ELECTRICAL RESILIENCE Generator rating
Generator fuel consumption 1/4 load 1/2 Load 3/4 Load Full Load
Generator life expectancy Generator annual operation
1 Annual full load run 800 kW
60 L/h 110 L/h 170 L/h 220 L/h
20 years 200 hours
Annual run for 200 hours every (years) 2 years 2 12h 100% (load day time) 3 12h 50% (load night time) 4 Monthly test @ 100% 2h
Carbon emissions from burning fuel 1L diesel
1L biodiesel
Generator embodied carbon (assumed, based on 9000 kg Co2
100 hours 100 hours 24 hours
2.4 kg CO2 eq 0.624 kg CO2 eq 12,000.00 kg CO2 eq for 500kW gen-set)
Long economic lifespan The biggest advantage of standby generators is their economic lifespan. Standby diesel generators have an economic life of up to 25 years, during which the generator remains predominantly inactive, and only accumulates maintenance hours.6
eq BESS rated capacity
Desired operation period BESS operational capacity BESS total cycles
BESS efficiency rating Initial energy
Avg BESS embedied carbon
1 Charging from Wind 2 Charging from Solar
800 kW 2 hours
1600 kWh 8,000
1 cycle per day = 20 years 0.96% 0.8%
55 kg CO2 eq / kWh
0.006 kg CO2 0.04 kg CO2
3 Charging from Grid at best month 0.046 kg CO2 4 Charging from Grid at avg
0.181 kg CO2
eq / kWh eq / kWh eq / kWh eq / kWh
Embodied carbon of selected BESS 88,000 kg CO2 eq
Figure 5 (left): Standby diesel generator parameters. Figure 6 (above): BESS system parameters.
When
the generator is required to operate during a LoM emergency, assuming there is a constant fuel supply and the engine has been properly maintained, it should run for prolonged periods without any issues. HTM 06-01, clause 7.22, suggests that ‘Generator reliability may be of the order of 99.95% (or 0.05% unreliable), which equates to 4.5 hours of unavailability per year’. Standby generators can be used for
short-term operational reserve (STOR) and other Distribution Network Operators’ demand side management schemes – via which a revenue stream can be generated to the owner. Due to the carbon footprint of standard diesel fuel, generator operation to accommodate this is not a sensible solution from an environmental perspective.
Better suited to revenue generation A BESS is better suited to revenue generation due to greater system flexibility. As previously mentioned, such systems are capable of almost instantaneous connection to the grid, which is beneficial for Dynamic Fast Frequency Response (DFFR) schemes. In addition, the BESS can be charged overnight when the grid has its lowest carbon footprint per kWh, and discharged during the day to provide demand peak shaving for the site in question. A downside of a BESS, however, is the sensitive electronics equipment incorporated within it, which regulates the system’s operation. The effects of dust accumulation over time, and incorrect battery temperature management, can render the entire system defunct. Diesel generator conversion to biofuel
operation brings additional maintenance requirements from a fuel perspective. Generator filters can get clogged up, and the injectors are at risk of damage due to ‘diesel bug’, where microorganisms present within the fuel start biomass-film formation.
To ensure 200-hour resilience provision
would require a significant size of BESS to replicate what a single diesel generator can provide. In addition, if the BESS runs out of power, there is no way to charge it should the grid be ‘down’; hence why the BESS has to be sized in respect to the site resilience strategy. However, the system can be charged during the day utilising local solar PV or wind power-generated energy, resulting in reduced operational carbon footprint.
Carbon footprint comparison Let us now consider the estimated carbon footprint associated with the two different systems based on the assumed economic lifecycle and the most likely operational regime. The tables in Figures 5 and 6 set out the assumed parameters for each system. While the data for two systems highlighted in Figures 5 and 6 have been based on the same 800 kW rated capacity, the duration for which the BESS is required to provide electrical back-up resilience is set to two hours. This running duration is considered typical for a BESS installation, in contrast to the run time for
September 2023 Health Estate Journal 55
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