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Solar system sizing

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  1. #1
    Naf
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    Default Solar system sizing

    Origin have a deal going for a 1.5kw system at the moment, paying it off over 2 years. The thing is I can't work out if it's big enough for my needs, our bill shows that our average is around 18kw per day, I'm sure we can reduce this by a bit though. How much can a 1.5kw produce per day? Is the equation as simple as: 1.5kwh X average hours of sunlight per day?

    Nathan

  2. #2
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    Hi Nathan,

    Check this site out, It has records for actual outputs of systems around australia. Note that summer outputs will be higher, but you can get a good idea of what a certain size system generates: PVoutput.org

    woodbe.

  3. #3
    Golden Member GraemeCook's Avatar
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    Quote Originally Posted by Naf View Post
    Origin have a deal going for a 1.5kw system at the moment, paying it off over 2 years. The thing is I can't work out if it's big enough for my needs, our bill shows that our average is around 18kw per day, I'm sure we can reduce this by a bit though. How much can a 1.5kw produce per day? Is the equation as simple as: 1.5kwh X average hours of sunlight per day?

    Nathan

    In Victoria 1.5kW system should produce around 1,800 - 2,000 kilowatthours per year depending on siting and set-up. But it should produce about five times more power in February than it does in August - longer days, more sun - and virtually no power on dull, heavily overcast, rainy days.

    I would suggest that you do your calculations on yearly average figures.

    Cheers

    Graeme

  4. #4
    Old Chippy 6K
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    First thing you should do is reduce your power usage as you say - you are sitting at a very high usage relative to Australian averages! So there are lots of cheaper alternatives to save money than a PV system on net tariff as you have in Vic & Qld.

    In any case unless you are thinking of an off-grid connection the two are simply unrelated except that you might like to think of offsetting your dirty power with some clean power (and the easiest and cheapest way to do this is to purchase a GreenPower option from your utility).

    Your assessment of PV should be a financial one - how much do you spend to get what size and what return (as you are converting cash into a fixed asset that will provide an income). The way incentives work with the Fed government at present the 1.5kW size is the sweet spot as they offer a 5x multiple on Renewable Energy Certificates (RECs) up to that size. For each REC after that it is 1 for 1 so the average capital cost for each kW capacity goes up after 1.5kW. But that's just capital cost - the return will vary according to the state or territory you are in.

    Feed-in tariffs (ie: the amount they will pay for each kWh of energy you supply to the grid) are available in most jurisdictions - some net (ie: they measure what you put into the grid and take away what you use in your house then pay you tariff for the remainder (they vary a lot though). In those with a gross tariff (I think only NSW & ACT at the present time) they pay you a high amount on ALL the power you put in and you simply pay your normal bill for what you use - - again the terms & conditions vary so check locally.

    What does this mean - firstly look at how much you can afford (assuming you have a suitable roof space to mount PV) to spend and the overall return you can expect (FiT payments are so far tax free - except for pensioners who are still being ripped off by Centrelink under some circumstances). So get some quotes and decide if that's how you want to invest - this is a comparison between alternative uses of your money. My guess is that right now you'll do better by investing in energy savings activities as they'll cost less and will be easier. PV costs will continue to come down.

    BTW - do not be tempted by 'no payment, no interest get a system free offers' - they are no such thing. These are simply finance arrangements that will cost you more than if you get funds yourself if you really want PV - and the real cost you will be paying are very hard to work out.

    Just so you know - I am very pro PV and have 3KW system on my roof (ACT so generous FiT) and will be going bigger soon too. But like all purchases I like real choices and good information about alternatives - including not being a leader & bleeder just because it seems the right thing to do. Investment in a PV system locks your money away into a fixed asset and the payback then return (vs an accessible bank deposit say) period will vary from a few years for a 1.5kW system to 9-12 years for a larger one such as mine. So if you are keen go ahead and get quotes, but follow you head not your heart!
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.

  5. #5
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    Totally agreed with Bloss.

    Assuming we're talking about a grid-connected system, it is an investment decision just like buying shares, property etc. You are making a decision to invest some capital in order to produce a product (electricity) in the expectation of making a certain financial return on that investment.

    What you have is essentially a fixed, long term investment with a high yield (interest) paid on the investment that is likely to increase over time with power prices. That is partially offset by a certain loss of at least part of the invested capital (since system prices are declining over time) and an inability to readily withdraw capital from the investment (ie you can't easily remove and sell the panels at a decent price).

    For me, that does stack up financially provided that the electricity price is sufficiently high. Certainly stacks up very well for a 1.5kW system that gets maximum benefit from REC's. Beyond that level, it can still be a good investment depending on what state you are in.

    A 1.5kW system is almost always worthwhile assuming you're not about to demolish the house etc and that you have a suitable roof to put it on, and assuming that you aren't borrowing money at high rates to purchase the system.

    All that said, don't forget that simply repaying debt and/or investing in energy efficiency are also low risk investment options with a reasonable rate of return (given that there's no tax to pay on the benefit gained).

  6. #6
    Naf
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    Wow, thanks for the replies, very helpful info. For the moment I think we'll fix our wasteful ways and then look at a solar system in the near future.

    Thanks again
    Nathan

  7. #7
    Golden Member GraemeCook's Avatar
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    Good Morning Nathan

    As usual, Smurf and Bloss have given some excellent advice.

    A slight refinement on what Bloss said; whilst its certainly true that the sweet spot is at 1.5kWt, sometimes it is quite attractive to go a little larger. You have to do the maths.

    In the installation there are some lumpy costs - meter (if you have to pay for it), inverter (limited range of sizes) and the electrician's wiring charges. If you install a 1.5kWt system it may cost you x$'s. If you add an extra panel then there may be sufficient capacity in the inverter to cover this extra panel, the meter will be the same, the electrician's bill will not change significantly and you are liable only for the cost of that panel itself. True you only get the 1:1 subsidy, not the 5:1 deal, but your lumpy costs have not increased. Sometimes you can fit in two more panels, rarely three. But it is worth running the numbers.

    As Bloss says, make the decision with your head, not your heart.

    Cheers

    Graeme

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