Q & A – Webinar: Maximizing PV System Performance with Single-Axis Trackers

By on July 30, 2018

Watch the webinar below. To download the webinar slides directly, please click here

 

For those who submitted questions during the webinar, thank you. We’ve compiled your questions and answered them below: 

Q: Regarding TrueCapture™, what does 3-4% more energy refer to? Is it 3-4% more than other rows at the site without TrueCapture enabled or is it 3-4% more than modeled performance?

A: The reported gain is measured by comparing TrueCapture and standard tracking on alternate days on the same block of tracker rows during the assigned testing period. 

Q: Does the TrueCapture system utilize feedback control (or another real-time control strategy) or is the tracking pattern pre-programmed based on specific site layout and topography?

A: TrueCapture utilizes real-time feedback as well as pre-programmed metrics. 

Q: Do TrueCapture and bifacial change the optimal ground cover ratio (GCR)/inter-row spacing?

A: Bifacial applications and TrueCapture may impact design parameters like GCR. A system level evaluation can be performed to determine optimal design when bifacial panels are used with TrueCapture.

Q: What technology do you use to recognize that there is diffuse light on the site?

A: We use a variety of methods to measure and calculate diffuse fraction at a site.

Q: The experimental results showing TrueCapture gain are impressive. How do you predict, in a forward looking manner, TrueCapture’s benefit? How can an independent third-party predict the benefit?

A: We’ve developed models to simulate the predicted benefit for a given typical meteorological year (TMY). NEXTracker runs these models to create benefit estimates on a project by project basis. NEXTracker has completed Independent Engineering validation of our prediction models. Please contact NEXTracker sales for an IE referral.

Q: I assume diffuse tracking is via light/photo sensor. Is there a risk of improper values and tracking errors due to sensor soiling from dust or other weather conditions? How do you handle and mitigate that?

A: We have redundant measurement capabilities at any given site, and data filters and algorithms that account for any invalid measurements.

Q: How can we ensure positive impact of the backtracking gain (row-to-row) in estimation stage (i.e. is the system size needed?)

A: NEXTracker estimates the expected TrueCapture gain using topographic information and project details. Please reach out to NEXTracker sales for an estimate on your project

Q: What additional energy yield modeling tool is needed to model TrueCapture or can tools such as PVsyst suffice?

A: NEXTracker has developed our own internal models to simulate the predicted annual benefit.

Q: When you mention getting “financed” with TrueCapture, what does that look like? What boosts are being underwritten and what are the additional hurdles financiers need to see before backing such boost?

A: Independent Engineers in the solar space are validating and providing TrueCapture gain estimates. Production gain estimates validated by or provided by IEs are typically financeable. We can direct you to an IE if you need a reference.

Q: For an existing NEXTracker site, can TrueCapture be deployed? Is it only a software change or does hardware need to be installed?

A: Yes, TrueCapture can be deployed to existing NEXTracker projects. It consists of a set of software, hardware and firmware additions that we deploy to enable TrueCapture at your site. 

Q: With TrueCapture, are you clawing back to the modeled performance on systems which may have been under-performing, or are you increasing the production compared to what was modeled in the design phase?

A: TrueCapture increases the production compared to standard tracking on any given site. If you have undulating rows and the plant simulation assumed a flat terrain, your (standard tracking) model will likely overestimate production. Some project owners apply a derate factor for undulating or sloped terrain, but this is not a common practice in the industry. 

Q: How do you include surface undulation conditions in the model in order to represent TrueCapture advantage?

A: We’ve developed our own internal models to simulate the predicted annual benefit.

Q: How does TrueCapture detect diffuse light versus shade avoidance so that it can do the transition properly?

A: It uses a variety of methods to detect and evaluate the combined effects of shading and the diffuse light fraction.

Q: How does TrueCapture row-to-row gain decrease when using half-cell modules (less shading impact)?

A: TrueCapture operation for split cell module designs is different compared to full cell module designs. Both versions generate meaningful gains.

Q: Most wind tunnel studies model the tracker tilt angle as consistent throughout the array. With TrueCapture’s diffuse tracking changing the tilt angle of one row relative to the adjacent rows (sometimes significantly), how does this affect the wind loading on the tracker?

