Utility-scale solar PV performance enhancements through system-level modifications
Performance of solar PV diminishes with the increase in temperature of the solar modules. Therefore, to further facilitate the reduction in cost of photovoltaic energy, new approaches to limit module temperature increase in natural ambient conditions should be explored. Thus far only approaches based at the individual panel level have been investigated, while the more complex, systems approach remains unexplored. Here, we perform the first wind tunnel scaled solar farm experiments to investigate the potential for temperature reduction through system-level flow enhancement. The percentage of solar irradiance converted into electric power depends upon module efficiency, typically less than 20%. The remaining 80% of solar irradiance is converted into heat, and thus improved heat removal becomes an important factor in increasing performance. Here, We investigate the impact of module inclination on system-level flow and the convective heat transfer coefficient. Results indicate that significant changes in the convective heat transfer coefficient are possible, based on wind direction, wind speed, and module inclination. We show that 30–45% increases in convection are possible through an array-flow informed approach to layout design, leading to a potential overall power increase of ~5% and decrease of solar panel degradation by 0.3%/year. The proposed method promises to augment performance without abandoning current PV panel designs, allowing for practical adoption into the existing industry. Previous models demonstrating the sensitivity to convection are validated through the wind tunnel results, and a new conceptual framework is provided that can lead to new means of solar PV array optimization.
The operating temperature has a significant effect on the cost of photovoltaic (PV) solar energy. PV panels in the field often operate 20–40 °C above their rated temperatures, and each rising degree decreases both panel efficiency and lifetime 1,2,3. For example, in a typical utility scale PV installation in Colorado, summer ambient temperatures average 28.6 °C and the panel nominal cell operating temperature (NOCT) averages 48.2 °C with summer maximum module temperatures reaching 59 °C. This increase becomes important as a 5 °C increase in temperature with respect to the standard test condition (STC) has the effect of decreasing the panel efficiency 1–3% 4,5. Therefore, these sizeable effects make temperature reduction a key strategy on the roadmap to lowering solar energy costs 6. Two general strategies exist to try to achieve this goal. The first is to maximize cooling through enhanced convection/conduction and radiative cooling, and the second minimizes the thermal load through increased efficiency or advanced reflectance 7. A variety of techniques have been proposed to lower panel temperature for individual panels including phasechange materials, heat sinks, and active methods such as air and water cooling 8. For example, Krauter 9 used spray water (4.4 L/min m 2 ) to increase the performance of the M55 module by 1.5%. Abdolzadeh and Ameri 10 improved the performance by 1.8%. Odeh and Behnia 11 reduced the operating temperature and electrical yield increased in the range of 4–10% by spraying 4 L/min. Hosseini et al. 12 showed an increase in the efficiency of PV modules of 60 W by 3.66% with spraying water. However these methods have not proved to be commercially viable due to their extra cost and/or maintenance requirements 13,14. Within the first strategy, no work has been performed to investigate means to enhance convective cooling of solar modules at the array-level 13,14,15,16. despite the potential gains of this approach 7.
In existing full scale solar arrays, varying system-level parameters such as row spacing, inclination angle, height from ground, and row orientation relative to predominant wind direction is impractical. Up until now, no scaled platform has existed for studying enhancements at the array level. This lack thereof has meant that any study on the array level has been limited to sensitivities of the convective heat transfer on wind speed 17,18. The experimental platform introduced in this work provides for the first time the opportunity to shift the FOCUS from the individual panel to the array. Through this new lens, we examine the fluid flow and heat transfer in a large scaled solar array, beginning with fundamental parameters of inclination angle and wind speed. Flow passing over and through a solar array can interact with the panels in distinctly different manners depending on these two parameters. Certain inclination angles can cause more turbulent mixing, increasing convection heat transfer while others redirect the flow in directions that can enhance or reduce convection. Here, we seek to develop an understanding of the fluid mechanisms that drive the heat transfer, and determine what magnitude of temperature reductions are possible through enhanced array convection. Further, the present study provides an opportunity for future work by examining the key parameters that govern heat transfer in large solar farms and ultimately informing improved layout designs 19. This approach to temperature reduction is particularly attractive as it is passive, and does not require costly new technology developments or maintenance. Thus, large solar farms with enhanced convection have the potential to have temperature reductions whilst still providing a similar aesthetic and utilizing existing labor skillsets to install and maintain.
