High furiousHarry !
Good that you found a better offer,confront your supplier with the numbers.Usually there is a 20% off in the pipe.
First question :Here in Irland the standard (drinking-)water system is a so called "open/vented system"(with a tank in the attic) contrary to the continental pressurised system.But more and more builders are changing to the pressurised system here as well.The problem with our conventional water is that it does not comply with hygiene regulations,30% of all Irish households have no access to clean water.One of the hygiene problems are bacteria.Tap water is -hopefully-treated with chlorine or UV light.But that happens at source,not in the house.Chlorine is a gas that evaporates once it is not under pressure,remember the smell at the public swimming pool.So after a while in the tank there is no chlorine pressent any more,at least not in the quantity that would kill germs resp. makes them "hibernating".And it can get warm in the attic.At around 30 degrees Legionella bacterias will grow.And these can be deadly to persons who are weak,namely the elderly,children and people with immune system deficiencys.But:Legionellas themself are weak.Sunlight(UV) and heat (above 40something degrees) will kill them.As well as desinfectants like chlorine.So the tank in the attic is the ideal breeding ground for them.
If you use an indirect water/solar system -like the one with the tubes and the tank- plus the tank-in-the-attic you need a heat source to make sure that the water reaching the tap is hotter than 40something degrees,a safe bet is 55 degrees.This can be achieved by a conventional boiler,a valve that closes once the safe temperature is not adhered to,an UV lamp or-the simplest method-a pressurised system.A pressurised system holds the chlorine in the pipe and therefore keeps the water more or less sterile.Provided there is chlorine in it in the first place,but that is common with public water systems.
(You must excuse my bad english,there is no spell checker here in the new bulletin any more.And an article in this lenght would take me ages to counter check with the aid of a dictionary.)
With the plumbing fittings there is no problem.The Germans -and the Chinese were the tubes are mostlikely coming from- use the imperial system in fresh water plumbing.The German plumbers say "Zoll" instead of "Inch".Expressed with the same signs,for example 2" are 2 inches resp. 2 Zoll. But they mean the same thing."Zoll" is also the German word for "Duty" i.e.what you pay for goods at the border (when you cross it) to the souvereign.A meassure stick,-tape, on a building site is still called a "Zollstock",an "inch stick".A twelfth of a length of fabric,timber ect. was the duty for the emperor.But that is history.
As I said: no problem with the fittings.The worst case scenario would be that you need a junction piece for a few cents/€s.But that is readily available from any plumbing center.The Irish have a "special" measurement in plumbing other than the imperial.I faced that problem when I installed my underfloor heating system.A few bangs with the pliers and it was "made" fitting-without special junction pieces.
Now to the import:
These glass tubes are expensive.And they are glass.They could break.
Make sure that they are well packed and insured for the transport.If they are shipped with lets say DHL-these are gangsters- then don't sign the delivery docket until you have unwrapped each of them.Let the delivery man wait,he is paid for it.Others, like for example UPS ,might be more tolerant but what I heard from DHL is not great when it comes to insurance cases.
To the tank size:
Keep in mind that the water kept in the storage tank is not boiling hot.Exept in summer.So calculate for a shower around 60-80 liters per person,for a bath around 150 liters.If you use a pressurised system the demand for the shower can be reduced to around 40 liters because you can use water(energy!) saving showerheads.LIDL has them cheap now and then,Argos is around double the price.Between € 10-20.
The tubes you have in mind will deliver large quantities of warm water when the sun is shining,but that is not always the case.The tank should cover the demand for 2-3 days,so I guess 500l would be more suitable for a 4 person household.And there are different tanks available.For example the simple one-unit tank and the more sophisticated 2 or even 3 stage unit.The advantage of a 2 (3)stage tank is that it always keeps the top 10 or 20% of the tank hot and heats up the rest of it only when there is plenty of surplus energy.That means no matter how dull the day is you will have some scalding hot water.But only in a very limited quantity.But here we go into border cases-a few more liters more or less won't matter in the daily routine.More something for a technic freak or a space ship where every watt matters.
If you have patience then try also some Dutch tube suppliers.They might be a few percent cheaper due to better contacts to China and shorter shipping routes.
P.S.
o you know the chocolate "Ritter sport"? Well,the old Mr. Ritter is now the boss of Chinas/the worlds lagest solar factory.For no wage,they call it something like "old to young management developement aid".So sweet can be retirement .
So good luck to you and your project.Every solar panel is a sign of peace.
And let us know about your experience.I myself will have one as well,either this or next year.The pipe work is already in place. And don't hesitate to ask.
heinbloed