What size Solar Panel?

[George Shardlow]

I am currently planning a solar setup for my 57 foot sailaway. It appears that Solar Panel prices have come down recently. Especially if you go for the larger sizes. City plumbing are doing a Longi 410w panel at £56.74. In reviews they get a good write up. However they are a bit big at 1134mm x 1722mm. I plan to have a 3 panel setup with the Midsummer narrowboat brackets. The are more efficient than the normal A frame ones. 

 

Has anyone else got any experience with these. Are they too wide? They will fit easy enough on the roof but will it be a bit tight under bridges etc?

 

Strangely, smaller panels cost more! I suppose it is a case of cost saving by scale. 400w panels are now the most common on houses.

 

I would love to hear other people's experiences.

 

Cheers

Martin

[jonathanA]

I've no direct experience but a quick look 410w at that size is approx 200w per square metre which seems reasonable to me but maybe compare with some good quality panels available elsewhere. What is the warranted lifetime?  My.house panels are guaranteed no less 80% max output for 25yrs. But are quite old now and still seem to be giving the same as they always did.

 

You'll need to know the max voltage to be able to size your controller too. 

[IanD]

21 minutes ago, jonathanA said:

I've no direct experience but a quick look 410w at that size is approx 200w per square metre which seems reasonable to me but maybe compare with some good quality panels available elsewhere. What is the warranted lifetime?  My.house panels are guaranteed no less 80% max output for 25yrs. But are quite old now and still seem to be giving the same as they always did.

 

You'll need to know the max voltage to be able to size your controller too. 

Most decent mono panels from all suppliers are about 22% efficient, which is about 200W/m2 (at 1kW/m2 solar flux which is how they're specified) by the time you allow for gaps, frames etc. Bigger ones are slightly better than smaller ones because the frames take up a tiny bit less of the area.

[Gybe Ho]

On 16/08/2024 at 21:37, George Shardlow said:

I plan to have a 3 panel setup with the Midsummer narrowboat brackets.

 

 

No experience but my head is deep in the same design options you are considering.

 

Are you looking for off-grid tow path self sufficiency between Nov and Feb? If not your proposed solar array is quite large assuming typical narrowboat daily consumption.

 

Have you opted for pedestal grab handles along the roof or rails at the roof edge? I ask because handles cut down your solar mounting space. I see some panels mounted offset from the roof centre line to create a narrow access path down one side of the roof however your panels are too wide for this option.

 

Re: bridges, many cruising blogs on YouTube have rooftop storage boxes that look like garden raised beds. The YouTubers get through tunnels and under bridges though it is possible their boats are configured for their local cruising area.

 

Midsummer narrowboat brackets will have a limited tilt angle with your wide panel. By the time in the season when you need a tilt to get  a daily 1 to 2 kWh in the bank, the optimum tilt angle will be higher than you will be able to obtain. I think you are looking at the Midsummer bracket design that has Allen screw adjustment and locking, if so it appears to be a bit of a faff unless you park up for the winter. Otherwise they look robust for a storm.

[IanD]

Don't forget that tilting only works if the mooring means your boat is oriented E-W, not N-S... 😉

 

And for best power in winter, you need something like 60 degrees of tilt.

[Bargebuilder]

8 hours ago, Gybe Ho said:

By the time in the season when you need a tilt to get  a daily 1 to 2 kWh in the bank, the optimum tilt angle will be higher than you will be able to obtain

We relied on solar panels through the darkest winter days, and it was a struggle. The optimum angle is way above what you are likely to be able to achieve, over 60⁰! The other problem is, that the sun is not only low in the sky, but its sweep from east to west means that direct sunlight isn't very useful apart from around lunchtime. 

 

On most winter days it is overcast and light is diffused, so panels work almost as well with the shallow angle that you can achieve, as they would if they were at the 'optimum' angle.

 

Our panels produced around 10% in the winter compared to summer, and ours were at 60⁰ facing due south!

[LadyG]

I believe that there are different quality panels available,  I have seen some that look very nice, very dark. If they are going to dominate the roof space, and they tend to,  I would take this in to consideration, plus maximum efficiency. 

I have to use the engine to get warm water if my stove with back boiler is unlit, this boosts the batteries first thing, leaving solar to trickle charge to some degree. So there are other things to consider, but I would not want to cover the whole roof on a narrowboat. I usually move every week, so again that keeps on top of charging.

I have 2x 275 panels, and they are OK in summer, not enough in winter.

Edited August 19, 2024 by LadyG

[Bargebuilder]

9 hours ago, Gybe Ho said:

to get  a daily 1 to 2 kWh in the bank

If you need 1-2 kWh a day, how much area of solar panel will you need?