Solar Array Experimental Platform
To be able to explore optimizations in the system-level parameter space, a new experimental platform was required. This solution had to scale properly to utility-scale, have sufficient rows to ensure flow convergence, and be highly configurable to a variety of angles, spacings, ground-mount heights, and wind directions 20. The resulting platform is shown in Fig. 1, where 40 individual panels are arranged into 10 rows. Key to satisfying scalability is the recreation of an incoming flow mimicking the atmospheric boundary layer, achieved with tapered blockage elements (strakes) followed by surface roughness elements (chains). Flow field measurements with high-spatial and temporal resolution were achieved with particle image velocimetry (PIV). This experimental platform allowed us to explore a question that was previously impractical to answer at full scale and identify the highest reward paths to PV farm layout optimization for lower operating temperatures.
In addition to mimicking the atmospheric boundary layer, further steps were taken to validate the applicability of the experimental setup to utility scale solar farms. Convergence tests were completed to analyze the flow and convective heat transfer coefficient to ensure that enough rows were present to create a fully developed flow. It was found that the flow became fully developed after 6–7 rows, and thus 10 rows were used, and data taken between the 8th and 9th rows. Scalability of the experiment was determined through experiments examining flow structure changes with inflow wind speed/Reynolds Number. Reynolds number independence was observed. Demonstrating this is critical to establish scalability, since a comparison of the Reynolds number between a full scale farm and the experimental setup is approximately equal to the size ratio of the panels (full scale to scaled panels). Hence, dynamic similarity on the individual panel level will certainly not be achieved. However, the FOCUS of this study is on the large-scale transport properties of the turbulence, where Reynolds number effects are known to be less dominant.
Using the solar array experimental platform presented above, we performed a series of experiments to determine the relationship between the panel inclination angles, inflow wind speed and convection heat transfer coefficient. Four inclination angles were chosen with respect to the main streamwise direction, representative of standard arrangements at different latitudes: [15°, 30°, 45°, −30°]. The negative inclination angle represents the same standard solar farm with 30° inclination for which the wind inflow is perpendicular to the back side of the panels. Figure 2 illustrates the flow field (normalized, ensemble-averaged velocity magnitude spatial contours and Reynolds shear stress) for the four inclination angles.
Characterization of momentum and heat transfer
Normalized velocity magnitude \(\sqrt^^/_\). or the resultant velocity vector normalized by the freestream velocity, is compared for the different cases beginning with top row of Fig. 2. U and V refer to the streamwise (horizontal) and wall-normal (vertical) directions, and u’ and v’ refer to the fluctuations about the mean in these directions. As expected, a well defined wake region is observed directly behind the panels for all angles. As indicated by the flow vectors, even a flow reversal can take place in several cases directly behind the panels. On this regard, it is of interest to realize that the spatial area with recirculating flow behind the panel increases with inclination angle, indicating an enhanced velocity deficit. Further, there is a reduction on mean advection (or transport of momentum by the bulk fluid motion) at all heights above the panel as the angle increases from 15° to 45°.
Comparing two of these configurations, the 30° case (Fig. 2a) with the −30° case (Fig. 2d), significant variations are observed in the sub-panel region. In comparison with the 30° case, the −30° case exhibits sub-panel velocities higher by almost 40%. This has great importance to the resulting heat transfer, as the extent of the cooling that can be accomplished with any given array configuration depends on the way in which incoming flow is divided into array flow and bypass flow. We refer to array flow as that flow traversing underneath and between the panels, while we refer to bypass flow as the incoming flow that does not or only slightly interacts with the array. When angled at −30°, the panels effectively act as downward baffles, guiding flow that would have been deflected upwards and channeling it underneath the panels, as demonstrated in the streamlines in Fig. 2a through 2d. The net effect is that an increased volume of fluid interacts with the panels compared with the 30° case (i.e. an increase in array flow relative to bypass flow). Further, the increase in streamwise subpanel flow shown in Fig. 2d is explained in part by the change in the Reynolds shear stress shown in Fig. 2h. The magnitude of the Reynolds shear stress is an indication of the turbulent mixing in the flow, and the sign of the shear stress indicates whether the flow is being entrained upwards or downwards (−). The quantity is normalized by the square of the freestreem velocity. Increased values of \(-\langle ^ \prime^ \prime\rangle /_^\) above the panel are directly proportional to increases in the vertical transport of momentum, which is an effective mechanism for replenishing the mean kinetic energy throughout the panel array, including the region below the panels. Further, this enhanced vertical momentum exchange facilitates a steady supply of cooler air from aloft to interact with the solar modules.
