**4.1 Determination of necessary financial volume**

In determination of necessary financial volume actual volumes for provision of individual kinds of auxiliary services are taken in account. These are in Table 5.

These values can be considered as maximums. In real operation they are not always achieved caused by various forces such as equipment failure, regular maintenance, financially underrated services (from the providers' point of view), unavailability on the market and other. Wider offer and competition on the auxiliary services market can be expected when new energy sources are being put into operation, e.g. combined cycle power plant Malženice, nuclear plant EMO 3 and 4 with expected favourable regulatory features and range.

Decision No. 0013/2010/E of the Regulatory Office for Network Industries determined prices and tariffs for auxiliary services provision for the time period of January 1, 2010 to December 31, 2010. Maximum prices for provision of auxiliary services are in Table 6.

Slovakia, as one of the members of interconnected European power system ENTSO-E, has to meet basic requirements for parallel operation of power systems. One of these basic requirements is also range and quality of auxiliary services, taking to account on one side global view of secure and reliable operation and on the other side, local nature of consumption of individual country. While the range of some service is strictly ordered from ENTSO-E (i.e. range of the primary regulation, which principally performs locally, reacts according to instantaneous frequency deviation, in tens of seconds, but impulse, i.e. origin of imbalance between electricity production and consumption can occur anywhere in interconnected system), ranges of other services can vary based on local behaviour of system and thus it has to meet only certain frame

Basically every power system must have power reserve secured for coverage of an outage of the largest source in order to be balanced in power in relation to other countries. This condition is secured by so-called stacking of various kinds of auxiliary services, or bi- or multi-lateral contracts with international partners, usually

In Slovak environment TSO SEPS acts as a partner for ENTSO-E. SEPS after consideration of before mentioned criteria elaborates i.a. a proposal of range of individual auxiliary services and in sense of valid legislation (as a regulated subject) submits to the national Regulatory Office for Network Industries, who in the form of decision defines range and price for a instantaneous availability of auxiliary services and

Fluctuation of electricity production from RES primarily imposes higher demands on regulation sources of SPS either on amount available reserves or on the quality of regulation. In the frame of interconnected system ENTSO-E the SPS is regulated for an agreed balance. SEPS has to keep the agreed value and quality of this regulation is monitored at the coordination centre level. Potential deterioration or violation of accepted standards in area of agreed balance would result in investigation of SPS by

In determination of necessary financial volume actual volumes for provision of individual

These values can be considered as maximums. In real operation they are not always achieved caused by various forces such as equipment failure, regular maintenance, financially underrated services (from the providers' point of view), unavailability on the market and other. Wider offer and competition on the auxiliary services market can be expected when new energy sources are being put into operation, e.g. combined cycle power plant Malženice, nuclear plant EMO 3 and 4 with expected favourable regulatory features

Decision No. 0013/2010/E of the Regulatory Office for Network Industries determined prices and tariffs for auxiliary services provision for the time period of January 1, 2010 to December 31, 2010. Maximum prices for provision of auxiliary services are in Table 6.

**4. Provision of auxiliary services and balancing electricity purchasing** 

requirements.

neighbouring countries.

balancing electricity

**4.1 Determination of necessary financial volume** 

kinds of auxiliary services are taken in account. These are in Table 5.

ENTSO-E.

and range.


Table 5. Informative ranges of auxiliary services values (MW) for 2010


Table 6. Maximum prices for provision of individual auxiliary services

Deriving from actual range (Table 5.) and prices (Table 6.) of individual auxiliary services financial volume necessary for provision of reserved power in 2010 can be determined – so called payment for instantaneous availability according to the following formulae:

$$\text{DE} = \text{O}\_{\text{PpS}} \cdot t\_r \tag{10}$$

$$\text{RN} = \text{DE} \cdot \text{C} \tag{17}$$

$$\text{CNN} \cdot \text{C} \tag{18}$$

where *DE* is instantaneously available electric energy

*O*PpS average range of auxiliary service

*t*r number of hours per year

*RN* yearly costs

*C* price for auxiliary services provision

Calculated financial volume for *PRV*, *SRV* and *TRV* as well as costs to secure voltage regulation and auxiliary service "Black start" are in Table 7. Summing up yearly costs for instantaneous availability of individual auxiliary services shown in Table 7 overall yearly cost can be obtained for 2010, which is 183 594 016 €.


Table 7. Yearly cost of individual auxiliary services

Different scenarios of installed RES capacities rise (300, 400, 500, 600, 800, 1000 and 1200 MW) include also pressure on auxiliary services primarily to *SRV* and *TRV*. The determination of accurate values with direct financial quantification is not simple as a number of unknown quantities are in play. To avoid placing a grave financial burden on consumers and excessively jeopardising power system operation appropriate effort will have to be given to harmonisation of these influences with the volume of *SRV* and *TRV* with regard to actual increase of RES energy production and continuously with verified impact on power system.


