solar water heating kit and questions

eao1

Hi all,

I've found a solar water heating kit I would like some opinions and advice, it's a uk site so im looking for the equivalent in ireland im not sure if i can post the site on this forum but if you pm me i can give you the web add to look, the kit is £1700

This is the kit-

2 x 20 tube 47mm vacuum tube solar panel - manifold type (sfb20-47)
Roof Mounting Kit [/COLOR][/FONT][/URL]
Twin Coil Hot Water Cylinder - (up to172litre double insulated, grade3 with grade2 base): - larger tanks incur additional cost
TDC 3 Solar Controller
Circulation Pump + Isolation Valves
anti-syphon valve
pressurised system kit (including filling loop, isolation valves and double check valve, pressure gauge and pressure relief valve)
10m armaflex ht high temperature
5 litres antifreeze.

I have a 3 bed house,only myself herself and the little one.
cyclinder is only bout 4 to 5 mts away at most.
Vented plumbing system
dont know the angle of the roof if you need that

Is this a good system?
does it have everything i need?apart from the regular plumbing and electrical fittings to install.
Is there anywhere i can get this or similer over here?
are the solor tubes measurements adaquate for the house?

Only thing is in the mounting kit there is nothing for the pipe work to come through the roof , flashing of some sort.

I will be installing this.

All advice appreciated.

quentingargan

I am familiar with this equipment - we used to buy from these people ourselves but now buy directly from China.

There's nothing wrong with the product, but I would use at least 200L with 40 tubes, and would put a heat dump into the circuit (requires a high temperature 3 port motorised valve and a radiator).

To optimise the output you should also have a thermal mixing valve on the outlet so you can let the cylinder run up to 85 degrees or so. (but if you are in a hard water area, don't let the water go over 60 degrees). Q

Evergreen

I checked out the panels you are talking about and yes they are correct, the panels are probably one of the best priced systems on the market, however, this comes at a cost.

I downloaded the data sheet for these panels and put it through a panel efficeiny/output calculation spreadsheet and the results were not pretty.

Here is a summary of the results (using 1000 kWh/m2 irraniance)

Gross Area 2.4 m
Aperture Area 1.74m
Panel Efficiency 47%
Output per m2 Aperture = 470 kWh/m2/a
Output per m2 of roof covered = 341 kWh/m2/a

To put these figures into persepective;

A good tube system you could expect the following results
Output per m2 Aperture = 612 kWh/m2/a
Output per m2 of roof covered = 532 kWh/m2/a

A medium flat planel system you could expect these results
Output per m2 Aperture = 520 kWh/m2/a
Output per m2 of roof covered = 477 kWh/m2/a

So, they are cheap for a reason :eek:

I have attached the efficency calculator if anybody wants to look at the data, or even use it later when working out the outputs or efficienies of other solar systems. All the blue coloured fields are changeable.

quentingargan

Evergreen's figures favour flatplates because the figures totally ignore incidence angle modifier and use noon efficiency only. Flatplates are at their most efficient at noon (obviously) whereas vacuum flask systems are at their most efficient during the morning and afternoon. The reasons for this are complex, but are explained here.

So at a time when a flatplates is at 60% of its noon efficiency, some vaccum flask systems are working at well over 100% of their noon efficiency.

On sunny days both will provide you with plenty of hot water - where vacuum flasks excel is in extending the seasons into spring and autumn and on cloudy days. This seasonal stretch isn't shown in the figures for overall annual performance.

I have no axe to grind on this - I work with both flatplates and tubes, but we sell flatplates based on their aesthetic appeal, not their efficiency.

Evergreen

quentingargan wrote: »

Evergreen's figures favour flatplates because the figures totally ignore incidence angle modifier and use noon efficiency only

Actually if you look at my figures you will see that I show a higher output when using decent evacuated tubes. How does this favour flat plate?

quentingargan

Evergreen wrote: »

Actually if you look at my figures you will see that I show a higher output when using decent evacuated tubes. How does this favour flat plate?

Because even for good tubes, you show a lower figure per gross area per year. My point is that the spread of that heat income is more important than the total heat. For many people, if aesthetics aren't a priority, neither is gross area. The issue is useful heat per €

I was also pointing out that an efficiency for flasks of 47% needs to be modified to take into account incidence angle modification which nobody seems to do (including SEI / Harp database etc.). Q

PeteHeat

Hi,

May I ask why buy in the UK when you can get a similar kit here for about the same price ?

I am not saying either kit is what I would recommend but if the consumer wants that product and is an informed buyer then who am I to argue ?


.

ferngreen

The kit sounds very cheap too cheap really.

I assume it is supply only.

Generally the systems from china have a very bad name <SNIP> details (dont want to get banned!)

the systems with antifreeze are outdated. the systems with glycol are more efficient.

I dont see it mentioning expansion vessels or a solar controller which can be costly





Mod edit: Read the forum charter please especially the bit about people seeking to gain from posting in the forum.

RVR

ferngreen wrote: »

the systems with antifreeze are outdated. the systems with glycol are more efficient.

Glycol IS antifreeze? As long as it's propylene glycol (non toxic) not ethylene glycol (do not ingest)...

quentingargan

ferngreen wrote: »

Generally the systems from china have a very bad name

Thats a pretty sweeping generalisation. There are over 2,000 factories making solar water heaters in China. They are the innovators behind the solar flask system which is very reliable and for which replacement flasks are incredibly cheap.

By comparison, other vacuum tube systems rely on a weld between copper and glass to hold in the vacuum, and replacement costs are prohibitive.

There are good and bad Chinese manufacturers, but there is no doubt in my mind that the best vacuum systems - and the worst - are probably made in China.

Many so-called European panels are in fact rebadged Chinese ones (re-priced as well!).

RVR

Have to agree with quentingargan there. You can't generalise like that.

We've seen chinese panels that are better quality than many european panels. Although, we've also seen the opposite!

Unfortunately it's suppliers who flog poor quality panels as cheaply as possible, with no support, that end up giving these products a bad name :rolleyes: