Lisa Göransson

Large Scale Integration of Wind Power in Thermal Power Systems

This chapter discusses and compares different modifications of wind-thermal electricity generation systems, which have been suggested for the purpose of handling variations in wind power generation. Wind power is integrated into our electricity generation systems to decrease the amount of carbon dioxide emissions associated with the generation of electricity as well as to enhance security of supply. However, the electricity generated by wind varies over time whereas thermal units are most efficient if run continuously at rated power. Thus, depending on the characteristics of the wind-thermal system, part of the decrease in emissions realized by wind power is offset by a reduced efficiency in operation of the thermal units as a result of the variations in generation from wind. This chapter discusses the extent to which it is possible to improve the ability of a wind-thermal system to manage such variations. The first part of the chapter deals with the nature of the variations present in a wind-thermal power system, i.e. variations in load and wind power generation, and the impact of these variations on the thermal units in the system. The second part of the chapter investigates and evaluates options to moderate variations from wind power by integrating different types of storage such as pumped hydro power, compressed air energy storage, flow batteries and sodium sulphur batteries. In addition, the option of interconnecting power systems in a so called “supergrid” is discussed as well as to moderate wind power variations by managing the load on the thermal units through charging and discharging of plug-in hybrid electric vehicles. Data from the power system of western Denmark is used to illustrate various aspects influencing the ability of a power system to accommodate wind power. Western Denmark was chosen primarily due to its current high wind power grid penetration level (24% in 2005 (Ravn 2001; Eltra 2005)) and that data from western Denmark is easily accessible through Energinet (2006).

A comparison of variation management strategies for wind power integration in different electricity system contexts

Variation management strategies improve the capability of the electricity system to meet variations both in the electricity demand and in the generation that relies on variable energy sources. In this work, we introduce a new, functionality-based, categorization of variation management strategies: shifting (eg, batteries), absorbing (eg, power-to-gas), and complementing (dispatchable generation, including reservoir hydropower) strategies. A dispatch model with European coverage (EU-27 plus Norway and Switzerland) is applied to compare the benefits of shifting and absorbing strategies on wind integration in regions with different amounts of complementing strategies in place. The benefits are measured in terms of the wind value factor, wind owner revenue, and average short-term generation cost. The results of the modeling show that the reduction in average short-term generation cost and the increase in revenue earned by the wind owner from shifting strategies, such as the use of batteries, are more substantial at low wind shares than at high wind shares. The opposite situation is found for absorbing strategies, such as power-to-gas, which are found to be more efficient at reducing the average generation cost and increasing profit for the wind owner as the wind share increases. In regions that have access to complementing strategies in the form of reservoir hydropower, variation management has a weak ability to reduce the average short-term generation cost, although it can increase significantly the revenue accrued by the wind power owner.