1. Introduction
The current geopolitical situation around the world, and especially in Europe, is conducive to the continuous development of renewable energy technologies (RES) and their application in various areas of life and the economy, including in Poland. Following the great boom in photovoltaic micro-installations aimed at prosumers, many companies have been investing in their own sources of electricity generation in order to become independent of electricity supplies and prices, and to participate in the energy transition of their country and the European Union (EU). In the situation that has arisen, individual EU member states have been creating their own programs aimed at achieving common RES targets set by the EU. At the end of 2022, the capacity of all generation sources in Poland had exceeded 60 GW (a year-on-year increase of 1 GW) and the share of RES was as high as 36% (22 GW), of which more than 55% is accounted for by photovoltaics and 36% by wind power. Thus, Poland had already met the minimum objectives for the amount of RES in the country’s power system for the year 2040 in 2022. However, large installed capacities in unstable RES cause problems in power grids and contribute to frequent shutdowns of PV inverters. Therefore, it is necessary to upgrade the power distribution grid, or to take other measures to support the local consumption and storage of energy generated from PV micro-installations. At the end of April 2023, the total capacity of PV plants connected to the electricity grid in Poland exceeded 13.5 GW, of which more than 70% (9.48 GW) were low-power prosumer installations. The average capacity of a new PV installation constructed in April 2023 was around 26 kW, while at the same time in 2022 it was approximately 14 kW. The result is a demonstrable increase in the per-unit installed capacity in micro-installations. This is due to the already quite strong saturation of the domestic installation market and the increased interest and investments in PV installations by small and medium-sized enterprises, which can install PV installations up to 50 kW under the Prosumer Act [
1,
2,
3].
An important factor in the design and analysis of PV systems is the costs of the installation over its lifetime. For this purpose, computer software is used to help analyze the energy potential of a designed PV system placed at a selected latitude. The use of programs such as PVSOL or PVsyst is common in many publications [
4,
5]. Calculating and selecting the appropriate equipment for a PV system is only the first part of the design process. The second, and equally important, parts are the economic considerations, which determine the profitability of the investment. This approach can be found in a great number of publications. One of these is [
6], whose authors estimated the discount rates and presented a profitability analysis for a photovoltaic installation located in Spain using the financial approach. On the other hand, in Malaysia and Indonesia, paper [
7] presents an analysis of the cost of energy generation and determines the payback time for different assumed values of the discount rate, which remain constant throughout the life of the installation. Another example is a technical–economic analysis of a PV system for a residential building located in the UK [
8], which provides indicators such as net present value (NPV) and discounted payback period (DPP) for feed-in tariffs (FITs). It was determined that the system was able to cover the building’s electricity needs between April and October, with excess electricity being exported to the grid during this period. The payback period for the investment was determined to be around nine years. In the article [
9], for a household located in Croatia, the capacity of the photovoltaic system was determined taking into account the payback period. A payback time set at 10 years, and discount rates of 0% and 4.5%, were adopted in the optimization. The authors in the article [
10] determined the cost-effectiveness of the investment using the NPV ratio for Germany, the state of Colorado and Spain. It was determined that the NPV over the entire lifetime may be overestimated without considering the possible replacement of system components (mainly inverters and energy storages).
Other types of investments, not limited to households, are also considered for this type of economic analysis. One example is an analysis of the possible transition from agricultural to manufacturing activities in Ukraine using PV [
11]. A discount rate of cost-effectiveness was determined, ranging between 1.26 and 3.24, together with carbon footprint per hectare of land occupied by a PV system. Furthermore, the payback period of the installation was determined to be between 5 and 10 months. Similar objectives were adopted by the authors of paper [
12], whose area of study focused on the establishment of willow and poplar plantations. For the 5% discount rate and three subsidy scenarios, economic profitability was analyzed on the basis of discounted cash flows, net present value (NPV), internal rate of return (IRR) and profitability ratio (PI).On the other hand, the article [
13] provided a comparative analysis for ground-mounted photovoltaics and agricultural crops for areas in Poland and Ukraine with the most insolation. Among the authors’ findings was the determination that the net present value of photovoltaic projects exceeds that of crop-growing projects. However, they have lower profitability rates than the commonly used agricultural practices.
The introduction of new solutions with bPV (bifacial) panels was presented, for example, in [
14]. Analysis based on the measure of the levelized net cost of electricity generation (LCOE) showed an increase in power output between 5% and 30% for initial costs that were 0–15.6% higher, and a decreased levelized cost of energy (LCOE) by 2–6% in comparison to single-sided technology (mPV). A similar study is presented in [
15], where the authors analyzed a photovoltaic system using flexible panels on flat, cylindrical and hemispherical bases. The determined annual energy production was, respectively, 810 kWh, 960 kWh and 100 kWh, followed by an economic analysis, identifying NPVs of approximately USD 697 and 956, with internal rates of return (IRR) of 34.81%, 39.29% and 40.47%.
The integration of photovoltaics into a smart building is also being studied. The paper [
16] presents a model of the McFarland Science Building at Texas A&M University Commerce in Texas, for which an economic analysis of two popular green roof systems and a BIPV system was carried out. The averaged results of the study show that the levelized cost of electricity (LCOE) of the green roof system is approximately 39.77% higher than that of the BIPV system at a discount rate of 5%. A study of building integration with photovoltaics has also been carried out, focusing on reducing the carbon footprint by replacing elements of the façade during building renovation in South Korea. The calculations of cost-effectiveness and carbon footprint were performed for the periods of 25 and 50 years. Data analysis indicates a 30% reduction in greenhouse gases, and a payback period from 12 years for flats to 41 years for multi-purpose buildings [
17]. An analysis based on deterministic methods was carried out in [
18], investigating a conventional and a BIPV installation in Brazil. It was found that the systems in the eight cities included in the study achieved a positive NPV. On the other hand, the authors of [
19] demonstrate a 25% decrease in electricity consumption when using smart building management systems without the necessity of altering the comfort of life of the users in any way.
Electricity management is a very important element of reducing peak energy consumption. The authors in [
20] present a PV management system combined with energy storage and an electric vehicle forming a microgrid, which is used to describe the advantages in the form of flattening the energy demand characteristics in the residential sector. Another example in which energy management increases self-consumption from approximately 20–30% to approximately 50% is described in [
21].This work focuses on the study of smart microgrid solutions with PV and energy storage connected to the internet with a view to optimizing the costs of electricity procurement. The authors of [
22] achieved a 50% reduction in energy costs. Another example is provided in paper [
23], wherein the authors demonstrate a hybrid PV installation, with management solutions that allow for increased consumption for their own needs from 7% to 18% in a monthly period, and 13% annually.
According to [
24], the use of BIPV technology facilitates, as well as energy savings, many other economic, social, cultural and architectural benefits. BIPV systems can be better integrated into building architecture without standing out; it can be argued that they bring about a positive effect on the building’s aesthetics, especially of historical and sacral buildings, in which case the Monument Conservator Office often does not give permission for installing traditional BAPV systems. Furthermore, BIPV components also have a positive impact on the entire energy performance of the building.
As follows from the literature survey, the current research efforts focus on managing the electricity generated by photovoltaic systems in order to increase energy self-consumption. To this end, the entire system design is often software-assisted. However, from the perspective of the investor, the payback period on the investment is the primary concern. In the articles presented, the authors use fixed discount rates over the period of the planned investment, which do not always provide representative results. Particular attention should be paid to recent years, in which economic instability has affected the profitability of many investments. One suggestion is provided by [
25], in which the authors suggest an adjustment to the discount rate value of investments based on natural resources, which will indirectly account for changes in resource prices.
The increase in the unit power in PV micro-installations, the problem of their frequent switching on and the resulting periods in which they do not produce energy under even the best possible weather conditions cause losses for investors, and call for countermeasures in the form of, for example, the installation of an energy management system and changes to the load profiles to match the current PV energy output. Therefore, the authors of this paper presented a concept of a BIPV installation in a primary school in Poland. An analysis of its operation and energy yields was carried out using a system that protects the energy outflow to the grid using an on-grid inverter. It was recognized that the period of energy production would not exactly correspond with the energy consumption in the facility (as the school is closed in July and August, when there is a large PV energy output). Therefore, a portion of the energy produced in this period will be lost, due to the protection system preventing its outflow into the grid. With the goal of reducing these losses, the authors of the study attempted to improve the current solution. Therefore, an economic analysis of the existing installation was carried out in several variants, with alternative solutions proposed to improve the economic indicators of the installation. A PV system based on traditional PV panels was analyzed, leading to a significant improvement in profitability, including automation and smart control of the distribution of the energy output, with the objective of not limiting the productivity of the installation. The impact of the discount rate on the values of the achieved economic indicators was also analyzed; in the current geopolitical and economic situation prevailing in the world, these remain significant factors influencing investment profitability and feasibility. The majority of available analyses still utilize constant discount rates throughout the entire lifetime of the installation, whereas the authors of this paper demonstrate that even minor changes to the rates, amounting to only a few percent accrued over a period of 25 years, will affect the feasibility of investment in a PV installation.
