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Increasing building`s self-sufficiency rates through PV plus storage hybrids

Increasing building`s self-sufficiency rates through PV plus storage hybrids EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Increasing building`s self-sufficiency rates through PV plus storage hybrids P Kisyov Dept. of Industrial Thermal Engineering, University of Food Technologies, Plovdiv, Bulgaria E-mail: [email protected] Abstract. Decarbonizing the building stock is of utmost importance for achieving sustainability as buildings are holding an important role for the clean energy transition. In this paper, the impact on the electrical consumption and building related CO2 emissions are analysed through real measurements by taking the effect from the implementation PV plus battery energy storage hybrids within 5 residential buildings in Plovdiv area. Increased self-sufficiency rates are quantified for a period of 3 years under pure self-consumption mode, where no power sells are taking place. Indicators such as monthly and yearly self-sufficiency rates with and without storage are compared. Building`s related CO2 avoidance are also compared in two scenarios- with and without battery energy storage system. 1. Introduction By 2050, several hundred million tons of CO per year should be avoided from the atmosphere, due to the rising greenhouse gas (GHG) emissions, as CO2 emissions are is destabilizing the climate [1]. Reducing CO emissions is the main goal of European Union (EU) policy. Decarbonisation of the building sector, st one of the most CO -intensive ones, is a key step towards a low-carbon Europe [2]. According to the 21 Conference of the Parties on Climate Change (COP21) the building sector accounts for 40% of the energy consumption and 30% of the generated GHG emissions [3]. World`s energy consumption could increase up to 50% compared to 1990 by 2035 [4]. Therefore, tackling this sector is of extremely important [5]. Responding to the Paris Agreement the EU has set an ambitious target by 2030 to reduce GHG emissions by at least 40 % below 1990-levels (European Commission, 2014b). To move forward, EU has elaborated a wide set of policies to transform its economy to climate-neutrality by 2050. A 55 % CO2 reduction target was set with the implementation of the European Green Deal [6, 7]. This can be achieved by reducing the fossil fuel consumption and by switching to renewable energy systems [8]. According to the International Energy Agency (IEA) the clean energy technologies are critical for achieving net zero consumption [9], where the decarbonisation of buildings is possible by supplying them with renewable energy [10]. The Energy Performance of Buildings Directive (EPBD) aims to transform Europe’s building to highly energy efficient and decarbonised by transforming them into nearly zero-energy buildings (NZEB). The concept requires that building`s thermal and electrical energy needs are covered by RES installed locally. One of the most promising technologies to decarbonize buildings and reduce onsite CO emissions is the Photovoltaics (PVs) technology. Recently, PVs have seen a significant growth as a result of the increased electricity costs and the price decrease of PV modules. [12]. As more rooftop PVs are installed in building, this could create stress on the distribution networks [13]. High PVs penetration levels Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 may result in electrical grids stress, such as over voltages, overloading of network equipment, and fault protection issues [14]. These technical issues can be resolved by coupling PVs and battery energy storage systems (BESSs), where the BESS are used to store the energy that can`t be directly consumed [15]. The mismatch between generation and consumption may also lead to voltage rise and grid congestion issues [16]. Technologies, such as PVs and energy storage hybrids are a promising solution to tackle these problems, as they are enabling significant increase of the household’s energy self-consumption and self- sufficiency by storing the surplus energy for use during hours with no PV generation [17, 18]. In order to evaluate the performance of such hybrids the self-sufficiency ratio is used, which is one of the most common indicators in the literature [19]. The impact of a battery energy storage system (BESS) on the SSR is that the index is considerably increased when BESSs is considered [20]. Moreover, by the additional integration of BESSs, prosumers also achieve CO onside reduction, decarbonizing building`s related CO emissions. A number of scientists have worked on improving building`s energy self-sufficiency and energy autonomy. Laitinen A et al. focuses on defining cost-optimal solutions to transform a pilot district in Finland into a self-sufficient through the integration of various RES - wind power systems, PVs, battery and heat storage and heat pumps. [21]. Nishimura A et al. assessed the SSR as a result of the implementation of a hybrid system consisted of building integrated photovoltaic (PV) and fuel cell (FC) systems in Japan. He evaluates a case where the pilot buildings are mainly supplied by PVs, while the gap between the energy demand and supply is solved by the FC, powered by the H produced by water electrolysis with the surplus power of the PVs [22]. Walker S, et al. demonstrated the self-sufficiency improvement of a renovated residential neighbourhood using heatpumps and PV systems [23]. Mahdi Z S discovered that the self-sufficiency of the exhibition buildings within the several dimensions achieves a sustainable building that meet its functional need in an integrated manner [24]. El-Bayeh C Z and Alzaareer K combines several solutions to increase the buildings energy independence – (1) integration of renewable energy technologies; (2) coordination of the energy demand in buildings [25]. Wang S et