Big Wind: How Many Households Served, What Emissions Reduction? (A Case Study)
Hawkins, Kent; and Hertzmark, Donald
Hawkins, Kent; and Hertzmark, Donald
In the midst of a bitter winter in North America and Europe, General Electric has announced a large wind project to be built in Oregon. Press reports in the Financial Times and USA Today describe a project of 338 machines of 2.5 MW each, giving a total capacity of 845 MW.
With power grids strained due to heating demand, increments to generating capacity are to be welcomed. But along with the usual hoopla about homes served and CO2 emissions savings, it is time for some “devil’s advocacy” by asking: – how much energy and capacity will this project really create? How much CO2 will be saved? And when the chips are down will consumers and grid operators be pleased that their funds have gone into wind rather than into some other generating source?
We strongly suspect that neither consumers nor grid operators will benefit greatly from this plant. Our brief analysis of this announcement shows that the claims for houses served and carbon saved are not supported, though some incremental, useful energy supply may be possible under some circumstances. All such claims depend on the system operator’s ability to use the wind farms’ output to offset hydro generation, the key generation resource in the Northwest United States (NW).
Contributing to Capacity: The Sine Qua Non of Power Generation Investments
In the service area where the new wind project will be located, total generating capability is 84 GW. Hydro accounts for 60% [1] of this total (nominally). Current peak demand in the NW power pool, into which the wind project will inject energy, stands currently at just over 60 GW, about the same size as the UK grid. In the winter season provisions for other claims on the water (irrigation, flood control, endangered species protection, etc.) reduce the available capacity of hydro by some 7 GW. The pool’s own capacity assessment [1] notes that “A severe weather event for the entire Power Pool area will add approximately 6,000 MW of load while at the same time reduce [sic] the capability by 7,000 MW.”
In other words, when the chips are down, hydro’s contribution to meeting a larger peak demand may fall by as much as 7 GW, with another 6 GW less capacity from other generation sources. Let’s do the arithmetic: the “normal” winter peak (50% probability) is 61 GW, generating capability (not the same thing as firm capacity) is 84 GW. Comes the storm and the peak rises to 67 GW, while the “capability” falls to 71 GW, providing just a bit more than the minimum reserve requirement of 5 GW.
How likely is it that wind can add to capacity in the midst of a winter demand surge and capacity restriction? From recent UK experience, not bloody likely. The following table [2] was taken from the UK system operator website for the first week of January 2010; most days [3] since the middle of December 2009, when winter weather gripped the nation, have looked similar.
The outstanding performer is gas-fired CCGT technology, ~34% of capacity and 38-40% of output. Coal and nuclear supply almost all the rest of the capacity and energy. So where is the wind? The UK, with more than 4 GW of wind generation capacity (~6% of total), saw essentially no help from wind in meeting demand during this entire period. With wind’s contribution to capacity ranging from just over 100 MW to about 500 MW for much of the crisis period, about a 2.5 – 9% capacity factor, and with wind’s contribution to energy at less than 1% for days on end, one would be hard-pressed to attribute much of a peak contribution to a large wind project in Oregon.
235,000 Homes Served? Is This Claim Likely or Even Possible?
The claim is that the project will provide enough energy to power 235,000 households. Assuming a generous capacity factor of 30 per cent this yields a reasonable average annual household use of:
845 MW × 1,000 (convert to KWh) × 0.30 × 24 (hours per day) × 365 (days per year) / 235,000 = 9,450 KWh per household
A reduction in capacity factor to 25 per cent reduces the households served to about 176,000. Is this a reasonable consideration? Recent experience world-wide shows that capacity factors are often less than that [4].
But these calculations rely on a measure that reflects the aggregate annual consumption. A more realistic representation would be based on meeting the peak demand per home, which is estimated to be approximately 1.5 kW. How do wind plants perform on this basis? Using the more applicable measure of capacity value (sometimes called capacity credit and explained further below), the proposed project will theoretically generate enough energy to meet the needs of about 49,000 households, at a cost of more than $2 billion for initial investment. Over a 20-year lifetime that electricity will cost the NW Power Pool about 17 cents/kWh for “average” power, and some of the costs can be made to “disappear” through the use of state and federal tax credits and other subventions. It is not easy to calculate a “firm” supply cost for wind, given the absolute reliance on backup, but this is in addition to the above 17 cents/kWh. For the kind of money that wind costs the pool could supply diesel generators to neighborhoods for an investment of less than $600 million and contribute a firm 845 MW at about 20 cents per kWh (including fuel). Those diesel units could reliably meet the peak demand needs of more than 563,000 households as follows:
Given an average peak requirement of a household, equal to about 1.5 kW, and assuming a coincident peak, then a firm 845 MW of generation, as supplied by the diesel units, can meet the needs of about 563,000 households.
i.e., 845 MW × 1,000 / 1.5 = 563,333 households
Even using the possibility that some of the diesel units would be unavailable, probably 2-3%, the number of households that could be served at peak reliably would still be more than 546,000 (97% plant availability at peak).
