RT1: affordably measure solar irradiation and panel temperature for rooftop PV installations

RT1: affordably measure solar irradiation and panel temperature for rooftop PV installationsarticle picture
Published: Monday, January 15, 2018 By Donald van Velsen, Kipp & Zonen Product Manager - Solar energy PV installations on building roofs are really taking off in many parts of the world. On apartment buildings, car parks, sports facilities and smaller industrial sites.

No land purchase or leasing is needed and the power is available on-site, where needed, for example powering air conditioners when the solar energy and heat input are greatest. If excess power is available it can be stored in batteries or (if feed-in tariffs are favourable) sold back to the grid operator.

Even though a commercial rooftop installation is much smaller than surface-based utility-scale solar energy parks, it is still vital to be able to check if your equipment is performing the way it should. How often do you go up on the roof for cleaning or repair?

Most maintenance decisions are based on the calculation of the actual power generated, for the incoming solar energy, compared to what it should theoretically generate. This is termed the Performance Ratio (PR) of the PV panels and is, in effect, the operating efficiency of the installation. For this calculation the incoming solar irradiation and the PV panel temperature are key parameters.

At Kipp & Zonen we listened to our distributors and customers and had a close look at the currently available instrumentation and decided to develop a new product that would be easy to install, easy to use, be resistant to soiling and still be affordable. Our answer to this problem is a brand-new smart rooftop monitoring system, the RT1.

Easy Mounting and Connection
RT1 has a robust housing that fits snugly to the corner of a PV panel and only takes one clamp screw to install; an adapter enables fitment to the side or top sections of a panel. A 20 m long cable connects power to the RT1 and provides data in the solar industry standard MODBUS® digital protocol via RS-485. MODBUS® is available on many inverters and SCADA systems and assists in making the collected data available in the cloud or on a dedicated server.

A PV panel temperature sensor is a standard part of the RT1 and plugs into the housing, so that it can be easily removed if needed, for example to recalibrate it.

Low Maintenance
The conical diffuser of the RT1 is similar to the well-proven design of the SP Lite2 with its self-cleaning and soiling-resistant properties, aided by wind and rain, that are superior to those of the conventional flat surfaces used in reference cells and other photodiode radiation sensors. 

 PV panel temperature sensor

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