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THE FUNDAMENTAL TRUTH ABOUT CHP:
1. CHP burns fuel ONCE to produce electricity AND useful heat SIMULTANEOUSLY
2. The Government's allocation method (1/3 heat, 2/3 electricity) is an ACCOUNTING CONVENTION
- It exists for emissions reporting and tax calculations
- It does NOT represent actual fuel division (which is impossible)
3. The REAL benefit is THERMODYNAMIC:
- CHP typically achieves 80-90% overall efficiency
- Separate generation (grid + boiler) achieves ~55-60% combined efficiency
- This means ~30-40% LESS PRIMARY FUEL for the same useful energy
4. For UK CHP in 2024:
- Total fuel input: ~60,000 GWh
- Total useful output: ~49,000 GWh (electricity + heat)
- Overall efficiency: ~82%
- Primary energy saved: ~20,000 GWh compared to separate generation
- CO2 avoided: ~3-4 million tonnes annually
5. RECOMMENDATION: Present CHP benefits as:
- Overall system efficiency (heat + power / fuel input)
- Primary energy savings vs counterfactual
- Absolute fuel and CO2 reductions
- NOT as arbitrary fuel 'allocation' between outputs
This gives engineers, building owners, and policymakers the honest picture they need to make informed decisions about distributed energy systems.
Page 1 UK CHP Performance -
Analysing DUKES data and ignoring the allocations for tax and emissions accounting [give me strength!!]
| ACTUAL SYSTEM EFFICIENCY | ||
| Overall CHP Efficiency (%) | 81.44 | Total useful energy out / fuel energy in |
| Electrical Efficiency (%) | 36.45 | Electricity out / fuel in |
| Heat Recovery Efficiency (%) | 44.98 | Heat out / fuel in |
| COUNTERFACTUAL: SEPARATE GENERATION | ||
| If the same electricity and heat were generated separately: | ||
| Reference Assumptions: | ||
| Grid Power Station Efficiency (%) | 45 | CCGT efficiency (typical UK grid) |
| Grid Transmission & Distribution Losses (%) | 8 | UK grid average losses |
| Conventional Boiler Efficiency (%) | 85 | Modern gas boiler efficiency |
| Fuel Required for Separate Generation: | ||
| Fuel for Grid Electricity (GWh) | 52,657.00 | Accounts for generation efficiency AND grid losses |
| Fuel for Boiler Heat (GWh) | 31,647.06 | Heat output / boiler efficiency |
| Total Fuel for Separate Generation (GWh) | 84,304.06 | |
| PRIMARY ENERGY SAVINGS | ||
| Absolute Fuel Saving (GWh) | 24,504.06 | THIS IS THE REAL BENEFIT |
| Percentage Fuel Saving (%) | 29.07 | |
| Fuel Saving per MWh CHP Output | 0.50 | MWh saved per MWh useful output |
| CO2 EMISSIONS IMPACT | ||
| Natural Gas CO2 Factor (kgCO2/kWh) | 0.184 | GCV basis - from UK GHG factors |
| CO2 from CHP Generation (ktCO2) | 11.00 | |
| CO2 from Separate Generation (ktCO2) | 15.51 | |
| CO2 Emissions Avoided (ktCO2) | 4.509 | REAL CO2 BENEFIT |
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