Subject: wind energy - comments on article
From: "carol chudy" <[email-masked]>
To: "Tom Hughes" <[email-masked]>
Cc: "winston sardine" <[email-masked]>, "paul serruys" <[email-masked]>, "mark and susan grant" <[email-masked]>, "Keith Simpson" <[email-masked]>, "grant church" <[email-masked]>, "doug miller" <[email-masked]>, "dale lane" <[email-masked]>, "carol & greg chudy" <[email-masked]>, "BROOKS Bill -LAMBTON" <[email-masked]>
Date: Tue, 16 Jan 2007 08:05:33 -0500

Here are some comments and responses to the last article sent regarding impacts of wind variability.

      James Hopf
      12.21.06  Roger, 
      You mentioned coal plants being the next-best choice for buffering wind output. First, I have a question. How useful would IGCC plants be for performing this function? Does the process inherently involve all the syngas being burned immediately, or can any gas (or energy) be stored for any time period? Barring that, to what extent can IGCC units be cycled. Given the gas situation, it would be nice if we could use IGCC plants, as opposed to gas plants, to backup wind. I'd rather use them than conventional coal for environmental reasons. 

      Another reason for the above concern is the possibility that high use of wind could actually increase our use of gas. The theory is that wind "doesn't get along with" baseload plants, because those plants do not like to be cycled. And because of their high capital but low fuel costs you wouldn't want to cycle those plants anyway. If one knew that there would be a lot of wind around, resulting in a highly variable and unpredictable remaining load, one might be inclined to build a gas plant as opposed to a coal or nuclear baseload plant. This leads to an interesting result. Whereas the initial (and intuitively obvious) effect of wind would be that it displaces gas generation when the wind is blowing (thus reducing gas consumption), the long term effect may be to increase gas usage by causing gas plants to be built in lieu of baseload (coal/nuclear) plants. In effect, wind would rope us into using gas for a higher generation fraction, because we need more reactive load (vs. baseload). 

      The above argument also leads me to another question for you. You say that coal plants are the next choice, behind hydro, for buffering wind. Why wouldn't gas plants be the next choice? As you say, wind is largely avoiding fuel costs, and the fuel costs for gas plants are several times as high as those of coal plants. If the wind is blowing hard, wouldn't you wait for all gas generation in the region to be shut down before throttling back any coal plants? Is part of the reason the fact(?) that combined-cycle plants are not good at varying their output? 

      Roger Arnold
      12.21.06  Thanks for the link to WTC, Len. I think their approach probably does make sense, but there still seems to be controversy in the wind community about upwind vs. downwind and 3-blade vs. 2-blade designs. Prior experience with 2-blade and downwind designs was discouraging. The problem was noise and vibration from passage of the blades through the turbulence in the wind shadow of the tower. WTC acknowledges that downwind designs are more "technically challenging" than upwind designs, but suggests that computer modeling and design optimization have allowed them to meet that challenge. Perhaps so, but I'd feel more confident if I knew a bit more about just how. They aren't using an approach that has always struck me as reasonable: a lightweight, free-turning fairing that smooths the airflow around the section of the tower upwind of the blade tips. 
      Regarding IGCC vs. gas vs. coal for dispatchable capacity: The gas-fired capacity that it sounds like you're thinking of, James, is simple CT peaking capacity, not combined cycle. Although cheap, it hasn't traditionally been very efficient. Most simple cycle turbines have been below 30%. So they weren't generally used until dispatchable intermediate capacity--usually coal--was fully committed. The high-efficiency GTCC units were both more expensive and less tolerant of cycling, so they tended to be reserved for baseload use. That's all begun to change, but not quickly. 

      The reason that coal is good for dispatchable capacity is that the key unit is a boiler, whose firing rate and steam output can easily be varied. It's true that the steam drives turbines which, like all turbines, operate best over a narrow throttling range. However, that's handled simply by varying the number of turbines being driven. 

      The same approach can be used with combined cycle plants of various types. The only difference is that instead of firing the boilers with flue gases from coal combustion, they're fired with high temperature exhaust from combustion turbines or (in the future) from high temperature fuel cells. With CTs, the firing rate would be stepped by stepping the number of CTs operating on the front end. The number of steam turbines operating would be stepped in parallel. The steam boiler and condenser remain at operating temperature at all times--aside from maintenance shutdowns. 