Wind cannot be relied upon to provide firm generation at full capacity coincident with peak demand. Wind might be capable of contributing to the peak demand requirements of the system at some times. However, this will rarely happen, and when it does it will be for brief periods. In these circumstances, the expectation of the number of households served will be just over 49,000. To calculate this it is necessary to introduce the factor representing the statistical expectation of wind production at peak demand times. This is capacity credit, or capacity value, which brings a number of considerations into play, but typical experience, and the figure used by the Texas system operator, is 8.7 per cent.
i.e., 845 MW × 1,000 × 0.087 / 1.2 = 49,010 households
In spite of all statistical expectations of output from wind generators, these households will not be served reliably in any manner that meets their needs. Taking this out of the comparatively benign case of households, can you imagine a hospital, a school or a business relying on an electricity supply dominated by wind? Calculations that are based on aggregations summed over a year and averages do not reflect the real world, which operates in real time.
For significant periods of time, no households will be served, as was demonstrated by the UK data. For almost all of the time, the electricity supply will be so unreliable as to be useless. If there were some way to store the wind-plant electricity produced, then some of this would make sense. Even granting such a widely available storage capability, there would be considerations of the relationship between the storage being filled compared to the draw on it, again in real time. Annual aggregations and averages are not a reasonable way to look at the fluctuating performance of industrial-scale wind power.
The message that emerges from both the calculations and experience is that claims regarding homes served by industrial wind power are not valid measures of wind’s value. The true measure of value is the displacement of hydrocarbon fuel and reduction in CO2 output by the power generation system. As shown in previous [5] articles [6], the need for shadowing and backup generation to ensure that load can be met despite fluctuations in wind output may result in little or no net decrement to fuel use or emissions.
However, our analysis shows that under some circumstances integration of industrial scale wind may permit small reductions in shadowing and backup fuel use, provided there is sufficient excess hydro capacity. For the Oregon wind farm case, wind would seem to be specifically excluded from meeting winter peak demand. However, wind may be able to contribute somewhat to meeting energy demand in the off-peak seasons.
In Part 2 we consider under what conditions and to what extent an industrial wind facility may save fuel or reduce CO2 emissions.
Part 2
Press reports in the Financial Times [7] and other news outlets describe a project with 338 wind machines of 2.5 MW each, giving a total capacity of 845 MW. The project sponsors claim that they will provide enough energy to serve 235,000 households and reduce CO2 output by 1.5 million tonnes annually. In Part 1 [8] of this article we showed that the claims for households served are fanciful. In reality, no more than 49,000 households could be “supplied”, and these with only a minimal degree of assurance. Indeed, the wind project is more costly than a diesel backup scheme that would actually be capable of supplying reliable power to several hundred thousand households. The wind project is also three times more costly than a replacement of just 211 MW of older coal capacity with new technology that would provide a similar reduction in emissions while supplying firm power to the NW Power Pool’s customers.
The key to wind providing some degree of fuel and emissions savings is its ability to deliver reliable electricity without shadowing or backup by hydrocarbon-using plants. These shadowing/backup requirements in the NW Power Pool may be able to take advantage of existing surplus hydro capacity in that region during off-peak periods (spring and fall), thereby permitting the proposed plant to reduce hydrocarbon consumption and emissions somewhat during those periods. It is not reasonable to expect to achieve the claimed emissions savings, but lower figures, less than half the publicized savings, may be possible.
In particular, the addition of wind generation, with shadowing/backup provided by reservoir hydro, may be able to reduce overall CO2 emissions in California, the ultimate customer for the electricity produced by the GE project during Oregon’s 2 surplus seasons. During the winter and summer peak demand periods less hydro output is available, peak demand is greater and the shadowing backup will be provided by some combination of gas-fired and coal plants. What is critical to keep in mind is that maintaining stability in the NW Power Pool requires the pool to shadow/backup not only the proposed new project, but the other 6.4 GW of existing wind as well.