Therefore, based on the results from Fig. 2, we introduce a conceptual connection between the convective heat transfer coefficient and the solar farm turbulent flow structure. This is schematically represented in Fig. 3. Increasing heat transfer through arrays of heated elements depends largely on two properties. the bulk mean velocity through the panels and the turbulent mixing. Concerning the first, bulk advection is largely a function of the local wind speed over the upper and lower surfaces of the solar farm, and can be augmented through spacings that prevent dead-spots and encourage key flow channels. Turbulent mixing on the other hand increases interaction with the overhead flow, and causes the turbulent boundary layer to grow more quickly over the surface of the panels and have larger convection coefficients due to the enhanced mixing of air masses with different temperatures. Figure 3 illustrates these two concepts and their effect on overall heat transfer. Three forms of interaction characterize how solar farms interact with the incoming flow. In the triple layer flow shown at the top of Fig. 3, a steep panel inclination angle causes two competing effects; large eddies are shed from the edges of the panels, increasing turbulent mixing while increased area normal to the incoming flow creates a larger velocity deficit. For the double layer flow, minimal interaction is fostered between the panels and the overhead flow, as no significant turbulence is induced. For both the triple and double layer flows, there is limited encouragement for the flow to pass underneath the panels. This is contrasted with the single layer flow shown at the bottom of Fig. 3, which is applicable to the case where the flow is coming at the farm from the rear. In this case, the panels act as downward baffles, increasing the Reynolds shear stress above the panels which in turn pulls the flow that would have been deflected upwards for the positive inclination angle cases into interaction with the panels.
What is a Utility-Scale Solar Farm?
Defining utility-scale solar farms is challenging because it depends on location, size, voltage and commercial solar interconnection type, final sale location, state laws, and solar electricity method.
Utility-scale solar farms typically produce 5 MW of power or less and are bigger than community solar farms. They cover acres of ground and have thousands of individual solar panels. These PV power project designers often arrange the panels to create eye-catching forms because they are big enough to be seen from an aircraft. For instance, Walt Disney World designed a solar farm and shaped it as Mickey Mouse.
A primary distinguishing feature of the utility-scale solar farm is that they sell the electricity directly into the electrical grid. Utility-scale solar projects are usually in front of the meter as opposed to distributed generation systems behind the meter.
It is a system matched with the facility’s energy load and directly provides the facility with electricity. The utility–scale solar facility uses solar energy to produce electricity and feeds it into the grid to power a utility.
Almost all utility-scale solar installations have a power purchase agreement (PPA) with a utility, ensuring a market for their electricity for a specific period.
The Capacity of Utility-Scale Solar Farm
Since 2010, the photovoltaic sector has experienced Rapid expansion. By the end of 2018, at least 480 gigawatts of installed solar PV capacity worldwide. In many areas, most of the newly added capacity comes from utility-scale installations rather than distributed systems.
By 2050, according to some recent projections, solar energy will generate nearly 60% of the world’s electricity. The size and amount of power produced by utility-scale solar farms set them apart from other distributed solar choices.
Utility-scale solar farms are solar arrays that can cover many acres of land and have a capacity of up to 1 GW. According to the Solar Industries Association, utility-scale solar installations are now more than a total of 37,000 MV, with another 12,000 MW in development.
Power purchase agreements (PPAs), often used instead of farm ownership by the utility, are used to sell the energy produced to utility buyers. The energy can then be sent to residential or commercial users who are connected to the electric grid by utility companies.
What is a Small Solar Farm?
Residents around a small solar program split the output of a single sizable solar installation called a solar farm or community solar farm. You can sign up for a local or commercial solar farm to start receiving solar energy credits from your utility to reduce your electricity costs.
Small solar uses state renewable energy subsidies to help businesses, tenants, and homeowners cut costs while promoting solar energy in their neighborhoods.
