Energy storage, i.e. effective use of renewable energy in residential buildings and industrial plants

2022-01-2615:55

There is a lot of talk about electricity storage in Poland, but they are still rarely installed. However, there are countries where a significant part of investors in a photovoltaic system - home or for the needs of a company - immediately decide to configure it with energy storage. Find out about the development of the energy storage market in Germany and how it currently looks in Poland. We answer the question of whether it is worth investing in energy storage and for whom it is profitable. Does electricity storage guarantee energy independence?

Contents

1. How energy storage is changing the electricity market
2. Home energy storage - what is it?
3. Energy storage for photovoltaics - why?
4. Energy storage - the share of self-consumption and the degree of autarky
5. The impact of energy storage on the power grid
6. Energy storage - an example from Germany
7. Can energy storage be dangerous?< /li>
8. Energy storage - what battery?
9. Energy storage on the German market and in Poland
10. New regulations supporting the development of energy storage in Poland
11. Is it worth it invest in energy storage?
12. Energy storage and the development of electromobility
13. Energy storage for PV and wind farms

How energy storage is changing the electricity market< /h2>

In recent years, the topic of energy storage has become very important due to the growing popularity of electricity generation systems in renewable energy sources (RES). However, contrary to appearances, the issue itself is not new, and some energy storage technologies are over 100 years old.

Commonly known pumped-storage power plants are in fact energy storage facilities, despite the fact that in Polish they have the word "power plant" in their name. Batteries in cars or mobile phones also serve to store energy. However, this does not exhaust the list of electricity storage methods. Depending on the required capacity and discharge time, a range of technologies are available.

The figure shows the different types of energy storage, grouping them by discharge time and capacity. Close to the origin of the coordinate system, supercapacitors are placed, which are characterized by extremely short discharge times. They are used more and more often and they are perfect wherever there are high impulse loads, such as in guaranteed power supply systems. In turn, high capacity and long discharge time are the characteristics of devices using combustible gases: hydrogen or synthetic methane. It is a technology that has the potential to solve the problem of storing electricity for up to months. Its possible application is, for example, the storage of surplus energy produced in photovoltaic installations in the summer, in order to use it in the winter. On a commercial basis, such storage facilities currently have no raison d'etre, but research on this method, known as Power-to-Gas, is conducted very intensively.

Other methods of energy storage are also used, such as superconducting magnetic energy storage (SMES) or compressed air storage. However, it is not these technologies that made the topic of storage so popular, both in the debate of professionals dealing with the energy market and end users, and went beyond the energy industry. This was due to the intensification of the use of lithium-ion batteries. The use of this solution in mobile phones, laptops and electric cars has increased awareness of the functions that they can perform, and the improvement of their parameters, accompanied by a decrease in prices, has translated into an improvement in the economics of their use. This has made the storage of electricity generated in RES installations, for example in photovoltaic, a viable option.

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Home energy storage - what is it?

In the press, experts' statements and even product data sheets, the term "home energy storage" is used. In fact, for the sake of accuracy, this name should be expanded with two words: "battery" at the beginning and "electric" at the end. We would then receive the term "battery home electricity storage", which would quite precisely describe the specificity of the devices in question.

The addition of "battery" is important as energy can be stored in the different types of storage listed above. Clarifying that it is an electricity storage is also important, because thermal energy, i.e. heat or cold, can also be stored. In practice, the term "home energy storage" currently most often means a solution that allows you to store electricity in a battery bank.

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Energy storage for photovoltaics - why?

An energy storage allows you to consume electricity at a time other than when it is generated in a photovoltaic installation. This is often referred to as 'postpone electricity consumption'. In practice, in the case of a household, this means that the surplus solar electricity produced during the day is directed to the energy storage. At a time when the demand in the house exceeds the production from the PV system, electricity is drawn from it. In the case of a household, the issue is important because the direct consumption of electricity generated in a PV installation for own needs usually amounts to approx. 30%. This is because when electricity production is at its highest, i.e. during the day, the household members are not at home.

In this situation, it seems reasonable to store the part of the electricity that cannot be used directly and use it when the yield from the PV system is not sufficient. However, it is worth considering the issue of energy storage in two options:

With an off-grid PV system, the user cannot draw electricity from the grid. If he wants to use electrical devices also when the PV system does not produce electricity, he should be able to draw it from the storage tank. Alternatively, it can use power generators. However, in practice, in economically developed countries, island PV installations in year-round residential houses are rare. They are used, for example, in summer houses or on boats.

The issue of off-grid storage is quite simple - all you need is batteries and a charge controller. In installations connected to the grid, the argument for energy storage is not the lack of access to electricity when the PV system does not produce it, because it is possible to discharge the surplus of electricity produced to the grid and to draw electricity from the grid when necessary. Despite this, energy storage in on-grid photovoltaic systems is increasingly used.

