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Hi! I have a fixed panel on the roof facing SW on my mooring! If facing South the panel angle should be 42 degrees! For you mathematicians out there, what is the ideal

angle or am I just clutching at straws?

Edited by Kalapattar
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Flat on the roof unless you are really struggling  for output. Even with it angled the angle varies throughout the year and you need to rotate it throughout the day to face the sun. Is it worth the effort?

 

I have seen it claimed that on cloudy days a horizontal panel produces more output because it catches more rays at 90 degrees from cloud scatter.

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1 hour ago, Tony Brooks said:

Flat on the roof unless you are really struggling  for output. Even with it angled the angle varies throughout the year and you need to rotate it throughout the day to face the sun. Is it worth the effort?

 

I have seen it claimed that on cloudy days a horizontal panel produces more output because it catches more rays at 90 degrees from cloud scatter.

Compared to an ideally angled south-facing panel, a flat panel loses about 10% of output on average.

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1 hour ago, Tony Brooks said:

 

I have seen it claimed that on cloudy days a horizontal panel produces more output because it catches more rays at 90 degrees from cloud scatter.

 

Ok ta!

8 minutes ago, IanD said:

Compared to an ideally angled south-facing panel, a flat panel loses about 10% of output on average.

Ok ta!

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7 minutes ago, IanD said:

Compared to an ideally angled south-facing panel, a flat panel loses about 10% of output on average.

 

 

Which is well worth having, but unless you are going to religiously track the position and height of the Sun in the sky every hour, it will only be giving that extra 10% for (maybe) an hour or so, and as the day progresses you will loose considerably more than the 10% you gained for that hour.

 

Lying flat on the roof will give you the best 'daily average' charge rate (unless you are prepared to track the Sun)

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2 minutes ago, Alan de Enfield said:

(unless you are prepared to track the Sun)

Well you could have a system which automatically adjusts the panel elevation and direction to maximise the solar input, but the system would probably use more power than the extra it generates.

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26 minutes ago, IanD said:

Compared to an ideally angled south-facing panel, a flat panel loses about 10% of output on average.

Ok ta!

9 minutes ago, David Mack said:

Well you could have a system which automatically adjusts the panel elevation and direction to maximise the solar input, but the system would probably use more power than the extra it generates.

Yes, I suppose so! I think I’ll leave panel as it is or drop 10 degs maybe!

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5 minutes ago, Kalapattar said:

Yes, I suppose so! I think I’ll leave panel as it is or drop 10 degs maybe!

 

 

You will 'lose' more output if you do not have your panels mounted with a suffcient air gap underneath (they get to hot) and will gain 30% by having an MPPT controller instead of a MWP controller, or by buying 'low light' panels instead of 'normal' ones.

 

 

Choice of equipment AND installation practices will affect your solar output way more than having a 'tilt' on them.

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3 hours ago, Alan de Enfield said:

 

 

Which is well worth having, but unless you are going to religiously track the position and height of the Sun in the sky every hour, it will only be giving that extra 10% for (maybe) an hour or so, and as the day progresses you will loose considerably more than the 10% you gained for that hour.

 

Lying flat on the roof will give you the best 'daily average' charge rate (unless you are prepared to track the Sun)

Sorry Alan but you're wrong -- that 10% figure is power yield over the entire day, and is for a flat panel compared to a fixed-elevation south-facing panel in the UK, not one which moves and tracks the sum.

 

Averaged over the entire year as well (including diffuse light from the sky) the penalty for flat mounting is a little bit bigger, 16% according to this:

 

https://www.viridiansolar.co.uk/resources-1-3-tilt-and-orientation.html

 

Again averaged over the year, each kW of flat-mounted panel (peak rating) will produce about 2kWh/day (allowing x0.84 for flat mounting):

 

https://www.viridiansolar.co.uk/resources-4-4-performance-of-pv-solar-panels.html

 

Bear in mind that this varies from maybe 4kWh/day in summer to 0.5kWh/day in winter, again these are averages so more on a sunny summer day and less on a dark rainy winter one. This also doesn't allow for any shading from trees or buildings, which will obviously reduce output further.

 

https://www.viridiansolar.co.uk/resources-1-2-seasonal-variation-solar-energy.html

 

This assumes mono panels, poly ones will be a bit less. The expensive "bifacial" panels which quote higher efficiency (e.g. 15% higher power) only work when mounted tilted and spaced over a reflective (white/silver) roof to catch light which misses them and bounces back up, these do nothing if flat-mounted and/or closely-packed like on a boat roof.

