Flexibility of energy system in solving the problem of “green and coal” paradox for Ukrainian NPPs

Flexibility of energy system in solving the problem of “green and coal” paradox for Ukrainian NPPs

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“Energy Strategy of Ukraine through 2035”, approved in 2017, sets ambitious objectives for achievement of energy effectiveness and energy security by introducing market mechanisms and integration into the EU energy markets. With regard to electricity generation, the Energy Strategy foresees acceleration of the tempo of renewables (RES) usage: 5 GW from renewables (without hydroelectric station) will be added through 2025. However, during this period the energy system will continue to rely on nuclear and coal generation, which is not supported in the most profitable sector – nuclear generation, that was devalued with some intentional actions by those, who in fact prosper from it.

As of today, this is an ambitious plan of synchronization of the entire Ukrainian power grid with the Western Europe and disconnection from the Russian grid https://ua-energy.org/uk/posts/buslavets-planuie-pryshvydshyty-intehratsiiu-ukrainy-z-entso-e?fbclid=IwAR3ShEOPQkrJL6Fcfn9mM7UcuWxvpiu-MIbXXmio80CvZmdkJCvB2ma3c2Y. However, prior to synchronization with Europe, Ukraine has to demonstrate that its grid can operate in the isolated mode. This is a task, which has to be thoroughly planned and which requires sufficient resources from the operator of the power transmission system. And we are still capable, prior to synchronization, to preserve necessary capacities of cheap energy from NPPs and ensure gradual RES increase without capacities of nuclear energy sector and slowdown of RES development.

All these challenges, to some extent, have one common problem: a need in more flexible power grid in Ukraine. This was demonstrated in an important study for Ukraine by Wartsila https://www.epravda.com.ua/rus/columns/2019/09/4/651261/, conducted with application of the optimization software PLEXOS?, developed by the Australian company Energy Exemplar?.

The study was performed for the purpose of optimization and preservation of the most effective and environmentally sound capacities. And considering today’s reality there is a need for immediate facilitation in adding flexibility to the power grid using the gas reciprocating motors, which would resolve a considerable part of the problems that currently have causes a breakdown of the market and payments by NNEGC Energoatom, and resulted in shutdown of more than 2 GW of NPP capacities in standby. DTEK is supporting balancing capacities with heat generation, and power grid confines RES capacities, which has to be paid with high tariff even in case of no usage of RES.

The results of modeling of the unified power system of Ukraine show that if we add 2-3 GW of flexibility through 2025, and let me add – also as a source of emergency power supply near constantly warm pools by the NPP sites, then this will allow the following:

??????????NPPs will continue to operate with the current load of 80-90 TW hours/year at the internal market with possibility for export of 15 TW hours/year of NPP energy via the synchronized energy bridges in the west in the south-west of Ukraine, which have to be restored without any DC links https://npsvvr1200.blogspot.com/2020/04/blog-post.html

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? ????????better integration of RES into power system both in Ukraine and at the moment of integration with power grid of Western Europe;

??????????reduce the scope of RES limitation from 30% to almost 0% at the installed RES capacity at the level of 7.5 GW through 2025 and 13.5 GW through 2030;

??????????reduce generation by coal power stations by 13-30%;

??????????reduce CO2 emission by 10-20%;

??????????reduce total cost of the power system for covering the load of 200-450 mln US dollars per year, which corresponds to costs reduction by 2-5%;

??????????only in the power grid of Ukraine, the total saving per a year will be from 600 to 700 mln EUR;?

