Hybrid Photovoltaic Thermal Systems Research Articles

Numerical investigation of the effect of operating conditions on performance of PV-PCM system

The photovoltaic module only manages to convert around 15% of the incoming light into usable electricity and the rest is lost as heat, reducing the module's overall efficiency. Hybrid photovoltaic thermal systems are therefore the best way to collect thermal and electrical energy. The cooling and heat storage benefits of PV cells are amplified using phase change materials (PCMs). In this article, a simple two-dimensional CFD model to forecast the temperature of the PV where it contacts the PCM. The findings of the numerical simulations show that PV systems equipped with PCM have been studied under a variety of situations. A contemporary thermodynamic study is performed to examine system behaviour under different operating settings by investigating the effect of some rather crucial aspects that have not been taken into account before. The research takes into account three instances, each with its own unique combination of wind speed, ambient temperature, and sun irradiation. It has been shown that the solar radiation is a key component for growth in the PV temperature. The findings show that an increase in PV temperature of 5–7°C is caused by an increase in solar irradiance of 1000 W/m2. The rise in wind velocity, heat dissipation rate increases resulting to the fall in the temperature of the PCM and glass, the decrease in PCM temperature leads to a further drop in glass temperature. More so than wind speed or solar irradiation, ambient temperature determines how quickly PV glass heats up. Furthermore, at an ambient temperature of 35°C, PCM is found to melt entirely in 435 min, whereas at an ambient temperature of 30°C, PCM melts up to a liquid fraction of 0.77 min. Therefore, the efficiency of the PV system improves dramatically as the outside temperature is lowered.

Experimental investigation on the performance of MXene/C-dot hybrid nanofluid-based photovoltaic/thermal system: An Energy, Exergy, and Enviro-Economic analysis

Nanofluids (NFs) with exceptional heat transfer properties are increasingly being adopted in solar collectors as heat transfer fluid (HTF). Hybrid photovoltaic thermal systems are becoming more popular because they increase overall efficiency by producing both high- and low-grade electricity. This research focuses on the application of thermally efficient NFs for enhancing the thermal and electrical output of a photovoltaic/thermal (PV/T) system. Indoor experimental investigation was conducted on the PV/T system to find the thermally efficient HTF. Carbon quantum dot (C-dot), MXene and MXene/C-dot hybrid NFs were selected for experimentation. Thermo-economic factors (thermal conductivity, volumetric heat capacity, thermal property degradation rate, and cost) were used to optimise the NFs' concentration. Optimized C-dot, MXene, and hybrid NFs were used for experimentation in the PV/T system. Energy, exergy, and enviro-economic analysis was conducted on the PV/T system with each HTFs. The results show that the thermal efficiency of PV/T was enhanced by 5.39, 3.87, and 9.45 % with C-dot, MXene and hybrid NFs, respectively. Hottel-Whillier-Bliss (HWB) analysis was performed on the collector from the generated experimental data. The analysis states that at zero heat loss conditions, the thermal efficiency of the PV/T was enhanced by 5.4 % with the hybrid NF. The maximum CO2 emission from PV/T with C-dot, MXene, and hybrid NFs, were calculated to be around 2.024, 1.979, and 1.931 kgCO2/day, respectively. Emission cost reduction analysis states that the hybrid NF achieved the highest reduction of 0.02 $/day which was a considerable decrement of 13.5 % over the water-based PV/T system.

Thermal and electrical analysis of the performance of a skeleton-shaped tubes via hybrid PVT cooling system

The study investigates methods to mitigate the decrease in performance of solar panels caused by increased cell temperatures. Using commercial computational fluid dynamics (CFD) analysis, two cooling methods for photovoltaic/thermal (PVT) modules are compared. Configuration 1 employs longitudinally connected tubes beneath the solar panels, while configuration 2 utilizes skeleton-shaped aluminum tubes inserted into the cells from below. Both configurations undergo cooling with air (case 1) and water (case 2) at a mass flow rate of 0.0025 kg/s. Results indicate that configuration 2, employing skeleton-shaped tube cooling, surpasses configuration 1 in both thermal and electrical efficiency. In case 1, configuration 2 achieves a notable improvement of approximately 24.3 % in thermal efficiency and a marginal increase of 0.16 % in electrical efficiency compared to configuration 1. In case 2, with water cooling, configuration 2 demonstrates a 7.27 % enhancement in thermal efficiency and a more substantial increase of 3.98 % in electrical efficiency over configuration 1. The hybrid PVT system utilizing skeleton-shaped tube cooling with water at a mass flow rate of 0.0025 kg/s proves highly effective in maintaining peak thermal and electrical efficiency.This work addresses the critical issue of solar panel performance decline due to increased cell temperatures, proposing innovative cooling methods and quantifying their effectiveness. The study’s novelty lies in the utilization of skeleton-shaped aluminum tubes for cooling, which outperforms traditional cooling configurations. These findings underscore the importance of advanced cooling techniques in optimizing PVT module performance, offering valuable insights for future research and practical applications in the renewable energy sector.

