Discuss Combined East and South facing panels impact using a bypass diode in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

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jaytee

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I am new to the forum so Hi to everyone out there! I am also a new DIY Solar PV user and I am looking for some technical advice on an unusual string configuration.

So some prelude before the question: I have been looking at Solar on and off bust its always been too expensive and the FIT's keep reducing, 20 year paybacks are not really doing it for me. However I recently found some £15 each panels on ebay and after a bit of messing about I am the proud owner of 20 Canadian Solar 330P panels. All with broken glass of course! Out of the 20 I also have two unbroken ones with slightly damaged frames so I do have a reference for a "good" panel.

Its toughened glass so its like the old car broken windscreens if anyone is old enough to remember them. After a lot of research and some experiments I have used an industial vinyl product to "waterproof" the panels to hopefully stop impacted Riso and current leakage and also prevent frost damage.

On a sunny September day I compared the broken and unbroken panels for open circuit voltage and short circuit current and they were within 5% of each other which tells me the broken glass has not damaged the solar crystals but there is some reflection due to the cracks and shading where the glass is broken into smaller pieces.

I have one string installed consisting of 5 panels at 66' angle West facing. A Power One PVI3.0 (2 string 3kW G83 inverter), DC21 isolators installed locally at the string before the SWA cable and also at the inverter input. The inverter runs through a local CU with dual pole isolator, 16A MCB and 30mA dual pole RCD into the kitchen ring which is connected to the main CU which has a 32A MCB and 30mA dual pole RCD (16th edition installation). Its working a treat!

I was planning to add an East facing string of 5 panels however I can fit 4 panels onto a South facing wall as an option. After running some simulations I am exploring adding 4 panels to the South facing wall, about 80' angle and 4 East facing panels with 60' angle.

As the Sun moves the East panels will become shaded before the South facing panels, and they will also receive direct Sun before the South facing panels. I am aware that one shaded cell will cripple the whole string and to mitigate this the panels have bypass diodes, 3 per panel built in. As each set of cells in the panel see shade the voltage will drop and the bypass diode will pass the string current over the low effort cells. This will operate whenever there is shading on a cell or a panel and the string voltage will be reduced accordingly.

I am thinking that by adding a high current bypass diodes at the appropriate place in the circuit the 4 panels facing South or East can be bypassed and the current from the panels in Sun will be free to flow current to the inverter.

Each panel has a optimum voltage of ~37V so I will get ~148V at the best available current as a minimum once the bypass diode conducts and between 148 and upto ~300V when both sets of panels are in the sun. Nominal current is 8.8A. 20A MC4 mounted bypass diodes are available on ebay as are the various MC4 adaptors to enable correct installation.

Now the question!

Is there any reason this would not work or it would be a problem in terms of safety or fire? I will not installa nother inverter so it will be a choice between South, East or both.

I'm looking forward to comments & opinions, just ask if I've missed out anything important. Cheers.
 
Wow....a truly green system. Generating power from recycled panels :)

The aurora 3.0 has dual power point tracking. What's your current array set up with regards to strings?
 
Hi, I like to try and be Green, apparently I have saved 500 grams of CO2 already?!

At the moment I have one input from 5 panels in a West facing position, the other input is up for discussion. If the bypass diodes will negate the major shading issues I think 4 South with 4 East will give the highest usage without having to fiddle around with a second inverter and cabling. After reading more today it may be that the bypass diodes already in the panels will achieve what I am thinking about and if not a bypass diode across each complete panel may be possible. I think one bypass diode across 4 panels would not have an advantage.

The West and potential East facing panels are/will be in the garden, only the South facing would be wall mounted.
 
Combined East and South facing panels impact using a bypass diode Solar - EletriciansForums.net
 
Hi bud,what is the set-up for use and integration?
Hi, can you rephrase that? Its a normal set up in most respects, the inverter is grid tied to the house. Once sufficient panels are connected I have a box which will divert any power in excess of what's consumed to a heater which will be plumed into the hot tub so all generated power will be used, no export. I got a max of 244W today. :sunglasses:
 
Actually, I think using one external bypass diode for each entire panel will have a benefit, there will only be one 0.6V drop per panel rather than 3 x 0.6V drop when using the integrated diodes. Considering 4 panels that gives 4.8V reduction in volt drop over the bypass diodes, potentially 42W. This circles back to wondering if one bypass diode can be used to bypass a group of four out of the eight series connected panels in a South & East dual aspect and if this is a sensible thing to do.
 
I was interested in how the two inputs were separated and utilised.