??????????nuclear safety of NPPs will significantly improve for the cases of plant blackout due to powerful and reliable emergency power source from the gas reciprocating motors, which will be always in hot standby and be ready to get into full power operation for 2 minutes. At that, the relative level of safety will not decrease, as it can happen during NPP shutdown modes and non-regulatory modes at energy levels, when the NPPs according to the power grid requirements have to operate in the constant dynamics or at non-optimal levels of reduced power;

??????????NPPs in the mode of base load will further provide for the maximum low and economically sound tariff for the population and multiplicative effect for the economy of Ukraine, especially with the opportunity of bilateral electricity sale contracts up to 26 TW hours/year for power consuming companies of export production (metallurgy, chemistry, etc.), which will make us competitive at the external market;

??????????NNEGC Energoatom will stop being a threat for the private sector, since a common economic interest?https://biz.liga.net/ekonomika/tek/novosti/dtek-anonsiroval-zapusk-sistemy-hraneniya-elektroenergii will not devour the national company and drag NPPs into a political process of searching opportunities for introducing of those into the company’s management, who will lead it to bankruptcy or will destroy it for the benefit of the RF;?

??????????the operator of energy transmission system will get an access to modern capacities with rapid startup and high flexibility for balancing the system and providing the reserves. This will create the future where Ukraine will be less dependent on the coal and will significantly reduce its CO2 emissions https://ee.sputniknews.ru/world_news/20191217/18783802/Evrosoyuz-okonchatelno-priznal-zelenymi-atomnuyu-energetiku-i-prirodnyy-gaz.html?fbclid=IwAR3S5RzgjNaFszgN9_r5YWtne-YBiJSWzXb-Dj5ZexpiZ9JKKSAXFJpvK0Y. This will allow Ukraine to create a system, which is ready for future challenges, for integration of larger scope of RES and achievement of stated objectives to reduce releases, increase energy effectiveness and energy security.?

To my mind, the nuclear generation has every reason to keep a maximum interest in increasing the flexibility of the power grid of Ukraine, and even to get fully integrated in the investment process of this important event. Because it coincides completely with the goals of preserving and increasing the achieved level of security and sustainable economic development of NNEGC Energoatom and Ukraine in general.

Therefore, introduction of necessary balancing capacities requires maximum interaction of all stakeholders both in the field of heat and nuclear generation and RES, and this should be done within the shortest timeframe – not less than 500 MW already in a year, and 2000 MW till the end of 2021.

It is also important for everyone, who will be involved in the decision making process in Ukraine, to know “where to look at” while considering the technologies for introduction of new capacities to the balancing market of Ukraine. It is especially important, if we consider the internal dispute between the gas and turbine and gas reciprocating motors. Here, the following has to be taken into account:

·????????????????????High environmental temperatures do not practically impact the operating characteristics of the motors;

·????????????????????Operation at high environmental temperatures (30-40° C) results in reduction of maximum productivity and effectiveness (efficiency factor) of the gas turbines;

·????????????????????Reduction of station productivity leads to the need for installation of more turbines to achieve the target production level;

·????????????????????Reduction of the efficiency factor (EF) at the extreme environmental temperatures results in more fuel consumption;

·????????????????????The power station with several motors can effectively operate at the partial load with only required items running;

·????????????????????The running items of motors are capable to operate at the maximum high load;

·????????????????????The motors have the required operational flexibility with high effectiveness even at very low loads;

·????????????????????The gas turbine unit loses its effectiveness very fast if the load decreases. As a rule, the turbine is not designed for operation at the load of less than 40-50% (typical environmental standards of the developed countries set limits to the minimum turbine load) at that the efficiency factor drops significantly and the station, for instance, with 10 motors can operate at 1% load and the EF continues to stay at its maximum of 45-47%);

·????????????????????The gas motors are not prone to worsening of efficiency during their lifetime;

·????????????????????The heat consumption of gas motors is restored during overhaul, after which the coefficient of the heat consumption returns practically to the initial value;

·????????????????????The gas turbines continue to lose efficiency during their lifetime, which leads to the need of additional capacity (losses make 3-5% after 100 000 hours of operation);

·????????????????????The heat consumption of gas turbine continues to worsen during its lifetime.

