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Solar for heating DHW

DavidAlgarve · 2025-02-04T21:30:12Z

My ancient brain is having trouble understanding this and I have a language problem with my solar installer. Could someone advise, please? If I have a 4kW inverter and panels producing 4.6kW; with a battery charged to 77% and then my ASHP demanding 4.5kW for DHW and 1.5kW for incidentals, should I be drawing anything from the grid? I.E. Shouldn't I be able to add the 4kW inverter to some output (2kW?)from the battery to satisfy the demand rather than 1.3kW surplus going to the grid My Mitsu takes around 4.5kW for DHW heating even on the "Eco" setting

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Air Source Heat Pumps (ASHPs)

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RobS

(@robs)

Estimable Member Member

Joined: 2 years ago

Posts: 138

07/02/2025 10:16 pm

Posted by: @davidalgarve

↑

Just tried to select "Quiet Mode" in advance of doing another 1 Hr, check whilst water heating and it reports "Invalid". Is there anything I can control that would unlock that?

That's odd, you should be able to set 3 or 4 levels of quiet in the installer menu.

Mitsubishis also have an Eco mode for DHW, you might want to try that instead?

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DavidAlgarve

(@davidalgarve)

Reputable Member Member

Joined: 3 years ago

Posts: 248

Topic starter 07/02/2025 11:23 pm

@robs I have "Eco" already, but it was suggested that I should use Quiet in addition. Eco certainly reduced the power significantly, but nowhere near enough to get down to my 4 kW.

I am almost thinking that the 3kW immersion heater is a more useful option, but only if I can be sure of solar production.

342sq m "Upside down" house in Algarve. Portugal
Mitsubishi PUHZ-120YUK 12kW ASHP
12 Solar Panels Growatt Inverter
2 x Growatt 7.5kW Batteries
Fronius EV Charger
Kia e- Niro 64kW

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Bart

(@bart)

Trusted Member Member

Joined: 1 year ago

Posts: 35

02/07/2025 6:45 am

Did you manage to reduce power requirement for DHW?

Given warmer ambient temps I'm testing 'quiet mode' for DHW in isolation and findings suggest quiet mode in conjunction with DHW eco mode does reduce costs (in my case 20%) as you would expect. Given the number of variables wanted to check if others found the same?

One thing I missed early on was I had to extend the 'DHW mode switch delay' to immersion to allow for the delayed reheat.

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5456

02/07/2025 7:21 am

Posted by: @davidalgarve

↑

I am almost thinking that the 3kW immersion heater is a more useful option, but only if I can be sure of solar production.

If you are thinking of heating on the immersion consider a solar diverter which precisely matches load to available power. I had one until I got an ashp and it worked a treat for 10+ years

However the cop is 1 no 2 or more so it's doubtful you will gain.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

👍

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