Not all solar coils created equal?

[gds]

Maybe thermal stores, cylinders etc need an A - G efficiency rating system along the lines of what fridges, washing machines etc use.

The first rating could measure a given temperature rise at a certain KW input and flow rate at 3 sensors.

The second could measure heat loss at the same sensors over a period of time to gauge how efficient the insulation is.

Both of the above should take into account the volume of water in the TS/cylinder - others may disagree with this though.

Whilst I know there would be a cost involved to get each unit tested, the above would give a basic level indication of how efficient each unit is - and would have the added benefit of raising the efficiency of TS/cylinders in general as no manufacturer wants one with a GG rating.

[Justme]

Both of the above should take into account the volume of water in the TS/cylinder - others may disagree with this though.

Fridges & freezers are rated on size / volume so I dont see why not.

they believe that you absolutely MUST maintain your store at 85^oC as that is what the manufactures say, (indeed they do say that , but merely to be able to claim say a 30l/min flow at x ^oC). 

Thats the problem I had.

None would think (or quote) outside the box.

[wookey]

gds, the heat transfer rate of the coil is not an 'efficiency' measure - it's a sizing measure, like how big the tank is. So it's not really appropriate for an A-G sticker. It should be quoted in W/K (as opposed to in 'not-exactly-area+material' which really isn't very helpful).
An A-G sticker for the insulation would be an excellent idea, although of course in practice the pipe coming out totally dominate that on a well-insulated tank and would be hard to measure. It would encourage more manufacturers to have bottom-exit pipes, which has got to be a good thing, so maybe it's not daft. I can see a massive argument between manufacturers in some committee room trying to set a test regime.

[TOMSEPPINGS]

The greater the collector power (absorber area) the greater the heat exchanger rating required.

The Domestic Heating Compliance Guide (DHCG) recommends at least 10% of panel absorber area for the heat exchanger. SolaPlugs follow this recommendation.

Obviously exceeding this figure is better, but in a well insulated system the difference in performance is very small.

Copper is a better conductor than stainless steel, but stainless coils are usually thinner which compensates for the reduced conductivity of stainless.

Finned coils have a larger surface area, but the heat has to travel further through the metal, so plain finned tube is usually considered better.