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Solar panel query... does colour matter?


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Hi All, just revisiting my solar project and have decided to definately go with solid panels. These seem to come in black or silver frames - the black ones also tend to have 'blacker' solar cells.  Is there any advantage/disadvantage to the colour or is this just aesthetics?  My simple thinking is the blacker ones may heat up more = not good??

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1 minute ago, matty40s said:

Monocrystaline tend to be black, polycrystaline more of a blue. Temperature of the panels in the UK on a boat roof not really significant in either lifetime length or power yield if there is a gap below.

So, yes, it's mainly how they look.

 

The slightly bluer poly panels look that way because they reflect a bit more blue light, but most of the energy in sunlight is at the redder end of the spectrum (or infra-red) where both absorb almost all the light, so there will be very little temperature difference between them.

 

Power drops off slowly between cold and hot, the panels need to heat up by about 25C to lose 10%.

 

Having a big gap underneath will help keep them a bit cooler, especially if there is some airflow (not always on hot days). Alternatively semi-flexible or flexible panels bonded down to a steel roof may actually run cooler, the roof and its support beams conduct heat across the the uncovered roof and cabin sides which helps dissipate heat.

 

But overall -- not much difference in any of these cases... 😉

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12 hours ago, IanD said:

The slightly bluer poly panels look that way because they reflect a bit more blue light, but most of the energy in sunlight is at the redder end of the spectrum (or infra-red) where both absorb almost all the light, so there will be very little temperature difference between them.

<pedant>A bit more detail. The actual energy of the light photons is more at the blue end of the spectrum, however, more sunlight is converted in to electricity at the greenish to red and in to the near infrared end of the spectrum. The glass over the panel absorbs most of the UV in sunlight, so doesn't reach the silicon at all. Deeper in to the IR, it just heats the panel up, isn't turned in to electricity and reduces the panel efficiency for the other wavelengths to boot. Most light is absorbed, only a proportion is converted to electric, depending on wavelength. More blue is reflected in poly crystalline panels, but that doesn't matter as silicon solar cells are rubbish at converting that light to electrical power anyway.</pedant>

 

 

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I do think that not all panels are created equal, so you are right to do a bit of digging into the question of efficiency.

For example. my front panels have a rating of 660 watts, and the rear are rated at 750 watts. So my (admittedly somewhat fragile) assumption was that the front panels should yield about 88% of the power that is yielded by the rear panels, right?

(I would implore our solar experts not to be too brutal in explaining why my assumption is nonsense- I'm just a simple peasant lad).

 

However, this was not the case. My incredibly detailed and scientific analysis has shown that the power yield from the front panels is about 95% that of the rear panels (and the font panels are at least 5 years old, whereas the rear panels are barely toddlers).

 

So my rear panels are not as 'good' as the front ones, in that they don't yield the amount of extra power that their generous wattage rating would lead a simple peasant lad to expect.

They were one of the cheapest available options, to be fair, but were bought from a UK retailer with an actual warehouse and workshop, so not absolute rock bottom stuff- whereas the front panels (which were installed before the current regime took power), look to be of a tad more quality in manufacture.  

 

Anyway, my advice would be to ignore all this nonsense about photons and spectrums.

It's all down to pixies, like so many things that relate to electricity. 

I think you need to not just look at the wattage, but also the SPQ rating (Solar Pixie Quotient). 

 

 

Edited by Tony1
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I make it about 45% of the total output, not 88% but I may be wrong and if not it is more perplexing. However are they connected in series, parallel or series parallel? (Can't be the last if only two). 

 

I also wonder what the open circuit voltage is of the two. If one is around 20V and the other 30v plus then all sorts of odd things might happen. If they are different then maybe connecting in series with an MPPT controller might get the bets output.

 

This assumes one controller, If you have two then that may affect things if one has gone to float.

 

Over to the real solar experts.

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1 minute ago, Tony Brooks said:

I make it about 45% of the total output, not 88% but I may be wrong and if not it is more perplexing. However are they connected in series, parallel or series parallel? (Can't be the last if only two). 

 

I also wonder what the open circuit voltage is of the two. If one is around 20V and the other 30v plus then all sorts of odd things might happen. If they are different then maybe connecting in series with an MPPT controller might get the bets output.

