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Estimation of Renewable Energy Potential - Short Guideline
By Gunnar Boye Olesen, INforSE-Europe Coordinator.
Industrial wood waste
In sawmills, pulp mills, and all wood-processing industries,
residues are made that can be used for energy purposes: bark
sawdust, edgings, chips, etc. An analysis of 7 European
countries shows that 30-70% of wood-industry residues are used
for non-energy purposes like paper and fibreboard.
Larger residual pieces can be chipped for use in wood-chip
boilers, while sawdust can be burned in special furnaces or
compressed into wood pellets or briquettes that can be used in
smaller furnaces and ovens.
Many wood industries use wood residues to meet their own energy
demands, but surpluses are often available at low or no cost.
Agricultural crop residues
Straw and prunings of fruit trees, as well as wine- and olive oil
residues, are among the agricultural residues that can be used
for energy purposes. In Northern and Central Europe, straw is
by far the most important, and is used in large quantities in
some countries. The straw surplus varies greatly from year to
year, depending on weather.
Straw surplus can be ploughed into the field to enrich the soil.
When this is needed for a sustainable agriculture, less surplus
straw will be available for energy. Pesticides and salty winds
can leave unwanted chlorine compounds in the straw in certain
Energy Crops
Agricultural overproduction and setting the land aside are now
common in the European Union and can be expected in Central and
Eastern Europe as well. This set-aside land can be used for
different purposes, one of them being energy-crop production.
Promising crops which can be planted for energy purposes in
Europe include short-rotation trees (coppices of various willows
and poplars), Miscanthus, and Sweet Sorghum.
Other promising energy crops include plants that can be processed
for liquid fuels, e.g. rape seeds for bio-oil.
The largest potential for biogas is in manure from agriculture.
Other potential raw materials are include organic, bio-degradable
waste from industries, in particular wastes from slaughter-houses
and food-processing industries, sludge from waste-water
treatment, and organic household waste. Care should be taken not
to include waste with heavy metals or harmful chemical substances
when the resulting sludge is to be used as fertilizer, which is
usually the case.
In sufficiently windy areas where little conflict exists with
human settlements (noise) or natural life (bird-protection
areas), the wind is one of the most environmentally benign
energy sources. The energy in the wind is highly dependent on
the average wind speed of the site, which depends on altitude,
the regional wind conditions, and local obstacles. Sites with
average wind speed below 4 m/s at a height of 10 m are not
considered viable for larger wind turbines, at least in the near
future, while in areas with wind speed above 7 m/s at a height
of 10 m, wind turbines are cost-effective compared with most
alternatives. Many areas still lack good estimates of wind
potential, and such estimates can be quite expensive to make.
Simple estimates can be based on averages of meteorological
measurements, but they give quite rough results.
Solar Heat
The most environmentally benign form of energy is probably direct
use of solar heat. The largest factor limiting its use is not the
amount of the resource, but the demand that can be covered with
present technologies. Solar hot water heaters are successful
because the steady hot water demand during summer can be met with
just one day's accumulation of heat.
Most renewable energy solutions generate more jobs than do
solutions that use fossil fuels. The following table contains
overviews of the direct employment in jobs resulting from some
of the proposals. In "direct employment" we include jobs in
manufacturing, installation, operation, and maintenance, as well
as jobs in suppliers of goods and services. The wider societal
employment effects of the activities such as the effects of
increased income, are not taken into account here. Such effects
are generally positive where societal costs and/or imports are
Figures are new, full-time permanent jobs in the construction,
operation, and maintenance of renewable energy technology to
generate 1 TWh annually of energy with current Western European
technology; except for small hydro, where the figure reflects
job-years to install hydro-power to replace 1 TWh annually.
Using the above-mentioned methods and local data we estimated the
renewable energy potential in Slovakia. The figure shows
potentials for renewable energy to deliver a total of 30.1
TWh/year with currently used technology in Europe. This is equal
to 13% of the country's energy demand of 230 TWh/year. The
potential for solar energy, estimated at 0.1 TWh/year, is not
included in the figure.
This article is based on the report "Guideline for Estimation of
Renewable Energy Potentials, Barriers, and Effects", which is
available from INforSE - Europe.

