Solar panel fitting

[ditchcrawler]

4 hours ago, Manxcat54 said:

After reading and watching  videos I have decided I'm not tilting them and I have a friend who runs a magnet company who will supply strong magnets rubber mounted with M8 studs, and I think in series because I don't want the fuss of those 3 way connectors, for once I have gained something from the forum. Thanks 

Are you sure that your controller will support three in series or did I miss where you gave us the panel specification

[Tony Brooks]

4 hours ago, Manxcat54 said:

After reading and watching  videos I have decided I'm not tilting them and I have a friend who runs a magnet company who will supply strong magnets rubber mounted with M8 studs, and I think in series because I don't want the fuss of those 3 way connectors, for once I have gained something from the forum. Thanks 

 

I don't understand the reasoning. https://www.12voltplanet.co.uk/pair-of-mc4-3-to-1-solar-connectors.html

shows the industrial way of doing it in parallel, you seem to what to daisy-chain the panels together by some unspecified means. The MC4 connector system is supposed to be waterproof and as they can be located under a/the panels will be shielded from rain, and you won't be able to see them.

[Psychalist]

17 hours ago, IanD said:

Sorry but that's not correct -- if you have identical panels with no shading it makes no difference to power output whether they're in series or parallel -- series gives higher voltage and lower current, parallel gives lower voltage and higher current, but power is identical.

It's a good point about the higher current at equivalent power, but another consideration, as you point out, is the higher voltage. It is no use having power at a voltage below the MPPT threshold for conversion to something useful for the batteries. Very dull days can easily see panel voltage lower to 1/3rd or less than peak VOC, barely above battery voltage. Having two in series will give the controller something to work with (as I understand it). I've only one panel so haven't been able to do this but have seen panel voltages at different times of day and weather conditions.

[jim mitchell]

Solar panels in midwinter in the UK produce most watt hours a day when angled at around 70 deg from horizontal - but that requires substantial support mounting.   Commercial sites receive money for every watt so they get a return on all the control equipment - i installed solar at a riding complex all at 70 deg because their demand and the cost benefit is highest in winter.

 

The max output in summer is reduced but then they do not need as much anyway - so if summer cruising only  i would ad=vise simple elevation to around 35deg   for live aboard all year cost benefit (when moored)  and able to get them facing south  consider 70deg.    

 

It's also possible to get individual  230 Vac   micro inverters that convert the solar energy to ac " at the panel" though that involves a completely different approach to harvesting using solar power on land , sea and canals .

 

 

[Tony Brooks]

7 minutes ago, jim mitchell said:

Solar panels in midwinter in the UK produce most watt hours a day when angled at around 70 deg from horizontal - but that requires substantial support mounting.   Commercial sites receive money for every watt so they get a return on all the control equipment - i installed solar at a riding complex all at 70 deg because their demand and the cost benefit is highest in winter.

 

The max output in summer is reduced but then they do not need as much anyway - so if summer cruising only  i would ad=vise simple elevation to around 35deg   for live aboard all year cost benefit (when moored)  and able to get them facing south  consider 70deg.    

 

It's also possible to get individual  230 Vac   micro inverters that convert the solar energy to ac " at the panel" though that involves a com pletely different approach to harvesting using solar power on land , sea and canals .

 

 

 

All nice in theory, but for maximum output the panels also need to be rotated to track the sun in the horizontal plane.  If you can't track the sun, I question how much a boater gains from angled mounting. Especially earlier and later in the day.

Edited June 11, 2024 by Tony Brooks

[ditchcrawler]

Victron dont give the maximum voltage of their solar panels but it looks to be around 36 volts, 3 in series would give 108 volts into the controller 

Bimble give the spec on theirs and three in serise would be a possible voltage over 130 Volts

Edited June 11, 2024 by ditchcrawler

[IanD]

4 hours ago, Psychalist said:

It's a good point about the higher current at equivalent power, but another consideration, as you point out, is the higher voltage. It is no use having power at a voltage below the MPPT threshold for conversion to something useful for the batteries. Very dull days can easily see panel voltage lower to 1/3rd or less than peak VOC, barely above battery voltage. Having two in series will give the controller something to work with (as I understand it). I've only one panel so haven't been able to do this but have seen panel voltages at different times of day and weather conditions.