al. investigated the zero energy buildings (ZEB) cases in South Korea in order to predict ana analyse the SSR through a standard model [26]. Papers of Bulgarian researchers working on energy efficiency increasing have been found [27-33], but no such papers in the field of energy self-sufficiency and energy autonomy of buildings have been identified. Thus, the scope of this paper is to quantify the increased self-sufficiency rates and the CO emissions reductions by taking the effect on the electrical consumption from the PV + storage deployment within prosumer in the residential sector. Taking above into consideration, this paper provides a detailed picture from the energy performance of 5 pilots located within Plovdiv area, Bulgaria under operating conditions, where data is obtained from real measurements for a period of 3 years - 2019, 2020 and 2. Pilots features 2.1. Pilot specifications The pilot installations were implemented the course of the PV-ESTIA [16] project (2018-2020). The project aimed to evaluate under real-field conditions the performance hybrid PV+Storage systems and to present new policies for the Balkan-Med region countries, in order to facilitate NZEB developments and an easier integration of PV+Storage systems in the building stock. Towards this objective, the project aimed to conceptualize PVs as systems that are efficiently interacting with the grids. To do so, number of different scale and type of pilot installations were implemented in 4 Balkan-Med countries – Bulgaria, Cyprus, Greece and N. Macedonia. In the course of the action within Plovdiv area 5 residential installations were completed and started operation by December 2018. Pilots were selected through an open procedure among interested stakeholders. Each pilot installation was consisted of PV system, LiFePO4 BESSs, 1-ph or 3-ph hybrid inverter, electrical energy metering equipment and data acquisition features. All pilots were completed through a DC-coupled system, since a single hybrid inverter integrates both PVs and the electrical battery system. 2 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 The entire implementation phase was coordinated by the local partner (Energy Agency of Plovdiv), whereas the electrical system installation and the technical support was provided by the selected contractor, i.e., residential PV installer, as per an official tender decision. More specifically, four 5 kW and one 6 kW hybrid battery inverters are responsible for charging and discharging battery systems within 5 prosumers. System have been coupled with a state-of-the-art battery asset, such as Lithium-Iron Phosphate (LiFePO ) battery. Each battery holds a nominal energy capacity of 9.8 kWh. Thus, a total of 13.5 kWp PV power capacity + 48 kWh storage capacity was deployed within the selected households, as follows.  2.70 kWp PVs+ 9.6kWh LiFePO4 BESS + 5kW 1-ph hybrid inverter within 4 prosumers.  2.70 kWp PVs+ 9.6 kWh LiFePO4 BESS + 6kW 3-ph hybrid inverter within 1 prosumer. Figure 1 illustrates the electrical configuration of the PV + BESS hybrid, while figures 2 and 3 are presenting the technical parameters of the installed equipment - hybrid inverter and battery unit Figure 1. Electrical configuration of PV+BESS pilots [34]. The private pilot residential households, described in details in table 1, featured various consumption profiles due to the mean of heating. i.e.:  Pilot 1 uses efficient pellets stove (90%);  Pilot 2 utilises electrical radiator for heating mean;  Pilot 3 utilises a wood boiler for heating;  Pilot 4 utilises 3-ph water to water (W2W) heatpump;  Pilot 5 utilises air to air (A2A) heatpump, while partially inhabits his home. Table 1. Technical specifications of pilots. BESS BESS PV Inverter BESS nominal usable Phase BESS Location size power power Heating mean capacity capacity (ph) technology (kWp) (kW) (kW) (kWh) (kWh) Hisarya 2.7 5 9.6 8.8 5 1-ph LiFePO4 Pellet stove Stamboliyski 2.7 5 9.6 8.8 5 1-ph LiFePO4 Electricity Markovo 2.7 5 9.6 8.8 5 1-ph LiFePO4 Wood boiler Topolovo 2.7 6 9.6 8.8 6 3-ph LiFePO4 W2W Heatpump Plovdiv 2.7 5 9.6 8.8 5 1-ph LiFePO4 A2A Heatpump 3 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 2.2. Monitoring Scheme To evaluate the performance of each installation a data acquisition system (figure 4) is implemented at each pilot side to serve for the collection of measurements, where objectives for data assessment according to the needs for data analysis were set. To do so, three power analysers were installed at different points of the system. All installations are reporting values from the individual devices, on average of 5 minutes and are send to a local server. Afterwards, the post-processing actions are performed to obtain the data required for the commonly defined dataset template. Data sets include, but not limited to the following electrical parameters: PV generation, Storage charge & discharge power, Grid import & export power, Direct PV consumption, Load consumption, Battery State-of-Charge (SoC), etc. Since data sets has been collected and stored from all installations, data analysis is conducted based on the measurements collected by the pilot installations. Figure 2. Topology of the data acquisition system [35]. 3. Performance assessment metrics 3.1. Estimation of self-sufficiency and self-consumption rates Since at the time of commissioning none of the installation was grid connected so as to back up excess power, only the self-sufficiency rate (SSR) indicator has been implied to assess each prosumer’s electrical behaviour, while operating the PV+BESS system. The analysis aims to extract SSR both monthly and annually. Monthly values were used to explore how indicators varied among different months of the year highlighting also the impact the mean of heating can have. SSR is the portion of the electrical demand of the installation that is covered locally by the PV and BESS. It equals to the ratio of the consumed PV generation and the total electrical demand for a certain period of time - equation (1). SSR = , (1) where А and F is the grid consumed electricity, kWh; C – direct PV consumption, kWh; D – charged power to the BESS, kWh; E – discharged power from the BESS, kWh. The typical daily power curves of a prosumer with a BESS are illustrated with the aid of figure 5. 