In writing Wednesday’s post ERoEI for Beginners, I prepared a number of charts that were not used and these are presented here. Where it has been measured and according to the literature, the net energy of oil, natural gas and coal is falling everywhere. Surface mined US coal has one of the highest energy returns of any fuel and is substantially higher than deep mined Chinese coal. In electricity equivalent (Eeq) form, Chinese coal is marching towards the Net Energy Cliff edge while US coal remains far from it. The image shows part of a 50 km long queue of coal trucks in China.
Estimates of ERoEI for solar PV are all over the place (1 to 12) because different analysts set different system boundaries, the energy return is latitude and site specific and its possible that the literature based on historic deployed panels is not up to date with most recent advances.
Sugarcane ethanol in Brazil has ERoEI of 8 to 10 at the refinery gate which at face value seems OK . But to be equitable with its FF cousins this needs to be reduced to 3 to 4 in Eeq form and is barely viable. Temperate latitude biofuels are not viable in liquid form at the refinery gate and converting them to Eeq cripples them completely. But I suppose burning them to make electricity is no less crazy than burning them in an internal combustion engine sat idle at traffic lights.
Most of the data in the following charts comes from Hall et al 2014 who summarise ERoEI research for a variety of fossil fuels and renewable energy flows (see table below) .
Oil and Gas
Note that this chart combines crude oil and natural gas and the data are for production which I assume to mean at the well head. Note that there is also a wide range of dates, which is part of the point of this chart.
Note how the ERoEI of world oil and gas production is deemed to have fallen from 35 to 18 in just 7 years. I’m not sure this is credible. USA production is deemed to have fallen from 30 in 1970 to 11 in 2007. Canada from 65 in 1970 to 15 in 2010. It is very true that more men, machines and energy are being used to extract oil all over the world and this has pushed the cost of extraction higher as ERoEI has fallen. Or is it high price that has encouraged companies to expend more effort? 😉 And those thinking that the price has collapsed need to be aware that the cost of extraction has not collapsed and this translates to massive losses for producers. The trend of falling ERoEI is certainly real, the extent is open to debate. But if it continues, increasing amounts of our human resources are going to be spent on oil and gas production.
In my previous post ERoEI for Beginners I introduced the concept of electricity equivalence (Eeq). This is a first step towards trying to normalise different energy sources to a common datum. Crude oil at the well head is not much use directly to anyone. But it can be used to make electricity and in doing so roughly 62% of its energy will be lost as waste heat (BP convention). This normalisation enables direct comparison with renewables and nuclear, that have the advantage of producing electricity directly.
Following this convention, oil and gas production in the USA and China has already fallen off the net energy cliff while global production is getting close to it.
In 2005 (pre-fracking) US natural gas had high ERoEI of 67. Freise (2011) charts the decline in Canadian gas ERoEI from 38 in 1993, to 26 in 2000, to 20 in 2009. This march towards lower ERoEI in Canada is sending Canadian gas Eeq towards the net energy cliff edge. Large quantities of natural gas in Canada are used in tar sands extraction and upgrading. High ERoEI gas is being traded for liquid fuel that has ERoEI of about 3 (own calculation based on published Canadian statistics).
Hall et provide ERoEI data for the USA and China. US coal has very high ERoEI of 80 in 1950 and 60 in 2007. The fall is only slight and that is because mining methods have not changed very much. US coal is mainly surface mined from vast surface deposits in the Appalachians and Wyoming. By comparison, Chinese coal had ERoEI of 35 in 1995 and 27 in 2010. The lower ERoEI of Chinese coal to large extent reflects underground mining compared with surface mining in the USA. The Chinese need to apply vast effort to extract and transport coal to drive their economy.
The open circles show the electricity equivalent values. The mine mouth values are reduced by 0.38 and no deduction is made for transport. We see that US coal Eeq is probably one of the highest energy value sources we have but it is being forced out because of concern over CO2 emissions. Part of the problem here is that US coal is too easy to produce making it a fuel of first choice for exploitation. Chinese coal Eeq is getting closer to the Net Energy Cliff edge.
There seems to be agreement that Hydro Electric power has high ERoEI. A large amount of energy is invested at the start in excavation, concrete and generating kit. But thereafter a dam may produce electricity for 100 years or more with little operation and maintenance energy costs. Although many dams today are getting fitted with new more efficient turbines, which means a new energy and economic investment.
