Holistic approach to electricity and district heating

The electric power industry and the district heating sector are now little interconnected, with the exception of thermal power plants (CHP), which produce electric and thermal energy, but are morally and physically outdated and lose sales volumes of both electric and thermal energy. The national electric power industry is the United Energy System of Ukraine (UESU), and district heating (CT) is a problem of local executive authorities. At the national level, centralized heat supply is mentioned only before the heating season in connection with debts and the rise in price of natural gas or with breaks in the pipes of heat networks.

At the same time, the EU Strategy for Energy System Integration (2020) is being implemented in economically developed countries, including EU member states. At the same time, the key role is given to the district heating sector as an effective tool to ensure the stability of the electric power industry in conditions of permanent build-up of changing solar and wind electric generation.

For the Ukrainian electric power industry, the basis of which, in accordance with the Energy Strategy until 2035, is nuclear power plants (NPPs), a holistic approach to the modernization of the electric power industry and district heating is especially relevant. The UESU has an urgent need for balancing capacities, the role of which today is performed by outdated coal-fired power units, which, in principle, as well as nuclear power plants, are designed to operate in the basic mode, hydropower, the capacity of which is limited, and outdated thermal power plants, many of which are not adapted to work in the segments of balancing and auxiliary services of the electricity market.As a strategic prospect of increasing the stability of the electric power industry in the face of increasing the share of changing solar and wind generation, powerful network storage of electric energy and hydrogen as an energy storage can be considered. However, both the first and the second directions now require technological improvement and are too expensive, at least for the domestic market of Ukraine.

In these circumstances, we need to take a fresh look at district heating, which we already have, and the problem of modernization of which in any case should be solved quickly, because this is not only a technical, but also an acute social problem affecting half of the country's population. I will not talk in the future about the problems of CT, they are considered in sufficient detail in a number of analytical studies, in particular in the publication ZN.UA (issue No. 36, 2019). The theme of this publication is the synergy of electricity and district heating in the context of energy decarbonization, when the concept of "energy" will be associated not with a powerful pipe with which black smoke is pouring in clubs, but with majestic silver giants that slowly do their work, sparkling in the sun with glass structures that go beyond the horizon.

So what are the synergistic effects of a holistic approach to the modernization of electricity and district heating? Let us briefly call these effects "co-production," "satisfaction of increased demand," "cutting off peaks" and "electric heating.The joint generation of electrical and thermal energy (cogeneration) is a well-known and fairly common thermodynamic principle that is implemented at CHP. Heat and power plants simultaneously produce electrical and thermal energy and save up to 30% of fuel compared to the separate generation of these types of energy at condensing power plants (IES) and in heating plants. However, in practice, the production of thermal energy at CHP in Ukraine is continuously falling and today has decreased four times compared to 1990. There are several reasons: our CHPs are physically and morally outdated, they are not competitive in the electricity market compared to nuclear power plants and coal-fired power plants, energy losses in thermal networks of CHPs are significant. However, all these reasons do not negate the fact that the joint production of electrical and thermal energy is the most economical way to obtain these types of energy. Rather, on the contrary, the elimination of these barriers is a way to develop cogeneration in the energy sector of Ukraine. CHP pipelines should be modernized, allocating appropriate funds for this. New thermal power plants should be built not only on natural gas, but also on biofuels and waste. And the preservation and expansion of district heating is the cornerstone of energy efficient production of both heat and electricity.Meeting the increased demand for electrical energy. The daily change in the electric power of the UESU can reach 30%, or 5-6 thousand MW in absolute terms. The installed capacity of the CHP, most of which runs on natural gas, is about 6 thousand MW, and the actual winter capacity is 2.5-3 thousand MW. It turns out that the power that the CHP has is comparable to the variable component of the daily schedule of the electric load of the United Energy System, which creates the prerequisites for their use to balance the electricity market. However, to realize this opportunity, it is necessary to modernize existing or create new maneuverable CHPs that can simultaneously provide consumers with thermal energy and work in the segment of balancing services in the electricity market.

For this purpose it is necessary to apply on CHP thermal accumulators and heat pumps. During periods of reduced demand for electricity, it is used in heat pumps to generate heat energy that accumulates in the battery. And during periods of increased demand for electricity, the CHP works on the power system without harm to thermal consumers, using energy from the battery. Thus, the main equipment of the CHP operates in the most economical basic mode.

A promising direction for the development of CT in Ukraine is also the creation of maneuverable gas piston cogeneration plants with a certain capacity of more than 20 MW, which operate in the segment of balancing services of the electricity market and provide settlements with heat.Cutting off the peaks of time-varying solar and wind generation is a new function of district heating, which has not yet been implemented in Ukraine, and in the European energy sector is the most important driver of the development of the CT. At the technical level, the implementation of this function requires the inclusion of heat accumulators and heat pumps in the CT structure to increase the maneuverability of the CHP. During periods of excess electrical power associated with increased solar and wind generation, the generated electricity is directed to heat generation, accumulated and stored in thermal batteries and used at the right time to provide consumers with thermal energy. The intensity of solar radiation in summer is almost twice as high as in winter, and we need thermal energy more in winter than in summer. Seasonal thermal batteries, the technology of construction and operation of which is well known and used in the world, will help here.

Wind electric generation is more harmoniously combined with heat supply. In winter, we need thermal energy, and the wind is stronger in winter, so we can limit ourselves to daily thermal batteries, which are much smaller in volume and cheaper than seasonal thermal batteries.
But back to the heat pumps. They don't just turn electricity into heat. With this successfully cope and electric boilers, which are much cheaper. But heat pumps draw energy from the environment, increasing its temperature level to the heating parameters we need. The most promising sources of energy, that is, the medium for heat pumps of district heating, are sea water (in the Black Sea its temperature does not fall below 70C), sewage (in cold periods not lower than 100C), waste heat energy of industrial enterprises (can reach 400S and above). At CHP, heat pumps can use all the waste heat energy of the energy production process cycle, from the boiler exhaust gases to the cooling systems of transformers and electric generators.

Electric heating should be considered as a regulator-consumer of the electric power system for leveling night dips in electricity consumption. This practice exists in Ukraine, but only at the level of individual consumers. The spread of this practice at the level of individual houses and residential quarters opens up wide prospects for the development of electric heating and seems relevant for Ukraine in connection with the preservation of the dominant role of nuclear power plants. Autonomous electric heating using relatively cheap night electricity of low-carbon (nuclear) origin is a worthy alternative to individual gas boilers. To implement such a solution, it is necessary to introduce pilot projects for heat-accumulating electric heating, as well as increase the institutional capacity of heat supply organizations and co-owners of apartment buildings to purchase electricity at minimal prices during periods of excessive generation.

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A holistic approach to energy and the key role of district heating are the basic provisions of European energy policy. By 2050, the EU countries plan to almost double the share of district heating, mainly on the basis of cogeneration, heat pumps, the use of industrial waste heat energy, solar energy.

The principle of such a holistic approach should be declared in Ukraine at the legislative level and supported by relevant regulatory and methodological documents and practical steps.

It is important to take into account not only the local economic effect for each settlement, but also the effect for the entire electricity system. It is also necessary to develop a stimulating tariff policy and increase the institutional capacity of district heating enterprises in their work in the balancing services sector of the electricity market.

District heating was created as an element of a holistic state energy policy. At the present stage of decarbonized energy development, the integrating role of centralized energy has increased. Therefore, the modernization of this sector cannot be considered only as a task of local authorities. Without systemic support at the national level, this task cannot be solved. The interaction of central and local authorities is a decisive factor in decarbonization and increasing the energy efficiency of Ukrainian district heating.