Unvented immersion heater by electric solar with gas combi boiler

[Igorsart]

Hi Guys,

I`m planning to add unvented electric immersion heater which will be powered by the solar panels and integrate it into gas combi boiler system.
In principle, when there is high level of sun then 3kw immersion heating element will be powered on and when there is low level of sun than 1kw immersion heating element will powered on. This system will controlled by automated PLC system. PLC system will detect amount of energy going back to the grid and switch on 1kw or 3kw heating elements or nothing at all.

Another thing I want to add is 3 port valve which will switch on (to allow hot water cylinder be used as a priority) when temperature in hot water cylinder is higher than 49 degrees. it will switch off when temperature is below 49 degrees to allow combi boiler to take over and provide DHW.

Has anyone done similar projects? is it worth doing it?

any help is appreciated

 

[desktop987456]

I am also interested in doing something similar at my home. I have 11kw PV at roof. Will be led by guidance from forum members.

 

[SpecialK]

I have a 210L unvented heated by PV solar. I built a MK2PVrouter to divert any excess solar to the immersion. My tank is remote from the boiler so I have 2 lever valves and manually switch between the two. Its a pain until about this time of year as I have to keep switching between them.

Ideally you would want a solar diverter valve that will automatically bypass the combi or prefeed it. (https://www.bes.co.uk/thermostatic-solar-valve-kit-with-bypass-21082/).

I would recommend fitting a TMV on the outlet of the cylinder so you can heat it up to 65 degrees+

If you get paid for export its not worth it as the export is worth more than the gas to heat the water.

 

[oldbutnotdead]

Have a look at your existing boiler specifications, see if it can take preheated water.

 

[JohnD]

If you have a gas boiler available, the cost of HW is so low that it is insignificant, and you will not save enough to recoup the cost of your controller.

Use the electricity for things that have to use electricity. Such as an EV.

A tumble drier or aircon are major users.

 

[desktop987456]

Have a look at your existing boiler specifications, see if it can take preheated water.

Do you know a few that take pre-heat water?

 

[desktop987456]

My solar PV is taking a lion's share in summer for cooling the house and running other appliances (10.8kw).

I have literally paid nothing to grid as excess units are net off during the night in my 16 months of PV use.

I don't know about UK, but in Pakistan, gas companies have slabs that goes up as you consume more so those who are using central heating will be paying more in winters. In my case if I could take the DHW component out of my gas usage I could prevent hitting the upper expensive slab of gas usage.

 

[oldbutnotdead]

Aah, no there are no tariff steps on domestic gas supplies in the UK.
I have no idea what boilers are available in Pakistan.
The 3 port valve idea won't work very well if you are considering a standard central heating 3 port- they are designed as 1 in 2 out and not suitable for drinking water.
The other downside of the changeover is wasting the energy used to heat the cylinder from ambient to 50°

 

[desktop987456]

I am planning to source a boiler from UK, can you recommend a few models in 18kw range? A daft questoin, my system is low pressure and open vent, would I be saving any gas if I go to a pressurised, sealed system for central heating?