      I don't know how widely that approach to CC generation is currently implemented, but I expect that we'll see more of it in the future. I don't know of any reason that it would matter whether the front end CTs were fired by gasified coal instead of natural gas. 

      In any case, the point about wind variation is that, to the system, there's no inherent difference between normal load variation and wind-related supply variation. My understanding is that the average daily peak in most RBAs is three times the average daily minimum; that implies that at most one-third of our generating capacity can be baseload. In fact, I think the usual is more like a quarter--although that quarter delivers abut half of kilowatt-hours consumed. The other three quarters or generating capacity is dispatched, and operates with low CF. 

      Graham Traynor
      12.22.06  Just a note on GTCCs. Going forward, they will be able to cycle even more than currently. Already most CTs operate at constant exhaust gas temp. between 50% and 100% load, thereby reducing stresses on the following boilers, and enabling quick CC load changes. In boiler design, we will see a lot of "once through" technology in the future, eliminating thickwalled components like boiler drums, and thereby enabling quick load changes in wider load ranges. 
     
      **** ****
      12.22.06  Septimus van der Linden 12.22.06 Some comments on open cycle Gas Turbines--these units today achieve 35% or better efficiencies.Some recent 100MW developments achieve 45 % efficiency.The low capital cost makes it easy to simply add this capacity for peak shaving. Energy Storage is one answer to increasing numbers of WTG's that do not live up to the installed nameplate rating. Why would the WTG Industry be interested in Storage when this concept would reduce trhe number of machines they can sell-subsidized with Tax Incentives..Pumped Hydro systems are limited by site availability and environ concerns.Bulk Energy Storage in the form of CAES(Compresed Air Energy Storge) can be widelly applied across the country. Smaller systems using pipe storage and adiabatic expansion can be applied to distributed systems keeping wind Energy "green" no fuel added.With a lack of Energy policy addressing Storage--it will just remain a topic of discussion--surely incentives for Energy Storage as for other technologies would change the equation substantially. 

            David Katz
            12.26.06  All the above discussions have an underlying premise that the electricity markets will be rational similar to other storable fuels. Unfortuneatly many system planning decisions are political due to the government being responsible to keep the lights on no matter what! While the Part 1 above notes the need to look at the larger system planning issues about where the renewable energy is produced and where it is ultimately needed, these engineering principles must also reflect the local economic and environmental considerations. Here in Ontario we are reverting back to the Intergrated Power System Plan, however it is still mired in political considerations about closing coal plants. Standard Offers for Wind but no transmission, and no real recognition of the sustainable development issues.  

      ...

      2nd: Care is required in making any assumptions of capacity value since the annual average can be considerably different than the capacity actually contributed by wind during peak periods. For instance, in the Midwest, the wind is not expected to produce significant generation duriing the hot summer peaks, or the very cold winter peaks. (Winds are usually low on hot summer days and most wind turbines shut down at -20 degrees F.) Unfortunately, these are the times peaker generation is needed and the price of gas is the highest. For instance, during the peak hours of July, the actual generation percentage of wind project namplate may frequently be in the single digits. 

      ...

      The reality is that depending on the wind regime of the location, they are generating most of the time, but at less than rated capacity. Some wind farms in Scotland average over 7,800 hours of generation per year, but only have annual capacity factors between 27% and 40%. Notwithstanding the above, it is hard to ascribe capacity credit to any single wind power installation (be it 1 or 1000 turbines) apart from a very few exceptions. This is because it is not possible to predict with sufficient accuracy what the wind speed or direction at any one location will be 1 hour in advance, let alone 24 hours. Direction is important because it affects the turbulence pattern and thus array losses within a wind farm. However, when a number of installations are geographically dispersed within a "regional balancing area", the level of accuracy in predicting the total wind output (within the area) rises. The more installations there are and the more widely they are dispersed, the greater the accuracy. Denmark realised this some years ago and the grid operators there are able to factor wind into their dispatch schedules. My understanding is that they begin their predictions 36 hours ahead and refine them until 1 hour ahead. With regard to the issue of matching peak load, this depends very much on the wind regime and demand profile of the area that the turbines are located in. In North-west Europe, peak load occurs during winter, when wind energy production is highest. It could therefore be argued that wind energy is worth more in Europe than it is in most of the continental US, where peak demand tends to be in summer.

