Modern society was born a hundred and fifty years ago when coal began providing sufficient energy to make lots and lots of steel and steam, lifting ordinary citizens out of poverty and into the newly-developing middle class. Soon after, we added oil. The energy obtained from these sources was obvious and immediate. It took little energy input to get a lot of energy out.
Energy Returned on Investment, or EROI, was an early concept that easily demonstrated the advantages, as well as the investment needed, to exploit these new energy sources (The Encyclopedia of Earth). Also referred to as Energy Returned on Energy Invested (EROEI), EROI is the ratio of energy returned to energy invested in that energy source, along its entire life-cycle.* When the number is large, energy from that source is easy to get and cheap. However, when the number is small, the energy from that source is difficult to get and expensive.When the number is one, there is no return on the energy invested, and the entire investment has been wasted. The break-even number for fueling our modern society is about 7.
When fossil fuel emerged in early 20th century America, the return on investment was enormous. In 1930, 1 joule of energy put into oil got 100 joules of energy out, an EROI of 100. Similarly for coal. The economies of the industrialized world became super-charged by fossil fuel, and their standard of living increased proportionately. In only a few generations, the planet had a billion middle-class humans.
But these early fossil fuel deposits were the most easily recoverable. As time went on, they became more difficult to recover, it cost more energy and effort, and the return was less. The environmental costs also became larger. So in 2006, 1 joule of energy put into oil got only 15 joules of energy out, still enough to bring billions in profits to oil companies.
New technologies have brought the EROI of unconventional sources like tar sands oil and shale gas into the profitable range, but they will always be lower than conventional sources. It’s why their production becomes marginal when oil prices drop below $60/barrel.
The decreasing EROI was obvious a hundred years ago even to J. Paul Getty, and the push to develop other, more diverse sources, resulted in the emergence of hydroelectric, natural gas and nuclear. Recently, we’ve added biomass, wind and solar, again as a result of technological advances that brought the EROI above 1.
But EROI is still the method to evaluate whether an energy source is sufficient to power our society into the future. Recent EROI determinations have become better at capturing the total life-cycle costs, and eliminating temporary economic fluctuations and politically motivated influences and policies that distort the actual return.
Results from the most recent study byWeißbach (2013) are summarized in the above figure. Other studies give similar results (Carbajales-Dale 2014). EROI was evaluated for power plants fueled by wind, photovoltaic solar, solar thermal, hydroelectric, natural gas, biomass, coal and nuclear. Because some sources require buffering, storage or load-following, there are two values for each source, with and without energy storage or buffering.
For societal needs, the buffered value, or the value with energy storage, is more representative of the EROI. Only in situations where the energy produced is used directly and the demand can vary with the supply, is the value without energy storage comparable. The buffered EROI for each energy source is –Nuclear 75, Hydro 35, Coal 30, Closed-Cycle Gas Turbine 28, Solar Thermal 9, Wind 4, Biomass 4, Solar PV 2.
Weißbach uses the least energy intensive storage technology, pumped hydroelectric energy storage, as the buffering technology that lowers the EROI the least. Batteries are about ten times more energy intensive than pumped hydro storage, so battery storage is not viable at all for very large-scale applications. As we keep finding to our dismay. Rooftop solar is an exception because it is used directly at the source and is not supporting the outside society at large.
There is a minimum EROI, greater than 1, that is required for an energy source to be able to power society (The Energy Collective). “An energy system must produce a surplus large enough to sustain things like food production, hospitals, and universities to train the engineers to build the plant, transport, construct, and all the elements of the civilization in which it is embedded.”
Weißbach calculates that this minimum viable EROI is about 7 for the United States and the European Union. Lower EROIs cannot sustain our society at our level of complexity or our standard of living. So I ask – is a lower EROI fair for a developing country?
It is critical to understand these EROI values when making difficult decisions on energy policy. The many claims that renewables alone, or in the majority, can fuel our future are not consistent with their EROI. America’s present EROI averages about 40. A mix of 50% renewables, 30% fossil and 20% nuclear gives an average EROI of about 25.
I am not sure our economy can survive such a drop in surplus energy. Economies with access to higher EROI energy sources have greater potential for economic expansion and diversification. Thus, the rush to coal by developing countries like China and India.
Because of this, coal is now the fastest growing energy source in the world. This is why serious environmentalists, and the United Nations IPCC, strongly urge the world to adopt some mix of nuclear, hydro and renewables as the best mix to can replace fossil fuels.
Dr. Judith Wright and I previously suggested a global energy mix by mid-century of a third fossil, a third renewable and a third nuclear, which has an average EROI of about 36. This mix would cut carbon emissions in half over the present mix and is achievable by 2040 with existing technologies.
If we are to enter a cleaner energy future, and continue to lift people out of poverty around the world, every country’s energy mix has to have as high an EROI as possible, or it will not be sustainable, or acceptable, to humanity as a whole.
*EROI = Quantity of Energy Supplied ÷ Quantity of Energy Used in the Supply Process. The units are usually given in BTUs, kWhs or other units available to both energy supplied and used.
Quantity of Energy Used in the Supply Process includes: – drilling, refining, construction, installation, smelting, operations, maintenance, decommissioning, transportation, roads, manufacture of specialized equipment and chemicals required for extraction.
Quantity of Energy Supplied includes: electricity, useable heat, power for useful work.
Follow Jim on https://twitter.com/JimConca and see his and Dr. Wright’s book at http://www.amazon.com/gp/product/1419675885/sr=1-10/qid=1195953013/
IMHO this relation Energy Out/Energy In is the most important number which will determine not only the outcome of many global conflicts but also our survival. IV.