The myth is often heard about a lack of the installed capacity density per kW/m2. Like, the turbine most effectively uses the occupied physical area of the unit. It is not really true. The module gas reciprocating units are so space effective that they are as good as gas turbines in terms of density indicators per kW/m2, and go beyond that.

Let me emphasize that the operational flexibility is the key feature of the gas reciprocating motors, which is defined by:

1.?????????????????Short startup time:

-????????Decision on startup can be maximally delayed till the latest data on weather forecast are received;

-????????Real-time operation at the energy markets;

-????????Fast startup can ensure support to the renewable energy sources in the mode without rotation. Starting up practically during 2 minutes to full power;?

2.?????????????????Low fuel consumption during startup;

3.?????????????????Startup cost;

4.?????????????????Offloading time:

-????????When the price leap for electricity is over, the opportunity for rapid offloading means absence of production at the unprofitable price;

-????????Allows several startups and trips during a day;

-????????Full optimization of the system.

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5.?????????????????Possible reduction / increase of the speed:

-????????Absence of minimum duration of operation and out-of-service time;

-????????Absence of minimum time of operation or out-of-service time allows effective optimization of the system;?

-????????Decision on startup can be delayed maximally;

-????????Flexibility in startup in case of uncertainties of weather forecasts.

6.?????????????????Minimum stable loading:

-????????Lower minimum stable loading ensures high flexibility of the unit;

-????????Minimization of the heat generation during high efficiency of the renewable sources allows complete usage of the renewables production;

-????????Units with the lower minimum loading can give more margin of rotation at minimum fuel consumption.

7.?????????????????Effectiveness of partial loading.

It is very important to take into account the operational element of the gas turbine maintenance, since its maintenance required consideration of several factors:

·????????????????????In the mode of continuous base load using the gas, the time schedule of maintenance is regulated by actual production hours;

·????????????????????Operation hours + startups/trips change the intervals of turbine maintenance;

·????????????????????The equipment, as a rule, has to be sent to the manufacturer’s workshops for overhaul – additional transportation and out-of-service time.

The following factors also influence the time schedule of gas turbine maintenance:

·????????????????????Startup and trip;

·????????????????????Cycling and peak mode of operation;

·????????????????????Operation using liquid fuel;

·????????????????????Number of cycles;

·????????????????????Cycle operation with daily startups can lead to significant increase of maintenance costs.

As for operation of the gas reciprocating motors, the picture here is quite different and much better for those goals and challenges that set the need of flexible balance, high effectiveness and reliability. At that, the most essential advantage of the motors are the following qualification features and technical characteristics:

·????????????????????Cycle operation and frequent startups do not impact the maintenance time schedule and costs;

·????????????????????Configuration with several units allows performing the maintenance in a successive manner, such that only the part of production capacities being in maintenance is lost;

·????????????????????All maintenance activities can be conducted on site, there is no need to send the equipment to the manufacturer;

·????????????????????Absence of factoring of operating hours, number of startups and trips, cycles and loads.

An important factor that influences the efficiency factor under the actual operation conditions and combined cycling during electricity production and heat, is:

·????????????????????Environmental temperature. Thus, at 30% load, the turbine’s EF drops significantly and the motor’s EF does not change practically;

·????????????????????The need for compensatory turbine cooling is greater than for motors;

·????????????????????As for the turbines, there is a need of gas turbo-blowing to get the pressure of 25 bars and more. If turbo-blowing is not available and the gas is used at normal pressure of 10 bars, the turbine’s EF decreases. At the same time, the motors do not require additional blowing, the pressure of 10 bars is optimum, the EF does not change;

·????????????????????The level of average load regulates some other factors of the EF effectiveness. It is already at 80% instead of 100% load, the turbine’s EF drops essentially, and the motor’s EF stays practically the same;

·????????????????????Wear-induced degradation, number of cycles, startup/trips, as indicated above;

·????????????????????Number of calculated operating hours is higher with the motors than with the turbine units.

07/29/2021

Georgiy Balakan