Las fincas del municipio de Anolaima

While today’s power systems are able to integrate ever growing amounts of wind energy, an innovative approach to expanding and running the systems is necessary, especially at higher penetration levels. Many of the studies mentioned in this chapter have concluded that it is possible to efficiently integrate large amounts of wind power (20% and up) when the power system is being developed in an evolutionary way. Many factors can help with this, and this chapter of the report attempts to address the major ones. It

shows which changes are necessary to the way vari- ous parts of the power system (generation, network and demand side) are operated. As a major principle, in order to efficiently integrate a large amount of vari- able renewable generation like wind power, the system should be designed with a higher degree of flexibil- ity through a combination of flexible generating units, flexibility on the demand side, availability of intercon- nection capacity and a set of power market rules that enable a cost-effective use of the flexibility resources.

Ph ot o: K ar el D er va ux

balaNcINgDemaND,cONVeNtIONalgeNeratION

aNDWINDpOWer

2.1 Introduction

Just like with any other major power source, when significant amounts of new wind generation are inte- grated in an economic and orderly way into the power supply, (relative) extra reserve power is required, the power cost changes, technical measures must be tak- en and the power market redesigned.

It is important to note that system balancing require- ments are not assigned to back up a particular plant type (e.g. wind), but to deal with the overall uncertainty in the balance between demand and generation. More- over, the uncertainty to be managed in system opera- tion is driven by the combined effect of the fluctua- tions both (i) in demand, and (ii) in generation from conventional and renewable generation. These individ- ual fluctuations are generally not correlated, which has

an overall smoothing effect and consequently, a ben- eficial impact on system integration cost.

System operators’ operational routines vary according to the synchronous systems and the countries they are in. The terminology of the reserves used also var- ies. In this document, we put the reserves into two groups according to the time scale they work in: pri- mary reserve for all reserves operating in the second/ minute time scale and secondary/tertiary reserve for all reserves operating in the 10 minute/hour time scale. Primary reserve is also called instantaneous, frequency response, or automatic reserve or regula- tion. Secondary reserve is also called fast reserve and tertiary reserve is also called long-term reserve (the term ‘load following reserve’ is also used for the latter two). The principles of how the power system is operated are explained in the Annex.

balancingdemand,conventionalgenerationandwindpower

Wind power’s impacts on power system balancing can be seen over several time scales, from minutes to hours, up to the day-ahead time scale. It can be seen both from experience and from tests carried out that the variability of wind power from one to six hours poses the most significant requirements to system balancing, because of the magnitude of the variability and limitations in forecast systems. At present, fre- quency control (time scale of seconds) and inertial re- sponse are not crucial problems when integrating wind power into large interconnected power systems. They can however be a challenge for small systems and will become more of a challenge for systems with high penetration in the future.

2.2 Effect of wind power on

scheduling of reserves

The amount of additional reserve capacity and the cor- responding costs when increasing the penetration of wind power are being explored by power engineers in many countries. The investigations simulate system

operation and analyse the effect of an increasing amount of wind power for different types of generation mix. The increase in short term reserve requirement is mostly estimated by statistical methods that com- bine the variability or forecast errors of wind power to that of load and investigates the increase in the largest variations seen by the system. General conclusions on increasing the balancing requirement will depend on factors such as the region size, initial load variations and how concentrated/distributed wind power is sited. In 2006 an agreement on international cooperation

was set up under the IEA Task 251 _{to compare and an-}

alyse the outcome of different national power system studies. The 2009 report of this Task 25 [Holttinen, 2009] gives generalised conclusions based on stud- ies from Denmark, Finland, Norway, Sweden, Germany, Ireland, Spain, Netherlands, Portugal, the UK and the USA. This experience is used in this report to illustrate the issues and solutions surrounding the reserves question. The value of the combined assessment in the IEA Task 25 is that it allows the systematic rela- tionship of the increased demand of system reserves to be shown as a function of wind energy penetration.

0 6 12 18

System Load

Days

Time [Hour of the day]

0 6 12 18 24 ? Cycles Transient stability & short-circuit Seconds to minutes Regulation Minutes to hours Load Following

Daily scheduling/unit commitment

Most results are here

Time [Hour of the Day]

fiGURE 1: tiMEsCalEs foR Utility oPERations [PaRsons, 2003]

predicted net load variations – demand minus wind). Figure 1 illustrates the time scales of relevance.