If I asked you to think of renewable energy, what comes to mind? I imagine it is skyscraper-sized wind turbines, solar panels on suburban roofs, or massive hydroelectric dams. You probably do not think of burning wood or converting crops to liquid fuel to be used in cars. Yet throughout the world bioenergy remains the biggest source of renewable energy. In fact its growth in the last decade has been greater than or similar to that from wind and solar in most places, and those places include the European Union and the United States of America.
Europe: A Reversal Of History
The Industrial Revolution was fundamentally an energy transition from burning biomass, mostly wood, to burning coal. Despite being called a revolution this was a rather protracted affair. America did not get the majority of its energy from coal until the 1880s, while China and India remained predominantly biomass powered until the 1950s and 1960s. And many countries, or regions within countries, still remain highly dependent on energy from biomass.
This transition from burning biomass to burning coal occurred first in Europe. By the mid-eighteenth century England was getting most of its energy from coal, and by the mid-nineteenth century biomass was in long-term decline in Western Europe. However this decline did not start until the mid-twentieth century in Eastern Europe.
(Source: Fernandez et al. 2007)
This long-term trend, however, has been reversed, and biomass is now seeing some form of renaissance in Europe. The reason for this is simple: renewable energy targets and subsidies.
In 2007, the European Union decided that it should get 20 percent of its final energy consumption from renewables by 2020. However, looking at the available options, countries quite clearly decided that wind and solar were not ready to be scaled up to the desired level that quickly. They turned to the oldest form of energy available: biomass.
Despite what many perceive, the renewable energy target has, so far, lead to a far bigger expansion of bioenergy than wind and solar energy. In 2000, biomass was the biggest source of renewable energy by a significant margin, and made up more than half of final energy consumption in the EU. As the graph below shows this dominance of biomass was still very much the case 11 years later.
The inclusion of hydroelectricity in the graph above is merely an obligation. Most EU countries have stopped building any hydroelectric capacity, so its growth over this period was essentially zero. The same holds for geothermal energy. Growth of renewable energy since 2000 therefore only really came from three energy sources: wind, solar, and biomass.
In percentage terms the two energy sources that saw the most rapid growth were wind and solar. This is unsurprising, given their low starting point. However, in absolute terms, biomass is the clear winner. Between 2000 and 2011 biomass grew by 49 million tonnes of oil equivalent (toe). Wind and solar only grew by 13 and 6 million toe respectively. In other words, the absolute growth of biomass was 1.5 times greater than in wind and solar, and so far the majority of new renewable energy since 2000 has come from biomass, not wind and solar.
Biomass is also the biggest source of renewable energy, on a final energy consumption basis, in all but two EU countries. The exceptions are Cyprus and Ireland. Denmark may get 30 percent of its electricity from wind farms, but it still gets more than twice as much of its final energy consumption from biomass than from wind farms.
Biomass In Germany
The supposedly rapid expansion of solar power in Germany gets a lot of attention. The even more rapid expansion of biomass however has received absolutely no attention. Final energy consumption from biomass grew by 16 million tonnes of oil equivalent between 2000 and 2011, while wind and solar grew by 3.4 and 2.1 million toe respectively. Absolute growth of biomass in Germany has therefore been three times higher than for wind and solar combined.
The increase in bioenergy in Germany has taken many forms. For example wood-chip heating systems have grown massively since 2000. In a decade, Germany went from burning almost no wood-chips for heating to burning 1.2 million tonnes each year.
Germany also now gets a significant portion of its electricity from bioenergy. In 2013, bioenergy was used for almost 7 percent of its electricity production, higher than that from solar PV and just short of that from wind power. Electricity generation from bioenergy receives approximately 4.5 billion Euros in subsidies each year, 30 percent more than is received by onshore wind in Germany.
The production of bioenergy is also now a significant form of land use in Germany. According to official statistics a total of 2 million hectares is devoted to crop-based biofuels. This is 17 percent of arable land and approximately 6 percent of total land in Germany. Yet it only produces around 2 percent of Germany's total energy consumption, a remarkably inefficient use of land.
However wood, not crop-based biofuels, is the biggest source of bioenergy in Germany. A total of 53 million cubic metres of wood are used each year for energy generation, which is 41 percent of the total annual German wood harvest. This corresponds to approximately 4 percent of Germany's total energy consumption, a figure that has more than doubled in the last decade.
This then is a rather different picture of the renewables revolution happening in Germany.
The United States: A Similar Theme
Here was the position in the United States in 2000: almost all renewable energy came from hydroelectricity and biomass. Biomass provided 49.2 percent, while hydroelectricity provided 46 percent. Of that provided by biomass 76 percent was from wood, 17 percent was from waste and only 7.8 percent was from liquid biofuels. Negligible quantities were derived from geothermal, solar and wind energy.
