How to choose a solar panel ?

[noelex]

Has anyone got a comment on bypass and blocking diodes?
Am I on the right track (or wasting my money?)

The main purpose of bypass diodes is to prevent internal damage to the solar panel. All reasonable quality solar panels will have several installed. They do have some benefit in increasing the output in shade, but the number does not make a huge difference.

If connecting solar panels in series, installing an extra external bypass diode that will bypass the whole panel is beneficial, but series connection has the poorest production in shade conditions so you would be better connecting the panels in parallel, or even better still, a single controller per panel.

It is usually not practical to add additional internal bypass diodes.

Blocking diodes have a very different function. Very few panels have one of these installed and they are rarely beneficial.

 

[RupertW]

Has anyone got a comment on bypass and blocking diodes?
Am I on the right track (or wasting my money?)

If you are in parallel then you don’t need to worry about blocking diodes so much, but they are essential either as part of the panel or separate if you wire in series. I have 8 small panels in parallel but may well switch them to pairs or quadruples in series if I ever run out of spare juice and want to minimise the loss on the wires to the MPPT.

 

[coopec]

If you are in parallel then you don’t need to worry about blocking diodes so much, but they are essential either as part of the panel or separate if you wire in series. I have 8 small panels in parallel but may well switch them to pairs or quadruples in series if I ever run out of spare juice and want to minimise the loss on the wires to the MPPT.

They can make panels with diodes on each cell but they would be prohibitively expensive. Therefore they divide the panel up into say X12 sections and put a bypass diode on each section.

On a yacht (particularly a ketch) they would surely give much more reliable/consistent power than the traditional panel?

 

[RupertW]

They can make panels with diodes on each cell but they would be prohibitively expensive. Therefore they divide the panel up into say X12 sections and put a bypass diode on each section.

On a yacht (particularly a ketch) they would surely give much more reliable/consistent power than the traditional panel?

In series, certainly. In parallel that’s not really an issue.

 

[ryanroberts]

Bimble are reliable. Considering these half cell panels under my boom on the pilothouse

325W JA All Black Solar Panel - Half Cell Mono Percium - Latest Tech - MCS Approved

 

[RupertW]

Bimble are reliable. Considering these half cell panels under my boom on the pilothouse

325W JA All Black Solar Panel - Half Cell Mono Percium - Latest Tech - MCS Approved

Bimble were great for my VSR chain for the solar hot water heating

 

[affinite]

Bimble are reliable. Considering these half cell panels under my boom on the pilothouse

325W JA All Black Solar Panel - Half Cell Mono Percium - Latest Tech - MCS Approved

Just read the spec. Any panel with a "passivated backside" gets my vote

 

[sailaboutvic]

Just a comment on parallel/ series/ parallels and Series .
As I sure some will know I had problems with my panels and batteries come to that and over the last few months I been experimenting , if you look at my solar arrays at the moment you wonder why there a mass of wires , well the reason I been trying them in all three combination including parallel and series with the same mppt although some people have said it's not possible with one control .
Well it is .

So any way I have taken weeks and weeks of reading and in my case I have found there very little different how they are connect the day KWH Are so close it's not worth talking about .
And yes in Series and parallel I do have some shading at times .

 

[ryanroberts]

Just read the spec. Any panel with a "passivated backside" gets my vote

Well if we are going to mine the rich seam of nautical double entendre, works even better under my boom.

 

[William_H]

Hi Clive
I think you might be over worrying about shading. Get 2 panels probably around 220w each at 40 volts from a domestic panel supplier. Assuming you have room for 2 panels. This will give you effectively 2 series panels which are connected in parallel. About the best arrangement you can hope for. You will need a MPPT controller especially if you have a 12v system. ol'will

 

[coopec]

Hi Clive
I think you might be over worrying about shading. Get 2 panels probably around 220w each at 40 volts from a domestic panel supplier. Assuming you have room for 2 panels. This will give you effectively 2 series panels which are connected in parallel. About the best arrangement you can hope for. You will need a MPPT controller especially if you have a 12v system. ol'will

Thanks for that William.
I'm hoping to mount two panels over the transom and I'd make them crudely adjustable (I don't want to be constantly adjusting them). But I already have mounts on the aft cabin also ( each side of the deck hatch) where I could mount another two if I think that is worthwhile. I'll certainly be thinking of solar panels shortly but right now I am putting a further 2½ tonne of lead ballast in the yacht.

Cheers

 

[Laminar Flow]

Has anyone got a comment on bypass and blocking diodes?
Am I on the right track (or wasting my money?)

We installed 300W solar on our ketch's wheelhouse roof. To reduce the losses due to shading we installed six panels @ 50W. Each panel has a blocking diode giving it two separate fields, hence 12 individual fields in total. I connected them in parallel to a MPPT charger. Our house bank has a total of 460 A/hrs.
On a sunny day (summer) we are fully charged by 10am; on a cloudy day by 14.00pm. No matter how long we've been off-grid, we never had to run the engine or the generator to keep the batteries charged. In the beginning I used to fuss about to tie the boom out of the way etc. to prevent shading; now, I no longer bother. We spend 4 months or so aboard each year.

We bought the rigid mono crystalline panels through a German mail order for 35 Euro each. They are commonly used for nav aids.

 

[sailaboutvic]

We installed 300W solar on our ketch's wheelhouse roof. To reduce the losses due to shading we installed six panels @ 50W. Each panel has a blocking diode giving it two separate fields, hence 12 individual fields in total. I connected them in parallel to a MPPT charger. Our house bank has a total of 460 A/hrs.
On a sunny day (summer) we are fully charged by 10am; on a cloudy day by 14.00pm. No matter how long we've been off-grid, we never had to run the engine or the generator to keep the batteries charged. In the beginning I used to fuss about to tie the boom out of the way etc. to prevent shading; now, I no longer bother. We spend 4 months or so aboard each year.

We bought the rigid mono crystalline panels through a German mail order for 35 Euro each. They are commonly used for nav aids.

Very interested in your posting .
country's are you in ? How many AH do you use over night ?
Reason I am asking is I give anything for my 400W panels to be fully charge by 10am .

 

[coopec]

We installed 300W solar on our ketch's wheelhouse roof. To reduce the losses due to shading we installed six panels @ 50W. Each panel has a blocking diode giving it two separate fields, hence 12 individual fields in total. I connected them in parallel to a MPPT charger. Our house bank has a total of 460 A/hrs.
On a sunny day (summer) we are fully charged by 10am; on a cloudy day by 14.00pm. No matter how long we've been off-grid, we never had to run the engine or the generator to keep the batteries charged. In the beginning I used to fuss about to tie the boom out of the way etc. to prevent shading; now, I no longer bother. We spend 4 months or so aboard each year.

We bought the rigid mono crystalline panels through a German mail order for 35 Euro each. They are commonly used for nav aids.

Thank you.

That's the sort of approach I want to take. It is encouraging to read the results of your effort.

 

[noelex]

Each panel has a blocking diode giving it two separate fields, hence 12 individual fields in total.

This suggests a bypass rather than a blocking diode, but if we look at the option of installing a blocking diode it will not harm anything, but are likely to slightly reduce the overall output.

It is possible to estimate the net gain/loss with some simple measurements. Firstly cover a panel (with a towel, or similar) and without a blocking diode measure the current flowing into the covered panel when connected to your system.

The resulting current does vary depending on the type of panel, but it is invariably extremely small. This current is the maximum that ever be lost, in partial shade the result will be even less. Just seeing this tiny current will probably convince you of the limited benefit of a blocking diode, but you can estimate the net loss/gain more accurately if you wish to go further.

At night almost all solar controllers will disconnect the solar panels so multiplying this current by the hours in a solar day will give you an estimate of the maximum Ahr saving that a blocking diode fitted to solar panel can produce under the worse possible situation of one panel totally in deep shade.

You can also estimate the power the blocking diode will consume. The calculation is more complex, but a rough estimation is simply the Vmp less the forward voltage loss of the diode divided by the Vmp. Multiply this ratio by the total power production of the panel (more accurately in watt/hours, but AHrs is close enough).

Even a simple crude estimation assuming the conditions where the blocking diode saves the maximum amount of power, will show that the power losses from installing a blocking diode are much greater than the gains.

 

[Laminar Flow]

This suggests a bypass rather than a blocking diode, but if we look at the option of installing a blocking diode it will not harm anything, but are likely to slightly reduce the overall output.

It is possible to estimate the net gain/loss with some simple measurements. Firstly cover a panel (with a towel, or similar) and without a blocking diode measure the current flowing into the covered panel when connected to your system.

The resulting current does vary depending on the type of panel, but it is invariably extremely small. This current is the maximum that ever be lost, in partial shade the result will be even less. Just seeing this tiny current will probably convince you of the limited benefit of a blocking diode, but you can estimate the net loss/gain more accurately if you wish to go further.

At night almost all solar controllers will disconnect the solar panels so multiplying this current by the hours in a solar day will give you an estimate of the maximum Ahr saving that a blocking diode fitted to solar panel can produce under the worse possible situation of one panel totally in deep shade.

You can also estimate the power the blocking diode will consume. The calculation is more complex, but a rough estimation is simply the Vmp less the forward voltage loss of the diode divided by the Vmp. Multiply this ratio by the total power production of the panel (more accurately in watt/hours, but AHrs is close enough).

