Understanding solar panels for use on van.

[HappyHippyDad]

Evening all..

Apologies if this is a bit basic. This is the first post I have done on the solar forum as I just do domestic electrics, but i fancy putting a solar panel on the roof of my van so I can have 2 lights in the back (low powered - haven't really looked so dont know the wattage) and also a 150W inverter for when I need to charge up my power tool batteries or the MFT.

I believe a 100W panel will give me 425Wh (based on 5 hours direct sunlight and 85% charge controller efficiency).

If my battery is a 12V / 105Ah then it will give me 1260Wh.....

so does that mean it will take 1260/425 (i.e 2.96) days to charge it fully?
Does this seem about the right size panel and battery(Ah) to go for or should it be a larger panel or smaller battery?

Thanks all...

Ps.. I'm also a bit unsure if the circuits need to be fused when they come off the battery? Its all a bit confusing compared to 230V!! :smiley2:

 

[Octopus]

Have you perused any canal boat magazines - I noticed a lot of barges now have panels on them.

 

[HappyHippyDad]

Have you perused any canal boat magazines - I noticed a lot of barges now have panels on them.

No, just been scouring the internet Murdoch, but canal boat magazines are probably a good idea.

 

[Worcester]

solarfred's your man for this stuff

 

[Gavin A]

you don't want to let the battery go down below about 50% charge at most, so if you actually need 1.2kWh storage, then double the size of the battery.

A 100Wp panel might do for what you're thinking about, but not if you intend to use it for anything more than a bit of lighting, and back up battery charging, at least not outside of the peak of summer usage / sunny days.

 

[HappyHippyDad]

Its only a Renault trafic SWB so 100W is probably all that will fit on, and 'yes' thats all I'll be using it for Gavin. I dont really 'have' to do it, but it would come in handy and its quite exciting the prospect of doing it (and learning about it)!

 

[telectrix]

fit a wind turbine instead. even with no wind, as you drive, it will generate. but steer clear of low bridges.

 

[amlu]

get a charge controller too, it will prevent battery getting too much discharged/charged... good one will show how much power you have left too

 

[Robotstar5]

I was looking for a system to charge the leisure batteries at the stables and found Photonic Universe to be well priced for reasonable quality gear.

 

[Gary K]

I was looking for a system to charge the leisure batteries at the stables and found Photonic Universe to be well priced for reasonable quality gear.

I see!.... that's what they mean by a cavalry charge....

 

[HappyHippyDad]

Thanks for the replies chaps but still a bit confused about the maths if anyone fancies explaining it?

I expect it will be x2 16W lights used for 1hour p/day and a 150W inverter (used just to charge power tool batteries and MFT).

My 2 real choices with the site where i plan to get the solar kit (12V Solar Panel Kits) are whether to get the 55Ah sealed battery or 105Ah flooded battery???

As for the maths:

I believe a 100W panel will give me 425Wh (based on 5 hours direct sunlight and 85% charge controller efficiency).

If my battery is a 12V / 105Ah then it will give me 1260Wh.....

so does that mean it will take 1260/425 (i.e 2.96) days to charge it fully?

Also....

100W (solar panel) ÷ 12V = 8.3A

Meaning this panel generates 8.3A p/hour, so ....

over 5 hours of sunlight I get 8.3 x 5 = 41.65Ah

charge controller at 85% efficiency makes it 35.4Ah in a day,

So does this mean the 105Ah battery will take 105/35.4 = 2.97 days to fully charge?

Just seems a coincidence that they are both the same figure (i.e 2.96 and 2.97) so i thought I must be on the right track although I'm starting to think that I'm just confusing the matter and should just decide between a 55Ah or 105Ah battery!!??

 

[Richard Burns]

You have the theoretical maths about right, if you have 5 hours of direct sunlight each day then the battery should recharge from flat in about 3 days.

The practical experience is that most days in UK are not uninterrupted direct sunlight! If the day is overcast then your solar output will drop by about 80-90%.
The angle of the panel on the roof would mean that most of the sunlight would impinge at an angle and again reduce the output.

For solar panels supplying batteries you really want to plan for a long period, say in the winter, where the output is low and still be able to use the power you require without flattening the battery.
Ideally you would want the system to be just topping up the slight loss of charge from use rather than trying to recharge the battery from say 50% charge as this would not be practical to implement unless you had a weekend to recharge without power use and woudl redcue the life of the abttery, even though leisure batteries should be designed for this usage.

The primary plan would be to minimise the use of power from the system.
You want 2 x 16W LED lights, this is a lot of light for LEDs, however by good positioning of say four 5W lights would you be able to manage? This would reduce the power usage from 32W to 20W. Even better would be to have a single 5W light that you could position, say on a magnetic base, to where you need it at the time.
Using an inverter to charge mains power tools can use more power than you expect because of losses in the inverter so try and plan to avoid using this if possible. If you were charging at a charger output of say 2A then this could equate to a drain of about 45A on the battery and it would not take long to drain the battery.

Also plan in battery replacement costs as this is a significant factor.

Overall it can be difficult to have a system that is suitable for high power use, however if you can have a small drain on the system and a good battery capability then it is possible. Probably the best way to find out is to build a system that can be modified if required and try out the things you expect to use and see how the system fares, upgrading as necessary; probably not very scientific but neither is the weather!

 

[HappyHippyDad]

Very useful as ever Richard, thankyou.

I probably dont really need to do it, but I just like the thought of having a bit of a dabble and a play with something like this on a small scale!

Thanks again,

I'll let you know how it goes when/IF I end up doing it!

 

[Richard Burns]

I did a similar thing running a 36W pump from a 40Ah battery and 30W solar panel through a charge controller, the battery slowly loses charge over a year and the panel is not very well set up for sunlight, but it has worked in general for the last four years or so. Two pump changes and one battery change so far.

Go for it and see what happens!

 

[solarfred]

You will never get the theoretical numbers so no point in planning on this basis. You need to work on averages and based on winter if you are wanting this for 12 months use. An accepted formula is 2 hours sun per day with a 90% loss through the panel. Then add in the losses via the battery and inverter and cabling. (maybe 80%)
The 100w panel will give you say 18v * 5 amps in full sun in cool conditions but trouble is panels warm up and the output drops so your maximum possible is brief.
Solar is great for intermittent use so you should be able to put this together easily. On my stable projects I use tubes for each stall lighting and maybe a bulb for the feed room as every watt saved is precious. Use a COB bulb for really effective output in a small space. I get E27 fittings so standard batten holder is pennies. No need for fancy kit or prices just results but the solar panel needs to be well made so it lasts 30+ years not 3.
For 32 watts * 1 hours per day I would get a decent 55ah sealed battery which is compact. The bigger the panel the better as said above you want to try and get as much service from the panel alone as the battery is only there for reserve back up on the bad days.
If you are talking about lighting the van inside then a 16w tube will be plenty. 5 watt spots are more directional as maximum angle is 120 degrees whereas tubes are 180 and can be adjusted to suit. (no glass)
You need a fuse from the battery feed to protect against a short which may unload a huge amount of power instantly. Size it for the system cabling.
No need for a fuse from the panel feed.
The inverter may need to be pure sine wave to run your tool chargers (they can be a bit funny about these) and over sized as the inverter needs to be well capable of handling your maximum load. I have started to use UK sourced inverters as they are a decent price and top quality up to 500watt. Beware of Ebay units as they are likely to be not capable of the maximum power advertised. Guarantees will be flakey.
If you average usage is covered by the combined daily solar power and the battery reserve it is a no brainer as it will work.