Thinking About A Solar Panel? Look At This.....

[Sniggib]

Thanks, I will research pros and cons of wiring in series or parallel.

May be looking at a separate MPPT controller

 

[Phil_G]

Parallel or series a lot depends where you connect them. On the roof (two wires coming in), at the controller (four wires)?
There are several 'cons' to series, the worst being the lack of output if one panel is in shadow
Personally I'd do neither.
Use the 100W panels on your shed roof, and buy a 200W for the van if thats what you need! Much neater

 

[Sniggib]

Thanks. Not sure what I will need yet, so will look into that more.

Thanks for the info

 

[Sniggib]

So looking at this article; [2020] Best Solar Panels For RV or Camper Van Buyer Guide (parkedinparadise.com)

Seems to recommend wiring in series? Any links on why its not so great?

 

[Phil_G]

Wiring Solar Panels In Series

• No need for fuses and wiring is simpler and cheaper.
• Higher voltage rather than amperage means the system is a more efficient.
• In certain light conditions, series is better. Overcast days or low light situations benefit from series wiring. If panels are only getting enough sun to output 13V, then two panels in parallel won’t be outputting enough voltage to properly charge the batteries at 13.8V. If you’re wiring in series, you’re getting 26V which can be stepped down for a proper charge.

Both methods are as simple as you can get, its just two wires. Cheaper? , no cos they come with cables attached, nothing else to buy. Series can be more expensive as you need to buy a HV controller. Agree high V low A is more efficient. Third point, disagree, at 13v a panel is almost inactive & wont be supplying any worthwhile current.

Wiring Solar Panels In Parallel

• Most PWM controllers need parallel wiring. These charge controllers are only rated to a slightly higher input voltage than the battery bank. So if you have two 18V panels and wire in series to put in 36V of power into a PWM controller, you’re loosing anything above the 13.8V that’s going into your batteries.
• In certain shade conditions parallel is better. If one panel is shaded and the other isn’t, you aren’t loosing as much power because you’re still getting the full voltage from the panel in the sun.
• Parallel solar needs bigger wiring, fuses, and combiners. Each panel must be fused at the combiner junction in case one shorts out. The wiring must be bigger as you are increasing amps.

Point 1 is a gross oversimplification as a decent PWM controller will be switch mode and wont 'lose anything above 13.8v', they simply lack mpp tracking. Doesnt apply to your Ctek anyway. 2nd point agree. 3rd point solar panels are inherently resistive compared to say a battery, they are incapable of massive currents and dumping into a short would be harmless. Thats what the Isc spec means. Cells are connected in parallel (and parallel bunches in series) within a panel anyway.

Shade
Another big thing to know about panels is that most solar tech is very sensitive to shade. Each of the little squares on your panels are wired in a way that if one of them is shaded, the whole row can’t produce energy. Because of this, you can reduce your energy produced by up to 90% if a certain 10% of the panel is covered.

...and with series wiring, if one is shaded the entire array goes down, not just one panel as is the case with parallel.

Up to you, either will work but you cant do series with your Ctek, if you go series dont park under a tree branch or lamp post, one shadow cuts the whole thing.
Cheers
Phil

 

[Loz]

I fancy a custom 4-panel series-parallel into my Victron (4 x 100w, 40v 200w) if this was available as a large single panel on the roof with a single pair of cables off the roof, that would be my ideal.

 

[Phil_G]

Yep one large panel is so much neater... at 400w they're usually rigids or multiple flexis though.
You'd think SCA, Reimo, Skyline, Austops etc poptop manufacturers would have cottoned on to this...

 

[Loz]

I was thinking or 4 x 100 flex panels moulded into one large panel bonded to the roof between the rails, wired series/parallel to a single pair of cables coming out the end into the van. I'm sure someone on here mentioned that they had a mate who made custom panels and that caught my eye.

 

[Ads_Essex]

I fancy a custom 4-panel series-parallel into my Victron (4 x 100w, 40v 200w) if this was available as a large single panel on the roof with a single pair of cables off the roof, that would be my ideal.

Yep one large panel is so much neater... at 400w they're usually rigids or multiple flexis though.
You'd think SCA, Reimo, Skyline, Austops etc poptop manufacturers would have cottoned on to this...

Would 4 panels fair better in the instance that one was fouled with bird poo, in that three of the four would continue to harness energy? Or has partial-blockages of solar panels been overcome?

 

[Sniggib]

@Phil_G many thanks for your input.

Tricky decision! Though I'm wanting to get it right first time! Leaning toward parallel now though to be honest because of the shading issue as you say. Though I would then need a separate solar controller. I presume whatever panels I wire in series I would need a separate controller anyway given that OCV would be double and most DC-DC controllers with solar input seem to stop at max 32v anyway. So at least I have not ordered the wrong thing getting s Ctek (he hopes!).

On the plus side I've worked out that if we have a fridge my power draw will be c. 50A per day, so will need 200W of solar to replenish in high summer. Luckily in winter fridge will be off which drops the draw hugely.

Cheers,

 

[Phil_G]

@Phil_G many thanks for your input.

