SOLAR TRACKER SITE DESIGN: HOW TO MAXIMIZE ENERGY PRODUCTION WHILE MAINTAINING THE LOWEST COST OF OWNERSHIP Comparative study examines the impact of power density, ground coverage, and range of motion on energy production, capital cost and return on investment at utility-scale solar sites. AUTHOR Stephen Smith, Principal, Solvida Energy Group REV 1.0 October 2017
SOLAR TRACKER SITE DESIGN: HOW TO MAXIMIZE ENERGY PRODUCTION WHILE MAINTAINING THE LOWEST COST OF OWNERSHIP Executive Summary Across the United States, Power Purchase Agreement (PPA) contracts are being signed at increasingly lower rates, making it challenging for solar asset owners to maintain a viable return on investment. This has increased the need for developers and owners to fully maximize energy production from photovoltaic (PV) panel systems to meet competitive PPA targets. Solar tracking systems are capably fulfi lling that need by boosting energy production and providing owners with a more optimized power delivery curve. While it s clearly established that solar trackers allow for 15-25% higher energy production over fi xed-tilt solutions, there is still room to further optimize performance. Designing tracker sites and tracker layouts for maximum energy production, while maintaining the lowest cost of ownership, is the next frontier. For solar tracking projects, there are three performance optimization strategies that solar designers can employ to maximize energy production for a given project site: Increasing Row/Area Power Density Optimizing Ground Coverage Ratio (GCR) Increasing Range of Motion (ROM) This paper examines these three strategies in-depth and how they impact energy production, cost, and the levelized cost of electricity (LCOE), at utility-scale solar project sites. The study fi nds that increasing power density is the most effective of the three strategies when implemented in singularity, and by a large margin. In comparison to the other two strategies, optimizing power density was found to be two times more effective at increasing energy production than adjusting a tracker s GCR, and up to three times more effective than adjusting ROM. Resulting impacts on system LCOEs followed a similar trend; the greatest improvement came from increasing power density, followed by adjustments to GCR and ROM, respectively. In addition, the study fi nds that increasing power density in conjunction with optimizing a tracker s GCR can further increase energy production and deliver the lowest LCOE from solar tracker projects. Background and Definitions Energy production from a PV project is maximized when the project s solar modules are positioned exactly perpendicular to the sun, commonly referred to as direct incidence. A tracker s main responsibility is to maintain as close to direct incidence as possible between the modules and the sun throughout the solar day. The challenge for solar tracker designers is to balance cost and land usage with optimized energy production to provide the best LCOE possible. For any tracker project, energy production can be maximized in one or any combination of the three performance optimization strategies discussed in this paper. Power Density Increasing the number of modules per land unit in a single tracker row or site. Ground Coverage Ratio (GCR) Increasing the east to west distance between module rows within a specifi ed plot of land. Range of Motion (ROM) Extending the degree modules can be rotated to track the sun. Site Data The project performance data used in this comparison was derived from PVsyst simulations comparing identical tracker arrays at 3 climatically diverse U.S locations: Fort Mohave, Arizona; Malin, Oregon; and Asheville, North Carolina. The solar modules included tier-1 330W modules and 1000VDC central inverter systems. LCOE determinations were derived using a proprietary LCOE model and current turnkey system pricing for a typical 20MWAC tracker project of $1.15/watt dc. 2
Site Design Layout Strategies & Their Impact on PV Energy Production Increasing Power Density Optimizing Ground Coverage Ratio (GCR) Optimizing, or relaxing, the tracker block s GCR increases the spacing or pitch between rows from East to West. Relaxing a tracker site s GCR is an effective energy boosting design technique because it increases the length of time that the tracker can stay close to direct incidence and limits the tracker s need for backtracking to avoid row-to-row shading. Power density per tracker block is maximized by reducing the space between individual solar modules, as well as the empty space, along N-S tracker rows, and between tracker blocks. This spacing is typically present due to structural gaps and protrusions, and can become wider with tracking