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Topic Title: 1.7kW PV New DHW Cylinder. Bespoke Immersion Heater
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Created On: 23 September 2017 05:36 PM
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 23 September 2017 05:36 PM
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Fm

Posts: 1713
Joined: 24 August 2011

So I'm installing a new boiler to replace a combi, it's a system boiler with a small 150litre capacity

It has will have a 3 kW immersion as a backup should the gas fail, but I would like to utilise the generated power onsite.

So do you go for a 500/750 watt immersion that may be on longer when the generation is low or 1kW immersion?

House is occupied by 2 adults and 2 kids.
4 showers every morning
House empty from 9-5 Mon - Fri. Weekend random depending on what's on

Appreciate your time for posting
 23 September 2017 06:17 PM
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mapj1

Posts: 9371
Joined: 22 July 2004

With a low wattage heater, it will need to be very well insulated, or it will be cooling down as fast as it warms up. It will depend on the water use pattern - if it all gets run off because everyone gets a bath at the same time of day, then it will remain cold longer. If folk spread their use out some AM some PM, there will always be plenty left.
How much local generation is realistic and it will be daytime only (solar ...) presumably normally less than the 1.7kw of the title...

Not sure who makes them but there used to be multi-element immersions on one flange - allows scope for series/single/parallel operation. Bit like a 3 phase heater, but not necessarily the same wattages.

-------------------------
regards Mike


Edited: 23 September 2017 at 08:25 PM by mapj1
 23 September 2017 06:57 PM
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dp11

Posts: 97
Joined: 18 June 2011

A good solar PV diverter won't mind if there is only 100W spare with a 3Kw immersion. If you want a kit or understand more : http://mk2pvrouter.co.uk/33001.html
 25 September 2017 02:19 PM
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Fm

Posts: 1713
Joined: 24 August 2011

Thanks for the input Gents.
May go for a 500 watt heater but although the link from dp11 was very informative, may choose a more standard option compared to a diy route
 25 September 2017 03:28 PM
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leckie

Posts: 4329
Joined: 21 November 2008

If your tank has two immersion heater bosses, I think I would wire a 3kW one in as well that you could use for a quick emergency boost. It will keep the kids happy!
 26 September 2017 07:43 AM
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Fm

Posts: 1713
Joined: 24 August 2011

Hi Leckie,

Yes there was always a 3kW immersion planned as a back up
The low power immersion was just to utilise excess PV, but to be honest I think I will just go with the 3kW, just trying to make all the systems in my house as simple as possible, should I not be always able to maintain them
 26 September 2017 07:39 PM
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AJJewsbury

Posts: 15849
Joined: 13 August 2003

just trying to make all the systems in my house as simple as possible, should I not be always able to maintain them

In which case forget using high-grade electricity to do low grade water heating, and put in a simple solar thermal system for the hot water - it'll be between 5 and 10x more efficient (both in roof area and capital cost per kWh generated) - and let the PV displace fossil fuelled generating plant.
- Andy.
 26 September 2017 10:23 PM
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Fm

Posts: 1713
Joined: 24 August 2011

Hi Andy,

Totally agree and for any buildings at work where this would be viable I would consider it.
I don't have the roof space for any more panels on the roof, personally only looking at this as I have the PV in place anyway.
Don't want any more wet systems installed, 3rd wood burner to go in soon too again standalone rather than integrated, just want each item separate
Thanks for the input
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