Hard News by Russell Brown

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Hard News: Going solar?

146 Responses

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  • Andrew C, in reply to Kumara Republic,

    as opposed to people acting out of property value self-interest

    I don't think that came into it at all.

    NZ is blessed with some great hydro schemes, but it doesn't seem easy to propose new ones nor extend existing ones.

    Auckland • Since May 2008 • 166 posts Report Reply

  • David Haywood, in reply to Lucy Telfar Barnard,

    A minor quibble, but presumably you’d need to adjust your shower mixer a bit in the early minutes of your shower, as the cold water starts to heat up and so the hot water needed becomes less?

    You can put the output of your HX into the HWC (saves energy only) or – as you say – into the shower, which means you have to bugger round with the mixer, but also that you can have a much longer shower for a given size of HWC.

    I’ve done heaps of modelling on these systems and they are good in theory. The problem is the HX cost and the cleaning. Most systems use some sort of horrible draino-type stuff every few weeks.

    I’ve actually developed a system that gets round both these problems (cleaning better than cost, alas) but I have yet to get it beyond a prototype (mostly my fault).

    Dunsandel • Since Nov 2006 • 1156 posts Report Reply

  • Rich of Observationz, in reply to David Haywood,

    2nd-hand batteries from electric cars start to enter the market

    Isn't there a fairly large conversion loss, especially on a battery that's nearing the end of its days? (Or are you assuming that the cars will suffer other mechanical failure or be totalled before the battery dies? We should maybe increase speed limits.)

    I believe there has been work on having plugged in vehicles act as a sink of off-peak power - similar to using an ex-vehicle battery, but you still get to drive the car.

    Back in Wellington • Since Nov 2006 • 5539 posts Report Reply

  • BenWilson, in reply to David Haywood,

    Russell, sorry not to have replied earlier but have had bad cold followed by possible “mild” influenza – also looking after children with same.

    You too, huh?

    Auckland • Since Nov 2006 • 10504 posts Report Reply

  • Moz,

    One retailer in Victoria is charging 14c/day if you have solar because they own Australia's dirtiest coal plant (Hazelwood) and solar is cutting into their peak demand profits.

    Sydney, West Island • Since Nov 2006 • 1028 posts Report Reply

  • BenWilson, in reply to David Haywood,

    Curious about using an idea like that in conjunction with tankless heating. The tankless unit would be right next to the shower. Presumably it would improve the overall flow of the system dramatically to get pre-heated water coming into it, and any issue with fluctuating temperature is controlled automatically.

    Auckland • Since Nov 2006 • 10504 posts Report Reply

  • Moz, in reply to Andrew C,

    What exactly do you mean by this? To be profitable, what happened to the price in this study?

    "profitable" meaning people made money out of it. Primarily electricity consumers, in this case, meaning the price of electricity was lower with 100% renewable than with the current approach (subsidised coal and gas with legislated advantages in terms of access to land etc). The full study is here

    Note that they also assumed people would do things like insulate their homes, and that there would be a change in government intervention in the market (requiring rental WoF, charging for carbon emissions, etc). Any 30 year forecast is necessarily a very political document.

    BZE left a bunch of advantages out of the study because they're contentious - the falling price of renewables, any generation that isn't already commercially available, the secondary costs of ie converting farmland to wasteland when fracking for gas.

    Sydney, West Island • Since Nov 2006 • 1028 posts Report Reply

  • Rob Stowell, in reply to David Haywood,

    We've had a Thermocell system since 1998. Runs brilliantly. We did blow the controller but that might have been our dodgy power. And Nick gave us a new one.

    Whakaraupo • Since Nov 2006 • 2062 posts Report Reply

  • Russell Brown, in reply to David Haywood,

    If you flip me the specs, I’d be happy to have a look at the proposed system for your house.

    Thank you! Nova sells a SolarElite system using these panels.

    The panels have “flow tubes” but I can’t tell from the comments here whether these are the good sort of tubes.

    Auckland • Since Nov 2006 • 22227 posts Report Reply

  • Andrew C, in reply to Moz,

    One retailer in Victoria is charging 14c/day if you have solar

    Is there a cost to the electricity supplier (or network supplier) to take excess power out from a house and put it back into the distribution network?

    I'm just wondering if this is the reason...?

