Article source: www.woodheat.org
Energy Return on Energy Invested
Looking at the energy cost of energy
Economists focus on the money cost of energy, but the energy costs of energy can provide better insights into environmental costs and the underlying reasons for the money cost. For this reason, the energy return on energy invested (EROEI) should be included in any appraisal of the quality, impacts and appropriateness of various energy sources. Here is a sample EROEI analysis for fuelwood compared to other energy sources. Note that the value of labour is not included in the calculation.
- hardwood fuel example: 24 million btu per cord of sugar maple
- 1 gallon of gasoline: 115,000 btu
- average round trip for fuel delivery: 50 miles
- fuel consumption of pick up truck: 15 mpg
- two round trips per cord = 6.7 gallons
- chainsaw fuel per cord: 0.5 gallon
- log splitter fuel per cord: 1 gallon
Total fossil fuel consumption: 8.2 gallons/cord x 115,000 = 943,000 btu
Calculation: Energy content per cord: 24 M btu divided by fossil fuel input: 943,000 btu.
Energy return on energy invested: 25:1
An EROEI of 25:1 may not be worst case for fuelwood, but it is close for rural areas. Harvesting from their own woodlot, some people probably produce firewood at an EROEI of 30 to 40:1.
For comparison, back in the heyday of oil, when discoveries were peaking and consumption was just ramping up, one barrel invested would yield about 100 barrels for sale, a cheap energy bonanza if there ever was one. Today, gushers are a thing of the past, most of the biggest oil fields are in decline and the ‘new’ oil fields are tiny and found under oceans. The EROEI of oil and gas has now fallen to 10:1 to 20:1, depending on age, type and location of the field. So-called unconventional oil such as the bitumen extracted from the Canadian tar sands has an EROEI of as low as 1.5:1 to a high of 4:1, depending on how the calculation is done and who does the calculating.
The green bars are the minimum EROEI and the baige parts are the observed range.
The chart at right was developed by Professor Charles Hall and his colleague John Day. Note that firewood is asigned an EROEI of around 30:1, which is a similar result to the analysis done for this paper.
Wood, in the form of natural firewood, compares favorably with other fuels regarding the amount of net energy realized after processing and transportation. This bodes well for a degree of price stability for fuelwood in the future. Price stability is not likely for the fossil fuels because as the easily accessible deposits are consumed the EROEI rises dramatically, as does the retail price.
What if everyone heated with wood?
This beautiful graphic was created for RSF-ICC, a fireplace and chimney company. Used with permission.Critics of wood heating like to say that if everyone decided to heat with wood, the air would be polluted and every forest in the country would be mowed down to produce firewood. Maybe, but the whole idea is pretty silly, considering that wood is a lousy urban energy source and is best used locally. Even the most ardent defenders of wood heating would never promote it as a universal energy source.
Large parts of the country are relatively thinly populated and have highly productive forests. These are the regions where wood heating makes sense. Foresters have said that wood heating could easily double or more in many regions without putting undue stress on the forest resource. Our forests do need to be managed sustainably, but the methods are well known and can be summarized in a single sentence: Uneven-aged selective harvesting, thinning of dense stands and removal of poorer quality trees, while leaving seed trees of all present species and ages, and some standing dead trees to provide wildlife habitat.
Many woodlots in farm country can offer a striking model of sustainable forestry. The careful work by generations of farmers and other woodlot owners, visible in healthy, productive woodlots that have provided generations of owners with their heating fuel and other products, provides the stewardship model that others can follow.
And while many woodlot owners understand and practice sustainable forest management, others exploit the resource for short-term profit. Unfortunately, some farmers have maximized short term profit by clear cutting their woodlots and converting the land to cash crop production. Some companies and individuals have made a practice of buying large parcels of unused forest land, stripping them of all the commercial trees and then reselling the depleted parcels. These profiteers do meet the definition of woodlot owners, but they do not maintain ties to the lands they buy and sell.
A healthy, well-managed woodlot can provide firewood and other products indefinately.It has long been said that a healthy, well-managed woodlot can yield half a cord of wood per acre per year forever – one full cord being a pile eight feet long, four feet wide and four feet high – and that a ten acre woodlot could sustainably produce enough firewood each year to heat a house. Although that guideline is old and not very precise, it still holds true. In fact, it takes a lot less than five cords of wood, and therefore less than a ten acre woodlot, to heat a new energy-efficient house using a modern wood stove. There is some evidence that carefully designed and built houses can be heated with as little as 1.5 cords of firewood.
Despite its considerable advantages, fuelwood is not a good solution for all households to the problems of high home heating costs and global warming. Fuelwood is not a suitable energy source in all locations, such as densely-populated urban areas, because its air emissions tend to be higher than other options, and the air is already burdened with pollution from industry and transportation. A winter’s supply of wood takes up a lot of space, and the price of firewood in urban areas is normally too high to achieve savings. Successful heating with wood also requires a level of physical fitness and the learning of a special set of skills. Clearly, wood heating is not for everyone.