Hard News by Russell Brown

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Hard News: Going solar?

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  • BenWilson,

    With the way projections of dropping cost are going, it looks to me like waiting is the way to go. A strong uptake of domestic solar will drive down domestic power costs, I'd think. And it's not like you're being a carbon using bastard in leveraging off that - you're taking the reverse grid power of other solar installations with excess capacity.

    It's still righteous to have, though. There's plenty of reasons to get it that aren't just about saving money. It's a lot like buying an electric car. The cost justification is now there...just. But the idea of being a part of bringing the future on has appeal all on its own. My comment above is targeted only at the biggest stallmeisters, like myself.

    Re: PV vs water heating, my economics is affected by being in a modern house that's easy to heat, but not so easy to cool. The next real electricity bill saver will be a heat pump, since it will also act as an air conditioner in summer, bringing blessed relief. That chews power, but fortunately, at a time when the cause of the problem can also be the cure. Also, I'm kind of over having a water cylinder at all. It seems like a really old fashioned idea.

    Auckland • Since Nov 2006 • 10657 posts Report

  • Lucy Telfar Barnard, in reply to linger,

    where was that electricity actually coming from?

    Same place as the rest of it, the wire from the street. It just came off the wire before the wire got to the meter, not after.

    Wellington • Since Nov 2006 • 585 posts Report

  • Josh Petyt,

    As it's often said about cars the greenest car is the one you’re already driving.
    If you need to replace your HWC then solar hot water may well be the best choice. I trained as an architectural technologist (a fancy name for a drafter and specifier) from ’06~’08 and at that time we were told that evacuated tubes were better than flat panels and naturally more expensive.
    As others have said, it’s more efficient to heat water than make electricity and then heat water. The heat exchange systems mentioned above are usually used if you are located in the south or at high altitudes where freezing is likely (glycol is an antifreeze) but they’re more expensive. I have not heard anything about direct heating evacuated tubes being less hardy than heat exchange ones. One would expect direct systems to be more efficient though I have no evidence about this.

    Japan • Since Apr 2014 • 45 posts Report

  • Robert Urquhart,

    I dropped about $7k a few years back replacing the hot water cylinder and putting in vac-tube/glycol (boils at a lower temperature than water for heat transfer at lower initial temperature) system - still requires a little mains power to run the pump. Like Simone, here in Canterbury I can turn the electric off altogether from about November to April and have enough hot water for the two of us here. Haven't regretted it.

    The circulating H2O does need the air bubbles purged and repressurised occasionally but that's fairly straightforward.

    (I also have a wetback and grid-connected PV is intended but likely to be a few years away yet.)

    Christchurch • Since Mar 2009 • 163 posts Report

  • artig,

    We bought an almost-new house 7 years ago that had solar hot water installed, together with a gas furnace for supplementing the solar, and for underfloor heating. These were European systems specially imported. There is a hot water cylinder with separate internal coils for the solar heated liquid with its own circulation pump, and another for the gas-heated liquid with another circulation pump. The gas only heats about the upper third of the HWC, whereas the solar heats all of it.

    Getting it to work well was confusing. On most days in summer there is no need for the gas to supplement the solar, but in winter the solar just doesn't provide enough hot water for 2 people. My solution is to set the gas furnace timer to start up every evening if the water temperature is below about 60 degrees, and then switch off again after an hour or two. It doesn't work too well when there are visitors requiring showers. Then the gas needs to be switched on again in the morning.

    The gas furnace sometimes has problems with the NZ LPG supply, and parts are not available here for it. When it dies my intention is to replace it with an on-demand gas water heater that takes the water from the HWC, pre-heated by solar, and only heats the water when its temperature is below about 60 degrees. That should work well all year round, with no fiddling or changeover required during the year.

    For some reason the underfloor heating is not installed in the rooms that need it most, and it's far too expensive to run on LPG, so we have never used it. It may be possible to run on a heat-pump system if we ever want to use it.

    After about 5 years of use the solar panels started to corrode, so sooner or later they will have to be replaced as well. I have also looked at the option of installing PV panels, but the only suitable location and orientation of the panels would be far from optimal.

    BoP • Since Oct 2010 • 41 posts Report

  • Lucy Telfar Barnard,

    There’s a nice summary of the relative advantages and disadvantages of solar and heat pump hot water systems on the first two pages of http://www.pce.parliament.nz/assets/Uploads/Comparison-of-solar-and-heat-pump-water-heaters-in-New-Zealand.pdf

    Lloyd and Kerr’s paper “Performance of Commercially available Solar and Heat-pump Water Heaters” is here: http://www.physics.otago.ac.nz/eman/hew/econtacts/resourcesabstracts.html .

