Flexible Panels, Mounting Methods and Heat

[Newcastle George]

Take my advice, get off and stay off the steroids, they gave me osteoporosis - the bones of a 95yo when I was 50yo. For the occasional bout of gout I take Moxicam, 1 x 15mg tablet/day for a couple of days.

George

[bagmaker]

Thanks George, There is a side issue with NSAIDs and ashmatics

[T1 Terry]

what "work" is done at night when a solar panel is powered by the battery without these diodes?

The become electric blankets. Midnite Solar and Outback Solar actually monitor the panel temp and apply a boosted battery voltage back into the panels at day break to melt the ice/snow off the panels and allow it to slide off, then revert to normal operation once a temp higher than 2*C from memory can be maintained.

Many web sites will tell you blocking diodes are a thing of the past and no longer required, but they are talking about back to grid supply systems that are never disconnected from the grid. In these cases there is no back current because the controller blocks reverse flow.
In a battery based system the controller does stop reverse current flow, when solid state relays are used this function from the controller is lost and SSR's have a built in reverse current diode to eliminate voltage spikes that would destroy the transistor used for rapid switching within the relay. Normally the voltage drop across the diode is enough to drop the reverse voltage sufficiently to stay below the required voltage to turn a solar panel into a rather inefficient heater. The catch is when a manufacturer uses very low reverse flow junctions within the solar panel, then virtually any voltage will trickle back through at night.
The serious problem is not the night time reverse current flow, it is the reverse current flow from the other panels when the controller or SSR stops current flow to the battery because the battery is full. Now the system on the roof climbs to the open circuit voltage of around 21v for a 12v parallel connected system and anywhere up to 150v for a series connected house panel system. All that is required now is a weak reverse current flow link within a solar panel to turn that module into a super charged heater. Quite some time back Jon (Jon & Kay) posted a thermal image photo of a panel with a very hot module clearly showing up. This is exactly what happens if blocking diodes are not used and are the most common cause of panel failure.
Bibs put up a few photos of what happens when crap panels are used on a house system and no blocking diodes installed, quite dramatic and the cause of more than few house fires.

T1 Terry

[bagmaker]

Thats fascinating thanks T1, I assume then there is an internal resistance that creates the heat?

[Eddy]

Hi Terry

When I get a few mins spare I'll put up a photo of how we are doing the diode thing

Could you describe how you attach blocking diode in wiring run - I can't work out how to avoid the wiring putting a strain on the diode pigtails.
(other than using another terminal block)

Thanks

Eddy

[bagmaker]

here is how I did mine Eddy, in the panel junction box.
swapped wires from one side to the other, run neg wire back to its terminal in a loop

panel diodes.jpg

Soldered a diode (16a schottke) onto the pos wire and shrinked some tubing over then put onto pos terminal.
You can see it in the top right hand corner of the pic
Test with meter to ensure working before closing up

[Eddy]

Thanks bagmaker
I did something similar in one of my panels (it is years old with a good size panel junction box and a built in terminal block)
In a recently purchased panel, the panel junction box seems a little squeezy to do anything inside
It always seems odd to me, we use a xx size cable to connect solar panels and then we connect up to a diode with paper thin wires
Trying to figure out a way to connect in diode so there is not too much strain put on diode leads by heavier solar cables (without adding in a another junction box/terminal strip)
Eddy

[T1 Terry]

Hi Terry

When I get a few mins spare I'll put up a photo of how we are doing the diode thing

Could you describe how you attach blocking diode in wiring run - I can't work out how to avoid the wiring putting a strain on the diode pigtails.
(other than using another terminal block)

Thanks

Eddy

If you have room for the original MC4 plugs, knock out the connectors, drill out the plugs large enough for the diode to fit through, feed the two connectors back through the plug and solder the diode between each connector, then add a bit of silicon into the cable end of each plug and screw the retaining nut on so it compresses the rubber grommet into the silicon/plug/cable and this will remove the cable strain.
If you are using the connectors only, solder the silver stripe end into the male connector on your positive extension lead and a second male connector onto the non banded end of the diode. Slip a length of heatshrink long enough to cover the connector lead male connector, diode, second male connector and the solar panel positive lead female connector and soldr the male/female connector together and slide the heatshink over the whole lot and shink to fit. A dob of sealant on the cable each side of the joint to secure it to the roof will stop the cables moving and weakening the diode legs.
A lot more work than just plug and play, but better and cheaper to do the job once eh

T1 Terry

[Eddy]

Thanks Terry - I will have a look at the mc4 plug and see if I can make the modification, if I butcher it up too much will go the extra junction box & terminal strip

[bagmaker]

you can also just buy the MC4 connector online....

https://www.aliexpress.com/item/MC4-Con ... autifyAB=0