4 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Figure 3. Visualization of the different types of consumption at the user with installed PV installation and BESS [39]. 3.2. Estimation of CO emissions reduction Building`s onside emissions reduction as a result of the PV generation and stored power is analysed. To do so, two CO reduction values are estimated based on the impact from the PV direct consumption (Scenario 1) and the PV electricity consumed directly adding the discharged power from the BESS. (Scenario 2). In the first case, the CO emissions reduction is calculated on the basis of the directly consumed power multiplied by the grid factor by equation (2). CO 𝑃 . , (2) where CO - CO emissions reduction for each period by the PV, kg/y; 𝑃 – generated power by the PV, kWh; – grid factor expressing the electricity emissions intensity, kgCO /kWh. The grid factor provides the emissions intensity in kgCO /kWh, where in the case of Bulgaria, the grid factor equals to 0,819 kgCO /kWh [39]. In the second case, the CO emissions reduction are 2 2 calculated by equation (3) on the basis of the reduced consumption adding the effect from the BESS. CO 𝑃 . , (3) where CO - CO emissions reduction for each period by the PV+Storage (kg/y); 𝑃 – generated power by the PV (kWh); – grid factor expressing the electricity emissions intensity (kgCO /kWh); 4. Pilots performance evaluation and results In this section, the paper compares and evaluates the generated impact in 2019 and 2020 from the installation of PVs plus battery electrical storage on the consumer’s performance through real measurements from five pilot case studies in Bulgaria. Pilots were implemented under pure self- consumption policy, where no power is grid injected and no power sells are taking place. Indicators such as monthly and yearly self-sufficiency rates with and without storage are compared. Building`s related CO avoidance are also compared in two scenarios- with and without BESS. 4.1. Performance evaluation In order to quantify the variation of the prosumer’s monthly electrical behaviour as an effect from the implementation of the hybrid systems data analysis is conducted based on the measurements collected by the pilot installations. Table 2 provides the SSR on monthly basis for 2019 per each pilot installation. As a main conclusion, the SSR are differing significantly given the different operational conditions and type and overall efficiency of the heating systems installed at each premises and varies between 48.54 % achieved in Pilot 4 to 74.17 % achieved in Pilot 3. 𝐺𝐹 𝐺𝐹 𝐺𝐹 𝐺𝐹 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 In particular, pilots using other mean of heating than electricity have higher self-sufficiency rates in winter months and in overall compared to Pilot 2, Pilot 4 and Pilot 5. Moreover, in summer months all pilots reach very high shares of self-sufficiency – between 67% and 90%, thus limiting their grid`s interaction, i.e. less power is imported from the grid. Table 2. Monthly figures of self-sufficiency rates of pilots. Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 Jan 40.00% 5.96% 65.88% 7.57% 20.12% Feb 75.18% 14.18% 38.11% 16.99% 23.12% Mar 85.83% 42.84% 78.20% 24.56% 77.62% Apr 83.40% 55.89% 72.20% 32.37% 77.74% May 86.78% 77.39% 82.70% 67.96% 89.08% June 87.67% 84.24% 87.32% 78.36% 85.39% July 84.40% 85.94% 87.00% 74.71% 86.25% Aug 90.00% 86.49% 87.04% 48.54% 88.94% Sep 85.32% 77.96% 88.07% 59,55% 90.57% Oct 82.74% 65.19% 84.73% 19.64% 76.69% Nov 43.90% 10.54% 56.85% 13.54% 13.10% Dec 30.56% 5.16% 61.97% 12.50% 15.73% 72.98% 50.98% 74.17% 48.54% 62.03% Figure 4 demonstrated the self-sufficiency rates achieved by pilots given the impact generated from using the 2.7 PV + 9.8 kWh BESS hybrids on monthly basis in a non-power sells mode. The monthly values were used to explore how the ratio varied among different months of the year. It is notable that self-sufficiency increases considerably when BESSs is connected, enhancing prosumer`s autonomy. Detailed analyses per each pilot installation is more precisely demonstrated within figures 5-a, b, c, d, e, where autonomy levels are significantly high in off-heating months for all pilots, reaching values in the range of 70-80-90% during summer months. Pilot`s increased annual SSR due to the BESS add-on is further demonstrated in figure 6, where the figure clearly demonstrates the effect, a BESS can have on the self-sufficiency of a prosumer. It is notable that without the BESS the SSR reaches between from 21 % for the lowest performing system to 36 % to the high performing one. On the other hand, with the BESS a prosumer can reach a significantly higher share of self-sufficiency – from 39 % for pilot 4 up to 73 % and 74 % for pilot 1 and pilot 3. Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 4. Graphic figure of self-sufficiency rates achieved by pilots. 6 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Pilot 1 PV Pilot 1 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure. 5-a. Self-sufficiency rates per Pilot 1. Pilot 2 PV Pilot 2 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-b. Self-sufficiency rates per Pilot 2. Pilot 3 PV Pilot 3 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-c. Self-sufficiency rates per Pilot 3. Pilot 4 PV Pilot 4 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-d. Self-sufficiency rates with and without BESS per Pilot 4. 