2016: State of the Art
The horizontal single-axis tracker and its supply company

The horizontal single-axis tracker (HSAT) has evolved commercially since the 1980's, when 357 MW of solar thermal electric "tube-and-trough" HSAT CSP power plants were constructed in California's Mojave Desert. 

Fast forward ten years, when HSAT commercialization ramped up for PV applications. In some cases, the decision matrix regarding PV fixed-array versus tracking-array began to favor tracking, largely due to the high cost of silicon PV and the HSAT performance promise of "22% to 32%" increased irradiance capture. It's the classic bang-per-buck product development driver.

The primary downside-tradeoffs of tracking were the perceived increased risks and costs of mechanical complexity, in contrast to the beautifully simple fixed application. Fix it in place properly, and mechanical maintenance was virtually a non-issue for the next twenty-five years. Tracking, on the other hand, meant motors and gears, moving structures and power bills, as well as the associated equipment controllers, protections, boxes, cabling, and monitoring, not to mention maintenance and replacements over time. If it didn't work, who was left footing the bill?

The early commercialized HSAT PV equipment was a linked-row drive system type, with approximately one grid-powered motor per 500 kWp of PV mounted on several linked torque-tube tracker structures. This design can still be seen in the HSAT PV market.

Fast forward to the present. The independent-row HSAT PV design, with about five years in commercialization, is gaining remarkable traction in the market, largely the result of a combination of features that augment the bang-per-buck driving force. 

Decision matrix parameters have evolved as well. The mechanical downside is largely accepted now that the installation and operation track record of HSAT PV is fulfilling its promise. In the current market, duly diligent entities will finance HSAT PV projects within the risk-averse finance and utility sectors, and moreover, while applying rigorous EPC criteria. 

They seem to work after all. Market analysts believe HSAT will take the lion's share of the anticipated US utility-scale PV installations market through 2020.

Those considering HSAT, and pursuing best bang-per-buck on the bottom line of yield, know that not all HSAT PV equipment is the same. They should insist on the following three key and interrelated aspects:
Highest yield potential, which is more than just power-fill on the tracker. The independent-row type provides greater site-fill yield potential. Look for 120⁰+ tracking range and configuration options providing highest tracker power-fill.
Land-use options, which have direct impact on yield potential. Look for high-slope tolerance on the North-South axis where yield may be increased, but where it may be expensive or not feasible to build. Look for greater installation tolerance on irregular land (short-steps, contours, not-square property) combined with shorter standard-blocks that will reach further into increased yield; along with the environmental and economic benefits of less grading and other civil works. 
Low-cost installation and maintenance. Look for wide assembly tolerances at the crucial pile-tracker interface, where misalignment can cause construction refitting and delay. Look for a lower piles-per-MW count to reduce first costs and environmental impact of construction. Look for self-powering provisions, wider aisles between tracker-rows, and the latest communication technology in local and wide area networks. 

PV specialist companies of the US utility-scale sector have evolved, as well. 
In the 90's, a Berkeley-based PV specialist broke some molds with "value engineering" steps that got us over the paradigm of satellite applications at any cost, in favor of pragmatic construction practices on earth; corresponding with the emergence of large-scale grid-connected PV applications.  

Greater market materiality heralded the entry of larger and non-specialist companies, and the crucial financial investment sector. Global reach was extended, and project bankability was established, for viable players. 

Today global reach is indispensable, and, thanks in part to technology, has become more accessible to a less extensive corporate structure. For better or worse, immediacy has become the norm. That, in turn, demands innovation in customer service and communications, as well as tapping into some astounding business technology.

Company experience is a vital credential. As of 2016, a preferred supplier threshold is likely 10+ years in the sector, with GW's of HSAT PV in the past few years. The scale of the 357 MW Mojave project, while unprecedented in the 80s, represents just a good quarter for one global HSAT PV supplier today. 

Companies must maintain a current knowledge and skill set to keep pace with the constant change and tremendous growth in the PV sector. The need for good people is ongoing, fed by the excellent quality of professional candidates. PV is now 20 years solidly into mainstream academics - a vast improvement from the 90's.

Although PV remains far from its potential in application for various reasons, this sector now has the people and product to deliver the goods.

Tim Murphy is the communications manager at Soltec America, LLC

Soltec America, LLC | www.soltec.com