Green synthesis of gold nanoparticles via Artocarpus odoratissimus peel extract for potential applications of optical filter and catalytic degradation

Gold nanoparticles (Au NPs) were synthesized via a green synthesis method, utilizing the peel extract of Artocarpus odoratissimus as both the reducing and capping agent. This study investigates the impact of peel extract concentration (ranging from 0.002 to 0.012 g/mL) and reaction temperature (including room temperature, 45 °C, and 75 °C) on the properties of the synthesized Au NPs. Various characterization techniques, such as UV–Visible spectrophotometry, transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and zeta potential analysis, were employed to analyze the synthesized samples. UV–Visible spectroscopy revealed absorption peaks of the Au NPs around 533–537 nm, varying with synthesis parameters, while TEM analysis indicated particle sizes ranging from 12 to 25 nm. XRD analysis confirmed the formation of Au NPs, with diffraction peaks aligning well with the standard. FTIR analysis suggested interactions between phytochemicals and Au NPs, contributing to their reduction and size control. The synthesized Au NPs exhibited remarkable optical filtering capability, with up to 87 % transmittance in the 751–1126 nm spectral range and significant absorbance in the lower wavelength region (300–751 nm). Additionally, catalytic studies revealed that Au NPs accelerated the degradation of rhodamine B dye, 0.0795 min−1, compared to 0.0445 min−1 without Au NPs. These findings underscore the potential of Au NPs for use in hybrid photovoltaic-thermal systems as filters, where transmitted light can be harvested for photovoltaic energy generation while absorbed light can be utilized for the thermal aspect. Moreover, Au NPs offer promise for improving wastewater quality by enhancing pollutant degradation.

Improving the overall performance of a hybrid photovoltaic system by reflectors and cooling with water jet

In the present research, the overall performance of the hybrid photovoltaic thermal PVT system used in the production of electric power and water heating has been evaluated. The PVT was coupled with reflectors to increase the energy production and cool it by water jet. The experimental tests were conducted in Iraq – Samarra located at the longitude (43 40 East) and the latitude (34 35 North). Several experiments were carried out through April 2021 in the outdoors. The highest overall instantaneous efficiency was 64%, and the highest percentage improvement in the PVT electrical performance with reflectors was 42.6% at a (0.0084 kg/s) load flow rate. The water temperature in the thermal storage tank increased by about (6°C/6 h) when the electric heater was turned on, while it decreased (6°C/6 h) without turning it on, and it consumed 18.7% of the total batteries energy, which makes it an ideal solution to compensate for the period of sun absence.

A novel concept of solar photovoltaic partial shading and thermal hybrid system for performance improvement

Large values from external causes, such as partial shade, can greatly influence output power of PV. The applications of partial shading are frequently utilized in simulation software. However, in this research work, partial shading and the integration of the photovoltaic Thermal (PV/T) Hybrid Solar Panel is implemented, and analysis is done to see how it affects the output power of solar panels under genuine climatic circumstances. Many research investigations have been conducted and researchers continue to look at PV/T systems to enhance their performance. The application is designed to provide information on solar panel output power under normal and partial shading situations. The maximum amount of power that solar panels can generate is 298.50 W. Under typical circumstances, partial shading in a solar panel can result in a maximum power value of 141.13 W, and this partial shading leads the power to increase.

