TS, UVC or Combi

[Gone West]

I have recently moved to an old stone walled cottage that was converted to a bungalow in the 70s. It has a 4kWp PV system and a 1.4kWp ST system with an oil fired boiler for CH and DHW. There is a 230l cold water tank in the loft and a 140l vented hot water tank. I shall continue to use the oil fired boiler and would like to have mains pressure hot water. The ST system is a Genersys 1200 with DC12 controller which was installed in 2009 and seems to be working well. I am trying to decide whether to keep the ST system and use a ~250l twin coil TS such as a Grant DuoWave TS or use a twin coil UVC. I looked at the Harlequin Heatstream Plus but it only has one heating coil so would mean using the PV to heat the water with the immersion. I had a UVC system in my last house which worked well but it would require annual maintenance. The alternative would be to remove the ST and use an external oil fired combi boiler. I have discounted Sunamps etc. Any ideas would be helpful.

[ProDave]

I would say get a Telford Stainless steel UVC with a standard and solar input coil.

 

Nothing to stop you using the PV and the ST at the same time.

[PeterW]

I would go 300 litre TS with solar coil, put a pair of immersions in so you can dump the excess PV in there too. The TS can then balance the oil boiler into the rads etc

[Gone West]

No consensus then and combis are out. 

[Mr Punter]

With the PV and ST, a combi may not work out.  Also you may want to ditch oil in future.

[Iceverge]

As the lately emigrated @Jeremy Harris found out thermal stores have their drawbacks. 

 

UVC is the cheapest to install however inspections do add up. 

 

For a given quantity of water you cannot extract the same energy as an UVC or traditional vented cylinder. 

 

As I understand this can be overcome by,

 

1. Using a heatbank type with a pump and an external heat exchanger. ( e.g Gledhill Torrent or Newark Cylinders Aquinox) 

2. Having a very large tank with a DHW coil in tank  (e.g akvatherm thermal store)

3. Running a normal store very hot (80-90 deg) Not sure if this is advisable however. 

 

However if your DHW requirements aren't huge I'd side with @PeterW on this and get the 300l TS.