Club 80-90 Forums

CovKid wrote:....but I'm not going to get obsessive about amps.

Wanna bet?

I need amps.. lot's of them, I am obsessed with amps,
BTW that was taken when the battery/panel had just spent 3 hrs heating 15 litres of water up with an 11 amp water heater, battery was down to 12 volts, as soon as the heater was turned off the amps went from 5.2 to that, it fully charged the battery by the time the sun went down.
It is a brilliant thing that is so cheap these days.

CJH wrote:

CovKid wrote:....but I'm not going to get obsessive about amps.

Wanna bet?

Actually, let me correct that. You'll measure your amps once or twice, you'll post your findings, and you may mention it occasionally round the campfire. You may not be obsessed, but it'll look that way to the rest of us. You should know this better than most of us.

CJH wrote:

CJH wrote:

CovKid wrote:....but I'm not going to get obsessive about amps.

Wanna bet?

Actually, let me correct that. You'll measure your amps once or twice, you'll post your findings, and you may mention it occasionally round the campfire. You may not be obsessed, but it'll look that way to the rest of us. You should know this better than most of us.

... ...

kevtherev wrote:
... ...

Oh dear, I think my loaded comment whizzed past Ralph's ear and hit Kev standing behind him instead.

I think its reasonable to ask how to fit one to a tintop given that no one seems to have done it, and the problem of the roof ribs, but trust me, if it tops my batteries up in between these four mile jaunts, my interest in the panel (unless it fails) will be zilch. I witnessed MattBW stuck with the late Grumpy Midget for an HOUR once after Matt foolishly asked if solar panels were any good. Its a memory that lingers and not one I ever want to see again - or instigate.

That said, if you want to be bored to within an inch of your life on the subject of upgraded T25 exterior lights, I'm your man.

One thought does occur to me. How about putting hollow, clear, polycarbonate roof sheeting under the flexi to raise it to rib height?

CovKid wrote: One thought does occur to me. How about putting hollow, clear, polycarbonate roof sheeting under the flexi to raise it to rib height?

Well yes, they do apparently work better if they're kept cool. That's going to be more of an issue on a tin top than a fibreglass top I'd imagine, and an air gap could be a good way to keep the panel cooler.

Only if there is a breeze. (joke by the way)

imho, Being predominantly black, the panel will absorb more heat than a lighter coloured roof, if the panel is firmly flat against the roof, it might actually use the roof as a heat sink? (Except Ralph's roof is dark blue, but you could easily alter that )

Hard to judge whether the additional airflow would make much difference although I do have concerns about it on a dark tintop. All solar panels see reduced capacity if they're too hot so trying to avoid that. The sheet will either help insulate the panel from the metal roof or worse, lock the heat in. Bit annoying having to buy a massive sheet when I only need a small bit though. For sure that roof gets hot in Summer though.

Capillary tubing heat exchanger / stand off, for a shower unit
Sorry, I'm getting silly

Anyway, as long as the heat only reduces the efficiency slightly, and does not damage the cells, then why worry. It's not hot sunny days when you need high efficiency, rather the days like we have now

Gut feeling - no real numbers to work from - but the amount of heat energy absorbed by the individual cells by virtue of them being dark will be quite small. They are wafer thin so have a low thermal mass. And they're stuck to a plastic substrate which I guess would slow the transfer of heat to the roof. So it doesn't 'feel' to me as though the 'roof as heatsink' theory would apply.

On the other hand, the thermal mass of the tin top is huge, and being dark it will absorb a lot of energy. The plastic substrate would be less of a barrier to that amount of heat energy I reckon. So gut feeling - heat is going to transfer from the roof to the panel.

With an air gap made of polycarbonate sheet this transfer of heat will be less (like double glazing). And what air there is under the panel will always be in shade, and it would be a rare day when there's absolutely no air movement. Provided the polycarbonate sheet will curve along it's cells to fit the curve of the roof I'd say go for it.

That's my reasoning and I'm sticking to it.

ghost123uk wrote: Anyway, as long as the heat only reduces the efficiency slightly, and does not damage the cells, then why worry. It's not hot sunny days when you need high efficiency, rather the days like we have now

Good point - probably not worth the bother. Let's see a graph of efficiency against temperature.

Semi flexible panels are constructed on aluminium, so have their own heat sink.
They don't get as hot as the rigid panel which are glass covered
Can't see it getting hot enough to worry about in the uk anyway,
It's raining and dull this morning and mine is charging at 2.1amps and definitely is not over heating !

Mocki wrote:It's raining and dull this morning and mine is charging at 2.1amps

I want what you have got !!!!

Mine must be a real crappy make, I'm lucky if I get 100mA on an overcast winters day.

Aluminium is common, but I don't think it's the only type of substrate. If Ralph has bought the one he linked to, it's described as "Lightweight design, laminated plastic sheet with flexible solar cells. This panel is only 4mm thick". I'm pretty sure the one I used is on a plastic substrate too. What that says about the importance of heat dissipation I don't know. But I think you're right - I haven't found a suitable efficiency/temp graph, but what I've seen suggests it's a gradual and shallow drop in efficiency rather than a cliff face at a certain temperature.