Designing for Value in Large-Scale PV Systems

Designing a high-value system is rarely about maximizing total production or specific yield, but is instead a process of optimizing economic performance based on customer expectations.

Booming demand for large-scale PV power plants in the US has required an evolution in solar project developers’ and contractors’ approaches to system design and engineering. Today, not just pure-play solar enterprises but, in growing numbers, power plant construction companies are building the world’s largest power plants in the southwestern US. These companies are outfits with massive balance sheets that have built thousands of megawatts of traditional and thermal power plants but are somewhat new to solar. Designing a PV power plant presents unique opportunities, challenges and risks compared to traditional power generation.

In this article, we discuss some of the strategies and approaches we have found useful in helping EPC contractors and project developers maximize the value of their utility-scale solar projects. Ultimately, our goal is to ensure that they view solar power as a mainstream solution for meeting future energy demand.

Evolution of Value-Based Design

Not even a decade ago, we would crack open a bottle of champagne to celebrate the completion of a 100 kW rooftop project. Projects like the 1,900 kW installation on the Googleplex rooftop, completed in 2007, were really big deals—not just because of their size, but because for the first time solar projects in the US were incorporating complex design considerations to maximize value for customers. Until then, most solar projects were too small to justify significant project design consideration.

For example, if you were going to build a 5 kW rooftop system at $10 per watt, it made little sense to invest much time in analyzing product performance data and tweaking design levers. You simply would not get a decent return on your time and energy, even if you did manage to improve the system’s energy yield by 10% with no additional equipment costs. Consequently, engineers at the time kept it simple by following some crude rules of thumb to maximize the energy output of their systems, such as installing fixed-tilt arrays facing due south with a tilt angle equal to the site latitude. Design flexibility was limited because the homeowner’s roof dictated the size and shape of the solar array. Installers could do little (short of building a new roof altogether) that would allow for a more sophisticated and productive design.

With the development of the commercial market, where rooftops were often a hundred times larger than those of private homes, for the first time design became a game worth playing. The prospect of increasing return on these larger projects, by even a few percentage points, warranted investment in analytics, equipment research and project design. This was an exciting time to be a project integrator. Against the backdrop of emerging solar-friendly utility tariffs featuring unique time-of-day or time-of-delivery (TOD) rate structures, to maximize project value PV designers started tweaking design levers such as rooftop orientation, power density, module tilt and inverter efficiency. Still, space and form constraints meant they could pull a limited number of design levers to improve project economics. It was a bit like playing checkers: The game involved some strategy, but it did not allow the great players to really distinguish themselves.

The game changer was the advent of the utility-scale solar market, characterized by megawatt-scale projects, which forced designers to give up checkers and start playing chess. Maximizing value for a massive, multimegawatt, open-field PV project requires designers to consider a much wider range of design levers, variables and permutations. For one, the game board itself is not defined at the outset. Unless virtual net metering is an option, designers working on a commercial solar rooftop project know exactly where they must build the array. However, utility-scale project developers have to start with site selection and control. The ability to choose and secure the right location is one of the single biggest drivers of project success. To a greater extent than for a gas power plant or other conventional generators, a move of as little as 10 miles in any direction can significantly impact the success of a solar generation facility. Whether due to microclimates, topography, the presence of endangered species, or proximity to transmission infrastructure, ROI can vary dramatically over a mere few miles.

How to Design for Value

Major design challenges begin once the developer has secured and permitted the site and signed a PPA with an off-taker, the entity that will purchase the solar-generated energy. At this point, EPCs huddle with their equipment vendors, especially experienced module manufacturers, and develop a game plan to construct the highest-value solar power plant possible. This design team must also assess owner requirements and account for the risk appetites of project stakeholders.

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