 

This assumes one controller, If you have two then that may affect things if one has gone to float.

 

Over to the real solar experts.

 

Thanks Tony- I should have explained that I have one controller for front and one for the rear.

Also, the front panels are a set of four smaller units, whereas the rear panels are a set of two larger units. 

 

I must confess I haven't checked the wiring on the front panels, I shall take a look later and see what may be discerned from the morass. 

I'm not rubbishing the science as such.

But just in case I have angered the pixies, I am going to hunt down a small mammal to sacrifice at noon in an effort to appease them. 

If it seems a bit eccentric, bear in mind the Aztecs used to sacrifice actual people for the sun.

Just saying.

 

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1 minute ago, Tony1 said:

Thanks Tony- I should have explained that I have one controller for front and one for the rear.

Also, the front panels are a set of four smaller units, whereas the rear panels are a set of two larger units. 

 

Try the calculation first thing in the morning after  a night aboard. I suspect one controller was at float voltage.

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The efficiency differences between decent-quality modern panels of the same type (e.g.mono PERC) are very small, unless you pay several times the price for ones with technology tweaks -- and even these give less than 10% more output for more than 100% extra cost, so aren't worth it.

 

If you have a lot of panels then it's worth breaking them down into groups with separate lower-current MPPT controllers for several reasons; one is squeezing the maximum output from each group even if some are partly shaded, the other is reliability and debugging any connection problems.

 

If you have a lot of parallel panels (or strings) on one big MPPT it's difficult to spot a bad connection (or bad panel) because all that happens is a bit of a drop in output and you've nothing to compare it to, but if you have several MPPTs (at least 2) this becomes obvious since one has lower output -- and then if you go out and start tweaking connections the low MPPT output will go back up once you find the bad one.

 

(Finesse use 3 MPPT controllers each with 4 series panels (48V system) for these reasons)

Edited by IanD
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31 minutes ago, IanD said:

The efficiency differences between decent-quality modern panels of the same type (e.g.mono PERC) are very small, unless you pay several times the price for ones with technology tweaks -- and even these give less than 10% more output for more than 100% extra cost, so aren't worth it.

 

If you have a lot of panels then it's worth breaking them down into groups with separate lower-current MPPT controllers for several reasons; one is squeezing the maximum output from each group even if some are partly shaded, the other is reliability and debugging any connection problems.

 

If you have a lot of parallel panels (or strings) on one big MPPT it's difficult to spot a bad connection (or bad panel) because all that happens is a bit of a drop in output and you've nothing to compare it to, but if you have several MPPTs (at least 2) this becomes obvious since one has lower output -- and then if you go out and start tweaking connections the low MPPT output will go back up once you find the bad one.

 

(Finesse use 3 MPPT controllers each with 4 series panels (48V system) for these reasons)

I seems that often 2 smaller MPPTs are cheaper to buy than one large one as well

image.png.e89c39e244d89bfb2a19c81f1ceaf44e.png

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17 minutes ago, IanD said:

The efficiency differences between decent-quality modern panels of the same type (e.g.mono PERC) are very small, unless you pay several times the price for ones with technology tweaks -- and even these give less than 10% more output for more than 100% extra cost, so aren't worth it.

 

If you have a lot of panels then it's worth breaking them down into groups with separate lower-current MPPT controllers for several reasons; one is squeezing the maximum output from each group even if some are partly shaded, the other is reliability and debugging any connection problems.

 

If you have a lot of parallel panels (or strings) on one big MPPT it's difficult to spot a bad connection (or bad panel) because all that happens is a bit of a drop in output and you've nothing to compare it to, but if you have several MPPTs (at least 2) this becomes obvious since one has lower output -- and then if you go out and start tweaking connections the low MPPT output will go back up once you find the bad one.

 

(Finesse use 3 MPPT controllers each with 4 series panels (48V system) for these reasons)

 

My decision to use two MPPTs was initially an economic one tbh.

The original MPPT for the front panels was a 40amp EPEVER unit, and I knew 40amps would not be enough with the extra panels on the rear.

The units that could handle 80 amps or more seemed very expensive, so the more affordable option was a second MPPT, a 50 amp victron unit.

