400w Solar And Ctek D250se

[bullracing]

I have my solar kit on the way. 4x 100w panels which I will wire in Parallel. It will stay 12v but what about the ampage as I am slightly confused how it all works. Is it simply 4x the amps?
I was hoping to fit the panels direct to the D250SE but I have spotted the max solar input is 25amp.

Each panel is Optimum Operating Current (Imp): 5.72A Short-Circuit Current (Isc): 6.24A
So I am JUST, JUST under the 25amp max input, will they ever reach the short-circuit current? If its the optimum then I am nicely under.

Should I still do this or is it too risky?
If not could I wire the panels to a controller then wire the controller output to the Ctek instead? Would that work?

 

[Loz]

You could do a series parallel combo if its within the max voltage.

 

[Pete C]

What’s the maximum output voltage of your panels ?

Pete

 

[bullracing]

hopefully this helps
Solar Cell Type: Monocrystalline
Cable outputs: 12AWG
IP65 Rated waterproof junction box
IP67 Rated waterproof MC4 connectors
Maximum Power: 100W Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 17.9V Open-Circuit Voltage (Voc): 21.6V
Optimum Operating Current (Imp): 5.72A Short-Circuit Current (Isc): 6.24A

 

[Pete C]

The max input voltage of that Ctek is 23 volts, so all 4 panels would have to go in parallel.

I don’t know if the 25A input current is limited by the Ctek device itself - need someone like @travelvolts to confirm if this was going to be an issue. Either way, you are approaching the maximum operating power of the Ctek, so make sure it is ventilated !

Pete

 

[Dellmassive]

In parallel the voltage stays the same but the current adds up.

In series the voltage adds up but the current stays the same.

Series's can be preferable in solar as you can use thinner cable, big currents need big cables.

Another option is to split the panels in half, have 200w on the ctek and add the other 200w to a standard MPPT like a victron or another.

Or split 300w/100w.....

You could move all the solar to a dedicated MPPT with higher input specs......but you would loose the reverse starter battery charge you mentioned before...

Unless you added one of those small diode/resistor based B2B charge boxes like @andys has???? (Have you managed to crack your one open yet and see what's inside? @andys )

 

[Salty Spuds]

Personally I don’t think it’s a balanced setup. 4x100W panels is an odd arrangement for starters. On a sunny day you’re pushing the limits of the Ctek and you’re going to have 25A wandering around the van Do you really need 400W of panel capacity? What batteries are on the other end? I’d either change the panel arrangement or fit a different MPPT controller.
Just sayin.

 

[travelvolts]

Agreed, no point in producing more power than you can store/use. Will four even fit on your roof? I would say use three in parallel. 300 watts is plenty, even for two x 100 ah ish batteries.

 

[t0mb0]

I agree that 400w may well be overkill but the point of high wattage solar is usually nothing to do with the peak power in perfect conditions. The point is to dredge up useful amounts of power in marginal conditions (especially in a UK climate!) which can make the difference between keeping the battery topped up and not.

Having said that, I have 250w of solar and never really felt the need for more. Although I would do if I camped out regularly without driving around over the UK winter. You can always run the engine with a DC-DC in a tight spot of course.

 

[travelvolts]

The problem is that when solar out put falls it's it's usually off a cliff!
I have 600 watts on our truck and in the winter it might as well not be there so I don't agree that overspeccing compensates for poor light conditions.

 

[Dellmassive]

This weeks data . . . 3x 150W panels (solar shed system) via Victron MTTP into 2x Leoch Xtreme AGM 110 ah, running garden and shed LED lighting and power via inverter.

not a daily large discharge of the battery bank . . . . but the setup is keeping the battery bank SOC above 90%



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heres a close up of yesterday . . . . .



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[travelvolts]

Be interesting to do a comparison with today as conditions are so different.

 

[Salty Spuds]

Be interesting to do a comparison with today as conditions are so different.

