Advice on my first solar setup for overland travel

[babweupatree]

Hi there, I’d like to do a check on a solar build I’m working on - it’s for when I do overland travel and need to charge my film equipment.

2 x poly 275W solar panels wired in parallel

optimal operating voltage / short circuit voltage 31V / 38V

optimal operating current / short circuit current 8.88A / 9.45A

module efficiency: 16.8% *

parallel wiring gives:

opt operating voltage / short circuit voltage 31V / 38V

opt operating current / short circuit current 17.76A / 18.9A

* reason I list this as it’s a cheap panel compared to other poly/mono panels at a slightly lower efficiency.

Victron MPPT BlueSolar 100V/30A solar charge controller

OmniPower 12V 120Ah AGM/GEL solar battery

Now, at this stage as it’s a quick trip with not enough time to plan a more advanced charging system so I have put this together intending to charge the battery entirely using solar power and with upgrading the system in mind. Where I am going (Richtersveld National Park in South Africa) there is no shortage of sun and it will be intense so I’m not worried about lack of available sun. Richtersveld is near Alexander Bay and from this link I am looking at 9.3 sunlight hours for October):

http://home.intekom.com/teltec/sunshine.htm

My question is whether this system I have put together is disproportionate? In other words is the size of the battery too large for the available power the panels can deliver? And is the charge controller correctly rated? 100V/30A given the two panels in parallel produce a maximum short circuit voltage/current of 38V/18.9A?

After this trip I intend to add a second 120Ah battery for a redundant system and more storage capacity and also plan to add a CTEK D250SA and 120 SMARTPASS so I can charge the battery bank using the solar power and vehicle alternator. I do know i will have to probably have to take out the Victron solar charge controller and replace it with the SMARTPASS.

I was hoping to get some feedback on whether I’m approaching this the wrong way!

Thank you!

[___]

2 hours ago, babweupatree said:

2 x poly 275W solar panels wired in parallel

So roughly 500W power at peak time (you rarely reach the full capacity, especially when it is hot).

2 hours ago, babweupatree said:

Victron MPPT BlueSolar 100V/30A solar charge controller

That's a little small for the full 500W. I've done something like that before. I used a 100/15 controller with 600W of PV on 24V bank. It ran at 14.3 ampere and around 420W for hours on end. Got so hot I could smell it. It didn't fail in the two weeks I used it like that, but the controller did raise overcurrent alarms every now and then (which you only see if you monitor it). Granted, I had a 50% oversized PV array. Yours is only about 25% oversized, so it should be okay I think.

2 hours ago, babweupatree said:

OmniPower 12V 120Ah AGM/GEL solar battery

Don't know the precise spec of this battery, but assuming that it wants a good 15% or so of the Ah capacity to do an absorption charge, you want 18 amps or so of capacity. You have 30. That's about 25% of the capacity which is technically a bit much, but again you could probably get away with it.

2 hours ago, babweupatree said:

whether this system I have put together is disproportionate?

It's not too far out of wack :-)

2 hours ago, babweupatree said:

In other words is the size of the battery too large for the available power the panels can deliver?

If anything, it's the other way round, the panels might be a bit much for the battery, but again, it's acceptable.

2 hours ago, babweupatree said:

And is the charge controller correctly rated? 100V/30A given the two panels in parallel produce a maximum short circuit voltage/current of 38V/18.9A?

The 30 amps is the rating for the battery side. At absorption voltage (14.5V or thereabouts) and 30 amps, it gets you 435 Watts. In my experience, it will cap at slightly less than 30 amps, around 28.5 amps on the battery side.

You could even put the panels in series, as the controller will down-convert from the roughly 80V input to the 12V output BUT... usually you don't want the conversion factor to be more than 3:1 or so, so I agree that you should keep the panels in parallel. Use cable that can handle 20 amps at least.

The panels will run at 31V and 17.7 amps, the job of the MPPT is to find this optimum point and keep them there.

[___]

The more I think about this, especially if you're also going to charge with the alternator, you could probably drop the one panel and still come out okay.

