The amount of operational reserves in a power system is affected by a number of factors. Especially large-scale integration of intermittent renewables inevitably requires a major reserve increase. Currently, a large share of the reserves has to be spinning, i.e. in active operation, in order to quickly be able to balance any fluctuations in supply or demand. In practice, this means that power plants must operate at part-load, which unavoidably decreases their efficiency and increases their costs per kWh. Looking at the Middle East, where gas-fired generation has a big role, reduction of part-loading through the introduction of non-spinning standby reserves would be of considerable value.

Recent electricity market studies have shown that there is a more efficient way of providing a substantial part of the reserves by utilising highly flexible power plants. This even applies for the secondary reserves, which are typically required to respond within 30−60 s after a contingency and to reach their full output within 5−10 min. With plants based on modern reciprocating gas engines it is possible to fulfil these requirements without spinning when at standby, since these plants are able to go from standstill to full load in less than 5 min. Consequently, while in standby-mode, such reserve capacity does not consume any fuel, generate any emissions, nor suffer from wear.

Moreover, the inefficient part-loading of the larger power plants can be reduced, which in turn allows the whole system efficiency to be further increased. Finally, by enabling more stable operation of the larger plants, the maintenance costs connected with frequent cyclic operation can be reduced. Several studies undertaken indicate that the annual system level savings of introducing non-spinning reserves can be up to 10% of the total generating costs, depending on the electricity market mechanisms in place.

This paper will assess the commercial and technical aspects of such non-spinning standby reserves. In doing so, mainly two questions will be investigated:

  • What should be the properties and specifications for balancing products for frequency
    restoration reserves in a system with a high degree of renewable energy sources that
    provide adequate frequency quality?
  • How does a selection of properties and specifications for balancing products as
    mentioned above influence the total system costs?

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  Christian Hultholm

   Content Manager, Marketing & Business
   Wärtsilä Energy Solutions
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