Is bigger better for a unvented tank for solar heating?

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Finally decided to have the old combi boiler replaced with a heat only one and a unvented system with a tank for hot water.

Will be doing this first then have solar panels fitted later to provide heating for hot water in order to spread the cost.

Question is what size tank do you think is best?

Thinking about a 300ltr tank after speaking to the person who will install it. Also it seems to make sense as renewable energy is all about having the means of storing the energy when the sun etc is out.

Any one have solar water heating that can share their thoughts?
 
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That's good.

But I would still be asking how many people live there!
 
That's good.

But I would still be asking how many people live there!

Three at the moment but family will get bigger, plus we often have family who stay.

My question would be, take the solar heating out the equation, how much more gas would it take to heat the hot water for and average family for a 300 ltr tank compared to a 200 ltr tank?

The tanks as most will know have an element at the top for gas heating and the bottom element is powered by the solar panels that makes sense in being more efficient.
 
You are missing the point.

The water is only heated up once. It is then stored until it is used.

The heat loss from the cylinder is very small.

With solar, the minimum storage should be to provide at least a day's use from the solar heating.

If more is provided then you have scope to continued using yesterday's hot water on dull days.

Typically about 50 litres per person per day is a good rule of thumb.

Tony
 
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Agile was right when he asked how many people were in the property, but in addition, what are your water use habits. My daughter can take 25 minutes in the shower, so at about 8ltrs per minutes, she'd go through 200ltrs without batting an eyelid, and wouldn't leave much for her mum to use afterwards. I can be in and out in 5 minutes, so with a tank, we'd need about 400 litres not 300, so a combi works better.

Assuming you're a normal family, and get by with about 50litres each, then a 300 tank should be fine, but do you have a good south facing position for the solar panels, and do you know how much of the year you'll get a good supply of free energy before you've got to start heating the tank with gas. The further north you go, the less justifiable solar heating gets.

And do you shower in the morning, or the evening, as the sun will heat the water during the day, so most of it will be available in the evening, with a slight heat loss overnight; and as you go into the autumn and the winter, then the boiler will kick in and top up what the sun hasn't managed to heat up.

In addition, do you have a good water pressure and flow rate to make best use of an unvented cylinder. You'll also need to service an unvented cylinder once a year.
 
He is pretty much as far north as you can get on the mainland! I seem to remember from my solar heating course that the incident heat there was about 22 % less than in the sunny south of the country.

But I am sure the Scotts don't let their daughters spend 25 minutes in the shower.

On the West Coast, a while ago I stayed in a B&B where the bathroom only had TWO taps, on the basin. The basin waste discharged into the bath!

Tony
 
We live in Lancashire and I have a 160 litre cylinder in the attic, which I plumbed in tandem with the 160 litre house cylinder, meaning that water from the header tank passes through the attic cylinder and is pre-heated by the panel before it goes on to the main house cylinder, where the bolier finishes the job. I fitted a 20 tube panel on the roof facing slightly south of west. In winter it does nothing but in June and July the panel will achieve 60c in the top cylinder by mid afternoon. We are a family of three so that gives adequate water for a shower each a day in summer.

One thing that concerned me was the weight of 160 litres of water in the attic but happily I was able to stand it on the studwork of the four walls surrounding the airing cupboard.
 
That is the best way if you have space for a second cylinder !
 

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