*3.1. Multi-Zone Parabolotoric Microconcentrators with Uniform Radiation Distribution in the Focal Region*

The reflecting surface of the developed multi-zone solar radiation microconcentrators was formed via the rotation of a certain curve (generatrix) around a symmetry axis that does not cross this curve and passes through the focal spot center. A microconcentrator with an internal mirror RS operates on the principle of collecting the reflected rays into a circular focal region.

Figure 6 shows examples of a single-zone concentrator and a five-zone concentrator, as well as the outlay of a finished concentrator with high-voltage planar PV cells (see Section 2.2).

The RS of a microconcentrator is composed of several zones lying one above another. The RS generatrix constitutes several smoothly merging parabolas each of which forms a separate zone. Each zone has the form of an axisymmetric solid with a symmetry axis that coincides with that of the concentrator. Each zone of the RS ensures a homogeneous reflected radiation distribution over the entire focal region, and the number of reflected rays incident on each point of the concentrator's focal region is equal to the number of zones (see Figure 6d). At the same time, the form of the RS meets the condition of minimizing the incident angle for rays reaching the RR's active surface.

The general system of equations describing the RS profile is as follows:

$$\begin{cases} \left(\frac{dx\_i}{dy\_i}\right)^2 + \frac{2y\_i}{x\_i - z\_i} \cdot \frac{dx\_i}{dy\_i} = 1; \; i = 1, 2, \dots, N\\ x(y\_i - 0) = x(y\_i + 0); \; x\_i \in [r\_i; R\_i]; \; R\_i = r\_{i+1} \text{ at } i = 1, 2, \dots, N - 1\\ x\_1 = r\_1 \text{ at } y\_1 = 0\\ \lim\_{y \to y\_i - 0} \frac{dx}{dy} = \lim\_{y \to y\_i + 0} \frac{dx}{dy}\\ \sum\_{i=1}^N \left|\frac{x\_i dx\_i}{z\_i dz}\right| = \sum\_{i=1}^N K\_i\\ K = 1 + \sum\_{i=1}^N K\_i; \; K\_i = \frac{R\_i^2}{r\_i^2}; \; K = \frac{R\_N^2}{r\_1^2} \end{cases} \tag{6}$$

where, as shown in Figure 6a, *xi* is the current position of the point of ray arrival at the *i*-th zone on the *X* axis; *xi* is equal to the radius of a section of the RS by the plane that is perpendicular to the concentrator's rotation axis and passes through the point *yi* (*ri* ≤ *xi* ≤ *Ri*); *yi* is the current position of the point of ray arrival at the *i*-th zone on *Y* axis coinciding with the concentrator's rotation axis; *zi* is the position of the point of arrival of the ray reflected from the *i*-th zone at the focal spot on the *X* axis (–*ri* ≤ *zi* ≤ *ri*); *Ki* is the concentration ratio in the focal region ensured by the *i*-th zone of the RS; *K* is the total concentration ratio in the focal region; *N* is the number of zones; and *ri* and *Ri* are the

radiuses of the smallest and largest sections of the *i*-th zone's RS, which are perpendicular to the concentrator's rotation axis.

**Figure 6.** (**a**) Example of a single zone design; (**b**) five-zone microconcentrator with planar highvoltage PV cells corresponding to Figure 6c,d; (**c**) beam path diagram for the uppermost points of each zone, in the five-zone microconcentrator (the first zone corresponds to Figure 6a); (**d**) beam path diagram, for beams falling onto one point of RR, in the five-zone microconcentrator shown in Figure 6c.

The equations for various options of the microconcentrator design are defined in [53]. There are four options for single zones in accordance with the four possible variants of ray paths in the concentrator [53]. The microconcentrator RS is formed via the alternation of four variants of single zones. For instance, the concentrator shown in Figure 6b–d begins from a zone that is similar to that shown in Figure 6a. Then, three more zones are added where the reflected ray consequently arrives from the uppermost point of the zone at the RS center or periphery. Additionally, the fifth zone is the same as the first zone but with different values of *r*, *R*, and *h*. Each zone of the microconcentrator exposes the focal plane to light with concentration ratios *K*1, *K*2, *K*3, *K*4, and *K*5, respectively. Generally, the concentration ratio of each zone *Ki* is distinct.