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Energy storage - the share of self-consumption and the degree of autarky

When talking about energy storage or storage in systems connected to the public grid, two concepts cannot be omitted:

The first one expresses what part of the electricity produced in a PV installation per year is used by the user for his own needs. In turn, the second one, also called the degree of autarky, determines what part of the electricity consumed in a household comes from its own installation. The use of an energy storage allows to increase both the first and the second parameter. However, it is worth taking a closer look at what motivates the user of PV installations to improve them.

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The share of self-consumption, without energy storage, is approx. 30% in a household. By adjusting the consumption to the profile of electricity generation in the PV installation, i.e. by switching on high-power consumers, such as a dishwasher, washing machine or dryer, during the day, the user can increase the share of self-consumption, although usually this value will not exceed 40%. Surplus electricity can be fed into the public grid or directed to an energy storage.

The user will probably choose the solution that will be more financially beneficial for him, which is confirmed by the observation of the development of the largest market for home energy storage - Germany. As long as feed-in tariffs were high, PV system users did not seek to increase the share of self-consumption. Quite the opposite - until the fee for energy fed into the grid was higher than the fee for energy taken from it, often the entire generation went to the grid.

The situation began to change when users began to receive less for the energy they gave to the grid than they paid for "electricity from the socket". At that time, they tried to use as much of the energy generated in their own PV installation as possible for their own needs, initially without using energy storage.

The justification for storage appeared when the difference in the price of electricity purchased and sold became large enough to include the energy storage in the investment costs. Of course, the economics of such a solution were influenced by the possibility of co-financing the investment in the energy storage under the support programme.

Raising the degree of energy independence is advisable because of becoming independent from the increase in electricity prices. For some investors, this is important because they feel less dependent on energy concerns. Is it possible to achieve 100% autarchy? Theoretically yes, but in practice it would mean oversizing the entire photovoltaic system - both the module power and the storage capacity. Therefore, from the economic point of view, this is not a deliberate solution.

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Impact of energy storage on the power grid

Energy storage devices that supplement micro-installations, ie installations with up to 50 kWp of installed power, have a relatively small capacity. On the German market, it is usually between 4 and 8 kWh. However, even such small values ​​multiplied by tens or hundreds of thousands of installations create a total storage capacity that may be relevant in the scale of the entire power system.

According to data at the end of 2019, there were approx. 160,000 energy storage systems in Germany installed in photovoltaic systems connected to the low-voltage grid. This number includes both home energy storage and storage units in companies. It is worth comparing this number to the number of PV installations in Germany. It may seem that 160,000 storage facilities compared to approx. 1.7 million PV installations are not much. It is worth bearing in mind, however, that PV installations began to be installed in Germany about 20 years ago, and energy storage facilities cooperating with them have only gained popularity in recent years.

At the beginning of 2016, 34,000 energy storages were installed in Germany, in August 2018 the number exceeded 100,000, and at the end of 2019 it was already 160,000.

In the face of such numbers, it is impossible not to ask yourself what impact the storage tanks installed in household PV installations have on the power grid? The example of our western neighbors shows that it is advisable to ask such a question earlier, before the market develops, because depending on the answers obtained, the growth of the market can be managed. The possible impact of decentralized energy storage in PV installations on the operation of low-voltage grids was particularly intensely discussed in Germany in 2013, when the introduction of a support system for the purchase of solar energy storage was considered. One of the most important analyzes that was created at that time was "Speicherstudie 2013" carried out by the renowned Frauenhofer Institute. The researchers attempted to answer the question about the impact of the large-scale use of energy storage in household PV systems. It showed that thanks to them, it is possible to reduce the peaks of solar power supply in the scale of the entire system (by approx. 40%), and up to 66% more installed capacity in PV systems can be connected to the same section.

The condition for achieving such an effect, however, is the use of energy storage in a way that supports the power grid, i.e. ensuring that electricity generated in a home PV installation during the southern peaks of supply will go to the energy storage, and not to the grid. If the energy storage users are not persuaded to exploit them in this way, it may turn out that the energy storage tank will be completely filled already in the morning hours, which means that during the peak production of solar electricity in the photovoltaic system, all surplus energy will go to the power grid.

Energy storage - an example from Germany

Conclusions from the analysis of the Frauenhofer Institute were reflected in the conditions of the program to support the purchase of energy storage, which was introduced in Germany in May 2013 and lasted until the end of 2015. in order to ensure that the storage is used in a way that supports the grid, the amount of electricity fed into the grid by the beneficiaries at peak times could not exceed 60% of the installed capacity of the PV system.

19,000 energy storages were purchased under this program, and the experience of using them confirms the conclusions of the "Speicherstudie 2013" analysis. It was a de facto continuation of the previous one, however, the condition regarding the amount of energy fed into the grid was tightened - it could not exceed 50% of the installed capacity of the PV installation.

