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Home My WebLink About2017 Diesel Published ArticleAn Alaska case study: Diesel generator technologies Nathan Green, Marc Mueller-Stoffels, and Erin Whitney Citation: Journal of Renewable and Sustainable Energy 9, 061701 (2017); View online: https://doi.org/10.1063/1.4986585 View Table of Contents: http://aip.scitation.org/toc/rse/9/6 Published by the American Institute of Physics Articles you may be interested in Preface: Technology and cost reviews for renewable energy in Alaska: Sharing our experience and know-how Journal of Renewable and Sustainable Energy 9, 061501 (2017); 10.1063/1.5017516 An Alaska case study: Electrical transmission Journal of Renewable and Sustainable Energy 9, 061702 (2017); 10.1063/1.4986582 Wind power project size and component costs: An Alaska case study Journal of Renewable and Sustainable Energy 9, 061703 (2017); 10.1063/1.4986579 An Alaska case study: Solar photovoltaic technology in remote microgrids Journal of Renewable and Sustainable Energy 9, 061704 (2017); 10.1063/1.4986577 An Alaska case study: Energy storage technologies Journal of Renewable and Sustainable Energy 9, 061708 (2017); 10.1063/1.4986580 An Alaska case study: Cost estimates for integrating renewable technologies Journal of Renewable and Sustainable Energy 9, 061709 (2017); 10.1063/1.4986581 An Alaska case study: Diesel generator technologies Nathan Green,Marc Mueller-Stoffels,and Erin Whitney Alaska Center for Energy and Power, University of Alaska Fairbanks, P.O. Box 755910, Fairbanks, Alaska 99775-5910, USA (Received 6 June 2017; accepted 26 September 2017; published online 8 December 2017) Diesel generators are the main source of electrical generation in remote Alaska communities; they also help to maintain grid frequency and voltage. In an analysis of key performance metrics for diesel generators in Alaska, we found that the size of the installed system directly affects capital costs, that is, larger systems are more cost-effective per kilowatt. However, appropriately sizing a system for a commu- nity is more cost-effective overall than signiﬁcantly oversizing the system. Capacity factors range from below 5% to over 25%. The low values are typically for diesel-hydroelectric hybrid systems, for which this measure is not entirely accu- rate. In addition, rural diesel plants may have low capacity factors since typically there are three to four generators in-house. These generators are sized so that one to two generators provide power at any given time; the remaining generators are available as backup. Generators of this size can be expected to operate for approxi- mately 60000–100000h, with larger engine blocks tending to have longer life- spans. An appropriately maintained generator operating for 35% of the time will last approximately 20 years, or 60,000 hours. The technology continues to see advances in power output, efﬁciency, noise reduction, and emission control. The shapes of combustion chambers in newer engines are designed to maximize the combustion rate of fuel, thus increasing output power and fuel efﬁciency. The common-rail fuel system can maintain high pressure from the fuel tank to injection, which allows for ﬁner vaporization of fuel and more complete combustion. Nitrous oxide can be reduced through exhaust gas recirculation and selective catalytic reduction. Control systems have also seen advancement. Mechanical control sys- tems have been slowly phased out in favor of electronic control systems, which allow for offsite monitoring of a system and reduction in the number of necessary service calls. Diesel generators in rural Alaska communities remain difﬁcult to maintain to the degree necessary for smooth operation. Additionally, supervisory control and data acquisition systems with remote control capabilities require con- tinuous Internet connection, which is not always available in rural communities. Published by AIP Publishing.https://doi.org/10.1063/1.4986585 INTRODUCTION In much of rural Alaska, as with other remote locations where microgrids serve a commu- nity, diesel generators are often used as the grid prime mover, meaning that they are responsi- ble for maintaining grid frequency and voltage. Due to the cost of diesel fuel, signiﬁcant energy cost savings revolve around reducing fuel consumption. The nameplate outputs of individual generators installed in rural Alaska vary from about 30kW to over 1MW. The best diesel gen- erator systems convert roughly 40% of diesel fuel energy content into electricity. The remaining fuel energy is converted into heat. Even in non-remote settings, microgrids (and diesel generators) are receiving increasing attention as insurance against power disruptions. According to the Electric Power Research Institute, outages