Table 8. Increase of demand rise of *TRV30MIN* for different scenarios of installed RES capacities increase

**Auxiliary service Yearly costs (€)** 

*PRV* 19 189 656

*SRV* 66 288 672

*TRV3MIN*+ 33 899 448

*TRV3MIN*- 6 047 028

*TRV30MIN*+ 37 054 800

*TRV30MIN*- 9 440 652

*TRV120MIN* 7 673 760

Voltage regulation 3 000 000

Black start 1 000 000

Sum 183 594 016

Different scenarios of installed RES capacities rise (300, 400, 500, 600, 800, 1000 and 1200 MW) include also pressure on auxiliary services primarily to *SRV* and *TRV*. The determination of accurate values with direct financial quantification is not simple as a number of unknown quantities are in play. To avoid placing a grave financial burden on consumers and excessively jeopardising power system operation appropriate effort will have to be given to harmonisation of these influences with the volume of *SRV* and *TRV* with regard to actual increase of RES energy production and continuously with verified

> **Rise of** *TRV30MIN* **at per-cent supply from installed capacity to power system**

**10 % 20 % 40 % 60 % 70 % 80 % 90 %** 

8,4 16,8 33,6 50,4 58,8 67,2 75,6 11,2 22,4 44,8 67,2 78,4 89,6 100,8 14 28 56 84 98 112 126 16,8 33,6 67,2 100,8 117,6 134,4 151,2 22,4 44,8 89,6 134,4 156,8 179,2 201,6 28 56 112 168 196 224 252 33,6 67,2 134,4 201,6 235,2 268,8 302,4

Table 8. Increase of demand rise of *TRV30MIN* for different scenarios of installed RES

Table 7. Yearly cost of individual auxiliary services

impact on power system.

**Installed RES capacity (MW)** 

capacities increase


Table 9. Final values of *SRV* at various scenarios of installed RES capacity increase and for *L*max (given) 2200 MW

Increase of demand rise of *TRV30MIN* for different scenarios of installed RES capacities increase for different per-cent supplies from installed capacity is in Table 8. The amount of per-cent power supply to power system is influenced mainly by weather factor, which is due to global climate change becoming more and more unpredictable, for example May and June 2010 with having the most rainy days in the whole recorded period of weather observation in Slovakia (approximately 130 years). Cloudy weather without solar flux does not allow electricity supply from PV plants to power systems with any available installed capacity. Wind power plants have the advantage of not being directly dependent on solar flux and can produce electric energy during the whole day depending on wind conditions.

During summer season electricity produced by PV plants can be ideally supplied from 6:00 to 18:00, while in winter season from 9:00 to 15:00 with characteristic curve, where again these assumptions are subject to almost full solar flux. Without long term observations or long term acquired data from the operation these values can hardly be estimated.

For the necessary volume of auxiliary services it is also important whether sunny conditions last for a longer period of time or are unpredictably alternating with cloudy conditions.

In a longer period of sunny weather electricity supply from PV plants settles in daily cycles allowing distribution system operator to credibly implement this supply into DLD. Thus demand for range or activation of auxiliary services decreases. The opposite situation occurs in unstable weather with sunny spells. In this case the demand for range or activation of auxiliary services depending on installed or available power from RES will be enormous. From this point of view for the higher values of installed capacity in these sources bigger emphasis must be put on the possibility of operative increase of range of required auxiliary service, or make provision of non-guaranteed balancing electricity in exposed periods of time more flexible.

Installation of RES will require apart from increased volume of necessary regulation reserves also changes in actual system of procurement of auxiliary services by SEPS. Currently the substantial part of auxiliary service is procured in the frame of yearly selection procedure what appears as very ineffective for these kinds of sources. SEPS will be forced to procure large amounts of auxiliary services only at a frame of daily procurement or during the day as an auction of non-guaranteed balancing electricity. In this way contracted volumes of auxiliary services can be optimised while preserving or even enhancing operational security of power systems.

For determination of necessary financial volume for provision of auxiliary services at various scenarios of installed RES capacity increasing of *TRV* is considered from Table 8 and final values of *SRV* at various scenarios of installed RES capacity increase and for *L*max (given) 2200 MW from Table 9. A modelling situation is considered, where for TRV increase (Table 8) an average supply of 40 % from installed RES capacity during whole day is estimated. Furthermore, actually prices for auxiliary service provision stated by Regulatory Office for Network Industries and values ranges are used from Table 6.

After summing-up these considerations, sum of financial costs necessary for auxiliary services provision, considering RES putting in operation for various scenarios of installed capacities at the day of *L*max (given) = 2 200 MW can be calculated.