The actual impact of using energy storage in photovoltaic systems with an installed capacity of up to 30 kWp was the subject of a monitoring and research program carried out in parallel with support programs by the Rhine-Westphalian University of Technology in Aachen (RWTH Aachen) and was obligatory for all beneficiaries. The conclusions drawn from it fully confirmed the analysis of researchers from the Frauenhofer Institute. They were also the basis for the Aachen researchers to terminate the recommendation to tighten the condition regarding the amount of energy introduced to the grid at peak times, which was reflected in the terms of the 2016 program.

In Germany, there is currently no nationwide subsidy program for the purchase of energy storage in addition to a PV system, but this effort is supported by a number of federal states and cities. Subsidies to encourage this type of investment are currently available in the following Länder: Thuringia, Saxony, Saxony-Anhalt, Bavaria, Berlin, Brandenburg and North Rhine-Westphalia. In Baden-Württemberg, a program of this type was implemented until July 2019. Residents of Munich, Münster and Freiburg can also count on subsidies for the solar energy storage.

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Can energy storage be dangerous?

The topic of safety of home energy storage was an important issue a few years ago. This was influenced by the use of lithium-ion batteries in energy storage. Lithium batteries are a relatively new technology – they started to be used only in the early 1990s in portable devices. For comparison, lead-acid batteries made their market debut about a century earlier.

Overcharging lithium batteries poses a fire hazard, and their transportation is subject to hazardous material conditions. All this meant that when lithium-ion batteries began to be used in home energy storage, no longer as small units in a phone, camera or laptop, but as storage tanks with a much larger capacity, doubts arose whether this did not pose a threat to residents of the house. Pictures of burning or exploding batteries could be seen on the Internet. Although a significant part of them was documentation of more or less professionally conducted tests, they showed the real risks associated with the use of lithium-ion batteries.

Thus, the issue of the safety of this type of battery has played a significant role in the discussion about the future of energy storage based on this technology for a long time. The threat that the vision of a fire would deter potential buyers was real. In 2014, leading German solar and electrotechnical associations, in cooperation with certification institutions, developed recommendations regarding the safety parameters of home energy storage based on lithium-ion batteries. They became the basis for the introduction of the VDE-AR-E 2510-50 standard in 2016.

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Energy storage - what kind of battery?

In the initial phase of development of the market of energy storage cooperating with PV micro-installations, two types of batteries competed with each other - lithium-ion and lead-acid. The properties of the former, especially in terms of specific energy, energy density or service life, both calendar and number of cycles, spoke in favor of their use in photovoltaic systems. However, the price was a counter-argument clearly in favor of using lead-acid batteries.

Just a few years later, however, this question in relation to the market segment of small-capacity solar storages has virtually ceased to be valid - lithium-ion storages have become the leading technology. Such an increase in popularity was undoubtedly influenced by the dynamic drop in their prices and the reduction of the prices of lead-acid storage tanks, which did not match this dynamics. Solutions based on other types of batteries, such as flow-through or sodium-ion batteries, are marginal in this market segment.

Energy storage on the German market and in Poland

As mentioned above, the German market is the largest market for solar storage in the world. There are solutions available on it from several dozen bidders, which gives a large variety of products. It applies to both functional features and appearance. Some systems work on the AC side of the inverter, others on the DC side, and there are also those that can be used in both configurations.

There are warehouses on the market with a built-in inverter and those for which you need to buy one. If the function of working in a swarm is important, allowing you to combine many units into a virtual warehouse, there will also be solutions with such functionality.

The buyer will also find it difficult to choose the appearance of the energy storage. Contrary to appearances, this is not without significance - the home energy storage is no longer a component of the photovoltaic system, the choice of which the investor leaves entirely to the designer of the system or the installation company. The perception of this type of goods by customers is shifting towards lifestyle products. For this reason, the appearance and image of the brand matter. In addition to uninteresting-looking cabinets with batteries visible inside, the customer can also choose those that aesthetically match the living room, even if in fact they are most often installed in the basement or garage. Some products are perfectly visually refined, for which they win prestigious awards in the Red Dot Design Award competitions, called the Oscar of design.

Unfortunately, the situation is different in Poland. Due to the lack of incentives for a wider use of solar energy storage, their sales are low, which is why manufacturers do not offer their solutions on the Polish market. This translates into a relatively small number of available devices with technical support and service in Poland.

Due to the fact that it was only in November 2021 that the regulations on energy storage were regulated in Poland, it can be said that we are crawling on this topic, compared to Germany. At the moment, our country lacks incentives to use energy storage in photovoltaic systems.

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New regulations supporting the development of energy storage in Poland

In Poland, only in 2021 the Meter Act created a legal framework for the development of modern technologies enabling the integration of distributed energy and lifted the existing barriers to the operation of storage energy, such as double billing of grid charges.

