West facing solar panels

There was a bit of a fuss on the US web late last year about whether solar panels should face south (that is, towards the path of the sun) or west (towards the setting sun). One point that emerged is that, while the electricity generated by west facing panels during the afternoon peak is more valuable, that isn’t reflected in the prices paid by consumers.

But thinking about the situation for new installations in Queensland, and particularly North Queensland, the case for facing west looks strong. The first thing to observe is that, in the tropics, the sun is in the south in summer and the north in winter, so there’s not a lot of benefit in choosing one or the other.

Second, Ergon now has a “time of use” tariff, to be used in conjunction with a “PeakSmart” airconditioner, which has a peak rate of 34c/kwh between 4 and 8 pm on weekdays. That’s almost as good as the 44c feed-in tariff that used to be on offer, and massively better than the 8c rate available to new installations. Even the shoulder rate of 24c is way above the feed-in tariff So, if you are installing panels, you really want to maximize your own consumption and minimise the amount fed back to the grid.

My first cut at a calculation suggests that, with this tariff, solar PV looks pretty good. Assume a cost of $2/watt installed, which is common for large systems, and suppose that, with the western orientation you get 1000 hours a year, equally divided between shoulder and peak. That is, each installed watt of capacity saves you 1 kwH/year, at around 30 c/kwh, for a 15 per cent rate of return. Even if you add back the 70c/watt or so saved by virtue of renewable energy credits, the return is still above 10 per cent.

Feel free to point out arithmetic or parameter errors here.

37 thoughts on “West facing solar panels

  1. @David Allen

    I have been progressively replacing my CFLs with LEDs. My kitchen had a large LED for general lighting and a string of tiny LEDs running under the cupboards the length of the food preparation bench.

    We do have a separate 2-in-1 fridge freezer combo, but we need every bit of space in the freezer as we have animals. We also have a second freezer, which is switched off for most of the year and only comes into service during the four weeks that the pet food supply drops off.

  2. Excellent post. Glad to see this getting in the main stream. I wish we were encouraged to add storage of energy too, but of course we all (should) know the issues there.

    I would also like to see discussion of the impacts to the main system of generation and grid of variations in solar such as cloud cover and its changes. Discussion on the costs and carbon of the requisite standby for that.

    Evolution of the urban metabolism should be slow and steady and (importantly) effective.


  3. Thanks for that info, Hermit. I thought that it would be something like that. It looks like the Propane for sure but then I will have to check the longevity of the supplies. I doubt that there would be a problem.

    I am a great fan of wood fuel as a reserve. In my boat design I am working on a gimballed stove design with a split heat source to include a wood fuel section. It might just be a separate narrow module beside the kerosene section (no gas on the boat). I’ve lived with a kerosene stove for years and am comfortable with the issues. Good venting and an electric feed pump make all the difference. The system has a hot oil reservoir (200 deg C) for heating water as required that can be charged from the stove with either fuel. 20 litres of hot oil produces a huge amount of hot water. That is the plan anyway.

  4. A properly designed FIT or value-of-solar tariff should give a premium to afternoon electricity, and to lesser extent to morning electricity. The aim is not really to get people to shift installations on existing roofs – most of the time there’s no choice – but to encourage installations on roofs where the only orientation available is angled to the meridian. Eventually, with really cheap solar, three-quarters of the compass rose becomes available, as in sailing.

  5. @pellicle
    From what I can work out the vanadium redox battery on King Island in Bass Strait has been replaced. The new system is based on lead acid batteries with capacitors. I understand there may have been problems topping up the electrolyte with different vanadium compounds, at least one of which was highly reactive. Others may know more about this.

    Note the problem common to both pumped flow batteries and tilt axis PV panels …moving parts which can break down.

  6. @BilB, no I haven’t, actually I have noticed a lot less private aviation than I expected. What appears far less than the population relative amounts I see back home.

    Sweet looking plane BTW, would be well suited to this place. I have a friend who works for http://www.flynano. com now that’s a fun looking toy 🙂

  7. @Hermit, thanks for the information on the batteries … always good to get more report oriented data. The point on pumps and mechanical failure certainly is an issue for remote and unattended operations. Around my home however I am comfortable with the possibilities of pump failure on my floor heating system. Its a good heads up though and I will build a warning system into mark 3.

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