Classification and Parametric Analysis of Solar Hybrid PVT System: A Review

A Hybrid Photovoltaic Thermal (PVT) system is one of the most emerging and energy-efficient technologies in the area of solar energy engineering. This review paper provides a comprehensive review of hybrid PVT systems in the context of the history of PVT, general classification, and parameter analysis. Several cell technologies with spectrum analysis are discussed to understand the application’s ability and energy efficiency. Hybrid PVT concept, characteristics, and structure analysis is also discussed in this study. An extensive analysis on the classifications of hybrid PVT systems from the recent literature is also presented here. These literatures are identified based on several criteria. In order to provide a complete and energy-efficient technology, an innovative classification of the hybrid PVT system is proposed in this paper. This proposed classification is a combination and upgrade of various existing classifications mentioned in recent research studies. Parameters have a significant and unavoidable impact on the performance and efficiency of the hybrid PVT system. A brief analysis of different parameters and the optimization of the system is conducted after reviewing recent research articles. This analysis provides insights into the impact of parameter variations on the system. A novel parameter model comprising parametric and optimistic analyses is also presented in this paper. It provides a detailed parametric description that significantly affects the performance and efficiency of the hybrid PVT system. Finally, the assessment focuses on a critical analysis of the main challenges in adopting PVT technology and suggests ways to overcome these barriers.

Enhancing Photovoltaic Thermal System Efficiency Using Micro-Channel Container and Nanoparticle Composited Phase Change Material: Effect of Dimensionless Water Flow

The photovoltaic thermal (PV/T) hybrid system has attracted significant interest from researchers in the solar field. These systems efficiently harness solar radiation, converting it into a usable source of energy and making use of any excess heat generated in the panel. In this study, PCM is utilized as a medium for combining with nanoparticles. Nanoparticle composited phase change materials (nc-PCMs) are created by mixing lauric acid (LA) with magnesium oxide (MgO) and containing them in a micro-channel container to enhance their thermal conductivity. The testing conducted on the water at various dimensionless Reynolds number (Re) of 1100, 2200, 3300, 4400, and 5500. Research studies have discovered that the presence of a water inlet reduces the temperature of the PV module, resulting in an enhancement of the overall efficiency. According to the results, it has been concluded that the best Re for a water system is Re = 5500. The enhanced photovoltaic (PV) modules boosted the electrical efficiency by 16.01% compared to the reference module, leading to an overall efficiency of 54.91%.

Numerical performance investigation of High Vacuum Flat Plate Hybrid Photovoltaic-Thermal devices.

We propose an innovative flat plate hybrid Photovoltaic-Thermal system under high vacuum (HV PV-T) optimized for solar-to-thermal energy conversion. It consists of a glass cover, metallic vessel, and the actual PV-T device, which englobes a low-emissive Transparent Conductive Oxide (TCO), a perovskite-based PV cell, a Solar Absorber, and a copper substrate. We investigate, through a 1-D model developed in MATLAB, the performances of the proposed PV-T system, still mined by radiative losses, varying the operating temperature (Top) and the emittance of the TCO (εTCO ) in the ranges of (25÷175) °C and (0.05÷0.45) respectively. The annual thermal and electrical productions are evaluated considering the Typical Meteorological Year of Naples, Italy. Specific annual costs and emission savings are evaluated and compared with the ones assured by commercial High Vacuum Flat Plate Solar-Thermal (HVFP ST) and PV collectors. Results indicate that the proposed HV PV-T increases the annual cost savings by 34% and 11% when compared to HVFP ST and PV collectors, respectively. Moreover, the presented HV PV-T increases the annual CO2 emissions savings by 7% and 48% when compared to HVFP ST and PV collectors, respectively.

An experimental analysis of a hybrid photovoltaic thermal system through parallel water pipe integration

The global research community has increasingly focused on sustainable energy solutions to combat the environmental challenges posed by extensive fossil fuel consumption. This paper presents a new simple approach to enhance the electric efficiency of photovoltaic (PV) panels through efficient cooling techniques using simple parallel water pipes on the back of the PV panel. Additionally, the waste heat generated during this process is harnessed as a valuable heat source for residential hot water systems. Experimental measurements were conducted on both the reference PV panels without cooling and the PV/T system equipped with cooling pipes. A comprehensive energy analysis was performed to compare their performance. The results demonstrate that the cooled PV/T system exhibits consistently higher electric efficiency due to effective cooling by about 10%, resulting in surface temperature reduction and enhanced performance. The system also demonstrates a significant improvement in waste heat recovery, making it a practical and promising choice for sustainable energy applications.