Community solar programs provide a method to participate in the renewable energy revolution and save money for individuals who cannot put rooftop installations on their own houses owing to the initial cost, roof restrictions, or the fact that they don’t own their property.
Local solar farms built with community solar in mind are available for residents to join, allowing them to earn solar energy credits to lower their electricity bills.
Hundreds or even thousands of households can be powered by the energy produced by these massive systems. Even though you aren’t receiving solar energy directly into your home, you are helping in adding that solar energy to the general grid.
Small solar farms can be built in various locations, some of which are vacant. Solar gardens can also be built in landfills and industrial areas. However, they can be outside the center of a sizable open field.
Solar panels can also be built on public structures, including parking lots which act as shared solar systems in several cities. All of these configurations are categorized as community solar systems.
How Does a Small Solar Farm Work?
You can profit from solar power without installing rooftop solar panels with the help of community solar. Clean energy is pumped into the grid by nearby solar farms; locals and companies can subscribe to a farm and receive credit for a portion of its power.
Government incentives have made these incentives available for citizens; you can gain a discount on your electricity expenses when you receive these credits; it is like a price for doing good deeds. A utility, a nonprofit organization, a regulatory body, or a business established mainly to construct and operate a solar farm can initiate or manage a solar community project.
The owner will collaborate with solar developers to choose a suitable location, acquire the necessary licenses, and begin construction. The construction procedure may take months.
The owner then extends an invitation to members of the neighborhood to participate in funding the solar installation by purchasing shares or subscribing to the project. To identify subscribers and oversee their entire project subscription experience, we operate on behalf of the solar farm owner.
When a solar farm is finished, it is joined to a local utility and starts supplying solar energy to the grid of that utility. An electric meter measures the farm’s energy output, converted by the utility into a financial value known as solar credit.
Your monthly community solar membership will produce these credits, eventually reducing the electricity cost on your utility bill. You will continue to pay your current utility company for electricity. Because you are not directly receiving power from the solar farm, joining a solar community program has no impact on your utility or electricity supply. But because of the credits, your bill is reduced.
Consider it a reward for protecting the environment. By promoting solar energy in your state, you’re assisting everyone’s transition to a cleaner, more reliable electric system. Your state offers you a discount on your energy costs in exchange.
To be clear, you do not personally own any part of the farm or its panels if you subscribe to community solar. But because it produces renewable energy, you get a portion of the credits it generates.
Utility-scale solar installation goes automated
Powered by installation robots, on-site assembly line and digital twin software, the Terabase automated power plant construction system aims to boost productivity and cut construction costs.
An automated rover installs solar panels in the Terabase field factory.
Terabase announced it is launching an automated utility-scale solar installation system, dubbed Terafab. The company describes the service as an automated “field factory” that can double installation productivity.
The installation system makes use of digital twins, logistics software, an on-site digital command center, a field-deployed automated assembly line, and installation rovers that can operate 24/7.
The company also announced the grand opening of a Woodland, California manufacturing facility; “a factory to make factories.” The facility is currently manufacturing the first gigawatt Terafab assembly line with capacity to make more than 10 GW of Terafabs per year.
Terabase said its system will double labor productivity when compared to traditional utility-scale installation methods. The system offers high-throughput, 24/7 operation, and modularity to enable Rapid ramp-ups and higher solar field construction speeds, significantly reducing project schedules.
“We successfully field-tested Terafab last year, building 10 MW of a 400 MW site in Texas. Today’s launch is the next step forward to Rapid commercial scale-up,” said Matt Campbell, chief executive officer and co-founder of Terabase.
Terabase has partnered with developer Intersect Power, engineering, procurement and construction firm Signal Energy, tracking hardware provider NEXtracker, and solar panel manufacturer First Solar to develop the Terafab facility.
“Not only does our partnership with Terabase bring advanced installation technology to our next-generation Series 7 solar module, but it also enables a closed-loop packaging recycling system consistent with our vision of responsible solar,” said Nick Strevel, vice president of product, First Solar. “The Terafab system is another example of how homegrown American innovation can help accelerate the deployment of solar, enabling our country’s decarbonization ambitions.”
Terafab is pegged for commercial deployment starting in Q3 2023.
The company said that the automated installation system reduces the levelized cost of electricity for utility-scale solar projects. It is also scalable, built on a modular design that can be replicated and deployed quickly.
