RESULTS AND DISCUSIONS

The power system is a dynamic, permanently active system, changing every second. The majority of producing facilities and appliances are nowadays optimised at a frequency of 50 Hz. “This frequency in the grid means that produced active power (which equals the total of all active power of producing gen-erators within the whole system) equals consumed power (the total of inputs of all appliances and losses in grids)” (see Šolc, 2008b, p. 50). A state of balanced electricity supply and its off-take is the optimum condition in the grid as well as the mandatory one, should the power system remain stable.

Change of both demand and supply scales is a logical order of events, where these changes must be immediately refl ected at the supply, respectively demand level, or else there is a risk of overvoltage or undervoltage, which can shortly after lead to the collapse of the power system and brownouts¹⁷³ or black-outs¹⁷⁴ or island operation¹⁷⁵. At the point when consumption (respectively demand) rises, there is a short-age at the level of production (i.e. supply), resulting in an immediate drop of frequency and, consequently, a drop of voltage. In order to maintain frequency, an immediate producing reaction must follow in order to increase the volume of produced power. Likewise, should consumption drop and production not respond to this situation, respectively, should production increase without considering the actual consumption, it would result in an increase in frequency and, consequently, overvoltage of the grid. Such a situation must be rapidly regulated through attenuating or disconnection of power plant production. Regulation power is not used for regulation of electricity from renewables only, although its use has signifi cantly increased with respect to Act No. 180/2005 Coll., on the promotion of electricity production from renewable energy sources and amending certain acts, which adds to the previous obligation of electricity purchase to all licensed third parties within the meaning of The Energy Act No. 458/2000 Coll. an obligation of prefer-ential purchase of electricity from renewables to all licensed third parties (TPA), provided that they have a license issued by the Energy Regulatory Offi ce.

The reasons behind the above-mentioned situations vary, starting from planned and unplanned de-commissioning of producing blocks, unexpected damaging of transformers, networks or distribution lines, weather impacts (for example, snowdrifts, sharp drops in outdoor temperatures, etc.) through to really drastic changes in electricity production from renewables (i.e. from wind and solar power plants). The cross-border interconnection of systems contributes to the safety of the power system because the larger the system the harder it is to signifi cantly affect its frequency by increasing or decreasing consumption or production in some of its parts.

Different types of power plant have a different capability of drastic reduction or increase in capacity.

For example, the Czech nuclear power plants can in a relatively fl exible manner change their capacity up to approximately 10 % of installed capacity.¹⁷⁶ Regulation above 10 % would require a major intervention in production, which would manifest at the point necessary to return to the previous capacity level, ranging with accordance to the demanded regular interruption for tens of hours, days or even weeks. Power plants powered by water (pumped-storage hydroelectricity, hydropower plants) are, in turn, capable of connec-tion or disconnecconnec-tion in couple of seconds up to tens of seconds¹⁷⁷, while power plants powered by gas (combined cycle, gas and fuel-fi red) reach this effi ciency within tens of seconds up to minutes. Following the regulation of capacity, the Czech Republic has built a grid of reserve and regulatory sources which are joined into the power system services.

173 A brownout is a partial outage or larger forced interruption or limited electricity supply within a larger area.

174 A blackout is a total or larger outage of electricity as a result of grid failure.

175 Island operation is a disconnection of a part of the grid and its operation as an independent system. The quality of supplies is usually signifi cantly worse and unstable.

176 The Temelin nuclear power plant, therefore, up to 100 MWe per block, i.e. 200 MWe, Dukovany up to 80 MWe per block, i.e. 320 MWe (see ČEPS, a. s., 2010d, p. 20). The Temelin nuclear power plant is in reality, however, as a result of technical limitations, capable of regulation at the level of +/- 5 %, while the Dukovany nuclear power plant undergoes regulation only exceptionally.

177 For example, the Dlouhe Strane power plant is capable of moving from sleep mode to full capacity in 100 seconds.

In the Czech Republic, CEPS is by law the entitled regulator of the power system, and is the coordina-tor and provider of the aforementioned system services. System services predominantly ensure regulation reserves and stability of transmission, ensuring adequate voltage levels and restoration following a total or partial system blackout¹⁷⁸. In terms of network stability during the balancing of electricity supplies and consumption, regulation reserves are a key feature, in more details displayed in table No. 8.6.

