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795 posts

Ultimate Geek


  # 1403222 9-Oct-2015 19:40
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Porboynz:
Anyone want to buy 2 x solar water panels, pump and controller? 




Solar hot water only makes sense when the cost is really low. 

What diverter are you using to send excess power to your HWC?

795 posts

Ultimate Geek


  # 1403240 9-Oct-2015 20:20
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PV .. perhaps once Enphase's batteries arrive, we'll know more of what we can at what price

http://www.geekzone.co.nz/forums.asp?forumid=141&topicid=181229

 
 
 
 


3885 posts

Uber Geek

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  # 1403265 9-Oct-2015 21:51

gchiu:
Porboynz:
Anyone want to buy 2 x solar water panels, pump and controller? 




Solar hot water only makes sense when the cost is really low. 

What diverter are you using to send excess power to your HWC?


Are the panels flat plate or vacuum tube? But I guess it won't matter so much anyway. If they are cheap enough.

I already have a 20 tube and a 30 tube solar hot water panels on my roof. So adding more is not much of a problem. Although want to add 250W or so of solar PV. To keep my backup batteries charged if there is a long term power cut. And to help offset some of the load from the charger.





110 posts

Master Geek


  # 1403612 10-Oct-2015 19:59
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What Power Crisis has a NZ made recently developed HWC diverter on their website but I built a kitset diverter designed in the UK called a Mk2PVrouter.  They are similar in operation, diverting any excess energy to the HWC element that would ordinarily be exported.  Once the thermostat opens you go back to exporting at $0.08 per kWh but while you are using it to heat your HWC your payback is equivalent to whatever your daytime per unit buy rate is.  In my case on a low user plan that's about $0.29 per unit. My traditional solar water panels are flat plate with hi solar gain glass, I'll bang them on TM when I can be bothered as a "can be viewed working" complete system.  If I take them down I will have to paint the roof under them, easier to do nothing smile

Anyway my point here is that using one of these HWC diverters can swing the payback equation back in solar PV favour if the panels are sized right for the house load.  I agree that buying excess generating capacity is no longer economic with buy back rates under $0.10 per unit.

5385 posts

Uber Geek


  # 1404975 13-Oct-2015 12:28
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What would happen if power companies were legally obliged to buy surplus energy from solar PV equipped houses at the spot price?




Mike

3988 posts

Uber Geek


  # 1405038 13-Oct-2015 14:15
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MikeAqua: What would happen if power companies were legally obliged to buy surplus energy from solar PV equipped houses at the spot price?


Over a whole year you would probably not make much more than the 8-10 cents/Kw that Contact and Meridian offer now,

If you took 2014 as an example, wholesale Spot moved to around 12c/unit in Feb-April as a drough condition existed in the South Island, but as rain cam in April, prices fell back to 6 c/unit until September/October, and then they gradually climbed to be about 8 C/unit by December,

see page 45 of this

https://www.ea.govt.nz/dmsdocument/19165

Basically in a Dry conditions, Spot will likely be more than the curret offered soalr buy in, but in times of plenty of Hydro inflow, spot will most likely be lower than the current buy in rates...



3383 posts

Uber Geek

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  # 1405043 13-Oct-2015 14:30
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MikeAqua: What would happen if power companies were legally obliged to buy surplus energy from solar PV equipped houses at the spot price?


Thats actually something I believe should be done. However it may not be as good a deal as what you get now, but its fair, and would legally give you some security on your investment.




Ray Taylor
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632 posts

Ultimate Geek


  # 1405352 14-Oct-2015 07:28
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So if spot prices drop when hydro is cheap and plentiful, and they rise when hydro is not...this is the perfect scenario for PV generators, because it is more likely that hydro won't be as plentiful in times of high sunshine levels yeah? possibly oversimplifying it...but still :)



35 posts

Geek


  # 1405448 14-Oct-2015 09:25
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E3xtc: So if spot prices drop when hydro is cheap and plentiful, and they rise when hydro is not...this is the perfect scenario for PV generators, because it is more likely that hydro won't be as plentiful in times of high sunshine levels yeah? possibly oversimplifying it...but still :)


Yeah, if the drought is at a sunny time (Jan-Mar) then you'd have higher spot prices coinciding with the time you export the most solar.

There's also a time of day element - most solar is exported in the middle of the day, so you're really being paid the "average middle of the day spot price" more than the overall average spot price. Turns out it's roughly the same amount (the highest prices are at breakfast and dinner, average prices during the day, and low prices overnight). Again that's very simplified.