7 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Pilot 5 PV Pilot 5 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-e. Self-sufficiency rates with and without BESS per Pilot 5. SSR PV SSR PV+Storage 80,00% 74,17% 72,98% 70,00% 62,03% 60,00% 50,98% 50,00% 40,00% 38,96% 36,09% 31,15% 30,00% 29,49% 23,59% 20,88% 20,00% 10,00% 0,00% Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 Figure 6. Compression of annual self-sufficiency rates achieved by pilots with and without BESS for 2019. The variation of SSR during a 3 years course (2019-2020-2021) for Pilots 1÷3 is demonstrated on figure 7, where there is some loss of data for Pilot 3 for 2021. From the figure it is evident that SSR varies on yearly basis. This variety is driven by combination of the monthly temperatures, households consumption habits, the heating system installed and the climate conditions for each year. SSR 2019 SSR 2020 SSR 2021 80,00% 71,73% 69,74% 64,91% 70,00% 58,83% 57,02% 60,00% 50,00% 40,00% 30,22% 30,00% 23,23% 20,28% 20,00% 10,00% 0,00% Pilot 1 Pilot 2 Pilot 3 Figure 7. Annual SSR for Pilots 1 and 2 for 2019, 2020 and 2021 and SSR for Pilot 2 for 2019 and 2020. 8 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Figures 8 and 9 provide information for the share of consumed energy that each technology holds within the dwelling`s annual electricity consumption – PVs, BESS and the grid consumption. Notably, pilots with different mean of heating than electricity (Pilots 1 and 3), have annual grid interaction of 28 % and 30 %, respectively for 2019 and nearly 41 % and 40 % in 2020, while Pilot 2 (heating with electricity radiators) have significantly high grid interaction 70 % to 80 %, respectively in 2019 and 2020. Direct consumption BESS UTILITY 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 Figure 8. Share of consumed energy per system for 2019 for the 5 pilots. Direct consumption BESS UTILITY 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Pilot 1 (2019) Pilot 1 (2020) Pilot 2 (2019) Pilot 2 (2020) Pilot 3 (2019) Pilot 3 (2020) Figure 9. Share of consumed energy for Pilots 1, 2 and 3 for 2019 and 2020. 4.2. Emission reduction evaluation per pilot and per technology Finally, building`s related CO emissions reduction for 2019 for all 5 pilots were analyzed. Within this context, figure 10 presents building ‘related CO reduction share per technology, while figure 11 presents the CO emissions reduction in kg/year. Both figures are presenting the values per technology (PVs and BESS) and per pilot. 9 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 CO2 reduction PV CO2 reduction BESS 100% 80% 47,13% 50,32% 51,39% 57,24% 56,48% 60% 40% 52,87% 49,68% 48,61% 43,52% 42,76% 20% 0% 12 34 5 Figure 10. Building ‘related CO reduction share per technology and per pilot. Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 CO2 reduction PV CO2 reduction BESS Figure 11. CO emissions reduction in kg/year per pilot and per system. 5. Conclusions In this manuscript, the impact of the PV+BESS hybrid on consumer’s behavior is analyzed, where no power sells are taking place and systems are used in full self-consumption mode. Additionally, the impact from the BESSs operation and how it affects prosumer’s self-sufficiency is analysed. Thus, the statistical analysis of the energy consumption before and after the hybrid implementation of 5 Bulgarian households led to the following conclusions:  The results from analyzed households showed that the self-consumption varies monthly, as it is related to household`s heating mean and heating/cooling demands.  Households with different heating mean achieve significantly different overall SCR – households relying on biomass are achieving the highest shares;  All households are achieving significant share of self-sufficiency during off-heating months, especially notable between May – September;  In many cases power production from PVs is limited, since none of the prosumers is injecting power to the grid. This is especially notable when prosumers achieve full battery and have load that is lower than PV production;  The deployed BESSs are significantly increasing the self-sufficiency of prosumers, enhancing their autonomy, especially in the case where the heating is done with different than electricity mean;  To facilitate the use of BESSs alongside PVs new policy schemes should be adapted promoting the increase of SCR at prosumers owning PVs;  Hybrids between PV+BESS should be integrated into legislation, especially in the NZEBs and positive energy buildings and districts implementation; 10 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023  PV+BESS hybrids are in huge favor of households to achieve autonomy and thus their integration into legislation and funding programs should be facilitated 6. References [1] Masson-Delmotte V et al 2021 IPCC Climate change 2021: The physical science basis. Contribution of working group I to the sixth assessment report of the intergovernmental panel on climate change (Cambridge University Press) [2] European Climate Foundation 2010 A practical guide to a prosperous, low-carbon Europe [3] Baek S and Kim S 2020 Potential effects of vacuum insulating glazing application for reducing greenhouse gas emission (GHGE) from apartment buildings in the Korean capital region. Energies 13 (11) 2828 [4] Ghosh A 2020 Potential of building integrated and attached/applied photovoltaic (BIPV/BAPV) for adaptive less energy-hungry building's skin: A comprehensive Review. J. of Cleaner Production 276 [5] IEA 2019 Perspectives for the clean energy transition: The critical role of buildings. 