Solar now seems much less efficient

Rheumatoid

Topping out at 3.2kW like yesterday against the usual 3.7kW. Doesn't seem that warm out there though and there is a decent breeze. 86% of what the system is capable of :-(

Exiled_Tyke

I'm currently on 1.7kW. Last month this time of day was giving me 3kW in full sun. I'm sure the lack of breeze isn't helping.

And don't forget that even if it isn't VERY warm, a little warmth with plenty of sun, and no breeze will greatly increase the heat level of the panels. Yet again it raises the question - does it pay to spray the panels in hot weather?

EricMears

Rheumatoid wrote: »

Reading around it seems you can lose about 0.5% for every 1 degree C over 25 degrees so on a hot day when panels can reach 45 degrees you can lose about 10%.

That strikes me as much more believable than the people who are convinced that a 25% or even 35% drop is attributable to panel temperatures.

Much more likely that the "panels being fully illuminated by brilliant sunshine" is a (faulty) impression prompted by it seeming a nice sunny day but that the haziness is difficult to spot let alone evaluate accurately.

Spraying panels with cold water might well 'help' - but that will only give you back the actual losses due to panel temp (c. 10%) not the 30% people suspect they're losing. But even that poses its own problems: are you going to pay for mains water (and waste it) or try to use recycled rainwater (which will get very hot as it lands on the panels and even hotter when it runs down over the equally hot roof tiles and not cool very much before you pump it back up to the roof).

Exiled_Tyke

EricMears wrote: »

That strikes me as much more believable than the people who are convinced that a 25% or even 35% drop is attributable to panel temperatures.

Much more likely that the "panels being fully illuminated by brilliant sunshine" is a (faulty) impression prompted by it seeming a nice sunny day but that the haziness is difficult to spot let alone evaluate accurately.

Spraying panels with cold water might well 'help' - but that will only give you back the actual losses due to panel temp (c. 10%) not the 30% people suspect they're losing. But even that poses its own problems: are you going to pay for mains water (and waste it) or try to use recycled rainwater (which will get very hot as it lands on the panels and even hotter when it runs down over the equally hot roof tiles and not cool very much before you pump it back up to the roof).

It wouldn't be the temperature of the water that matters. It's the evaporating of it from the surface of the panels which would cause the cooling effect.

Dave_Fowler

At midday today (GMT) the air temperature was 23, the loft temperature was 24, the inverter temperature was 37 and the panel temperature was 50 (in degrees C).

Panel output from the 3kWp system was 2.35kW.

The panels were therefore 25 degrees above the 'nominal temperature' so a drop of 12.5% in efficiency can be attributed to the panel temperature.

It is interesting to see how the loft temperature at midday was only one degree higher than ambient. The shading caused by the panels and the thermal lag due to the large space helps to keep the temperature very even. At the present time (2pm) the loft temperature has risen to 27 degrees, but the inverter output is already falling, 2.2kW, as the sun moves away from due south.

Dave F

EricMears

Exiled_Tyke wrote: »

It wouldn't be the temperature of the water that matters. It's the evaporating of it from the surface of the panels which would cause the cooling effect.

Nice theory - but in practice the water would run off long before it boiled away !

Exiled_Tyke

EricMears wrote: »

Nice theory - but in practice the water would run off long before it boiled away !

I disagree. My panels stay quite wet of a good while after a rain shower. Yes if you hose down the panels then most of that water would be wasted but that's not what I am proposing. I've just seen a posting stating that panels got to 50 degrees today. So I would have thought a mist of water over the panels could make a significant difference. And I'm definitely not talking about boiling the water with the panels just evaporation in exactly the same way that sweat evaporates from the skin to create a cooling effect, even though the sweat starts off at body temperature

Sterlingtimes

organum wrote: »

With the recent sunny days I thought the solar system would work rather better, but found that especially the rear panels are now giving out less that 1kW when last year they gave out a lot more, enough to heat the hot water anyway.

I tried to contact the supplier TP solar but they seem to have gone out of business.

Thank you
Richard

Yes, I used TP Solar. I never did get an answer as to whether they had installed M215 or M250 micro inverters. I suspect that I have M215 which would each yield a maximum of 225 watts AC output, i.e. in my case, driven to 14 * 270 watt panels, I max out at 3,000 watts. It is not necessarily a bad system, but I do not get optimised potential for my 270 watt panels. Another defect in the O system.

Martyn1981

EricMears wrote: »

That strikes me as much more believable than the people who are convinced that a 25% or even 35% drop is attributable to panel temperatures.

I'm not sure about 25%+, but I'm sure 20% is possible. That requires a temp close to 75C, and I'm sure I read years ago about dark cars, particularly black ones reaching 70C in direct sunlight.

When I chat/discuss PV maximums for the UK, I tend to suggest generation figures that max out in the summer (sunny Sunday afternoon) of 75% of GWp. I figure that a sustained generation (that would give national high generation, rather than cloudy weather, with higher individual peaks, but lower total GW) would need good direct sunlight, leading to 80% performance.

I then reduce down to a 75% national figure to account for non-south facing panels. I don't deduct diversion (water or battery) as these would probably have maxed out by the afternoon, when daytime demand is at its lowest. Again regarding Sunday afternoons, which can be 10GW lower than the other 6 days.

Mart.

defaultdriver

Rheumatoid wrote: »

Topping out at 3.2kW like yesterday against the usual 3.7kW. Doesn't seem that warm out there though and there is a decent breeze. 86% of what the system is capable of :-(

Mine was topping out at 3.1kW against the usual 3.2kW
I have not seen my system go over 3.2kW, is your 3.7kW a short burst or for a long period of time
I had one day in May in which I had 3.2kW for just over 3 hours.
I was expecting the same today but it was slowly moving upwards during the day till it topped out at 3.2kW 2.15 till 2.45 from which point it slowly started heading down again