Shady Business
Unfortunately this is a post about our solar aspirations...
Before we put the wind and hydro to work, I thought it would be a good idea to get in some “quick solar” to run the place, so I’ve been doing some research.
I know I left this waaaay too late. I didn’t even start looking at this until the plant room was nearly finished. The thought of getting stuck into something that is a fast-evolving field too early felt a little futile and the sheer vastness of sources, products and options seemed like a bit of a minefield. And now, having spent time looking at it, I can say it absolutely is.
But with our plant room essentially finished and waiting for the final roughcast coat this weekend (and maybe a door and some windows but let's not dwell on the details), we have no time to waste mulling over options.
Looking at our appliances, our shower is our biggest single consumer. With no space for a tank, we had to go with an electric shower so we need to start with a powerful inverter from the get-go. Now, this would have been a good thing to research before we bought and installed the shower, but even knowing what I know now, and inadvertently having mulled over alternatives of how we could have done in differently… I don’t actually know that I would have found a solution that didn’t compromise something else. So if the disadvantage is mostly the initial cost of the setup, that is sort of the thing I can move on from, unlike forever looking at a compromise of a solution as a reminder. Plus, having a system that can work most appliances and tools (as long as the shower is not running) without having to worry if I can boil the kettle, seems like something I’d want anyway. Because I have been known to multitask!
Now, funnily enough, the batteries that don’t tolerate cold very well, the whole reason we built the cob hut, are apparently a thing of the past… we can now get batteries that self-heat and are built for being fixed externally so we may as well take the whole thing down.
But the thing that seems to be the most difficult are the actual panels. There was way more to this than I anticipated. The thing that got me the most was the shading. I was aware that nowadays, solar panels have a decent output even on an overcast day. What I had not realised was that actual shadow from physical things, like buildings and trees, can have a huge impact. Of course I knew that if some part of your panel is shaded it will not produce power. What I had not realised is that if a tiny part or a cell of the panel is shaded, the output of the whole panel will plummet. Further, with panels connected on a string, the output of the whole lot will also reduce to match “the weakest link”. For that reason, one should also have all of one's panels on a string facing the same way, or the output will be reduced by the ones facing the wrong way all the time, and none will get the benefit of direct sun…
One of the interesting insights from an actual off-gridder is that having half the panels facing SE is a good thing, because morning time is when batteries are most depleted. The other has to do with the tilt. When I looked for commercially available ground mounts, I could not find anything higher than 30 degrees. I asked about this and was told that the usual feed-in-tariff setup that the system is geared towards targets a high summer output when the sun is actually out and high numbers can be generated to help the annual average (which is very likely a selling point). In an off grid system however, one needs to target the winter sun (and corresponding tilt of 50 degrees or so), because of course in summer the demand for electricity is low… winter is when the struggle happens.
So armed with all this information I used my topographical model to try and find the best place for our panels. The sun study below shows the final positions I decided on. The trouble is that the greatest overshadowing happens from trees and my model does not have the actual heights, nor can it show a “winter shadow”. They are represented by boxes.
There are four strings of four panels each with the same orientation within a string - eight panels facing SE, four South and four SW.
Because of the trees along the race, I had to move them all the way to the edge of the site, which of course increases the requirements for cable length and gauge. No wins here but it is what it is.
Chris and I spent the weekend before last moving a mound of earth from one side of the wetland to the other, to create a little bank that we hope will shelter the panels from wind. We now need to quickly make a mount and somehow fix it in as best we can.
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