The greater the number of the zone is, the lower the reflection from the RR's active surface, and the higher the efficiency; however, this also results in a larger concentrator height.

The concentrator size depends on the size of the focal region/active surface of the RR. The smaller the focal region is, the smaller the concentrator's dimensions would be. Its size may be reduced to a very small size by using the developed PV cells, which are quite serviceable with millimeter dimensions and may be determined based on the convenience of assembly of the relevant module. The weight characteristics will be only determined by the concentrator wall thickness. The concentrators have to be capable to bear their own

weight plus the weight of protective coatings used against the impact of the environment (sealing glasses or clear plastics).

The microconcentrators and PV cells as RR are used to assemble CPV modules with the dimensions of traditional planar PV modules on the basis of crystal silicon and may be employed instead of them without material changes in the design and equipment of PV systems.

Experiments were carried out with two-zone, three-zone, and five-zone mirror microconcentrators with 2*r* = 10 mm and *K* = 10. The construction height of the experimental samples ranged from 26.47 mm to 36.41 mm depending on the increase in the portion of concentration accumulated in the middle zone. With that, the average incidence angle cosine varied from 0.7307 to 0.8104.

The uniformity of the achieved concentrated radiation distribution was 98.3–98.5% all over the focal region of the samples except for the boundaries along the perimeter, with the expected concentration ratio of 10+. On the periphery of the focal region (approx. 2% to 4% inward of the perimeter), a light distribution inhomogeneity rate of 3% at the edge was observed. The estimated radiation distribution uniformity was 99.7%. The fact that the experimental values of the radiation distribution uniformity were lower than the estimated ones can be explained by the immaturity of the technique used to manufacture both the microconcentrators and CPV modules as a whole (i.e., the imperfect mutual adjustment of the concentrator and RR).

Furthermore, the dependence of the microconcentrator's optical efficiency on the solar ray incidence angle was not observed in the case of a planar PV cell, and this efficiency reached 0.9 with an angle of 3 degrees. The average cosine of the ray incidence angle on the focal plane, within the above limits, was greater than that for a two-zone microconcentrator, and its value was over 0.67. Such redistribution of concentrations by zones led to an increase in the eventual angles of microconcentrator disorientation, but simultaneously, the average value of the cosine of angles of ray arrival at the focal plane decreased.

The CPV modules were manufactured from five-zone samples (Figure 6b) and highvoltage planar PV cells described in Section 2.2 with a special grid (see Figure 7).

**Figure 7.** (**a**) CPV module in the assembly process; (**b**) *I*–*V* curve of CPV modules at CSTC.

On the concentrator RS, above the upper zone, a supplementary ring was used forming a hexagon at the ray entrance into the concentrator. This ensured that there would be no voids between the microconcentrators in the plane of the active surface. The inscribed circle diameter of the hexagon was equal to 2*R*<sup>5</sup> = 31.6 mm. The modules consisted of 29 parallel rows with 42 microconcentrators in each. The dimensions of the module's active surface were 1607.8 × 967.4 mm, and their height was 47.2 mm. Their *I*–*V* curve at concentrator standard test conditions (CSTC) (direct normal irradiance of 1000 W/m2, cell temperature of 25 ◦C, and spectral irradiance distribution of direct normal AM1.5) is shown in Figure 7b. The efficiency change corresponds to the following equation [11]:

$$
\eta\_{\mathbb{C}} = \eta\_1 (1 + \beta \ln K) \tag{7}
$$

where *β* = *AkT*/*qV*o.c and *β* = 0.03–0.07.

#### *3.2. One-Dimensional Double-Wing Concentrator with Low Fresnel Optical Loss*

The body of the developed concentrator (Figure 8) was similar to that of a compound parabolic concentrator with a mirror internal RS operating on the principle of collecting the reflected rays into a rectangular focal region. The proposed principle of reducing Fresnel losses caused by radiation reflection from the RR's active surface involves minimizing the incidence angles for the reflected rays falling onto the concentrator focal region. For this purpose, RS has flat sections (*r* ≤ *x* ≤ *x*0, 0 ≤ *y* ≤ *y*0) adjacent to the focal plane and smoothly passing into its curved surfaces (*x*<sup>0</sup> ≤ *x* ≤ *R*, *y*<sup>0</sup> ≤ *y*).