Terafab reduces the physical safety risk of construction workers by eliminating the need to lift heavy solar panels and steel structures, often in harsh weather conditions, by utilizing automation on a climate-controlled assembly line.
The system may offer a solution to the solar industry’s need to find more qualified installation technicians. A transition to a carbon-free energy sector is going to take a large, well-trained workforce, and readying that workforce may pose a challenge in the near-term, the company states.
The Interstate Renewable Energy Council (IREC) said 89% of solar firms reported in 2021 they’ve had difficulty finding qualified applicants. A recent survey by SolarReviews found that difficulty finding workers was the third-most common concern among survey participants.
Solar now represents 59% of the clean power capacity in development. gaining 4% in share from 2021 to 2022, said the American Clean Power Association. To reach the federal goal of 100% carbon-free electricity by 2035, the solar workforce will need to more than double from 255,000 to over 538,000, said the Solar Energy Industries Association (SEIA). Automation may offer a solution to the labor shortage as the nation works to rapidly decarbonize.
In August 2022, Terabase Energy announced a 44 million Series B financing from Breakthrough Energy Ventures and Prelude Ventures, with participation from SJF Ventures and other previous investors, bringing the company’s total funding to date to 52 million.
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Ryan joined pv magazine in 2021, bringing experience from a top residential solar installer, and a U. S.
Types Of Grid Scale Solar Projects
There are two primary solar power technologies in use at utility-scale solar plants.
Photovoltaic (PV) Solar Farms
These solar modules use sunlight to generate a current of electricity and are the same technology commonly used for residential and commercial solar PV systems. The solar cells contain a semiconductor material, typically silicon, and produce direct current (DC) voltage. Then, an inverter converts the power to alternating current (AC).
The greater the intensity of the sunlight, the greater the flow of electricity. The PV panels on the market today are commonly between 16% and 23% efficient; solar panel efficiency has increased significantly over the last couple of decades.
Concentrated Solar Power Plants
This technology uses mirrors to concentrate the sun’s heat to drive steam turbines or engines, producing electricity. In addition, plant operators can store the thermal energy generated from concentrated solar power (CSP) plants to generate electricity later. There are several types of CSP technology in use in the United States, including parabolic trough, compact linear Fresnel reflector, power tower, and dish-engine.
Challenges For Utility Solar
Although utility-scale solar is growing significantly, there are project development hurdles to content with.
Permitting For Utility-Scale Solar Projects
Unfortunately, permitting issues can delay projects or even stop them from progressing. Congested interconnection queues can slow renewable energy project development because interconnection studies can be time-consuming and expensive. Interconnection timelines and costs are among the biggest hurdles to Rapid utility–scale solar growth.
Transmission Capacity Expansion
Developers often locate utility-scale renewable energy projects far from load centers, so they require transmission capacity expansion to reach electricity markets. Therefore, generation interconnection requests often require transmission network upgrades.
Solar developers often foot part of the bill for needed improvements to the electricity grid, despite many of these upgrades creating system-wide benefits. These costs drive up the cost of solar electricity and create uncertainty as they can be challenging to anticipate.
Supply Chain Issues
Equipment shortages and bottlenecks have impacted the solar market, causing some projects to be delayed or even canceled. For example, solar panels from China are subject to antidumping laws and import tariffs. A recent investigation into numerous solar manufacturers in Southeast Asia, including Jinko Solar, Hanhwa Q Cells, Canadian Solar, and Trina Solar, has shown slowed imports to the United States. In addition, shipping bottlenecks and supply chain shortages have also been problematic.
Solar power plants require land. Unfortunately, large plots of land are often most available and affordable in rural areas far from load and population centers. Solar developers often lease land from landowners for the project’s lifespan or, in some cases, they purchase the land.
Utility-Scale Solar Installations Are Essential
As concern about greenhouse gas emissions and climate change continues to rise, utility-scale PV plants provide a solution. As the installed capacity of solar photovoltaics increases, the demand for fossil fuel power plants decreases. In addition, battery storage systems at solar plants enable solar power to meet peak energy demand, even when the sun isn’t shining.
Utility-scale solar comes with it’s own permit and engineering nuances and challenges – GreenLancer has a network of designers and engineers who specialize in AHJs across the country to navigate the process with simplicity.