High altitude wind
As explained in my earlier post, high altitude wind has potential to multiply the ERoEI of ground based wind turbines. The argument here is rather complex and will be explained in greater detail in a separate post. Suffice to say that the mass of the KiteGen, and hence energy embedded in the materials, is a fraction of that in a large turbine. This is specific to the design concept.
The ERoEI of a wind turbine is site dependent. A good windy site will produce more energy over the life of a turbine in a calm site. The wind industry has tended to focus on sites with good wind resource and so site specific factors are less than for solar. A large number of studies places the primary ERoEI of wind turbines in the ballpark 15 to 20 and there doesn’t seem to be too much disagreement on that.
The contentious issue for wind is treatment of intermittency. Is there an energy cost associated with that? Of course there is. Broadening the ERoEI boundary to create dispatchable power substantially reduces the ERoEI. At present this economic cost is not paid by the wind producers but is borne by others. Weisbach et al  reduce the primary ERoEI of wind by a factor of 4 to generate their buffered ERoEI assuming that pumped storage hydro is used. But they rightly note that using FF balancing services would have a lesser impact.
With a range of ERoEI from 1 to 12, anarchy reigns in the PV ERoEI business. There are a number of issues at play here. The first is that different energy boundaries are being used. I personally favour a wide boundary that includes direct energy use, materials and labour. And for intermittent technologies a reasonable energy cost needs to be apportioned to mitigating that intermittency. The second is that solar PV is site specific. A sunny tropical site may yield three times the lifetime energy of a cloudy high latitude site. The third is that the efficiency of PV is improving all the time. Mixing these factors to varying degrees underpins the anarchy. But adding battery storage to a good tropics-based system is going to substantially reduce the ERoEI. Proponents of Solar PV seem set to continue to promote optimum performance without backup while others will observe that normal performance is sub-optimal and that in the real world the sun does not shine at night.
Sugar cane ethanol is made in the Tropics where there is more abundant solar energy. And sugar cane employs a more efficient photosynthetic route than maize to manufacture carbohydrate more efficiently. No fossil fuel based fertiliser is required and the bagasse (left over organic cane waste) is combusted to make electricity in the refinery. These conditions combine to give sugar cane ethanol a viable ERoEI of 8 to 10 at the refinery gate . Too bad about the disappearing forest.
I have tried to develop an equitable way of comparing different renewable and fossil fuel based energy sources by reducing all to electricity equivalent. And I’m afraid that sugar cane ethanol cannot escape that net. In Eeq form, sugar cane ethanol falls off the Net Energy Cliff.
The temperate latitude biofuels (corn ethanol and biodiesel) are really not worth discussing again.
The energy debate continues to be partly driven by emotion and not by the laws of physics and needs of human society or nature.
My own opinion is that understanding ERoEI is vital to the continuance of industrial society as we know it. That does not mean projecting economic growth infinitely into the future but managing the energy and human resources and natural resources we have in a rational and responsible way. One that optimises benefits for humans and nature.
Understanding the intricacies of the human energy web is enormously complex and requires substantial resource to fully understand it. But it is not nearly as complex as understanding the climate system and I would argue that understanding our energy web is far more important. And so here is a challenge for the United Nations. Establish 10 working groups globally to study the human energy web, deliberately choosing ones with opposing outlooks at the outset (fossil fuel v nuclear v renewables v collapse) and challenge them to model the human energy web and to explore the multitude of outcomes.
And to then use that information to answer if asking Africa to skip over the fossil fuel stage of their energy development is beneficial to Africans?
 Jose ́ Goldemberg , Suani Teixeira Coelho, Patricia Guardabassi: The sustainability of ethanol production from sugarcane. Energy Policy (2008), doi:10.1016/j.enpol.2008.02.028
 Charles A.S. Hall n, Jessica G. Lambert, Stephen B. Balogh: EROI of different fuels and the implications for society: Energy Policy 64 (2014) 141–152
 D. Weißbacha,b, G. Ruprechta, A. Hukea,c, K. Czerskia,b, S. Gottlieba, A. Husseina,d (Preprint): Energy intensities, EROIs, and energy payback times of electricity generating power plants