The following assumptions have been made for the economic assessment of the novel trigeneration and equivalent base case system.
• System lifetime (N): 15 years (CFCL 2009)
• SOFC CHP system cost and installation: ?20,950 (Elmer et al. 2015b)
• SDCS cost: ?2700
• Potassium formate solution cost (20 kg): ?235
• SOFC stack replacement cost and system maintenance: ?5000 every 5 years
• UK microCHP feedintariff (FiT): 0.125 ? kWh^{1} (DECC 2014)
• Boiler and installation cost: ?1300
• VCS capital cost: ?500 per kW of cooling (Infante Ferreira and Kim 2014)
• Annual VCS maintenance cost: 10 % of VCS capital cost
• Annual gas check: ?60
• Average natural gas unit cost: 0.0421 ? kWh^{1} (EST 2014)
• Average electricity unit cost: 0.172 ? kWh^{1} (Goot 2013)
• Average yearly VCS COP_{d}: 2 (Welch 2008)
• Average heating system efficiency (boiler + distribution): 85.5 %
• Annual cooling time required: 1200 h year^{1} (Pilatowsky et al. 2011)
• Interest rate (i_{r}): 7 % (constant throughout assessment period)
• Inflation rate (if): 3 % (constant throughout assessment period)
• Scrap value (SV): 10 % of initial capital cost (Pilatowsky et al. 2011)
In the UK, fuel cell CHP of 2.0 kWe or less qualifies for the microgeneration FiT (DECC 2014). Under this scheme, the UK government pays 0.125 ? kWh^{1} of electricity generated, regardless of whether it is consumed or exported. Where relevant, the economic assessments consider the FiT.
Figure 8.1a, b shows the NPC of the 1.5 and 2.0 kW_{e} trigeneration systems and equivalent base case systems over a 15 year period. The assessment considers the performance of the trigeneration system with and without FiT support. The initial NPC in year 0 is the system investment cost, which is much higher for the trigeneration system compared to the base case. The NPC of the systems increases over time due to the annual operating costs. The trigeneration system with FiT support displays only a marginal increase in the NPC over the 15 year period because the FiT almost pays for the annual operating cost of the system. For the trigeneration systems, an NPC spike is seen at year five and ten; this is due to stack replacement. The small dip in NPC at year 15 is due to the scrap value of the systems.
Table 8.1 presents the NPC, EUAC and SPBP results for the trigeneration and base case systems.
Without FiT support, the NPC of both the 1.5 and 2.0 kW_{e} trigeneration system are 26 and 10 % higher than the equivalent base case system respectively. However, with FiT support there is a 31 and 90 % reduction in the NPC of the
1.5 and 2.0 kW_{e} trigeneration system compared to the equivalent base case system respectively. When the FiT is considered the annual revenue means the trigeneration system has a favourable NPC compared to the base case in year 11.5 for the 1.5 kW_{e} trigeneration system and year 7 for the 2.0 kW_{e} trigeneration system. The NPC of the 1.5 kW_{e} trigeneration system is lower than the 2.0 kW_{e }trigeneration system when no FiT is considered, but higher when the FiT is considered. The higher NPC seen in the 2.0 kWe trigeneration system without FiT is
Fig. 8.1 NPC comparison at a 1.5 kW_{e} in a and 2.0 kW_{e} in b capacity between the trigeneration system with and without the FiT and the base case system
Table 8.1 Economic assessment results
1.5 kW_{e} tri
1.5 kW_{e} base
2.0 kW_{e} tri
2.0 kW_{e} base
NPC (no FiT)
?40,544
?29,898
?44,818
?40,257
NPC (FiT)
?22,770