This analysis shows there are less costly and more effective alternatives readily available that rival or exceed the claimed benefits of this wind project.
Wind Shadowing/Backup Requirements
So what is needed to ensure wind plants deliver reliable electricity? They have to be paired with conventional, reliable generators capable of mirroring wind’s volatile and unreliable output. This can be called wind shadowing/backup capacity. It is shadowing wind when wind is producing, albeit it in a volatile manner. It is backup to wind, in the more usual use of the word, when wind is producing nothing, which can be for extended periods.
When claims are made about wind displacing fossil fuel plant production, the question that should be asked first is: what is providing wind shadowing/backup? With system reliability and power quality considerations coming to the fore, it becomes evident that the shadowing/backup is what is displacing the fossil fuel production, and wind is displacing some small measure of the shadowing/backup. An earlier article [9] explored the realities [5] of this and showed that a wind project that relies on fossil generators to shadow the wind machines may provide little net fuel or CO2 displacement and in some cases may actually increase fuel use and emissions. The latter result may obtain as a result of: (1) the imposed inefficient operation of the wind shadowing/backup, as well as (2) use of shadowing/backup technologies that are less efficient than the pool’s major generation resources – coal, nuclear, gas-fired combined cycle. The three generation sources listed above are in varying ways not generally suitable for providing shadowing for wind. In each case the ramp rate of the generator is too slow in reacting to many of the transients of wind production. Consequently, shadowing and backup must be provided by smaller, faster acting, but less efficient engines. If the shadowing/backup requirements are significant – that is, if wind output is large relative to overall system capacity, even approaching 5% – then the reliance on small, inefficient engines or combustion turbines (GTs) will arguably lead to a net increase in fuel use and therefore emissions.
The general considerations are:
Normally, the full and accurate computation of the technologies involved in shadowing/backup of wind will require a system dispatch model so that minute-by-minute variations in wind output can be shadowed by fast ramping engines or valves (hydro). Table 1 summarizes some of the possible scenarios.
Table 1 – Some Wind Shadowing/Backup Scenarios In the NW Power Pool
| Scenario | Wind Shadowing/Backup | Generation Displaced | Wind Displaces | Emissions |
| A | Gas turbine (CCGT, OCGT) | Coal | Gas turbine | Fall (relative to coal) Rise (relative to CCGT alone) |
| B | Gas turbine (CCGT, OCGT) | Gas turbine (CCGT) | Gas turbine | Rise |
| C | Coal | Coal | Coal | Rise |
| D | Hydro (impounded) | Fossil fuel | Hydro/Other | Fall |
| E | Hydro (run of river) | Hydro (run of river) | Hydro (run of river) | No change |
In scenarios A, B and C, the inefficiencies imposed by wind volatility on the shadowing/backup plants can more than offset the CO2 emissions “saved” at the point of wind generation. In any event, Scenario C is relevant in the NW Power Pool only insofar as coal is used as a resource in the pool, and coal-fired electricity enters this pool largely through imports. In case D, assuming no curtailment of wind during high wind production periods and no spillage of hydro is required because of the timing of wind production relative to reservoir levels, the wind production could be replacing that of fossil fuel, as indicated by “Other”. In case E, wind is replacing hydro and no CO2 emissions are saved (generally wind acts similarly to run of river hydro, in terms of system stability, with the exception of such cases as hydro plants at Niagara). Note that the conditions for case D are seldom met during annual peak demand periods in the NW Power Pool, as noted in Part 1.
The Oregon wind plant production is slated to go to Southern California Edison, which obtains over 50 per cent of its electricity from imports (out of state) and almost 40 per cent from thermal generation within its jurisdiction. As California as a whole gets 50 per cent of its in-state generation from natural gas and about 2 per cent from coal/oil, it is reasonably assumed that the wind/shadowing-backup combination is displacing gas, mostly in combined cycle plants. It is possible that some imported electricity is being displaced, which likely contains a higher proportion of coal.