    Wellington • Since Nov 2006 • 585 posts Report

  • bob daktari,

    We're keen to invest in solar at home in some form given the ever increasing power prices

    Hadn't planned on doing anything until after the election due to the Greens Solar Power in Homes policy which might be a real thing sooner than later (https://www.greens.org.nz/solarhomes) - which at worst should see the setup/install costs reduced

    auckland • Since Dec 2006 • 540 posts Report

  • Lucy Telfar Barnard,

    One thing to bear in mind with solar is that the savings may not be as great in future years as uptake increases (unless you’re completely off-grid).

    Running and maintaining the grid costs money. At present, that money is recouped through a combination of fixed costs (daily user charges) and variable costs (a portion of your cents per kWh).

    If solar (whether PV or hot water) uptake increases, the number of kWh of electricity sold will be less, so the amount collected for grid maintenance via the c/kWh will be lower. But the cost of running and maintaining the grid will remain the same, because we’ll all still want the grid there for when solar isn’t enough. At the moment, non-solar customers are effectively subsidising grid use by solar customers, but if solar use increases enough, the way the grid is funded will have to change to ensure grid costs are met. So you’ll end up paying either a higher fixed charge, or a higher c/kWh rate. This increase will reduce your savings from using solar.

    (Trying to think of a good analogy, because I don’t think I’ve explained it very clearly…)

    Wellington • Since Nov 2006 • 585 posts Report

  • linger, in reply to Lucy Telfar Barnard,

    The drop in grid demand from uptake of solar may not matter so much in the long term, as it could be completely offset by increasing use of the grid for recharging electric vehicles.

    Tokyo • Since Apr 2007 • 1944 posts Report

  • Downbeatdan,

    Good that you're looking at it Russell. I spent a while being a home energy assessor (about 500 homes) and looked at several homes with solar hot water.

    The most crucial things in having reliable supply is how big your hot water cylinder is, and when you're going to use the hot water.
    Yes these are very tricky systems, and I've seen several where the failure of one or other parts has caused the system to suck massive amounts of power. There have been no big advances in technology which have caused price drops for the heating units in this field. If anything, they are more expensive than ever. Average NZ family use is that 1/3rd of the electric usage will be hot water if using electricity. Savings from using solar hot water are only half of this third at best - more often only around 25%, from the units my company measured.

    If you look at PV system, you are collecting energy which can be used for any of the energy uses in the house. The cost of panels has dropped massively over the last several years, meaning that the long term cost of energy from these panels is getting very close to parity with grid produced power. Grid connected PV means that there are no finnicky batteries to maintain, halving the cost of the system, and minimising maintenance. The trickiest part of solar PV is not knowing what the future will be of grid exporting power. Seeing as you have a household with lots of use during the day, you'll be be using as much as possible as its made, so looks to suit you. Plus side is - you can stick with a standard, simple hot water cylinder, and you'll be able to spread your collection of solar energy across all of your energy uses, on existing cabling and wiring - no special plumbing set up required.

    Some people are now implementing solar hot water, by simply wiring PV panels to a second element in the hot water cylinder with a power controller. Simple dumping of PV electric into the hot water tank.

    Hope that helps.....

    Hamilton • Since Jul 2007 • 12 posts Report

  • Josh Petyt, in reply to Downbeatdan,

    Some people are now implementing solar hot water, by simply wiring PV panels to a second element in the hot water cylinder with a power controller. Simple dumping of PV electric into the hot water tank.

    That sounds smart. You can also then dump excess hot water into a swimming pool or spa/bath.

    Japan • Since Apr 2014 • 45 posts Report

  • Andrew C, in reply to Martin Connelly,

    At which point you should do a compare with heat-pump hot water tanks

    I have two friends who installed heat-pump hot water tanks, and neither have come remotely close to the promised savings. Both regret getting them.

    My neighbour below me got PV, and likewise he hasn't see the savings he was expecting and isn't recommending it to anyone.

    Just some annecdata, no idea if there are technical reasons for their under performance that wouldn't apply to others.

    Auckland • Since May 2008 • 169 posts Report

  • BenWilson, in reply to Lucy Telfar Barnard,

    At the moment, non-solar customers are effectively subsidising grid use by solar customers

    I don't follow that. The solar customers do pay for their grid use, don't they? Also, they supply power into the grid from their own investment, and at a massively discounted rate. How are they being subsidized? Surely it's the other way around?

    Auckland • Since Nov 2006 • 10657 posts Report

  • Alfie, in reply to BenWilson,

    Ben: The solar customers do pay for their grid use, don't they?

    You're right Ben. I have a 4Kw grid-tied solar system which cost just over $11k+GST installed and I certainly subsidise Contact Energy. In the summer we're generating 350Kw in an average month, but in winter (north of Dunedin) that drops to around 100Kw per month.