alone are estimated to cost anywhere from $104 billion to $164 billion. As severe weather events are predicted to increase, the number of outages related to these events 1941-7012/2017/9(6)/061701/11/$30.00 Published by AIP Publishing.9, 061701-1 JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY 9, 061701 (2017) and their economic costs are expected to rise. In such systems, diesel generators can provide a backbone for general operation and other energy generation contributions. This review of diesel generator technologies in Alaska is a result of Alaska Senate Bill (SB) 138. In this bill, the Alaska State Legislature created an uncodiﬁed section of law entitled: “Plan and Recommendations to the Legislature on Infrastructure Needed to Deliver Affordable Energy of the State to Areas That Do Not Have Direct Access to a (proposed) North Slope Natural Gas Pipeline.” To support the Alaska Energy Authority (AEA) in its development of an Alaska Affordable Energy Strategy, the Alaska Center for Energy and Power (ACEP) con- tracted with AEA to document technology development needs speciﬁc to Alaska with regard to renewable and sustainable energy technologies. The intention was to determine what targeted, energy technology development solutions could be implemented in Alaska to make energy more affordable in the Alaska Affordable Energy Study area. While the focus was on technol- ogy research solutions, other factors such as logistics, labor, and training were also addressed. This review speciﬁcally explores the lifetime cost of diesel generation. The other reviews resulting from SB 138 address additional technologies as well as the integration of those tech- nologies with existing diesel systems to form cogenerating hybrid systems. Drafts of technology reviews were vetted by expert roundtables in late February and early March 2016. These reviews are not meant to be exhaustive discussions of energy technologies in Alaska or proper designs for each technology, and they should not be used as guides for the choice and installation of speciﬁc systems. As such, not all possible issues with power production and each technology are addressed. Data for each technology were collected from surveys and pub- lically available databases. Only completed projects, or projects with clearly reported data, were included in each technology analysis. These distinctions and descriptions of data sources are included in each technology review. METHODS Data were collected from public sources. Installation costs were gathered from project Financial Close-Out Reports at the Denali Commission Project Database website (2016). Operation and maintenance (O&M) cost data were collected from the Regulatory Commission of Alaska (RCA). The numbers for kilowatt-hours (kWh) generated were collected from Power Cost Equalization data at the Alaska Energy Data Gateway website (2016). When relevant, costs were adjusted for inﬂation using Consumer Price Index data listed on the Alaska Department of Labor and Workforce Development website (2016). DISCUSSION Capital costs Each of the projects evaluated for this review received a Rural Power System Upgrade (RPSU) grant to replace existing diesel generation that has reached the end of its operational lifetime. Many, but not all, of the grants included a heat recovery system, an intermediate fuel tank, and/or a distribution upgrade, but the RPSU reports do not provide a cost breakdown to discern those costs. Some projects were built in parallel with others, thereby reducing costs compared to scenarios that have separate project completions. The cost categories include freight, labor, materials, planning and design, administration and overhead, and others. A list of communities examined, along with installed capacities and comments about the scope of the RPSU projects, is shown in Table I of the Appendix. The scale of the installed system directly affects capital costs, as shown in Fig.1. Larger systems are more cost-effective per kilowatt although more expensive overall. Appropriately sizing a system based and current and projected growth or contraction of a community is necessary and more cost-effective overall than oversiz- ing the system beyond the community’s needs. 