cm-50 module mounting kit.
The installed cost of the PV system, including helicopter time, averaged less than $14,000 (approximately $8,000 for the PV system components). When compared with the potash battery system, which had an average annual site operating cost of $9,800, the simple payback period for the PV systems was just over 1 year. NorthwesTel estimates that converting all sites to solar energy saves about $100,000 per year.
Lessons learned
In many cases telecommunication towers are located in remote areas, away from central-grid electricity. The traditional power solutions for these sites typically include diesel generators, thermoelectric generators and disposable batteries. It is now common for these more traditional remote power systems to be replaced or supplemented (in hybrid systems) by PV technology. In fact, PV is already meeting the power requirements of thousands of communication facilities around the world, having proven to be reliable and cost-effective.
Photo
Telecommunication - Repeater - Photovoltaic - Remote, British Columbia, Canada
References
Case study assignment
You have been hired by a telecommunications services provider to prepare a photovoltaic (PV) system pre-feasibility study on their behalf. As part of its telecommunications network, the firm operates 11 repeater towers for transmitting VHF radio signals in the northwestern part of Canada. These VHF repeaters consume a relatively small amount of electricity and are all located at remote mountaintop sites, typically accessible only by helicopter. Disposable potash batteries, which are replaced every 1 to 2 years, provide electricity to the repeaters. The potash batteries have proven to be less costly to use than conventional small diesel generators because of the high cost of transporting fuel and providing maintenance at these remote sites. They are still expensive, however, they must be replaced annually and due to their caustic nature they have special disposal requirements. The firm would like you to prepare a preliminary feasibility analysis to determine whether a PV system would be more cost-effective than the existing potash battery power supply.
Site information
The 11 sites are located in northern British Columbia and southwestern Northwest Territories, Canada; the nearest weather data are from Whitehorse, Yukon Territory, Canada. The total electrical load estimated by the telecommunications firm for the VHF repeater site is approximately 100 Wh/day (all equipment run on 12VDC). The total estimated daily load is assumed to be constant year-round. Given the firm's high reliability requirement for the site, the PV system design requires 30 days of autonomous operation by the PV system (i.e., operating off the batteries only) under worst-case conditions.
Financial information
Typical financial figures for the analysis are provided by the firm (income tax rate of 43.6%, inflation at 2.5%, debt ratio of 80%, debt interest rate of 8%, discount rate of 9% and a debt term of 10 years). The PV system capital cost is assumed to be depreciated using a straight-line method over the first 5 years of system use. The PV system is assumed to last 25 years. Subsequent PV battery bank replacements are required every 10 years. For the analysis, O&M costs are not considered, as they are relatively small and similar for both technology solutions. Potash battery systems are virtually maintenance-free while PV system maintenance is limited to a bi-annual inspection which can be performed as part of other regular trips to the site. The potash batteries are typically replaced each year at a cost of $9,800. The cost breakdown for this includes battery replacement costs, helicopter travel time, battery disposal costs and labour. The 100 Wh/day load equals 36.5 kWh/year. This works out to an astronomical electricity rate of approximately $270/kWh!
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 assignment states that a battery autonomy of 30 days is required. RETScreen was developed to model systems with battery autonomy of 1 to 15 days; whenever autonomy greater than 15 days is specified, the user should verify that RETScreen gives reasonable results.
- The battery capacity used is larger than that suggested by RETScreen. There are a number of reasons for this:
- RETScreen weather data is representative of a typical year; this telecom repeater must operate even under "worst-year" conditions of low solar radiation and low temperatures.
- The company places a very high value on system reliability. At some mountainous sites ice will accumulate on the photovoltaic modules for extended periods of time, requiring battery autonomy in excess of 30 days. Additional batteries have relatively little impact on the financial viability of the system, but can significantly improve reliability and heighten confidence.
- RETScreen does not account for the possibility of freezing the battery electrolyte at low temperatures. Using a larger battery reduces the risk of this happening.
- The cost of a simple feasibility analysis, which would not require a site visit, is included in the price of the equipment. The project costs are largely covered by the budget for potash battery replacement, so development costs are zero.
Results
In 1994, NorthwesTel requested that the CANMET Energy Diversification Research Laboratory (CEDRL) prepare a preliminary feasibility analysis study for a typical VHF repeater power supply in northern Canada. The objective of the analysis was to determine if a photovoltaic (PV) system is a more cost-effective alternative to typical potash battery power systems used within NorthwesTel's service area.
The original study prepared by CEDRL demonstrated that the conversion of the power supply at NorthwesTel's VHF telecommunication site, from disposable potash batteries to PV, would be highly cost-effective. Partly as a result of this study, during 1996 and 1997 NorthwesTel, along with supplier SOLTEK Solar Energy Ltd., converted 9 of the 11 potash battery sites to PV. The PV systems have been operating without problem ever since.
System description
The PV systems consisted of a 0.2 kWp monocrystalline PV array (4 Siemens Solar SM-50H 50 Watt PV modules); a 1,150 Ahr absorbed glass mat, maintenance-free battery bank (GNB ABSOLYTE IIP); a SOLTEK PV-5 regulator; and a SOLTEK cm-50 module mounting kit.
The installed cost of the PV system, including helicopter time, averaged less than $14,000 (approximately $8,000 for the PV system components). When compared with the potash battery system, which had an average annual site operating cost of $9,800, the simple payback period for the PV systems was just over 1 year. NorthwesTel estimates that converting all sites to solar energy saves about $100,000 per year.
Lessons learned
- On-site labour must be minimised to reduce costly installation time, for both the personnel and the helicopter. Pre-assembly of components and structure greatly contributes to this.
- A budget should include a contingency for adverse weather conditions that can inflate the cost of the project.
In many cases telecommunication towers are located in remote areas, away from central-grid electricity. The traditional power solutions for these sites typically include diesel generators, thermoelectric generators and disposable batteries. It is now common for these more traditional remote power systems to be replaced or supplemented (in hybrid systems) by PV technology. In fact, PV is already meeting the power requirements of thousands of communication facilities around the world, having proven to be reliable and cost-effective.
Photo
Telecommunication - Repeater - Photovoltaic - Remote, British Columbia, Canada
References
- Lapp, Steve, "Personal communication," SGA Energy, 2000.
- Martel, Sylvain, "Personal communication," CANMET Energy Diversification Research Laboratory, 2000.
- Martel, S., Leng, G. J. and Usher, E., Photovoltaic Power Supply for NorthwesTel's VHF Repeater Sites, report # EDRL 95-62 (TR), Energy Diversification Research Laboratory, CANMET, Natural Resources Canada, Varennes, August 1995.
- Egles, D. and Sugden, B., "Solar Power Systems for Mountaintop Radio Sites in Northern British Columbia," Proceedings of the Renewable Energy Technologies in Cold Climates '98 Conference, SESCI, Montreal, May 1998.