**Figure 8.** (**a**) Concentrator design (for the description of variables, see Equation (8)); (**b**) dependence of the concentrator specific height on radiation concentration; (**c**) *I*–*V* curve of the developed CPV module at CSTC.

The RS shape complying with the condition of uniform focal region illuminance with the maximum incidence angles value of rays falling onto the RR's active surface is described using the following set of equations:

$$\begin{cases} \left(\frac{dx}{dy}\right)^2 + \frac{2y}{x-z} \cdot \frac{dx}{dy} = 1; \ x\_0 \le x \le R; \ y\_0 \le y\\ \frac{dx}{dy} = \frac{x\_0 - r}{y\_0}; \ r \le x \le x\_0; \ 0 \le y \le y\_0\\ \frac{dx}{dz} = \frac{R - x\_0}{2r}; \ z = (x - x\_0)\frac{2r}{r - R - x\_0} - r\\ \text{tg}\,\rho = \frac{x\_0 + r}{y\_0} = \frac{\sqrt{(x\_0 + r)(3r - x\_0)}}{x\_0 - r} \end{cases} \tag{8}$$

where, as shown in Figure 8a, *x* is the current position of the point of solar ray arrival at the RS on the *X* axis that is parallel with the focal plane and perpendicular to the concentrator symmetry plane (*x* ≥ *r*); *y*(*x*) is the point position on the concentrator's longitudinal symmetry plane in relation to the focal plane (*y* ≥ 0); *z* is the position of the point of the reflected ray arrival at the focal region in relation to the concentrator's symmetry plane; *x*<sup>0</sup> and *y*<sup>0</sup> are the coordinates of the point on the junction line between the curved area (*x* ≥ *x*0, *y* ≥ *y*0) and the flat area (*r* ≤ *x* ≤ *x*0, 0 ≤ *y* ≤ *y*0) of the RS (*r* ≤ *x*<sup>0</sup> ≤ 3*r*); *K* is the concentration ratio in the focal region; 2*r* is the width of the concentrator focal region

−*r* ≤ *z* ≤ *r*; 2*R* is the concentrator aperture size in cross-section; and 0 ≤ *x* ≤ *R* and *ϕ* is the ray incidence angle.

The shape of the concentrator's RS generatrix forms a flux of reflected radiation uniformly distributed over the rectangular focal region, thus reducing the current-spreading resistance in the illuminated layer and increasing the efficiency of solar radiation conversion into electric energy. Including flat sections in the concentrator made it possible to achieve efficient steep-wise incidence of the rays onto the focal plane at small incidence angles, resulting in a decrease in the coefficient of ray reflection from the RR's active surface. The primary important optical and energetic peculiarities of the developed product involved the symmetric property of the concentrator design, which considerably eased the requirements for the orientation towards the sun and increased the possibility of achieving high optical efficiency.

The maximum angle of the ray arrival at the RR's active surface decreased with the size of the flat horizontal section equal to *x*<sup>0</sup> − *r*. For the minimum value of *x*<sup>0</sup> = *r*, there was no flat section, and rays fell from the lower part of the concentrator at angles close to 90◦, with a large reflection coefficient, while for the maximum value of *x*<sup>0</sup> = 3*r*, the incidence angle became equal to zero, and Fresnel losses were minimal. However, in this case, the size of the concentrator's flat section became unacceptably large, in a vertical direction.

The size and inclination of the flat section were chosen based on the conditions ensuring small angles of ray incidence onto the focal plane for acceptable values of the concentrator's entire height and weight. Varying this size and inclination angle enabled us to obtain a wide spectrum of concentrators ensuring target values of concentration ratios and relevant angles of radiation incidence on the focal plane.

