Archive for January, 2010

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Generating your own power – Wind

January 13, 2010

So, Wellington is a windy place, right? And if we’re flat out interested in energy efficiency we can go a step further than merely buying low-watt bulbs, or turning off lights when you leave the room, or putting on socks instead of turning the heater up, by generating your own power.

This old idea absolutely fascinates me.

What I figure is this. My household used around 6400 kWh of electricity last year, and that amount was elevated on account of washing nappies and running a shallow bath for the wee man every day (it was also an extremely cold winter). This means that we run and average of about 18kWh through the meter every day. Fortunately we’ve been in an apartment all year, with decent insulation, hardly any windows, and no real drafts. All the same, if I could have found a way to knock down the power bill I would have. After all, the ~$1600 we spent is nothing to sniff at, right?

Not being anywhere near running water (although we could have cheated and run a small hydro scheme in the bathroom, with all that free potable water the city provides), our options are pretty limited. Ignoring the fact that we’re in the apartment (the move to the suburbs impends), we can either run a wind turbine, hang some solar panels out for all those sunny days – I’m not joking there, Wellington has more sunshine hours per year than Auckland – or perhaps set up a bicycle with a generator (you can get up to 300w per hour, not bad really).

So I started thinking seriously about wind, and to my surprise it actually seems financially viable. The first thing I did was consider the resource. Why opt for wind?

Well, Wellington is a windy place. Using the handy table generator over at NIWA I was able to download a table containing daily windspeed and wind direction at the Kelburn station for the years 2000 – 2008. The figures I obtained were very similar to those presented at Wind Finder, with average windspeed siting around 16 or 17 metres per second year round. With the NIWA figures I drew up the following graph.

Windspeeds Wellington, 2000-2008

What this fancy box and whisker graph tells us is how strong the majority of Wellington’s winds are. As you can see, the boxes (which mark 50% of all wind) consistently sit above 10m/s or 36km/hr. Now with most models of wind turbine requiring a minimum of 2.5m/s to activate you’re going to think you’ll have no trouble with an idle fan.

In fact, the more I investigated it the trouble with Wellington isn’t so much the absence of wind, but the abundance of it. Many turbines are rated to hurricane+ speeds 60m/s, and the windiest it gets here is a little about 40m/s (about 140km/hr). But that amount of very high wind actually places a fair amount of stress on a turbine, something we’ll return to.

So. How much power can all this lovely wind generate for us?

The short answer is that it depends on the model. As I said, our power consumption was around 6400kWh last year, well below the ‘typical’ consumption of 8000kWh. This means we’d need a turbine that could make a decent dent in that usage, and drop it low enough to make the savings offset the cost of whatever turbine we need.

It was then I started phoning power companies, and what I discovered was very interesting. There seems to have been a slight shift here in New Zealand and the companies have started allowing what are called ‘import-export’ meters. What this does is allow you to import power from your local supplier. But, if you have a generator, you are also allowed to export power back out to the grid! Awesome. In principle this means that if you have a turbine going, and nothing switched on in the house, you can actually watch the metre turning backwards. Then when the metre reader turns up, hey presto! They might actually owe you money!!

Naturally… it isn’t that simple.

The first people I emailed were Contact Energy, who eventually informed me that they’ll buy my power for 17c a kWh. And they’ll also sell me power for whatever the cost of my plan is. If this is 17c then great. If not, then I lose a little.

The next people I spoke to were Meridian, and they informed me that they don’t bring in cost. They have a 1 for 1 approach, where my kWh is taken off the meter directly. And that I found pretty interesting. Essentially, If I have a 26c per kWh plan (which is what we’ve been using), then I’m ‘saving’ 26c every time my turbine generates a kWh.

At this point the calculations started. What’s great about wind is that it can potentially generate power 24 hours a day. You can be lying in bed at 3am and know that all the fresh air out there is making you money. Even better, it averages that production out across the entire year. You can run the meter backwards during our windy summers, and forwards during the power-hungry winters. The trick of course is getting the right sized turbine for your place.

So, how big to go? Turbines, like anything, come in different sizes and quality. Wellington being Wellington I figured we’d need something pretty heavy duty, otherwise maintenance would become an issue. And if we have to maintain we lose our offset costs to a repairman. Worse still, we might have to replace it.

One turbine I saw was a 1.25kWh job. Designed for the Shetlands, and looked like it was built by Soviets.

So let’s say we get around about 80% efficiency per day (perhaps it isn’t windy enough all day, or it only runs slowly). This will turn out around 25kWh, and a whopping 9075kWh annually!!

This is though, from looking at our wind graph above Wellington has wind in excess of 5m/s over 95% of the time, so we can pretty much guarantee ourselves the 80%. The sensible thing then was to work out the appropriate sized turbine. What I did was compare 4 different sizes: the big 3.5kWh boys you’d use if you lived out on a lifestyle block (but still had connection to the grid), the 1.25kWh job, and a more modest 1kWh and 800Wh models.

Potential kWh generation from wind turbines - Wellington

As you can see, the amount of power generated can be pretty big. The totals for each model are:

  • 3.5kWh – 25410kW
  • 1.25kWh – 9075kW
  • 1kWh – 7060kW
  • 800Wh – 5808kW

Which leaves me wondering – assuming my calculations are correct (and I stand to be corrected), then a modest 800kWh turbine could be just the thing. The price should come in under $10k, and the savings at the current price of electricity (taking into account the almost 6% annual rise in power we’ve been experiencing), I should be able to recoup around $1400 of my power bill per year.

