The Solar on my roof April 3, 2015

Summer Production

Summer Production.

The eBook, Solar on my Roof is more than a simple thought experiment. It is the result of years of applying the techniques mentioned in the book and finding out what works, what works but is a pain to maintain and what can be ignored completely. This meant that I needed to have a rooftop solar Photo- Voltaic (PV) system with a variety of options. In this post I will explain how I put my system together.

I designed the system around several core principles. The first was that I needed to maximise the available roof space. Only a small portion of my roof faces North. The system had to be able to draw the maximum from separate arrays facing North, East and West. This meant that I needed at least three different maximum power point trackers (MPPT).

Winter Production

Winter Production

To have three maximum power point trackers, I could have used three inverters each with a single MPPT. This is by far the most common configuration. Another option is to use inverters that have more than one MPPT, These are not as common but do provide advantages when there are split arrays that have different orientations or experience different shading conditions. The Power-One, Aurora range of inverters above 3kW all have two MPPTs per inverter. This allowed me to make use of only two inverters to have the three MPPTs I needed. This also left me with a single unused MPPT that would be useful for further experimentation and design.

When I put together my system in 2011 the best panels I could get were the 245 watt Kyocera KD245. The North facing roof space dictated a maximum of seven panels. This meant that I could have a single series connected string of panels on an input.

The power input under standard temperature conditions is

245W x 7 = 1.715 kW.

That fits nicely into the 2kW maximum for each input. The voltage and current limits are also safely within the operating envelope of a single MPPT for the Power-One Aurora inverters.

This array configuration was duplicated on the East and West facing roof surfaces. The North facing PV array feeds into an Aurora 3kW PVI-3000-OUTD inverter for a maximum power output of 1.715kW and the East and West facing arrays feed into the two inputs of an Aurora 3.6kW PVI-3600-OUTD inverter for a maximum power output of 3.43kW. The combined maximum power output is 5.145kW but this is unlikely to occur since there is no single position of the sun that will be optimal for all three arrays.

Seasonal Yield

Seasonal Yield for a North facing array

I have a minimal amount of shading just after sunrise and just before sunset. This is because the neighbourhood is surrounded by eucalyptus forests. The minimal loss of early morning and evening production to Koala habitat is certainly not a concern at all.

Monthly Production

Monthly Production

The last component in my system is a data logger that collects data from the two inverters at 5 minute intervals. This data has allowed for detailed analysis of the operation of my system. This provided beautiful datasets that clearly demonstrate the difference between the production of the three arrays. I have also been able to clearly see the differences in system production as the seasons change.

The images displayed in this post are all generated from data collected since the system was installed.

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