Enhancing Efficiency and Power Output of a Typical Hybrid Photovoltaic Thermal System

Enhancing Efficiency and Power Output of a Typical Hybrid Photovoltaic Thermal System

Performance investigation on an agricultural photovoltaic thermal system based on spectral separation

Based on cascade utilization of full spectrum solar energy, a spectral splitting agriculture photovoltaic thermal hybrid system has been proposed in this study. The red and blue light is assigned to farmland for plant photosynthesis, while the photovoltaic active light is absorbed by solar cell for electricity generation, and the rest to thermal receiver for high temperature production. To maximize the power output of proposed system, redundant waste heat is recovered through ejector and converted into electricity in organic Rankine cycle subsequently. By such incorporation, the proposed system can not only increase the overall utilization efficiency of solar energy, but also achieve the cogeneration of crops and electricity on the same land. Energy, exergy, and economic analyses are performed to evaluate the performance of proposed system. Results show that the overall utilization efficiency of solar energy reaches 39.67 % with the highest losses of 79.65 MW in organic Rankine cycle. From the point view of exergy, photoelectric conversion in solar cell is responsible for the largest exergy destruction and finally the overall exergy efficiency of proposed system reaches 40.65 %, which is 16.13 % higher than that of equivalent agricultural and photovoltaic system with separate land use.

Effects of partial shading on thermal stress and exergetic efficiency for a high concentrator photovoltaic

Highly concentrated photovoltaic systems can produce higher energy yields than conventional photovoltaic panels but have yet to reach widespread deployment, partly because of lower lifetime and hence cost effectiveness. One limiting factor in the lifetime is the excessive generation of thermal stress. This study takes a multi-objective approach to the calibration of a highly concentrated photovoltaic thermal hybrid system. Novelty is found by exploring the relationship and trade-off between thermal stress and exergetic efficiency. A variety of optical configurations are compared by partially shading the input aperture of the primary optics. Similarly, adjustments to the receiver are made by changing the angle of the solar cell by 45°. To minimise light spillage. The primary and secondary optic positions stay the same throughout all calibrations.By experimentally validating a COMSOL model of the concentrator photovoltaic system (including irradiance distribution) a thorough analysis is conducted. It was found that the maximum thermal stress within the solar cell in this study could drop by almost 10 % with small losses (<3.5 %) to total exergetic efficiency after only small changes to receiver position. Further investigations into other specialised concentrator photovoltaics are required to understand the range of impact on thermal stress.

An open-loop hybrid photovoltaic solar thermal evacuated tube energy system: A new configuration to enhance techno economic of conventional photovoltaic solar thermal system

One inherent problem of the conventional hybrid photovoltaic solar thermal system is the gradual loss of module power efficiency with low energy harvesting due to steady increase in module temperature with repeated circulation of the cooling water as a result of its closed loop configuration. This poor energy harvesting couple with high initial investment has made investment in this technology unattractive. This study proposes an enhanced hybridisation of the Photovoltaic Solar Thermal System collector with an evacuated tube based on an open-loop cooling configuration and unique flow control strategy. The aim is to improve cooling of solar panel leading to higher energy harvesting and utilisation that improves economic viability that will promote faster adoption. A numerical model is formulated using TRNSYS 18 software to assess the techno economics of the hybrid system. The model is validated using the verification and experimental methods. Overall, the findings show that the enhanced hybridisation and flow control strategy has resulted in higher annual renewable power generation and utilisation by 10 % than the basic hybrid Photovoltaic Solar Thermal system. This has resulted in significant economic savings, cutting operating expenses by 48 %. The ability to tailor the intended use of the system to meet with hot water and electrical power demand of different residential building is another attribute of proposed system that improve its energy harvesting reducing it payback period and doubling it economic benefit hence promoting it fast adaptability.