No probs!

Tricky decision! Though I'm wanting to get it right first time! Leaning toward parallel now though to be honest because of the shading issue as you say. Though I would then need a separate solar controller.

Why? its only over the Ctek voltage if you go series.

On the plus side I've worked out that if we have a fridge my power draw will be c. 50A per day

No fridge will take 50 amps. Maybe 5, usually 3-4 for a Waiko/Dometic and thats only when the compressor is running. With minimal door-opening, my Dometic runs about 6:1 off/on duty cycle so over 24hrs maybe 16-20Ah ish.

...so will need 200W of solar to replenish in high summer.

200 is a nice size. It not about peak power when its sunny, larger panels are preferable for getting some charge under poor conditions

Would 4 panels fair better in the instance that one was fouled with bird poo, in that three of the four would continue to harness energy? Or has partial-blockages of solar panels been overcome?

It depends how the 4 panels are wired. Maximum resilience is with all 4 in parallel. If you do them series-parallel,
within either series pair, the output of this pair will be low if either one of the two is in shadow. Meanwhile the other two in series, which are in parallel with the shaded pair will continue to give good output (assuming they're not shaded)
In a nutshell, a single low cell will stop a series array producing. Paralleling gives an alternate path. Series-parallel of 4 panels is a good compromise

 

[Sniggib]

Agggh so i've got myself confused, as usual haha!

Re-reading your post from earlier and this from Renogy; Series vs Parallel Connections Explained | Renogy Solar where I am looking at possibly getting panels

So! will the below work;

- CTEK max OCV 23V and MAX 20A solar input
- Wire 2x 100W panels in parallel which results in OCV remaining at 23 or less V and doubles the amps
- So 2 x100W panels would deliver a max of 16.6A which is lower than the MAX 20A of the CTEK.

Hope I have it the right way round this time!

Struggling to find a 200W panel with OCV less than 23V, but considering fitting a separate controller for this so it is a neater install.

Cheers,

 

[Phil_G]

Thats right. In the UK you'll never get full rated output from a panel anyway! I think they must be specc'ed on the equator

 

[Sniggib]

Magic that's great, thanks again @Phil_G

As you say my main reason to go for 200W is so we get some charge on cloudy days etc. Looking at the cost of a separate solar charger I think I may aswell go for 2 x 100W panels, don't mind the aesthetic, though it does potentially mean more holes in the roof, something to figure out next.

Thanks for the info on the fridge, it was a difficult one to try and figure out. Id got it to 45A per day based on the info I had but good to hear it will last longer than that.

Now I have hijacked this post so much I think I better start my own build thread!

 

[Phil_G]

Id got it to 45A per day

be careful with your units, I know it sounds pedantic but its important, presumably you mean 45Ah not 45A
45Ah per day sounds a lot for a campervan fridge, but it depends on the type of fridge, usage, thermostat setting, ambient temperature etc.
45Ah would last me a weekend easily

 

[Sniggib]

Now I am again going to show my inconsistent electrical knowledge.

I though they were comparable? i.e. 45A = 45Ah?

 

[Pete C]

Amps is an instantaneous thing i.e. 45 Amps are flowing at this point in time.
45Ah means 45 Amps flowed for an hour (or 1 Amp flowed for 45 hours).

Pete

 

[Phil_G]

...and a fridge, which cycles on/off, has to be measured over a period much longer than its duty cycle,
which is why you see weird units like "Ah per day" and "kWh per annum"

An amp is a unit of current. An amp-hour is a unit of charge. Its like apples and tuesdays, different thing entirely

 

[Sniggib]

Thanks both.

I see where I got confused as I was using A and Ah interchangeably to work out my max current for cable sizing which hopefully is correct as 45A is 45A regardless of how long it takes to flow.

So I have calculated my total Amps over a 24 hour period on the basis that it gives me a max Ah for battery and solar power sizing. i.e. 0.5A per hour for 3 hours gives me 1.5A over 3 hours. Presumably this would equate to 1.5/3 = 0.5Ah.

I think that what the fridge has been hard to calculate as the documents read on it have 1.73A/h over 24 hours, which I took to mean 1.73Ah per hour for 24 hr and hence 40 odd amps per day.

Cheers,

 

[Qnapper]

Sniggib, you are so of correct in that yes the total amps drawing from device will say 1.73Ah per hour MAX, but that is if it is cooling down stuff added. Once the fridge reaches max -temp it will start to withdrawn less amps from battery. So...... may drop down to less than 1amp............. until you open lid to remove or add something.
I would say (do have my van yet) that if used on battery 24hrs a day the draw on battery would be closer to 24amps across the whole period. I have owned until last week a motorhome for the passed 12 years and have a good understanding of batteries. My last bank for 300amps worth of batteries lasted for 7 years before failing.
I intend to add solar power to my van as I had with old motorhome. I have 300watts of solar good sunny day in Spain would have battery fully charged (not topped up) by midday. This was whilst watching TV and charging phones, iPads etc. If your not going to use EHU then solar is the way ahead.