However, the early 21st century saw the mass-subsidization of corn ethanol, and today almost half of bioenergy comes from liquid biofuels. The conversion of food crop into fuel is nothing new. Rudolf Diesel ran some of his earliest engines on crop-based fuels. However the scale of the conversion of corn into fuel in the United States in the last decade and a half is something new. In 1980 only 0.7 percent of US corn consumption was used for producing fuel. By 2000 this percentage had reached 8 percent, but last year it reached an astonishing 43 percent.
Between 2000 and 2013, total growth of renewable energy consumption from liquid biofuels was almost identical to that from wind and solar combined. Liquid biofuels grew by 1768 trillion Btu, from 233 to 2001 trillion Btu, while wind and solar combined grew by, 1820 trillion Btu, from 95 to 1915 trillion Btu.
In the 21st century growth in US renewables was essentially restricted to the three previously mentioned energy sources: liquid biofuels, wind energy, and solar energy. As in Europe, there was practically no new hydroelectricity capacity and very little new geothermal capacity.
This is where the US was last year. Biomass still provides almost half of renewable energy, but now provides almost two times more than any other source of renewable energy.
As in Europe the land required to produce liquid biofuels is significant. Last year a total of 95 million acres was used to produce corn. This produced 14 billion bushels of corn, of which 5 billion were used for corn ethanol production.
So approximately 140,000 square kilometres of America is now used to produce corn ethanol, which is 1.4 percent of American land. However based on official government statistics only 1.1 percent of US primary energy consumption comes from corn ethanol.
Fundamental physical realities mean that there is an upper limit to how much of our energy consumption can come from biomass. This is made clear by considerations of power density. Power density is an energetic analogy with that of crop yield. But instead of tonnes per hectare we work in watts per square metre. Typical biomass energy sources provide us with less than 0.5 watts per square meter. In the case of corn ethanol it is around 0.2 watts per square metre.
These power densities of energy production can then be compared with the power density of energy consumption. In many densely populated affluent economies, such as the UK, Germany and Japan, this is above 1 watt per square meter. In other words, powering these economies purely with biomass will require more than two times more land than they have.
A similar calculation can be made with corn ethanol in the US. Moving to 100 percent corn ethanol would require a landmass of roughly the size of the US to be converted over to corn ethanol, a very unlikely prospect.
Physical realities therefore mean that it is implausible that bioenergy can provide anywhere close to the majority of the energy needs of affluent economies.
And whether the large-scale expansion of bioenergy is desirable is increasingly questionable. The expansion of corn ethanol and biodiesel around the world has lead to a significant diversion of cropland over to biofuel production. Some commentators have referred to this a "crime against humanity," a perhaps justifiable claim given the potential impact this has had on global food prices.
Similarly the environmental benefits of biomass are increasingly in doubt. The expansion of cropland to accommodate liquid biofuels production has almost certainly resulted in large amounts of deforestation, and the carbon released during this has quite probably offset whatever emissions are supposed to be saved by the biofuels in the first place.
Liquid biofuels also have very problematic energy returns on investment. If you want to grow crops you will need to dump fertilizers on fields and these fertilizers are produced using fossil fuels. For these and other reasons the carbon dioxide used to produce corn ethanol may not be that much different from the carbon dioxide emissions they apparently save.
Environmental groups are also increasingly opposed to the large-scale expansion of bioenergy. A recent report from Friends of the Earth and Greenpeace suggested that getting electricity from burning wood may be worse than getting it from coal. And there is now an ongoing argument between many British environmental groups and some renewables lobby groups over the issue. Subsidies and mandates for liquid biofuels are also now routinely opposed by many environmental NGOs.
"Advanced" biofuels however may solve some of these problems, or they may not. And a recent report claims that cellulosic biofuels may become cost-competitive – there is always a report saying a technology will become cost-competitive by a particular date – by 2016. The recent IPCC WG3 report on climate change mitigation also gave what could be called a qualified thumbs-up to both large-scale bioenergy and bioenergy with CCS.
These forms of energy conversion therefore may become a vital part of our attempts to combat climate change. However whether they will, or whether we should even try, ought to be a matter of important debate.
Robert Wilson is a PhD student in mathematical ecology at the University of Strathclyde. His secondary interests are in energy and sustainability, and writes on these issues at The Energy Collective, where this article first appeared.
1. EU renewable energy statistics come from Eurostat.
2. US renewable energy statistics come from EIA.
3. EU statistics are in terms of final energy consumption, whereas US statistics are in terms of primary energy consumption. I explained the difference between these in a recent article. I use the units used by the official statistical bodies. In the US case it is the British Thermal Unit, which Americans continue to use in an ironic post-colonial fashion.
4. Estimates for European biofuel use from 1850-2000 are taken from Fernandez et al. 2007. These statistics are in tonnes of biomass, so are not directly comparable with the other measures.
5. US total energy consumption statistics are taken from EIA.
7. German electricity production statistics can be found here. It's in German, but the German for biomass is biomasse.
8. Vaclav Smil's primer on power density is an excellent introduction to the spatial requirements of energy generation.
9. The inability of bioenergy to power industrial civilizations is explained in depth in E.A Wrigley's excellent book Energy and the English Industrial Revolution.