True, you obviously need the minimum panel voltage to be high enough for the MPPT to start (typically 5V above maximum battery voltage) as well as having the maximum panel voltage below the MPPT rating. Depending on the panel, a single one might not have high enough voltage.

[GUMPY]

2 minutes ago, IanD said:

Depending on the panel, a single one might not have high enough voltage.

A good reason for adding panels in even numbers and wiring Series/Parallel which you can't do with three.

[IanD]

1 minute ago, GUMPY said:

A good reason for adding panels in even numbers and wiring Series/Parallel which you can't do with three.

You think that's bad, I've got 13 panels in a 48V system -- now work out what to do with them... 😉

[beerbeerbeerbeerbeer]

…unlucky 😉 

[blackrose]

On 10/06/2024 at 20:03, IanD said:

Sorry but that's not correct -- if you have identical panels with no shading it makes no difference to power output whether they're in series or parallel -- series gives higher voltage and lower current, parallel gives lower voltage and higher current, but power is identical.

 

Sorry but that's not quite correct.  The bit you're missing is that a series connection will have a much higher voltage than a parallel connection. eg: if the Vmp of the panel is, say, 25v max then in series the total voltage will be 50v, whereas, in parallel, it will only be 25v. 

 

Since the MPPT requires the initial voltage to be 5v above the battery voltage, (so around 18v), the series connection will require far less light to switch on the MPPT. 

 

Likewise, in the evening, the series connection will still be producing a high enough voltage, long after the parallel panel voltage has fallen too low. 

(The MPPT needs about 18v to switch on, but will switch off around 14v).

So, a series connection will be “switched on” far longer than a parallel connection and therefore harvest significantly more power over the day. 

eg: when the series connection reaches 18v, high enough to switch on the MPPT, the parallel connection will have only reached around 9v. 

By the time the parallel connection reaches 18v, the series connection will be at around 36v and pumping lots of power into the MPPT. 

 

If the day is dull, the series will still be producing sufficient voltage to produce battery charge, whereas the parallel will have switched off. 

 

Furthermore, the series setup uses much thinner cable, owing to much lower current than the parallel setup. 

(power = voltage x current, hence higher voltage equates to lower current, for the same power). 

This means that thinner, cheaper cable can be used which is also easier to run, as well as saving money. 

 

The only advantage of parallel is it’s slightly better at dealing with shading. Though, nowadays, all quality panels utilise “bypass” diodes, so that only a small section of the panel switches off in shade, rather than losing the whole panel. 

 

Bottom line, ALWAYS go series connections if possible.

 

7 hours ago, Tony Brooks said:

 

All nice in theory, but for maximum output the panels also need to be rotated to track the sun in the horizontal plane.  If you can't track the sun, I question how much a boater gains from angled mounting. Especially earlier and later in the day.

 

I already said I get about a third more output from my panels by tilting them when the sun is low. That's true for a significant part of the day. I can raise and lower the panels and see the difference on my monitors. Of course as you say, for maximum output they'd have to track the sun throughout the day but that doesn't mean without tracking the output won't be significantly increased compared to flat panels.

Edited June 11, 2024 by blackrose

[IanD]

1 hour ago, blackrose said:

 

Sorry but that's not quite correct.  The bit you're missing is that a series connection will have a much higher voltage than a parallel connection. eg: if the Vmp of the panel is, say, 25v max then in series the total voltage will be 50v, whereas, in parallel, it will only be 25v. 

 

Since the MPPT requires the initial voltage to be 5v above the battery voltage, (so around 18v), the series connection will require far less light to switch on the MPPT. 

 

Likewise, in the evening, the series connection will still be producing a high enough voltage, long after the parallel panel voltage has fallen too low. 

(The MPPT needs about 18v to switch on, but will switch off around 14v).

So, a series connection will be “switched on” far longer than a parallel connection and therefore harvest significantly more power over the day. 

eg: when the series connection reaches 18v, high enough to switch on the MPPT, the parallel connection will have only reached around 9v. 

