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. When I installed solar panels they ended up facing W-N-W. There was little choice. The roof slopes down to the east and west (mainly) but there was more room on the west facing side.

    Afterwards I was very pleased. The afternoon sun from spring to autumn really racks up the kWh to the grid. In winter, as you say, it doesn’t matter too much. (There would have been a small added penalty if they’d been east facing, because of morning fog, which isn’t uncommon here.)

    I’m in Victoria where it would make more of a difference than it would in Queensland.

  2. I should mention an added bonus. In the hot summer afternoons the solar panels take probably three degrees or more off the inside temperature. They are a terrific insulator.

  3. It’s simple for battery installations (as opposed to grid feed) in that the panels are faced north at an angle equal to your latitude. So at the equator you could lie them flat to maximise insolation. Sun trackers are out of favour because of the low price of panels nowadays and the reduced maintenance of fixed installation.

    My advice to new installers is to install the maximum area of panels you can given suitable roof areas. Modern inverters have multiple input connections that allow north facing as well as west facing if desired. Each “string” of panels is handled separately by the inverter. Also it’s very important to look at your entire power usage and retrofit efficient appliances and lighting. Don’t just add panels like a band-aid.

    I’m currently enjoying the 66c input tariff with a 5kw system. Power company sends me a cheque every year until 2024 (or there abouts). I will go hybrid (batteries and grid + wind) when the scheme ends and install a bunch more panels.

  4. Several general comments rather than specifics. If indeed the calculations are valid the obvious question is why weren’t the panels installed with a westerly tilt in the first place? I don’t think re-positioning of existing panels is practical.

    I understand for grid tied PV the electricity retailer typically gets the small scale renewable energy credit of 3-4c per kwh. If the aim is thermal comfort after 6pm other options are aggressively cooling the house in the middle of the day, adequate batteries to run aircon which are currently bulky and expensive, variable tilt panels and phase change materials. A simple example of the latter is making lots of ice cubes. With single axis (ie east-west) and double axis tilt there is the problem of moving parts that may malfunction. Thermal comfort is also partly a matter of perception so if the sun is lower in the sky we think we’ll cope better regardless of actual temperature.

    Perhaps the bigger issue is that residential PV now requires spare cash or people who calculate rates of return. It’s not like when people got a 44c-66c feed-in tariff and/or a $4k-$8k purchase rebate. That’s why I doubt we’ll get from 1.2m PV roofs (+ 0.7m solar hot water) to say 2m PV roofs unless major incentives are restored.

  5. Whether north facing or west facing panels are best will depend firstly on future price and feed-in decisions by Governments and/or energy corporations. Secondly, it will depend on each household’s situation. We can’t predict precisely what decisions Governments and their favoured corporations will make. We probably can predict in general that these decisions will favour corporates and wealthy stakeholders and disfavour ordinary householders.

    With panels so cheap why not get more panels than you might have otherwise got (at least up to the allowable feed-in limit) and hedge your bets 50-50 (50% north – 50% west)? Of course, if your property situation means there is a line of trees just west of your house you won’t want western facing panels, for example. Also, look at your household useage patterns. When do you need and use the most power?

    Finally, long term, I think there might soon be considerable incentive to go off-grid or at least put in a bank of batteries so that you rarely use the grid even if connected to it. Grid supplied power looks like going up in price at something like 10% per annum indefinitely. Getting an electric car might help. That car, properly configured, can be an ancillary back-up battery pack for your home.

  6. I know someone who lives in a town with a lot of fog and drizzle who tried to install 15 kw of PV on an L-shaped house and shed. The result was quite a few panels ended up positioned facing south. Coincidentally a kilometre away another family put up a 10 kw vertical axis wind turbine. It blew over and was dismantled.

    At $2 a watt it is probably better to have extra fixed panels and avoid issues with tilting panels. Daily connection fees to the grid are nudging $1 call it 4 kwh X 25c so like making traditional tea have one for the pot. Long life batteries like nickel-iron lose 2% charge a day I believe so they need an extra panel to top up. Elsewhere I’ve seen a suggestion that practicalities of home batteries in the suburbs effectively limit them to 3 days energy storage so disconnecting is not a good idea. People who get effing generators should be shot case in point Baghdad has them everywhere.