Even a simple crude estimation assuming the conditions where the blocking diode saves the maximum amount of power, will show that the power losses from installing a blocking diode are much greater than the gains.

You are correct. I misspoke, I meant to say bypass diode.

Very interested in your posting .
country's are you in ? How many AH do you use over night ?
Reason I am asking is I give anything for my 400W panels to be fully charge by 10am .

We sail in Northern Europe: NL, France, Southern UK, mostly. Have been as far North as Baltic, Sweden. In October and in the higher latitudes, such as the Baltic, performance of course declined dramatically. But, in our experience, my statements hold true in NL and Brittany (summer). We have been cruising with this set-up for three years. Our single biggest consumer is the fridge wich runs 24/7.
Our MPPT charger records and displays it's performance - for the first two years I obsessively monitored the output, now I have let that go and can, once again, enjoy the landscape.
I can say in all honesty that solar has completely transformed our cruising experience. Not having refrigeration is simply not an option for us ... lets just say it's not about the butter or the Chablis.

Even when panels have bypass diodes, the orientation of a shadow across the fields can determine their effectiveness. Consequently, having a number of smaller panels helps deal with the issues of "wandering interference" of shading on a boat.

 

[affinite]

I now understand the potential benefits of breaking the array into smaller panels but I will be mounting my panel(s) on a stern gantry where shading isnt an issue and I will retain smaller panels as backup panels
So (deep breath) having considered the advice I'm still thinking of swimming against the tide and opting for a single SunPower 400w panel (22.6% efficiency means 1690x1046mm form factor so I can get it on the gantry)

 

[sailaboutvic]

You are correct. I misspoke, I meant to say bypass diode.

We sail in Northern Europe: NL, France, Southern UK, mostly. Have been as far North as Baltic, Sweden. In October and in the higher latitudes, such as the Baltic, performance of course declined dramatically. But, in our experience, my statements hold true in NL and Brittany (summer). We have been cruising with this set-up for three years. Our single biggest consumer is the fridge wich runs 24/7.
Our MPPT charger records and displays it's performance - for the first two years I obsessively monitored the output, now I have let that go and can, once again, enjoy the landscape.
I can say in all honesty that solar has completely transformed our cruising experience. Not having refrigeration is simply not an option for us ... lets just say it's not about the butter or the Chablis.

Even when panels have bypass diodes, the orientation of a shadow across the fields can determine their effectiveness. Consequently, having a number of smaller panels helps deal with the issues of "wandering interference" of shading on a boat.

Don't get me wrong I not saying your posting is untrue , we have 400w that 4x 100 w panels .
We In the med and on the days my panels go into float it be late after noon , so I was surprise when you said your are fully charge by 10am .
Our over night uses is 70 to 80 AH so on day we stay on anchor the only thing that comes out of the batter is 4A per hour for the fridge and Freezer.
For the last two days they not even reach ABS .

 

[noelex]

I now understand the potential benefits of breaking the array into smaller panels but I will be mounting my panel(s) on a stern gantry where shading isnt an issue and I will retain smaller panels as backup panels
So (deep breath) having considered the advice I'm still thinking of swimming against the tide and opting for a single SunPower 400w panel (22.6% efficiency means 1690x1046mm form factor so I can get it on the gantry)

The SunPower panels are excellent. They have great low light and temperature performance. With one large panel there is a little less shade tolerance than multiple smaller panels, but more efficiency. Installation is easier and cleaner.

So, good choice

 

[Laminar Flow]

Don't get me wrong I not saying your posting is untrue , we have 400w that 4x 100 w panels .
We In the med and on the days my panels go into float it be late after noon , so I was surprise when you said your are fully charge by 10am .
Our over night uses is 70 to 80 AH so on day we stay on anchor the only thing that comes out of the batter is 4A per hour for the fridge and Freezer.
For the last two days they not even reach ABS .

We do not use anywhere nearly as much as you and certainly not over night when the fridge door is not opened as often. We also do not have a separate freezer. Our fridge draws 4A; with a 30% cycle rate in our northern clime, that works out to about 16A over a 12 hour period.
300W of solar should, in theory, deliver about 1200W on average per day in our cruising latitude.
Having, pre solar, struggled to keep our banks charged we are suitably neurotic about the use of power and anything of importance has been converted to LED and we often use candle light in the evenings.

Our longest and most arduous drain on our batteries was when we sailed non-stop from Ijmuiden to Dieppe in 35hrs. This was done under sail only, running an electric pilot continuously, nav equipment and tablet (for Navionics), running lights, Webasto (at night), fridge (as usual, 24/7) water system etc The first day was overcast, the second sunny, sea conditions for the pilot, lively - there never was even the slightest hint of an electrical power shortage.