What is standard benefit? - Part 5

Electrical energy is the only product that always has to be generated literally at the same moment it is consumed. Nevertheless, it is practically always available in full - whether it is used or not. How does that work? And can electroplating systems perhaps help to keep it that way?

2.6 Keeping the clocks ticking: Quaternary regulation

Is the world finally back to normal? Not necessarily, because the "frequency restoration reserve" has merely restored the frequency after its dip or overshoot. The dip or hump in its course from the past remains, which is why the number of periods driven on the day in question does not correspond to its target value. The frequency is then increased or decreased slightly to correct the number of periods so that, on average over the year, a grid synchronous clock on the UCTE grid never deviates by more than 20 seconds. Other interconnected grids are far less stable, but in the meantime the UCTE grid, like the EU, is expanding further and further east, pushing back the Eastern European interconnected grid - which, however, is not yet an ENTSO-E member. The border once ran along the inner-German demarcation line, whereas today it has already retreated very far to the east (Fig. 6), and West Berlin was an island of electricity. In 1984, West German students of electrical power engineering at Dortmund University of Applied Sciences were advised: "Don't give your friends in the GDR any mains synchronous clocks! They won't enjoy them." Electricity was already being exchanged between the grids at that time, but only via HVDC short-circuits - although the nominal frequencies were the same - because the grids were not synchronized, as frequency maintenance in the East was still quite poor [1, 2].

As a result of the Balkan war, during which the state of Yugoslavia broke up, the UCTE network also broke into two parts. These were reunited in 2004 [3]. 14 years later, the electricity world experienced déjà vu: all European users of grid synchronous clocks noticed from mid-January 2018 that their clocks were starting to lag. By the end of February to the beginning of March 2018, the deviation had accumulated to 6 minutes [4]. So what had happened here? Ultimately, the Serbia - Macedonia - Montenegro control area failed to meet its obligations for political reasons. It is said that 113 GWh less was fed into the grid there than was withdrawn. This is orders of magnitude more than the kinetic energy rotating in the power plants of the entire interconnected grid. If there were no balancing power plants, the deficit would have put the whole of Europe in the dark within a few minutes. This is exactly what does not happen in an interconnected grid! However, the control algorithm, as explained (section 2.2), works in pretty much the same way:

If there is a shortfall of 113 GWh over the course of almost 8 weeks, then that is pretty much exactly 2 GWh per day, corresponding to an average output of just under 100 MW. This is roughly 0.5 ‰ of the average capacity in the entire UCTE grid. This means that it would theoretically take 2000 s - a good half hour - for the generators to come to a standstill if there were no balancing power. It would therefore only take 8 s to reach the threshold for full control power at 49.8 Hz. The clocks that are 6 minutes behind mean that 18,000 periods of 241.92 million periods were missing in the 8 weeks in question, which results in an average grid frequency of 49.996 Hz - and here we have the salad: This value still falls within the dead band, within which no control power is activated! If the power and energy balances within the control zones and the power and energy flows between the control zones always correspond to the previously agreed target values, the deviations in frequency are statistically just as often in the plus range as in the minus range; however, deviations from the schedule result in imbalances! This case therefore has the same effect as if the frequency setpoint had been set to 49.996 Hz. This shows how important both compliance with the agreements and the control performance are for dealing with unintentional deviations from them. In the event of intentional violations, the control power prevents power outages, but does not protect against all risks and side effects on its own

Accordingly, after the incidents in the Balkans, experts predicted that the missing energy would be replenished - and with it the missing periods. In fact, the grid synchronization clocks were running correctly again at the beginning of April 2018 - unless someone had manually corrected them when they were lagging. You shouldn't do that, just wait and see, otherwise they will go ahead afterwards. After all, an incident like this is unprecedented - and yet it was met with an appropriate action plan.

