Tuesday, 24 January 2012

Solar Power - so far, a mixed success

One of the unexpected benefits of losing my job was that my wife, who had taken over paying the household bills, took a close look at the power bills and had conniptions. She decided right there to get a solar power system installed.

This was quite an undertaking - the roof was getting old so we decided to have that redone at the same time, which in turn involved overhauling the solar heating panels for the pool which were there. The couple of weeks before Christmas were extremely noisy and dirty as big, strong men jumped up and down on the roof.

Now, the installation is complete - well, we've paid all the bills anyway. PG&E came by yesterday and installed the new meter, so now we can sell them electricity, That's good. But sadly, it isn't actually working completely, and it's not clear whether the problems can be fixed. That's not so good.

The system consists of 26 separate panels mounted at a slight angle on the roof, facing slightly east of south. Why they didn't make them face true south, I have no idea. We went for the highest-tech system on offer, using high grade panels from SunPower, each with its own inverter. This allows each panel to function separately and optimise its use of the available light, rather than wiring them in series so the output is always set by the weakest. This also allows us to get accurate real-time reporting of the power generation. At least, it should.

Our first problem is some trees on a neighboring property. In the winter (i.e. now), they start to shade the panels from about 11.30. From the pretty graphs the system produces, I can see that we're losing about a third of the production due to those trees. Generally I like trees, and I don't particularly want them cut down, even if the neighbor would agree. What is really annoying, though, is that if the panels had been placed differently on the roof, the shading would not have been as bad. This is something that the survey should have caught, and didn't. Once the sun is higher in the sky, I guess from some time in March, this won't be a problem. But still, it is probably going to lose us 10% or so of the total annual production.

The second problem is with the "fancy technology" part of the system - specifically, the Envoy box that monitors the panels and sends the data off to a company called Enphase. This is a Kleenex-box sized gadget, which communicates with the panels over the power line. This makes perfect sense rather than running a second set of cables. Or at least, it would make sense if it worked.

Initially this box was in my office, next to the router which it also needs to be connected to - by a cable, since for some reason they didn't use WiFi. That didn't work because the data-over-power couldn't get a good enough signal. So they moved it to the garage, close to the breaker box. That meant installing a second, completely separate, powerline bridge to carry the data.

I've always been suspicious about data-over-power. The idea of mixing all those tiny, sensitive little data bits with all the noise, inductive loads and general mess of electric power just doesn't seem like it should work - try connecting an oscilloscope to your power line and you'll see what I mean. I suppose I should feel reassured that it doesn't work. It's just that I'd rather it did.

Two of the panels simply don't show up on the Envoy. When I queried this, it turns out that the data signal to the panels isn't strong enough. "You'll have to move it to an outlet closer to the panel," the installer said. Well, but there isn't one. I tried anyway just moving it to another outlet. (The thing takes up two outlets, incidentally, and must not use any kind of an adapter or extension cord). But this time, the powerline bridge didn't work. And given that, there was no way to find out whether the communication to the panels was any better or not.

For now, we're stuck. The controller can only see 25 out of the 26 panels which are installed, at great expense, on the roof. It isn't clear to me whether the 26th panel is actually able to generate any power under these circumstances - since it's the one that receives the worst shade, maybe it doesn't matter much!

Even with the system as it is, there's a certain satisfaction to paying less to PG&E each month. But it would be even better if it worked properly, considering what we paid for it.

No comments: