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Thread: Solar Water Heating

  1. #1
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    Default Solar Water Heating

    Have any forum members any recent experience with the cost and efficiency of solar water heating? I'll be living north of Auckland - probably Whangarei or Bay of Islands.
    Thanks in advance.

  2. #2
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    If you're looking at the payback time for energy saving products, you'll need to decide how long you will be living in the house for. Fortunately where you live the payback would be quicker as dealing with frost is 1 less of a problem with solar hot water. I've been hearing payback times of around 8 years minimum and that all depends on how much hot water you use? It's not a wonder why these energy saving installs aren't a standard install in NZ homes because of the uncertainty of home owners not knowing how long they will live in their home to realise any payback. The other aspect is many don't like it's unsightly setup on the roof which could ruin the appeal of the house. As an example in Christchurch, my cousin paid around $8K for his setup and installed at the time the house was being built (Costs would be higher on existing homes) and this was suited for a 300L size tank. Less than 2 years and the pump had failed (covered by warranty) so there is no such thing as a trouble free setup.

    There are many types to choose but I have preference for the newer evacuated (vacuum) tube modulars that connection to a common manifold. The water only passes across the manifold and not through each tube which greatly reduces damage from below 0C temperatures. The tubes have greater efficiency than conventional flat panel units where the water circulates throughout.

    For those in the S. Island, I don't find solar hot water working that great because of the much colder winter climate. It's not that there's less sun in the S. Island than in the N. Island but rather, during the winter months, solar hot water setups can actually cost you $. The computer controller reverse cycles by taking some of the stored hot water and circulates it through the solar panels in the roof when the temperatures drop below frost. Other less common solar panel setups that deal with frost use antifreeze in the panel and is mated with a heat exchanger (which you will lose say 20% efficiency).

    Installation plays a major part too. Ideally you want the solar tubes/panel to be mounted steep as possible, minimum 45 degree angle but most houses don't have a 45 degree slope. City bylaws have restriction on how steep of an angle you're allowed. The reason for having a steep angle is during winter, the sun goes at a low angle and having the tubes/panels tilted up, they get more of the sun's light. Alternatively if the panel/tubes are mounted more flat, during the summer time it will get far too much heating as the sun goes at a high angle.

  3. #3
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  4. #4
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    Thanks BQ! I appreciate the info.

  5. #5
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    Super_BQ
    If you're looking at the payback time for energy saving products, you'll need to decide how long you will be living in the house for.


    Of course you are allowed to take a slighty longer term/broader view than that!

    We installed a solar hot water system around 10 years ago now and are still very happy with it. Ours uses anti-freeze in the pipes and a heat exchanger and in summer we generally only have to boost on one or two days a month and even in winter it probably still supplies around a quarter of our needs. All in all it has probably performed better than expected and we are now going to add a further 6 or so panels to use for underfloor heating in winter and for the pool in summer.

    In Northland you're bound to have more sun, especially in winter and you won't have to worry about freezing so you'd have more options to choose from.

    While the article BQ referred to was an interesting read, in my view it doesn't really apply to your situation. I think it's more about a macro view of the grid and whether subsidies are sensible than about the efficiencies of solar water heating at a micro level. And there is nothing stopping you from only topping up electrically at night when the demand on the grid is lowest, especially if you have access to a night and day rate.

    Financially, we have hit payback about 2/3 years earlier than we were expecting to, due to power costs rising more quickly than anticipated. When we installed the system we had no idea how long we'd be living here but thought that it could only help boost the resale value of the house should we sell. Now that we're still living here we get to enjoy lots of free hot water! Additionally we're now "low" power users which gets us a better electricity price overall.

    For the new system we're putting in the ROI is even more hazy at the moment as I'm still in the first stages of getting quotes and again we can't be sure how much longer we'll be living here, but having a warmer house in winter with minimal ongoing costs is very appealing to me!
    And a pool that costs a lot to heat is NOT a bonus when you're wanting to sell.

    When we built the house we incorporated the panels into the design so they're not in the way from that POV either and of course putting solar into a new build is cheaper than retro fitting but with the way power prices are going up and the cost of solar panels is going down it should still be a viable option, particularly if you take into consideration that the system should last around 25 years.

    HTH

  6. #6
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    Quote Originally Posted by Super_BQ View Post
    Snip...


    Other less common solar panel setups that deal with frost use antifreeze in the panel and is mated with a heat exchanger (which you will lose say 20% efficiency). ....

    .

    20%, really?


    BQ Do you have any literature to back up that statement? I would appreciate it.

  7. #7
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    I appreciate the replies. Thanks for the info - will look into this further.

  8. #8
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    we got a quote for solar water heating when we moved into our (1970s built) house 2.5yrs ago - quote was +$5k. Didn't win the lottery yet, so will reconsider it when I do!

  9. #9
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    20%, really? BQ Do you have any literature to back up that statement? I would appreciate it.
    This 20% figure given by a solar panel installer and that would be a conservative figure, the installer claimed that there needs to be a great enough temperature difference between the hot & cold in order for the heat exchanger to work and most often this is not the case in winter months. Other factors he mentioned that affect efficiency are, the use of glycol antifreeze (which should be replaced every 2 or 3 years - an added cost) and type of heat exchanger if it's single or double wall plate.

    Of course you are allowed to take a slighty longer term/broader view than that!

    When we built the house we incorporated the panels into the design so they're not in the way from that POV either and of course putting solar into a new build is cheaper than retro fitting but with the way power prices are going up and the cost of solar panels is going down it should still be a viable option, particularly if you take into consideration that the system should last around 25 years.
    No one has to take my word for that. One just has to look at all the home building companies in NZ and see how many of them openly advertise the use of solar hot water panels or electric PV panels in their home designs? Here in Christchurch i've seen zero building companies that are promoting the installation of solar panels - I mean large volume home building outfits that use solar panels as part of their home selling packages. Perhaps the reason is the average house in NZ gets changed every 6 - 7 years and builders know that they can't see the payback (or added value).

    North facing solar collector is very important and unfortunately this doesn't fit for many of the new or existing homes. We're in a new residential sub-division and I would say 1 in 20 houses would of had hot water solar collectors installed on the roof. As i've mentioned before in past posts, if you want people to have solar panels, stop slowly raising electricity prices. Instead make the power prices go up like 20% or 30% every year so that that average kiwi house sees $1000/month electricity bills in a short time frame. The slow gradual price increases like we see how petro prices go up is like a drug ; not high enough to make everyone switch to hybrid / electric cars.

  10. #10
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    Quote Originally Posted by Super_BQ View Post
    This 20% figure given by a solar panel installer and that would be a conservative figure, the installer claimed that there needs to be a great enough temperature difference between the hot & cold in order for the heat exchanger to work and most often this is not the case in winter months. Other factors he mentioned that affect efficiency are, the use of glycol antifreeze (which should be replaced every 2 or 3 years - an added cost) and type of heat exchanger if it's single or double wall plate.
    So no literature.
    In case you're wondering why I asked; 20% is a pretty bold statement without any backup information. I wouldn't have minded if you had mentioned it was something an installer told you in your original post (rather than stating it as a fact) as then I could have judged the value of that statement for myself and would have probably left it at that.


    Quote Originally Posted by Super_BQ View Post
    No one has to take my word for that. One just has to look at all the home building companies in NZ and see how many of them openly advertise the use of solar hot water panels or electric PV panels in their home designs? Here in Christchurch i've seen zero building companies that are promoting the installation of solar panels - I mean large volume home building outfits that use solar panels as part of their home selling packages. Perhaps the reason is the average house in NZ gets changed every 6 - 7 years and builders know that they can't see the payback (or added value).

    North facing solar collector is very important and unfortunately this doesn't fit for many of the new or existing homes. We're in a new residential sub-division and I would say 1 in 20 houses would of had hot water solar collectors installed on the roof. As i've mentioned before in past posts, if you want people to have solar panels, stop slowly raising electricity prices. Instead make the power prices go up like 20% or 30% every year so that that average kiwi house sees $1000/month electricity bills in a short time frame. The slow gradual price increases like we see how petro prices go up is like a drug ; not high enough to make everyone switch to hybrid / electric cars.
    What I meant with the bigger picture is that there are other benefits to solar hot water than just short-term payback. It's green, the grid doesn't need to grow at the same rate as electricity use and you might get payback when you sell your house as your buyers might see it as an advantage.

    Building companies in general are hardly known for their forward thinking ability, their customers will have to specify what they want before anything will happen in that area.
    I think the problem lies more in the initial outlay, as Lin's post above shows it's a lot of money to pay up front, not everyone has the opportunity to spend that kind of money even if it will be cheaper in the long term.
    Last edited by miep; 3rd December 2012 at 09:39 PM.

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