(As an aside, I ended up liking the new victron MPPT so much (with the bluetooth control etc) that I bought a second one for the front panels, to replace the EPEVER.) 

 

One of the interesting things is that the front panels, because they are mounted in a square pattern, are not worth tilting (because the two that are on the side nearest the sun, when tilted, will then partly obscure the two behind, and that seems to reduce the overall output significantly). 

I do tilt the rear panels at times, and so this gives me a chance to compare the difference in power output from two very similar-performing sets of panels, one set tilted and one flat, in a wide variety of situations.  

 

I'm not saying I would recommend that people should get tilting panels, or that I'd even get them again myself. But in those occasional situations when tilting works, it does work really well. 

E.g. because

1. we have bright and direct sun this morning (a rarity, as we know), and

2. the side of the boat is facing roughly southwards, AND

3. there is very little vegetation to the south (again a bit of a rarity)

 

Today is one of those ideal tilting days, and the rear panels are yielding 25-28 amps (before 11am), whereas the non-tilted front panels are giving a little less than 10 amps. 

But in fairness, most of the time, with it being overcast, they are all laid flat. 

 

 

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6 minutes ago, Alan de Enfield said:

 

That is of course the problem with these 'Fred in a shed' (market stall operations)

 

SPQR = Small Profit, Quick, Run

 

I think my panels were from Bimble, so in fairness a pretty decent company by all accounts- although there are plenty of rather more dubious suppliers out there, of the SPQR persuasion. 

 

 

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3 minutes ago, Tony1 said:

 

I think my panels were from Bimble, so in fairness a pretty decent company by all accounts- although there are plenty of rather more dubious suppliers out there, of the SPQR persuasion. 

 

 

 

Well I personally think that Bimble are one of the best - all my panels have been from them and they have given excellent service and delivered when promised.

 

I think my 'best buys' were the 170 watt / 120 volt panels which are far more productive than the typical 170watt / 20 volt panels.

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I think I was being a bit unfair in suggesting they were not nearly as well-made as my older panels. 

The flat surface feels more flimsy, but then it would do, since the surface area is much greater on the larger panels, and more prone to wobble and movement in general. The front panels are something like half the size, and maybe that's why they feel more rigid and well-made.

 

That said, the frame and fixings on my older panels do feel rather better put together, but I suspect the previous owner paid a lot of money for them. 

I agree with Ian's suggestion that its not worth paying the extra for the very best panels available. It makes much more sense to buy from a company like Bimble at a reasonable price, and get perhaps 90% of the power whilst paying half the price. 

These are just tools, and in perhaps 10-15 years even better ones will come along at a lower price- so they dont need to last forever anyway. 

 

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30 minutes ago, Tony1 said:

 

 

I think I was being a bit unfair in suggesting they were not nearly as well-made as my older panels. 

The flat surface feels more flimsy, but then it would do, since the surface area is much greater on the larger panels, and more prone to wobble and movement in general. The front panels are something like half the size, and maybe that's why they feel more rigid and well-made.

 

That said, the frame and fixings on my older panels do feel rather better put together, but I suspect the previous owner paid a lot of money for them. 

I agree with Ian's suggestion that its not worth paying the extra for the very best panels available. It makes much more sense to buy from a company like Bimble at a reasonable price, and get perhaps 90% of the power whilst paying half the price. 

These are just tools, and in perhaps 10-15 years even better ones will come along at a lower price- so they dont need to last forever anyway. 

 

https://www.bimblesolar.com/panelcompare?sort=price_per_watt

 

The most efficient panels are the huge 655W ones, which cost about 10% more per W than the absolute cheapest in exchange for 7% higher output (21.1% efficiency compared to 19.8%).