    My lines charge each month is just over $80+GST... that's before we start using any power. There's not much competition in our rural area so Contact generously charge us 0.3176 per unit and only pay around half that amount for the power we feed to them. The power companies are still making ridiculously healthy profits.

    Even so, I reckon we'll repay our solar investment in 10-12 years... even sooner if power prices continue to rise the way they have in recent times. And it feels great to see those pretty little passive panels knocking out usable energy every day.

    Dunedin • Since May 2014 • 1440 posts Report

  • Moz, in reply to BenWilson,

    The solar customers do pay for their grid use, don't they? Also, they supply power into the grid from their own investment, and at a massively discounted rate. How are they being subsidized?

    The argument is AFAIK that the fixed supply charge is less than the cost of providing the grid, so net-zero {1} solar users benefit from the usage charges paid by others. For people using the grid as a battery (net usage zero or negative) that argument has some weight, except that the usage charges are normally structured so that you pay a lot more than you earn meaning those people are paying a hefty fee for their "battery" (over 50%, sometimes 90%).

    The underlying problem is that the more people rant about the evils of low or negative power users, and the higher the fees they have to pay, the more attractive it becomes for them to drop off the grid entirely. It's called the "grid death spiral" problem.

    The funniest suggestion I've seen is that every land title would be charged a "grid access fee", basically for running the infrastructure past the property. In the US attempts at this have failed because it's so obviously unreasonable. Those laws have to deal with "20km from the nearest road" farm blocks ($500k+ to run a power line in) as well as "back section urban densification" sites with no road access, as well as dwellings built over multiple titles and occupied by little old ladies who fought in WWII (and thus make great media stories).

    {1} net zero by whatever definition you want to use, typically either "generate enough that their total bill is zero" or just "net usage is zero".

    Sydney, West Island • Since Nov 2006 • 1233 posts Report

  • Richard Grevers,

    I can't give any direct comparisions since we are several km from the grid. Our hot water is wetback off the kitchen range supplemnented by a doesn't quite work well enough (water pressure too low?) gas califont. From older phhotos the house used to have solar h/w - presumably it was removed when it broke down (I know the cylinder has been replaced since then).
    So while it would be nice not to have to run the fire in summer, our savings would be hard to calculate (what is the cost of our labour in harvesting and storing firewood) - and we spend so much time "in the cloud" during winter that annual solar energy gain is greatly reduced.

    So: General thoughts:
    In general, heating water and storing it isn't very efficient. However, the only fuel source fast enough to run a zero-storage system is gas - which would have been a great resource for several hundred years if we hadn't burned most of it to make underpriced electricity in the 80's and 90's. Neither solar nor electricity is fast enough for on-demand hot water.
    The biggest cost component of solar hot water is the plumbing. This varies in complexity depending on water pressures and cylinder type. An ideal system uses thermal siphon, but some need pumping.
    Solar may well not meet needs year round, so what is the winter backup going to be?
    Last time I spoke to someone a chinese-made vaccuum tube unit cost $1200+GST landed. You could get about three decent sized PV panels for that price. So if your existing cylinder could be fitted with a 12-24V DC element, (I don't even know if there is such a thing as a cylinder with dual element options) PV direct to water could have lower capital costs (a controller triggered by a thermostat should be around $200, cable can be expensive if you can't keep distances short).
    Excess PV can power other things, too, whereas SHW can only heat water.
    Using PV in a grid-tied or battery storage system to power a 240V AC heater element would increase the size of inverter required ($$$) - which is why, in conventional off-grid energy design, water heating is the first thing you throw out of the electric equation.

    In our system, going back to Solar Hot water might be something as simple as branching the cold water feed to our HWC before it gets to the house and running it through 40m of alkathene pipe attached to a black concrete wall. If that raises the temperature of the mountain stream water by even 10 degrees, it's a significant fuel saving.

    New Plymouth • Since Jul 2011 • 143 posts Report

  • BenWilson, in reply to Moz,

    the fixed supply charge is less than the cost of providing the grid

    Therein lies the solution. The fixed supply charge should be the same as the cost of providing the grid. Which would, incidentally, be fair – passing on the real cost, rather than slipping it into the usage charges which fluctuate with the price of power.

    And, of course, it’s not like the power supplied back into the grid is of no value. It’s being purchased wholesale from solar owners, and sold retail to the person next door. There’s complexity in the storage/smoothing of the fluctuating supply, but there is presumably a hugely reduced transportation cost. I bet this complexity is quite substantial, even, but really, if a bloody power grid company can’t handle it, then perhaps they could mandate that the suppliers have some level of smoothing of their own (but they would have to pay them more for that high quality power). Really, it seems to me like something that they would want to do, rather than complain about having to do.