The power co's base their prices roughly on the long-term expectation of spot/futures prices so you'd expect to get about the same 7-8c over the long run.


Porboynz: What Power Crisis has a NZ made recently developed HWC diverter on their website but I built a kitset diverter designed in the UK called a Mk2PVrouter.  They are similar in operation, diverting any excess energy to the HWC element that would ordinarily be exported.  Once the thermostat opens you go back to exporting at $0.08 per kWh but while you are using it to heat your HWC your payback is equivalent to whatever your daytime per unit buy rate is.  In my case on a low user plan that's about $0.29 per unit. My traditional solar water panels are flat plate with hi solar gain glass, I'll bang them on TM when I can be bothered as a "can be viewed working" complete system.  If I take them down I will have to paint the roof under them, easier to do nothing smile

Anyway my point here is that using one of these HWC diverters can swing the payback equation back in solar PV favour if the panels are sized right for the house load.  I agree that buying excess generating capacity is no longer economic with buy back rates under $0.10 per unit.


Do you know roughly how much extra power you managed to use for hot water, instead of exporting it?

632 posts

Ultimate Geek


  # 1405518 14-Oct-2015 10:15
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I had a chat with the guys who did our PV installation (who also sell those diverters, and also just a simple/cheaper HWC timer option too), and we both concluded that (unless you can do it yourself), by the time you sink the cash into getting the diverter plus the installation that the ROI figures didn't look that smart.
At the end of the day in the current climate the best possible way to maximise your ROI is to have a properly sized PV solution that means reducing/eliminating the volume of exports. 



35 posts

Geek


  # 1405543 14-Oct-2015 10:28
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E3xtc: I had a chat with the guys who did our PV installation (who also sell those diverters, and also just a simple/cheaper HWC timer option too), and we both concluded that (unless you can do it yourself), by the time you sink the cash into getting the diverter plus the installation that the ROI figures didn't look that smart.
At the end of the day in the current climate the best possible way to maximise your ROI is to have a properly sized PV solution that means reducing/eliminating the volume of exports. 


It's a really interesting problem - too big and you end up exporting too much in summer, but too small and you don't get the full potential savings in autumn & spring.

Also if you go too small you could end up not being able to 100% power individual appliances - e.g. if you put a 1000W kettle on at 10am on a sunny day with a 2kW system, you might still be drawing power from the grid.

110 posts

Master Geek


  # 1405846 14-Oct-2015 18:18
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Sizing to load is important indeed.  Then there are simple choices you can make like boiling the kettle after you make your toast so the load is more distributed reducing instantaneous load.  Our dishwasher and washing machine both have a delayed start function to operate during the daytime.  Then there are the soft benefits, never underestimate the feel good factor.    Regarding diverted power, the PVRouter is diverting  4 - 5kWh per day to the HWC, that's about $1 per day.  That's with a solar water system supplementing the HWC though, so maybe 7 - 8kWh per day without the solar water panels?  Remember though we have a 310 litre HWC so we do not need to use electricity in the evening and still have plenty of hot water if we get it up to temperature during the day.

928 posts

Ultimate Geek


  # 1405851 14-Oct-2015 18:25
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trig42: I think the payback there is pretty optimistic, but if you take power price rises into consideration, it may make it better (cost of power from your retailer is never going to go down is it?)

My parents are getting  a system installed, they know it isn't likely to pay them back for quite some time, but they like the idea of 'doing their bit' and they are in a position of being able to afford the outlay.

I'm sure having smaller power bills wont hurt either.



Well my boss is an electro-chemist who has developed various battery technologies and his view is, no, they are not worth while.

Break even period is over 10 years, but if you start adding in battery storage, by the time you keep replacing them every x number of years you will almost never catch up. 

The further south you go, the longer the payback period.



110 posts

Master Geek


  # 1405861 14-Oct-2015 18:36
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Here is todays solar and usage graph, 4.2kWh diverted into the HWC during the morning then the HWC thermostat opened at about 2.40pm after which any surplus (yellow) is again exported.  It was an overcast morning with an afternoon of scattered sunshine, usually the HWC is up to 60C by midday.


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  # 1405883 14-Oct-2015 19:00
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My HWC is a 2 element one with a top one so am thinking once I get solar will put the bottom one on a diverter and leave the top one always on. The thermostat for the top one cuts the bottom one so the thing only takes 3kw maximum anyway, but I can see that only heating the bottom with solar may help.

Waiting on the roof guy to get around to looking at the shed roof leak before getting vector out to price it up. Im hoping the 6mm cable to the shed is enough for a 5kW system because replacing that would be a prick.




Richard rich.ms

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