As an aside, we have a 4kW solar system on the house, peak output today is 240W, 0.5kWh for the day. It doesn’t matter what size system you have, no sun=no power. The argument for having more capacity to scavenge as much power on poor days is nonsensical.

 

[Dellmassive]

Be interesting to do a comparison with today as conditions are so different.

its proper dark now, so here todays data SE/London location - been grey and rainy all day - no sun at all =[

again next to no load-drain on batteries . . . . . . so the SOC is very high, so the MPPT output-amps is low . . .

Ill try and run some loads and drain the bank for next time so we can see a real-world attempt at charging a low battery bank.



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and close up of last 6hrs . . . .





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[Salty Spuds]

its proper dark now, so here todays data SE/London location - been grey and rainy all day - no sun at all =[

again next to no load-drain on batteries . . . . . . so the SOC is very high, so the MPPT output-amps is low . . .

Ill try and run some loads and drain the bank for next time so we can see a real-world attempt at charging a low battery bank.

View attachment 56137

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View attachment 56138

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and close up of last 6hrs . . . .

View attachment 56139

View attachment 56140

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So 3/4 of bugger all
What’s the installed capacity of the panels?

 

[bullracing]

Thanks guys.
I have 2x 110ah batteries plus the starter. I had 300w on my last van which done ok but this time want to have more then enough rather then be close to the limit.
I do many trips to wales per year, loads of camping trips with the kids and hoping to get away to Europe again a few times this year. I also compete in Croatia and Poland on the quad so I go off grid for 10 days. We never use EHU too so I go fully off grid.
All those saying 400w is OTT, do you have 400w or ever had? Maybe go EHU?
I would say I have plenty of stored power with fridge on it, kids charging bits and bobs, TV, stereo and amp on during the day. The power gets used.

I have had an email back from Ctek. They have said the D250SE can handle 400w BUT it wont do anything because it can only really process 300w.

I do question if I actually need the Ctek. The panels will keep the leisure all sorted and I could just run the engine if I need to. I just want to be able to charge the starter without starting the van if I can do it without too much problem. Is there another Ctek which would work to connect Leisure and starter batteries together? Forget going to the Ctek with the solar and I do not really need the alternator to do the leisure batteries either. A confusing one and I am not sure what the best way to go about it is, however I would rather do it all properly now rather then later.

 

[bullracing]

same batteries as Dellmasive has in the shed

 

[t0mb0]

Very obviously, if it's lashing with rain all day or the cloud cover is thick and constant, no panel is going to help much. However, whilst this fact is true, it's not actually very helpful in trying to determine what wattage it is worth installing. It's obviously equally invalid to assume you're going to get anything like peak output except on exceptional summer days. Either good/bad extreme isn't really very useful in sizing a solar panel, it's the marginal days that count. The fact is that the UK has a wildly variable climate, both with respect to seasons and day to day that mean the range of solar outcomes is a wide and continuous distribution - it is very obviously not a sun/no-sun binary distribution.

Consider the rough cases:

1) Beautiful summer's day.
2) Cloudy summer, reasonable spring/autumn day.
3) Average/poor winter's day.

In case (1), any half-sensible van solar panel will likely do, in case (3) no realistically van-sized panel will do much (get the alternator with DC-DC on!) but in case (2) which is actually pretty common in the UK, the difference between a 100w and a 300w panel, for instance, could be substantial.

To make this more concrete, consider this plot (from http://www.iesisenergy.org/agp/Aris-Solar-paper.pdf) of nationwide solar production through the year.



