Optimisation of PV installations for partial shadowing Micro-inverters and decentralised DC-DC optimisation boxes Leonardo ENERGY Guy Kasier E&D Systems January 2011

Problems with a conventional configuration PV panels are connected in a string to a central inverter When there is shadowing on one panel (e.g. from a chimney or tree) the production of the entire string falls The generating capacity is not fully utilised Leonardo ENERGY

Partial shadowing of panel 4 causes a production loss in all panels of the string Problems with a conventional configuration Leonardo ENERGY

Two possible solutions Decentralised micro-inverters or Decentralised DC-DC optimisation boxes Leonardo ENERGY

1. Micro-inverters (1) No central inverter, but a micro-inverter for each PV panel Micro-inverters convert the DC from a PV panel into 230 VAC The outputs are connected together in parallel and fed to the distribution board via a cable Leonardo ENERGY

1. Micro-inverters (2) Each PV panel has its own inverter (fitted at the back of the panels) The output of each PV panel can be monitored via a website Leonardo ENERGY

2. DC-DC optimisation boxes Each PV panel has its own optimisation box The boxes maximise the energy output for each PV panel and ensure a fixed DC string voltage The boxes are connected together in series, and to a central inverter The output of each PV panel can be monitored via a web page or smartphone Leonardo ENERGY

Benefits of the two systems The output of each panel is optimised individually Shadowing on one or more panels has no effect on the generation of the other panels Total generation can thus rise by 5% to 25% Generation can be monitored from a web page. A poorly operating panel, inverter or optimisation box can thus be detected quickly Inverters and optimisation boxes can be replaced individually in the event of any faults. Leonardo ENERGY

Disadvantages of the two systems The cost is higher than in a conventional system with one central inverter The total installation time is somewhat longer In the event of a fault in a micro-inverter or DC-DC optimisation box, the roof has to be accessed for maintenance Leonardo ENERGY

Micro-inverters versus DC-DC optimisation boxes Micro-inverters Output 230 VAC No central inverter required Parallel connection Monitoring via web page DC-DC optimisation boxes Output DC voltage Central inverter required Serial connection Monitoring via web page and smartphone Both systems ensure a higher output in the event of partial shadowing of the PV panels. Leonardo ENERGY

A few links Enphase website: Enphase training video: video video Solaredge website: Solaredge training video: video page video page Pros and cons of solar panel micro-inverters: video video Leonardo ENERGY