Just interested in set-up...always have been...i did my first Heath Robinson solar thermal and rain water harvesting rigs,in my teens,late seventies :)
 
Hi PEG,

The inverter has two MPPT inputs, it was bought on ebay for £106 delivered. I got it because I quite like the design and they seem to be a good quality product, now seem to be ABB. It has RS485 so there is scope for logging in the future.

I have an old house and the roof is East and West facing, almost exactly E&W. There are several Scientists promoting E&W opposed to South because of the slightly extended generation time to avoid a peak at midday when consumption is not normally as high as mornings and evenings.

This is DIY and the panels are compromised so I did not really fancy a roof mounting as there are additional formal processes to comfy with, I don't like roofs much either! So I plan to mount them I the garden close to the fence, not above it or attached to it.

The West facing array is connected and running, the panels are 1960 x 990 (huge!), the pic is posted earlier in the thread. The Eastt facing array was going to be 5 panels as well but I am considering adding 4 panels on the South facing gable wall as part of the East array to give 8 or 9 panels, this is in the open circuit range of the inverter and this will be the second MPPT input.

I got used switches, DC21 spec on ebay, there is one next to the panels so each string can be isolated at the panels. There is also a dual isolator next to the inverter so it can also be isolated there. I had a small consumer unit for the Septic tank pump where the inverter is now installed so this CU has been enlarged and split to run the septic tank pump and the inverter.

The inverter injects into the Kitchen ring via a non fused immersion heater face plate into the 32A ring. The feed into the ring is protected by a 16a MCB and RCD.

The remaining electrical concerns are if the panel frames need to be earthed via an earthing rod locally to the panel. Watching on YouTube some panels appear able to conduct to the frame if the glass is broken and the panels are wet. I plan to try and find out if I can wire an RCD locally to the string to trip if there is leakage to earth potential. The panels are covered in Vinyl so they should be reasonably water proof again but it's better to have some protection locally. Solar panels are current sources and it's difficult to detect failure modes.

Just a comment on DCV, it is much more unfriendly than AC mains and it is likely to cause death or fire if anything goes wrong. This is important when choosing the dc isolators, they should be DC21 rated, the design is quite different to an AC product. This goes for MCB and RCD as well, so only DC versons must be used. There are several videos YouTube showing the effects of breaking DC current.

If there are any questions just let me know!

Does anyone have any comments and experience with bypass diodes?
 
Hi PEG,

The inverter has two MPPT inputs, it was bought on ebay for £106 delivered. I got it because I quite like the design and they seem to be a good quality product, now seem to be ABB. It has RS485 so there is scope for logging in the future.

I have an old house and the roof is East and West facing, almost exactly E&W. There are several Scientists promoting E&W opposed to South because of the slightly extended generation time to avoid a peak at midday when consumption is not normally as high as mornings and evenings.

This is DIY and the panels are compromised so I did not really fancy a roof mounting as there are additional formal processes to comfy with, I don't like roofs much either! So I plan to mount them I the garden close to the fence, not above it or attached to it.

The West facing array is connected and running, the panels are 1960 x 990 (huge!), the pic is posted earlier in the thread. The Eastt facing array was going to be 5 panels as well but I am considering adding 4 panels on the South facing gable wall as part of the East array to give 8 or 9 panels, this is in the open circuit range of the inverter and this will be the second MPPT input.

I got used switches, DC21 spec on ebay, there is one next to the panels so each string can be isolated at the panels. There is also a dual isolator next to the inverter so it can also be isolated there. I had a small consumer unit for the Septic tank pump where the inverter is now installed so this CU has been enlarged and split to run the septic tank pump and the inverter.

The inverter injects into the Kitchen ring via a non fused immersion heater face plate into the 32A ring. The feed into the ring is protected by a 16a MCB and RCD.

The remaining electrical concerns are if the panel frames need to be earthed via an earthing rod locally to the panel. Watching on YouTube some panels appear able to conduct to the frame if the glass is broken and the panels are wet. I plan to try and find out if I can wire an RCD locally to the string to trip if there is leakage to earth potential. The panels are covered in Vinyl so they should be reasonably water proof again but it's better to have some protection locally. Solar panels are current sources and it's difficult to detect failure modes.

Just a comment on DCV, it is much more unfriendly than AC mains and it is likely to cause death or fire if anything goes wrong. This is important when choosing the dc isolators, they should be DC21 rated, the design is quite different to an AC product. This goes for MCB and RCD as well, so only DC versons must be used. There are several videos YouTube showing the effects of breaking DC current.

If there are any questions just let me know!

Does anyone have any comments and experience with bypass diodes?


