Supplement coppice wood with peat, coal, solar heat, biogas or wood gas to reduce pressure on any one source, remembering that each costs something: on a net-heat basis about 1.11 t of peat, 1.14 t of lignite or 0.53 t of bituminous coal replaces 1 t of air-dried wood. Peat and coal spend a deposit that does not regrow, and biogas uses manure that would otherwise feed the fields.
Part of Coppicing & Fuel Management
Other fuels that can top up a coppice supply, how much of each replaces a tonne of wood, and what each one uses up.
Exchange Rates
Using the net heat of air-dried wood at 20% moisture (wet basis), 14.3 GJ/t, and the other fuels at the values in BTU Content Compared to Wood and Coal Types & Quality:
| Fuel | Net heat, GJ/t | Tonnes to replace 1 t of air-dried wood |
|---|---|---|
| Peat at 30% moisture | 12.9 | 14.3 ÷ 12.9 = 1.11 |
| Lignite (midpoint 12.5) | 12.5 | 14.3 ÷ 12.5 = 1.14 |
| Bituminous coal (midpoint 27) | 27 | 14.3 ÷ 27 = 0.53 |
The coal midpoints are of the parent coal article’s ranges (10-15 and 24-30 GJ/t). The comparison ignores differences in stove efficiency and does not apply across ranks: lignite and bituminous coal differ by roughly a factor of two.
What Each Option Uses Up
| Option | What it spends | Note |
|---|---|---|
| Peat (Peat Harvesting) | A bog that regrows about 0.5-1 mm a year | Transitional fuel only |
| Coal (Coal Surface Mining) | A finite seam | Mining hazards: roof, gas, dust |
| Solar heat (Solar Thermal Collectors) | Collector materials and land for the collector | Free hot water and cooking in summer |
| Biogas (Biogas Digesters) | Manure, which would otherwise fertilise crops | Needs livestock |
| Wood gas (Biomass Gasification) | Wood, drawn from the same coppice | Not an extra source |
Wood gas is not a separate supply: it burns the same wood. Biogas competes with manure’s other job as fertiliser, so a household using it should account for the nutrients it no longer returns to the soil.
Method: Building A Mix
Step 1: Plan the coppice as the base and size it from the budget (Fuel Budgeting).
Step 2: Use quick wins first. Solar water heating in summer and efficient stoves cut demand.
Step 3: Use peat or coal only to bridge the start-up years or a poor season, and keep records of the amounts.
Step 4: Review yearly. Retire the non-renewable fuels as coppice matures.
Common Mistakes
- Using the same exchange rate for every coal. Rank changes it greatly.
- Treating peat as renewable. It is not on a human timescale.
- Mixing fuels in the stove without checking the grate and air. Peat and coal need different air and ash handling (Coal Stove vs Wood Stove Differences).
Safety
Every added fuel brings its own hazard
Coal mining kills by roof fall, gas and dust. A peat bog hides deep water and underground fire. Biogas is flammable and can asphyxiate in confined spaces. Wood gas contains carbon monoxide. Read the safety section of each article before adding a fuel, and keep carbon monoxide detection in mind wherever fuel burns indoors (Carbon Monoxide Risks).
What’s Next
- Learn next: Peat Harvesting — the nearest bridge fuel
- Combine with: Fuel Budgeting — the whole plan