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)
Each PV panel has its own inverter
(fitted at the back of the panels)
Leonardo
ENERGY
The output of each PV panel can be
monitored via a website
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
• 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
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