In summary, the authors of this paper, based on the analysis of data from an actual photovoltaic installation integrated with a school building, propose the following:
- -
The PV installation is to be equipped with a building automation system, enabling the use of more energy generated by the PV system (reducing the non-productive time of the existing installation, which results from the existing off-grid implementation together with a protection system preventing energy outflow into the power grid), which serves to reduce the payback period of the investment, as well as to limit the occurrences and frequency of system shutdowns;
- -
The SCADA system is to be employed to monitor the operation of the PV installation together with the electrical devices in the school facility, with the option to control their operation and also data archiving.
The authors performed comparative economic analyses of different PV solutions: an existing off-grid school BIPV system, an on-grid BIPV system, and a free-standing system based on traditional PV panels. In addition, they demonstrated the impact of adopting a fixed and variable discount rate for the NPV of the investment.
The work has been structured as follows:
Section 1 contains the literature background and an indication of the authors’ contribution to the researched topic.
Section 2 describes the weather conditions and energy yields of the BIPV installation installed in a school in central Poland. The improvements introduced to the PV installations through the integration of SCADA systems and building automation are presented in
Section 3, while the economic analysis of the analyzed PV systems is provided in
Section 4.
Section 5 presents a comparative discussion of the results of the implementation of the various systems that were analyzed, and
Section 6 provides synthetic conclusions drawn from the work.
3. SCADA and Intelligent Building Systems as Methods to Increase the Profitability of Investments in Photovoltaics
As shown in the earlier part of this paper, the photovoltaic installation under consideration could generate a significantly higher amount of electricity when compared to an on-grid inverter system with an ERS controller to manage the building’s own needs. From an economic point of view, the difference in the amount of energy generated and managed represents a loss that will lengthen the payback period of the investment. Thus, mechanisms need to be introduced to increase the level of self-consumption, i.e., the correlation of generation characteristics to load characteristics. This can be done in two ways. The first is to install some type of energy storages, allowing the storage of excess energy at times of overproduction, to be used at times of increased demand. Unfortunately, this solution entails large investments, further increasing in proportion to the increased level of self-consumption. The second approach is to fine-tune the load characteristics to the momentary values of the generated energy, by switching on additional receivers whose operation is not necessary but possible at a given moment. This can be achieved in a number of ways, each of which will be based on real-time operation with data regarding generation and demand and the ability to control individual groups of receivers. This method, albeit in a very simplified way, was used in the previously mentioned ERS controller. Two main types of approach are considered as far as these types of solutions are concerned: SCADA systems and modern BMS systems.
3.1. SCADA System
The implementation of the SCADA (Supervisory Control and Data Acquisition) system typically entails a computer system managing the devices connected to the grid, which collects and processes the relevant data, allowing for their mapping for visualization purposes, at the same time recording them for archiving purposes and exerting control capabilities. This allows a three-layer control of device operation, with current changes being tracked in real time and the initiation of appropriate responses. If the connection with the SCADA system is lost, this role is taken over by the PLC. The functions of alarm signaling, reporting or data archiving serve to significantly improve process efficiency and reduce the risk of failure. The SCADA systems have been used in many applications, but are the most prevalent in industry as well as in the energy, water and wastewater sectors. The broad range of functionality and flexibility of this software makes it ideal for supervising the process of energy generation in photovoltaic systems. The rapid detection of failures of photovoltaic system components, reporting of actual conversion efficiency of DC energy into AC energy, monitoring the actual efficiency of photovoltaic modules and provision of information about the necessary inspections and expiring warranties are among the basic functionalities the SCADA system employed in the control of photovoltaic installations [
37,
38,
39].
In the installation discussed in
Section 2, the presence of several actuators and different applications monitoring the operation of the photovoltaic system necessitated the decision to create a SCADA system designed in the CitectSCADA 2016 software (
Figure 6). Its main objective was to simultaneously monitor the operation of all installations (belonging to the Rokietnica Municipality and installed in several schools under its authority) in a single software environment with the possibility of extending the control algorithm of the receivers and better adapting the load characteristics to the generation output. This was enabled by attaching an additional PLC unit, whose outputs could activate individual loads; the activation algorithm is based on the programmed event systems in the SCADA environment. This solution does not replace the ERS controller, but supports it by performing additional actions. The HMI panel of the implemented SCADA system also serves an educational function, displaying information about, e.g., the reduction in CO
2 emissions, energy production by the installations and graphs showing irradiance and energy produced as a function of time.
