About the article: This special Renewable Energy Focus power generation focus previews REMIPEG's latest update, carried out in the first four months of 2011 by Lahmeyer International, and presents an overview for each renewable power sector, based on scenarios up to the end of 2010.

This article is taken from the July/August issue of Renewable Energy Focus (REFocus) magazine. For a free subscription, click here.

Biomass is the renewable source most widely used within the overall energy system. Conversion processes of varying complexities convert organic material into solid, liquid, and/or gaseous biofuels. These biofuels can then be used for producing electricity, heat, and/or power for transportation.

Electricity generation from biomass is characterised by a wide spectrum of technologies available worldwide, many quite mature. Solid biofuel made from wood for example has a long history, with favourable fuel properties, and large quantities can easily be stored. And the power generation techniques available on the market are technologies adapted from coal fired power plants.

The technologies used in developing and emerging countries show (on average) comparatively low efficiencies compared with those used in developed nations. They also have higher emissions of airborne substances.

In contrast, industrialised countries have access to innovative and highly-efficient conversion technologies, as well as more environmentally sound processes (due to challenging legal emission limits). Technology and research trends illustrate a push into better efficiency, for example by:

• Minimising heat loss and improving heat recovery from exhaust gases;
• Increasing conversion rates;
• And developing interim heat storage capacities (i.e. for more flexible operation in Combined Heat & Power plants) - this is especially true for the lower power range (below 5 MW of electrical power), mainly due to the decentralised availability of biomass, and the fact that only a proportion of the heat produced in CHP to achieve higher overall efficiencies can be used locally.

The corresponding technologies are units with small steam turbines that have relatively low electrical efficiencies i.e. plants using an Organic-Rankine-Cycle (ORC).

In future, gasification technology may become more important (i.e. the Güssing-concept may be developed further, as well as IGCC based on biomass gasification). And due to the varying price level of fossil fuels – compared to reasonably priced biofuels – the use of organic residues from agricultural and forestry primary production (as well as from industry) is becoming more prominent.

This tendency is also supported by the ongoing sustainability debate and the fuel vs. food discussions. Thus, R&D is focusing more on the development of more efficient conversion technologies for the “classic” solid biofuels. In parallel, other R&D programmes aim to develop more specialised technologies – those able to cater for unfavourable fuel properties such as high concentrations of nitrogen, chlorine, potassium and/or sulphite.

In addition, fuel and logistic concepts which are based on the use of compacted biofuels with relative high energy densities (i.e. pellets) will become more viable in the future, improving the total efficiency and economy of bioenergy supply concepts. Such fuels also allow the development of a global fuel market based on different producers, to ensure a certain security of supply.

Electricity generation from the organic fraction of Municipal Solid Waste (MSW) will probably decrease in importance in the future, because more and more of the energy-rich fractions of household waste will be collected separately – at least in industrialised countries. Thus, it is likely that “classic” electricity generation from the organic share of MSW via combustion (in CSP plants for example) will decrease.

This decrease is unlikely to be compensated for by an increase in developing countries, because in these regions there is often a need to catch up with thermal waste treatment.

Solid biofuels

By the end of 2009, at least 36 GW of plants using solid biofuels were in operation worldwide (this figure excludes waste-to-energy). Assuming an operation of between 4,000 and 7,000 full load hours per year, solid biofuel was generating between 144 and 252 TWh (due to missing data it is likely that in reality more capacity is installed, and thus the electricity generation potential is higher).

Assuming growth of roughly 5% during 2010, total installed capacity would have amounted to around 38 GW, capable of providing between 150 and 265 TWh of electricity.

The biggest share of the overall installed capacity (ca. 8.5 GW) is operated within the U.S.; where solid biomass is co-combusted with coal to a large extent. Within Europe, roughly 14 GW is installed. Half of these plants are operated with solid biomass alone; this is especially true for the Scandinavian countries, as well as in Germany and Austria.

In countries like China and other power-hungry countries, solid biofuels are used more intensively for electricity generation. For example in 2009, 3.2 GW was installed in China, a 14% increase over 2008; 0.8 GW in India; and 4.8 GW in Brazil, using mainly bagasse (sources – REN21: Renewables Global Status Report; 2010; EurObserv'ER: Solid Biomass Barometer; 2010, http://www.eurobserv-er.org/downloads.asp, accessed May 2011).