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Series: Materials Science and Engineering 881 012008 [25] El-Bayeh C Z and Alzaareer K 2020 Steps toward smart energy self-sufficient buildings IEEE Smart Grid [26] Wang S, Tae S and Jang H 2021 Prediction of the energy self-sufficiency sate of major new renewable energy types based on zero-energy building certification cases in South Korea, Sustainability 13, 11552 [27] Valchev MS, Raichkov GR, Georgieva MG 2014 Permanent ventilation of premises and buildings - a factor of healthy comfort, Toplotechnika 1 (6) (Technical University Publishing House - Varna) pp. 7 – 9 (in Bulgarian) [28] Georgieva M, Raynov P, Atanasov D and Tashev I 2019 Analytical and numerical investigation of heat exchange in fin-tube refrigerating heat exchanger IOP Conference Series: Materials Science and Engineering Journal 595 (1) [29] Iliev I K, Terziev A K, Beloev H I, Nikolaev I and Georgiev A G 2021 Comparative analysis of the energy efficiency of different types co-generators at large scales CHPs Energy 221C 119755 [30] Kolev Z D, Kadirova S and Nenov T R 2017 Research of reversible heat pump installation for greenhouse heating INMATEH - Agricultural Engineering No 2 pp 77-84 [31] Komitov N, Shopov N and Rasheva V 2020 Model of a building heating system with renewable energy sources. 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Increasing building`s self-sufficiency rates through PV plus storage hybrids

Kisyov, P
Journal of Physics: Conference Series , Volume 2339 (1): 12 – Sep 1, 2022
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Abstract

EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Increasing building`s self-sufficiency rates through PV plus storage hybrids P Kisyov Dept. of Industrial Thermal Engineering, University of Food Technologies, Plovdiv, Bulgaria E-mail: [email protected] Abstract. Decarbonizing the building stock is of utmost importance for achieving sustainability as buildings are holding an important role for the clean energy transition. In this paper, the impact on the electrical consumption and building related CO2 emissions are analysed through real measurements by taking the effect from the implementation PV plus battery energy storage hybrids within 5 residential buildings in Plovdiv area. Increased self-sufficiency rates are quantified for a period of 3 years under pure self-consumption mode, where no power sells are taking place. Indicators such as monthly and yearly self-sufficiency rates with and without storage are compared. Building`s related CO2 avoidance are also compared in two scenarios- with and without battery energy storage system. 1. Introduction By 2050, several hundred million tons of CO per year should be avoided from the atmosphere, due to the rising greenhouse gas (GHG) emissions, as CO2 emissions are is destabilizing the climate [1]. Reducing CO emissions is the main goal of European Union (EU) policy. Decarbonisation of the building sector, st one of the most CO -intensive ones, is a key step towards a low-carbon Europe [2]. According to the 21 Conference of the Parties on Climate Change (COP21) the building sector accounts for 40% of the energy consumption and 30% of the generated GHG emissions [3]. World`s energy consumption could increase up to 50% compared to 1990 by 2035 [4]. Therefore, tackling this sector is of extremely important [5]. Responding to the Paris Agreement the EU has set an ambitious target by 2030 to reduce GHG emissions by at least 40 % below 1990-levels (European Commission, 2014b). To move forward, EU has elaborated a wide set of policies to transform its economy to climate-neutrality by 2050. A 55 % CO2 reduction target was set with the implementation of the European Green Deal [6, 7]. This can be achieved by reducing the fossil fuel consumption and by switching to renewable energy systems [8]. According to the International Energy Agency (IEA) the clean energy technologies are critical for achieving net zero consumption [9], where the decarbonisation of buildings is possible by supplying them with renewable energy [10]. The Energy Performance of Buildings Directive (EPBD) aims to transform Europe’s building to highly energy efficient and decarbonised by transforming them into nearly zero-energy buildings (NZEB). The concept requires that building`s thermal and electrical energy needs are covered by RES installed locally. One of the most promising technologies to decarbonize buildings and reduce onsite CO emissions is the Photovoltaics (PVs) technology. Recently, PVs have seen a significant growth as a result of the increased electricity costs and the price decrease of PV modules. [12]. As more rooftop PVs are installed in building, this could create stress on the distribution networks [13]. High PVs penetration levels Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 may result in electrical grids stress, such as over voltages, overloading of network equipment, and fault protection issues [14]. These technical issues can be resolved by coupling PVs and battery energy storage systems (BESSs), where the BESS are used to store the energy that can`t be directly consumed [15]. The mismatch between generation and consumption may also lead to voltage rise and grid congestion issues [16]. Technologies, such as PVs and energy storage hybrids are a promising solution to tackle these problems, as they are enabling significant increase of the household’s energy self-consumption and self- sufficiency by storing the surplus energy for use during hours with no PV generation [17, 18]. In order to evaluate the performance of such hybrids the self-sufficiency ratio is used, which is one of the most common indicators in the literature [19]. The impact of a battery energy storage system (BESS) on the SSR is that the index is considerably increased when BESSs is considered [20]. Moreover, by the additional integration of BESSs, prosumers also achieve CO onside reduction, decarbonizing building`s related CO emissions. A number of scientists have worked on improving building`s energy self-sufficiency and energy autonomy. Laitinen A et al. focuses on defining cost-optimal solutions to transform a pilot district in Finland into a self-sufficient through the integration of various RES - wind power systems, PVs, battery and heat storage and