The question remains: what is being used as wind shadowing/backup? Oregon has the following electricity production profile – hydro 61 per cent, gas 27 per cent, coal/oil 8%, and other renewables 4%. A reasonable assumption is that impounded hydro is being used within Oregon for this purpose during shoulder seasons (spring and fall), while gas and possibly coal are used during peak seasons (Summer and Winter). In off-peak seasons in Oregon and the NW Power Pool, case D generally applies and Oregon is basically exporting hydro and some wind. Case A or B applies during peak seasons, and gas or coal is likely exported.
CO2 Emissions Saved From Wind Generation
The foregoing illustrates the complexity of determining the impact of wind plants on fossil fuel and CO2 emissions reductions in electricity systems. The following completes the application of this to the new Oregon wind plant.
The wind project sponsors claim that 1.5 million tons of CO2 emissions per year will be saved as a result of this investment. Accepting the premise that no shadowing/backup will be needed the most likely result is for the wind to displace gas-fired CCGTs, at 0.4 tons CO2 emissions per MWh:
845 × 0.30 × 24 × 365 × 0.40 = 890,000 tonnes or about 0.9 million tonnes per year
For a 25 per cent capacity factor, more reasonable for onshore facilities, the CO2 emissions saved become about 0.7 million tonnes per year. The actual savings are likely to be far less than this calculated figure, since hydro capability is reduced during the winter peak demand period, one that coincides with troughs in wind availability as well. As a result, and as indicated above, the NW Power Pool is likely to be exporting gas/coal generated electricity to Southern California during the winter demand peak as well as during the summer peak. In fact, any coal-generated electricity exported to cover the supply obligation of the wind farm is likely to come from the same plants in Utah, Montana, Arizona and Nevada that currently provide the overall grid stability for Southern California Edison and California in general – a contractual round trip that contributes little or nothing to net energy supplies and saves little or no fuel/emissions.
It should be noted that potential savings of fuel/emissions during shoulder periods (fall and spring) comprise a special case because of the large hydro capability in Oregon during such periods. In the more general case and during the summer and winter peak demand periods, with gas or coal used for wind shadowing/backup, the CO2 emissions savings would reverse and net fuel use/emissions would rise due to the inefficiencies imposed on these plants. In fact with wind, currently at 6.4 GW, expected to approach 10% of pool generation capability in the NW Power Pool with the new project, the ability of the smaller, faster responding and more efficient shadowing engines described in Power Magazine [10] are likely to be impracticable, since more than 800 of such engines would be required, meaning that shadowing/backup will be supplied by gas turbines, with the attendant inefficiencies and high fuel consumption, especially during startup. During lulls in wind a system of this size will require significant conventional generation resources for shadowing/backup.
At this point, a reasonable expectation is that half of the reduced CO2 emissions shown above would be achieved, given that the generation savings are valid for roughly half the year, spring and fall seasons; that is:
50% of 0.7 = 0.35 million tonnes per year
Since providing shadowing/backup for the NW Power Pool’s overall wind generation capacity of 7.3 GW, including the proposed GE project, involves large combustion turbines, then the fuel used just for startup, about 8-10 tonnes for each turbine each time, needs to be debited from the emissions reductions account to the wind plant. Each startup cycle, using liquid fuel or pressurized gas, produces about 100 tonnes of CO2 . To back up the NW Power Pool’s wind capacity would put roughly an additional 90 million tonnes of CO2 into the air, that is:
75 units × 12 start ups for each x 100 tonnes CO2/startup = 0.090 million tonnes per year
The GE project’s share of the shadowing/backup startup CO2 emissions (~11%) would be roughly 9,900 tonnes, offsetting about 3% of entire calculated CO2 savings for the 845 MW project.
Emissions savings identical to those claimed for the new wind project can be accomplished at significantly lower cost simply by replacing older coal-fired power plants (<35% conversion efficiency and relatively dirty) with current “ordinary” coal fired plants (~41% efficient and much cleaner). “Ordinary” current technology would reduce emissions in the pool by 0.22 million tonnes/year for 211 MW of firm capacity, roughly the amount of energy that the proposed wind project generates. Higher technology coal plants (~45% efficient and very clean), more efficient still, will reduce emissions by more than 0.35 million tonnes/year for the same amount of electricity generated by 845 MW of wind. As noted previously on this blog, many willing investors [11] are anxious to make such investments. Only a perverse [12] system of government permits and approvals and uninformed environmental groups stands between newer combustion technology and improved power supply. These are truly the “shovel-ready” projects.
