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Power - Photovoltaic - Industrial - 3.1 kW - Off-grid / Canada
Case study assignment
As the technical services manager of a telecommunications company with several remote transmitter sites, you want to explore the potential cost savings of adding photovoltaics to diesel genset/battery power systems. This type of system, used to power remote telecommunications equipment, stores the electricity from a diesel genset in a bank of lead-acid batteries. Adding a photovoltaic array to the existing system will reduce the fuel and maintenance required by the diesel genset. Your company's remote, off-grid sites are accessed by helicopter, so this will result in considerable savings. You decide to determine, at a pre-feasibility level, the system cost and annual rate of return on investment before you submit a request for project funding.
Site information
The site is located in Labrador, near Goose Bay, Newfoundland, Canada. South-facing locations are available for the PV array. The site is accessible by helicopter all year or by snowmobile in winter. The cost of travel and accommodation during the design stage is moderately expensive due to the remote location. Presently, two 10 kW diesel gensets charge a 48 VDC lead-acid battery bank of 3,385 Ah. The batteries and the genset are maintained at 25 ºC by a heating system on a thermostat.
The electric loads at the site are given in the table. All loads are DC and operate continuously.
Case study assignment
As the technical services manager of a telecommunications company with several remote transmitter sites, you want to explore the potential cost savings of adding photovoltaics to diesel genset/battery power systems. This type of system, used to power remote telecommunications equipment, stores the electricity from a diesel genset in a bank of lead-acid batteries. Adding a photovoltaic array to the existing system will reduce the fuel and maintenance required by the diesel genset. Your company's remote, off-grid sites are accessed by helicopter, so this will result in considerable savings. You decide to determine, at a pre-feasibility level, the system cost and annual rate of return on investment before you submit a request for project funding.
Site information
The site is located in Labrador, near Goose Bay, Newfoundland, Canada. South-facing locations are available for the PV array. The site is accessible by helicopter all year or by snowmobile in winter. The cost of travel and accommodation during the design stage is moderately expensive due to the remote location. Presently, two 10 kW diesel gensets charge a 48 VDC lead-acid battery bank of 3,385 Ah. The batteries and the genset are maintained at 25 ºC by a heating system on a thermostat.
The electric loads at the site are given in the table. All loads are DC and operate continuously.
Financial information
The number of site visits for refuelling and maintenance will be reduced by the addition of PV to the existing genset/battery system. The existing system consumes about 4,200 litres of fuel per year. A helicopter can transport about 1,000 litres of fuel to the site per trip. In addition to these refuelling visits, each year the existing system requires approximately fifteen maintenance visits. You assume that the number of site visits required for maintenance is proportional to the number of hours that the genset operates; this, in turn, is proportional to fuel consumption. The price rate for the helicopter is $1,000/hr and each helicopter round trip takes three hours. Diesel fuel at this remote location costs $1.00 per litre.
Typical 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%, debt term of 10 years and a 25 year project life. The company pays income tax at a rate of 42.6%. The photovoltaic system can be depreciated using the declining balance method at a rate of 30%.
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
Newtel (now part of Aliant) operates 15 telecommunication transmitters at remote sites in Newfoundland that have no grid power. In the past, the electricity for these systems was provided by diesel gensets that charged lead-acid battery banks. Maintenance and refuelling was very expensive, since many of the sites could be accessed only by helicopter. In fact, the annual cost of helicopter flight time was much greater than that for diesel fuel.
Over the past few years, photovoltaic arrays have been added to the existing systems. This reduces the fuel consumed by the genset, and, more importantly, the number of refuelling and maintenance visits required. The PV systems have therefore produced more savings through reduced charges for flying time associated with genset maintenance than through reduced fuel consumption.
The operators have a design philosophy of keeping the PV systems simple, as the cost savings are created by reduced diesel maintenance. Their experience in creating simple, effective PV-hybrid systems is now being marketed to other telecommunications companies internationally.
Newtel has 15 PV-Diesel hybrid sites now and estimates savings of approximately $60,000 per site due to reduced maintenance, helicopter fees and fuel usage. The simple payback is less than 3 years for some of these systems.
System description
The typical site has a maximum electrical load of about 1 kW peak and energy requirements of about 21 kWh daily. Electricity is stored in 24, 2 VDC deep-cycle lead-acid batteries of 3,385 Ah capacity each. The battery string voltage is 48 VDC, the standard in the telecommunications industry. Peak power of the PV array is 8.5 kW. Two 10 kW diesels provide power whenever the PV array's output is inadequate. The basic operating strategy is to let the PV array and batteries power the system until the batteries are at a predetermined lower voltage limit, at which point the diesel gensets are started. The diesel generators may fully charge the batteries or may be shut down early depending on projected weather conditions and other factors.
The equipment shelter is heated by an oil-fired furnace that still requires significant quantities of fuel to be delivered by air. The oil-fired furnaces are necessary to keep the diesels warm so that they can start when required.
