Green Building Forum - Using solar panels with megaflow ( pressurised cylinder) Thu, 11 Jun 2026 15:02:15 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73380#Comment_73380 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73380#Comment_73380 Tue, 02 Feb 2010 20:46:26 +0000 wertert Really been round the houses during the last few weeks, thinking about using some green technology in our new house. We are part way through a refurb and my fafing about is now starting to delay the project !

We've binned the woodburner-connected-to-the-cylinder idea because it was relatively complex and, if i’m honest, we probably will only light it at the weekends etc. Overall I don’t think it will really make that much difference to our heating costs / carbon footprint.

So I’ve been considering Solar panels. We’re using a dual coil cylinder like this

http://www.santon.co.uk/292.htm

plan is for a 300L tank.

We would use the second coil for the connection to the solar panels on the roof. These are the things that I am currenty worrying about.

1) My experience of megaflows is once you draw off, for example, a bath full of hot water cold water rushes in and cools the remaining hot water down. You try and top up the bath after 10 mins and you just get luke warm. So if I’ve got a lovely tank of hot water heated via my solar panels during the day and someone has a shower at 5pm we will will probably end up with a tank full of water too cool to use for anything else without firing up the boiler.

2) 300L is too large and to heat this with solar panels I will need to buy panels I don’t really need. Tank supports the following ( 2 adults + 4 children ).

En suite bathroom (2 x baths a day) + 2 sinks
Another Bathroom ( 1 x bath a day ) + 1 sinks
Kitchen sink
Utility room sink
WC sink.

This is only half the house BTW.

So i’m thinking 300L is overkill. Maybe 200L/250L would be a better fit ? I normally think bigger is better but
If 1) is true then it is doubley daft to heat 300L before cooling it down after using just 60L on a bath.
Any advice would be excellent as I’ve really got to move forward and I’m meeting the plumber on Thursday. He already thinks i’m insane...which is partially right actually.

Thanks

Jeff]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73381#Comment_73381 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73381#Comment_73381 Tue, 02 Feb 2010 20:59:40 +0000 tony
i dont like mains pressure hot water though --- nor stainless steel cylinders.]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73389#Comment_73389 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73389#Comment_73389 Tue, 02 Feb 2010 22:22:38 +0000 wertert
Slightly off the initial question but does anyone out there have similar issues with pressurised cylinders ? Could mine simply not be set up correctly. ie partial run off causing drop in temp of whole tank.

I was thinking I could always use a thermal store instead of the pressurised cylinder ? Just for hot water. That way I wouldn't undo all the good work by the solar panels by running a bath. I would lower the temp of the store ( by one baths' worth of heat via the exchanger ) instead of letting 60L of mains pressure cold water run into the tank.

am i making sense ?

Thanks again

Jeff]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73393#Comment_73393 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73393#Comment_73393 Tue, 02 Feb 2010 22:33:56 +0000 dimengineer
Tim]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73394#Comment_73394 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73394#Comment_73394 Tue, 02 Feb 2010 22:35:56 +0000 dimengineer Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73397#Comment_73397 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73397#Comment_73397 Wed, 03 Feb 2010 00:22:07 +0000 Julian By "megaflow" do you mean a mains pressure cylinder? As you probably know megaflow is a brand. A (taller, narrower) solar cylinder like the one you linked to maintains the stratification of different temperatures effectively. The cold water will replace hot drawn off but won't mix it up. If your solar is correctly sized for your needs and your store you will probably find in the fine weather you are getting a whole tank of water at 60/70/80 degrees. Even if 'only' at 50 degrees it would be too hot for you to have a bath in without being mixed down. If (as you should) you have a mixing valve fitted this will prevent scalding water being drawn off. Even three baths a day you would be hard pushed to use all that hot water. I understand Tony's preference for non mains pressure but now, having used a mains pressure, s/s 300L solar cylinder I wouldn't change back.]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73401#Comment_73401 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73401#Comment_73401 Wed, 03 Feb 2010 09:12:16 +0000 wertert
Thankyou for all your comments. This is a really great forum. Really helpful.

@Julian - Thanks for your info. I will google later but which make of tank do you have i.e s/s ? Yes - Megaflow is a brand. I use it incorrectly all the time. i.e hoover, selotape.

Any idea what your mains pressure is? I'm wondering if mine is too high and this causes the stratification to break down. i.e lower it down to 1 or 2 bar may be an option.

@dimengineer - 3 baths is alot but we are 2 adults and 4 children ( all girls! )
Typical day is
1x morning bath or shower (wife)
1x evening bath (me)
1x evening bath ( all 4 children ! ) and it's hell !

Really like to hear more about your system. Are you able to run your system completely without the boiler during the summer months ?
Does your cylinder cool down like mine ? ie new cold diluting hot ?



I should mention that we really only have a west facing roof ( or a flat roof ) so that also has a huge impact on how many panels we are likely to require. South is shaded for most of the day by trees on the other side of the road.