Swirling jet impingements for thermal management of high concentrator solar cells using nanofluids

Large intensity of irradiance in high concentrator solar cells leads to extremely high temperatures causing an adverse effect on the performance of solar cells. Efficient cooling systems are crucial for the optimal performance of high concentrator cells, which are typically required to operate within a prescribed temperature range (⁓ 110 °C). The implementation of effective cooling strategies poses a significant challenge for High Concentrator Photovoltaic Thermal (HCPV/T) hybrid systems to ensure sustained performance and longevity of the modules. This study proposes a novel method for the thermal management of High Concentrator Solar Cells (HCSC) using swirling nanofluid jets impinging on a heat sink. The study applies RANS (Reynolds-Averaged Navier-Stokes) method with the SST k-ω turbulence model and energy equation to resolve a conjugate heat transfer analysis for three different flow ratios: Qr = 0, Qr = 0.5 and Qr = 1 and two water-based nanofluids: Al2O3-Water and CuO-Water. The numerical results demonstrate a significant decrease in cell temperatures, reaching as low as 71 °C. At a mass flow rate of 50 g/min, the use of Al2O3-Water nanofluid increases the overall electrical efficiency by a maximum of 39.43%. In contrast, a minimum electrical efficiency of 39% for CuO-Water nanofluid is obtained for a lower mass flow rate (25 g/min). Al2O3-Water nanofluid yielded a maximum PEC (Performance Evaluation Criteria) of 116%, while CuO-Water nanofluid yielded about 113%. In addition, an increase of the mass flow rate results in an improvement of temperature uniformity, as demonstrated by a reduction of temperature variation from 6.8 to 5.2. These results suggest that the use of nanofluids is promising. The proposed swirling jet impinging on a heat sink in combination with nanofluid provides an effective cooling technique for HCSC, thereby potentially contributing to the improvement of the cell's performance and longevity.

Hybrid Photovoltaic Thermal Systems: Present and Future Feasibilities for Industrial and Building Applications

The growing demands of modern life, industrialization, and technological progress have significantly increased energy requirements. However, this heightened need for energy has raised concerns about its impact on the environment and the rising costs associated with it. Therefore, the engineering sector is actively seeking sustainable and cost-effective energy solutions. Among the promising innovations in solving the problem is the photovoltaic thermal system (PVT), which aims to capture electrical and thermal energy from solar radiation. Despite its potential, the application of PVT systems is currently limited due to the unpredictable nature of solar energy and the absence of efficient thermal energy storage capabilities. To address these challenges, researchers have explored the use of phase change materials and nano-improved phase change materials (NEPCMs) to optimize energy extraction from solar systems. By incorporating these materials, the PVT system can maximize energy utilization. This article provides a comprehensive overview of the potential applications of PVT techniques in both industrial and building settings. It also offers a detailed assessment of their commercial and environmental aspects. The research findings highlight several advantages of PVT systems, including reduced electricity consumption, efficient utilization of cooling and heating loads during off-peak periods, improved temperature stability, and enhanced thermal comfort. Furthermore, the integration of NEPCMs in PVT systems has demonstrated superior thermal performance, enabling 8.3% more heat energy storage during charging and 25.1% more heat energy release during discharging. Additionally, the implementation of solar-assisted combined heating and power systems showed the potential to prevent the emission of 911 tons of CO2 per year compared to conventional PV systems. These systems offer a promising pathway towards mitigating environmental impacts while meeting energy demands. Overall, this review article serves as a valuable resource for fellow researchers by providing detailed insights into the viability of PVT systems for various applications in the industrial and building sectors.

Indoor experimental analysis of Serpentine-Based cooling scheme for high concentration photovoltaic thermal systems

High concentration photovoltaic thermal hybrids are expected to play an important role in meeting growing energy demands. When approaching concentrations over 1000 suns, a cooling system is needed to maximise both the thermal and electrical performance of the multi-junction solar cell without producing excessive parasitic losses.This study develops a novel simulation model to provide an in-depth understanding of the functionality of a concentrated photovoltaic thermal hybrid system with serpentine-based cooling systems. An ultra-high concentrator photovoltaic optic irradiance profile (peak effective concentration ratio: ∼1500 suns) is considered within the simulation model, which has been validated through indoor experimentation. The effectiveness of cooling is also evaluated through maximum thermal stresses generated in the multi-junction solar cell. The double serpentine design was deemed the highest performing, primarily because of the single serpentine’s excessive pressure drop. Copper as the heat sink material yielded superior performance because of its higher thermal conductivity. The maximum total exergetic efficiency achieved by the receiver was ∼ 10.9% with this configuration. Compared to some examples in the literature this value may seem low, however, it is more accurate due to the inclusion of a specific irradiance profile. All serpentine-based cooling systems could maintain the recommended operating temperature.

