3kW Grid Tied Solar PV: Watts and Warts.

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1268 posts

Uber Geek

#989263 17-Feb-2014 22:02

When you install a hot water cylinder with an electric element that element will typically be 3kw. If you take the 2kw element option instead it should drain less from the mains and more from the PV than a 3kw element would.

Don't have too much faith in "A Grade" cylinder insulation ratings as they can still leak plenty of heat. A cylinder insulation wrap should still more than pay for itself.

mattwnz

20164 posts

Uber Geek

#989639 18-Feb-2014 14:03

Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

kiwitrc

4123 posts

Uber Geek
Inactive user

#989665 18-Feb-2014 14:49

mattwnz: Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

What maintenance do conventional solar water heaters need?

mattwnz

20164 posts

Uber Geek

#989670 18-Feb-2014 15:00

kiwitrc:
mattwnz: Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

What maintenance do conventional solar water heaters need?

Apparently they need checking once a year by a pro, that it is working properly, as they can self destroy themselves if something stops working on them. They have to have water constantly cyling through them, and some can potentially can have problems with temperature extremes. They also can get scale build up. There are quite a few websites that list the pros and cons with each system. The advantage of PV is that there is no water going through it, so you are not having to worry about all those extra external pipes.
Historically the conventional systems were teh way to go, as PVs were too expensive. But now PVs have come down so much in price, apparently PV is best way to do it. At least overseas, but in NZ who knows. I do know there is at least one company in NZ that are now doing them, as they were at the home show, but can't find their details.

kiwitrc

4123 posts

Uber Geek
Inactive user

#989673 18-Feb-2014 15:07

mattwnz:
kiwitrc:
mattwnz: Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

What maintenance do conventional solar water heaters need?

Apparently they need checking once a year by a pro, that it is working properly, as they can self destroy themselves if something stops working on them. They have to have water constantly cyling through them, and some can potentially can have problems with temperature extremes. They also can get scale build up. There are quite a few websites that list the pros and cons with each system. The advantage of PV is that there is no water going through it, so you are not having to worry about all those extra external pipes.
Historically the conventional systems were teh way to go, as PVs were too expensive. But now PVs have come down so much in price, apparently PV is best way to do it. At least overseas, but in NZ who knows. I do know there is at least one company in NZ that are now doing them, as they were at the home show, but can't find their details.

Maybe it depends on what type of system is installed, open, closed etc? I have a Microsolar which is dead simple and I couldn't see how or what could be destroyed as there isn't much to go wrong.

mattwnz

20164 posts

Uber Geek

#989678 18-Feb-2014 15:15

kiwitrc:
mattwnz:
kiwitrc:
mattwnz: Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

What maintenance do conventional solar water heaters need?

Apparently they need checking once a year by a pro, that it is working properly, as they can self destroy themselves if something stops working on them. They have to have water constantly cyling through them, and some can potentially can have problems with temperature extremes. They also can get scale build up. There are quite a few websites that list the pros and cons with each system. The advantage of PV is that there is no water going through it, so you are not having to worry about all those extra external pipes.
Historically the conventional systems were teh way to go, as PVs were too expensive. But now PVs have come down so much in price, apparently PV is best way to do it. At least overseas, but in NZ who knows. I do know there is at least one company in NZ that are now doing them, as they were at the home show, but can't find their details.

Maybe it depends on what type of system is installed, open, closed etc? I have a Microsolar which is dead simple and I couldn't see how or what could be destroyed as there isn't much to go wrong.

Is that with the tubes or panels? I have heard that someo of the pnel ones corroded on the outside which cuased them to stop workings as well.
Apparently frost and very hot days can cause problems, and if the pump that circulates the water stops working it could potentially cause problems. I can also understand scale built up and corrosion could be problems longer terms. It maybe that some of these PV companies are using scare tactics in their marketing. But it does make sense that if you were putting in a system today, the PV ones are now at least worth looking at.

kiwitrc

4123 posts

Uber Geek
Inactive user

#989700 18-Feb-2014 15:38

Glass tubes so maybe panels can give issues. Open system isn't affected by frost or hot days either, closed systems usually have anti freeze. If the pump stops the water just boils off and is replaced by cold water so no issue there. If scale was a problem then I think we would have a bigger issue with the house water pipes :)

It does sound like FUD to me. I like the idea of PV and a heat pump but I think there is a hell of a lot more to go wrong there (at a far higher repair cost) than a passive system. I realise that PV directly into an electric element isn't as efficient as a heat pump but after 7 to 10 years and a heat pump/inverter/controller failure it might work out a lot cheaper in the long run, but to be fair I have no idea on the life cycle of the above or repair costs.

Porboynz

110 posts

Master Geek

#989847 18-Feb-2014 18:00

bfginger: When you install a hot water cylinder with an electric element that element will typically be 3kw. If you take the 2kw element option instead it should drain less from the mains and more from the PV than a 3kw element would.