2.7 Summary of the standard performance

A tabular overview (Table 1) has been compiled here for the purpose of summary. The following should be explained:

• The time of ≈ 5 s for the range of the second reserve is a very rough guide value in accordance with the moments of inertia estimated above (Section 2.1) and the proviso that the UCTE grid should be able to withstand a sudden, unplanned loss of 3 GW of power plant capacity without having to interrupt the supply to any customer. Depending on how much load is currently connected to the grid and what drop in frequency is considered acceptable, values of ≈ 1 s to ≈ 25 s result.
• "Remuneration as a grid service" here means additional remuneration as balancing power / balancing energy, not the market value or the consumer's regular electricity price, which has to be paid anyway. This does not exclude the possibility that one value is positive while the other is negative.
• Economic optimization" here means that the FRR is initially applied automatically by those systems that are able to do so most quickly, but is then transferred manually to systems that can continue this task more cost-effectively and possibly also have a longer range.

An analysis of the costs incurred for balancing capacity and balancing energy in Germany in 2019 (Table 2) allows the following observations and conclusions to be drawn:

• Around €49 million was spent on primary balancing power (as previously mentioned, the energy supplied is not remunerated here).
• The secondary balancing power called up amounted to around 1.7 million. What is striking here is that almost twice as much had to be spent on curtailment as on balancing. This is presumably related to the EEG (Renewable Energy Sources Act).
• Secondary control energy had to be remunerated with 91 million, of which 81 million was for delivered energy and 10 million for the omission of agreed deliveries (so to speak "compensation" for the need to withdraw from contracts).
• The peak energy price of 6295.25 euros/(MWh) on July 31 at 6:45 a.m. is 153 times higher than the average EEX exchange price for 2019 and 52 times higher than its annual peak value. Strikingly, the Federal Network Agency's exchange price statistics [5] stop at EUR 38.66/(MWh) on July 30 at 10 p.m. and only start again at EUR 39.00/(MWh) on July 31 at 11 p.m.! Presumably an emergency situation had arisen which - quite rightly - made other things appear more important than electricity trading. Ultimately, the loss of 39 euros/(MWh) over 24 hours may be minor compared to the above-mentioned price of 6295.25 euros/(MWh), which was available for balancing energy for around half an hour.
• However, the causal relationship may also have been the other way around: If the exchange was suspended, this may have been due to the fact that the data flow between the control areas was not working, i.e. the data on the current power flows was also missing. This is already a crisis situation in itself.
• The expenses for minute control power are around 20 million euros, while those for minute control energy are only slightly higher - both of which are predominantly positive, i.e. used to increase output or supply more energy.
• The prices for minute control power are approximately 25 times more positive than negative, while those for minute control energy are noticeably more negative than positive. This is probably also due to compliance with the EEG, which requires that all renewable electrical energy is actually generated and fed into the grid. As a result, there tends to be too much energy rather than too little, while the output often drops sharply and unexpectedly. The fact that it is available again minutes later is no consolation, but a task for the minute reserve.
• The hourly reserve relates more to the normal power plants and hardly to the plants intended exclusively or predominantly for balancing processes. For this reason, there are no plans to keep reserve capacity / power reserve available here, only the energy is considered and remunerated. A good 180 million euros are spent on additional generation, and lost generation (just under 24 million) is actually deducted from this.
• The price for the hourly reserve peaks at 78 times the average value for additionally supplied energy! The price for curtailed energy is not quite as high, but similarly negative. In contrast, the average price is slightly lower than that on the EEX.

Literature

[1] G. Brauner: High-voltage direct current transmission as a connection in transmission grids, ETG Journal 2(2018), 78
[2] Volume-weighted average price with taxes across all contract categories for household customers from 2500 kWh/a to 5000 kWh/a, Monitoring Report (2019) of the Federal Network Agency(https://www.bundesnetzagentur.de/DE/Sachgebiete/ElektrizitaetundGas/Unternehmen_Institutionen/DatenaustauschundMonitoring/Monitoring/Monitoringberichte/Monitoring_Berichte_node.html)
[3] C. Carnal; P. Reinhardt: PSGuard contributes to the reconnection of the UCTE network, https://library.e.abb.com/public/0b29ca3a582a1944c1257046002569f9/ABB_Technik_PSGMS_Petra.pdf
[4] https://www.entsoe.eu/news-events/announcements/announcements-archive/Pages/News/2018-03-06-press-release-continuing-frequency-deviation-in-the-continental-european-power-system.aspx
[5] R. Grebe: Of growing importance: grid stability in large interconnected grids, etz Elektrotechnik-Zeitschrift 6(1998), 35