Adding a 2nd solar Panel DIY

[VXman]

At the moment I have one 175W solar panel going to a NDS Sun Control 2 controller. I have the SCE320 which will accommodate 2 solar panels up to 320W https://www.ndsenergy.uk/prodotto/sun-control-2/

So if I were to buy a 2nd solar panel would that mean I could only get one up to 145 watts.

What would happen if I had something over that? Is there an alternative way of wiring them to by pass this restriction?

I predict someone will say buy a new Victron controller but I'm trying to keep this cheap and not spend any unnecessary money.

Also, on fitting - would it be simple enough to route the cables down the current gland and re seal. Would prefer not to redrill the roof.

 

[Lenny HB]

Most controllers won't handle more than there rated input apart from Victron's., although you would probly get away with it I the UK. So you could fit a smaller panel or a new controller, or try it and see.

Normal way of wiring a second panel is to parallel them on the roof using MC4 commbining adaptors then you only have one pair of cables to the controller.

 

[GMLS]

If it were me and thinking purely short term with a budget in mind, I'd add an additional panel of absolute max 175w (to satisfy my ocd) giving a total of 350w but being pretty sure I'd never actually reach that in the UK but also in the hope there would be some tolerance in the 320w rating. If you holiday in Spain, Portugal, Southern France, I'd probably upgrade the MPPT. But that is not advice

 

[autorouter]

I know 2 x 175W panels is 350W, but it's flat on the roof rather than tilted, you'll be lucky to get over 300W out of them, even in sunny Spain. Solar controllers are quite good at limiting power output. For example, when your batteries are full, they will avoid generating the more than 250W they are capable of, and just put in a few milliamps of trickle charge. Obviously within limits, but I'd have thought up to 400W of panel wouldn't overstress it.

You can join the panels in parallel on top of the roof, with weatherproof MC4 connectors, and use the existing wire through the roof - assuming it's thick enough. 2-to-1 and 3-to-1 MC4 adapters are available to parallel them together.

 

[Dorwyn]

You can get Y cables with the standard male/female connectors, so you don't need to reroute the main down cables

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[Raul]

Yet again we confuse ourself. I explained many times, and if you think of it, it makes sense. Lenny almost said it, “rated input”. That input it’s not W it’s ADC in and VOC. if you do t exceed this input parameters, the watts out doesn’t matter.
Everyone is thinking if you hook 300w, you will output 300w, wrong.

You need to dig the manual, and read max Vdc in, and max Adc in. If the panels in parallel do not exceed the amps and volts in it’s ok, Don’t try series as that controller is 30v max.

 

[VXman]

I know 2 x 175W panels is 350W, but it's flat on the roof rather than tilted, you'll be lucky to get over 300W out of them, even in sunny Spain. Solar controllers are quite good at limiting power output. For example, when your batteries are full, they will avoid generating the more than 250W they are capable of, and just put in a few milliamps of trickle charge. Obviously within limits, but I'd have thought up to 400W of panel wouldn't overstress it.

You can join the panels in parallel on top of the roof, with weatherproof MC4 connectors, and use the existing wire through the roof - assuming it's thick enough. 2-to-1 and 3-to-1 MC4 adapters are available to parallel them together.

Yet again we confuse ourself. I explained many times, and if you think of it, it makes sense. Lenny almost said it, “rated input”. That input it’s not W it’s ADC in and VOC. if you do t exceed this input parameters, the watts out doesn’t matter.
Everyone is thinking if you hook 300w, you will output 300w, wrong.

You need to dig the manual, and read max Vdc in, and max Adc in. If the panels in parallel do not exceed the amps and volts in it’s ok, Don’t try series as that controller is 30v max.

Ah -so, I was thinking of running a second set of cables down as there are 2 solar panel inputs in the controller but you are suggesting linking the 2 panels in parallel and only using the one input. Would make life easier. Is the power output just the same this way?

What about this? This is from Suncontrol2 manual. Is it saying it can only handle 200Watt if using one input?

FAQ

SUNCONTROL2 - Maximum supported voltage is 29,5V.

Is it possible to connect one 200W solar panel only, on a single SUNCONTROL2connection?

It’s possible to connect just one bigger solar panel (200W), for example on SUNCONTROL 2 Pin N°5, but you must connect Pin N°5 and Pin N°6. Use, at least, a 6 mm 2cross-sizecable.

 

[dunnah01]

Or just max out on panel size and use a £10 PWM controller direct to battery.

 

[autorouter]

What about this? This is from Suncontrol2 manual. Is it saying it can only handle 200Watt if using one input?

Yes I think you're right, I was assuming it had inputs like other solar controllers, but this one has separate inputs. So it will take two panels, but with two separate pairs of wires from the panels to the solar controller. That's a pain, it looks like you need two more wires through the roof.

Actually you could probably get away with one extra wire, because the two solar panel negatives are commoned together at the terminal block input, so no reason why you can't common them together on the roof first. But it looks as if the positives have to be separate.

