Need Electricity In Mozambique

[KevinGilmartin]

Hi all, thanks for the add to the forum. I have absolutely no experience or knowledge of solar or inverter systems etc. However, I do have a dilemma that Im hoping someone on this forum can assist with. 

We have booked a place in Mozambique during the December holidays but it doesn't have any electricity. Now during the day this isn't a problem as there is plenty to do and keep busy with without electricity. My concern is the nights, mainly the heat and the mosquitoes. I have 2 small boys who seem to have blood the mozzies love. I want to run 2 pedestal fans and 2 mosquito machines through the night, +- 8 hours (without the noise of a generator). So I went and bought an Ellies 1200w inverter trolley, now I have done some research and basic calculations and Im confident it will last through the night running the 4 small items. I also got hold of 2 solar panels (1 x 255w & 1 x 270w) and a 20a solar charge controller which Id like to use to recharge the batteries during the day. 

Firstly, is this setup going to work as i want it to? Secondly, how do I connect it up so the solar panels charge the batteries? I have attached an image of the unit I bought. 

TIA

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Since you've already bought the unit, one way to go about it is to simply test it. Indeed, I've also found that simply turning on a fan does wonders for getting rid of mosquitos. A ceiling fan works absolutely brilliant for this.

The inverter on that unit might be a modified sine-wave inverter (which is a fancy way of saying it makes a square wave with the equivalent power value), but I'm sure it will be fine for your intended use. Small electrical motors (like those in the fans you want to use) usually don't like this kind of power, and they buzz a little, but other than running a bit warmer there is usually no detrimental effect and it does not seem to cause premature failure, so a week away on holiday is going to be fine.

How to connect the solar panels? You'll have to open the box at the bottom. I don't know for sure, but as I recall it has 2 x 12V 100Ah batteries in there, wired into a 24V bank. You will then connect the battery terminals from your solar charger directly to the battery (I would advise that you put a 25A fuse in this line), and connect the PV modules to the other side of the solar charger. To make it easier, go to your local 4x4 place, or Outdoor Warehouse, and get some Brad Harrison connectors to make it easier.

Make sure the charge controller you bought can handle 24V.

Count the "dots" in your solar panels. If it has 36 cells, it's an 12V panel (actually more like 18V)  and you need two of them in series for a 24V bank. If it has 60 or 72 cells, it makes 30V and up and can be used on their own. Of course you need to make sure the charge controller can handle that voltage too.

I assume you bought a cheap PWM solar charger, but without knowing more, it is difficult to say.

[KevinGilmartin]

Thanks Plonkster, you make it sound so simple. I did get a 20a PWM solar charger with the kit.(pic below) Is it going to be enough to charge the batteries fully during the day? Or do i need one with a higher amperage? Another thing, is it an issue that the solar panels are different watts? (255w & 270w)

[Bobster.]

The weight is an issue here as well. I've a similar system at home, and the batteries make it very heavy indeed. 

Also, and going back to what Plonkster already said, try it ahead of time. Mine is not that noisy, but it's also not silent when discharging.

[___]

6 hours ago, KevinGilmartin said:

Thanks Plonkster, you make it sound so simple. I did get a 20a PWM solar charger with the kit.(pic below) Is it going to be enough to charge the batteries fully during the day? Or do i need one with a higher amperage? Another thing, is it an issue that the solar panels are different watts? (255w & 270w)

Right, this is where things get a little shocking. So if I assume that the battery arrangement in there is 24V (I have probably about an 85% chance of being right), here is how this will pan out.

Generally speaking any panel above 150W will be a 60-cell or a 72-cell module. You can roughly multiply the number of cells by 0.6 to get the open circuit voltage, so the panels you mention will make around 36V to 44V if you just measure them on their own. If you look at the spec sheet of that charger, that's within limits: The solar charger can handle up to 50V.

Now comes the interesting part. A solar cell makes its peak power at around 0.5V per cell, so if I assume you have 60-cell modules, that's around 30V, so you can divide 255 into 30 and get the peak charge current, which is likely around 8.5A (but you can look on the back of the panel, it's will show an Imax value).

Your batteries are however at a nominal voltage of 24V, and this is where the cheaper PWM controller loses out: The power you're going to get out will be 24 * 8.5 ~= 200W. So you're losing around 20% on the cheaper controller. But that does not matter as long as you get the batteries fully charged.

A 100Ah battery does not really want to be charged at more than 15A (around 15% of its capacity), so if you throw those two panels on in parallel, you should be below the 20A rating of the PWM charger and also within the 15A-20A recommended charge current for the batteries. So you definitely don't need more PV (again, assuming I guess right as to the battery capacity).

Now the remaining question: Will it charge fully in a day? That's difficult to answer, because lead acid batteries slow down towards the end, which essentially means you want them to be almost full by around noon already so you have the whole afternoon to float them. So you have maybe 4 hours to get 90% of the work done, but you only really have 5 hours of equivalent peak sunshine in Southern Africa, so I would probably not take them lower than 50% DoD because if you do you might not get them all the way back up again.

(I'm thumb-sucking most of this... your job to check my math ).

That means you have around half of your 2.4kwh available, or 1.2kwh (again,  I assume 100Ah batteries in there). If the kids sleep 9PM to 7AM, that's 10 hours, so you can afford to run 120W of stuff. Very crudely calculated.

Also, you have to lug around 100kg of lead batteries on your trip.

Edited July 16, 2019 by plonkster

[Guest]

24v system, I'll bet on that.
Yes, 100ah batts - the infamous "deep cycle" leisure batts. Perfect for this excursion until they need replacement in a couple of years.
+-32kg per battery x 2 = +-64kg plus the cabinet - call it 68kg - see idea below, dump the cabinet.
150w panels are scarcer than chicken teeth or very expensive if found - last I checked.

If it was mine, Victron MPPT and a 275w panel or closest one smaller than that - price being the driving factor - that can fit inside the vehicle. 
Don't mount the panel onto the roofracks - read on a 4x4 forum that they can crack when fastened to the vehicle's roof racks.
Mount panel on a frame that can be bolted / locked down when on the ground - as Moz has some issue at some place I read.

Another idea:
Install a alternator that can charge the 2 x 100ah batts AND the cars battery alternatively. Or check that the alternator can do it as is - some 4x4 shops have all the expertise with this.
Then connect the 2 new batts to a charge point somewhere in the vehicle to charge them both at the same time - some 4x4 shops have really cool stuff for that. 
Fit the batts in the vehicle as well as the inverter and run a extensions lead into the accommodation. Less chance of "redistribution of wealth".

So when the car drives the batteries are charged and if enough driving takes place daytime, no panel is required.