Q & A – GTM Webinar: Advancing Utility Scale Solar to 1500V and Beyond

By on December 13, 2016

Watch the webinar below. 

We were excited to receive so many thoughtful questions during the webinar session, see below for answers from the NEXTracker team.

Q: When designing 1500V DC systems, does the number of modules per inverter change?

A: Since 1500V inverters tend to have increased rated capacity versus comparable 1000V inverters, the quantity of panels per inverter will be greater for 1500V systems. However, we typically expect the DC/AC ratio to be similar for a given project as the drivers for optimal DC/AC are the same for both system voltages. 

Q: At what minimum system size do single-axis trackers make economic sense?

A: We’ve found, in collaboration with our customers, that project economics can work just under 1MW size projects.  In fact, our smallest systems have proven the economics at 500kW and on the upper range, we’re doing projects as large as 800MW.

Q: Why does the overall inverter cost go down?

A: Typically, 1500V inverters have a $cost/watt advantage due to the kW scaling-up effect of higher operating voltages. Current, not voltage tends to drive the cost for key inverter components.

Q: Why is there a reduction in installation labor with a 1500V system?

A: With a 1500V system, power per string circuit is increased by 50%, thereby reducing the quantity of strings, DC home runs and combiner boxes per MW. Labor savings come because many of the electrical installation costs, such as setting equipment and terminating DC circuits, scale with the quantity of components independent of the power. In addition, the inverter capacity typically increases for a 1500V design, reducing the quantity of inverters for a given project size. This also drives reduced installation costs.

Q: Are system losses greater on the AC Inverter Output circuit than on the String 1500V DC Circuit? Does it then make sense to run the DC Circuits longer and shorten the AC inverter runs?

A: Yes, 1500V enables longer DC runs with reduced DC losses. This advantage is typically leveraged by designing 1500V power plants with larger inverter ratings, thereby reducing the quantity of inverter locations per project and minimizing the amount of AC conductor. The optimal trade-off on inverter size, DC collection design and AC design will vary depending on site conditions.

Q: The 1000V design was based on 4 strings per row, but the 1500V design showed 3 strings per row. Why is this?

A: Typically, the optimal structural configuration for NEXTracker is between 80 and 90 modules per row.

Q: Are electrical BOS suppliers (combiner boxes, breakers, switches, fuses, etc.) onboard with equipment tested for 1500 V DC operations?

A: 1500V rated equipment is now available across all of these component categories. We expect availability and pricing to continue to improve as demand for 1500V products continues to ramp up.

Q: Is 1500V also economical for systems in 500kW- 1MW range?

A: Over time, we believe 1500V systems will also be adopted for projects in this size range. There is a trend towards string inverters for smaller-scale ground systems, and we expect a new class of 1500V string inverters to emerge going forward.

Q: How do you approach AHJs to discuss 1500V Systems?

A: AHJ’s can, at their discretion, refer to the latest NEC code edition even if the state has not yet adopted it. A proactive discussion with plan checkers prior to submitting for permits is recommended. Establishing measures to prevent site access by unauthorized personnel and getting approvals for key electrical equipment will be helpful.

Q: How does NEC code treat 1500V systems?

A: The 2011 NEC code edition changed “low voltage” threshold from 600V to 1000V. The 2014 Edition added section 690.81, which permits the use of components over 600V but below 2000V, in accordance to their listing. This opens up 1500V for use provided the electrical equipment is listed for the voltage used.

Q: Digitized O&M and access to SCADA points was mentioned in the presentation.  What is NEXTracker doing in this area?

A: NEXTracker continues to develop additional capabilities for remote monitoring and integrated SCADA systems. We see predictive O&M as key for the evolution of the industry, and future product launches will build on these capabilities. See a snapshot of our commissioning software in action with this video.

If you have additional questions, please email ProductTeam@NEXTracker.com.