[blackrose]

On 16/08/2024 at 21:37, George Shardlow said:

I am currently planning a solar setup for my 57 foot sailaway. It appears that Solar Panel prices have come down recently. Especially if you go for the larger sizes. City plumbing are doing a Longi 410w panel at £56.74. In reviews they get a good write up. However they are a bit big at 1134mm x 1722mm. I plan to have a 3 panel setup with the Midsummer narrowboat brackets. The are more efficient than the normal A frame ones. 

 

Has anyone else got any experience with these. Are they too wide? They will fit easy enough on the roof but will it be a bit tight under bridges etc?

 

Strangely, smaller panels cost more! I suppose it is a case of cost saving by scale. 400w panels are now the most common on houses.

 

I would love to hear other people's experiences.

 

Cheers

Martin

 

That does sound remarkably cheap. I paid about £200 each for Canadian Solar 455w panels about 2 years ago. They're a bit more than 2m x 1m each.

 

In terms of size it's whatever fits on your roof. I'm on a widebeam but use my roof a lot so I had to be about to walk around them.

 

On a NB that's not so easy. With large panels if you want the ability to tilt them you also need to make sure they can be lowered flat for high winds and they are mounted securely. Also you need to make sure 3 large panels won't get in the way of your centre ropes, unless yours is a boat that never moves.

 

Do you have a link to the panel specs? What's the open circuit voltage of the panels (Voc)? When I bought my panels I was told to look for panels with an open circuit voltage of over 40v. 

 

Edited August 19, 2024 by blackrose

[Torblimey]

On 16/08/2024 at 21:37, George Shardlow said:

I am currently planning a solar setup for my 57 foot sailaway. It appears that Solar Panel prices have come down recently. Especially if you go for the larger sizes. City plumbing are doing a Longi 410w panel at £56.74. In reviews they get a good write up. However they are a bit big at 1134mm x 1722mm. I plan to have a 3 panel setup with the Midsummer narrowboat brackets. The are more efficient than the normal A frame ones. 

 

Has anyone else got any experience with these. Are they too wide? They will fit easy enough on the roof but will it be a bit tight under bridges etc?

 

Strangely, smaller panels cost more! I suppose it is a case of cost saving by scale. 400w panels are now the most common on houses.

 

I would love to hear other people's experiences.

 

Cheers

Martin

Hi Martin,

 

I bought similar sized panels from them last year, 2x 500w for £80 a panel.

Pic attached to show how I fitted them and yes they work really well.

I can still walk down the sides of the roof and having used the triangle supports the grab rails are still available.

They do sit perfectly "square" overlapping the rails tho so you may have to factor that in dependant on your rail position.

 

Works for me and they make a semi decent dryish storage area underneath 😊

[jacob]

We've got 3 of those Longi 410w panels on our 56ft NB, 2 on boxes and one on a mount. There's a chunk of roofspace left over, and not yet fallen in at a lock trying to navigate round them...

 

I put them in around April, and they've been supplying all our electricity since (CCing), although I'm sure we'll be relying on the engine come October/November to supplement them. This month they've supplied between 2-4KWh each day, with a solar dump setup heating our water to make the most of them.

[Gybe Ho]

36 minutes ago, Bargebuilder said:

If you need 1-2 kWh a day, how much area of solar panel will you need?

 

Mid winter? If so more than a narrowboat can accommodate on its roof. The size of the batterybank is also part of the equation because at some point in the season the running average across 2 weeks will equate to solar self sufficiency and a large bank will get you through a succession of dull days. 

[Bargebuilder]

6 minutes ago, jacob said:

This month they've supplied between 2-4KWh each day

 

Very roughly, if your 3 panels produced about 3 kWh on a summer's day, then during the bleak winter months one might only expect 10% of that, so if 1 kWh is needed as a minimum, then 10 panels would be needed in December. 

 

Of course, one could run the engine or a generator, or as we did, turn off the freezer and anything else we could do without.

[Baralacha]

21 minutes ago, NarrowboatTor said:

Hi Martin,

 

I bought similar sized panels from them last year, 2x 500w for £80 a panel.

Pic attached to show how I fitted them and yes they work really well.

I can still walk down the sides of the roof and having used the triangle supports the grab rails are still available.

They do sit perfectly "square" overlapping the rails tho so you may have to factor that in dependant on your rail position.

 

Works for me and they make a semi decent dryish storage area underneath 😊

Sorry to be critical, but your grab rails appear to reduce the already limited tilt angle of your panels on the brackets.

As @Bargebuilder comments, you want a good tilt in the winter - 45º minimum, 60º ideally.
I went for flat mounted, 3x 295W mono and haven't regretted it. The winter of 22-23 (my first with solar power) needed no supplementary power to charge my batteries; last winter I ran my generator about six times, as there was both the seasonal low angle of the sun and layered clouds attenuating the light to contend with. Maybe in this case tilting panels might have helped, but it cost me less than £8 in petrol for the Honda.