heat pumps. [21]. Nishimura A et al. assessed the SSR as a result of the implementation of a hybrid system consisted of building integrated photovoltaic (PV) and fuel cell (FC) systems in Japan. He evaluates a case where the pilot buildings are mainly supplied by PVs, while the gap between the energy demand and supply is solved by the FC, powered by the H produced by water electrolysis with the surplus power of the PVs [22]. Walker S, et al. demonstrated the self-sufficiency improvement of a renovated residential neighbourhood using heatpumps and PV systems [23]. Mahdi Z S discovered that the self-sufficiency of the exhibition buildings within the several dimensions achieves a sustainable building that meet its functional need in an integrated manner [24]. El-Bayeh C Z and Alzaareer K combines several solutions to increase the buildings energy independence – (1) integration of renewable energy technologies; (2) coordination of the energy demand in buildings [25]. Wang S et al. investigated the zero energy buildings (ZEB) cases in South Korea in order to predict ana analyse the SSR through a standard model [26]. Papers of Bulgarian researchers working on energy efficiency increasing have been found [27-33], but no such papers in the field of energy self-sufficiency and energy autonomy of buildings have been identified. Thus, the scope of this paper is to quantify the increased self-sufficiency rates and the CO emissions reductions by taking the effect on the electrical consumption from the PV + storage deployment within prosumer in the residential sector. Taking above into consideration, this paper provides a detailed picture from the energy performance of 5 pilots located within Plovdiv area, Bulgaria under operating conditions, where data is obtained from real measurements for a period of 3 years - 2019, 2020 and 2. Pilots features 2.1. Pilot specifications The pilot installations were implemented the course of the PV-ESTIA [16] project (2018-2020). The project aimed to evaluate under real-field conditions the performance hybrid PV+Storage systems and to present new policies for the Balkan-Med region countries, in order to facilitate NZEB developments and an easier integration of PV+Storage systems in the building stock. Towards this objective, the project aimed to conceptualize PVs as systems that are efficiently interacting with the grids. To do so, number of different scale and type of pilot installations were implemented in 4 Balkan-Med countries – Bulgaria, Cyprus, Greece and N. Macedonia. In the course of the action within Plovdiv area 5 residential installations were completed and started operation by December 2018. Pilots were selected through an open procedure among interested stakeholders. Each pilot installation was consisted of PV system, LiFePO4 BESSs, 1-ph or 3-ph hybrid inverter, electrical energy metering equipment and data acquisition features. All pilots were completed through a DC-coupled system, since a single hybrid inverter integrates both PVs and the electrical battery system. 2 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 The entire implementation phase was coordinated by the local partner (Energy Agency of Plovdiv), whereas the electrical system installation and the technical support was provided by the selected contractor, i.e., residential PV installer, as per an official tender decision. More specifically, four 5 kW and one 6 kW hybrid battery inverters are responsible for charging and discharging battery systems within 5 prosumers. System have been coupled with a state-of-the-art battery asset, such as Lithium-Iron Phosphate (LiFePO ) battery. Each battery holds a nominal energy capacity of 9.8 kWh. Thus, a total of 13.5 kWp PV power capacity + 48 kWh storage capacity was deployed within the selected households, as follows.  2.70 kWp PVs+ 9.6kWh LiFePO4 BESS + 5kW 1-ph hybrid inverter within 4 prosumers.  2.70 kWp PVs+ 9.6 kWh LiFePO4 BESS + 6kW 3-ph hybrid inverter within 1 prosumer. Figure 1 illustrates the electrical configuration of the PV + BESS hybrid, while figures 2 and 3 are presenting the technical parameters of the installed equipment - hybrid inverter and battery unit Figure 1. Electrical configuration of PV+BESS pilots [34]. The private pilot residential households, described in details in table 1, featured various consumption profiles due to the mean of heating. i.e.:  Pilot 1 uses efficient pellets stove (90%);  Pilot 2 utilises electrical radiator for heating mean;  Pilot 3 utilises a wood boiler for heating;  Pilot 4 utilises 3-ph water to water (W2W) heatpump;  Pilot 5 utilises air to air (A2A) heatpump, while partially inhabits his home. Table 1. Technical specifications of pilots. BESS BESS PV Inverter BESS nominal usable Phase BESS Location size power power Heating mean capacity capacity (ph) technology (kWp) (kW) (kW) (kWh) (kWh) Hisarya 2.7 5 9.6 8.8 5 1-ph LiFePO4 Pellet stove Stamboliyski 2.7 5 9.6 8.8 5 1-ph LiFePO4 Electricity Markovo 2.7 5 9.6 8.8 5 1-ph LiFePO4 Wood boiler Topolovo 2.7 6 9.6 8.8 6 3-ph LiFePO4 W2W Heatpump Plovdiv 2.7 5 9.6 8.8 5 1-ph LiFePO4 A2A Heatpump 3 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 2.2. Monitoring Scheme To evaluate the performance of each installation a data acquisition system (figure 4) is implemented at each pilot side to serve for the collection of measurements, where objectives for data assessment according to the needs for data analysis were set. To do so, three power analysers were installed at different points of the system. All installations are reporting values from the individual devices, on average of 5 minutes and are send to a local server. Afterwards, the post-processing actions are performed to obtain the data required for the commonly defined dataset template. Data sets include, but not limited to the following electrical parameters: PV generation, Storage charge & discharge power, Grid import & export power, Direct PV consumption, Load consumption, Battery State-of-Charge (SoC), etc. Since data sets has been collected and stored from all installations, data analysis is conducted based on the measurements collected by the pilot installations. Figure 2. Topology of the data acquisition system [35]. 