  7. Having a deep and abiding hatred for cynical exercises that solely aim to “raise awareness” (an astro-turfing concept designed to bring about inaction, compliance and complacency), I note that we have just finished another “Once-a-Year-Day” event – Earth Hour.

    In SEQ ‘Energex’ has a meter on their website showing demand:

    At 8:45pm SEQ usage was 2867mW

    At 9:15pm SEQ usage was 2839mW

    That could mean anything, of course. But I still hate cynical marketing exercises designed to achieve nothing.

    I learned from the Energex website:

    Millions of dollars are spent on extra electricity infrastructure just to cater for these peak times. In fact, 16 per cent of the capacity of the network is used for only a few hours, on a few hot days each year.

  8. @Megan

    Well, nothing destroys the planet like Christmas. Think of all the extra unnecessary consumption: Xmas lights, food gorging, presents, waste paper and so on.

  9. Hi guys. Its normal…. We ran out of south facing roofs ages ago! Imagin how much space is wasted on flat roofs when you leave space to disallow partial shading. Its even better on a domestic when you consider that most consumption is in morning or evening here. The UK does not have the same cooling demand as much of the States so this may be less relevant…. but hey, if if you have the cash for the install you’ll be at work anyway!
    Need any help for system design… get in touch charles at reallyrenewable.co.uk
    Peace out y’all!

  10. @Megan

    Millions of dollars are spent on extra electricity infrastructure just to cater for these peak times. In fact, 16 per cent of the capacity of the network is used for only a few hours, on a few hot days each year.

    And rooftop solar is hurting their profits. Because it is those peak demand hot days when the wholesale price of electricity goes through the roof. They make most of their profit from those times. But solar rooftop essentially adds more generating power at these peak times – thus reducing the generators profits.

    But the generators have perverse incentives. Naively one would think they would build enough capacity to cater for peak periods. But they maximise their income by not quite coping with peak periods. Usually this strategy would work, as you’d expect competitors to join the party and decide to service a generator or two when demand gets high. But solar rooftop just keeps kicking in. Luckily the MRET will be going soon, and generators will re-establish their control over the supply of energy (not really a good thing, is it?).

  11. @Ikonoclast

    Christmas is probably the role-model for cynical “Once-a-Year” days.

    ‘Peace on earth, good will to all, let’s all be nice to each other….etc.’

    And then it’s back to BAU for the next 364 days.

    John Brookes: I was trying to express my astonishment at the fact that, according to Energex, we have 16% ‘rolled gold’ capacity just sitting there for a handful of days. That is crazy. Of course generators have perverse incentives: since they are no longer publically owned they want to produce and sell as much electricity as they can, if they were still owned by us they would be doing everything to reduce (fossil fuel produced) electricity consumption.

    PS: Looks like the Northern NSW ‘Bentley’ anti-fracking protest is shaping up to be interesting.

  12. Electricity producers who ignore the new energy reality of needing the refuce CO2 emissions are destined to waste their investments sooner rather than later. Global Warming hasn’t stopped or slowed just because Australia temporarily has a Denialist government. Globally governments are collectively realising that serious change to our fossil fuel dependence is essential and urgent.

    The fact is that distributed solar energy production is good business for the producer/user, and the value of the self investment only improves over time. Power distributors are greedy and the consolidation if the greed is achieved with the “smart meter” and the time of use charging regime that they establish. Once installed uniformally this is a totally open ended device to alliw distributors to reach into people’s pockets and extract money as it suits them and in the same manner as banks (fees) and telcos (call and data charges) are able to do. The UK is in the process of installing 15 million smart meters to electricty and gas connections for this very purpose.

    The only defence the average consumer has against this self regulation of their energy consumption and self production of the bulk of their energy requirements.

    Westward facing? Not so simple. The bulk of panels installed in Australia are 15% efficient. 20% efficient panels are available now and soon 35% efficient panels will be more available. Apart from that panels can be fitted with water heating thermal absorbers which lift the functional efficiciency a further 20%. The higher the overall efficiency of an installation the fewer the number of panels required. So with a small installation the prospect and the benefit of a limited tracking system becomes a reality. There is a further 20% energy capture functional efficiency available here from a simple panel tilting apparatus.

