Boiler & PV Which System is Optimal

[Richini]

Good afternoon,

 

Looking for some advice on which route to take. 

Our 17 year old combi boiler is on its final legs and will shortly need replacing. Rather than just swapping like for like I'm trying to explore all avenues to ensure we've futureproofed ourselves a little bit.

 

We have a 5.46kWp PV system installed. Due to quotes received ASHP isn't an option currently, so we're looking at alternative options to maximise self consumption of generated electric.

Two options that occur to us are:

• installing a new combi and preheating the DHW water with  a direct electric unvented cylinder
• Changing to a system boiler and using some thermal store option, possibly a Gledhill Torrent or Mixergy, which could benefit CH & DHW .

 

With young children our hot water usage is quite high with daily baths year round.

 

I'd be grateful for any advice or suggestions on which option I should take, if indeed any of these.

 

Thanks. 

[ProDave]

Change to an Unvented hot water tank, not a thermal store.  Choose one with a high capacity input coil, then it it ready for an ASHP.  

 

Once you have a HW tank, a PV diverter to send surplus PV to the immersion heater.

 

How is your heating delivered?  UFH or radiators?  Why don't you think an ASHP is suitable?

[JohnMo]

As Dave says.

 

But we have a combi, with preheat cylinder upstream, if you go this direction, you need to install a PV thermostatic valve between the cylinder and boiler.  Since I installed the PV thermostatic valve (2 months ago) I have halved the gas consumption month on month.

 

The valve stops the boiler firing needlessly when you have a cylinder above 45 degrees.

 

The risk of an unvented cylinder upstream is lots of Luke warm water for prolonged periods if solar PV is low performing.

 

I am just using a cheap vented thermal store. As no drinking water is stored.

 

 

[Richini]

Thanks for the replies. 

Heating is delivered by radiators. 

ASHP quotes came in way beyond what we can afford currently unfortunately. Really like the idea of getting the cylinder in and potentially swapping over in the future, with the bulk of plumbing already complete. 

 

Is the consensus to stick with a combi boiler then? 

I've approached WH Cylinders and they've been really helpful and suggested their Superflow direct electric unvented cylinder. Does this sound right? The suggestion was to have 2 x 3kW immersion heaters if I could split the power from the PV, which I think the eddi can do. 

Is there any schematics of how this setup would be achieved?