With the appropriate user access level, it is possible to access the control panel of the selected photovoltaic system after logging in (
Figure 7 shows the synoptic screen for the analyzed BIPV installation in Cerekwica). The designed SCADA software contains many typical functionalities characteristic of this software environment. The software generates reports providing information on the energy generated by the system and the energy load status of the school building. It sends alerts regarding the limit values generated by the system and records user activity in the system.
Such a solution both facilitates the control of the electricity generation process in the installation and also serves as an interesting method for educating students about renewable energy sources.
3.2. Grenton BMS System
The use of BMS serves as an alternative to the previously presented SCADA control implementation. By definition, a Building Management System collects all the information from the building in one place. It allows for a real-time response to external and internal changes in order to achieve the optimum performance of a given building in terms of economy, comfort and safety. As an integrated building management system, the BMS connects all the smaller systems of a building. This includes ventilation, air conditioning, heating, lighting, irrigation, as well as alarms, the opening of windows and doors or controlling blinds and shutters. A properly designed system allows:
Individual system components to be tracked and controlled;
Operating parameters to be changed;
Schedules and operating scenarios to be defined;
System diagnostics and optimization of energy consumption.
The analyzed building, equipped with the photovoltaic installation under consideration, does not have a BMS, but is provided with the necessary actuation for its implementation. Grenton’s (wired/wireless) system components will serve as an example. The main and most important component is the “CLU” (Common Logic Unit) module, which stores the system’s pre-programmed configurations (push-button configuration, light scenes, logics, scenarios). Other input/output modules can be connected to it via the bus or wirelessly. In this case it is necessary to employ the “Gate MODBUS”, i.e., a module facilitating the integration of devices that communicate via the MODBUS protocol. It enables the integration of heating systems, ventilation systems and photovoltaic systems, as well as electricity meters and any other devices supporting the MODBUS RTU standard. It will enable the acquisition of all the necessary data relating to the current energy generation and demand. The BMS installation can be equipped with other Grenton modules that increase the possibilities of controlling load characteristics. These include [
40]:
Relay 4HP—high-power relay output module, allowing four different independent devices (consuming a maximum current of 16A) to be switched on, with simultaneous measurement of the energy consumed by them;
Analog In/Out—integration by means of voltage and current analogue signals, i.e., control of temperature, humidity, wind speed or light intensity;
Roller Shutter—allowing the control of shutter drives or blinds (including those incorporating photovoltaic elements to increase the amount of energy generated);
Gate HTTP—allowing for even wider integration with external devices and systems with http and https protocol support such as weather services, IFTTT-type websites;
I/O Module 8/8—control of eight independent low-power electrical devices and additionally the possibility of connection of eight elements containing contact inputs.
The implementation of the BMS on the above-mentioned systems (presented in
Appendix A to
Figure A2)allows for an increase in the amount of consumed energy from the examined photovoltaic installation through an extended and more diversified range of receivers that can be switched on immediately. The Relay 4HP module can switch both large receivers, such as hot domestic water tank heaters, and small systems, such as cleaning robots, with the simultaneous and continuous monitoring of energy consumption.
Additionally, the use of the BMS will result in the rational use of energy through preset automatic operating algorithms, such as:
Switching off the recuperation systems in favorable weather conditions and tilting the windows via a system of actuators;
Automatic lowering of the window blinds on the south side of the building to reduce heat build-up in the summer months and vice versa in the winter months;
Automatic closing of windows in the event of extreme wind conditions preventing unwanted cooling of the building.
These measures will not only facilitate the adjustment of electricity generation and consumption, but also affect user comfort and the overall energy demand of the building from the standpoint of various utilities.
5. Discussion
As follows from the presented data and analyses, when designing an off-grid PV system, special attention should be paid to the proportion of energy generated by the PV system in relation to the energy consumed by the facility together with its load profile, so that generation and consumption periods coincide. Based on the data collected in
Table 6, the earlier analysis concludes that the examined installation would need to be improved or supplemented with other elements in order to be able to fully exploit its energy generation potential.