 

[Stealaway]

My original 100w panel cables whe big enough to carry the extra amps from the second 125w panel. I simply connected them together under a new dual waterproof cable roof connection block.
I have changed the solar controller to a 30a dual battery controller.

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[VXman]

Sorry for the questions but I am learning as I go along here.

So, a regulator limits the voltage to delivered to the battery to around 14 volts as to high a voltage with fry a battery. So if my one 175W battery is delivering the full voltage there would be no benefit to having an additional one? Or is it to do with amps? Will a higher ampage charge a battery quicker?

My original 100w panel cables whe big enough to carry the extra amps from the second 125w panel.

I read somewhere that when connecting in parallel it is best to have matching panels as you would with batteries. Having one 100 W and one 125 W means you wouldn't be getting the full benefit of the larger one.

 

[VXman]

Yes I think you're right, I was assuming it had inputs like other solar controllers, but this one has separate inputs. So it will take two panels, but with two separate pairs of wires from the panels to the solar controller. That's a pain, it looks like you need two more wires through the roof.

Actually you could probably get away with one extra wire, because the two solar panel negatives are commoned together at the terminal block input, so no reason why you can't common them together on the roof first. But it looks as if the positives have to be separate.

I think the question is NDS /Sun Control 2 saying 200w is max through one input or was that just an example. The unit overall accommodates 320W. I just depends where there is a limit the the amount allowed through one input. The manual is not clear. Might try to contact NDS.

 

[ontheroadagain]

We also have a NDS Sun Control 2 fitted to our Adria.
As I understand it, you can run one cable to it from two panels, but you must bridge (connect) the two positive input terminals together on the controller, as each terminal can only take a max of 160W.
Joining the two together increases this to 320W. The other way to do it is to run two cables to the controller (one from each panel).

 

[Lenny HB]

Sorry for the questions but I am learning as I go along here.

So, a regulator limits the voltage to delivered to the battery to around 14 volts as to high a voltage with fry a battery. So if my one 175W battery is delivering the full voltage there would be no benefit to having an additional one? Or is it to do with amps? Will a higher ampage charge a battery quicker?

The regulator will control both the voltage and the current to the battery, if it is a normal 3 stage regulator it works in the same way as a battery charger.
This is an approximation of how they work. It will deliver whatever current the battery can take within its capability until it reaches the charged voltage say 14.4, it will then go into an absorption phase holding the voltage around 14 - 14.4v at a reduced current for a time depending on the type of battery, then it will drop to a float/maintenance charge or around 13.8 amps with limited current.

In your case it would make a lot of sense to replace the regulator with a good quality MPPT one it would simplify your wiring and give better results & no extra holes in the roof.

 

[Lenny HB]

My original 100w panel cables whe big enough to carry the extra amps from the second 125w panel. I simply connected them together under a new dual waterproof cable roof connection block.

You don't have to go too mad on the cable size to the panels as when you have the highest output a small percentage loss won't worry you and in winter the panels will be producing so little power the volt drop will be negligible.
For up the 200 watts 4mm sq is fine above that 6 mm sq is better but not essential but it is always worth using a decent size cable from the regulator to the batteries 6 or 10 mm sq depending on the length of cable run & current.

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[autorouter]

So, a regulator limits the voltage to delivered to the battery to around 14 volts as to high a voltage with fry a battery. So if my one 175W battery is delivering the full voltage there would be no benefit to having an additional one? Or is it to do with amps? Will a higher ampage charge a battery quicker?

I have a 5A mains charger and a 15A mains charger. Both will charge a flat battery until it is full. When charging they take the battery to about the same voltage, around 14.5V.

The 15A charger will charge three times faster than the 5A one.

There's a limit to how fast you can charge a battery, but it's not a problem for smallish solar installations. About 20A for each 100Ah battery, for example.

 

[VXman]

We also have a NDS Sun Control 2 fitted to our Adria.
As I understand it, you can run one cable to it from two panels, but you must bridge (connect) the two positive input terminals together on the controller, as each terminal can only take a max of 160W.
Joining the two together increases this to 320W. The other way to do it is to run two cables to the controller (one from each panel).

That makes sense - I was just confused by the example given in the manual which gives 200W as an example and doesn't really explain the maximum it can take. You are right though - the specs state max of 160 per input. I guess bridging the 2 connections spreads the load.

 

[Stealaway]

I read somewhere that when connecting in parallel it is best to have matching panels as you would with batteries. Having one 100 W and one 125 W means you wouldn't be getting the full benefit of the larger one.

I think the extra 25W would compensate for the loss with the possible imbalance.
Also- I am buying these 125W panels for £50 each

My connection block - I have dispensed with the rock now

 

[VXman]

I think the extra 25W would compensate for the loss with the possible imbalance.
Also- I am buying these 125W panels for £50 each

where? I want to soure a 175 watt one. The cheapest I am finding a matching NDS one is £300.

Oddly that deal includes a SunControl 2 regulator and a cable entry gland. The nearest competitor is £310 without those extras!

 

[Stealaway]

A maker of mobile road signs in Matlock. They sell off the old stock when they build new signs.

It could be these people ---- https://m-vis.co.uk/

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