Jul 13, 2012
Energy return on energy investedBack
Engineering|Natal|Diesel|Hydropower|Turbines|Waste|Water|Europe|University Oil Drum October|Diesel Fuel Energy|Energy|Energy Cost|Energy Return|Energy Sense|Energy Source|Equipment|Steel|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 (150 word limit)
Other Terry Mackenzie-Hoy News
Recent Research Reports
Steel 2015: A review of South Africa's steel sector (PDF Report)
Creamer Media’s Steel 2015 report provides an overview of the key developments in the global steel industry and particularly of South Africa’s steel sector over the past year, including details of production and consumption, as well as the country's primary carbon...
Projects in Progress 2015 - First Edition (PDF Report)
In fact, this edition of Creamer Media’s Projects in Progress 2015 supplement tracks developments taking place under the Renewable Energy Independent Power Producer Procurement Programme, which has had four bidding rounds. It appears to remain a shining light on the...
Electricity 2015: A review of South Africa's electricity sector (PDF Report)
Creamer Media’s Electricity 2015 report provides an overview of State-owned power utility Eskom and independent power producers, as well as electricity planning, transmission, distribution and the theft thereof, besides other issues.
Construction 2015: A review of South Africa’s construction sector (PDF Report)
Creamer Media’s Construction 2015 Report examines South Africa’s construction industry over the past 12 months. The report provides insight into the business environment; the key participants in the sector; local construction demand; geographic diversification;...
Liquid Fuels 2014 - A review of South Africa's Liquid Fuels sector (PDF Report)
Creamer Media’s Liquid Fuels 2014 Report examines these issues, focusing on the business environment, oil and gas exploration, the country’s feedstock supplies, the development of South Africa’s biofuels industry, fuel pricing, competition in the sector, the...
Water 2014: A review of South Africa's water sector (PDF Report)
Creamer Media’s Water 2014 report considers the aforementioned issues, not only in the South African context, but also in the African and global context, and examines the issues of water and sanitation, water quality and the demand for water, among others.
This Week's Magazine
While economic forecasts for the African continent are most favourable, African airlines may not be able to benefit from the expected growth in the region’s gross domestic product (GDP), International Air Transport Association VP: Africa Raphael Kuuchi has warned....
The Automotive Production and Development Programme (APDP) will need to change substantially post 2020, says Metair Investments South African operations COO Ken Lello. “We must not make tweaks. We have to change. What we are doing is not sustainable.”
Banking group Absa’s forecast is for the rand to end the year at around R13 against the dollar, weakening further to R13.50 by 2016, says Absa sectoral analyst Jacques du Toit. He warns that possible interest rate hikes in the US may see capital being pulled from...
The Dispute Resolution Centre at the Bargaining Council for the Civil Engineering Industry (BCCEI) is now open to handle party-to-party disputes. The BCCEI represents the interests of all level four to nine Construction Industry Development Board companies.
Communications technology firm Ericsson sub-Saharan Africa head Fredrik Jejdling says the company’s commitment to sustainability and corporate responsibility has been integrated into all facets of its operations, which has provided it with sustainable revenue...
Next ArticleMore about acoustics