How Effective is Wind Energy at Reducing Greenhouse Gases?
An answer requires a distinction between the concepts: "clean electricity generated" and "greenhouse gases displaced".
Wind turbines do not emit greenhouse gases while generating electricity. So a simple (and wrong) conclusion is that each unit of wind generated electricity displaces an equivalent amount of greenhouse emissions from a fossil fuel power plant.
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The reason this is NOT so stems from the intermittent nature of wind as an energy source as illustrated from the record of peak demand days in Victoria between Sept 2003 and January 2006 (Source: Origin Energy 1): It is impractical to power an electrical grid with wind alone. Wind power is viable only as a co-operating member of a portfolio of generating technologies and it is the emissions of the overall portfolio that must be considered when estimating emissions abatement of wind power. |
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There is no long term capacity for the electricity grid to store energy. Power being consumed at each moment is generated at that same moment and the overall supply is balanced against demand dynamically by the grid manager. From a grid managers perspective there is little difference between a sudden increase in demand or a sudden drop in wind energy. Generating units are dispatched or closed down as required to match the shortfall or surplus. The order in which this is done depends on the availability of units, their ability to respond in the time required, and the cost of power on offer. (More details are on the NEMMCO website)
- Hydro Power Generators
- Respond quickly to sudden fluctuations in demand. Produce no greenhouse emissions
- Combined Cycle Gas Turbines
- Can take between 15 and 30 minutes to reach maximum output1. Convert fossil fuel to electricity efficiently. Produce greenhouse emissions.
- Coal Fired Power Plant
- Respond slowly to demand fluctuations. Produce greenhouse emissions. Produce electricity at least dollar cost.
So the level of greenhouse emissions displaced by wind energy reflects the mix of generating units used to manage grid variations. The table below shows the emissions contribution of each component
Table 1
| Thermal Efficiency | CO2 Emissions | |
|---|---|---|
| (%)* | tonnes/MWh | |
| Cogeneration Natural Gas | 77 | 0.26 |
| Conventional Generation | ||
| Combined cycle – natural gas | 48 | 0.39 |
| Thermal – natural gas | 38 | 0.49 |
| Thermal – black coal | 35 | 0.93 |
| Thermal – brown coal | 29 | 1.23 |
Source:
Australian Cogeneration Association 1998, Submission To The NECA Review Of Transmission And Distribution Pricing.
* Note:
Some new combined cycle gas turbines are achieving thermal efficiencies of around 55 percent, while the latest super critical conventional coal fired plants are achieving 40 percent efficiencies.
Analysis and Conclusions
The "mix" of energy sources displaced is critical to assessing wind's greenhouse gas abatement effectiveness as the following table illustrates:
| Mix | Mix Percentages | Greenhouse Emissions |
|||||
|---|---|---|---|---|---|---|---|
| Hydro | C. Cycle gas | Thermal gas |
Black coal | Brown Coal |
tonnes/MWh | ||
| Mix 1: Pure Brown Coal | 0 | 0 | 0 | 0 | 100 | 1.2 | |
| Mix 2: Aus. Average | 7.2 | 4 | 3 | 59.8 | 25.7 | 0.9 | |
| Mix 3: High Response | 25 | 15 | 20 | 20 | 20 | 0.6 | |
"Mix 1" provides an upper bound on the CO2 emissions abatement potential of wind.
"Mix 2" is representative of the average consumption of fuels use for electricity generation in Australia3. It is not necessarily representative of the marginal mix of fuels used to balance wind energy on the grid.
"Mix 3" Shows emissions abatement achieved where predominantly high response generating units are used . It is not necessarily representative of the marginal mix of fuels used to balance wind energy on the grid. The purpose of including it is to show the sensitivity of emissions abatement to the context of wind energy use.
NEMCO manages electricity supply to the grid dynamically so the source of fuels used will vary from moment to moment. A study4 conducted by The Electricity Supply Industry Planning Council in March 2003 concluded that:
"wind generation reduces national CO2 emissions in the order of 0.52Mt per MW installed on a Short Run Marginal Cost(SRMC) basis".
References
- "Driving Investment in Renewable Energy in Victoria - 1 February 2006: - Origin Energy (Extract)
- Australian Cogeneration Association :- Emissions estimates
- Parliament of Australia : - Provisions of the Renewable Energy (Electricity) Amendment Bill 2006
- Electricity Supply Industry Planning Council :- SOUTH AUSTRALIAN WIND POWER STUDY : March 2003
Spring Range Comment:
Approval of a wind plant requires a tradeoff between the cost to the community required to host the turbines and the benefit they bring to wider society. Since wind generated electricity costs more dollars than electricity produced by alternative means, the benefit of wind energy is concentrated in a single factor: Its ability to displace greenhouse gas emission.
The figures contained in Table 1 and reference 4 above are devastating in their implication:
Relative to a coal fired power station (and at the energy market penetration achievable by wind), the ability of wind power to displace greenhouse emissions is less than a modern combined cycle gas turbine power plant.
We realise this is contrary to the public perception, and the advertising thrust of the wind industry. We invite impartial inspection of the figures and scrutiny of the references. If the figures are correct (and our research indicates they are reliable) then the conclusion is inescapable: Society is embarked on a costly path which is diverting resources from more effective ways of reducing greenhouse emissions.
Accurate and credible information needs to be available for the public to properly evaluate greenhouse abatement benefits. It is not sufficient for a development approval to blandly justify a proposal on "number of homes" powered or "Tonnes of CO2" displaced without showing how the figures were arrived at and the assumptions behind them.
The electricity generating record of existing wind plants and their greenhouse performance also need to be tabled as an integral part of any proposal. Sufficient experience has accumulated with the technology for a track record to exist. The need for open public scrutiny outweighs any considerations about the commercial sensitivity of the material.
If a community is required to make sacrifices for wind energy it is vital the proponents demonstrate that the sacrifice is justified.