Link existing hot water tank with new solar installation

[SHEPSTER]

Have just got listed building consent to install solar thermal water heating much to my surprise! I have got a sadia megaflo 210L tank. I understand that anew twin coil tank is needed. Is there any way that I can keep the sadia and piggy back it to the new one. It would be useful as I want to have extra hot water as am going to start b&b!

[TwoHorsePower]

why do you need a second tank for the solar? there are various ways in which you can link solar thermal to your existing unvented tank without employing a second tank , e.g., external plate heat exchanger (see wookey's arrangement), willis solasyphon (works the same way as the PHE), and, if you have an immersion heat port on your tank, a retrofit coil such as the solaplug.

[ecogeorge]

If you have 2 elements, remove the btm element and fit a retro fit coil (often on ebay) to connect to solar. Did this to my 160 litre megaflow -works a treat. Off course available hot water is reduced if poor solar day but top element only should be fine unless you have many 200 litre baths in winter.
rgds George.

[solar_cambridge]

Have just got listed building consent to install solar thermal water heating much to my surprise! I have got a sadia megaflo 210L tank. I understand that anew twin coil tank is needed. Is there any way that I can keep the sadia and piggy back it to the new one. It would be useful as I want to have extra hot water as am going to start b&b!

210 is waaaay too small for most houses on solar. If you're running a b&b your boiler will be running nearly constantly anyway to keep up with demand! Paying guests won't give much thought to conserving hot water.

[SHEPSTER]

Fair comment. What size tank is recommended for large 4 bed house with 2 showers and a bath. Usually 6 people (adults) staying there. I say usually, thats not true, when I do b&b there are 6 normally there are just 2 of us!  I anticipate being full about 4 months of the year,. Great for DHW in the summer months but wont need quite as much in winter. I suppose that means possibly having a 350L tank heated by oil then? Or is there another solution?

[Stoozy]

44 litres of hot storage per person is what the energy saving trust told me.

[solar_cambridge]

44 litres of hot storage per person is what the energy saving trust told me.

Perhaps for an energy concious household. I'd say the OP would be looking at a 500 litre cylinder with boiler coil heating just 150litres on timed demand to keep the guests happy. For that spec you will probably need it made to spec as most boiler coils will heat almost 2/3rds the cyl. There are a few manufacturers out there who will build to spec. I think I got my last one done via pts. I'd say stainless steel is a must. You'll be looking at circa £2k for that cylinder.

[TOMSEPPINGS]

The Horizontal SolaPlug is designed to fit into a 210litre megaflow.
You can connect up to 4m² of panels into your cylinder.
http://www.solaplug.co.uk/HorizontalImmersions.aspx

All single cylinder solar systems (twin coil or retrofit) are sensitive to backup heating timing.
The backup heater must come on at the end of the day only, ( so that the solar is not competing with the boiler ).
Before deciding to retrofit to the existing cylinder check whether you have enough hot water with just one evening blast of boiler heating.
If you need the boiler to heat the water more frequently, you will need a bigger twin coil cylinder, or add a preheat cylinder for the solar.