Watching the prices recently for utility-scale solar power-purchase agreements has felt a bit like being a spectator at an ultra-competitive Olympic event, where each successive race delivers a new world record.
The headline-grabbing 1.79 cents per kilowatt-hour tender announced in Saudi Arabia this past October is just one indicator of a global trend, in which PPA prices have been steadily dropping. Mexico’s new record-low solar bid for Latin America is another example.
This is a mixed blessing for the solar industry. Price declines are making solar highly competitive with all other forms of generation, which is undeniably good news. However, low and still-falling PPA prices make it increasingly challenging for solar project owners to develop utility-scale power plants that achieve a viable return on investment (ROI).
“We are seeing falling PPA prices, and what that creates with the customer is a desire to reduce overall costs of the system, whether it’s through capital expenditures or operating and maintenance expenses on the projects, or through increased power production,” said John Williamson, executive chief engineer for the tracker manufacturer Array Technologies, Inc. “If they can increase power production without increasing those other two variables, that seems like free money.”
Using trackers to maximize ROI
It’s widely acknowledged that solar trackers are an essential tool for achieving higher energy production -- as a rule, trackers increase energy production by between 15 and 25 percent compared to fixed-tilt racking systems. But while selecting solar trackers alone is an important first step, there are additional steps that should be taken to produce the most kilowatt-hours possible from a utility-scale solar power plant. It’s also vital for the designers of solar projects to carefully consider optimal tracker layouts and site designs, as this can boost energy production by an additional 5 or 6 percent.
Employing optimal design strategies to maximize energy production is especially important in northern areas of the United States, where steeply declining system prices have made solar financially viable despite the fact that solar insolation is so much lower than in places like California and Arizona.
“If you were to look solar availability or solar potential in some of the newer northern markets, you would find that the solar resource is a lot less [than in the Southwest]. Developers need to squeeze every kilowatt-hour out of every project, and they are doing that by utilizing trackers and optimizing their layouts,” said Stephen Smith, principal at Solvida Energy Group, a technical consulting firm that is currently engaged in 1.5 gigawatts of projects around the world.
Smith believes that the particular interest utility-scale solar project developers and owners in northern areas have in utilizing optimal tracker layouts will soon be the norm regardless of geography. Looming tariffs from the Section 201 trade case are part of the reason, though the eventual end of the federal Investment Tax Credit makes it a necessity.
“As the ITC fades away, we are going to be looking at getting more kilowatt-hours out of our systems because the tax piece of a project’s ROI is going to decrease and the production piece is going to get bigger,” he said. “The basic idea behind trackers is you get more production by exposing the modules to more sun.”
The importance of power density
The obvious question for utility-scale solar designers and owners is this: What are the best strategies for harnessing trackers to maximize energy production? A new study, Solar Tracker Site Design: How to Maximize Energy Production While Maintaining the Lowest Cost of Ownership, by Solvida Energy Group uses project performance data gleaned from simulations in three diverse geographic and climactic locations (Arizona, North Carolina and Oregon) to assess these three common tracker optimization strategies:
- Power Density: Increasing the number of modules per land unit in a single tracker row or site.
- Ground Coverage Ratio: Refining the east to west distance between module rows within a specified plot of land.
- Range of Motion: Extending the angle that modules can be rotated in order to track the sun.
According to the report, increasing power density is by far the most effective strategy for optimizing energy production, boosting the kilowatt-hours generated by as much as 6 percent.
Increasing power density can be achieved in two very different ways. One is by simply adding more modules to a plot of land by eliminating access roads used to maintain a solar power plant. “That’s easy. Anybody can say, ‘Let’s get rid of a road,’” said Smith.
“But it also comes at a cost,” he added. “You increase your time getting from one point to another, and you have to balance that access with local permitting and fire department requirements.”
Improved tracker design, improved energy production
What’s harder, but ultimately more effective, is using trackers that are designed to improve power density. Array’s latest tracker does that by eliminating what are known as “dead spaces.”
“Those are any linear areas on the tracker that don’t have a solar panel. Many of our competitors have spaces for motors and bearings, but we have panels on top of all of that, which minimizes the gaps between panels so that we can increase the area where you can mount panels by 5 to 10 percent,” said Williamson.
Making use of trackers to improve power density is also a compelling strategy because it allows for the higher energy production that makes low PPA prices viable in markets where large, flat expanses of land are not available.
“We are working on a few projects where a developer has a piece of land that they want to put solar and use trackers on, but it’s full of these hilly areas with ravines running through them, and it’s hard to lay it out in such a way that you avoid doing major grading of the slopes,” said Williamson. “It becomes important to be able to look at that site in terms of the densest form factor possible, because if you have a product that takes up more land, then you may have to do much more grading to fit the same amount of power on the site.”
Array makes a tracker with a linked articulating driveline, which Williamson says is like the driveline under a car. “It has two joints on either end, and a telescoping driveline in the middle, so if you move it, it can accommodate different property slopes by moving that driveline north-south, or up-down, at different angles,” he said.
In its research, Solvida found that while there are certain instances when increasing ground coverage ratios and expanding a tracker’s range of motion can provide a boost to energy production, the improvements can often be limited to very specific sites and conditions.
But Williamson said he’s already seeing more instances where a mix of tracking configurations and optimization strategies are employed on a single project -- an understandable development if utility-scale solar is to be financially viable in any geography or climate.
“One of the innovations that we are working on is some different flavors of the same product. If you have some aspects of your site that don’t fit our larger footprint system, we will have a smaller footprint system to fit in those areas,” he said. “Other parts of the site may have a north-facing slope where it gets so steep that you don’t want a tracker on it at all, so you might have half tracker and half fixed-rack. I think that is how things are going to develop.”
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