When comparing the energy yield of an existing BIPV system, which is limited by ERS, approx. 32% of the energy that could have been used and would contribute to improved economic indicators and a faster payback time is lost. The cost of generating energy in a BIPV installation connected to the power grid, despite the much higher investment outlays due to the use of this technology instead of traditional PV panels, would be comparable to current market electricity prices. The replacement of BIPV with traditional PV solutions would lead to an approx. 60% decrease in the costs of energy generation. However, BIPV systems should not be considered solely as energy generation systems, as they perform additional functions that are sometimes difficult to measure in terms ofa monetary equivalent. Instead, it is important that the investment is profitable and provides a return on investment.
The economic indicators of the examined installation could be improved if it were to be expanded to include additional proposed components such as energy storage, SCADA systems or building automation systems to manage the operation of the entire arrangement. With a relatively small financial outlay, it would be possible to make full use of the generating capacity of PV installations, even with the use of the BIPV technology, as indicated, for example, by such ratios as
NPV or
LCOE shown in
Table 6.
The analysis of the data included in
Table 4 and presented graphically in
Figure 10 confirms the information regarding the impact of the adopted discount rate (the change in the value of money in time) on the obtained financial profits past the installation’s lifetime. The higher the value of the
p factor, the lower the final total profits from the investment (including the possibility of achieving no return on the invested funds).
Special consideration should furthermore be made of the analysis of the proposed changes in the
NPV of PV systems, with consideration of the variability in the discount rate
p during the lifetime of the installation, as presented in
Figure 11 and
Table 5. It appears that the fixed value of parameter p, which is frequently adopted in the economic analyses of PV systems, leads to a distorted picture of the actual cash flows over the lifetime of the installation. Comparing, for example, variant W3 with W5, where the adopted p-values are 3, 5 and 7% every 6 years, but in a different time frame, one can see a change in the
NPV from PLN 32,327 to PLN 80,267, which results in an increase in expected profits by 2.5 times, representing approximately 50% of the investment value.
6. Conclusions
The presented installation is an example of the use of an on-grid inverter to create an island installation that is not connected to the power grid. This required the use of a special protection system to prevent excess energy from flowing into the grid. However, the analysis demonstrates the drawbacks of these solutions, such as limitations to the operation of the generation system during periods of reduced demand for energy by the facility. It is therefore important to properly correlate the generation profile with the consumption profile, or to use additional devices and control algorithms to limit possible losses. The use of an energy storage, installation control and visualization system, or the automatic management of the elements of an electrical installation, can optimize the energy consumption profile of a facility and allow the energy generation system to be used at full capacity, leading to a positive impact on the economic parameters of the investment. In Poland, as part of the investment in photovoltaic systems, it is even possible to obtain additional funding for energy management systems and energy storages utilized as system components.
In the case of the examined school building, the main challenges relate to the fact that during the holiday months (July, August), the school functions are limited and its energy demand is much lower than in other months. For facilities with a uniform energy demand, the process of system selection would be easier. However, the presented data show unequivocally the importance of the proper correlation of energy generation and consumption, studying the load profile of the building (not only on an annual or monthly basis, but also on a short-term basis (e.g., daily)), and taking into account school holidays and plant downtime, which would affect losses of generated energy not collected by the local RES systems.
The appropriate choice of parameters for the economic analysis is particularly important at the time the decision to invest is taken, as this illustrates its profitability and potential financial profits. Analyses should take into account the dynamic change in the value of money over time, just as in the case of investments based on natural resources, as this affects the final financial outcome.
In summary, the research and analyses conducted lead to the following conclusions:
- -
When design ing a PV system, accounting for the facility’s own needs (off-grid), its size and productivity should be carefully correlated with the facility’s energy needs;
- -
The use of SCADA and building automation systems allows for precise control of electrical receivers, management of the distribution of the energy generated from the PV system, as well as data-archiving and device monitoring;
- -
The energy management system allows for an increase in the level of self-consumption of the generated energy, which also improves the profitability of the investment;
- -
In the analyzed case of the school’s BIPV system, the calculations show a potential increase in energy generation by 32% if properly managed. This value is comparable to other studies, where the level of self-consumption with an integrated energy management system together with building automation can change from 20% to up to 50%;
- -
Proper correlation of the size of the energy generation system and energy consumption through the use of a distribution and equipment management system serves to improve the economic indicators of the investment;
- -
The use of dynamic discount rates in the economic NPV analysis allows for a more precise determination of the financial flows of the investment.