systems that require more mechanical and electrical components. Through innovative engineering, some tracker designs have been able to reduce space along each module row, eliminating gaps and dead space throughout the system. Increasing power density along tracker rows results in an energy production boost of 5-6% as compared to other tracker systems. Relaxing a tracker s GCR from 33% to 25% leads to 1.5-2.2% more energy produced from PV panels, depending on specifi c site location. However, because relaxing GCR requires more land for the project, a tracker designer may not be able to utilize this strategy. It is increasingly common that utility-scale solar plants are sited on less optimal project sites with limited land availability and/or land constraints. In addition, since increasing power density allows for a denser tracker block, there s an added advantage of reducing land unit per tracker, whereas the other two performance optimization strategies typically require additional land to be most effective. As a key energy production differentiator, the density advantage lends well to all sites, independent of land characteristics and latitude. In cases where land for a project site is not constrained, higher density allows the site designer to pack in more DC power because of the reduced tracker footprint. For project sites that are land and/or topographically constrained, increasing power density allows designers to locate trackers on areas without undulations or obstructions, and to design projects to avoid grading. KEY FINDING: Increasing power density means site designers and asset owners can add more solar modules per land unit. Estimated costs to add 6% total installed modules is 2.4% of the total project cost. For that additional investment, owners receive a 5-6% energy boost which translates into a LCOE improvement of 3.3%. KEY FINDING: Relaxing GCR has a very minimal impact on the total cost of a project. Relaxing GCR from 33% to 25% has an estimated impact of.05% on the total cost, mostly in the form of additional land occupancy. For that additional investment, owners receive a 2.2% energy boost which translates into a LCOE improvement of 1.8%. Increasing Range of Motion (ROM) Increasing a solar tracker s ROM can allow the project s solar modules to stay as close to direct incidence earlier in the morning and later in the day. However, the amount of available solar radiation in the early and late hours is minimal compared to the rest of the solar day. Additionally, the benefi t of increasing ROM varies greatly by latitude and GCR. In northern US latitudes, tracker systems don t benefi t from additional ROM, especially if they are laid out with typical GCRs between 35% and 45%. In southern US latitudes, tracker systems may benefi t from additional ROM with a GCR below 35%. The benefi t of increasing ROM always needs to be analyzed and balanced with the tracker s GCR design and site latitude. In other words, the case for utilizing an extended ROM as a performance optimization strategy is limited to specifi c applications in only specifi c areas. 3
Typical tilt angles specifi ed by tracker manufacturers are +/- 45 degrees, +/- 52 degrees, and +/- 60 degrees. Increasing ROM from +/- 45 to +/- 52 will result in in an energy production boost of 1%, while increasing ROM beyond +/- 52 is incremental. Increasing from +/- 52 to +/- 60 only increases production by a maximum of 0.25% across the United States, given a 33% GCR. Increasing ROM from +/- 52 degrees to +/- 60 degrees, given a relaxed GCR of 25%, only results in an 0.33% production boost. KEY FINDING: Increasing ROM has a very minimal impact on total project costs, estimated at less than.05%. For this investment, the greatest benefi t is found when increasing ROM from +/- 45 to +/- 52 for 1% boost in energy production, while owners will only receive.25% energy boost when increased from +/- 52 to +/- 60. Thus, LCOE improvement for increasing ROM beyond +/- 52 is negligible. Designing for Maximum Energy Production When designing solar trackers for maximized energy production, increasing power density and/or optimizing GCR are exponentially more effective than increasing ROM. Improving power density alone provides 5%-6% more energy production. Secondary benefi ts can include reducing upfront land costs and operational costs, such as vegetation management by reducing the amount of land to be maintained. When designers combine strategies, increasing power density while also optimizing GCR may achieve an even higher energy production boost. Using a high-density tracker allows designers to free up land space on a utility-scale site. With the additional land gained through increasing power density, designers