Exactly on November 5, 2021, the Regulation of the Minister of Climate and Environment was published in the Journal of Laws of the Republic of Poland, containing the implementing provisions to the Act. Currently, warehouses are not subject to registration and are treated as production units. The Meter Act introduced the obligation of electronic registration of energy storage facilities of the area 50 kW. This will allow to monitor the development of storage technology in Poland. The regulation on the register of electricity storage facilities will specify the model of the register of electricity storage facilities, the pattern of information provided by the holder of such a storage facility in order to make an entry in the register, and the format of data entered in the register of energy storage facilities.

Is it worth investing in energy storage?

In the case of prosumers, i.e. energy consumers who generate electricity in their own PV micro-installations for their own consumption, the purchase of a storage is not economically justified, because in accordance with the RES Act they use the discount system. This means that for each kWh fed into the grid, they receive 0.8 kWh if they generate energy in an installation with a capacity of up to 10 kW, or 0.7 kWh if the electricity comes from an installation with a capacity of 10 to 50 kW. It is important that the definition of a prosumer, apart from natural persons, also includes local governments, associations, religious associations, hospitals, schools, parishes and companies, regardless of size, and thus practically exhausts the catalog of potential investors in energy storage. The settlement of the energy introduced and taken from the network takes place during the year. In practice, this means that for prosumers, the grid is de facto an energy store.

Enterprises generating electricity in installations with an installed capacity of more than 50 kWp may potentially be interested in the purchase of energy storage facilities. They do not meet the definition of a prosumer, so they do not benefit from the discount system. In addition, in the case of this group, the argument for increasing the consumption of energy generated in own installations are the rising prices of electricity. More and more often they decide to produce it on their own. If they are not able to use all the energy produced directly and feed it into the grid, they get a price from the wholesale market for it, which is much lower than the one they pay by drawing electricity from the socket. This fact opens the possibility of using energy storage by this group of investors.

However, it is necessary to carry out an investment profitability calculation for a specific enterprise each time. The argument which, in Polish conditions, induces energy consumers to consider the purchase of a storage facility is the reliability of electricity supply. The indicators used to assess the reliability of the distribution network are SAIDI (System Average Interruption Duration Index) and SAIFI (System Average Interruption Frequency Index). The first one describes how long an average end user was without electricity during the year. The second in turn indicates how many times during the year it was affected by a power outage.

Unplanned power outages in 2018 in Poland in the networks of individual operators ranged from 56 (innogy Stoen Operator) to 153 minutes (Enea Operator) per end customer. In addition, there were planned power outages ranging, depending on the operator, from almost 12 (innogy Stoen Operator) to even 87 minutes (PGE Dystrybucja). On average, each customer, depending on which operator's network they are connected to, experienced a "power outage" once (innogy Stoen Operator customers) or even four times (PGE Dystrybucja customers) during the year.

Energy storage and the development of electromobility

The increase in the number of electric cars and the need to build infrastructure for charging them justifies the installation of energy storage. If there is not enough connection capacity in a given location or the investor seeks to reduce the costs associated with increasing the connection capacity for the needs of electric car charging stations, an energy storage is an appropriate solution, especially if it complements the RES generation installation.

Energy storage for PV and wind farms

Energy storage is currently used not only in photovoltaic micro-installations located on the roof of a building or on the property, e.g. on trackers, but also in photovoltaic or wind farms. Manufacturers offer energy storage in the form of containers, delivered as a ready-to-install solution. In the case of those with a capacity of several hundred kWh and larger, the issue of the type of batteries is not as clear as in the case of warehouses intended for micro-installations.

In addition to lithium-ion batteries, other types are also used in this segment, sometimes in combination, depending on the requirements of a specific project. The first and so far the largest storage facility of this type in Poland is a lithium-ion storage facility with a capacity of 0.75 MW and a capacity of 1.5 MWh, owned by Energa Operator, located near Puck.

In the near future, a hybrid storage facility with a capacity of 6 MW and a capacity of 27 MWh will be commissioned at the Bystra wind farm near Pruszcz Gdański. In its case, two types of batteries were used: lithium-ion and lead-acid. The project is being implemented by Energa Wytwarzanie in cooperation with PSE and Hitachi.

Investments in megawatt-scale energy storage by private investors in Poland are still a thing of the future, although the first installations of this type have a chance to be launched this year - for the purposes of cooperation with wind turbines, a private entrepreneur from Lower Silesia will install 4 storage facilities lithium-ion batteries, each with a capacity of 1.9 MW and a capacity of 3.8 MWh.

Barbara Adamska, expert in the field of distributed energy and energy storage, expert of the Parliamentary Energy and Climate Team, director of the Energy Storage Section at the Polish Photovoltaic Society