061701-2 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) Operation and maintenance Operation and maintenance (O&M) represent the cost to keep a generator operational throughout its expected life. Such costs include labor and materials for inspections, repairs, and other tasks but exclude the cost of fuel. A model was developed by the AEA and modiﬁed by ACEP to approximate O&M costs for three generator classes: 4 cylinders, 6 cylinders, and 8–16 cylinders. These categories generally correspond to rated power outputs of 60–150kW, 151–600kW, and 601–1300kW, respectively, although there is overlap. The three cost models are shown in Fig.2. The assumed maintenance intervals used in the model are shown in Table II of the Appendix. The duration of each maintenance task is based on manufacturer speciﬁca- tions and shown in Table III of the Appendix. In-house labor, which was assumed at $60/h, includes wages, beneﬁts, and overhead. Contracted labor was assumed at $120/h plus travel and per diem. Price escalation was not taken into account in these calculations. Daily inspections and oil changes were the dominant cost factors of O&M because these tasks must be done fre- quently. The total O&M costs for each size category were normalized by the assumed number of operating hours over the life of the engine: 60000h for 4- and 6-cylinder engines and 100000h for 8- to 16-cylinder engines. It was assumed that the generators were operating with a load factor that was 55% of nameplate capacity on average. The cost per kilowatt-hour, shown in Fig.2, decreases as the size of installed capacity increases because the load factor remains constant. However, for a given load, larger machines are more costly to operate (overall and per kWh), which illustrates the importance of right- sizing generators for the expected demand. FIG. 1. Capital costs (2014 $) of RPSU diesel systems normalized by installed capacity. Larger systems are more cost- effective per kW; however, appropriately sizing a system for a community is more cost-effective overall than signiﬁcantly oversizing the system. FIG. 2. Operations and maintenance costs per kWh from calculated models and RCA data. According to the model, O&M costs per kWh decrease as the generator size increases for a constant load factor (not a constant load). According to RCA data, O&M costs per kWh are nearly ﬂat for power plants ranging from 200 to 1500kW. 061701-3 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) The cost to operate a single generator does not necessarily scale with the cost to operate an entire powerhouse. Operations and maintenance cost data were collected from the Regulatory Commission of Alaska (RCA) for the communities seen in Table IV of the Appendix. The val- ues include personnel costs, routine O&M, generator repairs, and other operating expenses; they do not include ofﬁce expenses, debt, insurance, depreciation, interest, and other administra- tive costs. The values are plotted in Fig.2 along with the O&M cost model. The RCA data indicate that O&M costs are relatively ﬂat across different-sized plants as opposed to the O&M model, which indicates an inverse relationship. There may be factors not fully understood from the available dataset which contribute to power plant level O&M, causing the costs to differ from generator level O&M. Levelized cost of electricity (LCOE) The levelized cost of electricity (LCOE) was determined by dividing the expected total cost of a system over its lifetime by the expected total kilowatt-hours. To calculate lifetime kilowatt-hours generated, we assumed that the generators in each community operated for 60000h with an average load factor of 55% of nameplate capacity. The costs for a diesel pow- erhouse included fuel, O&M, and initial capital costs. Administrative costs were not included, as they were not tracked at the level of detail necessary to separate general utility administra- tion from speciﬁc diesel-related costs. Capital cost data were gathered from the Denali Commission and the Alaska Energy Authority RPSU projects. Regulatory Commission of Alaska data was used for O&M costs because the model discussed in the Operation and Maintenance section broke down when scaled from an individual generator to an entire power- house. The fuel costs were calculated by assuming an efﬁciency of 12kWh/gal of diesel and lower and upper cost boundaries of $3/gal and $7/gal. These assumptions yielded fuel costs ranging from 0.25 to 0.58 $/kWh. In reality, fuel costs vary signiﬁcantly by community and over time. A full economic anal- ysis and projection of diesel fuel prices are beyond the scope of this report. The range of calcu- lated LCOE values is shown in Fig.3. Fuel represents 30%–50% of total LCOE under the $3/ gallon assumption and 50%–80% of total LCOE under the $7/gal assumption. Fuel represents a signiﬁcant portion of LCOE, and its cost varies the most, which makes cost projections over the lifetime of a project difﬁcult without specifying a range of potential fuel prices. Calculated LCOE values are similar to but not the same as residential rates (before power cost equalization adjustment) in these communities because residential rates are calculated based on administrative, O&M, and fuel costs. Generally, RPSU project capital expenses are paid for by the Denali Commission and other grants, rather than by the community or local FIG. 3. Levelized cost of electricity by installed capacity for two different fuel cost assumptions. Fuel represents a signiﬁ- cant portion of LCOE, and its cost is highly variable, making it difﬁcult to accurately predict lifetime costs for generating diesel electricity without accurate fuel cost models. 