Investigation of Techniques for Enhancement of Efficiency of a Hybrid Photovoltaic and Solar Thermal System: Literature Review on Applications and its Advancement

Abstract: Over the most recent couple of decades, tremendous consideration is drawn towards photovoltaic–thermal systems because of their advantages over the solar thermal and PV applications. This paper intends to show different electrical and thermal aspects of photovoltaic–thermal systems and the researches in absorber design modification, development, and applications. From the previous review articles, it has been concluded that the heat energy exhausted from the PV module can be further utilized in different ways and helps in achieving better efficiency. Furthermore, the types of photovoltaic–thermal systems such as air collector, water collector, and combi system, coupling with heat pump and their application to buildings are also stated. This paper also discussed certain design aspects like modifications in the flow channel by adding fins, thin metallic sheets, rollbond absorber, and porous media and the effect of these modifications on the hybrid system’s efficiency. Further- more, the use of the latest technologies such as nano fluids, thermoelectric generators, and phase-change materials improves the overall system performance. The role of soft-computing techniques is forecasting the impact of various parameters on the photovoltaic–thermal system is also discussed.

Electrical and thermal performance enhancement of a photovoltaic thermal hybrid system with a novel inner plate-finned collective cooling with different nanofluids

ABSTRACT In the present study, an experimental and mathematical analysis was performed in a novel nanofluid-based collective cooling consisting of inner-plate heat fins in order to explore a photovoltaic-thermal (PV/T) system efficiency for Al2O3, TiO2, and CuO-based nanofluids. The electrical efficiency increase, temperature decrease in the panel surface, thermal efficiency increase, and heat transfer performance of Al2O3-water, TiO2-water and CuO-water nanofluids which were prepared in three different ratios (0.2%, 0.4%, and 0.6%, in mass) and constant fluid flow rates were investigated. The highest electrical efficiency increase was observed in the 0.2% nanofluid Al2O3-water, at amount of 1.467% that correspond to 5.49% increase rate. The highest panel temperature drops were observed at the rate of 0.2% nanoparticles of Al2O3-water, TiO2-water, and CuO-water. The highest thermal efficiency was observed in the Al2O3-water nanofluid with 0.2% nanoparticles as the amount of 49.59% in average. For 0.2% nanofluid cooling, the averages of panel temperature drops were 13.28 ºC, 11.64 ºC, 11.06 ºC, and 9.14 ºC for TiO2-water, Al2O3-water, CuO-water nanofluid cooled panels, and water-cooled panel, respectively. Finally, appropriate amount of nanofluid cooling not exceeded 0.4% can be recommended in practical application for its benefits on improving the efficiency of system.

Development and economic evaluation of a CPVT system with PHP cooling; An experimental study

In this paper, the experimental investigation of the performance of a concentrated hybrid photovoltaic thermal solar system is sought. Accordingly, there is a parabolic trough concentrator receiver that consists of three components: a triangular duct, photovoltaic cells covering the duct, and a three-turn PHP. The PHP cools down the photovoltaic cells efficiently and regenerates waste heat. The duct is filled with a heat transfer fluid surrounding the PHP’s evaporator. The condensation section of the PHP is located outside the solar concentrator. Using a one-axis polar mechanism, the concentrator tracks the sun from east to west. The system experiment setup was fabricated and tested outdoors in Tehran’s climate. Different heat transfer fluids, including Glycerine, Ethylene Glycol, and Calcium Chloride water mixture, were tested. Given the enhancement of PHP performance, a variety of working fluids were tested, including graphene oxide nanofluid/water, acetone, and pure water. The experiments showed that graphene oxide nanofluid/water mixture provided the highest thermal performance. With the use of graphene oxide nanofluid/water (as a working fluid) and glycerine (as heat transfer fluid), experiment results showed a decrease of 7.84 °C in PV temperature and a consequent increase of 21.85% in electrical efficiency in best condition. Furthermore, the provided cooling system recycles a maximum of is 190.4 kJ of thermal energy equivalent 52.5% thermal efficiency, increasing overall efficiency by 74.35%. Lastly, the IRR of 65.41%, PBT of 1.04 years, and LCOE of 1.84 $/kWh demonstrate appropriate financial profitability.