Experiments were carried out with the concentrator option having the following parameters: *r* = 12 mm, *x*<sup>0</sup> = 2*r* = 24 mm, *R* = 37.64 mm, and *K* = 10. The concentrator height was *H* = 75.42 mm. Modules composed of vertical high-voltage PV cells (Figure 2b) were used as RRs. For 10-fold radiation concentration, the required area of the RR's active surface decreased 10 times, and concurrently, RR efficiency increased by relatively 15–18 percent. These effects together led to a considerable reduction in cost. The chosen value of parameter *x*<sup>0</sup> = 2*r* approximately corresponded to the optimal concentrator design in terms of the coordination of Fresnel optical losses and concentrator height, i.e., its materials content and weight. The maximum angle of ray arrival at the RR surface was *ϕ* = 60◦. The concentrator ensured a uniform radiation distribution of 98.9% over the RR. At the same time, as in Section 3.1, unevenness was localized on the periphery of the RR. These areas were not above the cells without substantial losses of the RR's active surface thanks to the form of the vertical PV cells.

The height values *H* increased with the concentration ratio *K*, leading to the decrease in the angle of ray incidence on the focal region and thus reducing Fresnel optical losses. The dependence of the concentrator height related to the width of the PV module's active surface (concentrator focal region) on the concentration ratio, for concentrators having different values of the design parameter *x*0/*r*, is shown in Figure 8b. Additionally, in Figure 8c, we can see the averaged *I*–*V* curve of one section of the developed CPV modules at CSTC. The dimensions of the RR's active surface, for one module section, are 10 × 1020 mm. The efficiency change corresponds to Equation (7).

## **4. Increasing Energy Production by Increasing Systematization Level—Optimization of the Power Supply Process as a Whole**

It should be noted that in many recent studies on normative instruments (e.g., [54–58]) the approach to the construction concept of PV systems for individual facilities is close to the one we investigated. In [58], the consuming equipment (consumption circuit) is supposed to be a part of the PV system. Additionally, in the event that the consuming equipment would not be included in the PV system supply contract, such equipment shall be detailed in the technical documentation for the PV system. Nevertheless, the evaluation of the system was limited to that of its PV part. In [57], efficiency was assessed through a conventional parameter called "service ratio", which rather schematically describes the relationships between the generated energy and satisfied needs. This methodology is only fit for a theoretical comparison of PV systems using this conventional parameter but not for the design process of PV systems and the efficiency assessment of real functioning systems.

The final objective of PV system operation, similar to any other power-generating equipment, is to provide the consumer with the required kind of energy in the specified and required quality.

The analysis of the process of power supply to individual facilities shows that the total losses caused by inefficient operation of power supply systems are 28–73% (see Figure 9). The average losses caused by improperly arranged power supply amount to 26% of the aggregate power losses. The losses caused by the unreliable performance of such systems as a result of their design features are 28% [6,17,59].

**Figure 9.** Diagram of the process of power supply to individual facilities.

Therefore, the actual efficiency of the power-generating equipment is determined not only by the characteristics of the generating equipment themselves, e.g., a PV system (*E*<sup>g</sup> and *EL*<sup>1</sup> or *E*<sup>g</sup> + *E*nw and *EL*<sup>1</sup> + *EL*<sup>2</sup> shown in Figure 9) but also by the peculiarities of the equipment, structures, and factors influencing the energy generation, transmission, and use processes (*EL*3–*EL*6). Moreover, due to the specificities of PV system functioning, even an inconsiderable change in losses (in conjunction with the time of day and of year, weather, load conditions, etc.) may substantially influence the PV system's operation and the quantity of energy delivered to the consumption points. The assembly of the above-mentioned equipment, structures, and factors, into a system and the optimization of such a system will allow for the minimization of losses, thus substantially increasing the amount of energy used by a consumer with the same output power of the PV system (both as stand-alone generating equipment and in combination with any other generating equipment and/or a network). Hence, by taking into account the final objective mentioned above, the operation of the generating equipment can become as efficient as possible.

At present, the efficiency of power supply with the use of PV systems is evaluated on the basis of their characteristics at the consuming equipment input. As seen in Figure 9, from the point of power input to the consuming equipment until the moment of meeting consumer needs, significant energy losses are possible. Accordingly, to estimate the efficiency of the PV system realistically, it should be determined based on the final result, i.e., the degree to which consumer needs are met.

