Jul 13, 2012
Energy return on energy investedBack
Engineering|Natal|Diesel|Hydropower|transport|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|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)
Creamer Media Senior Deputy Editor
Other Terry Mackenzie-Hoy News
Updated 4 minutes ago JSE-listed Clover has acquired a 51% stake in Frankie’s Olde Soft Drinks, resulting in the establishment of a new business, Clover Frankie’s. The new company would manufacture, sell, market and distribute a range of carbonated soft drinks, hot chocolate powder and...
Updated 8 minutes ago Hundreds of workers from various unions across the country have taken to the streets of Cape Town to march to Parliament for workers' rights. Members from Cosatu, NUM, Sactwu and other unions gathered in Kaizergracht to start the protest at around 10:50 on Wednesday.
Updated 36 minutes ago The South African International Renewable Energy Conference (Sairec) has wrapped up with a declaration to upscale and mainstream renewable energy globally. Delegates also pledged to make universal access to electricity a reality by 2030, with more than 1.3-billion...
Recent Research Reports
Liquid Fuels 2015: A review of South Africa's liquid fuels sector (PDF Report)
Creamer Media’s Liquid Fuels 2015 Report examines these issues in the context of South Africa’s business environment; oil and gas exploration; fuel pricing; the development of the country’s biofuels industry; the logistics of transporting liquid fuels; and...
Road and Rail 2015: A review of South Africa's road and rail sectors (PDF Report)
Creamer Media’s Road and Rail 2015 report examines South Africa’s road and rail transport system, with particular focus on the size and state of the country’s road and rail infrastructure and network, the funding and maintenance of these respective networks, and...
Defence 2015: A review of South Africa's defence sector (PDF Report)
Creamer Media’s Coal 2015 report examines South Africa’s coal industry with regards to the business environment, the key participants in the sector, local demand, export sales and coal logistics, projects being undertaken by the large and smaller participants in the...
Real Economy Year Book 2015 (PDF Report)
There are very few beacons of hope on South Africa’s economic horizon. Economic growth is weak, unemployment is rising, electricity supply is insufficient to meet demand and/or spur growth, with poor prospects for many of the commodities mined and exported. However,...
Real Economy Insight: Automotive 2015 (PDF Report)
Creamer Media’s Real Economy Year Book comprises separate reports under the banner Real Economy Insight and investigates key developments in the automotive, construction, electricity, road and rail, steel, water, gold, iron-ore and platinum sectors.
Real Economy Insight: Water 2015 (PDF Report)
Creamer Media’s Real Economy Year Book has been divided into individual reports under the banner Real Economy Insight and investigates key developments in the automotive, construction, electricity, road and rail, steel, water, coal, gold, iron-ore and platinum sectors.
This Week's Magazine
Black-owned investment holding company Sphere Holdings plans to raise a further R1-billion in the coming months in support of its strategy to become a leading black industrial enterprise, which could ultimately seek a listing on the JSE.
Energy analyst and EE Publishers MD Chris Yelland warned recently against excessive optimism regarding timescales for the proposed construction of new nuclear power plants (NPPs) in South Africa. He was speaking at a Nuclear Roundtable in Johannesburg. “I think we...
Malawi’s Lilongwe Water Board (LWB) is inviting eligible bidders to prequalify for the board’s efficiency improvement works, which will be implemented as part of the E24-million Lilongwe Water Resources Efficiency Programme. LWB CEO Alfonso Chikuni explains that...
CROATIA, AN EU MEMBER BUT NOT A TDCA MEMBER On July 1, 2013, Croatia officially became the twenty-eighth member of the European Union (EU). Despite Croatia’s accession into the EU, it is yet to become party to the Trade, Development and Cooperation Agreement (TDCA)...
The Council for Scientific and Industrial Research (CSIR) has announced that its new Inundu airborne electronics testing, evaluation and training pod had made its first test flight on September 10. The successful flight was undertaken from Lanseria International...