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Based on specific examples in the UK and elsewhere. These figures are given as guidance and precise energy requirements for a given building will depend on many constructional and operational factors.
| Building |
Annual energy
demand
(MWhth) |
System
size
(kWth) |
Wood chips required p.a. |
Wood pellets required p.a. |
Weight
@ 30% MC
(tonnes)
See note 1 |
Volume
@ 30% MC
(m3)
See note 2 |
Weight
@ 10% MC
(tonnes)
See note 3 |
Volume
@ 10% MC
(m3)
See note 4 |
Domestic
house |
20 |
20 |
5.7 |
23 |
4.2 |
6.3 |
Small industrial
unit |
140 |
100 |
40 |
160 |
29 |
44 |
Large farm
with
outbuildings |
400 |
150 |
114 |
460 |
83 |
125 |
| Hotel |
660 |
250 |
190 |
760 |
138 |
205 |
Municipal
complex |
360 |
300 |
100 |
400 |
75 |
115 |
District heating
scheme |
600 |
500 |
170 |
700 |
125 |
190 |
Municipal
buildings |
1,000 |
700 |
290 |
1,150 |
210 |
315 |
| Greenhouse |
4,200 |
1,200 |
1,200 |
4,800 |
875 |
1300 |
| CHP (ORC) |
14,800
(thermal) |
1,850
(400 kWe) |
6,600 |
26,400 |
4,800 |
7,200 |
| CHP/Power station |
16,000
(electrical) |
2,000
(kWe) |
20,000 |
80,000 |
14,600 |
21,800 |
Notes:
1. 3.5 MWh/tonne (12.6 GJ/t) mixed hard and soft wood
2. 250 kg/m3 = 0.9 MWh/m3 (3.2 GJ/m3)
3. 4.8 MWh/tonne (17 GJ/tonne)
4. 670 kg/m3 = 3.2 MWh/m3 (11.4 GJ/m3)
Energy conversion factors
| |
MJ |
GJ |
kWh |
toe |
Btu |
| MJ |
1 |
0.001 |
0.278 |
24 x 10-6 |
948 |
| GJ |
1000 |
1 |
278 |
0.024 |
948,000 |
| kWh |
3.6 |
0.0036 |
1 |
86 x 10-6 |
3,400 |
| toe |
42,000 |
42 |
11,700 |
1 |
39.5 x 106 |
| Btu |
1.055 x 10-3 |
1.055 x 10-6 |
295 x 10-6 |
25.3 x 10-9 |
1 |
Typical calorific values of fuels
| Fuel |
Energy density by mass
GJ/tonne |
Energy density by mass
kWh/kg |
Bulk density
kg/m3 |
Energy density by volume
MJ/m3 |
Energy density by volume
kWh/m3 |
| Wood chips (30% MC) |
12.5 |
3.5 |
250 |
3,100 |
870 |
| Log wood (stacked - air dry: 20% MC) |
14.7 |
4.1 |
350-500 |
5,200-7,400 |
1,400-2,000 |
| Wood (solid - oven dry) |
19 |
5.3 |
400-600 |
7,600-11,400 |
2,100-3,200 |
| Wood pellets |
17 |
4.8 |
650 |
11,000 |
3,100 |
| Miscanthus (bale - 25% MC) |
13 |
3.6 |
140-180 |
1,800-2,300 |
500-650 |
| House coal |
27-31 |
7.5-8.6 |
850 |
25,500-25,400 |
7,100-7,300 |
| Anthracite |
33 |
9.2 |
1,100 |
36,300 |
10,100 |
| Heating oil |
42.5 |
11.8 |
845 |
36,000 |
10,000 |
| Natural gas (NTP) |
38.1 |
10.6 |
0.9 |
35.2 |
9.8 |
| LPG |
46.3 |
12.9 |
510 |
23,600 |
6,600 |
Fuel costs per kWh
Fuel prices per kWh (excluding VAT)
Typical prices for bulk purchase of fuels at domestic scale, January 2010
N.B. These prices are intended for guidance only and represent the typical cost per unit of fuel energy for comparison. This is not the same as cost per unit of delivered heat which will depend on the efficiency of the boiler or stove, and may also include other charges such as service and maintenance for heat supply contracts.
All prices are prone to significant variation with geographical region, order quantities, overall contract size and duration, time of year, delivery distance and time, etc. Woodfuels in particular are available at prices both significantly above and below those quoted, and bulk prices will be subject to a minimum delivery size of perhaps 3-5 tonnes. Wood pellets bought in bags may be significantly more expensive than those bought in bulk.
Delivery method (speed of delivery) also has a pronounced impact on cost per tonne. It will be far easier, quicker and cheaper to tip a trailer into a chip store than to have to use a chip blower (for example). Additional expenditure on a chip store can have profound financial benefits over the lifetime of the installation.
The market for woodfuels is currently relatively immature which, combined with its unsuitability for long distance transport, supports considerable variation in prices from place to place. Figures have been chosen to represent the mean price achievable across the UK for a single bulk order of 5 tonnes of wood pellets or 10 tonnes of woodfuel quality chips. In the case of the latter however, the prices we see around the country and from different suppliers can vary by a factor of two or more, with £70 - £100 a typical range, but figures both above and below this are not uncommon. For some producers, prices may be subsidized by other activities.
| Fuel |
Price per unit |
kWh per unit |
pence per kWh |
| Wood chips (30% MC) |
£80 per tonne |
3,500 kWh/t |
2.3p/kWh |
| Wood pellets |
£185 per tonne |
4,800 kWh/t |
3.9p/kWh |
| Natural gas |
4.1p/kWh |
1 |
4.1p/kWh |
| Heating oil |
44p per litre |
10 kWh/ltr |
4.4p/kWh |
| LPG (bulk) |
40p per litre |
6.6 kWh/ltr |
6.1p/kWh |
| Electricity |
13.3p/kWh |
1 |
13.3p/kWh |
CO2 Emission Factors
| Fuel |
CO2 emission factor kgCo2 |
| Natural Gas |
0.194 |
| LPG |
0.234 |
| Biogas |
0.025 |
| Oil |
0.265 |
| Coal |
0.291 |
| Anthracite |
0.317 |
| Smokeless Fuel (incl coke) |
0.392 |
| Biomass |
0.025 |
| Grid Supplied Electricity |
0.422 |
Information above has been kindly provided by - www.biomassenergycentre.org.uk
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