Don't have too much faith in "A Grade" cylinder insulation ratings as they can still leak plenty of heat. A cylinder insulation wrap should still more than pay for itself.

That's a good idea, spread the power demand over daylight PV producing hours with a time clock. In my situation I also have solar flat plate collectors for HW, after todays sunny afternoon I now have 310 litres of water at 75 deg C. The element rarely turns on over most of the summer months. The tempering valve does a fair job of reducing the dangerously hot water to under 55 deg C so that will last us about 2-3 days normal use without sunshine.

Today was a milestone event, the solar PV panels had generated 2000 megawatt hours at 2pm today since installation in Oct 2013. That's from 1690 hours of sunshine, about 15.4kWh average daily production. I checked the power company meter and I have exported 924 of those 2000 kWh and used the rest.

Porboynz

110 posts

Master Geek

#989859 18-Feb-2014 18:13

mattwnz: Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

Good idea, but it will not work sadly without expensive batteries and an inverter. A HW heat pump needs a continuous power supply so the compressor can ramp up, they have a protection timer built in to delay restart if they lose power. A PV panel output fluctuates a lot on normal cloudy days as you can see in my post above. So if you want a heat pump for your HW you can still get a solar PV that's grid connected to smooth out the supply, but not directly connected. I can recommend Econergy as a NZ made HW heat pump manufacturer with a very good Consumer result. I would have one installed in a flash if I did not already have solar water panels installed purely because the performance is the same summer and winter.

Porboynz

110 posts

Master Geek

#989867 18-Feb-2014 18:25

mattwnz:
kiwitrc:
mattwnz: Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

What maintenance do conventional solar water heaters need?

Apparently they need checking once a year by a pro, that it is working properly, as they can self destroy themselves if something stops working on them. They have to have water constantly cycling through them, and some can potentially can have problems with temperature extremes. They also can get scale build up. There are quite a few websites that list the pros and cons with each system. The advantage of PV is that there is no water going through it, so you are not having to worry about all those extra external pipes.
Historically the conventional systems were the way to go, as PVs were too expensive. But now PVs have come down so much in price, apparently PV is best way to do it. At least overseas, but in NZ who knows. I do know there is at least one company in NZ that are now doing them, as they were at the home show, but can't find their details.

Without wanting to provoke Murphys law, my solar flat plate HW system has been reliably making HW for 5 plus years now and the only fix has been a $20 one way valve that was affected by excessive heat. I have now reduced the operating temp to a maximum 85-90 degrees C, after which a safety valve opens on the panels which introduces cold water via the HW cylinder. The circulation pump does sound a little louder, maybe scale build up, maybe imagination. Living in Auckland means I can manage without a closed antifreeze system as frosts are somewhat rare and the controller kicks in to save the panels when the temp dips below 3 degrees C, as long as the pump has power.

Porboynz

110 posts

Master Geek

#989869 18-Feb-2014 18:28

kiwitrc: Glass tubes so maybe panels can give issues. Open system isn't affected by frost or hot days either, closed systems usually have anti freeze. If the pump stops the water just boils off and is replaced by cold water so no issue there. If scale was a problem then I think we would have a bigger issue with the house water pipes :)

It does sound like FUD to me. I like the idea of PV and a heat pump but I think there is a hell of a lot more to go wrong there (at a far higher repair cost) than a passive system. I realise that PV directly into an electric element isn't as efficient as a heat pump but after 7 to 10 years and a heat pump/inverter/controller failure it might work out a lot cheaper in the long run, but to be fair I have no idea on the life cycle of the above or repair costs.

I think you are bang on with a 7 to 10 year life span for a correctly sized HW heat pump. Its got a fan, compressor and inverter controller just like any heat pump. They do not last forever, but they are a great idea giving 3 to 1 heat, especially if you do get 10+ years service.

mattwnz

20164 posts

Uber Geek

#989877 18-Feb-2014 18:42

Porboynz:
mattwnz: Anyone know of any NZ companies who do PV installation directly connected to heatpump water heaters? . So no battery is needed, all the power goes straight into the water heater AAPparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance. I did come across one a while ago but can't recall who they are.

Good idea, but it will not work sadly without expensive batteries and an inverter. A HW heat pump needs a continuous power supply so the compressor can ramp up, they have a protection timer built in to delay restart if they lose power. A PV panel output fluctuates a lot on normal cloudy days as you can see in my post above. So if you want a heat pump for your HW you can still get a solar PV that's grid connected to smooth out the supply, but not directly connected. I can recommend Econergy as a NZ made HW heat pump manufacturer with a very good Consumer result. I would have one installed in a flash if I did not already have solar water panels installed purely because the performance is the same summer and winter.

