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 |
End Page
Page 2 usingin recast DUKES data to see the Thermodynamics
| UK REGIONAL CHP - THERMODYNAMIC EFFICIENCY | ||||||||
| Region | Schemes | Capacity (MWe) | Fuel Input (GWh) | Elec Output (GWh) | Heat Output (GWh) | Total Output (GWh) | System Efficiency (%) | Primary Energy Saving (GWh) |
| England | 1673 | 5146 | 51000 | 18600 | 22900 | 41500 | 81.37 | 20,868.71 |
| East Midlands | 112 | 168 | 1400 | 510 | 630 | 1140 | 81.43 | 573.06 |
| Eastern | 184 | 406 | 3400 | 1240 | 1530 | 2770 | 81.47 | 1,395.17 |
| London | 257 | 274 | 2300 | 840 | 1030 | 1870 | 81.30 | 940.75 |
| North East | 97 | 282 | 2400 | 875 | 1080 | 1955 | 81.46 | 984.11 |
| North West | 251 | 753 | 6300 | 2300 | 2830 | 5130 | 81.43 | 2,584.97 |
| South East | 255 | 914 | 7700 | 2810 | 3460 | 6270 | 81.43 | 3,158.03 |
| South West | 153 | 155 | 1300 | 475 | 585 | 1060 | 81.54 | 535.58 |
| West Midlands | 178 | 187 | 1600 | 580 | 715 | 1295 | 80.94 | 642.14 |
| Yorkshire/Humberside | 186 | 2005 | 16800 | 6130 | 7550 | 13680 | 81.43 | 6,889.12 |
| Scotland | 186 | 588 | 4900 | 1790 | 2200 | 3990 | 81.43 | 2,011.91 |
| Wales | 117 | 268 | 2200 | 800 | 990 | 1790 | 81.36 | 897.07 |
| Northern Ireland | 83 | 101 | 850 | 310 | 380 | 690 | 81.17 | 345.85 |
| UK Total | 2059 | 6104 | 59800 | 21800 | 26900 | 48700 | 81.44 | 24,504.06 |
End Page
Page 3 Notes on representing the numbers
| EMISSIONS ACCOUNTING vs THERMODYNAMIC ANALYSIS | ||
| Why the DUKES 1/3:2/3 Method Obscures Real Benefits | ||
| DUKES Accounting Method | Thermodynamic Reality | |
| What it measures | Allocated emissions per output type | Actual energy flows and efficiency |
| Heat fuel allocation | 1/3 of fuel 'goes to' heat | No allocation - single combustion process |
| Electricity fuel allocation | 2/3 of fuel 'goes to' electricity | No allocation - single combustion process |
| Shows efficiency as | Implied separate efficiencies | Overall system efficiency (80-90%) |
| Primary benefit visible? | Hidden in accounting conventions | Clear: fuel saved vs separate generation |
| CO2 savings calculation | Complex with allocation assumptions | Simple: less fuel burned = less CO2 |
| Useful for | Tax relief calculations, emissions reporting | Engineering decisions, true performance |
| Misleading because | Suggests fuel is 'divided' between outputs | Shows actual thermodynamic advantage |