[MtB]

My own experience with panels laid flat on the roof, is in the dead of winter one gets about 1% of the peak summer energy output, not the 10% mentioned by others.

 

Just sayin'! 

[Bargebuilder]

5 minutes ago, Gybe Ho said:

The size of the batterybank is also part of the equation because at some point in the season the running average across 2 weeks will equate to solar self sufficiency

Have you estimated how big the battery bank would need to be? We found November to be the most gloomy, misty month and often solar contributed almost nothing for almost two weeks at that time.

[Torblimey]

6 minutes ago, Puffling said:

Sorry to be critical, but your grab rails appear to reduce the already limited tilt angle of your panels on the brackets.

As @Bargebuilder comments, you want a good tilt in the winter - 45º minimum, 60º ideally.
I went for flat mounted, 3x 295W mono and haven't regretted it. The winter of 22-23 (my first with solar power) needed no supplementary power to charge my batteries; last winter I ran my generator about six times, as there was both the seasonal low angle of the sun and layered clouds attenuating the light to contend with. Maybe in this case tilting panels might have helped, but it cost me less than £8 in petrol for the Honda.

Yep,

I'm not to worried about adjusting the angles, it was mainly to get under low bridges or weird shaped sections.

Jenny stored safe for winter and the engine also tops up quite happily.

February this year and things were topping up solar wise to absorbtion if not fully to float.

I don't get to stuck on every little detail, if it works fab, if it doesn't I'll find a way to make it work 😆

[jacob]

1 hour ago, MtB said:

My own experience with panels laid flat on the roof, is in the dead of winter one gets about 1% of the peak summer energy output, not the 10% mentioned by others.

 

Just sayin'! 

My plan's to install a 10,000Ah lithium battery and charge it up over summer to get us through winter

/s

Edited August 19, 2024 by jacob

[Gybe Ho]

4 minutes ago, Bargebuilder said:

Have you estimated how big the battery bank would need to be? We found November to be the most gloomy, misty month and often solar contributed almost nothing for almost two weeks at that time.

 

There are no absolutes but the principal is sound, all other things being equal a narrowboat with 600 Ah of lithium will experience more 2 week periods of solar self sufficiency over a year than another boat with 200 Ah of same batteries. If I build a diesel powered narrowboat my minimum would be 600 Ah that I hope will see me through 3 to 4 days with zero contribution from solar. 

1 minute ago, jacob said:

My plan's to install a 10,000Ah lithium battery and charge it up over summer to get us through winter

 

Have you got your decimal point in the right position? 10 kWh of lithium sounds doable and would be £4,400 at Victron prices.

1 hour ago, Bargebuilder said:

We relied on solar panels through the darkest winter days, and it was a struggle. The optimum angle is way above what you are likely to be able to achieve, over 60⁰! The other problem is, that the sun is not only low in the sky, but its sweep from east to west means that direct sunlight isn't very useful apart from around lunchtime.

 

 

Yes in mid winter the mathematicians have calculated that the optimum tilt angle is around 75 degrees.

 

This is the mounting system I plan to use, the same channel has another earlier episode showing the install:

 

 

[IanD]

Panel angle doesn't make as big a difference as some seem to think, especially in summer.

 

I ran the numbers for my setup (flat-mounted 2100W panels), assuming all the solar energy can be used. For flat/30deg/60deg tilt (south-facing) I get this:

 

(daily averages using real weather data from https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#api_5.2 )

 

Dec: 830/1660/2140Wh (50%/100%/129%)

Mar: 3750/4660/4700 (80%/100%/101%)

Jun: 7130/7090/5940Wh (101%/100%/84%)

Sep: 3940/4870/4900 (81%/100%/101%)

 

Year: 3960/4640/4480Wh (85%/100%/97%)

 

So flat-mounting loses nothing in midsummer compared to tilting, 15% averaged over the year, but 50% (of much less) in midwinter. A steep tilt in midwinter gains another 30% compared to 30deg tilt.

 

And if your boat only tilts the panels sideways -- which most do, certainly to any angle -- you only gain this if the boat is moored E-W (panels facing south). If the boat is moored N-S you gain nothing by tilting sideways, if moored at 45 deg (NW-SE or NE-SW) you gain 70% of the south-facing gain.

 

The numbers for flat-mounted panels (which is what I've got) agree with what I've seen over the last year from VRM logging data.

 

In all cases the numbers are averaged using actual UK weather data for the time of year; on a good (sunny) day output is at least 50% higher, on a bad (dull cloudy) day at least 50% lower based on what I've seen.

