Spinning Reserve

In order to ensure reliability, electricity grids need a certain amount of “spinning reserve”.  This is a source of generation that can be turned up quickly, to accomodate unexpected surges in demand, or loss of generation or transmission.

For fossil plants to be used as spinning reserve, they must be already warmed up, and that means they must burn some fuel just to keep them ready.  Waterpower provides Ontario with much of its quick start reserve, but we do use fossil units as well.

The rule that the grid operator uses is that we must always have an ability to replace the loss of the largest generating unit.  In Ontario, that is a unit of the Darlington nuclear station, or 900 MW.  So we always have to be able to replace that at a moment’s notice.  It can of course be replaced from multiple sources, including imports.  Because of our hydraulic and import abilities, we don’t need to keep fossil units running very much just for spinning reserve (but we do warm them up in advance of forecasted demand).
Nuclear can not be used for spinning reserve.  It is either on or it is off.  The same is true of co-generation or combined heat and power installations.

Interestingly, wind has been used in Denmark for spinning reserve.  The 200 MW offshore Horn’s Rev project can be throttled back by changing the pitch on the wind turbine blades.  And the offshore winds are very steady and predictable over the short run.  Wind turbines are easy to control, because they are modular.  It is easy to cut the output from a wind farm – just shut some turbines down.  And it is just as easy to turn them back on, and they will be producing power in less than a minute, when wind is available.  This can all be done under central control if needed, using the turbine’s SCADA system.

Of course, if you shut down a wind turbine, you lose the energy in the winds.  But if you shut down, or throttle back on a waterpower station, you can usually preserve the energy the storage pond.  So waterpower is always the preferred source of spinning reserve.

Reserve power is essential to maintaining a reliable electricity grid.  Wind’s flexibility to be shut down in small increments is a desirable characteristic, that could be used to maintain grid reliability.

10 Responses to “Spinning Reserve”

  1. Shanmugham Kangala Says:

    Wind Energy cannot be treated as a Spinning reserve.

    Wind Energy is intermittent, fluctuating and not ‘network friendly’ . There is no technology yet for Storage which is commercially viable. Solar systems may be more steady and predictable, but again may become more effective if there is a Storage facility.

    There is a urgent need for Storage system, besides Generation, Transmission and Distribution.

  2. Glen Says:

    Wind IS used as spinning reserve occasionally on the Horns Rev project in Denmark. Spinning reserve is power that is able to come on line at short notice. The Horns Rev project is offshore, where winds are steady. The turbines used can curtail their output to a certain level, by feathering the blades. So while the capacity of the wind turbine is 1.8 MW, they can operate, for example, at 1.2 MW. If the winds are such that they would always be producing 1.8 MW on a particular hour, then the remaining .6 MW can be engaged in a matter of seconds.

    Of course wind is not ideally used as spinning reserve, as it can only be done when spilling wind. You need to operate at less than you capable of in order to have the reserve available. And you can never recapature that wind energy like you can if you have waterpower storage. But it IS being done. It can be done. We are limited only by our ingenuity, and nowhere is this more true than in the utility business.

    And you are right – we could use some low cost storage solutions – both for spinning reserve, peak shaving, and overcoming transmission bottlenecks by transmitting during off peak times.

  3. David Says:

    There’s a company in Texas called EEStor that may be able to turn wind farms into spinning reserve systems.

    They’re developing a capacitor based energy storage unit (ESU) that is predicted to cost $4,000 to store 85kW. In a racked and stacked system, that’s equal to roughly $50,000 to store each 1MW of electricity.

    In a peak shaving situation, the system could theoretically pay for itself in about 4 1/2 years if the daily spread is a minimum of $30/MWh.

    There isn’t yet much information on EEStor. Their initial product will show up in electric cars made in Toronto by a company called ZENN. The real value, other than the price, of this type of technology is that since it’s a capacitor, it doesn’t lose its ability to store the same amount of energy, no matter how many cycles it goes through. Batteries have a limited number of cycles in them before they become uneconomical to operate.

    In a “behind the interconnection” spinning reserve situation, the ESU could have the ability to turn a 100MW 35% capacity factor intermittent supply into a 35MW 100% capacity factor -non intermittent – electricity generating system.

