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Forum Index : Solar : Hot water heating
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shawn Senior Member  Joined: 30/03/2010 Location: New ZealandPosts: 210 |
Hi all its been a bit since I've posted, but a little advice needed I was hoping this might work  putting PV on the roof series/parallel the dc output to around 300 dc with around 3kw of PV then connecting it straight to the hot water system 240v ac element using the normal thermostat that shuts off the power to the element when temperature reached.
Hope this will work, pros/cons? Shawn |
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Shawn, intuition tells me that a thermostat designed to switch 240V AC would not last as long switching up to 300V DC. A different type of contacts is required for DC switching. Klaus |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
You could use the existing thermostat to operate a relay that is rated to do the job. You must have your reasons for wanting to use the PV panels but why not use solar hot water panels? There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Shawn, A work-mate has designed a system to do this properly. If you want a relay suggestion I'll ask him. Dave |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yep agree with the others, the thermostat would quickly expire ( probably after the first cycle ) switching DC instead of AC, so a high voltage relay or electronic relay would be needed. You will need a low voltage circuit to drive the relay too, say 5, 12 or 24 volts, depending on the relay. Be careful with safety, 300 volts DC is much much more dangerous than 240 volts AC. Also consider fuses suited to high DC voltage, a standard 240VAC fuses will light up like fireworks with DC and could start a fire. The element should be fine with DC, provided it does not go too much over 330 volts. I can see advantages to using electric solar panels instead of water solar panels. No problems with frost, leaks, pumps, etc. Plus you can mount the panels far from the tank, and they would probably have a longer life. But its an expensive option. Water solar panels are fairly easy to find 2nd hand, I paid about $70 for mine, and are very efficient. You would need many more electric panels than water panels to do the same job. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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MadRat Newbie  Joined: 30/09/2008 Location: United StatesPosts: 21 |
If you aren't too far south then it's more efficient and less costly to use a heat pump in the attic to preheat the water. Hot water storage itself is inefficient, so you're taking an expensive route to be more inefficient. If you already use propane or natural gas then the natural route is hot water on demand systems. Go Huskers! |
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| shawn Senior Member Joined: 30/03/2010 Location: New ZealandPosts: 210 |
Thankyou for your replies your advice is appreciated. Its for a frend and he already has the PV panils so I think the best advice would be to just buy and connect a grid tie inverter onto them for him to save power. My system is off grid and I have heaps of hot water  |
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norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
For cold country that has ample solar potential, probably solar-inverter-heat pump combination would be the better compromise. Price of heat pump hot water systems will drop as they evolve and become popular. Apparently in QLD you cannot legally install an element hot water system in new houses. We come from the land downunder. Vic |
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