may be able to relax the tracker s GCR. The end result for combining these strategies is a high-density tracker row footprint with a production-optimized GCR in the E-W direction. Regarding ROM, production benefi ts are limited by geographic circumstances, and it s important to carefully analyze the optimization of ROM vs Density and GCR. As solar trackers vary in their ROM capability +/- 45 degrees, +/- 52 degrees, or even +/- 60 degrees the ability to gain more energy is very latitude-specifi c when exceeding +/- 52. For example, with the reduced available sunshine in booming U.S solar markets, such as Oregon and North Carolina, a 60-degree ROM provides extremely marginal benefi t over a 52-degree rotation resulting in only a 0.05-0.23% gain, respectively. Even in irradiance-rich Arizona the gain is still only 0.25%. Layout Option 1 33% GCR Layout Option 2 33% GCR Layout Option 3 25% GCR Option not available for lower density systems 4
Key Findings It s well known that the most effective means for increasing energy production at utility-scale sites is the utilization of solar trackers, primarily for their ability to allow solar arrays to maintain as close to direct incidence as possible with the sun throughout the day. System owners rely on solar trackers to provide a vital energy boost that helps maintain a viable ROI while delivering energy to their clients at increasingly lower and competitive PPA rates. Tracker layouts can be optimized through three distinct means: increasing power density, relaxing ground coverage ratio (GCR), and extending range of motion (ROM). Of these three performance optimization strategies, increasing power density is exponentially the most effective, yielding a 5%-6% energy gain that translates into a signifi cantly lower LCOE. A 100 MW solar tracker project, utilizing an energy dense design approach can expect to invest $2.8M in additional modules and BOS and earn an additional $10.9M in cumulative revenue at the end of a 20-year PPA contract. Sites with optimized power density can also result in a smaller system footprint which is meaningful for projects that are area or topographically constrained sites. To maximize energy production, combining an increased density with a relaxed GCR results in a highly optimized tracker project that yields maximum benefi ts for the project s fi nancial stakeholders. 5
Appendix TABLES COURTESY OF PVSYST Ft Mohave Arizona Asheville, North Carolina Malin, Oregon ROM Comparison 60-52 ROM Comparison 60-52 ROM Comparison 60-52 ROM 60 52 ROM 60 52 ROM 60 52 GCR 33% 33% GCR 33% 33% GCR 33% 33% Density 100% 100% Density 100% 100% Density 100% 100% DC Size 2.54 2.54 DC Size 2.54 2.54 DC Size 2.54 2.54 MWH 5655 5641 MWH 4340 4338 MWH 5161 5149 KWH/KWP 2225 2220 KWH/KWP 1708 1707 KWH/KWP 2031 2026 Delta 0.25% Delta 0.05% Delta 0.23% ROM Comparison 52-45 ROM Comparison 52-45 ROM Comparison 52-45 ROM 52 45 ROM 52 45 ROM 52 45 GCR 33% 33% GCR 33% 33% GCR 33% 33% Density 100% 100% Density 100% 100% Density 100% 100% DC Size 2.54 2.54 DC Size 2.54 2.54 DC Size 2.54 2.54 MWH 5641 5585 MWH 4338 4309 MWH 5146 5098 KWH/KWP 2220 2198 KWH/KWP 1707 1696 KWH/KWP 2026 2006 Delta 1.00% Delta 0.67% Delta 0.94% Density Comparison Density Comparison Density Comparison ROM 52 52 ROM 52 52 ROM 52 52 GCR 33% 33% GCR 33% 33% GCR 33% 33% Density 100% 106% Density 100% 106% Density 100% 106% DC Size 2.54 2.69 DC Size 2.54 2.69 DC Size 2.54 2.69 MWH 5641 5974 MWH 4340 4579 MWH 5149 5413 KWH/KWP 2220 2218 KWH/KWP 1708 1700 KWH/KWP 2026 2010 Delta 5.90% Delta 5.51% Delta 5.13% GCR Comparison GCR Comparison GCR Comparison ROM 52 52 ROM 52 52 ROM 52 52 GCR 33% 25% GCR 33% 25% GCR 33% 25% Density 100% 100% Density 100% 100% Density 100% 100% DC Size 2.54 2.54 DC Size 2.54 2.54 DC Size (MW) 2.54 2.54 MWH 5641 5729 MWH 4338 4418 MWH 5149 5263 KWH/KWP 2220 2254 KWH/KWP 1707 1738 KWH/KWP 2026 2071 Delta 1.53% Delta 1.82% Delta 2.22% DENSITY ROM GCR Capital Cost 1.20% Capital Cost 0.05% Capital Cost 0.05% Production Benefit 5% Production Benefit 0.025% Production Benefit 2.2% $0.060 Base LCOE $0.060 Base LCOE $0.060 Base LCOE $0.058 Updated LCOE $0.05999 Updated LCOE $0.0589 Updated LCOE 3.33% Lower LCOE 0.02% Equivalent LCOE 1.83% Lower LCOE 6
About Solvida Energy Group Solvida Energy Group (SEG), located in Berkeley, California, is a technical consulting fi rm consisting of experts at building practical and profi table solar projects. Since 2009, SEG has participated in the construction of more than 3 GW of utility-scale solar projects. SEG s innovative consulting approach helps other solar companies make informed decisions to help lower costs and optimize performance. To learn more visit www.solvidaenergy.com or call 1.510.343.5983. 7