Wednesday, May 03, 2006

Is it really worth it?

In a mixture of environmental goodness and nerd curiosity I have been looking into renewable energy sources for the home lately.What I have found looks good on the surface, but in the end it definitely makes you question whether it is really worth it...

I found this cool 400W windmill that just attaches to your roof (no need for tall towers) and is a generally reasonable AU$1190. This item set me on the trail for setting up a house using renewable energy.

I then started looking into what sort of battery requirements are needed to store the wind energy you can capture. To power an average home, you need about 10kWh per day to meet all your general needs without sacrificing the luxuries. If we take this battery (306 Ah @ 100 hr cycle or 255 Ah @ 20 hr cycle) for $949. To work out how many of these batteries you need, you take the amp-hour figure of the intended batteries and multiply by the voltage. So using these batteries on a daily cycle, 255 Ah multiplied by 12 V gives you a figure of 3060 Wh or 3.06 kW.

So to power an average home using these batteries, the minimum requirement would be 4 batteries, of course this would only power the house for a day, I was thinking 3 days of backup would be a safe figure to aim for so that means 12 batteries (AU$12K, ouch). Using the above windmill, if the wind was blowing for 24 hours per day, you would get 9600 W of 'free' power.

As we all know the wind doesn't blow constantly, in the last week here in Perth there hasn't been much wind to speak of so one windmill definitely wouldn't supply the power you need. We need to get the shortfall from somewhere. That leaves us with a few options... 1) add more windmills 2) add more batteries 3) add another power source and 4) supplement from grid power.

Option 1. Adding more windmills
Not a bad option at *ONLY* AU$1190 each, but there are limitations to roof space and neighbourly tolerance to the whooshing noises of windmills.

Option 2. Add more batteries
A very expensive option but still viable, having more than a weeks worth of backup power would help smooth out your charge/discharge cycles but you had better have a lot of room for the batteries to be installed. Having a basement would be good for this. 7 days of batteries would be somewhere near AU$28,000...

Option 3. Add another power source
Adding solar power to this set-up would be nice, but again there is a large cost involved. You need to decide how much you are willing to spend to get your power for 'free'. If you bank on getting at minimum 4 hours of direct sunlight in winter per day and assuming that the solar panels take up half the charging requirements, you would need about 1200 W of solar panels to meet that need. Using this panel as an example (125 W for AU$1100), 10 of these panels would be needed. The cost would be a tidy AU$11,000.

Option 4. Supplement from grid power
Supplementing you battery-sourced power with grid power is a totally cost effective solution. Plus you can opt into green-power programmes where you pay a slightly higher rate per kWh (14c versus 17c per kWh in the case of Western Power) for your electricity but the power utility places that extra into installing more renewable energy sources such as large scale solar and wind farms.

If we take the most cost-effective solution from the above options being a single windmill, 3 days of batteries and supplementing from the grid only when needed using green power, you have a cost of approximately AU$13,000 just for the hardware, you still need to install and connect the system and purchase an inverter to convert the 12V DC into 240V AC.

The general lifespan of a windmill and battery set-up is in the region of 20 years, so per day over the 20 years, it would only cost AU$1.78/day. Compare this to purchase power from the grid at 14c/kWh and you reach a figure of AU$1.40/day. Add 30c for green power. Only those with a very big environmental conscience would even bother to go to all this trouble, nevermind the horrendous up front costs associated with it.

Reducing the battery backup to 1 day would reduce the 20 year cost to AU$0.68/day. In Perth, this would actually make a little bit of sense due to Perth's reputation for being quite a windy city. During spring and summer when we get those days that have the sou'wester blowing non-stop, you could reduce your dependence on the grid to nothing. Also in winter when the cold fronts move through you get two to three days of howling winds.

Setting your house up for renewable energy is a bit like installing a solar hot water system, for a majority of the time you don't need to use any form of fossil fuel based power but when needed you have a nice backup system. You are cutting your power bills back significantly and also reducing emissions. In the end, I suppose every little bit counts.

1 comment:

James said...

You can reduce the cost significantly by using much cheaper batteries and more of them. Of course they need to be wired properly in series and also vented... Solar panels, windmills and a backup link to the grid would be the way to go I think...