By the time the parallel connection reaches 18v, the series connection will be at around 36v and pumping lots of power into the MPPT. 

 

If the day is dull, the series will still be producing sufficient voltage to produce battery charge, whereas the parallel will have switched off. 

 

Furthermore, the series setup uses much thinner cable, owing to much lower current than the parallel setup. 

(power = voltage x current, hence higher voltage equates to lower current, for the same power). 

This means that thinner, cheaper cable can be used which is also easier to run, as well as saving money. 

 

The only advantage of parallel is it’s slightly better at dealing with shading. Though, nowadays, all quality panels utilise “bypass” diodes, so that only a small section of the panel switches off in shade, rather than losing the whole panel. 

 

Bottom line, ALWAYS go series connections if possible.

 

 

I already said I get about a third more output from my panels by tilting them when the sun is low. That's true for a significant part of the day. I can raise and lower the panels and see the difference on my monitors. Of course as you say, for maximum output they'd have to track the sun throughout the day but that doesn't mean without tracking the output won't be significantly increased compared to flat panels.

I did say that you need the panels -- however they're connected -- to have enough voltage that the minimum panel voltage is greater than the maximum battery voltage plus MPPT startup margin (typically 5V).

 

So long as you meet this requirement, parallel panels are better in partial shade than series --- for example 1s4p is better than 2s2p which is better than 4s1p.

 

Bypass diodes work when there is no light on one panel, which is not the usual case.

 

I did mention the cable size, but the losses from this should be negligible -- if not, you need thicker cables.

 

In the end, what really matters is getting as much solar on the roof as you can; the exact panel configuration is much less important. 

3 hours ago, beerbeerbeerbeerbeer said:

…unlucky 😉 

But that's what fitted on the roof... 😉

 

Ended up with two MPPT controllers, one with 4s2p and one with 5s1p. Which has the advantage that you can spot any connection problems by comparing the two outputs...

[Gybe Ho]

On 09/06/2024 at 22:12, IanD said:

Series connection works and can mean a cheaper MPPT controller and easier wiring, which is why many do it. If you have the choice, parallel connection is better to maximise power under partially shaded conditions.

 

 

I have read an interesting counter argument, the theory goes like this:

• A narrow boat with +700 watts of solar installed typically generates a surplus amount of daily power during 5 summer months relative to consumption.
• The decision over series or parallel becomes more interesting during spring and autumn.
• Solar panels need the sun to reach minimum elevation and strength before panels gets electrically excited enough to deliver useful volts to the MPPT.
• Panels in series reach the minimum excitement voltage sooner and as a result, during shorter days, they generate more cumulative watt hours than a parallel config.

A similar argument can be made for tilting panels i.e. not worth the bother in summer but a high tilt of up to 75 degrees is a benefit in winter when mooring in an east/west orientation.

 

[Tony Brooks]

5 hours ago, Gybe Ho said:

Solar panels need the sun to reach minimum elevation and strength before panels gets electrically excited enough to deliver useful volts to the MPPT.

 

Whilst this is true for maximum output, you do not take account of the small but useful output from cloud scatter when overcast, when flat panels may be more effective.

[Jen-in-Wellies]

12 minutes ago, Tony Brooks said:

 

Whilst this is true for maximum output, you do not take account of the small but useful output from cloud scatter when overcast, when flat panels may be more effective.

Which, let's face it, is much of the time in the UK, where the sky is a uniform grey from horizon to horizon.

[Torblimey]

Probably been posted before but I found the following really helpful deciding my setup.

 

https://explorist.life/solar-charge-controller-calculator/

 

 

[Gybe Ho]

4 hours ago, Tony Brooks said:

 

Whilst this is true for maximum output, you do not take account of the small but useful output from cloud scatter when overcast, when flat panels may be more effective.

 

The theory I described is more about which panel configuration (series or parallel) generates enough voltage to reach the minimum threshold for the MTTP to swing into action and do its power transformation magic.

 

Optimum winter panel tilt and irradiation from cloud scatter is an interesting point I should consider. At 11am on November 1st the sun is 20 degrees high, my hunch is that expecting cloud scatter to bend a useful amount of solar energy through 70 degrees to a flat panel is a big ask. Great news if true. I have been influenced by tests from youtubers MinimalList who designed a winter tilt mechanism set at 76 degrees, on a clear day the gain was a few hundred percent. However as you indicate clear days are not typical, hmm back to the drawingboard.

