5 Commercial Rooftop Challenges and how to Overcome Them

12/31/2019

The Commercial and Industrial (C&I) space are both complex and environmentally demanding for solar installations. High ambient temperatures, high irradiance, obstructions, setbacks or pathways are all challenges for design, installation and operation & maintenance (O&M). So what's the best way to overcome them? This article sheds light on these challenges and lays out solutions. Hint: the inverter plays a key role in this!

1. High temperatures

2. Obstructions

3. Rapid shutdown

4. Accessibility

5. Serviceability

1. High temperatures

By their nature, flat rooftops on commercial buildings are harsh environments with excessive heat and inclement weather. While it is commonly known that higher temperatures have an impact on the efficiency of solar modules, the impact on inverters is often times overlooked. Even in temperate climates commercial roof tops can quickly reach temperatures of 110°F or more. The typical ambient operating temperature of commercial inverters goes up to 140°F. Power electronics in the inverter automatically (de-rate) as a protective measure when temperatures are too high affecting system yield.

There are several options to keep the inverter's temperature lower and to avoid de-rating: choosing a location that is not exposed to direct sunlight or installing a shade cover for the inverter. Natural airflow around the inverter is also beneficial and following manufactures specification for distance and positioning between multiple inverters all minimize high temperature challenges.

Furthermore, inverters with active cooling (fan) perform better in high temperatures than inverters with only natural convection in the demanding roof top environment.

2. Obstructions

Commercial rooftops are complex usually coming with multiple architectural obstructions, impacting design and cost solar system installation. HVAC units, chimneys, setbacks or pathways are only a few obstructions that designers and installers have to deal with. Correct Inverter choice for rooftop makes a big difference in profitability. Distributed inverter placement at zero tilt with minimal sub-arrays provides more design flexibility, leading to efficient conduit and conductor management, and making installation both simpler and faster. Choosing the correct Inverter for the roof top environment matters and the right size string inverter is not necessarily the largest kW available (bigger is not always better).

Commercial Rooftop installation by Vulcan Solar

Rooftop installation by Vulcan Solar using Fronius Shade covers and MC4 connectors

3. Rapid Shutdown

Rapid Shutdown requirements for NEC compliance can be confusing and a big cost adder to commercial systems, especially in cases where multiple sub-arrays are necessary (e.g. due to obstructions). Proximity of the inverter mounting is a simple and most cost-effective way to fulfill NEC 2014 and 2017 requirements by mounting inverter next to the array and meeting 690.12 (XX) NEC rapid shutdown requirements. This way the inverter acts as rapid shutdown device and eliminates the need for additional equipment - reducing complexity and number Balance-of system (BOS) cost enhancing margins. In order to do so, the size of the inverter is crucial, as well as the capability to mount the inverter at zero tilt and the option to protect the inverter from exposure to direct sunlight (e.g. through a shade cover).

4. Accessibility

Access to commercial rooftops can be another challenge a solar installer has to manage. Often times, rooftops can only be accessed via narrow stairs, steep ladders or tight roof doors. Thus, using lightweight equipment that is easy to handle is key in such situations. Compact string inverters have a clear advantage over large string inverters or central inverters in this regard.

5. Serviceability

A solar system is an investment for 20+ years, so operation and maintenance (O&M) aspects need to be taken in to account when planning for any system. Especially in commercial systems, where the focus is even stronger on returns on investment, a quick service solution around the inverter can make a big difference. Pre-installed MC4 Connectors on the inverter not only decrease installation and commissioning time, but also simplify ongoing preventive maintenance, as there is no need to check DC conductor torque at the terminal block for the life of the system. In trouble shooting scenarios, string voltages can easily be checked by pulling MC4 connectors, eliminating the need to open the inverter.

Conclusion

The inverter choice is key in order to overcome typical challenges in commercial rooftop projects. Choosing the optimal string inverter size with the right accessories such as shade protection and pre-installed MC4 Connectors make the difference. The Fronius Rooftop Solution, consisting of the Fronius Symo 24.0 with pre-installed MC4 Connectors and the Fronius Shade Cover, offer a comprehensive solution to address all the above challenges.