 

Edited by IanD
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Back in the 20 naughties, solar panels were very very expensive. I had a gadget, made in Slovakia, that turned the two 80W panels that I could afford to follow the sun through the day, then return to the start position overnight. If you were really keen, you adjusted the tilt angle between the seasons manually. Part way through the solar panel price crash of the previous decade, I bought a third 80W solar panel and mounted all three flat to the roof of the boat. Still get more out of them than two panels following the sun. No more dismantling the panels to cruise. No more worries about the wind catching them.

 

Jen

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  • 3 weeks later...
On 13/04/2021 at 14:12, Alan de Enfield said:

 

 

You will 'lose' more output if you do not have your panels mounted with a suffcient air gap underneath (they get to hot) and will gain 30% by having an MPPT controller instead of a MWP controller, or by buying 'low light' panels instead of 'normal' ones.

 

 

Choice of equipment AND installation practices will affect your solar output way more than having a 'tilt' on them.

My controller is what was supplied with panel! Not sure if it’s MPPT or MWP

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25 minutes ago, Kalapattar said:

My controller is what was supplied with panel! Not sure if it’s MPPT or MWP

 

It should say on it, or in the manual.

 

If you plan to keep it, whatever it is, then it doesn't matter, but if you want to maximise the output of your panels than you need to know if it is an MPPT or an MWP, and, will need to buy an MPPT if it is an MWP.

Edited by Alan de Enfield
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Just now, Kalapattar said:

Hi! A PWM controller was stated in another post! What is that please?

PWM = pulse width modulation. MPPT = maximum power point tracking. MPPT will get more out of your panels in sub-optimal conditions like the early morning, or late evening. Beware that if buying an MPPT controller, a lot of the cheap no name Chinese ones will actually be PWM, but with two, or three charging strategies for different conditions and called MPPT when they are not.

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9 minutes ago, Jen-in-Wellies said:

PWM = pulse width modulation. MPPT = maximum power point tracking. MPPT will get more out of your panels in sub-optimal conditions like the early morning, or late evening. Beware that if buying an MPPT controller, a lot of the cheap no name Chinese ones will actually be PWM, but with two, or three charging strategies for different conditions and called MPPT when they are not.

Ok ta!

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  • 2 weeks later...

Tilting made quite a big difference to my total power through the day when I did it last March / April. I have some absolute figures I think. I used a website that told me the angle of the earth for the time of year and aimed for that amount of tilt, I aimed for 40deg I think. I'll dig out the figures for you

 

(my two had been flat for years, which was fine until I was working from home running monitor, laptop and stereo etc 

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40 minutes ago, sirweste said:

Tilting made quite a big difference to my total power through the day when I did it last March / April. I have some absolute figures I think. I used a website that told me the angle of the earth for the time of year and aimed for that amount of tilt, I aimed for 40deg I think. I'll dig out the figures for you

 

(my two had been flat for years, which was fine until I was working from home running monitor, laptop and stereo etc 

There was a discussion on another thread recently about this, optimum tilting south-facing gives about 15% more average power than flat mounting. If the panels on the roof can only tilt sideways, this only happens if the boat is moored East-West.

Edited by IanD
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I don't have any panels yet, but it seems pretty obvious to me that if you tilt your panels towards the arc of the sun so that they're perpendicular to it's arc and approximately 90 deg to the sun at its highest point, then you'll get more out of the panels than if you just leave them flat on the roof where they'll never be perpendicular to the sun's arc at any point throughout the day.

 

It's a no-brainer surely.

Edited by blackrose
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14 minutes ago, blackrose said:

I don't have any panels yet, but it seems pretty obvious to me that if you tilt your panels towards the arc of the sun so that they're perpendicular to it's arc and approximately 90 deg to the sun at its highest point, then you'll get more out of the panels than if you just leave them flat on the roof where they'll never be perpendicular to the sun's arc at any point throughout the day.

 

It's a no-brainer surely.

Yes, and the difference is about 15% comparing tilted facing south to flat.

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1 hour ago, alistair1537 said:

I think the consensus on solar forums is that the tilt should be around your latitude angle - this gives the best average performance year round.

 

 

Actually the best results are achieved when the angle of tilt is 15 degrees less than your latitude, so (say) you latitude is 53 degrees (central England) the best angle of tilt is ~38 degrees.

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9 hours ago, IanD said:

Yes, and the difference is about 15% comparing tilted facing south to flat.

Just add 20% more solar panels than you need and keep them flat, that's a win win situation ?

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