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Chris Hobson


Having spent time on this forum I was ready to tackle the project. The bulk of the materials was sourced from Rubicon and a couple of design decisions was decided on. 

  1. I decided to do a ground mount which resulted in a slightly more expensive structure but our roofs are steep and old and suitable roof space was largely shaded and not exactly north more like NNE. The ground mount meant I could implement a seasonal tilt very cheaply and so gain a bit as my solar day is short in winter as we are nestled in a narrow valley. In winter the sun hits the panels at 8:35 am and disappears at about 3:30pm. So I need autonomy for about 17 hours in winter.
  2. I decided to maximise our panels as we would use the bulk of our electricity during the day - washing,ironing etc. I should perhaps have put more cash into batteries but at the time batteries were scarce and I might have had to wait even longer for a second string of batteries.
  3. I decided against having the batteries outdoors since a battery box would be on the northern side of the house with its elevated temperatures.

The install was largely uneventful with me checking polarity of connections twice before making any connection. Something that I did find strange was that with MC4 connectors the metallic male part is housed inside the female plastic portion and visa versa. It would have been very easy to have the male portion inside the male housing and the same with the female portion. Care needed to be taken not to muddle the MC4 connectors and ensure each solar cable extender was male on one end and female on the other. I built them in pairs so if one string needed a long red cable the next string needed a equal length black cable. I marked the pairs with series of Tippex dots and so could always identify each string's cable pair. Working meticulously we did not make a single wiring mistake ( inverter PV and battery connections and rewiring the old DB and installing two new ones). I found http://www.solar-wind.co.uk/cable-sizing-DC-cables.html particularly useful and collected design information in a haphazard spreadsheet which eventually gained some semblance of order. I used http://www.midnitesolar.com/sizingTool/ to work out PV string configurations.  I have since written my own string sizing tool which I find easier to use http://powerforum.co.za/topic/1590-pv-array-sizing-tool/


The one incident we did have was amusing. We were re-wiring the gennie supply from the DB (behind the front door) to the northern wall of the house  (against which the inverter is mounted. This new wiring needed new conduit and we were in the loft laying out wires and conduit when all of a sudden one of my employees ran over the ceiling of my son's bedroom. With our high ceilings I had visions of having to take him to hospital and having to repair the ceiling. Fortunately he is very light and did no damage.  In my least tactful voice I asked what on earth he thought he was doing having previously carefully explained that we were to only walk on the beams or the tops of the internal walls. Running across the ceilings was not part of the SOP. He told me a snake had hissed at him. There are recesses in the brickwork for the chimney an sure enough there was a female boomslang curled up in one of these recesses. When we were in the loft again a couple of days later she sailed between two staff joining conduit and went and curled up in her recess watching proceedings intently.

The day we went "live" was cloudy and overcast but at least I could confirm that my PV wiring was correct. The next day dawned a glorious winter's day and I had the full benefit of the fruit of our labour.

The next purchase was a BMV 702. I was ridiculed on the "my broadband" forum for having wasted so much money but to my mind is still the a most important piece of kit. The BMV alerted me to the fact that my batteries were way out of kilter in spite of being brand new. This precipitated the purchase of three HA01s from Lithuania of all places. Within about 6 weeks the HA01s (which are not as efficient as the HA02s) had whipped my batteries into shape.

We have had two years of largely uneventful solar power. Two deep accidental discharges did my batteries no favours but I have got the rated cycles out of my batteries. My future expansion includes paralleling the Axpert and moving over to Lithium.

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