This means that an increase in the PV system's efficiency can be achieved by expanding the boundaries of the system, which is mainly the new and higher level of generalization and systematization characterized by the following features:

	- The power supply facility (e.g., a building) is a part of the system;
	- The principle of integrating functions is applied to the maximum possible extent: Each structure, technical means or subsystem shall perform as many functions as possible. When a structure (technical means, subsystem) can be built to perform the functions of several structures (technical means, subsystems), it has to be designed to combine maximum of these functions (e.g., BIPV modules);

The block diagram of such a highly efficient PV system is shown in Figure 10.

**Figure 10.** Design of highly efficient PV system for individual facilities created as a complex system of energy supply to the facility (SS means "subsystem").

Unlike ordinary network systems, the problem of the interconnection of all processes, from power production to power consumption, is critically important for PV systems. If a system is improperly organized or its structure is not optimized, there will be an energy shortage, or even an absence of energy supply, on the consumer side. It is obvious that in particular cases, the assertions of inapplicability (inoperability) of a PV system or its lower efficiency compared with the expected values of parameters, are, first of all, associated with improper organization and structure of the PV system. When a PV system is used for power supply to a facility, its maximum efficiency may only be achieved when it is designed in accordance with the foregoing principles.

The efficiency criterion of highly efficient PV systems is formulated as follows: "maximum satisfaction of needs with minimum costs", and the objective function, generally, is as follows:

$$\mathcal{W} = \begin{cases} \mathcal{S} \to \max \\ \mathcal{C}\_{\mathcal{E}} \to \min \\ HE \to 0 \end{cases} \tag{9}$$

Provided that

$$(\text{C}\_{\text{E}} \to \text{min}) \equiv \begin{Bmatrix} E\_{\text{cn}} \to \text{min} \\ E L\_{\Sigma} = E L\_1 + E L\_2 + E L\_3 + E L\_4 + E L\_5 + E L\_6 \to \text{min} \end{Bmatrix} \tag{10}$$

$$(E\_{\rm cm} \to \min) \equiv \begin{Bmatrix} E\_{\rm d} \to \min \\ E L\_6 \to \min \end{Bmatrix} \tag{11}$$

(*E*<sup>d</sup> → min) ⊃ Need optimization/correct assessment of needs Consumption equipment optimization (12)

where *S* is the degree of need satisfaction (if *S* is expressed as a percentage, then *S* → 100%); *C*<sup>E</sup> is the energy expenditure; *HE* is the environmental damage; *EL*<sup>d</sup> is the energy demand; and *EL*<sup>Σ</sup> is the aggregate energy losses. *E*cn, *EL*1, *EL*2, *EL*3, *EL*4, *EL*5, and *EL*<sup>6</sup> are shown in Figure 9.

With that, the cost minimization is assumed to be, first and foremost, the minimization of energy expenditures and, therefore, the minimization of losses. Additionally, the maximum satisfaction of needs is understood to be the maximum number of needs met and the maximum satisfaction of each need. Methods for numeric evaluation at the level of individual facilities do not yet exist for all the indices through which the needs are expressed. In this case, one proceeds from the affirmation that a greater observance of this condition corresponds to greater satisfaction of needs and is always preferable, e.g., more ecologically sound solutions are always preferable.

The correct assessment and formalization of needs is the most difficult task in the creation of PV systems in accordance with the proposed efficiency criterion in Equation (9). This occurs in the following manner:

The consumer is described by a set of needs N for the satisfaction of which electrical energy (or electrical energy from a PV system) may be required. Each need *ni* is described from 1 to J by parameters *pij*. In a general case, the number of parameters characteristic of different needs is different. Each of the parameters is characterized by a value (or permissible value range) of *vij* corresponding to the state of "need is satisfied", or a number of values/ranges and the relevant degrees of need satisfaction are established for each parameter. The general outline of consumer need formalization may be presented through the following identical relations:

where NP is the set of parameters characterizing all consumer needs that require electrical energy to be met, NP*<sup>i</sup>* is the set of the parameters characterizing the *i*-th need, NPV is the set of the parameter values characterizing all needs, and NPV*<sup>i</sup>* is the set of parameter values characterizing the *i*-th need.

The task of creating a PV system is to ensure that the energy generated by it meets each need. Formally, this means that the value of each parameter from the set of parameters in Equation (13) is equal to the desired value (i.e., it is within the desired range of values).

The process that is fully applied today is shown in Figure 11. The system efficiency evaluation is carried out in reverse order.

