Caravan solar system

[Diggerdude]

I have been researching what components to get for my caravan solar system over the last few days and jeez can it get complicated! Since getting my satellite which has a receiver running of an inverter I have been regularly running my battery out. So have decided to do a complete redesign.

My current system is pretty basic-
- cheap 120w folding panel ( the output seems more like a 80w )
- built in charge controller ( have found the same model on bay for $10 )
- 100ah AGM battery ( that I have killed from flattening daily for last 12months )

My power usage is
- a Waeco CR110L fridge
- satelite receiver through a 150w inverter
- a 20" led 12v tv
- led lights
- 12v iPad charger
- occasional laptop and printer through the same inverter as above

From the load calculations I have worked out I need about 480w of solar panels just to keep up :8

There has been a lot to consider including
- cheap panels sometimes fib about there wattage and don't have required diodes etc to stop back charging
- some regulators/charge controllers are $20 and similar looking ones are $500?
- system voltage 12 or 24v
- required battery bank size

After much arguing with myself I have decided on
- 3 x 200watt 12v panels with built in diodes
- Morningstar 45a MPPT charge controller
- 6mm2 wiring
- 2 x 100ah AGM batteries

I still am not 100% sure so if anyone can contribute advice/suggestions it would be appreciated. I am pretty sure I have the panel wattage correct bit other factors could be-
- do I really need a $600 controller or will the $100 ones be good enough?
- is it better to wire in serial or parallel, and wire size?
- is my battery bank big enough?
- will mounting the panels flat on my van roof reduce there output too much?

Looking forward to hearing what the Prospecting Australia brains trust has to say.

DD

Ps. My Honda 2.0i gennie has also died after only two years which Honda tell me is due to it being worn out from over use so not covered by warranty! So instead of forking out another $2000 I have been looking at these cheapies on eBay to replace it. I could get a new one of these every twelve months and its still cheaper than the Honda.

http://www.ebay.com.au/itm/BBT-Inve...mping-Fishing-Caravan-Pure-Wave-/251050407066

Any thoughts on this also

 

[AU Fever]

DD, this is one area that I do have a lot experience in so hopefully I can help.

Firstly, I always recommend that you can run two battery banks. One bank is being charged by solar and the other is running your loads. Why? Because batteries don't like being charged and discharged at the same time. This means you have to swap them from charge to load and vice-versa every day, but your batteries will last twice as long if you do.
I also recommend flooded lead-acid batteries over AGM's as you can maintain them better. "Maintenance free" batteries are designed for you to replace them every 3-5 years, flooded lead-acid will last 15 years if you take care of them.
With batteries you pretty much get what you pay for, so try and get the best ones you can afford. Generally the heavier they are, the thicker the plates are so if you have to decide between two brands choose the heavier one.

When I size an off-grid solar system I work from the load back to the panels. I also recommend running 12v systems, as they will charge better with solar. It's and impedance thing, which is a bit technical to describe.

Looking at you loads it sounds like your not going to pull any more than about 250w peak - given your 150W inverter can't deliver more than 150w , the fridge is 2.5Ah/h (30w), tv & LED lights about 70w. You won't always run at peak power, but to give you enough to not kill the batteries I usually I size a system at 50% of peak - 125w in your case. So you need enough battery to run 125w for approx. 20 hours. This calculates to about 10A @ 12.5v. 10A for 20 hours is 200Ah. So I would recommend a pair of 12v 200Ah batteries (twice your calculations)

Next is the panels. With those batteries, you'll want to fully charge your batteries to 15.3v each day to prevent them sulfating and reducing their life. Assuming you will average 8 hours of GOOD charging each day you will need panels that can deliver 25A (200Ah/8 hours). 25A x 17.5v (panel load voltage) = 437 w so go for 450w of 12v panels.

The last item is the charge controller. Now since the max output of your panels will be 25A, the Morningtar 45A is a bit of over-kill. You only need a 30A model. Outback and Xantrax are good and will give you many years of fault-free service. Alternatively, I am part owner of a company that sells battery chargers, including solar for off-grid. If you are interested PM me and I'll send you a link to our web-site or provide you with a quote. (Don't want to advertise here without asking Nugget first)

I hope this helps DD, feel free to ask any questions and I'll be more than happy to help out.

Au

 

[Dogmatic]

What a top response to a technical question. I am sure that this post will be viewed by many in the future as they work out their solar systems.
Well done AU Fever and thanks for sharing this info.

 

[backcreek]

Hay DD,
I'm no expert on this but from what I know from helping my mate set up his solar system on his off grid weekender/farm house I think you'r in the ballpark.


The batteries need to be deep cycle and balanced to your load ie you need enough storage to run all your gear at least overnight without hitting the minimum cut out voltage on you inverter plus a bit.
This then dictates the size of the cells you will need to be able to recharge in a reasonable time.
As far as the number and size of the panels compared to your estimated load I think 20 to 50% more would allow for cloudy days and quicker recovery after heavy discharge/use.

You also have to take into account your pattern of usage, if you use power during the day this will increase your recharge time.

My mate has an 8000 watt inverter with a big battery bank and he needs to turn it off when not in use to allow the batteries to recharge in a reasonable time frame as he only has 400 watts of panels.
This is enough to charge his large battery bank during the week when he isn't there. Your requirement will differ from this.

We also set up a 200 watt wind generator to supplement the solar panels when overcast. You may want to have a look at those as well, more bangs for the bucks.

As far as the tilt on the panels goes it is obviously better to have them facing directly towards the sun. They will work laying down but the output will be significantly reduced especially in winter when the sun is low in the sky. I have seen panels mounted on hinged stand up frames on the top of vans with a push up bar inside the van.

Have a search on the net, I'm sure there are some calculators which can spec' a system for you after you enter all your loads etc.

Hope this helps

Cheers
Mick

 

[froghoppers]

Thanks AU Fever - very informative. We too are doing our research as to the best set for our van.