A: Wind stow always has priority over tracker operation, regardless of whether TrueCapture is employed. Our trackers move to a defensive wind stow position if wind stow criteria are met. 

Q: On a percent basis, what is the cost difference between TrueCapture and NX Horizon™?

A: NEXTracker will provide a price estimate for NX Horizon and TrueCapture for your project location and specifications. Please contact NEXTracker sales for more information.  

Q: Is it possible to power the controller directly from the string of modules (instead of battery) and keep the battery as backup supply for the controller?

A: NX Horizon is self-powered and utilizes a dedicated PV module for tracking power. In normal operation, the battery does not power the trackers, it is simply a backup.  

Q: Have you tried 2H arrangement for bifacial with short side support – when allowed on loading aspects?

A: Module manufacturers do not typically allow mounting to the short side of the module and such an arrangement is generally not cost effective. 

Q: What is the net additional energy gain of the NX Horizon tracker in terms of LCOE? Does the gain presented include a reduction of the cost of the tracker in addition to the panels?

A: We consider bifacial applications as an increase to annual energy production given the same balance of system equipment, not a nameplate power increase of the panels or reduction in BOS costs. 

Q: What is albedo gain and how does it occur by design?

The bifacial gain is the amount of annual irradiation which is received by the rear-side of the PV panels, relative to the front side irradiation. The albedo factor of the ground is one of the most important factors determining how much bifacial gain should be expected at a particular site, along with the tracker height/width ratio.

Q: Does NEXTracker have any plans to add a high albedo reflective material to the rear or attached to the tracker itself?

A: NEXTracker is exploring a range of optimization opportunities to take further advantage of bifacial panel technology. Stay tuned.

Q: In a 2P tracker with a gap in the torque tube, you can see an increase in irradiance. Do you consider this gap?

A: While creating a gap in the center of a 2P tracker may increase total back-side irradiance, it also increases the effective E-W ground cover ratio (GCR) of the array, meaning more backtracking will be required. We expect that for most sites, the improvement in rear-side irradiance is a smaller kWh/kWp gain than the loss due to higher GCR.

Q: Do your trackers contain algorithms to adjust their movement in order to optimize bifacial gain?

A: For most operating conditions, the optimum tracking behavior for monofacial panels will also be the optimum behavior for bifacial panels. NEXTracker’s standard tracking technology will deliver optimal results for bifacial, including the TrueCapture row-to-row and diffuse light functions.

Q: What is the inter-row and module to module distance required for bifacial? 

A: For optimal bifacial performance, we recommend ground coverage ratios (GCR) of 35% or less. Higher GCRs will still see a benefit from bifacial panels, but the additional energy will be smaller.

Q: What is the high wind resistance for the 1.5 M array?

A: NEXTracker has standard solutions for up to 130mph wind zones (ASCE 7-10 3-sec gust). 

Q: Does bifacial require more mowing operations at a site? Is there any research about increased cost versus gain and the loss of energy due to plant growth?

A: We expect that taller vegetation growth will reduce the effective albedo, depending on the specific site conditions. In locations with seasonal vegetation patterns, we recommend measuring the albedo for different ground cover conditions to best determine mowing strategy.

Q: Does single-axis tracking provide benefits north of 49 latitude, ie. southern Canada? Do you have a table that might show the benefit based on latitude or GHI? 

A: While it is unusual to deploy single axis trackers at latitudes greater than 50 degrees, there will still be a performance advantage relative to fixed-tilt. We recommend using PVSyst or similar energy prediction tools to compare fixed vs. tracker for a specific location. 

Q: Single axis tracking is the predominant method of tracking. Has dual axis tracking been reconsidered?

A: For almost all site locations and system sizes, single axis tracking offers the optimum combination of energy production, total system cost and land utilization. Best overall system economics / lowest LCOE is the reason why single-axis trackers are the fastest growing mounting technology for ground mounted systems. 

Interested in maximizing your energy yield? Contact our sales team about pairing NX Horizon with two of the most promising product technology trends in solar today: the bifacial PV module and TrueCapture Smart Control System.