Design Complete

The design for our solar panel installation has been completed and approved (by me).  The installer has informed us that they will be here Tuesday to start the work.  

The original bid included 22 solar panels, however the revised design was able to include one additional panel.  This was done by changing the configuration from a portrait arrangement of the panels to a landscape one (each panel is 1 x 1.8 meters).  

The other design decision was the choice between string inverters and micro inverters [1].  Inverters are the component that change the AC power generated by the panels to DC power fed into the grid.  In the former, panels are strung together into a single line that is fed into a single (shared) inverter which converts the generated DC into AC (which is then fed into the grid). The later method places micro-inverters under each panel, with individual feeds into the grid connection.  The key issue with the string inverter design is that should a single panel fail or produce less electricity, then the production from all panels on the string is impacted.  The micro-inverter design overcomes this problem by having individual inverters per panel.  

However, the micro-inverter design is more expensive and complex. Complexity of course increases the risk of failure.  

Typically the reasons a panel fails to produce is if it gets dirty, is covered in shade or the roof has multiple different angles (which implies different level of electricity production from each of the “angles”).  As our roof is a single surface facing south, the third consideration is not a design factor.  The first two root causes can be managed and thus do not force a micro-inverter design, so we decided on the simpler (and more resilient) design.   

In addition to the above components will be a squirrel guard to prevent those rodents from getting under the panels and eating the wiring. We went back and forth on this point and decided on the feature being an insurance item as we have had squirrels in the attic.

At this point it looks like the installation will generate about 60% of our annual needs and pay back about 150% of our costs.