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Optimisation of PV installations for partial shadowing. Micro-inverters and decentralised DC-DC optimisation boxes. Guy Kasier E&D Systems January 2011. Leonardo ENERGY. www.leonardo-energy.org. Problems with a conventional configuration.
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Optimisation of PV installations for partial shadowing Micro-inverters and decentralised DC-DC optimisation boxes Guy Kasier E&D Systems January 2011 Leonardo ENERGY www.leonardo-energy.org
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 www.leonardo-energy.org
Problems with a conventional configuration Partial shadowing of panel 4 causes a production loss in all panels of the string Leonardo ENERGY www.leonardo-energy.org
Two possible solutions Decentralised micro-inverters or Decentralised DC-DC optimisation boxes Leonardo ENERGY www.leonardo-energy.org
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 www.leonardo-energy.org
1. Micro-inverters (2) The output of each PV panel can be monitored via a website Each PV panel has its own inverter (fitted at the back of the panels) Leonardo ENERGY www.leonardo-energy.org
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 www.leonardo-energy.org
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 www.leonardo-energy.org
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 www.leonardo-energy.org
Micro-inverters versus DC-DC optimisation boxes Micro-inverters DC-DC optimisation boxes Output DC voltage Central inverter required Serial connection Monitoring via web page and smartphone • Output 230 VAC • No central inverter required • Parallel connection • Monitoring via web page Both systems ensure a higher output in the event of partial shadowing of the PV panels. Leonardo ENERGY www.leonardo-energy.org
A few links • Enphase website: www.enphaseenergy.com • Enphase training video: video • Solaredge website: www.solaredge.com • Solaredge training video: video page • Pros and cons of solar panel micro-inverters: video Leonardo ENERGY www.leonardo-energy.org