Opportunities, Strategies & Best Practices for Electrical Balance of Systems Optimization
Inside this Article
As module prices have fallen—dropping roughly from $4 per watt in 2006 to $0.60 per watt in 2016—the costs for BOS components in general and electrical BOS (eBOS) components in particular have become a larger percentage of installed PV system costs. Moreover, the industry has largely identified and leveraged the low-hanging fruit of eBOS cost reductions, such as increasing the nominal system voltage on nonresidential systems from 600 Vdc to 1,000 Vdc and making widespread use of aluminum rather than copper conductors on large-scale systems. So where will eBOS cost reductions come from next?
For this article, I reached out to two stakeholder groups—solar project engineers and equipment vendors—to identify opportunities, strategies and best practices for eBOS cost reductions. The myriad responses, organized here according to different perspectives, illustrate that squeezing additional value out of commercial and large-scale PV systems is very much a multidisciplinary effort that requires holistic thinking. Design responses also vary depending on whether owners are most concerned about low up-front costs or the impact of O&M costs over time.
Large-Scale Project Perspective
Blue Oak Engineering (BOE) is a multidisciplinary solar engineering firm based in Davis, California, with both civil and electrical engineers on staff as well as in-house project management and construction teams. The company has extensive experience engineering, constructing and operating large-scale PV assets. BOE’s director of engineering, Bill Reaugh, connected SolarPro with a cross-section of the company’s subject matter experts.
SP: What eBOS optimization strategies have been most effective for BOE in recent years?
BOE: BOE has identified cost savings in two major areas: array harmonization, whereby we keep the dc blocks of a project as homogeneous as possible, and the specifics of wire management within the block. In the first case, we reduce design customization in the project, which cuts down engineering and installation time and increases installation quality since it leaves fewer opportunities for mistakes. Savings in the second case come from paying attention to wire management details and identifying the most appropriate approach for each project.
Wire management strategies include placing combiner boxes so that homeruns to the inverter are straight or have the fewest number of right angles, sharing trenches with the largest number of conductor runs possible, using direct-buried conductors rather than conductors in conduit, and specifying racking with integrated grounding or integrated string wire management. While these approaches have all yielded procurement and installation cost reductions, not every wire management technique is applicable on every project. For example, using direct-buried cables in areas with a high concentration of underground rodents may lead to maintenance headaches.
—Jayme Garcia, PE, senior engineering project manager
SP: What are the most promising opportunities for additional eBOS cost reductions in the near term?
BOE: There is some potential for savings when increasing from 1,000 Vdc to 1,500 Vdc. However, these savings are not as significant as the move from 600 Vdc to 1,000 Vdc, which represents a 66% increase in string length and a 40% reduction in the number of module strings. Moving from 1,000 Vdc to 1,500 Vdc represents only a 50% increase in string length and 33% decrease in string count. Moreover, an increase in eBOS component costs may offset the potential savings associated with this reduced string count in the near term because 1,500 Vdc is not a standard voltage rating for electrical equipment. At present, equipment rated to 2,000 Vdc commands a premium price compared to that rated to 1,000 Vdc.
A second area that could improve project economics is SCADA integration, which has so far been largely an afterthought in project design and planning. This lack of foresight can lead to cost and schedule overruns when you do not plan well to allow time for integration and testing. If you consider SCADA early in the process, you can better harmonize the design with the rest of the project, minimizing cost and schedule impacts.
—Jayme Garcia, PE