Monday, 1 July 2013

Turbine economics

Last week I had one of those experiences which felt at the time like small defeats but which actually are steps forward - although not necessarily in the direction I really want to go. Call it a tactical withdrawal. I moved my computer from the Winter Palace up to the Void. In the Void - the huge old cattle shed which forms the hub of our community-that-is-not-a-community - it can use mains power, rather than depending on my wind turbine. Also, it can use the landline broadband, rather than using my satellite connection. The truth is that at this time of year my wind turbine is not generating enough power for my day to day use, and as I am now running low on the money I earned last year and need to start looking for employment again, I need to use my computer (and the Internet) more.

So this is a post about the energy economics of living off grid.

Let's start by saying that electricity isn't necessary for life. It isn't even necessary for a good, comfortable life. Candles, oil lamps and gas lamps all work perfectly well for lighting, although candles aren't particularly bright, and to get a bright light from oil you need some sort of pressure system. All the other things we use electricity for are nice to have, but not necessary. When I lived in the Summer Palace I had none, and when I built the Winter Palace I thought that it would be a long time before I could afford electricity.

But electricity - particularly electric light - is very nice to have. Electric light comes on at the flick of a switch and is a much less significant fire risk than any kind of flame. I greatly enjoy Radio Scotland and Radio 4; my life would be impoverished without them. The condition of my teeth has improved significantly since I started using an electric toothbrush. And so on. Finally, I am something of an Internet junkie - a great deal of my life, particularly of my intellectual life, is lived online. Electricity is very nice to have.

But, here's the rub. All my lights together consume nineteen watts, and they are very rarely all on together. Charging my phone, my my toothbrush, my radio are each small loads - twenty-five watts at the very outside, but probably more like five (yes, I should check this). All these things I can afford.

My wind turbine is rated at 750 watts but only generates this amount in absolutely ideal conditions, which means a steady force four wind. Also, it depends on the wind direction. Here, the prevailing wind is from the southwest, so I have sited my turbine to be in clean wind from the southwest. But because the turbine needs to be reasonably close to the house and the house is in the wood, the turbine is close to the wood; when the wind blows from the north west, the turbine is in turbulent air off the wood and does not run efficiently. Finally, in winds stronger than force six, the turbine automatically shuts down to avoid damage. As the energy of the wind varies with the square of the wind speed, the amount of electricity generated falls off very sharply as the wind drops. My estimate is that the long term average is that my turbine generates less than 10% of its rated output, which is to say I get between 1 and 2 KWh per day.

But my internet connection comes via a satellite, which is about forty thousand kilometres away. To communicate via that satellite I need to shine a light (OK, it's radio frequency not light frequency, but it's effectively the same thing) that's bright enough not only to illuminate it but to be visible to it against all the background clutter of all the other radio emissions from Earth. That costs me 43 watts, and it seems to me that's remarkably efficient. My laptop consumes 45 watts, but currently it's away being repaired. My desktop computer - the one I've moved to the Void - consumes about 250 watts peak and about 180 watts average during normal working. So to do serious work and use the Internet I currently need about 300 watts.

In theory five hours charging at average of 60 watts should give me one hour of use, so in theory you'd think that I'd get about four hours use a day. But it isn't like that. Lead-acid batteries - which is what I use for my power storage - are fairly inefficient, and get more inefficient as they are depleted. Also, in summer, there are many days on which there isn't a great deal of wind and charging is negligeable. Once the big storage battery has been depleted, it takes a very long time to bring it back.

Wind is great in winter to provide power when there isn't much sun, but as soon as I have some spare cash I shall invest in solar panels. For a given rated output solar is now substantially cheaper than wind, and I believe that on long term average solar panels will produce a higher proportion of their rated output.

Finally, because wind turbines have moving parts they require maintenance. My guess (but it is just a guess) is that for similar investment, solar panels have a longer working life expectancy than wind turbines.

In brief, if I was starting again now I would install solar first and wind later. I didn't, because when I first built my house I was very concerned to keep it hidden, and consequently I built it where the sun don't shine; I've now built a wood shed out in my orchard, where it will catch the sun, precisely so I can install solar panels. But even if I had chosen solar panels first, I would still install both, because I believe that they are complimentary: when you have no wind you tend to have more sunlight, when you have less sunlight you tend to have more wind.

Oh, and, if I had a stream of any consequence running through my land, I think I'd prefer a water turbine to either wind or solar - it's more predictable, more continuous, and easier to get at for maintenance.

Having said that, none of these solutions are cheap electricity. To the cost of the turbine or panels must be added the cost of the tower, of the cabling, of the controller, of the battery, of the inverter. The total cost of my installation so far is £4,000. At 1.5KW/h a day and an expected lifetime of ten years, that's around 5.5GWh total, or at least 70 pence per kilowatt hour (more, if I need to do significant maintenance). If you're on grid, you're probably paying about 16 pence per kilowatt hour, or a quarter of what I'm paying. However, going off grid may well be a cheap lifestyle choice over the longer term because it does make you think seriously about the energy you use, and consequently you use less. It's also, arguably, on balance, better for the planet.
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