ABB/Powerone 3.0 inverter you have is transformerless so the array should be bonded to earth. It is not electrically separated and there will be a PD between DC and earth when panels generating. Particularly important in the case of yours as your array is accessible and the damaged modules have a higher chance of leakage.



I'm not gonna comment on your grid tied connection to RFC with regard to BS7671 (although a fused FCU would likely remedy it) and also G83 for DNO :)
 
1) Can you not fit more panels to the right of these?

2) The pitch looks very steep - nearly vertical. Are you aware that a shallower pitch will give you a greater yield when facing west (or east)? If you bring the pitch down to 15, 10 or even 5 degrees, you should see higher output. Horizontal will theoretically perform even better although you may have to clean them. (Need to avoid shading, of course.)

3) Have you assessed if you need planning permission for a ground-mounted system?

Planning Permission: Stand alone solar equipment (panels not on a building but within the grounds of a house or a block of flats) | Solar panels | Planning Portal - https://www.planningportal.co.uk/info/200130/common_projects/51/solar_panels/3
 
Hi TJ Anderson, Whinmoor, thanks for your comments.

I did look at the inverter manual, it requires the panels to be floating, the panels are outisde the Equipotential Zone and the house is PME. The frame earthing decision tree says to bond to an earth rod and I cometely agree with you that this is the right thing to do as the panels can be accessed. Just in case!

Suprisingly the PV installation guides only seem to say that an inverter must not be connected by a 3 pin plug. It seems that the need for a fuse and the ability to lock off the connection point can be achieved with a fused spur face plate. That's not very nice really so the CU approach must be better and that gives the ability to add an RCD to maintain the earth leakage protection to the ring. I have the G83/1 forms and the pack with wiring diagrams, equipment specs and certificates etc will be sent off in the 28 day limit after commissioning, it is still in build and test stage at the moment. It seems the DNO aspect can be self certified, it's only the FIT that needs an MCS person.


Two more panels would fit to the right but a Bush has grown under the fence and my Wife likes it :) I cut half of it down to get the last panel in.

The angle is set by a void, the ground falls about 400mm under the panels, I built wooden frames which go down to the concrete and are fixed and ballasted. The width of the gap and the lawnmower wheels set the angle.

I put a link to a calculator in my initial post, it's really handy because it gives the expected output based on your exact position and the inclination and rotation can be entered or it will give nominal values. 37 degree inclination and 6 degree East is nominal for me.

With a nod to the planning aspects, I want the panels to be lower the the fence and take up as little space as possible. 400mm is OK because a small garden border fit nicely underneath (it will be like this on the East facing string on the opposite side of the garden.

The cracked panels and the orientation of the panels is all a comprimise but the whole lot including electrics and swa is only costing around £400. My base load is around 450W and any extra generation will go to the hot tub. I cannot get FIT so 100% usage is ideal, even if I only generate half of an optimal system I think it should pay for its self in a bit over a year.


Have you ever looked into bypass diode configurations?
 
More reading later it looks like this can be achieved by having an east and west series string in parallel. In this case the string voltage will be very close but as the sun moves off a string of panels the capability to deliver current reduces, but the voltage remains stable. The MPPT will drive the shaded string voltage to the maximum power point voltage of the productive string as the shaded string cannot provide current.

The result is that the voltage remains around 160 to 180 due to the number of panels in my string and the current delivered by each string will vary based on sun position and string shading which is handled by the integrated bypass diodes. At some point during the day the output will be the sum of the maximum currents and at others the dominant string will define the current output.

I spoke to ABB today because my inverter has a Imax per MPPT spec of 10 Amps. They basically said the inverter will derate and will not be damaged. I think this is correct because the inverter design will control how much current it will absorb. ABB said to use the string sizer and if it shows an available option it is fine. So I did this by editing a panel to provide a current of 18Amps and an appropriate voltage and the program gave me an option with the inverter clipping at 2kW on the MPPT and installed power of 2.95kW. This means there may be more to have by changing to the PVI-3.6 inverter which accepts 16A per MPPT. One of the 3 strings will connect to the second MPPT.

Interestingly a couple of sources have said that a 90' separation with paralleled strings is the most effective but I have not done the calculations to see the difference yet.

Panels in parallel apparently will not draw current if the voltages are close unless there is a fault and blocking diodes are not essential but it seems reasonable to drop a blocking diode on each string just to ensure control of unexpected current flow.

Running some more calculations today I should be able to use most of the generated power without dumping to the hot tub which is nice, my usage is an average 30kWh per day and the best day of the year generating is indicated as 14.8kWh. Annual is estimated at 3600kWh or £790 out of an pre solar age bill of £1500.

Cheers,
 

Reply to Combined East and South facing panels impact using a bypass diode in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

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