Lessons learned
The cost of operating remote sites requiring electrical power can be reduced significantly with PV-genset hybrid systems. The reduction in costs associated with maintenance site visits is a major factor in the financial viability of these hybrid systems. Payback periods for the PV array and associated controls of around two years are possible. As control systems further evolve and become more reliable, PV-genset hybrid systems will be optimised to reduce engine maintenance, increase battery life and improve system autonomy.
Photos
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 1
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 2
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 3
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 4
References
The number of site visits for refuelling and maintenance will be reduced by the addition of PV to the existing genset/battery system. The existing system consumes about 4,200 litres of fuel per year. A helicopter can transport about 1,000 litres of fuel to the site per trip. In addition to these refuelling visits, each year the existing system requires approximately fifteen maintenance visits. You assume that the number of site visits required for maintenance is proportional to the number of hours that the genset operates; this, in turn, is proportional to fuel consumption. The price rate for the helicopter is $1,000/hr and each helicopter round trip takes three hours. Diesel fuel at this remote location costs $1.00 per litre.
Typical 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%, debt term of 10 years and a 25 year project life. The company pays income tax at a rate of 42.6%. The photovoltaic system can be depreciated using the declining balance method at a rate of 30%.
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 nominal battery capacity has been set to the nominal capacity of the existing battery bank. The days of autonomy was then adjusted such that the suggested nominal battery capacity matched the figure that had been entered. Thus, by working backwards, we see that the battery autonomy is approximately 5.5 days.
- The genset specific fuel consumption has been set to the figure that results in the base case power system consuming 4,200 litres of fuel per year.
- All transport costs have been lumped together and are included under balance of equipment.
- No periodic costs for battery replacement have been included, since these should be the same regardless of whether or not the power system includes PV.
- The annual credit accounts for reduced charges for helicopter flying time. It is assumed that base case power system would require an average of 15 maintenance and 4.2 refuelling visits per year. Each visit costs $3,000 in helicopter fees. Thus the total cost is $57,600 without PV. Adding PV reduces fuel consumption. If refuelling and maintenance visits are reduced proportionately, this results in savings.
- Note that the reduction in the costs for genset maintenance itself - as opposed to associated flight time - have not been included. This would make adding PV look even more attractive, but since the internal rate of return is already in excess of 100%, this hardly seems necessary.
Results
Newtel (now part of Aliant) operates 15 telecommunication transmitters at remote sites in Newfoundland that have no grid power. In the past, the electricity for these systems was provided by diesel gensets that charged lead-acid battery banks. Maintenance and refuelling was very expensive, since many of the sites could be accessed only by helicopter. In fact, the annual cost of helicopter flight time was much greater than that for diesel fuel.
Over the past few years, photovoltaic arrays have been added to the existing systems. This reduces the fuel consumed by the genset, and, more importantly, the number of refuelling and maintenance visits required. The PV systems have therefore produced more savings through reduced charges for flying time associated with genset maintenance than through reduced fuel consumption.
The operators have a design philosophy of keeping the PV systems simple, as the cost savings are created by reduced diesel maintenance. Their experience in creating simple, effective PV-hybrid systems is now being marketed to other telecommunications companies internationally.
Newtel has 15 PV-Diesel hybrid sites now and estimates savings of approximately $60,000 per site due to reduced maintenance, helicopter fees and fuel usage. The simple payback is less than 3 years for some of these systems.
System description
The typical site has a maximum electrical load of about 1 kW peak and energy requirements of about 21 kWh daily. Electricity is stored in 24, 2 VDC deep-cycle lead-acid batteries of 3,385 Ah capacity each. The battery string voltage is 48 VDC, the standard in the telecommunications industry. Peak power of the PV array is 8.5 kW. Two 10 kW diesels provide power whenever the PV array's output is inadequate. The basic operating strategy is to let the PV array and batteries power the system until the batteries are at a predetermined lower voltage limit, at which point the diesel gensets are started. The diesel generators may fully charge the batteries or may be shut down early depending on projected weather conditions and other factors.
The equipment shelter is heated by an oil-fired furnace that still requires significant quantities of fuel to be delivered by air. The oil-fired furnaces are necessary to keep the diesels warm so that they can start when required.
Lessons learned
- Diesel fuel savings are significant with the PV-Diesel hybrid but the major financial benefit of the hybrid system for these sites is the reduced need for expensive genset maintenance visits.
- PV system and its associated controls should be kept simple in order to minimise maintenance requirements; reducing the number of maintenance trips results in significant cost savings.
- Remote monitoring of the system and its components - especially the batteries - facilitates trouble-shooting and lowers costs.
The cost of operating remote sites requiring electrical power can be reduced significantly with PV-genset hybrid systems. The reduction in costs associated with maintenance site visits is a major factor in the financial viability of these hybrid systems. Payback periods for the PV array and associated controls of around two years are possible. As control systems further evolve and become more reliable, PV-genset hybrid systems will be optimised to reduce engine maintenance, increase battery life and improve system autonomy.
Photos
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 1
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 2
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 3
Telecommunication - Transmitter - Photovoltaic - Remote, Newfoundland, Canada - Photo 4
References
- Lapp, Steve, "Personal communication," SGA Energy, 2000.
- Sheppard, Wayne, "Personal communication," Newtel Communications, 2000.