The costs to the electricity consuming public for emissions reductions on the order of what is produced by the proposed Oregon wind plant are less than one half what will be required to keep the new wind project in operation and shadowed/backed up properly. An investment of a similar magnitude to the wind plant in high technology coal combustion, by replacing roughly 1,000 MW of older, less efficient, dirty coal generation capacity, would reduce emissions [13] of CO2 (and a lot of other things like SOx and NOx [14] and mercury) by more than 1.65 million tonnes annually, more than five times the emissions reductions that can be credited to the wind plants with the plus of a substantial improvement in grid reliability. Investing $1.9 billion in new high efficiency coal [11] plant of 845 MW could replace older ones and reduce emissions considerably. Alternatively, such a plant would serve 600,000 additional household customers in the NW Power Pool or Southern California for about 6.5 cents/kWh, roughly one third the cost of wind, including its shadowing/backup requirements without the need to resort to arithmetic sleights-of-hand about reliability.
Conclusions
The considerations of wind availability, system operations and hydro availability are likely to be more complex than the treatment given here. However, a more complete system simulation is unlikely to be more favorable to wind than is the present treatment, especially if increased reliability standards [15] are implemented for power pools. The proposed CO2 savings from the Oregon wind project are overstated to a significant degree and it is likely that net fuel/emissions savings will only be possible during periods of surplus hydro availability – the off-peak spring and fall seasons.
The lesson from this case is that reported claims of benefits from the introduction of industrial wind plants, such as, households served and CO2 emissions saved should be carefully reviewed – they are generally difficult to support.
And since wind competes with other projects for investment capital the funds that are devoted to wind may actually reduce potential emissions savings from efficiency and technology improvements in coal, improvements that can be supplied without tax credits or other fiscal chicanery.
[from masterresource.org (part 1 [16] and part 2 [17])]
URL to article: https://www.wind-watch.org/documents/big-wind-how-many-households-served-what-emissions-reduction-a-case-study/
URLs in this post:
[1] 60%: http://www.nwpp.org/pdf/NWPP%20Winter%20Assessment%202008-009%20Draft_2.pdf
[2] table: http://eureferendum.blogspot.com/2010/01/very-very-sick-joke.html
[3] most days: http://eureferendum.blogspot.com/2010/01/its-still-global-warming.html
[4] capacity factors are often less than that: https://docs.wind-watch.org/Boccard-Capacity-Factor-Of-Wind.pdf
[5] previous: http://www.masterresource.org/2009/11/wind-integration-incremental-emissions-from-back-up-generation-cycling-part-ii/
[6] articles: http://www.masterresource.org/2009/12/wind-integration-incremental-emissions-from-back-up-generation-cycling-part-iv-further-reflections/
[7] Financial Times: http://www.ft.com/cms/s/0/4d5ea0bc-e5f4-11de-b5d7-00144feab49a.html
[8] Part 1: https://www.masterresource.org/natural-gas/how-many-households-can-a-large-wind-project-serve-lessons-from-texas-and-the-uk-part-1-of-2/
[9] An earlier article: http://www.masterresource.org/2009/11/wind-integration-incremental-emissions-from-back-up-generation-cycling-part-i-a-framework-and-calculator/
[10] Power Magazine: http://www.powermag.com/issues/cover_stories/Top-Plants-Goodman-Energy-C
[11] willing investors: http://www.masterresource.org/2009/02/mr-president-how-about-these-shovel-ready-projects/
[12] perverse: http://www.masterresource.org/2009/03/the-energy-strangulation-strategy-the-obama-game-plan-emerges/
[13] reduce emissions: http://www.masterresource.org/2009/06/coals-criteria-pollutants-down-substantially-due-to-the-availability-of-technology-and-vast-resources-of-low-sulfur-coal-not-a-model-for-greenhouse-gas-reductions/
[14] SOx and NOx: http://www.masterresource.org/2009/06/air-quality-compliance-latest-costs-for-so2-and-nox-removal-effective-coal-clean-up-has-a-higher-but-known-price-tag/
[15] reliability standards: http://www.nerc.com/files/SPP_ICT_CT_Final_Report_D0.pdf
[16] part 1: http://www.masterresource.org/2010/01/how-many-households-can-a-large-wind-project-serve-lessons-from-texas-and-the-uk-part-1-of-2/
[17] part 2: http://www.masterresource.org/2010/01/how-many-households-can-a-large-wind-project-serve-lessons-from-texas-and-the-uk-part-2-of-2/