About 50% of the total electricity generated from solid biomass in OECD-countries was produced within the EU (62 TWh). In this region, the main producers are Germany (11.3 TWh, 2009); Sweden (10 TWh, 2009) and Finland (8.4 TWh, 2009) – sources as above.

In many countries, energy recovery from the organic fraction of municipal solid waste (MSW) is counted as solid biomass. Within the OECD nations around 26 to 30 TWh of electricity – based on an installed capacity of roughly 10 GW – was generated in 2009. This is additional to the installed capacities stated above (source – International Energy Agency - IEA: Renewables Information 2010; OECD/IEA, Paris, 2010).

Biogas

Electricity generation from biogas takes place mainly in industrialised nations, but there are some exceptions (i.e. Malaysia and Thailand – with around 51 MW of installed capacity).

Biogas is produced from a broad variety of different feedstocks including dumped organic waste (i.e. landfill gas); sewage sludge (sewage gas); organic waste streams from households and industry; as well as energy crops (mainly maize silage, especially in Germany – due to certain legal conditions).

For 2010, this report estimates that a total of 38 to 43 TWh was generated from biogas worldwide, based on an installed capacity of around 7 GW. This figure was reached by looking at the 35 TWh generated from biogas in OECD countries during 2009 (growth rate of 14% compared to 2008).

More than 70% of the electricity generated from biogas was produced within the EU. The most important players on the biogas stage in 2010 included Germany (ca. 13 TWh); the U.S. (ca. 8 TWh); and the UK (ca. 6 TWh).

Around half of the biogas in the EU is generated by landfill sites, of which almost half is produced in the UK. The remaining biogas is provided by agricultural biogas power plants, using mainly liquid manure and maize silage (only in Germany), and by sewage gas power plants (sources - REN21: Renewables Global Status Report; International Energy Agency, IEA, Renewables Information 2010; 2010EurObserv'ER: Biogas Barometer; 2010).

There are several major trends that can be observed in the biogas sector:

• The production of biogas offers compelling advantages when organic waste with high water content is available, in a sector requiring large amounts of energy. One example would be the food processing industry. Here, the organic waste can be used to produce energy, as well as compost rich in nutrients that can then be sold. More and more companies within the food processing sector are seriously looking at this option as energy prices rise and environmental standards become more stringent;
• The technology to provide biogas has made significant progress during the last decade. More efficient bacteria are now available, which are able to use less robust substances and feedstocks. Nowadays, biogas plants are more reliable, robust and much more efficient. This technological progress will continue in the years to come, making biogas production even more promising;
• The use of biogas within a CHP-plant (i.e. a gas engine providing heat and electricity) is optimum from an efficiency standpoint. But experience has shown that there is not always sufficient heat demand at the location of a biogas plant, especially when animal manure is used as a substrate. Therefore, more often than not, biogas is upgraded to Natural Gas quality, and fed into the existing natural gas grid. In such cases, highly-efficient use is possible at each location connected to the gas grid. Additionally, the upgraded biogas can be used within the transportation sector (i.e. within CNG vehicles available on the market). It is likely that this option will become more widely used in the future.

Liquid fuels

Only a small proportion of the liquid fuel produced globally is used for electricity generation, and this is mostly used for Combined Heat and Power (CHP).

Additionally, this limited use is only recorded in a few industrial nations. Compared with previous years, the use of liquid fuels for electricity generation in CHP plants stagnated (in selected countries, during 2010).

For example, within the OECD, approximately 4.3 TWh was generated from liquid biofuels (mostly in small scale CHP-units) in 2009. Germany accounted for 3.3 TWh and Italy 0.5 TWh (sources – International Energy Agency, IEA: Renewables Information 2010; Bundesministerium für Umwelt Naturschutz und Reaktorsicherheit, BMU: Erneuerbare Energien in Zahlen; 2010).

For 2010, this report anticipates no more than 4 TWh.

Notations in table "a" - as far as statistical data is available; "b" - only OECD-countries.

Part seven: Geothermal power makes stuttering progress...