    Auckland • Since May 2008 • 166 posts Report Reply

  • Andrew C, in reply to Moz,

    meaning the price of electricity was lower with 100% renewable than with the current approach

    I had a quick scan of their document Moz. Showing prices of $120 by 2020 is considerably higher than most business-as-usual forecasts I have seen. I haven't picked it apart to see what it contains, and probably won't, but their claim seems to rest considerably on the assumption that their price forecast is not much higher than the bau will be. From what I have seen, it's a strong assumption.

    Auckland • Since May 2008 • 166 posts Report Reply

  • BenWilson, in reply to Andrew C,

    Is there a cost to the electricity supplier (or network supplier) to take excess power out from a house and put it back into the distribution network?

    Yes. They do need altered infrastructure if the amount of that power gets large, which it could if there’s a huge growth in home PV.

    But. There is also a lowered transportation cost, in theory, since the power is being produced nearer to where it’s being used. And obviously the power is, itself, of value. It’s power they don’t have to supply from elsewhere.

    Auckland • Since Nov 2006 • 10504 posts Report Reply

  • Rob Stowell, in reply to BenWilson,

    The cost of building new large-scale generation is likely the biggest driver of solar in the home.

    Whakaraupo • Since Nov 2006 • 2062 posts Report Reply

  • Che Tibby,

    i've done the math on this time and time again, and the only reason we haven't gone solar PV is that our bills are so low - mid-winter we only pay $150 a month. a large part of that is having a modest home and a big woodburner (total monthly heating is at least $200 per month in winter, but if we get free firewood anywhere it drops dramatically). but we also work hard on not wasting electricity.

    like someone said earlier (thread is currently a bit tl;dr for my cold-addled brain), the most carbon efficient car is probably one already built - but i'd argue that it's one you don't use at all. frugality is the key.

    the back of an envelope • Since Nov 2006 • 2038 posts Report Reply

  • Rich of Observationz, in reply to BenWilson,

    Would that work with an instant hot water (all house, rather than shower only) type setup.

    It's to be noted that gas is way cheaper than electricity, which changes the (financial) economics if you have a mains gas connection.

    Back in Wellington • Since Nov 2006 • 5539 posts Report Reply

  • Moz, in reply to Andrew C,

    their claim seems to rest considerably on the assumption that their price forecast is not much higher than the bau will be

    That's right. Remember that their study is primarily an answer to two claims: first, that 100% renewable can't be done at all; and second: if it can be done it will be economy-wrecking expensive. It's also a 40 year forecast, so if it's within a factor of 2 it's a great deal better than most long term economic forecasts.

    For context, in Australia we've just backed away from spending $40 billion on a national fibre to the home project, but in the last 10 years or so we've spent $45 billion upgrading that electricity grid to deal with twice the demand we currently have. Demand is dropping{1}, and that seems likely to continue in the short-to-medium term (5-10 years).

    So the question "what if we spend $40 billion on the electricity sector and it turns out we didn't need to" has already been answered: power bills double. We did that as a result of political error, and it seems increasingly likely that one consequence was the election of Abbott (people wrongly linked the doubling of power prices to the carbon tax, when it was the states linking grid owner profits to the capital value of the grid).

    {1} in some areas peak demand is growing due to air conditioners - our peak load is hot summer afternoons. Which is exactly when PV is most effective, meaning that home PV is not just reducing the need for new peak generation capacity, it's reducing the need for grid expansion. We all save twice... except those off the grid, obviously.

    Sydney, West Island • Since Nov 2006 • 1028 posts Report Reply

  • Andrew C, in reply to Moz,

    if it can be done it will be economy-wrecking expensive

    I guess I am saying that they are saying it wont be much different to bau prices, yet are showing forecast bau prices quite a bit higher than most forecasts I have seen lately.

    It’s also a 40 year forecast, so if it’s within a factor of 2 it’s a great deal better than most long term economic forecasts.

    Yeah, but 2020 aint 40 years away, and they are talking about seeing $120 then. So saying they're better than most is up for debate.

    Auckland • Since May 2008 • 166 posts Report Reply

  • Moz, in reply to Andrew C,

    showing forecast bau prices quite a bit higher than most forecasts I have seen lately.