Tab. 8.6: A Simplifi ed Division of Regulation Reserves as part of CEPS System Services

System Service Mark Time

Frame-work

Description

Regulation Reserve Seconds RZV 30 seconds It serves for the primary regulation (RZPR) Positive Minute Reserve available

with-in 5 mwith-inutes

RZ5+ 5 minutes Positive minute reserve available within 5 minutes (RZMZ5)

Regulation Reserve available within 15 minutes

RZ15 15 minutes It serves for secondary regulation, it consists of sources starting as positive or negative in a rapid manner, available within (RZSR, RZ15+, RZ15-) Positive Minute Reserve available

with-in 30 mwith-inutes

RZ30+ 30 minutes It serves for tertiary positive regulation, it consists of dispatch reserve, emergency exchange and regula-tion reserve from abroad, all available within 30 min-utes (RZMZ30+, EregZ30+, EregZG30+, Ereg30+) Negative Minute Reserve available

with-in 30 mwith-inutes

RZ30- 30 minutes It serves for tertiary negative regulation, it consists of regulation reserve for power reduction, dispatch reserve, emergency exchange and regulation re-serve from abroad, all available within 30 minutes (RZSV30+, EregZ30-, EregZG30-, Ereg30-)

Regulation Reserve (Non-Rotary) avail-able in over 30 minutes

RZN>30 Over 30 min-utes

It consists of dispatch reserve, regulation energy and regulation energy from abroad, all available in over 30 minutes (Ereg>30+, Ereg>30-, EregZ>30+, Ereg>30-)

Note: a positive reserve means an increase in capacity, while a negative reserve means an increase in consumption. RZSV = regulation reserve for power reduction.

Source: ČEPS, a. s., 2013, p. 4.P3; modifi ed by T. Vlček.

Table No. 8.7 shows the maximum regulation reserves recorded in 2013. If installed capacity of the Czech power system was as of December 31, 2012, at a level of 20,520 MW (see table No. 8.1) and total daily regulation during the working days at a level of 1,585 MW (night regulation 1,395 MW), the potential of regulation capacities is, therefore, 7.72 % of installed capacity. In the case of the regulation of electricity from renewables (a total of 2,349 MW), then it is 67.48 % of installed capacity. In terms of the provision of a stable network within the scope of currently installed capacities, we hereby speak about a satisfactory situation¹⁷⁹, however, with regard to the numerous of approved applications of photovoltaic power plants to connect to the network, ensuring additional reserves will require signifi cant investment (for more detail, see below).

178 It is the capability of island operation or the capability of a black start (capability of running the blocks without the support of an external voltage source, capability of reaching the given voltage, possibility of connecting to the network and its running in island operation mode).

179 When renewables are involved, it is necessary to pay attention to the real potential of electricity generation and never to installed capacity. For example, in the research carried out by Liberalni institute, o.s. Negative Impact of Network Industries Regulation and the Change of Regulatory Framework in 2006 it turned out that wind power plants would in the Czech Republic for 40 % of the operating period supply less than 4 % of installed capacity, while at least a half of installed capacity can be expected only during 7 % of the period (see Ryvolová, 2006, p. 23).

Tab. 8.7: Maximum Regulation Reserves in the Czech Republic in 2013

RZV RZ10, RZ15 RZ15, RZ30

RZ15-RZPR RZSR MZ5+ MZ15+, MZ30+

MZ15-Night Day Night Day Night Day Night Day Night Day

Working days 85 85 280-290 350 550 550 230-240 330 220-230 270

Non-working

days 85 85 280-290 350 550 550 220-230 310 230-240 280

Note: All data indicated in MW; RZPR: Primary Regulation Reserve; RZSR: Secondary Regulation Reserve; QS10: Quick Start 10 Minute Reserve; RZTR+: Tertiary Positive Regulation Reserve; RZTR-: Tertiary Negative Regulation Reserve; RZN+:

Regulatory Positive Reserve (Non-Rotary) available within 30 minutes; RZN-: Regulatory Negative Reserve (Non-Rotary) available within 30 minutes.

Source: ČEPS, a. s., 2013, p. 4.P4-4.P5. Modifi ed by T. Vlček.

System services are ensured by means of ancillary services (PpS), which are purchased on the special market, Day-Ahead Ancillary Services Market (DT PpS), which has functioned since October 1, 2001, and it is organized by OTE. CEPS buys these services from the electricity producers in the Czech Repub-lic. Approximately 90 % of PpS is purchased on long-term contract bases, while the remaining 10 % is provided through the means of the Day-Ahead Market.

With regard to the necessary rapidity of connection of reserve sources, pumped-storage hydroelec-tricity, gas and combined cycle and some steam power plants are important. CEPS purchases more than 50 % of ancillary services from the CEZ Group. System services are paid by all users of those services, i.e.

by end users, producers connected to the power system and to a certain extent also by users within island systems. Money from the ancillary services is then delivered to CEPS through the regional distribution op-erators and producers. The price is regulated and it is decided by the Energy Regulatory Offi ce on a daily basis (see ČEPS, a. s., 2010a).

CEPS in that manner also takes care of covering the losses within the distribution system and, based on its own predictions, purchases electricity to cover the losses at tenders for single products and at the special short-term electricity market organized by OTE (see ČEPS, a. s., 2010a).