    TLDR version: Do they want to lose their monopoly? Because acting like home solar isn’t coming is a sure way to do that.

    Auckland • Since Nov 2006 • 10657 posts Report

  • Alfie,

    The power companies will always moan that solar costs them money and that we're somehow leaching off the grid.

    The worst example is in Hawaii where conventional grid power is three times the cost of mainland electricity. Power companies have imposed a moratorium on new solar connections and want to impose a fee on people with solar installations of around $120 a year. In Arizona the PowerCos tried to impose a $50 per month "penalty" on solar powered houses - legislators turned that idea down.

    We have no government incentives to install solar in NZ, and no guaranteed feedback tariff. So unless the government changes, our power companies are still running the show to their advantage.


    Dunedin • Since May 2014 • 1440 posts Report

  • BenWilson,

    However, the only fuel source fast enough to run a zero-storage system is gas

    You think? I've used electric versions that were OK. You don't get huge pressure, but I don't want huge pressure. I almost never want it to produce scalding hot water at a high flow rate. For boiling water, there's the stove and kettle. For showers, colder water is better. For baths, yes, a higher flow rate would make pouring the bath quicker, but a bath isn't a quick thing in the first place, quite aside from being an outrageous luxury :-). For other purposes: Dishwashing: I want to be able to put my hands in it. I tend to use lukewarm. Washing machine: It's a machine. I don't care how long it takes. Dishwasher: Same comment.

    I'd happily give away the hot water cylinder one day, when my budget stretches to it, without wanting to have gas in my house.

    Auckland • Since Nov 2006 • 10657 posts Report

  • Stamper Stamp,

    Folks - if it was a 'no brainer' to move to solar - every one would do it; instead we have the arguments for/against for trying to save planet/energy/money.
    It you have to argue - it is obviously NOT compelling.
    So - are we going to save planet/energy/money - or are we just going to "feel good" ?
    Maybe green energy isn't a reality after you have looked at the whole picture - a bit like the bio-energy fiasco.

    Auckland • Since Feb 2014 • 27 posts Report

  • JonathanM,

    Given your requirements (4 adults, most of whom enjoy long showers) then be careful as capacity is likely your largest constraint. In the summer you'll probably be OK as the sun will reheat things fast enough to not be a problem, but in winter unless you also supplement with electricity, wet-back, or possibly both, you'll likely learn to shower a lot quicker or face the no-hot-water left problem.

    Efficient shower heads may reduce this somewhat, but at 10l/min (decent, but not overly high flow) will mean about 4-6l/min hot water from the tank, so between 50 and 75 minutes from a 300l tank. For 4 people who enjoy long showers, that could get a bit tight, though a 10minute shower is longer than you think...

    PV or heat pump HW doesn't have that problem, nor does instant gas. The latter works well - use the HW cupboard for something else - but may not be as green!

    All the systems add complexity, so make sure you take into account maintenance costs (I'd allow double from whatever is quoted).

    Since Jul 2012 • 64 posts Report

  • John Morton, in reply to Russell Brown,

    Choosing solar water heating now over PV later might matter if you where using up all your roof surface area (you're not), and there is a significant difference in efficiency between the two — PV is about 15%; I don't know what solar heating is, but it's unlikely to be much worse.

    I found this helpful:


    Wellington • Since Mar 2014 • 4 posts Report

  • Alfie, in reply to Stamper Stamp,

    Maybe green energy isn't a reality after you have looked at the whole picture - a bit like the bio-energy fiasco.

    You mean the rest of the world has it wrong? Germany is going solar big time, the UK is heading for 10% of homes, AU is a very solar-friendly country and the US is putting up panels like there's no tomorrow.

    You may feel that electicity prices will drop in the future, but I can't see that happening. I did the figures before installing solar and I'm very happy with a 10-12 year payback. My system has already halved my power bills and the panels are guaranteed to be producing 85% efficiency after 25 years. That's 15 years of almost free power and that certainly works for me.

    Dunedin • Since May 2014 • 1440 posts Report

  • BenWilson, in reply to Alfie,

    You may feel that electicity prices will drop in the future, but I can’t see that happening.

    I can. But it will be solar supply causing it. Every one of you guys going solar is good for me too, because that's one less person competing for the hydro, and even some increased supply when it's extra sunny.

    Auckland • Since Nov 2006 • 10657 posts Report

  • Raymond A Francis,

    Don't piss around put in one of these big boys
    We went the vacuum tube way a couple of years ago when upgrading bathrooms and water system, it is great. A friend who put in a wet back as well has not paid a heating bill since
    There is talk that electricity prices may fall but that is not the way of the world

    45' South • Since Nov 2006 • 578 posts Report

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