    That $120 is $/MWh wholesale in Australia, for those who (like me) needed to look it up. I'm interested in the numbers you've seen so we can compare. The report talks about the price increase in these terms:

    This increase is less than electricity price increases already experienced by household consumers. For example the Independent Pricing and Regulatory Tribunal in NSW has proposed annual tariff increases of between 7 and 10% over 3 years to June 2013. This rise was motivated by the need to “enable higher levels of investment in the electricity distribution networks”. The price increases mean that after 3 years the price of electricity will increase by up to 42% which equates to a 8.6 c/kWh increase.

    A significant chunk of the price rises you're talking about have already happened. Although the BZE modelling was not quite right, the actual prices doubled over 5 years. Admittedly that retail price increase had little to nothing to do with generation costs, it was mostly network costs. But now we're starting to see generation costs rise as Australia starts to sell gas internationally so the local price is going up. Suggesting that prices rises will be more restrained in future means you have much more confidence in Australian politicians than I do.

    Sydney, West Island • Since Nov 2006 • 1028 posts Report Reply

  • James Green, in reply to David Haywood,

    I’ve done heaps of modelling on these systems and they are good in theory. The problem is the HX cost and the cleaning. Most systems use some sort of horrible draino-type stuff every few weeks.

    Hi David,
    As we are about to install one, I'm curious about the cleaning issue (many claim to require no cleaning). Is it that the kind of scum that normally builds up in drain pipework reduces the HX efficiency, or another kind of problem? Would we be wise to plumb it in so that it could be mechanically cleaned (with an oversize bottle brush)?

    Dunedin • Since Nov 2006 • 703 posts Report Reply

  • Russell Brown, in reply to James Green,

    You just about had me sold, so I, too, am curious!

    Auckland • Since Nov 2006 • 22227 posts Report Reply

  • James Green, in reply to Russell Brown,

    David's is the first piece of skepticism I've come across, so I'm super keen to hear to!
    (Plus, I've actually bought, but not yet installed one).
    I've spent a lot of time investigating this as, on the face of it, it just seems like a no brainer. And so we wait :) :)

    Dunedin • Since Nov 2006 • 703 posts Report Reply

  • Steve Barnes, in reply to Rich of Observationz,

    Would that work with an instant hot water (all house, rather than shower only) type setup.

    Yes, as I described on the previous page.

    I would suggest a hybrid system of gas hot water on demand, which is far cheaper as you are not storing hot water at around 55c and solar preheating to your existing cylinder which can and will reach quite high temperatures on sunny days, in this country in summer I have managed to boil water in a roof panel in less than 30 mins. (considering we get over 1Kw per square meter in average sunshine, even in winter, this is not surprising)
    With a thermostatically controlled system pump, switching @ 55c feeding a 185 ltr cylinder in sunny weather your water will heat faster than using a 2Kw immersion heating element. Run that through an on demand gas water heater and the thing won’t even fire up unless the water in the cylinder is lower than 60c (in theory at least) so on sunny days you use virtually no gas and on cold cloudy days you will have constant, limitless hot water

    A little verbose I suppose, tl, dr?
    We use a system similar to this with a separate pump for the hot water (before the gas water heater but after main pump, keeps constant pressure to water heater) we are on tank water, it works well.

    Peria • Since Dec 2006 • 5521 posts Report Reply

  • BenWilson, in reply to Rich of Observationz,

    It’s to be noted that gas is way cheaper than electricity, which changes the (financial) economics if you have a mains gas connection.

    Changes again if you don't, though? And changes again if you're making your own electricity at the time :-).

    Auckland • Since Nov 2006 • 10504 posts Report Reply

  • David Haywood, in reply to James Green,

    I’m curious about the cleaning issue (many claim to require no cleaning). Is it that the kind of scum that normally builds up in drain pipework reduces the HX efficiency, or another kind of problem?

    Yes, the scum reduces the heat transfer. Is your one a gravity film (i.e. mounted vertically) unit? If so, it seems that these are much less prone to fouling.

    The horizontal units seem to be a problem, particularly the ones with the corrugations on the inside to increase the heat exchange.

    Either way, you should definitely install it so that it can be easily cleaned (hopefully just a single grub screw that allows you to remove the final plastic section that diverts the wastewater into the drain). If you can clean it every couple of months it should be no problem at all (regular cleaning is beyond most people, alas!)

    Dunsandel • Since Nov 2006 • 1156 posts Report Reply

  • Hebe, in reply to James Green,

    I remember this article: I bored Beloved senseless about it. Where can the systems be obtained?

    Christchurch • Since May 2011 • 2880 posts Report Reply

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