Edited August 19, 2024 by IanD

[blackrose]

50 minutes ago, jacob said:

This month they've supplied between 2-4KWh each day, with a solar dump setup heating our water to make the most of them.

 

 

Can you tell us more about your solar dump water heating setup please? I know Bimble sells a kit and this involves changing the mains immersion heater to a 12v unit. Bimble were honest enough to put me in touch with their 12v immersion supplier as they said it's very easy to damage the calorifier trying to remove the mains immersion. The supplier confirmed this.

 

Also there have been a couple of threads about solar dumps and one of those threads concluded that it wasn't as simple as it sounded, so I'd like to hear your experience please.

18 minutes ago, IanD said:

Panel angle doesn't make as big a difference as some seem to think, especially in summer.

 

 

In summer it won't make much difference but it can make a big difference on clear winter days. I haven't run the numbers, I'm just going by my own first hand experience. I think your 30% gain figure is about right but my comparison was for a approx 35 deg tilt compared to flat panels.

[IanD]

5 minutes ago, blackrose said:

 

Can you tell us more about your solar dump water heating setup please? I know Bimble sells a kit and this involves changing the mains immersion heater to a 12v unit. Bimble were honest enough to put me in touch with their 12v immersion supplier as they said it's very easy to damage the calorifier trying to remove the mains immersion. The supplier confirmed this.

 

Also there have been a couple of threads about solar dumps and one of those threads concluded that it wasn't as simple as it sounded, so I'd like to hear your experience please.

 

In summer it won't make much difference but it can make a big difference on clear winter days. I haven't run the numbers, I'm just going by my own first hand experience. I think your 30% gain figure is about right but my comparison was for a approx 35 deg tilt compared to flat panels.

The numbers I gave (see percentages) compared flat/30/60deg tilt; they come from solid data and theory, and stack up with what I've measured. From them you can easily work out all the possible gains/losses over the year for different tilt angles (and boat orientation -- if you're moored N-S then sideways-only tilt doesn't work).

[blackrose]

5 minutes ago, IanD said:

The numbers I gave (see percentages) compared flat/30/60deg tilt; they come from solid data and theory, and stack up with what I've measured. From them you can easily work out all the possible gains/losses over the year for different tilt angles (and boat orientation -- if you're moored N-S then sideways-only tilt doesn't work).

 

Yes, I don't disagree with your numbers, but those numbers seem at odds with the opening statement of your previous post, because as your figures suggest, tilting the panels can make a big difference albeit in winter. I suppose it depends on what one imagines "some seem to think" about the benefits of tilting panels.

[Gybe Ho]

26 minutes ago, IanD said:

Panel angle doesn't make as big a difference as some seem to think, especially in summer.

 

...

 

Dec: 830/1660/2140Wh (50%/100%/129%)

Mar: 3750/4660/4700 (80%/100%/101%)

Jun: 7130/7090/5940Wh (101%/100%/84%)

Sep: 3940/4870/4900 (81%/100%/101%)

 

 

I see a 160% difference in your figures when it counts. My expectation is that my 1.4kW of panels will be left flat for 8 months of the year. Tow path electric self sufficiency is about getting through Nov to Jan with a minimum of generator charging hours, this is where high tilt can help given the right mooring location/orientation.

 

The OP has not clarified his usage requirement for solar so this stage of the thread discussion might not be relevant to him.

[IanD]

14 minutes ago, Gybe Ho said:

 

I see a 160% difference in your figures when it counts. My expectation is that my 1.4kW of panels will be left flat for 8 months of the year. Tow path electric self sufficiency is about getting through Nov to Jan with a minimum of generator charging hours, this is where high tilt can help given the right mooring location/orientation.

 

The OP has not clarified his usage requirement for solar so this stage of the thread discussion might not be relevant to him.

The numbers speak for themselves. Tilting -- especially to 60 degrees -- does give a big benefit in winter, but the output is still only 30% of that in summer -- look at the Wh yield numbers, not just the percentages.

 

Which is a lot better than the lousy 12% with flat-mounted panels, but still may not be enough to keep up with demand, which is usually higher in winter. Tilting still only works if you can choose a mooring location where the boat is oriented E-W not N/S... 😉 

 

People often seem to look at the peak panel power and think "Wow, that much for hours a day will sort me out!" without allowing for actual sunlight and how it varies over the year -- and also how much real improvement tilting gives (or doesn't depending on mooring...) in return for the added complexities and disadvantages of being tiltable, especially to large angles.

 

 I'm not telling people what to do, that's their decision -- just providing actual numbers/facts so they can make an informed decision, because there's a lot of non-factual BS out there... 🙂 

Edited August 19, 2024 by IanD