General off grid system questions from a newbie, input apprecaited

cdn_downunder · November 2012

I've been super impressed by the knowledgeable, on topic advice given on Wind-Sun.com so I thought I'd throw my problem out there and see if I could tap into the experience and advice of your members. Thank you in advance for your assistance!

I'm in the process of designing an off grid camping setup for short (3-4 day) and extended (2wk+) camping trips here in Australia.

As we have an abundance of solar energy here, solar will be my preferred recharge method, with methanol fuel cell in lieu of a gen set as my backup, once prices get a little more reasonable here!

My typical usage is pretty standard, using the system for the following:

Occasional charging of:
UHF radios
iDevices
NiMh batteries for flashlights, pumps etc (via 12v charger)

Powering of:
Waeco 12v fridge/freezer (primarily acting as a freezer) CFX40 model
Small iPod speaker doc via 12v
limited LED lighting
possibly an inverter for other random items (see below)

Possible use case: recharging of electric bicycle / scooter which uses either 24 or 36v ~12ah batteries (2 or 3 in series). Not sure if I'd need to use the inverter and AC charger for this, as the charger / controller gets a bit complex with mixed voltages unless I charge the batteries individually - any thoughts?

I have a 120w (3x40w folding poly cell) solar panel with integrated PWM controller

I'm looking to size the right battery system and decide whether to buy a commercial system, which all have their pros and cons or build my own.

1. Can I use 2x6v batteries in series if I build my own, as 6v high AH batteries appear to be much more affordable than 12v

2. What is the best way to charge the 24v or 36v scooter? What sort of inverter would I need if AC is the best route (charger is 4amp or 8amp)?

3. Are Lion batteries worth considering on a performance vs price against AGM batteries?

Ultimately I'd like to add an EFOY methanol fuel cell to the mix for when the load is high or the sun is not shining, but the $8k cost down here is out of my budget for the moment. This will mean that my battery requirements are going to be higher for the time being (with no fuel cell, only solar to charge them) than they will be ultimately, so a pair of smaller batteries might be ideal (I can drop one later, if I find it's not required).

Commercial systems I've been looking at running 60ah - 90ah seem to be a good match for the 120w solar, but are incredibly expensive for what you get - thus I'm considering rolling my own...

Many thanks for your time!

Cariboocoot · November 2012

Re: General off grid system questions from a newbie, input apprecaited

Welcome to the forum, eh?

(Refrain from making terrible Canadian joke.)

What can I say? You need better definition of your loads, otherwise you'll either buy far too much stuff or run out of power. How are you fixed for back-up should the power run short? Is this a permanent installation or portable one?

What can I answer?

1). Yes, two 6 Volt batteries in series is quite typical power source. Often very economical. Consider this. A couple of 220 Amp hour 6 Volts will supply a bit over 1.2 kW hours and would need around 350 Watts to recharge. This may be quite flexible as your system looks to be mostly DC and you do get a lot of sun down there. Why aren't you here freezing your putine like the rest of us?

2). Scooter power at 8 Amps @ 120 VAC is a lot of Watts: 960. How long does such a charge take? It's a whole 'nother situation.

3). Lithium Ion batteries are probably not practical at this point. Others may have a different opinion of this. AGM's are great, but a bit new-user unfriendly.

$8,000 would buy you a lot of solar power at today's prices. I think you're right to wait on that fuel cell.

Small solar (120 Watt range) is expensive per Watt. 90 Amp hours isn't much power either: about 540 Watt hours max.

newl · November 2012

Re: General off grid system questions from a newbie, input apprecaited

Cariboocoot wrote: »

Why aren't you here freezing your putine like the rest of us?

Because unlike you Canooks heading into winter, we're heading into lovely summer. (disclaimer, I know all about winter...I used to get lake effects from the Great Lakes and didn't enjoy 40 below).

niel · November 2012

Re: General off grid system questions from a newbie, input apprecaited

coot is right that you need to define your loads with real current draws from each item and figure in the time for each item over the course of a day (24hrs) because the solar will be called upon to deliver the whole day's power needs to the batteries in around 5hrs or so. the actual best battery arrangement will depend on the total ah you will need over 24hrs and then that will be multiplied by at least 2 because you never design to go more than 50% dod on batteries.

the electric bike could be done with either an inverter and go through an ac charger or have a separate solar array with controller to handle the odd battery voltage. that would be a small array as far as watts go, but you'd need to be sure of the voltage on the bike to know what you may need in solar equipment there.

you must've been in the northern area of the lakes as i'm near pittsburgh and it doesn't get to -40 here.

edit to add-duh he said canadian so that last statement of mine was dumb. sometimes i read, but don't see.

cdn_downunder · November 2012

Re: General off grid system questions from a newbie, input apprecaited

Thanks guys,

I'll do some more work on estimating the load. The scooter has a 24v charger at 4amps (240v AC down here).

It's a portable system for festivals and camping, so I'm limited in the amount of solar panels and batteries I can transport, thus the fuel cell option when it's affordable.

Come back to you soon with more info.

Thanks again.

General off grid system questions from a newbie, input apprecaited

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