    Of course, this is all vapourware for now, but if EEStor comes through, it will have the capacity to change the entire energy network with affordable, modular, distributed and relatively inexpensive electricity storage.

  4. M, Anderson Says:

    Why don’t you people accept the fact that there is something fundamentally inadequate about “wind energy”. No amount of tweaking or theorizing is going to change that.

    Irreliability and electricity do not mix. Whoever can bottle this magic potion that you keep hoping for will be a rich man. Keep investing that capital, boys. Read your history books and you’ll see what’s happening now.

  5. Glen Says:

    If there is something inadequate about wind energy due to intermittency, there is something inadequate about all sources of power. No power source works all the time. Waterpower suffers from drought. Nuke plants fail regularly. Fossil plants require maintenance. Perhaps we should shut down the electricity grid. There is no way it can operate. All sources of power are not always available. Oh no!

    Evidently “irreliability” and electricity do mix. You just have to plan for it.

    And wind is mixed in around the world. The history books show that the grid works.

  6. Bernadette Says:

    I concur with Glen; Anderson, all you need do is refer to your electricity market, which has short term and long term contingency plans for electricity generation from primarily conventional electricity generation i.e. coal fired power generation, gas turbines, nuclear, etc. Your comment regarding reliability only serves to highlight you have minimal knowledge behind your view points, it would serve you better to research your argument prior to publishing it.

  7. Mahesh Kumar Gupta Says:

    Spinning Reserve-Fossil Fuel Based Generating Plants:
    1. Coal Based:
    Typically, there are two scenarios of a Coal-Based unit supposed to be on spinning reserve.One, the unit is on turning gear. Other, the unit is on rated speed ready for synchronization.When the unit is on turning gear, the variable cost or the fuel cost is nil. But when a unit is on rated RPM, say 3000, for 50 Hz Machines, it is incurring fuel cost as well as substantial auxiliary loads.In true definition of spinning, the unit should be hooked with transmission within 10 minutes. A unit on turning gear would take more than an hour to be ready for delivering power, while the one on rated RPM would be sycnchronized within 10 minutes. But I have yet to see any Regulator giving the benefit of fuel cost for the unit that is spinning. As far as I know there is no separate account head for the costs that are incurred during spinning. Plant Owners have to account for these in the overall operating expenses, which is not reflecting the actual specific fuel consumption and the fuel cost per Kwh delivered.
    Gas Based CCGT:
    The unit can be on Turning gear. Or it can be on FSNL(Full Speed No-Load). From turning gear it would take more than 90 minutes minutes ,while from FSNL it can be synchronized only in open cycle mode within 10 minutes. So, truthfully, a CCGT can not contribute to spinning reserve. Only a simple cycle unit can.

  8. neerja mathur Says:

    I have some basic questions on how spinning reservecould be made operational in the Indian system. It is not very clear as to who would build up capacity for spinning reserve and why. It also needs to be determined as to what type of a plant would be built up and at what location. Also how the charges would be recovered for providing this capacity.

  9. Jeff Sutter Says:

    It seems to me that the gold standard ought to be “just in time generation” where it is practical to adjust throttleable generation to have produced no more than 100% of demand over time. To achieve this it is necessary to provide a buffer having a fast enough response to changes in demand and supply interruption that is able to store or produce energy long enough for variable generation to respond in its low wear-producing mode.

    The fuel saving from decreased spinning reserve utilization and increased reliance on fuel efficient solar and wind assets produces the cost benefit needed to judge the applicability alternate strategies. Batteries have not been considered for grid stabilization use because it was not possible to engineer sufficiently large amounts of storage that would provide fast response, MW scale power levels, and high round-trip efficiency reliably with cycle life measured in decades. Until now.

    Here is a link to the Altairnano website where you can read about the on-line two module testing done early last year and the pilot production installation of a single module 1MW / 250kwh (e.g. 15 minute buffer) battery facility by the AES power company and the third party evaluation done by KEMA. With greater than 90% round trip operating efficiency, this approach is the holy grail compared to “smart grid” plans and it will be much more cost efficient not to mention simpler to implement and administer. Actually, “is” would be better – in its third generation, this technology is ready for prime time.


  10. Robert Baertsch Says:

    Nuclear CAN serve as spinning reserve.

    France is leading the way with modern reactors that are capable of load following.


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