Ireland’s national broadcaster RTÉ has a top level undertaking to ensure the highest standards of energy management at its numerous locations throughout Dublin and beyond. RTÉ is a leading public body and is well on its way to achieving the 2020 energy targets set by the SEAI (Sustainable Energy Authority of Ireland). The recent installation of a 16kWp solar PV array was therefore considered integral to its ongoing commitment.
Paul Silke, RTÉ’s head of property and services, agreed a capital allocation in early 2015 to proceed with the first phase of the PV works. The initial phase of the PV system comprises some 66 x 250Wp polycrystalline, silver framed modules mounted in a landscape configuration installed on the flat roof in two adjacent arrays. Both arrays were installed using the Novotegra aluminium flat roof solution designed, manufactured and supplied by Wales-based BayWa r.e. Solar Systems from their Ballynure warehouse in Northern Ireland.
The Flat Roof II Novotegra mounting system is ballasted using 600 x 600mm paving slabs. The innovative base trough also allows additional ballasting using the existing roof pebbles. Using a ballasted system in this way ensures that there is no need to fix to the concrete roof or penetrate the roof membrane, ensuring the installation is robust and fully weather-proof and also makes for a cost-effective speedy installation.
Electrical design considerations
When it came to the electrical design, RTÉ opted for the Enphase microinverter system. Each module has a microinverter mounted on the reverse which converts the DC power generated by the module to AC power on the roof. This eliminates high DC voltages and allows for easy expansion of the system without the need to upgrade a standalone inverter.
The AC load is now connected to a distribution board in the roof plant-room with the panels equally balanced across three phases. As you can see in the image, each row on the array also includes an isolator switch to allow disconnection at the local level if required.
The base load of the building exceeds the rated maximum output of the installation, so the maximum output was limited to just under 11kWp by isolating a number of panels. This helped to ensure that the array complied with restrictions imposed by the local Distributed Network Operator (DNO) ESB Networks. (
Notification Form for Micro-Generation NC6).
An application was also made to ESB Networks under the
Application form for Generator Connections NC5 to allow further expansion of the install. This required Embedded Generation Interface Protection (EGIP) to be installed and witnessed by ESB Networks.
Click on this link to find out more about
ESB Networks Generator Connections.
Enphase energy microinverters
RTÉ decided to use Enphase microinverters for this installation as the technology allows it to closely monitor the performance of each module on a daily basis using the bespoke Enphase Enlighten app and software platform.
As well as converting DC to AC on the roof, another key advantage of microinverters over a more ‘traditional’ string inverter system means that overall system performance is improved. On a string inverter system the output of any PV array is restricted by the lowest performing module as the system is wired in series.
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Enphase Energy M250 Microinverter[/caption]
Using microinverters allows each module to deliver its power directly, so if one or more modules should be affected by shading or soiling, only that single module under-performs rather than affecting the whole string and array. Microinverters also allow the system to be extended at a later date once RTÉ decide to invest further in its energy management requirements and will allow modules of a different watt output to be installed when their efficiency inevitably increases with ongoing advances in PV technology.
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Flat Roof II Novotegra dimensions side view (click to enlarge)[/caption]
The array was installed using BayWa r.e. Solar Systems’ innovative Flat Roof II Novotegra mounting system. Accurate wind and snow loading calculations were essential due to the coastal location and building height. Novotegra is ideal for such installations due to its low angle and robust design using highly durable aluminium and stainless steel components produced to strict Eurocode requirements.
BayWa r.e.'s free online design software Solar Planit allows PV system specifiers to quickly calculate the amount of ballast required for any challenging location. Register on the website
www.solar-planit.co.uk to see how easy it is to use.
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The Flat Roof II Novotegra system also features a wind deflector panel to maximise stability[/caption]
The system was fitted and commissioned by RTÉ staff to reduce costs and allow for easy expansion. Overall design and project management was by Troy Bannon, property and services projects manager at RTÉ. The electrical works were carried out by RTÉ Property and Services staff under the design and supervision of Gerard Roche and James McConnologue. Specific PV consultancy provided by Tim Cooper.