Making power while the sun shines

Posted by steve on Aug 26, 2011 in Hardware, international, network, New Zealand, Personal |

Tech, let us not forget, is not simply limited to Apple and the internet. You could be forgiven, to be fair, from reading this blog, for thinking that the world of technology begins in Cupertino and ends with the ‘net. But my most recent tech project is possibly the most spectacularly techie I’ve ever done. And it has no specifically Apple element in it, although it does involve the Web.

As has been documented quite extensively elsewhere, I moved a couple of years ago to New Zealand, where I find life to be, in so very many ways, a thoroughly pleasant experience. One of the few entries, however, in the debit column is the cost of living, and one of the most significant aspects of this headache is the price of electricity. While I’d never wish to return to living in Florida, among the few aspects of life there that I miss is the low, low cost of electricity.

As I said, we’re not going back, and so we — the lovely and talented Mrs. McCabe and I — decided that we needed to find a way of reducing our monthly spend on electricity. Back there, a unit — a  kilowatt-hour or KWh — cost, typically, around 8¢. Here, it’s more like 23¢. This does not, of course, please us, particularly when we were paying for electricity to heat our home. But what does please us is the abundance of sunlight that streams down on New Zealand much of the year, and so we have, finally, commissioned our very own solar-power installation.

The system is fairly straightforward. On our north-facing roof (this being the southern hemisphere), we have sixteen 190-watt solar panels. What this means, then, is that when the sun shines, and especially when the sun shines directly on the panels, we can expect to see up to 3KW of electricity being generated. Of course, we don’t expect to be getting that much power constantly, and, of course, we only get peak output when the sun is high in the sky, but we’re still optimistic that we’ll see plenty of power being generated.

The panels feed a 3KW grid-tied inverter, which takes the DC output from the photovoltaic panels and converts it to AC. This is essential for two rather critical reasons. Firstly, our home is, like most homes, an AC installation, full of appliances that are designed to take a 240V AC input. Secondly, and this is a rather cool and groovy consideration, the national grid in New Zealand is also a 240V AC system.

The practical upshot is simple. During the day, when our panels are generating a stream of as much as 3KW of power, whatever we need is used to power the house. Any surplus is sent off to the grid. When the sun either goes down or hides behind a cloud or two, then any shortfall is supplied by the grid. Meridian Energy, our new power supplier, will give us 23¢ for each unit we sell them — the same price they charge us for electricity they generate. In effect, we’re using the grid as our battery, storing any surplus we crank out during the day so that we can then use it back up at night.

So far we’ve had the system running for three days, and we’ve liked what we’ve seen. It’s late winter, or, if today is any measure, very early spring in northern New Zealand. We’ve bought about fifteen units from the grid, generated a dozen, and of that dozen sold five back. In other words, we’ve used, in total, about 22 units today, but only actually paid for ten. That’s a positive step; when the months and months of golden sunshine that characterise a New Zealand summer roll around, we expect to be, on a daily basis, net exporters, and, if we’ve done our calculations right, we expect that, over a year, what we buy from the grid should be, within a significant figure or two, pretty much what we sell back.

And let’s not forget the Web aspect. The inverter that converts our solar array’s DC output to an appliance-and-grid-friendly AC also contains a monitoring system and a web server, which, as soon as it was up and running, I patched into my own home server system, so it can be monitored worldwide. My very own personal power station is now online at — take a look at how much electricity we’re not paying for!

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