061701-4 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) utility. The levelized cost of electricity calculations represents the full cost of generation, not the cost of delivery for the utility. Conditions for greatest efficiency The efﬁciency of diesel generators is often reported as the number of kilowatt-hours gener- ated per gallon of fuel. Typical values for generators used in Alaska are 11–15kWh/gal. Generators tend to have poor efﬁciency when lightly loaded, but efﬁciency plateaus at around half the rated load and above. The steady-state efﬁciency of a diesel generator can be deduced from fuel consumption (gal/h) curves. Oversizing generators leads to poor efﬁciencies and an increase in total costs when compared to generators operating near rated output. Unfortunately, not all generators in a powerhouse can maintain a ﬁxed output due to varying loads. Control schemes are often employed within power plants to provide the most cost-efﬁcient combination of generators for a given load. Installation of auxiliary equipment can also affect efﬁciency. Heat is generated during the non-ideal adiabatic compression of the cylinder air charge. After-coolers help to remove this heat, which allows fuel to combust more completely. Also, poor fuel quality can lead to incom- plete combustion and decreased efﬁciency. Filters and other emission-control devices reduce the output of nitrogen oxide (NOx) and particulates but typically decrease overall efﬁciency. Costs over time In order to track the change in installation costs over time, the effect of the power plant size must be taken into account. The installation cost ratio of each project was calculated rela- tive to the cost curve. A value of 1 indicates that the project cost lies directly on the cost curve. A value of 2 indicates that the project cost is double the curve. Installation cost ratios are plot- ted over time in Fig.4. No trend is noticeable over the time for which installation cost data are available. However, it is expected that costs increase over a longer period due to increased emission standards and other regulatory drivers. Certain increased emission standards saw national implementation beginning in 2007. Alaskan communities, however, received exemp- tions and delayed implementation until 2014 which is outside the date range of the RPSU data- set. The regulations are discussed further in the Technology and Regulatory Trends section below. Transportation Project materials must be transported through Anchorage. Locations closer to Anchorage and barge routes tend to have lower costs associated with transportation, but the distance to the nearest hub is not the only factor. Even within established Alaskan regions, towns and villages may not be comparably accessible. Communities that require equipment to be delivered via ice FIG. 4. Installation cost ratio relative to the cost curve of Fig.1 by year. There is no signiﬁcant trend over the time for which installation cost data are available. 061701-5 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) road or air have much higher freight costs. Unfortunately, there is not a sufﬁcient deﬁnition of remoteness to perform a rigorous analysis of transportation costs. Additionally, any existing trend will be less discernable from statistical noise after breaking up the dataset by regions. Expected life The nameplate outputs of individual generators installed in rural Alaska vary from about 30kW to over a megawatt. Generators of this size can expect to operate 60000–100000h, with larger engine blocks tending to have longer lifespans. An appropriately maintained generator operating for 60000h 35% of the time will last approximately 20years. However, the lifetime of an individual generator does not necessarily match the lifetime of the powerhouse because generators and other components can be replaced without rebuilding the powerhouse. Capacity factor The capacity factor of a diesel powerhouse is calculated by dividing the number of kilowatt-hours generated by the number of kilowatt-hours the powerhouse would generate if each of its generators were running at full capacity. The number of kilowatt-hours generated was collected from Power Cost Equalization data on the Alaska Energy Data Gateway website. The capacity factors for the RPSU projects are shown in Fig.5. Systems with a mixture of die- sel and other sources are differentiated from systems that only use diesel generators. Rural diesel plants typically have three to four generators in-house. The diesel plants are sized so that one or two generators provide power at any given time; the remaining generators are available as backup. The operating generators are not necessarily running at a full rated load. There are several examples in Fig.5 for hybrid systems before and after the addition of a wind or hydroelectric resource. For diesel-hydroelectric hybrid systems, it appears that the capacity factor of the diesel plants drops signiﬁcantly after hydroelectric power is added. The trend is less clear for the addition of wind power. This is likely due to the relative predictability of hydroelectric power compared to wind. Since the changes in river ﬂow occur more gradually than wind ﬂow, a larger portion of the grid can be reliably supported by the hydroelectric tur- bines. Wind is intermittent by nature, and therefore, wind turbines should be sized more conser- vatively in order to reduce extreme swings without storage to compensate. Furthermore, hydro- electric turbine generators can operate synchronously, meaning that they can maintain a grid with diesels turned off. Wind turbine generators cannot do so without energy storage and addi- tional infrastructure. FIG. 5. Capacity factor of diesel power plants by installed capacity. Rural power plants have low capacity factors because at any given time, most generators are not running. 061701-6 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) Technology and regulatory trends Diesel engines have been in use for over a hundred years, yet, the technology continues to see advances in power output, efﬁciency, noise reduction, and emission control. The shapes of combustion chambers in newer engines are designed to maximize the combustion rate of fuel, thus increasing output power and fuel efﬁciency. Common-rail fuel systems can maintain high pressure from the fuel tank to injection. High pressure consequently allows for ﬁner vaporiza- tion of the fuel and thus more complete combustion. Nitrous oxide (NOx) is caused by high combustion temperatures in an oxygen-rich environ- ment; NOx can be reduced through exhaust gas recirculation. This process lowers the adiabatic ﬂame temperature and increases the heat capacity of the air mixture in the combustion cham- bers, allowing for combustion at a much lower temperature. Another method of NOx reduction, selective catalytic reduction (SCR), passes the exhaust through a reducing catalyst such as ammonia or urea to convert NOx into diatomic nitrogen and water. Control systems have also seen advancement. Mechanical control systems have been slowly phased out in favor of electronic control systems. Electronic control systems allow for offsite monitoring of a system, reducing the number of necessary service calls. From 2007 to 2014, the Environmental Protection Agency phased in mandates for non-road diesel engines to use low-sulfur compared to ultra-low-sulfur diesel in most of the United States. Additionally, new stationary diesel engines are required to meet certain emission stand- ards. However, small facilities in rural Alaska have been given some exemptions due to the high cost and the difﬁculty of operations in remote areas (ADEC, 2016). Pre-2014 model year engines are exempt from diesel fuel sulfur requirements. Engines may be certiﬁed to marine engine standards rather than land-based non-road engine standards. After-treatment devices for NOx reduction, such as SCR, are not required. After-treatment devices for particulate matter are not required for pre-2014 model year engines. CONCLUSIONS Diesel generators are the main source of electrical generation in remote Alaska communi- ties; they also help to maintain grid frequency and voltage. In an analysis of key performance metrics for diesel generators in Alaska, we found that the size of the installed system directly affects capital costs, that is, larger systems are more cost-effective per kilowatt. However, appropriately sizing a system for a community is more cost-effective overall than signiﬁcantly oversizing the system. Capacity factors range from below 5% to over 25%. The low values are typically for diesel-hydroelectric hybrid systems, for which this measure is not entirely accu- rate. In addition, rural diesel plants may have low capacity factors since typically there are three to four generators in-house. These generators are sized so that one to two generators pro- vide power at any given time; the remaining generators are available as backup. Generators of this size can expect to operate approximately 60000–100000h, with larger engine blocks tend- ing to have longer lifespans. An appropriately maintained generator operating for 35% of the time will last approximately 20 years, or 60,000 