    Ten years forward 60% efficient rooftop systems with energy maximising tracking will be the standard rooftop application. And we are going to need all that as we will be charging our cars from these panels as well as electrically powering our homes, and solar thermally heating our water.

    Heads up. Keep an eye out for the new generation of hybrides arriving. The best that I am aware of will be the VW GTE which offers 50 to 80 kpl on petrol and 50 klms range from its 8kwhr battery (battery only speed 130 kph max).

    50 klm range might not sound like a lot but it is everything if your daily commute is 45 klms round trip. Realise that to charge the 8kwhrs costs just $1 at off peak rates. That is very cheap transport, particularly when realise that by driving mostly electrically the need to service the petrol engine us minimal.

    It is only through charging vehicles that the power companies will be able to claw back business liat ti distributed energy production.

  13. I’m in Germany, where it’s been really fine today and Germany got 40% of its energy from solar.

    It makes me sad to think of Australia and how Tony Abbott is holding us back.

  14. All this expensive stuff like batteries and electric cars will require lots of spare cash. I’m not sure that will be the case when 10,000 people we know of lose their jobs in the next few years. Small scale solar installation has appreciably slowed according to January data from the Clean Energy Regulator. Something would need to turn that around.

    As for Germany their emissions went up 1.2% between 2012 and 2013. I’m fairly sure emissions reduction was one of the main reasons for going solar. On top of that Germany’s power prices are 70% higher than in France. Perhaps someone can explain why the combination of higher emissions and higher power prices is a good thing.

  15. There is only one cost Hermit, and that is putting a roof over ones head. What is on the roof should be taken to part of that cost and handled in the same way. If you compare the increased mortgage payment to the the savings in offset costs any anbd every family is far better of. The car of course is a different part, but then again we all find the money to have a car available for our needs.

  16. @Hermit

    Perhaps you can explain why more Chernobyls and Fukushimas are a good thing.

    The 10,000 people you know of who are losing their jobs would not be losing jobs if this country was running solar energy, wind energy and electric car manufacturing Commonwealth initiatives. Yep, that’s right. We need the Federal Govt to begin nation building programs by creating Commonwealth companies again. While they are at it they should re-nationalise Comm Bank, Telstra, Aus Post, CSL etc. etc.

    The stupidest thing we do is waste people. To feed and higher educate a person to age 21 costs at least $250,000 for the family and maybe as much as $500,000 when all societal costs are added in. Do you know any company that would willing waste intelligent, self-regulated, self-actuated, self-repairing, fully servo-controlled machines? (Which it what well socialised, well trained humans are in one respect.)

    So why does this country spend half a million on each human “machine” and then throw it on the scrapheap of young adult unemployment? Given that you must make this expenditure anyway for ethical and humane reasons then you ought to employ the final product usefully. Building subsidised factories actually makes financial sense when you factor in the costs of the human “machines” and compare the outcomes of getting product or no product from them.

    We could easily be making our own solar panels, wind turbines, energy efficient houses, public transport systems and electric cars and easily have an unemployment rate of a mere 2% (frictional). We could easily fund our universities properly again and have full free tertiary education. These things can be easily done. They were done (2% unemployment and free tertirary education I mean) in the 1960s and 1970s when we were less wealthy per head in real terms. It is an outright lie that these things could not be done now.

  17. The Hybrides at present do come at a premium cost, and that is harder to justify the difference against the fuel savings without considering the sense of satisfaction from quiet clean transport against the noisy polluting standard.

  18. If the professor will indulge me, could I hijack this thread a bit, given the expertise on display? Or please just delete it if not appropriate.

    We’re just about to take possession of an 80s BV on a slab in Gippsland. It is currently 100% grid electric, for water, cooking and an older A/C. No idea about insulation, that will be seen to. Windows, aluminium framed single panes – can anything be done with them affordably?

    The first thing we will do is install LP gas lines, for cooking, as my wife refuses to consider induction stovetops and we both like gas ovens.

    Heating is with a reasonably modern wood fire. We’ll consider it with an ultra low emission model with a wetback, though due to funds this may be a few years away.

    PV with current levels of subsidies in Victoria don’t seem to add up right at the moment, as we’re not keen on the upfront cost, but in the long term I would like a reasonably large system (4-5kw) grid connected. The coldest winter days we get are 8 with all day rain down to hard frosts at minus 4. The old A/C will have to be replaced with a modern split system for heating at some stage.