Graphical comparison of the costs for auxiliary services provision at the day of *L*max (given) = 2 200 MW for various scenarios of installed RES capacities against the costs for auxiliary services without RES are in Fig. 4.

Fig. 4. Comparison of costs for instantaneous availability of auxiliary services at the day of *L*max (given) = 2 200 MW for various scenarios of installed RES capacities and 40 % of supply

These values should be considered as the first estimation, without having possibility for results precising according to history. A simplification was used in calculations – use of averaged power supply from installed RES capacity during given day – in the amount of 40 % of average power supply. From this value a necessary range of *TRV30MIN* is derived. Based on at least one year data (better on couple of years data) acquired from RES in operation, this parameter can be precised, what will lead to more reliable estimations. Costs for auxiliary services are determined for the day of summer maximum for 24 hours. The reason is, that individual volumes of auxiliary services without RES are changing during the year and are depending on the load (expected maximum load was not mentioned in study entry values). Supplementary costs for auxiliary services for RES regulation are calculated only from estimated installed capacity and estimated production of RES.

For determination of necessary financial volume for provision of auxiliary services at various scenarios of installed RES capacity increasing of *TRV* is considered from Table 8 and final values of *SRV* at various scenarios of installed RES capacity increase and for *L*max (given) 2200 MW from Table 9. A modelling situation is considered, where for TRV increase (Table 8) an average supply of 40 % from installed RES capacity during whole day is estimated. Furthermore, actually prices for auxiliary service provision stated by

After summing-up these considerations, sum of financial costs necessary for auxiliary services provision, considering RES putting in operation for various scenarios of installed

Graphical comparison of the costs for auxiliary services provision at the day of *L*max (given) = 2 200 MW for various scenarios of installed RES capacities against the costs

Fig. 4. Comparison of costs for instantaneous availability of auxiliary services at the day of *L*max (given) = 2 200 MW for various scenarios of installed RES capacities and 40 % of supply These values should be considered as the first estimation, without having possibility for results precising according to history. A simplification was used in calculations – use of averaged power supply from installed RES capacity during given day – in the amount of 40 % of average power supply. From this value a necessary range of *TRV30MIN* is derived. Based on at least one year data (better on couple of years data) acquired from RES in operation, this parameter can be precised, what will lead to more reliable estimations. Costs for auxiliary services are determined for the day of summer maximum for 24 hours. The reason is, that individual volumes of auxiliary services without RES are changing during the year and are depending on the load (expected maximum load was not mentioned in study entry values). Supplementary costs for auxiliary services for RES regulation are calculated

only from estimated installed capacity and estimated production of RES.

Regulatory Office for Network Industries and values ranges are used from Table 6.

capacities at the day of *L*max (given) = 2 200 MW can be calculated.

for auxiliary services without RES are in Fig. 4.

Mentioned calculations shown that influence of RES upon the SEPS economics will be circa 10 mil. € per year, even at the lowest scenario.

Costs for auxiliary services are not the only costs that can be expected from RES installations caused by electricity production fluctuations. The highest costs will definitely be imposed to distribution systems operators. They will be charged for caused balance. Increasing of value of costs for balance in the whole SPS is hardly forecasted in advance, any calculations would be distorted. SEPS can expect also increase of additional costs for system operation in case of overloading of some parts of system due to energy production from RES, i. e. circular power flows, necessary network topology changes, re-dispatching of energy production (within the SPS or in adjacent regions) and other corrective measures. Their price can only be determined ex-post.

Graphical presentations of increase of costs for auxiliary services provision at various scenarios of installed RES capacities and for different per-cent supplies from RES capacities are depicted in Figs. 5 and 6. Values of auxiliary services, *TRV30MIN* and S*RV* are in Tables 8 and 9. For costs calculation an actual prices of auxiliary services are used from Table 6. Yearly costs for instantaneous availability of auxiliary services forced by RES are on Figs. 7 and 8.

Fig. 5. Comparison of costs for auxiliary services at the day of *L*max = 1 700 MW for various scenarios of installed RES capacities and 20 % of supply

Fig. 6. Comparison of costs for instantaneous availability of auxiliary services at the day of *L*max = 2 600 MW for various scenarios of installed RES capacities and 60 % of supply

Fig. 6. Comparison of costs for instantaneous availability of auxiliary services at the day of *L*max = 2 600 MW for various scenarios of installed RES capacities and 60 % of supply

Fig. 7. Yearly costs for instantaneous availability of auxiliary services forced by RES at 10 % of supply from installed capacity

Fig. 8. Yearly costs for instantaneous availability of auxiliary services forced by RES at 90 % of supply from installed capacity