hours. The technology continues to see advances in power output, efﬁciency, noise reduction, and emission control. The shapes of combustion chambers in newer engines are designed to maxi- mize the combustion rate of fuel, thus increasing output power and fuel efﬁciency. The common-rail fuel system can maintain high pressure from the fuel tank to injection, which allows for ﬁner vaporization of fuel and more complete combustion. Nitrous oxide can be reduced through exhaust gas recirculation and selective catalytic reduction. Control systems have also seen advancement. Mechanical control systems have been slowly phased out in favor of electronic control systems, which allow for offsite monitoring of a system and reduction in the number of necessary service calls. Diesel generators in rural Alaska communities remain difﬁcult to maintain the degree nec- essary for smooth operation. Additionally, Supervisory Control and Data Acquisition systems 061701-7 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) with remote control capabilities require continuous Internet connection, which is not always available in rural communities. ACKNOWLEDGMENTS The authors wish tothank the Alaska Energy Authority for its funding tosupport this project. Many people have contributed information and insight to this report. For their review and comments, we wish to thank John Cameron of Marsh Creek LLC; Steve Stassel; Ingemar Mathiasson of the Northwest Arctic Borough; and Kris Noonan, Alan Fetters, and Neil McMahon ofthe Alaska Energy Authority. APPENDIX: ADDITIONAL DATA AND TABLES TABLE I. List of communities examined in installation costs with some description of the RPSU grant. Community Installed capacity (kW) Notes (all grants include the powerhouse, generators, and controls) Akiachak 1500 Grant also includes a 15000 gal intermediate tank and a waste heat recovery loop Angoon 1575 Grant also includes a waste heat recovery system Arctic village 395 Grant also includes a distribution upgrade and a waste heat recovery system Buckland 1125 Grant also includes a 12000 gal intermediate tank, a distribution upgrade, and a heat exchanger for the existing waste heat recovery loop Chefornak 1050 Grant also includes a 22000 gal intermediate tank and a heat exchanger for the existing waste heat system Chitina 302 Chuathbaluk 175 Grant shared with other middle Kuskokwim projects. Grant also includes tank farms for the powerhouse, school, and village Crooked Creek 220 Grant shared with other middle Kuskokwim projects. Grant also includes tank farms for the powerhouse, school, and village Deering 585 Grant also includes a 5000 gal intermediate tank and a heat exchanger for the existing waste heat recovery system Diomede 460 Grant also includes a distribution upgrade and a heat exchanger for the existing waste heat loop Elﬁn Cove 347 Built in parallel with a distribution upgrade project on a separate grant Elim 1105 Golovin 580 Grant also includes a 12000 gal intermediate tank and a heat exchanger for the existing waste heat system Gustavus 840 Built in parallel with a Hydro system on a separate grant Hughes 230 Grant also includes a 6000 gal intermediate tank Karluk 108 Grant also includes a distribution upgrade King Cove 2602 Hydro and diesel system Kokhanok 490 Built in parallel with the bulk fuel project but on a separate grant Kongiganak 755 Grant also includes a 12000 gal intermediate tank, a distribution upgrade, and a heat exchanger for the existing waste heat loop Kotlik 1390 Grant also includes a 12000 gal intermediate tank, a distribution upgrade, and a heat exchanger for the existing waste heat loop Koyukuk 202 Grant also includes a 12000 gal intermediate tank, a distribution upgrade, and a heat exchanger for the existing waste heat loop Kwigillingok 580 Grant also includes three 22000 gal bulk fuel tanks, a 12000 gal intermediate tank, a distri- bution upgrade, and a heat exchanger for the existing waste heat loop Manokotak 830 Grant also includes a 12000 gal intermediate tank and a heat exchanger for the existing waste heat loop Nikolski 200 Grant also includes re-plumbing for the existing intermediate tank 061701-8 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) TABLE I. (Continued.) Community Installed capacity (kW) Notes (all grants include the powerhouse, generators, and controls) Pedro Bay 260 Grant also includes a distribution upgrade and a waste heat recovery system Pelican 920 Project was done in parallel with a bulk fuel storage project and preceded a hydro system upgrade Pilot point 318 Built in parallel with a bulk fuel project on a separate grant Sleetmute 320 Grant shared with other middle Kuskokwim projects. Grant also includes tank farms for powerhouse and school Stevens village 290 Grant also includes a distribution upgrade