Jul 13, 2012
Energy return on energy investedBack
Engineering|Natal|Diesel|Energy|Hydropower|Turbines|Waste|Water|Europe|University Oil Drum October|Diesel Fuel Energy|Energy|Energy Cost|Energy Return|Energy Sense|Energy Source|Equipment|Steel|Transport|Cutler Cleveland|Dirk Heydorn|Ernst Van Niekerk|Jeremy Wakeford|Phillip Pare|Power|Turbines|Waste|Water|Engineering News|Diesel
© Reuse this
“This would seem to be at variance with my understanding of one of your earlier comments that the energy harvested from a wind turbine would take a very long time (perhaps in the order of 23 years) to be greater than the energy used to manufacture the turbine. Is there, perhaps, something that I have misunderstood?”
The concept of ‘energy return on investment’, or EROI, is one of those terms which have popped up recently. The definition of EROI is: (usable energy acquired)/(energy expended to create the energy source). Simply put (oh, yes, for the Natal graduates), if you take a diesel fuel machine and use it to plant a field of sugar cane, then you will get a certain tonnage of cane. If you use another machine to harvest the cane and take it to a mill in a truck and, at the mill, use cane knives and presses and so on, then, potentially, you will end up with some ethanol.
The EROI for this process is then (diesel fuel energy for machine for planting and harvesting and transport)/(energy content of ethanol).
You will find that this figure is about 5 – so, it makes energy sense to plant cane to get ethanol. The EROI figure for photovoltaic is about 5.8 and for hydropower it is about 100. For wind, it is about 18. The EROI figure is misleading. There is the question of the energy input to manufacture the machines in the process and the timeline to which the EROI relates.
In our example, do we allow for the energy input to melt the steel to fabricate the sugar cane machine for planting and harvesting? If not, why not? Say, it takes two years to build a processing machine. Once built, it uses 5 ℓ of diesel an hour, takes in sunlight and water and garden waste and, 2 000 hours later, produces 20 000 ℓ of diesel. The EROI is, thus, 10. But, if the machine needed 10 MWh to build, then the whole sum is negative. For the EROI to make sense, the energy input (say, sugar cane) and output (say, ethanol) must be much greater than the energy cost of fabricating the equipment used in the process.
This brings us to the second point – the time-line. If I make a wind turbine out of a bicycle wheel and it produces 50 W when the wind blows and if my little turbine lasts for 50 years, then the EROI will be much different to it lasting, say, two years.
Stating that wind turbines have an EROI of 18 does not mean you get back the input energy in one year – it all depends on how long and often the wind blows.
However, a summary of all the reports and studies to date was compiled by Cutler Cleveland (Boston University Oil Drum October 19, 2006). He found that wind turbines typically pay for their energy content within the first year of operation. Which settles it, right? Well, Engineering News readers Dirk Heydorn and Ernst van Niekerk came up with energy requirements to melt 267 t of steel (the mass of a 2 500 kW wind turbine) and the lowest estimated ‘payback time’ based on energy produced by the turbine was about eight months.
I have my own (higher) estimate. The thing to note is that many estimates ignore the fact that there is an energy cost in transport from Europe, erection, manufacture of rare-earth magnets, power lines, cabling, alternators, and so on, and generation estimates are often based on the turbine producing 50% of rated power for 25% of the time when, in fact, these figures may not be reached.
In summary, the EROI is a figure which estimates energy return but, for a variable- energy supply, such as wind, the time taken for that return is also variable.
Edited by: Martin Zhuwakinyu© Reuse this Comment Guidelines
Other Terry Mackenzie-Hoy News
Updated 6 minutes ago The International Monetary Fund (IMF) has once again lowered its 2014 growth forecast for South Africa to 1.7%, having previously forecast that Africa’s second-largest economy would expand by 2.3%. The 0.6% downward revision, which is contained in the World...
Updated 19 minutes ago A study on the economic state of the City of Johannesburg’s (CoJ’s) economy has revealed lagging growth and a lack of diversification as the city struggled to return to pre-financial crisis growth levels. The ‘CoJ Economic Overview 2013: A Review of the State...
Updated 24 minutes ago With the right reforms and investment, Nigeria had the potential to raise its gross domestic product (GDP) by 7.1% a year through to 2030, to more than $1.6-trillion, which could make the country a top 20 global economy, a new report by the McKinsey Global Institute...
Recent Research Reports
Real Economy Year Book 2014 (PDF Report)
This edition drills down into the performance and outlook for a variety of sectors, including automotive, construction, electricity, transport, steel, water, coal, gold, iron-ore and platinum.
Real Economy Insight: Automotive 2014 (PDF Report)
This four-page brief covers key developments in the automotive industry over the past 12 months, including an overview of South Africa’s automotive market, trade figures, production and the policies influencing the sector.
Real Economy Insight: Construction 2014 (PDF Report)
This five-page brief covers key developments in the construction industry over the past 12 months. It provides an overview of the sector and includes details of employment in the sector, infrastructure and municipal spending, as well as insight into companies’...
Real Economy Insight: Electricity 2014 (PDF Report)
This five-page brief covers key developments in the electricity industry over the past 12 months, including details of State-owned power utility Eskom’s generation activities, funding and tariffs, independent power producers and prospects for the sector.
Real Economy Insight: Road and Rail 2014 (PDF Report)
This six-page brief covers key developments in the road and rail industries over the past 12 months, including details of South Africa’s road and rail network and prospects for both sectors.
Real Economy Insight: Steel 2014 (PDF Report)
This four-page brief covers key developments in the steel industry over the past 12 months. It provides an overview of the global and South African steel and stainless steel markets, South Africa’s major steel producers and events that have shaped these markets.
This Week's Magazine
Local aerospace company Denel Aerostructures (DAe), part of the State-owned Denel Group, has won a fourth contract to manufacture parts for the Airbus A400M military air transport and air-to-air refuelling aircraft. The new contract, which was won in an international...
Although CEO Mark McChlery and chief marketing officer Bob Skinstad likened themselves to children in a playground when taking on the task of “reengineering and repositioning” the Seartec brand, the “young, dynamic and enthusiastic guys” were like proud...
An increasing number of buyers, in both the new and used car markets, are opting for finance structures that lower their monthly repayments, says asset financing company WesBank. These include the use of large balloon payments (also known as residuals), as well as...
Tertiary education institutions can use search engine giant Google’s Chromebook to provide secure mobile end-point devices for students on which they can share documents, work collaboratively on documents and access education materials and applications being used...
Local ceiling and partition company Abbeycon has beaten global competition at the Saint-Gobain Gypsum International Trophy competition, which was held last month in Berlin, Germany.