?21,120

EUAC (no FiT)
?4451
?3283
?4921
?4420
EUAC (FiT)
?2500

?2319

SPBP (no FiT)
19.8 years

14.7 years

SPBP (FiT)
9.8 years

7.3 years

due to the higher fuel input requirement, and thus higher annual operating costs. However, when FiT is considered the 2.0 kW_{e} trigeneration system provides greater annual revenues and thus a lower NPC. Both with and without FiT support, the 2.0 kW_{e} trigeneration system has a lower SPBP compared to the 1.5 kW_{e} trigeneration system. Although the 2.0 kW_{e} trigeneration system suffers an electrical efficiency reduction and thus a greater fuel input, the higher electrical capacity means it is offsetting more grid derived electricity. Per kWh, grid derived electricity has a higher associated cost compared to natural gas, and thus the SPBP of the 2.0 kW_{e} trigeneration system is lower. Furthermore, the 2.0 kW_{e} trigeneration system has a greater cooling output, and thus the equivalent base case system requires more grid derived electricity for the VCS. In all cases the trigeneration system generates annual operating cost savings compared to the base case system. The high NPC and SPBP of the trigeneration system are therefore due to the capital cost of the SOFC.
Figure 8.2a compares the economic performance of the 1.5 kW_{e} trigeneration system and equivalent base case system with respect to the unit cost of electricity. No FiT is considered. The unit cost of electricity does not affect the NPC of the trigeneration system, only the base case system. As the unit cost of electricity increases from 0.05 to 0.6 ? kWh^{1} the NPC of the base case system increases, and thus the economic feasibility of the trigeneration system improves. At an electrical unit cost of 0.2458 ? kWh^{1} there is a NPC breakeven point between the trigeneration and base case system. Above 0.2458 ? kWh^{1} the 1.5 kW_{e} trigeneration system has a better NPC and should be considered over the base case system. At an electrical unit cost of 0.2458 ? kWh^{1} the trigeneration system has a SPBP of 12 years. For the SPBP to fall below 5 years, an electrical unit cost of 0.55 ? kWh^{1} is required. In comparison, the 2.0 kW_{e} trigeneration system has a NPC breakeven electrical unit cost of 0.1955 ? kWh^{1}. Due to the continual rise in utility electricity prices, the breakeven electrical unit costs which produce trigeneration system economic feasibility are realistic and not too far off current prices as demonstrated in Fig. 8.3.
Figure 8.2b compares the economic performance of the 1.5 kW_{e} trigeneration system and equivalent base case system with respect to the unit cost of natural gas. No FiT is considered. Natural gas unit cost affects both the trigeneration and base case systems NPC. As the unit cost of natural gas increases from 0.01 to 0.1 ? kWh^{1} the NPC of both the trigeneration and base case systems increase. The trigeneration system is more sensitive to changes in the unit cost of natural gas compared to the base case system due to a greater proportionate demand. For the
1.5 kWe trigeneration system there is not a natural gas unit cost that makes the trigeneration system favourable i.e. a NPC breakeven point. As the natural gas unit price is increased the reduction in NPC between the base case and trigeneration system increases, and as a result the SPBP increases. As the natural gas unit cost is increased from 0.01 to 0.1 ? kWh^{1} the trigeneration system SPBP increases from 14 to 51 years. The 2.0 kW_{e} trigeneration system does have a NPC breakeven
Fig. 8.2 NPC and SPBP comparison between the 1.5 kW_{e} trigeneration system and base case system with a electricity unit cost, and b natural gas unit cost
natural gas unit cost of 0.0233 ? kWh^{1}. However this is very low and not realistic in the current economic climate where fossil fuels have such value.
Figure 8.3 shows the NPC of a 1.5 and 2.0 kW_{e} equivalent base case system in a range of different counties with respect to electrical unit cost data published by the International Energy Agency (IEA 2012). The NPC of the respective trigeneration systems (horizontal lines) are plotted to indicate which countries the novel system is currently economically viable in. Based on the current assumptions, the novel trigeneration system (1.5 and 2.0 kW_{e}) is only economically viable in Denmark where the unit cost of electricity is 0.262 ? kWh^{1}. The largest different between the NPC of the trigeneration and base case system is in China, where the unit cost of electricity is as low as 0.0512 ? kWh^{1}. Based purely on economic performance, the novel trigeneration system is more suited to European locations, where on average the unit cost of electricity is higher than Asia and the Americas.
Fig. 8.3 NPC comparison between the 1.5 kW_{e} trigeneration system and base case system with respect to country of operation
As discussed in Fig. 8.2a, the 2.0 kW_{e} trigeneration system has a lower NPC breakeven electrical unit cost. As a result, the 2.0 kW_{e} system is almost feasible in the current Australian economic climate. Section 8.3 assesses the environmental performance of the trigeneration in the same countries. The aim is to highlight any geographical differences between the economic and environmental feasibility of the novel system.
Figure 8.4a shows the NPC of the 1.5 kW_{e} trigeneration system and equivalent base case system with respect to the SOFC capital cost. The capital cost of the trigeneration system, operating at a 1.5 kW_{e} capacity, needs to be ?9715 or less for it to be economically viable compared to the base case system. At a 2.0 kW_{e} capacity the required SOFC capital cost is ?16135. As the capital cost of the SOFC increases, the SPBP increases. At the 1.5 kW_{e} NPC breakeven point of ?9715 the SPBP is 12.8 years. Although not shown in Fig. 8.4a, variation in the liquid desiccant system capital cost has a negligible impact on NPC and SPBP. Reducing the liquid desiccant system capital cost by 50 % results in a 4.5 % reduction in the SPBP. Reducing the SOFC capital cost by 50 % results in a 32 % reduction in the SPBP, demonstrating that trigeneration system economic viability presides with reducing the capital cost of the SOFC.
Figure 8.4b shows the NPC for the 1.5 kW_{e} trigeneration and equivalent base case system with respect to SOFC capital cost and unit cost of electricity respectively. Up to an electricity unit cost of 0.11 ? kWh^{1} the base case system is always better than the trigeneration system. However at the electrical unit cost reference value of 0.172 ? kWh^{1}, the 1.5 kW_{e} trigeneration system is competitive when the SOFC capital cost is less than ?9500. At the intersection point, the trigeneration system is economically favourable if the SOFC capital
Fig. 8.4 NPC and SPBP comparison between the 1.5 kW_{e} trigeneration system and base case system with a SOFC capital cost, and b electricity unit cost and SOFC capital cost cost is less than ?4750 with an electrical unit cost of greater than 0.14 ? kWh^{1 }(i.e. UK, Australia).
Next, Sect. 8.2.3 contextualises the presented economic assessment results and concludes the section.