 

The double-the-price LG ones aren't actually more efficient, though other suppliers do more expensive panels (e.g. N-type IBC) which are a teeny bit better, especially over temperature -- maybe 10% higher output than PERC or 15% when hot, but at least 50% higher cost (can be up to double) -- see here:

 

https://www.cleanenergyreviews.info/blog/best-solar-panels-review

https://www.cleanenergyreviews.info/blog/most-efficient-solar-panels

 

There are various new technology panels with higher efficiency being proposed, but none of them are in production -- and even if the efficiency increase is large (up to 25% higher output has been claimed), they'll have the chicken-and-egg problem that they can't get anywhere close in cost per W to mono PERC panels while they're made in small volumes, so few people will buy them, so the price stays high, so... 😞

 

 

 

Edited by IanD
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5 minutes ago, IanD said:

https://www.bimblesolar.com/panelcompare?sort=price_per_watt

 

The most efficient panels are the huge 655W ones, which cost about 10% more per W than the absolute cheapest in exchange for 7% higher output (21.1% efficiency compared to 19.8%).

 

The double-the-price LG ones aren't actually more efficient, though other suppliers do more expensive panels (e.g. N-type IBC) which are a teeny bit better, especially over temperature -- maybe 10% higher output or 15% when hot, but at least 50% higher cost.

 

There are various new technology panels with higher efficiency being proposed, but none of them are in production -- and even if the efficiency increase is large (up to 25% higher output has been claimed), they'll have the chicken-and-egg problem that they can't get anywhere close in cost per W to mono PERC panels while they're made in small volumes, so few people will buy them, so the price stays high, so... 😞

 

See here for some really good information:

 

https://www.cleanenergyreviews.info/blog/most-efficient-solar-panels

https://www.cleanenergyreviews.info/blog/best-solar-panels-review

 

I personally would consider paying a bit more (not loads) for certain panels, but maybe based more on dimensions.

What I mean is that the 655watt panel, for example, is 1300mm wide, so that will probably fit on the roof. Because it would take up all of the roof, I wouldnt put it aft of the boats centre. 

For the aft panels, you need to be able to walk along the roof at times, so the width of the rear panels has to be about 80cm (or maybe a metre if you dont mind tiptoeing past them a bit as I do). 

 

My own assumption was that I wanted the most solar I could reasonably fit. There are some limitations, e.g. you need to allow enough room that the centre line isnt getting caught on the panels, and you need a foot or two of free space on the rear of the cabin roof, so you have somewhere to place your hands (and backside) when climbing on and off the roof. That kind of thing.  

 

But you dont normally walk on the roof forward of the centre line, so you could consider filling the forward roof completely- and thats where those 655 watt panels come in. On a 57ft boat you might get two of those wider panels on the roof forward of the centre, and perhaps another 2 or 3 of the 80cm panels on the rear part of the roof. 

It might be that you could reasonably fit 3x220 watts on the rear part of the roof, and 2x655watts on the front, so nearly 2000 watts in total.

At only 50ft long, my boat wont fit that much, but at about 1400 watts its not too bad, and I'm expecting great things come the Spring.  

 

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7 minutes ago, Tony1 said:

 

I personally would consider paying a bit more (not loads) for certain panels, but maybe based more on dimensions.

What I mean is that the 655watt panel, for example, is 1300mm wide, so that will probably fit on the roof. Because it would take up all of the roof, I wouldnt put it aft of the boats centre. 

For the aft panels, you need to be able to walk along the roof at times, so the width of the rear panels has to be about 80cm (or maybe a metre if you dont mind tiptoeing past them a bit as I do). 

 

My own assumption was that I wanted the most solar I could reasonably fit. There are some limitations, e.g. you need to allow enough room that the centre line isnt getting caught on the panels, and you need a foot or two of free space on the rear of the cabin roof, so you have somewhere to place your hands (and backside) when climbing on and off the roof. That kind of thing.  

 

But you dont normally walk on the roof forward of the centre line, so you could consider filling the forward roof completely- and thats where those 655 watt panels come in. On a 57ft boat you might get two of those wider panels on the roof forward of the centre, and perhaps another 2 or 3 of the 80cm panels on the rear part of the roof. 

It might be that you could reasonably fit 3x220 watts on the rear part of the roof, and 2x655watts on the front, so nearly 2000 watts in total.

At only 50ft long, my boat wont fit that much, but at about 1400 watts its not too bad, and I'm expecting great things come the Spring.  

 

 

Completely agree, getting the right size panels to make the best use of your roof space is far more important than worrying about 20% or 21% efficiency -- I was simply answering the efficiency question.

 

To take this to the extreme, the way to get the largest area of panels onto most roofs (so highest output -- 12 x 160W in my case, could fit more if pushed but want some gaps for various reasons) is to use semi-flexible ones which span the entire width between handrails and can be walked on, but this certainly doesn't make sense from a cost point of view because these are way more expensive than rigid PERC panels...

Edited by IanD
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4 minutes ago, David Mack said:

Unless you are in a wide lock and the ladder on your side is at the far end of the lock.

 

Yes, thats what I meant by saying 'normally'. 

I think in this case I'd do as some have suggested and tow the boat by hand, rather than use the ladder. 

I think it refocuses on the point that each of us will assign our own level of importance to solar, and decide how much we want/need, and balance that with the hassle we are prepared to put up with. 

 

Edited by Tony1
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10 minutes ago, Tony1 said:

 

Yes, thats what I meant by saying 'normally'. 

I think in this case I'd do as some have suggested and tow the boat by hand, rather than use the ladder. 

I think it refocuses on the point that each of us will assign our own level of importance to solar, and decide how much we want/need, and balance that with the hassle we are prepared to put up with. 

 

 

I wouldn't like not being able to walk across (or along) the roof, I've had to in locks on several occasions. A group of 4 semi-flex mono PERC panels is 2.7m long, and I can get three of these groups on the roof with cross-roof gaps in between and at both ends -- and the panels themselves can be walked on, though not in hobnailed boots or stilettos... 😉

 

As far as cost is concerned, better stick your fingers in your ears and go "la-la-la" -- all I'm willing to say is that they're much cheaper than the LFP battery bank, and only add about 1% to the cost of the boat...

Edited by IanD
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2 hours ago, IanD said:

 

I wouldn't like not being able to walk across (or along) the roof, I've had to in locks on several occasions. A group of 4 semi-flex mono PERC panels is 2.7m long, and I can get three of these groups on the roof with cross-roof gaps in between and at both ends -- and the panels themselves can be walked on, though not in hobnailed boots or stilettos... 😉

 

As far as cost is concerned, better stick your fingers in your ears and go "la-la-la" -- all I'm willing to say is that they're much cheaper than the LFP battery bank, and only add about 1% to the cost of the boat...

 

It might be my faulty memory, but most of the ladders I can remember were reachable if you were able to get to the centre of the boat, so I haven't prioritised roof walking on the forward part.

In fact I cant access the roof forward of the centre, now that I consider it, because the forward panels obscure the roof almost completely. That decision was made before I got the boat.

Maybe its partly that I'm only cruising once or twice a week, but I can only remember having to reach a ladder forward of the centre once in recent months, although I cant remember where it was. 

But I do need to be ready for it, because I will come across the odd one. I'm guessing that if you're in a double lock alone, there will be space to walk forward the full length of the boat along the gunwales, although you'd want to be pretty quick to reach the ladder before the boat starts drifting away from it. And you dont want the boat flush against the lock wall, or you'll get slime from the wall on your clothes. 

If there is another boat in a double lock, I would ask their crew if they didn't mind me staying on my boat for this one- most people could see your issue and would hopefully not think you were shirking. If they want help with the paddles, I'd ask to use their roof to reach the ladder. But I cant remember that ever happening so far.

If its a narrow lock and there's no space at the sides to walk along the gunwales without getting slimed, I guess I'd have to tow the boat in, as I've heard some people do a fair bit. 

I'm not sure how well the towing would go in a strong bywash, or high winds, so it doesnt feel like a 100% reliable method, but sometimes you have to just figure things out on the fly, especially when singlehanding.  

 

I had to try towing for the first time when I got to the Beeston Iron lock and realised that there were no ladders in there, so I passed the rope from one hand to the other under the footbridge as the boat came out- fortunately it was narrow enough to allow this. More recently, a boater showed me the trick of letting the boat go forwards so the centre line passes under the footbridge, holding the line up against the bottom of the footbridge, and then reaching for the line on the other side - and because its being held high up close to the footbridge from your other hand, its easy to reach. 

 

Maybe its because my boat was envisaged to mainly be used on the EA waterways when built, but whatever the reason, not being able to walk on the forward part of the roof has very seldom caused me any issues.

 

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