    The HWS I was expecting to change to solar plus instant gas backup. I expect this is still the right decision? I’ve heard so many negative things about heat pumps in our climate. We got an OK deal on solar HWS with Origin a few years ago, but I didn’t like the Dux unit they installed, so am keen to look elsewhere. Last I looked some years ago, evacuated tubes were not worth the price. Have they improved?

    Anyway, if any of you have any advice, that would be greatly appreciated.

  19. Drving home from Bunnings yesterday with a load of Eucy mulch I couldn’t help but notice all the attractive large flat unused surfaces on warehouse and shopping centre rooves, and even on the covered walkways at Toongabbie Station, which are neatly titlted towards the sun.

    It strikes me that there’s a massive untapped resource there and across pretty much every urban or semi-urban area. You don’t need to have everyone place them on their rooves. Plainly, too, the state has the ability to manipulate some elements of electricity demand that require electricity — such as pumping water to reservoirs — to take advantage of surpluses produced at periods of low demand — such as on Sunday afteroons in mild weather. Similarly, if PEVs could tap into this system for a fee, (easy enough with e-payment) a lot of demand for petrol could be wound back and the EVs could be themselves a “reserve battery” for the system, discharging to meet fluctuating demand/supply.

    And let’s not even reflect on their ability to take advantage of pumped storage in the hydro-electric system.

  20. Most instantaneous hot water systems require grid power to operate. Check that out with your supplier. The features that I am talking about are available if you hunt around but I will be building my own system as a prototype of the lower cost compound solar pv/thermal. They are available in the US. Solar absorptive air conditioners are available in Europe at a relatively high price. The Chinese chillers are mainly pitched at the commercial market with the smallest of them that I am have connections for is rated as 8kw.

    Gas for cooking is by far the smartest move. I intend to install a gas cylinder system as I value the storage aspect of these. It would be good if you could mix the systems but somehow I think that mains gas and bottle gas are a different mix. Don’t know for sure. The beauty of the absorptive aircon is that it can be powered by gas.

    Let us know how it turns out.

  21. @BilB
    Natural and coal seam gas are 80%-98% methane with a low boiling point hence the need for high pressure (300 bar) or cryogenic (-171C) cylinders. Bottled gas is mainly propane and butane with a much lower liquid pressure (~15 bar I think) at ambient temperature so that for example you can see liquid inside a disposable cigarette lighter. The burner nozzle apertures and air mix requirements are also different.

    I think people in snow storm prone areas of the northern hemisphere should keep bottled gas for emergencies. After 2030 or so when we’ve flogged off our best gas reserves Australia should move to electrically powered heat pumps for thermal comfort. By then summers will routinely hit 50C with a large 20th century built housing stock of fibro and brick veneer homes. That’s a problem we’ve foisted on today’s schoolkids and they’ll have to solve it.

  22. @wilful

    The best money is spent on energy reduction rather than generation.
    1. Insulation. I like polyester bats rather than fibre-glass. No irritation when installing or climbing around in the roof. Buy the best R rating. Consider adding another layer over existing.
    2. Get the most efficient fridge you can. This is a 24/7 appliance. An efficient fridge is worth quite a few solar panels. Consider an all-fridge fridge plus a chest freezer. Works for us. The cold doesn’t fall out of a chest freezer.
    3. Down lights are awful. Each one puts a hole in your ceiling letting heat through and adding fire risk with transformers.
    4. Most brick veneers tend to have multi-faceted roofs which make them awkward for solar. A good north-facing roof without obstruction or shadowing is mandatory for solar.
    5. Beware of instantaneous gas hot water. You can use a lot of gas unless you are careful. Consider vacuum tube solar hot water with electric boost. We have such a system. the controller only comes on at 5 pm if the water is below temp. simple. works.
    6. Shade your east and west windows externally to keep the summer heat out.

    If you’re in a town/city wood burning can be problematic. Supply is expensive and smoke annoys neighbours. We’re out of town and have our own supply so it works out.

  23. @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.

  24. 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.


  25. 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.

  26. @Hermit, are you aware of vanadium redox battery technology? Kw/kg is not good, but for houses its not such an issue.


  27. 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.

  28. @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.

  29. @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 🙂

  30. @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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