Last juli we made a calculation regarding the EROI of wind power, making some assumptions regarding the weight of the wind tower, see link below.
Now we have more accurate data, coming from the implemented Gemini wind farm, consisting of 150 Siemens 4 MW wind turbines. One of these wind turbines weighs in total 1.347 ton max. Annual electricity production Gemini wind farm: 2.6 TWh. That would be 17,333 MWh per turbine annually or 47,487 kWh/turbine/day. We again apply 5555 kWh/ton energy cost in steel production or 7,483 MWh/turbine. Payback time in energy terms: 158 days. Assuming again the worst case scenario of having to transport iron ore from Australia to Europe: 1600 kWh/ton or another 1600 * 1347 = 2,155 MWh which corresponds to 2,155/17,333 = 45 days. Energy payback tower construction + transport iron ore from Australia: 203 days [*]. Assuming an economic life time of 30 years, we arrive at an EROI of 54.
Ignored here is the energy cost of maintenance and installation. And then there is storage.
[*] – Note that after 30 years the energy to create a new turbine from the scrap steel of the old one is less than the energy required to create a wind tower + turbine from iron ore from Australia. There is no transport energy cost other than to bring the tower to a smelter in Europe and in general the energy cost to create steel from scrap metal is (much) lower than from ore. According to Wikipedia the energy required to produce 1 metric ton of steel from scrap metal in an arc furnace is merely 440 kWh/ton (theoretical minimum 300 kWh). It goes without saying that electricity from wind power and arc furnaces are a match made in heaven and can operate on moments when supply of electricity from power is high. In the link “EU Economic Papers” (p14) it is confirmed that the energy intensity of producing 1 ton of steel from ore is a factor of 10 more intensive than producing 1 ton of steel from scrap metal in an arc furnace. If you take this in account than it follows that the EROI of a wind tower produced from the scrap metal of a previous wind tower is in the order of 500-600 [**] rather than the values 54-60 we calculated for the “first generation” wind tower. In other words, the whole EROI discussion of wind energy is obsolete.
[**] EROI 500-600 too optimistic. Here an older piece of information from 2008 concerning a 600 kW onshore wind turbine:
Onshore wind turbine: 0,6MW, height = 50 m, rotor diameter = 40 m
Production 1900 GJ (embodied energy tower + nacelle)
Installation 495 GJ
Maintenance (20 year) 774 GJ
Total 3169 GJ generated energy
Annual electricity production 5015 GJ
Energy payback time 7-8 maanden
EROI 32 for a very conservative lifetime assumption of 20 years
If we recycle the old turbine we will have a vastly reduced embodied energy for the 2nd generation machine. But we need energy for extraction and transporting the tower back onshore. With maintenance remaining unchanged we arrive at an EROI of 51 instead of 32. But not “500-600”. Note that this is for a very conservative 20 years life time. So far, to our knowledge two windfarms have been decommissioned, one in Denmark and one in The Netherlands, both functioned for 24 years and there is no reason to assume they could not have functioned for many additional years. If lifetime would increase to 40 years you achieve a doubling of EROI (ignoring maintenance). Note that EROI is a logarithmic (see graph at the top), not a linear entity. For all practical purposes an EROI of 50 is not that different from an EROI 500.
The currently most efficient way to store excess renewable electricity is seasonal thermal storage. Think for a country like the Netherlands of thousands of low-tech concrete basins of say 70 m in diameter and 30 m deep, filled with water, that during the Spring and Summer is “charged” with hot water of up to 95 C, using heat pumps, the very same heat pumps installed in homes to heat the homes in the Winter with the storage used as either a direct source or “cold side” once the water temperature begins to drop during the heating season.
[deepresource] – EROI of Offshore Wind
[geminiwindpark.nl] – Gemini wind park
[wikipedia.org] – Electric arc furnace
[ec.europa.eu] – EU Economic Papers
[energy.gov] – Theoretical Minimum Energies To Produce Steel
[steeloncall.info] Over the past half century energy intensity of crude steel production fell with 60%
[eia.gov] Over the coming 23 years energy intensity of steel production is expected to come down even further from 11 to 8 units or 27%.