Stony River 130 Grant shared with other middle Kuskokwim projects. Grant also includes tank farms for powerhouse, school, and village Takotna 205 Grant shared with other middle Kuskokwim projects. Grant also includes tank farms for powerhouse, school, and village Tenakee Springs 240 Grant also includes a distribution upgrade, and some equipment for waste heat recovery was installed, but no heat loop was close enough to utilize it Tuluksak 490 Grant also includes a 12000 gal intermediate tank, a road upgrade, and a distribution upgrade Tuntutuliak 610 Grant also includes a 4000 gal intermediate tank and a heat exchanger for future waste heat recovery systems TABLE II. Assumed Intervals of maintenance tasks. Note that each manufacturer speciﬁes different maintenance intervals for machines. The assumed intervals are simply approximations. 60–150 kW 151–600 kW 601–1300 kW Maintenance category Interval (h) Interval (h) Interval (h) Repeating maintenance tasks: contracted Replace the oil cooler and injectors 15000 10000 15000 Replace generator bearings 6000 6000 6000 Unscheduled maintenance/repair 15000 15000 15000 Repeating maintenance tasks: in-house labor Daily inspection 14 14 14 Check the battery electrolyte level, adjust belts, and clean the radiator 250 250 250 Change oil and ﬁlter 250 250 500 Clean the crankcase breather 250 250 500 Check/lubricate fuel control linkage 1000 1000 1000 Drain fuel tank water and sediment 250 250 1000 Replace fuel ﬁlters and glycol ﬁlter 500 500 1000 Replace the air ﬁlter, hoses, and belts 2000 2000 2000 Adjust the valve lash 3000 3000 2000 Inspect turbocharger 2000 2000 2000 Inspect generator including bearings 2000 2000 2000 Replace coolant 6000 6000 6000 Inspect the engine speed sensor, starting motor, and water pump 6000 6000 6000 One-time maintenance tasks Initial 250 service hours of inspection and valve lash adjustment 250 250 250 First top end rebuild 15000 15000 15000 Second top end rebuild 30000 30000 30000 In-frame rebuild 45000 45000 45000 Third top end rebuild … 60000 60000 Fourth top end rebuild … 75000 75000 Fifth top end rebuild … … 90000 061701-9 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) TABLE III. Labor duration of maintenance tasks. 60–150 kW 151–600 kW 601–1300 kW Maintenance category Labor (h) Labor (h) Labor (h) Repeating maintenance tasks: contracted Replace the oil cooler and injectors 30.0 30.0 30.0 Replace generator bearings 30.0 30.0 30.0 Unscheduled maintenance/repair 30.0 40.0 40.0 Repeating maintenance tasks: in-house labor Daily inspection 1.0 1.0 2.0 Check the battery electrolyte level, adjust belts, and clean the radiator 2.0 2.0 2.0 Change oil and ﬁlter 2.0 2.0 2.0 Clean the crankcase breather 1.0 1.0 1.0 Check/lubricate fuel control linkage 1.0 1.0 1.0 Drain fuel tank water and sediment 2.0 2.0 2.0 Replace fuel ﬁlters and glycol ﬁlter 2.0 2.0 2.0 Replace air ﬁlter, hoses, and belts 4.0 4.0 4.0 Adjust the valve lash 4.0 4.0 4.0 Inspect the turbocharger 1.0 1.0 1.0 Inspect the generator including bearings 1.0 1.0 1.0 Replace coolant 4.0 4.0 4.0 Inspect the engine speed sensor, starting motor, and water pump 2.0 2.0 2.0 One-time maintenance tasks Initial 250 service hours of inspection and valve lash adjustment 6.0 6.0 6.0 First top end rebuild 40.0 60.0 80.0 Second top end rebuild 40.0 60.0 80.0 In-frame rebuild 150.0 300.0 400.0 Third top end rebuild … 60.0 80.0 Fourth top end rebuild … 60.0 80.0 Fifth top end rebuild … … 80.0 TABLE IV. List of O&M costs reported for RCA and the installed capacity for the respective community. Community Installed capacity (kW) O&M cost ($/kWh) Akiachak 1500 0.14 Atka 200 0.13 Arctic village 395 0.38 Atmautluak 547 0.15 Buckland 1125 0.09 Chignik 577 0.18 Chitina 302 0.15 Deering 585 0.17 Diomede 460 0.26 Elﬁn Cove 347 0.18 Hughes 230 0.21 Kokhanok 490 0.18 Koyukuk 202 0.15 Manokotak 830 0.06 Nikolski 200 0.15 Ouzinkie 350 0.14 Pedro Bay 260 0.14 Pelican 920 0.17 061701-10 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017) ADEC (Alaska Department of Environmental Conservation),https://dec.alaska.gov/air/anpms/ulsd/ulsdnsps.htm for Internal Combustion Engine Requirements, April 2016. Alaska Department of Labor and Workforce Development,https://laborstats.alaska.gov/cpi/cpi for Consumer Price Index data, January 2016. Alaska Energy Data Gateway,https://akenergygateway.alaska.edu for Power Cost Equalization Data, January 2016. Denali Commission Project Database,https://denali.gov for Rural Power System Upgrade (RPSU) projects, January 2016. TABLE IV. (Continued.) Community Installed capacity (kW) O&M cost ($/kWh) Pilot Point 318 0.09 Takotna 205 0.24 Tenakee Springs 240 0.16 Tuluksak 490 0.15 Tuntutuliak 610 0.16 061701-11 Green, Mueller-Stoffels, and Whitney J. Renewable Sustainable Energy 9, 061701 (2017)