On the thermal store side of things I would be going for a pressurised model.

Thanks again. Any more advice from the day shift would be gratefully received.]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73404#Comment_73404 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73404#Comment_73404 Wed, 03 Feb 2010 09:35:47 +0000 wertert
On the pressurised thermal store for hotwater I would go for something like this

http://www.advancedwater.co.uk/prod-480-088-3003.html

Any other suggestions ? Don't seem to be thant many about which you can run at pressure ?!

Thanks

J]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73442#Comment_73442 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73442#Comment_73442 Wed, 03 Feb 2010 14:43:09 +0000 acroiso
When you fit solar you will fit a thermostatic mixing valve on the hot outlet to regulate temp. of water reaching the taps. This will help reduce the amount of water being drawn from the cylinder, which might also help reduce the mixing a little bit.

I'd have thought 300L is about right for a 6P family. I'm guessing there will be a time when 4 x children can't get in 1 bath, so your DHW demand will increase.

For a 300L cylinder I'd typically recommend about 5m2 of south-facing flat plate collector or 4m2 evacuated tube. If your west facing you may want to increase this or just accept you will gain less energy over the year.]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73446#Comment_73446 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73446#Comment_73446 Wed, 03 Feb 2010 15:13:12 +0000 tony Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73456#Comment_73456 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73456#Comment_73456 Wed, 03 Feb 2010 17:48:36 +0000 wertert Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73489#Comment_73489 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73489#Comment_73489 Wed, 03 Feb 2010 22:20:42 +0000 Julian I have a Gledhill stainless lite 300L. Am near Lyme Regis if you're down this way and want to take a look (email on profile). These have a pressure reducing valve included to give you balanced hot and cold water. I think it's 3.5 or 4 bar. You can also fit a pressure reducing valve on the incoming cold main.]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73490#Comment_73490 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73490#Comment_73490 Wed, 03 Feb 2010 22:24:40 +0000 dimengineer
My experience is as follows, based on the last 2 years of operation, SE England. We have a family of 4 (5 in the summer when eldest daughter is home from uni). 250 litre megaflow solar cyclinder, and a 21 x 58mm Kloben tube array.
The panel is mildly undersized for us, in that for the peak 4 summer months we can turn the boiler off, but we do need to press the +1hr boost button a couple of times a week. It provides about 90% of out HW then.
We mainly take showers, with only occasional baths (2 -3 total a week).
The thing about 3-4 baths a day is that solar is a "one hit" heating - you get a tankful and thats it. So your 3 baths will probably drain your 300litres of hot water. What you may have to do is set your heating to fit with your water use patterns and maximise the solar benefits.

Hope this helps

tim]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73527#Comment_73527 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73527#Comment_73527 Thu, 04 Feb 2010 10:46:00 +0000 Jimbo1 Have used Thermal Stores in the past but maybe don't get the best out of solar due to the high operating temp. but certainly mean you can use your sold fuel!]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73537#Comment_73537 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73537#Comment_73537 Thu, 04 Feb 2010 12:26:37 +0000 wertert
Thanks again for your help. I was wondering something on the way into work today.... i'm getting obsessed !

If you take a 250L unvented cylinder heated to 70 degrees and you run off 60L of hot water you get a temp drop caused by the unrush of cold mains water. Imagine in this example that the hot and cold fully fix.

Would this temp drop be the same as a 250L thermal store heated to 70 degrees which was used to run off 60L of hot water ? ( via the heat exchange )

ignore stratification for the moment.

So what i'm asking is if you took the two systems and extract the same amount of energy ( hot water ) would the drop in temperature be the same on both systems.

Thanks

J]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73538#Comment_73538 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73538#Comment_73538 Thu, 04 Feb 2010 12:56:34 +0000 Sigaldry
Generaly speaking work on 15l for kitchen sink, 15l if there is a Utility room, 30litres per shower in the dwelling, 60 litres per bath in the dwelling. Add that together and divide by 0.70 to get approximate peak requirement.

On top of that allow around 25litres per m² of solar 'panel' for solar storage for DHCG compliance.

Obviously up cylinder size to closest available applicable commercially available (well insulated) cylinder size. Make sure you go for a cylinder with a good (low) Manufacturers Declared Loss Factor (kWh/day). The less the cylinder loses heat, the less it needs heating.

Commonly available cylinder sizes 90l, 110l, 120l, 150l, 180l, 210l, 250l and 300litre]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73539#Comment_73539 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73539#Comment_73539 Thu, 04 Feb 2010 13:15:18 +0000 davidfreeborough Posted By: wertertIf you take a 250L unvented cylinder heated to 70 degrees and you run off 60L of hot water you get a temp drop caused by the unrush of cold mains water.

Would this temp drop be the same as a 250L thermal store heated to 70 degrees which was used to run off 60L of hot water ? ( via the heat exchange )

ignore stratification for the moment.
If the flow rates are the same & you extract the same amount of energy from the two tanks then the energy remaining will be the same. If you ignore stratification & assume perfect mixing then the temperatures will also be the same.