The real question is whether 120ah is enough for all your loads. That's the first question you should ask. First you pick the right size battery. Then you pick the right size charger :-)

[pilotfish]

For long term camping 2 batteries is the way to go - but you are planning that anyway. Until then you have more PV panel than necessary but when the 2nd batt goes in the system will be well balanced (you are fortunate to have the space).

Have you considered this item; http://www.hcdpelectronics.co.za/index.php?page=product_categories&catID=14

I use the 30amp HCDP charge controller with 2 x Omnipower 120Ah batteries which charge via the alternator while driving and 1x 250w panel while standing (which I only add when camping). It does a great job of maintaining the batteries in both circumstances. 

[babweupatree]

Hi plonkster and pilotfish - thank you very much for your responses much appreciated! Okay, good that I can remove one of the panels as that's going to make it cheaper and easier to setup at last minute as I'll be doing the installation myself. 

Here are my loads - this is pretty much all the equipment I will be running over the course of a day:

DSLR chargers: 12Ah (4 chargers x 2.5 hours)
AA chargers: 6Ah (2 chargers x 5 hours)
Drone battery charger hub: 21Ah (4 batteries/1 hub x 5.5 hours)
Drone controller charger: 4Ah (1 usb charger x 2 hours)
Laptop: 6Ah (two hour charge time)
=============================
TOTAL: 49Ah
=============================

This is the maximum load I'll be drawing off the battery in the evening - some days most of the equipment will be used to the max so this is pretty much my requirements to make sure I'm covered on the equipment front.

I read somewhere that I should be sizing a battery that gives me 25% of 50% DOD - so the battery I should be choosing is 200Ah? Then I'm not entirely sure how long it will take to replenish this lost charge used to charge up the equipment (±50Ah).

pilotfish - that is a cool looking item - will definitely consider it as an option! For now I'm not going to bother with the alternator wiring up as it's a bit of a job and I want to test the solar system alone to see how it works out before I do further modifications. If I can get away with one panel that would be fantastic as it frees up space on top of my canopy and keeps some dollars in the bank!

 

[Chris Hobson]

On 10/4/2017 at 8:46 AM, babweupatree said:

2 x poly 275W solar panels wired in parallel

Victron MPPT BlueSolar 100V/30A solar charge controller

If/when you have 2 panels I would wire them in series rather than parallel. Panels in series will result thinner cables and greater efficiencies. As we approach summertime in the Richtersveld panels flat on your vehicles roof tilt is going to be close to ideal. Summer temperatures however are going to reduce you panels productivity to about 80% of maximum.

I would add 20% to your envisaged "needs". You are going to kick yourself if you travel to the Richtersveld and miss stunning photographic opportunities because you skimped on solar hardware.

[pilotfish]

 

2 hours ago, babweupatree said:

If I can get away with one panel that would be fantastic as it frees up space on top of my canopy and keeps some dollars in the bank!

I would stick with 2 panels, or 1 panel and alternator charging - and definitely 2 batteries.

If you have 1 panel and 1 battery you will from time to time have a poor solar day without adequate recharge, your batteries will soon get over-discharged and damaged which will ruin your trip.

[___]

3 hours ago, Chris Hobson said:

If/when you have 2 panels I would wire them in series rather than parallel

I initially thought the same thing. The controller has a Voc of 100V, and the two panels will only bring you to around 80V, so it is perfectly safe. But buck converters are generally happier if the ratio of input voltage vs output is between 2:1 and 3:1. It is difficult to say exactly, it really depends on the design of the particular MPPT, but this is what I was told back in the day. From 80V down to 12V is a bit steep, so leaving the panels in parallel might be the way to go.

5 hours ago, babweupatree said:

I'm not entirely sure how long it will take to replenish this lost charge used to charge up the equipment (±50Ah).

Depends on a lot of factors, but generally... the answer is not a good one for lead acid. If you look at it simplistically, and you assume that you're charging at noon (when the MPPT is running balls-to-the-wall 30 ampere), then technically you can replace that 50Ah in about an hour and forty minutes. But in practice, lead acids screw you over. As you go over 85% SoC, charging becomes less efficient and the current it will accept starts to taper off. By the time you go over 95% that battery only accept a few ampere and it literally takes hours to get from 95% to 100%. It's probably best to assume that it will take all day to recharge :-)