The system I saw may not have been connected to a heat pump one, but just a normal electric hot water cylinder. I can't really remember too much, just that it was a simple PV system that was powering just the cylinder, instead of water panels/tubes on the roof. I can see issues with connecting it to a heat pump one, and simply having a HW heat pump maybe a more cost effective solution instead of panels.
I wonder if anyone independent has done any costing on different systems over 10 years. The one problem with contacting any company offering any solution, is that they will usually say their system is the best option becuase they want to sell you their system.

bfginger

1268 posts

Uber Geek

#990615 19-Feb-2014 16:55

APparently they are now more cost effective and relaibly than conventional solar water heating systems and don't need the maintenance.

A good quality solar thermal system should have at least a 50% longer working life than a good quality heat pump hot water system. A bad quality setup of either would be lucky to last seven years.

Apparently they need checking once a year by a pro, that it is working properly, as they can self destroy themselves if something stops working on them. They have to have water constantly cyling through them, and some can potentially can have problems with temperature extremes. They also can get scale build up. There are quite a few websites that list the pros and cons with each system.

The solar thermal systems that require regular checking are closed loop systems with antifreeze in them. Places with infrequent cold snaps don't require antifreeze systems as the controller can pump small amounts of hot water through the panel. Open loop solar is more cost effective than closed loop solar. I'd only think about closed loop solar in a place with high sunshine hours.

Some solar systems will say in the fine print that they need proof of yearly plumber checks before they honour the warranty. General hot water cylinders may have the same kind of warranty conditions. It's a way of offering a long warranty in big print.

Only a baldy set up solar system would have water constantly pumping through the collector. What you're thinking of is stagnated water overheating in some panels and being released through an overheat valve. Sometimes the valve would need replacing if it happens too many times but that shouldn't destroy the panel.

Thermosiphon solar is much simpler but it's rare in New Zealand.

Is that with the tubes or panels? I have heard that someo of the pnel ones corroded on the outside which cuased them to stop workings as well.

Only a badly made flat plate would rust itself out of service. But that has been a common experience in New Zealand with imported flat plates. The scandal was on Close Up in the 2000s
http://rustypanels.blogspot.co.nz/

High charges, poor quality products and bad installations have been all to common. The average plumber in New Zealand knows nothing about solar hot water. You should make sure any PV installer is competent too.

I would have one installed in a flash if I did not already have solar water panels installed purely because the performance is the same summer and winter.

Hot water heat pumps perform slightly better in summer than winter but the seasonal difference is much smaller than solar. Although solar thermal doesn't perform well in cloudy winter weather it performs so well during summer that over the course of a year it should perform similarly if not slightly better than a heat pump.

I can't see how patching PV into a hot water cylinder would be effective without some kind of special controller and element setup.

Porboynz

110 posts

Master Geek

#990742 19-Feb-2014 21:05

The heat pump option is attractive because its output is predictable summer and winter (small variance aside) I did the sums and having both heat pump and solar water panels did not stack because the HP would only be used 6 months of the year. I do get useful solar gain during the winter months from the panels but electric top up is necessary most winter days. I have a time clock to heat the top third of the tank morning and night to ensure HW is always available. I'm all for saving the planet but there better be HW when I want a shower. Therefore if I did not have the solar water panels I would give a HP serious consideration. The life span is a concern however.

On the subject of directly connecting a PV to the heater element in a HWC, it sounds attractive but could be fraught without a controller of some sort, and if you need a controller you may as well have a grid tied inverter. The element is rated at 240V AC but what about 320V DC? Other reasons I can think of are switching high voltage/current DC will probably destroy the thermostat electrical contacts plus DC will likely cause some sort of galvanic activity. Running a HWC without a thermostat could cause the safety pressure/temperature valve to open and once they open they do not shut off until most all the hot water in the cylinder is replaced by cold incoming water. I know this from being too greedy when I first set up my solar water panels and I set the controller so that the HWC reached 95 degrees C before the circulating pump shut off. The basement filled with steam as the pressure change from turning a tap on and off was enough to pop open the 100 degree C safety vent valve on the cylinder. Almost all my lovely HW went down the overflow drain before I could get the safety valve to stay closed. Now the pump shuts off at 85 degrees and the safety valve on the panels opens to vent super hot water which is quickly replaced by cooler water and the valve shuts off by itself and the cycle repeats. Its essential to have a system failsafe enough to operate unsupervised that does not turn into a gigantic bomb. Having the 2 x safety valves and the controller shutting off allows for 2 x failures at the same time.

E3xtc

773 posts

Ultimate Geek

#993104 24-Feb-2014 07:21

Interesting(ish)....well not really....regardless of the 'experts' opinion, I am still 100% satisfied on spending the coin last year...
http://www.stuff.co.nz/business/money/9755423/Is-solar-power-worth-it

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