http://www.engineeringnews.co.za
  SEARCH
Login
R/€ = 13.83Change: -0.12
R/$ = 11.04Change: -0.17
Au 1172.85 $/ozChange: 3.68
Pt 1231.00 $/ozChange: -0.50
 
 
Note: Search is limited to the most recent 250 articles. Set date range to access earlier articles.
Where? With... When?








Start
 
End
 
 
And must exclude these words...
Close Main Search
Close Main Login
My Profile News Alerts Newsletters Logout Close Main Profile
 
Agriculture   Automotive   Chemicals   Competition Policy   Construction   Defence   Economy   Electricity   Energy   Environment   ICT   Metals   Mining   Science and Technology   Services   Trade   Transport & Logistics   Water  
What's On Press Office Tenders Suppliers Directory Research Jobs Announcements Contact Us
 
 
 
RSS Feed
Article   Comments   Other News   Research   Magazine  
 
 
Jul 13, 2012

Energy return on energy invested

Back
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|Transport|Cutler Cleveland|Dirk Heydorn|Ernst Van Niekerk|Jeremy Wakeford|Phillip Pare|Power|Turbines|Waste|Water|Engineering News|Diesel
Engineering||Diesel|Hydropower|Turbines|Waste|Water|||Energy|Equipment|Steel|Transport|Power|Turbines|Waste|Water||
engineering|natal|diesel-company|hydropower|turbines-company|waste-company|water-company|europe|university-oil-drum-october|diesel-fuel-energy|energy|energy-cost|energy-return|energy-sense|energy-source|equipment|steel|transport-industry-term|cutler-cleveland|dirk-heydorn|ernst-van-niekerk|jeremy-wakeford|phillip-pare|power|turbines-person|waste|water|engineering-news-published-medium|diesel
© Reuse this



One of my readers (the only one?), Phillip Pare, sent this email: “In the June 15 edition of Engineering News, I read an article by Jeremy Wakeford, in which he talks about the energy return on investment which, he claims, averages about 18:1 for wind power.

“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
I recently spent time with a group of teachers. I told them that I guessed a major drawback was dealing with parents who wanted to make sure their child was getting the best attention possible and that the teacher, who probably knows that the child in question is a...
Accountants make bad engineers. Engineers make bad accountants. Less than 20 years ago, most basic accountancy was carried out using a pen, a ledger book and a calculator. When computers became common, manual bookkeeping became redundant, though, as Thomas Hardy...
I was wandering around the Congo (Congo Brazzaville, for anybody knowing the difference) the other day and a few things caught my attention, the most compelling of which was the currency, which is the Central African Franc CFA). It trades at about 50 CFA to R1, or...
More
 
 
Latest News
The retail price of 95-grade petrol in South Africa will drop by 45 cents or 3.3 percent a liter from next Wednesday, while wholesale diesel will decrease by 4.9 percent, the government said on Friday. Petrol will cost 13.16 rand ($1.20) a liter while the wholesale...
Special purpose vehicle GreenCape will, by the end of 2014, make an application to the Department of Trade and Industry (DTI), the Western Cape provincial government and the City of Cape Town to declare Atlantis, on the Western seaboard, a special economic zone...
The German government has committed a further R70-million towards the second phase of the Non-Motorised Transport (NMT) programme. The NMT programme forms part of the Department of Environmental Affairs’ 2010 FIFA World Cup National Greening Legacy Programme.
More
 
 
Recent Research Reports
Defence 2014: A review of South Africa's defence industry (PDF Report)
Creamer Media’s Defence 2014 report examines South Africa’s defence industry, with particular focus on the key participants in the sector, the innovations that have come out of the sector, local and export demand, South Africa’s controversial multibillion-rand...
Road and Rail 2014: A review of South Africa's road and rail infrastructure (PDF report)
Creamer Media’s Road and Rail 2014 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 network, the funding and maintenance of these respective networks, and the push to move road...
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.
 
 
 
 
 
This Week's Magazine
In the next 20 years, it was expected that, in Africa, more people would live in cities and towns than in rural areas, United Nations Habitat executive director Dr Aisa Kirabo Kacyira said at the Human Settlements Indaba that took place earlier this month in...
Tough-talking Human Settlements Minister Lindiwe Sisulu has committed government to building 1.5-million low-cost houses over the next five years, telling the Human Settlements Indaba in Johannesburg on Wednesday that the State would achieve this target through the...
Over the past 20 years there has been persistent concern about deindustrialisation in South Africa, as well as the fact that locally produced manufactured products have been increasingly displaced by imports.
Financial agreement for Ghanian independent power producer (IPP) Cenpower Generation Company’s $900-million, 350 MW combined-cycle gas-turbine power plant was finalised earlier this month, paving the way for the project’s construction to begin before 2015 in Tema,...
The revenue implications for South Africa of ‘base erosion and profit shifting’ by corporate taxpayers are firmly in the crosshairs of the Davis Tax Committee (DTC) and Judge Dennis Davis hinted last week that recommendations were being considered to “detect and...
 
 
 
 
 
 
 
 
 
Alert Close
Embed Code Close
content
Research Reports Close
Research Reports are a product of the
Research Channel Africa. Reports can be bought individually or you can gain full access to all reports as part of a Research Channel Africa subscription.
Find Out More Buy Report
 
 
Close
Engineering News
Completely Re-Engineered
Experience it now. Click here
*website to launch in a few weeks