- Employment potentials

- Wood from forests: 450 jobs/TWh
- Agricultural waste (straw): 350 jobs/TWh
- Biogas: 560 jobs/TWh
- Wind turbines 300 jobs/TWh
- Solar heating 700 jobs/TWh
- Small hydro 30,000 job-years/TWh
Evaluation methods:
- Unused potential from commercial forests
Method 1: Estimate theoretical available wood volume
(in m^3 of solid wood, including bark) in terms of annual growth
of the forest (from forest statistics) minus annual removals. To
estimate net potential reduce the first amount by the estimated
volumes of unofficial use and of branches that must be left in
forest for ecological reasons; often a 50% reduction is
appropriate. Estimate energy content from the wood's density
(e.g., 600 kg/m^3 for pine & spruce, 800 kg/m^2 for beech, both
at 20% humidity) and lower heating value (e.g., 4.2 kWh/kg at 20%
humidity for most trees).

Method 2: When forest growth statistics are not available,
estimate the real potential as a fraction of annual removals.
With European forest practices, a volume equivalent to 25% of the
timber production (including bark) is available for wood chips.
- Waste from wood industries
Method 1: Evaluation of wood residues can be based
on trade statistics of non-energy wood and wood products compared
with total removals from forests. The difference is available for
energy purposes, and is probably to some extent already used as
such in wood industries.

Method 2: One rule of thumb is that residues in general are
25-35% of total forest removals, and, of these, 30 - 70% is often
used for non-energy purposes.

- Agricultural crop residue: straw

Method 1: Produced amount of straw (in tons) is estimated
from agricultural statistics. The total amount should be reduced
to the fraction that is available for energy (up to 59% in
Denmark, about 35% in Northern Bohemia). Energy content is about
4.1 kWh/kg at 15% humidity.

Method 2: If agricultural statistics do not include
straw, a crude estimate can be made by setting the amount of
straw (in tons) equal to the amount of grain.
Energy Crops
When the available area and type of land are known, the annual
yields can be estimated, e.g., by using the following average
annual yields per ha for better soil in Central Europe:
- Salix (Willow): 15 dry tons = 67 MWh
- Miscanthus (Elephant grass): 20 dry tons = 94 MWh
- Sweet Sorghum: 25 dry tons = 125 MWh
Method 1: Estimate the amount of available material and the solid
fraction of the material (solid fraction is about 20% for cow
manure, 25% for pig manure, and 6-10% for manure in the form of
slurry). Per tons of dry material, the biogas and energy
production will be about 300 - 450 m^3 of biogas and 2000 - 3000
kWh, depending on material and biogas process. Production yields
are usually high from fatty materials, slaughterhouse waste, and
pig manure and lower from cow manure and wastewater sludge.
Reduce estimate by 20% to account for heating of the process.

Method 2: From the number of animals one can estimate the amount
of manure, depending on the race and species of animal, and
fodder. For Denmark and the Czech Republic, the amount of biogas
and energy is estimated to be:

- Milking cow: 1.2 - 1.7 m^3/day, 2,500 - 3,500 kWh/year
- Sow: 0.3 - 0.45 m^3/day, 630 - 970 kWh/year
(Energy estimates are for animals kept in a stable all year, and
have been reduced by 20% to account for biogas process heat.)
When the average wind speed is known, the available wind
energy can be estimated, e.g.:
With 4 m/s average wind at a height of 10 m and with some
obstacles (as at a Danish inland site), wind turbines on 1 km^2
can yield 6.4 GWh/year.
With 7 m/s average wind at a height of 10 m and with no obstacles
(at sea or at windy mountaintop location, wind turbines on 1 km^2
can produce 23 GWh/year. (One km^2 can accommodate 16 wind
turbines of 450 - 500 kW capacity. In Denmark, the average wind
at a height of 10 m varies from 4 m/s at a fair inland sites to
8 m/s at sea. In the Czech Republic, this figure varies from 2.5
m/s below 600 m altitude to 7 m/s at 1500 m height (both at sites
with few obstacles).
Solar Heat
Solar heating (standard systems) can cover (figures for Northern
/ Southern Europe, respectively):
- 60% / 80% of hot water heating in households
- 25% / 50% of space heating in households
- 10% of district heating to households for Northern Europe (with
12 -hour storage tank)
- 100% of heating of pools in summer.
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ISSUE #13 Sustainable Energy News (16 pages) (1996-06-30)
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