Welcome to Stewart Island & Sails Ashore +64 3 219 1151 tait@sailsashore.co.nz

Ladies Slipper Orchids & Solar

Ladies Slipper Orchid  ….Dendrobium cunninghamii

These pretty epiphytic orchids are quite common around our forests, and we have several  growing in our garden.  They are a Christmas bloom, so imagine my surprise to find a happy bloom, together with several about to open buds in our garden.  The buds look like a tiny high heeled ladies shoe, so hence the name. Also known as Winika (Maori) or the Christmas Orchid.  Perhaps they, like the Pohutukawa we now find self seeding on our road sides and gardens are confirming to us the  reality of climate change

Pohutukawa Seeding self introduced int a corner of our garden

Ladies Slipper Bloom & Bud

 

Getting the Most out of our Solar.

One of the issues we discovered quite early after installing our Solar System was how to both prioritise ensuring our batteries were “first filled” when the panels were producing but at the same time then activating what we would call “discretionary” loads once the batteries were fully charged… State of Charge  100%  … water heating, car charging etc. ..

We had initially set up a voltage sensitive relay which would turn on at 54.7 volts and off at 54.0. This range sort of reflected the battery SoC of around 97% full charged. But not that accurately. There were two issues in two areas :-

  1.  If a very bright day and so a high charge rate the batteries would sometimes reach the 54.7 volts at 90% SoC. That wasn’t such a problem
  2. But once the batteries became fully charged they would drop to a “float” voltage of around  50, and so shut off the discretionary circuits, even though there was lots of sunlight.

 

 

 

 

 

What we needed was a relay that was driven by SoC.  This is effectively an amperage totaliser….. counting the power into and also out of the battery.
There didn’t appear to be much (or anything) available. But then we came across the  Victron Energy BMV-712 smart. Around $300
A couple of weeks ago Shane from Tansleys .came across and fitted it.  Not that complex but I was certainly NOT going to play with the sort of currents our system could produce.

It took a while to get it adjusted… a few things like battery voltage, capacity etc had to be programmed into it. That was easy. But the critical variable seems to be the” Puerket Exponent”

The Peukert exponent (or constant), denoted by the letter k, is a measure of how a battery’s effective capacity decreases as the discharge rate increases. A lower Peukert exponent, closer to 1.00, indicates better efficiency at higher discharge rates, as seen in lithium-ion batteries, while a higher exponent, such as those common in lead-acid batteries (e.g., 1.2-1.6), signifies a significant loss of usable capacity under heavy loads.

It took a while, but seem stable at 1.2  and although occasionally it will drift the SoC by 1 to 2% that’s well within the range we want.

Not in itself a big thing, but does allow us to better utilise the output of of our system. And saves the irritation of discovering we HADN”T turned something off and thus dropped the batteries down into the “oops” level.