The difference is that in the unvented DHW cylinder case the water coming out of the tank (before the thermostatic mixer) will be at exactly 70 degrees. In the thermal store case the water coming out of the heat exchanger will be at slightly less than 70 degrees because the heat exchanger is not able to heat it from mains supply temperature to tank temperature in the few seconds it takes to flow through the heat exchanger. So less energy will be extracted from the thermal store & it's temperature will be correspondingly higher than the unvented DHW cylinder.

Note that this ignores the fact that if the heat exchanger itself has a capacity of 25 litres then the first 25 litres will be at exactly 70 degrees.

David]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73547#Comment_73547 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=73547#Comment_73547 Thu, 04 Feb 2010 14:33:19 +0000 Jimbo1 Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141403#Comment_141403 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141403#Comment_141403 Mon, 02 Apr 2012 19:18:31 +0100 narcosi
In this post a couple of you say you dont like mains hot water - can i ask why? why on earth would you not want pressurized hot water?

I have lived with a megflow for years and just moved into a house with tanks in the loft and it is hell - low pressure, small tank runs out etc and the pump drains the cold water faster than it can fill so you left with no water at all.

We have solar so more questions to follow, but just wandering if I am missing something.

ta]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141428#Comment_141428 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141428#Comment_141428 Tue, 03 Apr 2012 08:03:09 +0100 tony
If they didnt there would be water supply problems

If the mains flow is low then mains pressure wont work very well,

If the loft cistern is getting empty then may be it is not large enough.

Mains hot water is intrinsicly more dangerous and should be tested annually but not many do this.]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141452#Comment_141452 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141452#Comment_141452 Tue, 03 Apr 2012 11:43:56 +0100 narcosi
Why more dangerous?

It does not really describe why people dont like it though...our pressure has always been above 3 bar maybe we are lucky

J]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141466#Comment_141466 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141466#Comment_141466 Tue, 03 Apr 2012 13:03:55 +0100 wookey Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141471#Comment_141471 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141471#Comment_141471 Tue, 03 Apr 2012 13:35:57 +0100 narcosi Posted By: wookeyjust about nothing went wrong.

Love it!

mine never exploded so I reckon thats proof they are fine :-)]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141512#Comment_141512 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141512#Comment_141512 Tue, 03 Apr 2012 17:50:13 +0100 borpin Posted By: tonyMains hot water is intrinsicly more dangerous and should be tested annually but not many do this. I really do think this advice is FUD (Fear Uncertainty and Doubt).]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141529#Comment_141529 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141529#Comment_141529 Tue, 03 Apr 2012 20:59:03 +0100 narcosi Posted By: borpin
Posted By: tonyMains hot water is intrinsicly more dangerous and should be tested annually but not many do this.
I really do think this advice is FUD (Fear Uncertainty and Doubt).

Sound like it doesnt it, but when you imagine 300l at 3 bar bursting it is not a pleasant thought.....:-)]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141531#Comment_141531 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141531#Comment_141531 Tue, 03 Apr 2012 21:11:39 +0100 borpin Posted By: narcosi
Posted By: borpin
Posted By: tonyMains hot water is intrinsicly more dangerous and should be tested annually but not many do this.
I really do think this advice is FUD (Fear Uncertainty and Doubt).
Sound like it doesnt it, but when you imagine 300l at 3 bar bursting it is not a pleasant thought.....:-) Why on earth would you run it at 3 bar? Put a pressure limiting valve on the incoming water supply to just over 1 bar and that is more than enough. Equally how do you ever check all the hidden pipes and fittings?]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141544#Comment_141544 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141544#Comment_141544 Tue, 03 Apr 2012 21:37:21 +0100 narcosi Posted By: borpin
Posted By: narcosi
Posted By: borpin
Posted By: tonyMains hot water is intrinsicly more dangerous and should be tested annually but not many do this.
I really do think this advice is FUD (Fear Uncertainty and Doubt).
Sound like it doesnt it, but when you imagine 300l at 3 bar bursting it is not a pleasant thought.....:-)
Why on earth would you run it at 3 bar? Put a pressure limiting valve on the incoming water supply to just over 1 bar and that is more than enough. Equally how do you ever check all the hidden pipes and fittings?

because 3 bar is better for showers!

You don't check them you just pressure test it!]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141548#Comment_141548 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141548#Comment_141548 Tue, 03 Apr 2012 21:44:10 +0100 borpin Posted By: narcosiYou don't check them you just pressure test it! I'm going to resist....]]> Using solar panels with megaflow ( pressurised cylinder) https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141553#Comment_141553 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5287&Focus=141553#Comment_141553 Tue, 03 Apr 2012 22:08:52 +0100 narcosi Posted By: borpin
Posted By: narcosiYou don't check them you just pressure test it!
I'm going to resist....

don't resist - go ahead!

i am in the slightly fortunate position with this house to be replacing the kitchen which is the only hidden pipes..]]>