It should be obvious from this that the distribution of daily solar outcomes is very continuous, and basing anything on the extremes is a bad idea. If we take a bit of a leap (likely they're rather optimistic for our van case given we don't have great control over orientation and placement and the plot above is nationwide so includes geographical averaging we don't have so our error-bars will be much wider) and actually use the capacity factors on the right hand side, I can calculate (very!) rough expected potential Ah generation for each of my three cases above for my 250w panel, using the equation:

daily_Ah = (250w / 12v) * 24h * capacity_factor

Case 1 - Beautiful summer's day (capacity factor = 0.16):

(250 / 12) * 24 * 0.16 = 80Ah

Case 2 - Cloudy summer, reasonable spring/autumn day (capacity factor = 0.08):

(250 / 12) * 24 * 0.08 = 40Ah

Case 3 - Average/poor winter's day, or a day of significant rain in any season (capacity factor 0.025)

(250 / 12) * 24 * 0.08 = 12.5Ah

These numbers, whilst probably a bit optimistic, do feel ballpark-accurate from my experience of using my 250w solar panel for wild camping over the last three years. It should be very clear from this that the size of the solar panel will make a significant difference in the range of seasons and power requirements that van campers do genuinely care about. To simplify, if you want to extend your wild camping through Spring/Autumn, putting on a decent amount of solar is a good idea. In winter, whilst solar will help to top up, expect to have to run the engine to fill in the gaps.

For my personal use, my 250w panel has been ideal.

 

[t0mb0]

Thanks guys.
I have 2x 110ah batteries plus the starter. I had 300w on my last van which done ok but this time want to have more then enough rather then be close to the limit.
I do many trips to wales per year, loads of camping trips with the kids and hoping to get away to Europe again a few times this year. I also compete in Croatia and Poland on the quad so I go off grid for 10 days. We never use EHU too so I go fully off grid.
All those saying 400w is OTT, do you have 400w or ever had? Maybe go EHU?
I would say I have plenty of stored power with fridge on it, kids charging bits and bobs, TV, stereo and amp on during the day. The power gets used.

I have had an email back from Ctek. They have said the D250SE can handle 400w BUT it wont do anything because it can only really process 300w.

I do question if I actually need the Ctek. The panels will keep the leisure all sorted and I could just run the engine if I need to. I just want to be able to charge the starter without starting the van if I can do it without too much problem. Is there another Ctek which would work to connect Leisure and starter batteries together? Forget going to the Ctek with the solar and I do not really need the alternator to do the leisure batteries either. A confusing one and I am not sure what the best way to go about it is, however I would rather do it all properly now rather then later.

With 400w of solar, my preferred option would be a dedicated mppt controller. You can get a £25 Votronic Battery Master or similar to trickle charge the starter. I have one built into my solar controller and it works great to keep the starter topped up.

 

[andys]

As an aside, we have a 4kW solar system on the house, peak output today is 240W, 0.5kWh for the day. It doesn’t matter what size system you have, no sun=no power. The argument for having more capacity to scavenge as much power on poor days is nonsensical.

Well I sort of agree with you and sort of not... Yes on a day like today where it’s grey and overcast you’re going to get sod all regardless of how big a panel(s) you have on yourmroof. But on a day where there are periods of sunshine in between longer periods of cloud, then a bigger array will undoubtedly be able to grab more of the solar energy while it’s available. It’s also worth sizing up a bit on what you need to allow for efficiency losses in panel, wiring and solar controller. I’ve seen people on here who say they’ve calculated they need 100W so have gone out and bought a 100W panel - well they’’ll definitely never see 100W from that. I have a 250W panel and the best I’ve seen (not in the UK) is 221W. This works out at 90% efficiency, which I’m very happy with, I’ve read that often 80% is about all you’ll get and I put this down to the high quality of the panel.
The best I’ve had in the UK, in near perfect conditions, is 212W which still works out at 85% so still very good, but it shows you that that 100W panel is likely to never see 85W in this country. Couple that with the sun frequently being blocked by cloud and it may then not give enough to cover your requirements. My 250W has been perfect for me, giving me enough power to run lights, diesel heater, fridge, recharging phones, tablets, cameras etc, recharging my emtb with an inverter and even running my electric water heater for showers - all without running out ever. I don’t even take a hookup cable with me any more. I’m certainly glad I didn’t opt for a smaller panel as I know that would have been a different story.