Additionally, the efficiency of such PV systems is as follows:

$$
\eta\_{\rm syst} = \frac{E\_{\rm cn} - \Delta\_E}{E\_{\rm in}} \cdot 100\% \tag{14}
$$

where *E*in is the amount of energy supplied to the system (the product of the aggregate irradiance of PV module active surfaces or CPV module aperture by the aggregate area of active surfaces or aperture). In the case of power supply with the use of PV systems, these are only *E*in = *E*cn + (*EL*PV + *EL*<sup>3</sup> + *EL*<sup>4</sup> + *EL*<sup>5</sup> + *EL*6); *EL*PV = *EL*<sup>1</sup> is the losses in

the generation process; and Δ*<sup>E</sup>* is the difference between the energy required for consumer needs to be fully met and the clean energy directly used to meet consumer needs.

**Figure 11.** Diagram of PV system implementation and its efficiency evaluation.

Instead of energy, power may be used to simplify the evaluation process. In this case, to assess the efficiency, instead of Δ*E*, it is necessary to determine Δ*P*, which is the total power of all needs that are not fully met.

The efficiency evaluation according to the proposed criterion and the creation of a PV system in accordance with Figure 10 indispensably include the possibility of amendments, adjustments, and modifications as a normal functional condition of the process, from changing settings to the replacement of equipment, software logic, etc. This includes the possibility of modifications due to the inaccurate assessment of the state of need satisfaction resulting from (1) PV system's imperfection due to any errors in design and inaccurate determination of the consumer needs from the outset as well as (2) a change in needs.

The described approach may be quite properly combined with modern software possibilities, which allows for the implementation of the diagram in Figure 11 in practice.

#### **5. Approbation of Proposed Solutions**

The final characteristics of the developed PV/CPV modules, as well as typical average characteristics of conventional mono-Si modules, are shown in Table 3. As can be seen from the *I*–*V* curve of the developed modules (Figures 2c, 5b, 7b and 8c), it is possible to further increase the PV/CPV modules' efficiency, especially the modules based on planar high-voltage PV cells.


**Table 3.** Characteristics of the newly developed PV/CPV modules and typical characteristics of conventional crystalline Si PV modules.

<sup>1</sup> Under 10 suns.

In the period from 2011 to 2022, the concept considered above was used for designing PV systems in various climate conditions and at facilities with different needs [43,60–64]. The functioning of those systems confirms the correctness of the proposed approach. The composed systems can satisfy 30–50% more needs than PV systems with a conventional systematization level simultaneously installed at similar facilities, i.e., they are equivalent to PV systems with a conventional systematization level but generate more energy by 30–50%. The points of PV systems' installation were in various regions of rural territories with different climates, so the results may be deemed quite representative.

The research results presented in Sections 2–4 were combined in the base experimental project of an ecological complex (Lat 58.01 N, Lon 43.34 E) consisting of two main buildings and free-standing identical cottages whose number grew from year to year. The PV system was implemented from the outset as a comprehensive power supply system with conventional mono-Si PV modules located on the roof and integrated into the balcony rail and flexible a-Si panels on the roof with an arched form [60]. As new PV/CPV modules were developed, these new devices would be partially installed for conventional planar modules. The power supply to one of the cottages, in comparison, was ensured from the very beginning using a conventional PV system. The rest were designed with a different higher level of systematization. Depending on the particular cottage, the systematization level increased with the extension options by incorporating into the system other components involved in the power supply process (see Figures 8 and 9). Additionally, the level of systematization of parts of the PV system of the main buildings was gradually adjusted.

Thanks to the installation of the developed PV and CPV modules, the total maximum power at STC (CSTC) was 1120.86 kW. That said, thanks to a higher output voltage and other specific features of the modules, the losses inside the system decreased by 12 to 15%, and also maintenance losses decreased. In the case of PV systems of the cottages built simultaneously with the cottage equipped with a traditional PV system, the power directly used to meet consumer needs was 21% to 23% higher. As the proposed approach was improved, in the construction of new cottages, losses were reduced, and *E*cn was increased by 12% to 16%.