      ...

      With regard to matching wind to another technology to resolve variable output, I disagree with the view that wind matches well with hydro. Firstly, much of the hydro power being developed today is run-of-river, and thus itself is a variable resource, Secondly, the experience in Europe over the last 20 years has taught us that in years when wind speeds are below average, rainfall is also below average! Realistically, matching depends on the portfolio of generating plant available within the "regional balancing area", however a personal observation is that the more diverse the generation mix, and the larger the balancing area, the more easily it seems that variable energy sources can be accommodated.

      ...

      2. Grids are dynamic entities, the generation mix will change (as gas becomes more expensive and new coal & nuclear are brought on line) and demand profiles are changing (in response to higher energy costs). Therefore, in developing models to calculate the amount that can be accommodated, a lot of assumptions have to be made about the conditions that will exist in the future. Call me a cynic but I suspect that most of the assumptions are likely to be proven wrong when that future becomes the here and now. After all, twenty years ago who was predicting that gas fired power stations would expand so rapidly (and get into difficulties so rapidly)? 

      3. When people talk about variable power sources, they tend to think exclusively about wind power. They ignore the effects of other variable sources such as run-of-river hydro and combined heat and power (which when it is operated primarily for heat production, is the most variable generation source of all). In the distant future, we may also have to contend with meaningful amounts of solar, wave and tidal power 

      ...

            John K. Sutherland
            12.29.06  Comment continued: The over-riding problem with wind electricity is that it occurs on an intermittent, unreliable, and unpredictable basis that usually requires dedicated standby operation of a reliable source of power (nuclear, coal, or imports) that must be constantly available within seconds. This logically requires that the assumed costs of wind should also include the costs of the needed standby generation. 
            As one must build and have, the necessary reliable replacement power on hand - along with all of its costs - for those times when the wind does not blow, the obvious question should be asked: why bother with wind power at all? It is a surplus and un-needed environmentalist dream that causes capital costs of electrical energy derived from it, to be a factor of three to five and more, higher than the cost of electricity from the reliable 'standby' asset - in this case - Nuclear Power. If it is from coal or other fossil fuels, then having such stand-by power ticking over at a low level, as in Germany, Denmark, and Spain, also contributes much more to air pollution; pollution that should also be chalked up against wind energy operation. Not surprisingly, nuclear power and nuclear refurbishment look like great investments, and wind power doesn't. Similar projects with similar very high costs relative to nuclear power are planned and under construction in Manitoba (Schneider Power), and at Melancthon and Grey Highlands in Ontario. 

            The Melancthon-GH project, to be constructed by Canadian Hydro Developers will cost $126 million in Capital Cost to erect 45 windmills each of 1.5 MW, for a total of 67.5 MW capacity. The maximum theoretical output (100% operation) from these windmills, and which cannot be achieved anywhere in the world, is 591,300 MWh. With a more likely operation of about 20% of capacity in the year - not even achieved by either Germany or Denmark, which are closer to 15% - the output will be about 118,000 MWh (118 GWh, costing $120 million) - the company assumes 190GWh. A comparable nuclear facility (details above) can generate 4,580 GWh or more, costing $1.4 billion. 

            And now a proposed wind farm at Taber in Southern Alberta with similar excessive cost: $140 million for 80 MW capacity, and unavoidable intermittency and unreliability. 

            Gigawatt for gigawatt, these projects demonstrate that wind project electricity costs more than three times more than that of nuclear electricity. Definitely not a good deal. 

            Invariably, all wind power projects clearly demonstrate that they are not only unjustified and unnecessary, but that they are too expensive, grossly unreliable, and environmentally damaging to an unacceptable degree. The British recently estimated the costs of their various options. Onshore wind costs are 5.4 pence/kWh (about 12 cents Canadian/kWh). Offshore wind costs are 7.2 p/kWh (these also include the fractional costs of the essential standby backup energy sources for when the wind does NOT blow and the reliable alternatives must be brought on line), and nuclear power, whose costs are 2.3 p/kWh. 

            The Utility Data Institute figures in the US show coal and nuclear as the cheapest overall, followed by gas, then oil and above all of them (but not shown by the UDI),is wind and solar.