 

Is there any good whole-year UK data that clarifies the optimum solar panel tilt month by month?

[GUMPY]

https://re.jrc.ec.europa.eu/pvg_tools/en/#api_5.2

 

[IanD]

12 hours ago, Gybe Ho said:

 

I have read an interesting counter argument, the theory goes like this:

• A narrow boat with +700 watts of solar installed typically generates a surplus amount of daily power during 5 summer months relative to consumption.
• The decision over series or parallel becomes more interesting during spring and autumn.
• Solar panels need the sun to reach minimum elevation and strength before panels gets electrically excited enough to deliver useful volts to the MPPT.
• Panels in series reach the minimum excitement voltage sooner and as a result, during shorter days, they generate more cumulative watt hours than a parallel config.

A similar argument can be made for tilting panels i.e. not worth the bother in summer but a high tilt of up to 75 degrees is a benefit in winter when mooring in an east/west orientation.

 

That's not how solar panels work...

 

They'll reach close to full voltage with even a small amount of sunlight, the current generated then determines the power output -- they're effectively photodiodes which act as current sources, with the current proportional to light intensity, and into an open circuit they'll simply rise up to their open-circuit voltage -- which only changes slightly with light intensity, see these curves:

 

https://www.researchgate.net/figure/Voltage-Current-characteristic-curves-of-a-PV-module_fig2_263243375

[jim mitchell]

what if you use a polished metal reflector (not behind glass) to reflect direct sunlight through an angle onto flat mounted panels? would that allow most of the additional capture from angling the panels and preserve the scattered energy ?

[nicknorman]

On 10/06/2024 at 20:03, IanD said:

Sorry but that's not correct -- if you have identical panels with no shading it makes no difference to power output whether they're in series or parallel -- series gives higher voltage and lower current, parallel gives lower voltage and higher current, but power is identical.

However a high voltage low current panel configuration will lose less power between the panels and the batteries, the panel cable losses and the losses within the MPPT controller will be less.

[IanD]

2 minutes ago, nicknorman said:

However a high voltage low current panel configuration will lose less power between the panels and the batteries, the panel cable losses and the losses within the MPPT controller will be less.

That was already pointed out earlier as an advantage of series panels -- however cable losses are small compared to the gains with parallel ones when partial shading happens (but cabling is thinner and cheaper with series panels).

 

MPPT controller efficiency depends mostly on output current, meaning output power and battery voltage -- so a 24V system is more efficient than 12V and 48V is better still because the current is smaller.

[Gybe Ho]

1 hour ago, GUMPY said:

https://re.jrc.ec.europa.eu/pvg_tools/en/#api_5.2

 

 

Thankyou for the reference to the solar calculator. The ability to compare solar power across the year at a selected tilt was illuminating, I chose 75 degrees. There is a clear advantage to a high tilt through much of the year, sometimes by a wide margin. However caution is needed because unless a boat is moored close to an east/west orientation the benefit would soon become a negative.

 

The monthly figures vary across years which indicates the data must be actual historic data that was affected by real weather patterns.

[IanD]

11 minutes ago, Gybe Ho said:

 

Thankyou for the reference to the solar calculator. The ability to compare solar power across the year at a selected tilt was illuminating, I chose 75 degrees. There is a clear advantage to a high tilt through much of the year, sometimes by a wide margin. However caution is needed because unless a boat is moored close to an east/west orientation the benefit would soon become a negative.

 

The monthly figures vary across years which indicates the data must be actual historic data that was affected by real weather patterns.

A high tilt like 75 degrees will give the highest power in winter (when there's less sum anyway) but less in summer and over the year than a lower tilt -- assuming the boat is moored E-W with sideways tilting panels, which is the usual case. I looked at this for my boat and got the following:

 

"I ran the numbers for my setup (2100W panels), assuming all the solar energy can be used. For flat/30deg/60deg tilt (south-facing) I get (daily averages using real weather data):

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."