That’s a pretty snappy repayment. Perhaps 6 or 7 years, and far better than solar power.

And at that, I have to admit why I wouldn’t do it.

For starters, getting council approval for anything even the tiniest bit unusual in Wellington is, by all accounts, a freaking nightmare. Most turbines need to sit on a 10 or 15m high pole, and that’s something every NIMBY in the world will complain about. But assuming you actually get the thing up in the air, and enjoying all that sweet, sweet free energy?

Noise. Turbines are really seriously noisy. Really noisy. They recommend that you don’t have them within a 100m of your dwelling to be on the safe side. Now, when you closest neighbour is likely to be about 3m away from your property line, you’re sunk. Enough complaining and the council could actually try to take your $10k turbine away, permanently.

Then there’s the noise for you. That 3am enjoyment could actually be, “WTF! This turbine is putting out 50 decibels, almost 24hours a day!” FYI, that’s the volume of a noisy office conversation, outside your bedroom, in the middle of the night.

Worse, in high speeds they can put out something like 85decibels – a fire alarm, or siren.

So maybe on the farm. Otherwise? Idea kaput.

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Energy Efficiency – Why bother?

January 8, 2010

In the big news in the Tibby household stakes is our impending move to suburbia. We’re very excited, and mostly because of the requirement to make a lot of plans.

Now some would call this nesting. And they would likely be right. But! In our defence a large part of the planning concerns ways to, firstly, save money compared to living in a city apartment (our first choice…), and secondly to add value to our property (like all good New Zealand home owners).

Other than servicing the mortgage and feeding/clothing ourselves, the big cost to any household is energy – including petrol for the automobile, another post altogether. It’s important then to make sure that your place is as energy-efficient as possible. It’s a mantra the green movement has been speaking for years, and I’m well-sold on it. Not only does it assure us that we’re not being wasteful, it also ensures that we save a little money. After all, $10 a week saved on the power bill, if transferred to the right account, amounts to about $30k off the cost of a mortgage.

So in looking at this issue I started considering alternative power sources as a means to drop costs. The outcome is another post entirely, but in doing so I uncovered one big long-term reason for looking at energy efficiency – the ongoing rising cost of purchasing electricity.

Snooping around the net I discovered this handy page on the Ministry of Economic Development (MED) site. What you have there is a quarterly survey of power costs for a household using 8000 kilowatt hour’s (kWh) of power a year, around about the average for a New Zealand home. And there was some pretty interesting stuff provided in this excel spreadsheet.

The spreadsheet provides costs of electricity purchasing across the entire country since August 1999, and that’s a reasonably good time series. With a little very simple manipulation this turned up some very interesting information about power prices across the country, and how much they have changed over the decade. The first graph, below, gives us raw costs in cents per kWh averaged nationally (and yes, they include the 10% prompt payment discount).

Power Prices, National average

What’s more than clear from this graph is that prices have been increasing steadily since 2001. What this made me wonder is, how much will they increase in future? The thing about alternative energy is that once the initial outlay has been made you’re (hopefully) no longer subject to increasing in pricing – again the subject of another post.

If you consider the minimum tariff line the average household will be paying about $1800 per annum for electricity alone, a fair amount. This is especially the case if you earn close to the average weekly income of $830 (which is around $43k per annum, before tax, meaning the income in the hand is actually only $34k). In effect, the average house earning the average weekly income spends around 5% of it’s total budget on electricity. Higher earners usually have bigger houses, so they’ll also likely spend around that percentage (or more).

Now consider what prices are actually doing. As you can see in the above graph, prices trend up, as is normal. What I did then was find out the how much these prices have increased, and how much they are likely to increase in future. And I was mildly surprised.

The graph below shows both the percentage in quarterly increase in prices relative to an August 1999 benchmark. As you can see, the quarterly price difference (i.e. the amount prices change every three months) kind of bubbles along, but the cumulative cost places current prices 80% higher than in 1999 (the blue line, measured on the left axis). And that’s a fair bit. The green line (measured on right axis), shows that kWh are today costing around 23c each (whereas they cost around 12c in 1999).

Price Increases, Wellington Region only

The next thing to do was to attempt to project prices out to 2019, to see what we could be paying here in Wellington by then. To do so, I averaged the total quarterly price increases since 1999, and applied them to cost of kWh’s. When applied to the graph above I got the graph below. Of course, this assumes a constant rate of price increases close to my average – but considering the time series of data I had to work with thus far, it’s likely not far from the truth.

Future Retail Cost of Electricity, Wellington only.

As you can see, assuming a constant increase of 1.47% per quarter (the current average quarterly increase), electricity prices should rise to around 44c per kWh. This is almost 90% higher than now, and if we go back to our Joe Average family consuming 8000 kWh per annum, their bill will increase to around $3.5k!

Why I found this all interesting is that if you’re making energy efficiency savings in your house now, the ongoing saving in real terms actually increases every year. This means that as the price of energy increases – which it must – then you’re actually saving more over time, because that kWh you don’t use today hopefully won’t be used in 10 years when it will cost you almost double.

Furthermore if you’re installing some kind of energy generating device or system (the real reason I set out on this analysis), then the offset of your initial cost is actually higher as the years pass, because you’re generating the same amount of kWh you were when you installed, but saving more on money not spent. If you get my meaning.

Now the only question is how to generate that electricity… The subject of another post.