The reduction values of the maximum power at STC/CSTC, and, consequently, those of the energy production of the developed PV modules, were from 0.2% to 0.24% per year under wet atmospheres with high concentrations of dissolved ammonia (see Figure 12). These values of the developed PV modules were from 0.22% to 0.37% per year. Measurements were carried out on a livestock complex experimental site and using an accelerated aging method in laboratory conditions. For comparison reasons, Figure 12 shows the deterioration range for conventional mono-Si PV modules, in a normal environment. The average annual deterioration of their performance may attain 5% to 7%, in a wet ammonia environment.

**Figure 12.** Reduction in the energy production of modules during their operation lifespan: 1, 2—newly developed PV modules with high-voltage PV cells in wet ammonia environment (1—maximum, 2—minimum); 3, 4—newly developed CPV modules in wet ammonia environment (3—maximum, 4—minimum); 5, 6—conventional mono-Si PV modules in normal operation conditions (5—maximum, 6—minimum).

#### **6. Conclusions**

The use of PV equipment is a real efficient method for fighting against climate change, and the protection and restoration of the environment. For the mass implementation of PV systems in agriculture in rural areas, their attractiveness to consumers should be increased, for which it is necessary to improve the energy output of PV devices, as well as their reliability and environmental resistance, to improve their aesthetic quality, as well as enhance the diversity of efficient PV equipment for any operational conditions ensuring the versatility of PV systems use as an energy source.

High-voltage vertical Si PV cells for terrestrial applications and high-voltage multijunction planar Si PV cells were proposed and developed. A significant increase in the output voltage of the PV modules and PV arrays was attained with the design of PV cells that enabled a reduction in power losses, material consumption, required space, and cost. At the same time, the design of planar multijunction PV cells allowed for adherence to the conventional mass production technology for PV modules.

The modules based on high-voltage vertical PV cells composed of 40 cells had a size of 60 × 10 mm, a maximum power point voltage of up to 1000 V, specific power of up to 0.245 ± 0.01 W/cm2, and an efficiency rate of up to 25.3%, for radiation concentration ratios from 10 to 100. The samples of the second type of modules composed of 60 PV cells (156.75 × 156.75 mm) had *V*o.c = 439.7 V, *I*s.c = 0.933 A, and *P*max of 348 W, at STC. The maximum power degradation at STC was estimated to be within 0.2% to 0.24% per year in a wet ammonia environment.

New designs of concentrators with uniform radiation distribution in the focal region were developed, including a parabolic cylindrical concentrator with minimized Fresnel optical losses and a multi-zone parabolotoric microconcentrator whose dimensions enabled CPV modules similar in size to conventional planar modules to be manufactured. Two types of CPV modules were designed: (1) modules consisting of a parabolic cylindrical concentrator and an RR composed of vertical multi-junction cells, and (2) modules comprising multi-zone microconcentrators with a planar high-voltage multi-junction cell as the RR. The second-type CPV modules included 42 × 29 microconcentrators and had the dimensions of 1607.8 × 967.4 ×47.2 mm. These modules had the following average values of output parameters at CSTC: *V*o.c = 512.9 V, *I*s.c = 1.051 A, and *P*max of 361.57 W. The degradation of maximum power at CSTC was estimated at 0.22% to 0.37% per year in a wet ammonia environment.

Through the use of PV and CPV modules based on the developed cells and concentrators, projects using the power supply on the basis of PV systems were designed. The projects implemented the principles of complex energy supply systems, which allowed for the minimization of the losses and requirements for the output power level of PV systems. The thus-created systems satisfied 30–50% more consumer needs than PV systems with a traditional systematization level simultaneously installed at similar facilities. Thanks to a higher output voltage and other specific features of the developed modules, the power loss inside the PV system decreased by 12% to 15%, along with a reduction in maintenance loss.

**Author Contributions:** Conceptualization, O.S.; methodology, O.S.; validation, O.S., A.I., Y.L. and A.D.; formal analysis, O.S.; investigation, O.S.; resources, A.I., Y.L. and A.D.; data curation, A.I., Y.L., and A.D.; writing—original draft preparation, writing—review and editing, O.S.; visualization, O.S. and A.D.; supervision, A.I., Y.L. and A.D.; project administration, A.I., Y.L. and A.D.; funding acquisition, A.I, Y.L. and A.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