3. Performance assessment metrics 3.1. Estimation of self-sufficiency and self-consumption rates Since at the time of commissioning none of the installation was grid connected so as to back up excess power, only the self-sufficiency rate (SSR) indicator has been implied to assess each prosumer’s electrical behaviour, while operating the PV+BESS system. The analysis aims to extract SSR both monthly and annually. Monthly values were used to explore how indicators varied among different months of the year highlighting also the impact the mean of heating can have. SSR is the portion of the electrical demand of the installation that is covered locally by the PV and BESS. It equals to the ratio of the consumed PV generation and the total electrical demand for a certain period of time - equation (1). SSR = , (1) where А and F is the grid consumed electricity, kWh; C – direct PV consumption, kWh; D – charged power to the BESS, kWh; E – discharged power from the BESS, kWh. The typical daily power curves of a prosumer with a BESS are illustrated with the aid of figure 5. 4 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Figure 3. Visualization of the different types of consumption at the user with installed PV installation and BESS [39]. 3.2. Estimation of CO emissions reduction Building`s onside emissions reduction as a result of the PV generation and stored power is analysed. To do so, two CO reduction values are estimated based on the impact from the PV direct consumption (Scenario 1) and the PV electricity consumed directly adding the discharged power from the BESS. (Scenario 2). In the first case, the CO emissions reduction is calculated on the basis of the directly consumed power multiplied by the grid factor by equation (2). CO 𝑃 . , (2) where CO - CO emissions reduction for each period by the PV, kg/y; 𝑃 – generated power by the PV, kWh; – grid factor expressing the electricity emissions intensity, kgCO /kWh. The grid factor provides the emissions intensity in kgCO /kWh, where in the case of Bulgaria, the grid factor equals to 0,819 kgCO /kWh [39]. In the second case, the CO emissions reduction are 2 2 calculated by equation (3) on the basis of the reduced consumption adding the effect from the BESS. CO 𝑃 . , (3) where CO - CO emissions reduction for each period by the PV+Storage (kg/y); 𝑃 – generated power by the PV (kWh); – grid factor expressing the electricity emissions intensity (kgCO /kWh); 4. Pilots performance evaluation and results In this section, the paper compares and evaluates the generated impact in 2019 and 2020 from the installation of PVs plus battery electrical storage on the consumer’s performance through real measurements from five pilot case studies in Bulgaria. Pilots were implemented under pure self- consumption policy, where no power is grid injected and no power sells are taking place. Indicators such as monthly and yearly self-sufficiency rates with and without storage are compared. Building`s related CO avoidance are also compared in two scenarios- with and without BESS. 4.1. Performance evaluation In order to quantify the variation of the prosumer’s monthly electrical behaviour as an effect from the implementation of the hybrid systems data analysis is conducted based on the measurements collected by the pilot installations. Table 2 provides the SSR on monthly basis for 2019 per each pilot installation. As a main conclusion, the SSR are differing significantly given the different operational conditions and type and overall efficiency of the heating systems installed at each premises and varies between 48.54 % achieved in Pilot 4 to 74.17 % achieved in Pilot 3. 𝐺𝐹 𝐺𝐹 𝐺𝐹 𝐺𝐹 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 In particular, pilots using other mean of heating than electricity have higher self-sufficiency rates in winter months and in overall compared to Pilot 2, Pilot 4 and Pilot 5. Moreover, in summer months all pilots reach very high shares of self-sufficiency – between 67% and 90%, thus limiting their grid`s interaction, i.e. less power is imported from the grid. Table 2. Monthly figures of self-sufficiency rates of pilots. Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 Jan 40.00% 5.96% 65.88% 7.57% 20.12% Feb 75.18% 14.18% 38.11% 16.99% 23.12% Mar 85.83% 42.84% 78.20% 24.56% 77.62% Apr 83.40% 55.89% 72.20% 32.37% 77.74% May 86.78% 77.39% 82.70% 67.96% 89.08% June 87.67% 84.24% 87.32% 78.36% 85.39% July 84.40% 85.94% 87.00% 74.71% 86.25% Aug 90.00% 86.49% 87.04% 48.54% 88.94% Sep 85.32% 77.96% 88.07% 59,55% 90.57% Oct 82.74% 65.19% 84.73% 19.64% 76.69% Nov 43.90% 10.54% 56.85% 13.54% 13.10% Dec 30.56% 5.16% 61.97% 12.50% 15.73% 72.98% 50.98% 74.17% 48.54% 62.03% Figure 4 demonstrated the self-sufficiency rates achieved by pilots given the impact generated from using the 2.7 PV + 9.8 kWh BESS hybrids on monthly basis in a non-power sells mode. The monthly values were used to explore how the ratio varied among different months of the year. It is notable that self-sufficiency increases considerably when BESSs is connected, enhancing prosumer`s autonomy. Detailed analyses per each pilot installation is more precisely demonstrated within figures 5-a, b, c, d, e, where autonomy levels are significantly high in off-heating months for all pilots, reaching values in the range of 70-80-90% during summer months. Pilot`s increased annual SSR due to the BESS add-on is further demonstrated in figure 6, where the figure clearly demonstrates the effect, a BESS can have on the self-sufficiency of a prosumer. It is notable that without the BESS the SSR reaches between from 21 % for the lowest performing system to 36 % to the high performing one. On the other hand, with the BESS a prosumer can reach a significantly higher share of self-sufficiency – from 39 % for pilot 4 up to 73 % and 74 % for pilot 1 and pilot 3. Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 4. Graphic figure of self-sufficiency rates achieved by pilots. 6 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Pilot 1 PV Pilot 1 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure. 5-a. Self-sufficiency rates per Pilot 1. Pilot 2 PV Pilot 2 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-b. Self-sufficiency rates per Pilot 2. Pilot 3 PV Pilot 3 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-c. Self-sufficiency rates per Pilot 3. Pilot 4 PV Pilot 4 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-d. Self-sufficiency rates with and without BESS per Pilot 4. 7 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Pilot 5 PV Pilot 5 PV+Storage 100,00% 80,00% 60,00% 40,00% 20,00% 0,00% Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 5-e. Self-sufficiency rates with and without BESS per Pilot 5. SSR PV SSR PV+Storage 80,00% 74,17% 72,98% 70,00% 62,03% 60,00% 50,98% 50,00% 40,00% 38,96% 36,09% 31,15% 30,00% 29,49% 23,59% 20,88% 20,00% 10,00% 0,00% Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 Figure 6. Compression of annual self-sufficiency rates achieved by pilots with and without BESS for 2019. The variation of SSR during a 3 years course (2019-2020-2021) for Pilots 1÷3 is demonstrated on figure 7, where there is some loss of data for Pilot 3 for 2021. From the figure it is evident that SSR varies on yearly basis. This variety is driven by combination of the monthly temperatures, households consumption habits, the heating system installed and the climate conditions for each year. SSR 2019 SSR 2020 SSR 2021 80,00% 71,73% 69,74% 64,91% 70,00% 58,83% 57,02% 60,00% 50,00% 40,00% 30,22% 30,00% 23,23% 20,28% 20,00% 10,00% 0,00% Pilot 1 Pilot 2 Pilot 3 Figure 7. Annual SSR for Pilots 1 and 2 for 2019, 2020 and 2021 and SSR for Pilot 2 for 2019 and 2020. 8 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 Figures 8 and 9 provide information for the share of consumed energy that each technology holds within the dwelling`s annual electricity consumption – PVs, BESS and the grid consumption. Notably, pilots with different mean of heating than electricity (Pilots 1 and 3), have annual grid interaction of 28 % and 30 %, respectively for 2019 and nearly 41 % and 40 % in 2020, while Pilot 2 (heating with electricity radiators) have significantly high grid interaction 70 % to 80 %, respectively in 2019 and 2020. Direct consumption BESS UTILITY 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 Figure 8. Share of consumed energy per system for 2019 for the 5 pilots. Direct consumption BESS UTILITY 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Pilot 1 (2019) Pilot 1 (2020) Pilot 2 (2019) Pilot 2 (2020) Pilot 3 (2019) Pilot 3 (2020) Figure 9. Share of consumed energy for Pilots 1, 2 and 3 for 2019 and 2020. 4.2. Emission reduction evaluation per pilot and per technology Finally, building`s related CO emissions reduction for 2019 for all 5 pilots were analyzed. Within this context, figure 10 presents building ‘related CO reduction share per technology, while figure 11 presents the CO emissions reduction in kg/year. Both figures are presenting the values per technology (PVs and BESS) and per pilot. 9 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023 CO2 reduction PV CO2 reduction BESS 100% 80% 47,13% 50,32% 51,39% 57,24% 56,48% 60% 40% 52,87% 49,68% 48,61% 43,52% 42,76% 20% 0% 12 34 5 Figure 10. Building ‘related CO reduction share per technology and per pilot. Pilot 1 Pilot 2 Pilot 3 Pilot 4 Pilot 5 CO2 reduction PV CO2 reduction BESS Figure 11. CO emissions reduction in kg/year per pilot and per system. 5. Conclusions In this manuscript, the impact of the PV+BESS hybrid on consumer’s behavior is analyzed, where no power sells are taking place and systems are used in full self-consumption mode. Additionally, the impact from the BESSs operation and how it affects prosumer’s self-sufficiency is analysed. Thus, the statistical analysis of the energy consumption before and after the hybrid implementation of 5 Bulgarian households led to the following conclusions:  The results from analyzed households showed that the self-consumption varies monthly, as it is related to household`s heating mean and heating/cooling demands.  Households with different heating mean achieve significantly different overall SCR – households relying on biomass are achieving the highest shares;  All households are achieving significant share of self-sufficiency during off-heating months, especially notable between May – September;  In many cases power production from PVs is limited, since none of the prosumers is injecting power to the grid. This is especially notable when prosumers achieve full battery and have load that is lower than PV production;  The deployed BESSs are significantly increasing the self-sufficiency of prosumers, enhancing their autonomy, especially in the case where the heating is done with different than electricity mean;  To facilitate the use of BESSs alongside PVs new policy schemes should be adapted promoting the increase of SCR at prosumers owning PVs;  Hybrids between PV+BESS should be integrated into legislation, especially in the NZEBs and positive energy buildings and districts implementation; 10 EEPES-2022 IOP Publishing Journal of Physics: Conference Series 2339 (2022) 012023 doi:10.1088/1742-6596/2339/1/012023  PV+BESS hybrids are in huge favor of households to achieve autonomy and thus their integration into legislation and funding programs should be facilitated 6. References [1] Masson-Delmotte V et al 2021 IPCC Climate change 2021: The physical science basis. 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