Solar PV Panels for my Shed

BadCharlie · 22-04-2014 9:45am #1

Hi guys,

You might be able to help me on this.

I need & want solar for my shed at home. At the moment I have 3 energy bulbs in there and I run them off my Marine 110AH 12v Battery. I also use my Battery to charge up the kid’s car which has a 7AH 6V Battery.

What I would like to do is fit a 100W solar to the shed Roof. I had a quick look around on Adverts & EBay but im not sure what is a good option & good value.

1. I would like it to be pre Built; I don't want to stick/glue/fit all those cells together.
2. I need it for lighting, Maybe a TV/Radio in the future & use it to charge things up.
3. I have an inverter all ready "€40 one so cheap, so cheap im thinking it’s no good?” It’s a 300w with peak at 600w "Lidl/Aldi".
4. I charge my 110AH marine Battery by connecting it up to my house every few weeks "heavy". Takes a good 6hours or so to charge. At the start of the charge it draws about 46w and then drops down to under 10w coming to the end of its charge. Not sure of the charge I use, as it was bought in Lidl/Aldi.
5. I might add another Battery to the bank, same type as before. My Marine battery is about 1month old at the moment.
6. In future I might add more Solar PV panels.

Would anyone have a link to what I should get? I was hoping to not spend over €200.

If you have any questions pls ask.

22-04-2014 11:25am

Is the Lidl/Aldi charger a 3.5A AutoXS? It's a piece of junk, I have one and it's dangerous. I've tried it on a few batteries in different places in their lives and it behaves badly on them all. The voltmeter is highly inaccurate, it doesn't hold float and it doesn't charge so much as equalise. I left it overnight once to find it in the morning boiling away with a 15.2v float going into a fully charged battery. CTEK is a better bet.

Are you using a 12v battery to charge a 6v battery or have you a regulator/charger between them? The 6v won't last long if there isn't. The most you ought to charge that is at 7.4v

I use one of these 150W panel for €200. Have a look on Ebay, last time I checked the going rate was about €1.20 per watt, but you'll probably find cheaper since somewhere.
You need a solar charge regulator as well any of these are quite good. 4mm diameter cable from the panel to the controller for a run under 10m and hefty cable from the controller to the battery.

22-04-2014 12:16pm

You have to be aware of system losses on voltage drop with long DC runs, industry standard is < 3% I aim for < 1% myself because I'm a pedant.

These are useful tools in calculating voltage drop.
Voltage Drop Calculator
Poxy AWG to Metric

As a rule of thumb I go 2 grades higher on all DC cable requirements to compensate for cable alloy, contact resistance etc.

BadCharlie · 22-04-2014 1:55pm

Did a little bit of googling and this is what i have.

Charger that i have used to date for my 12v or 6v Battery. Can do away with this onces i get my Solar up and running.
http://www.lidl-service.com/static/2844174/52513_GB.pdf

Inverter : used on my lights, charge the 6v Battery. Might run a TV/Raido from it in the future. Item might not be up to the task & can always upgrade it in the future.
http://www.lidl-service.com/static/6388825/61667_PL_HU_SL_CS_SK.pdf

Also use this, but EU with 240V & not 120V
http://www.p3international.com/products/p4400.html
This lets me know what an item is drawings.

I will do a bit more looking into solar panel on ebay when at home. Would a 150watt be over kill ?
My run will be short. Cant see it more then 5M at most.
Any web-link to the cables required ? or the spec of the cables ?

I been thinking of doing this for the past 3 years. And this is a good start & want to get the correct items & not have to rebuy a year down the road.

22-04-2014 3:18pm

I'd verify the output voltages of that Lidl charger with a reliable multi-meter and keep an eye on it. If you hear the battery boiling below "14.2v" then it's suspect. If you disconnect after charging then the risk is lessened, I'm dubious it'll achieve a full charge this way. There's no economy to be had with cheap chargers, it'll cost you batteries. If you are running solar as a primary then it's hardly required.

The inverter can't say, it may or may not last, wouldn't worry about it too much. If it breaks you know then to get something different. I'd screw down new leads onto the battery clamps rather than the croc. clamps, you'll get much better conductivity and replace the DC fuse for a 30A. I don't advise ever using the cig. lighter adapter...likely to melt the wiring upstream. Cig. lighter sockets aren't designed for 32A loads, usually you're lucky to get a 15A allowance with huge voltage drop and bad contacts.
If you want beefy power tools in the shed ever you'll need more batteries and at least 700W and perhaps an RCD for safety.

The kill-a-watt is an AC meter, you are talking about a DC system with AC abilities. That won't monitor charging or inverter inefficiencies. It'll under-evaluate your system consumption by ~20%.

Better off with an ammeter & voltmeter or a proper battery monitor...I'm still looking for an accurate battery monitor I could recommend the least inaccurate ones but they're very expensive.

4mm solar flex is pretty common most sellers of panels will stock it and MC4 connectors. I just use whatever I have to hand, mostly mains flex, welding cable and automotive cable, overspec. it and heat shrink it to change the colour if I can be bothered. Mostly I just pretend brown = red and blue = black.

Better off running 12v lights from a 12v source. Pointless running the inverter at losses to achieve the same thing.

Don't forget fuses/breakers.

Yeah 150W is probably overkill alright, 80W would probably suffice angled to the sun on a South-ish facing and no year round shading. Depends on how much you use it really but being a shed I'd expect 3 days downtime between cycles? Something like this maybe?
I think that bundled solar controller is junk though and I wouldn't touch the thing bar to chuck it into the scrap electronic salvage department, that's just my humble opinion though.
You'll probably have more of a problem with short-cycling tbh. I'm still looking for an automatic remedy for this, I think it's an Arduino solution, there's not a lot of voltage sensing relays on the market pertaining to this lesser publicised problem. Charging batteries that are higher than 90% capacity shortens their lifespan so an idle battery on a big solar panel gets a daily thrashing. Currently I just turn my module and solar reg. off when it's idle until the voltage drops to 12.5v and then I turn it on again.
Don't expect a lot late October to early March a wee 100watt would be lucky to produce 3-5Ah a day with reduced light.

BadCharlie · 22-04-2014 3:54pm

Thanks Liamalot for that.

I will look into the links more when not in work "work computer blocks them here".

Will ponder the solar spec also.

Have time & don't need to rush buying it. But do want to make my mind up in the next month. Good idea on turning on & off solar when battery is full. Have a big orange Multimeter must relearn how to use it again

.

23-04-2014 1:38am

Thought it worth a mention if you're going for circuit breakers over fuses ('cos they're easy to turn off and resettable and you can't lose them when you turn them off)

You need to get DC specific breakers (MCB type), AC versions are not suitable and will not protect you.

I like these they're good to 150V and 100% rating.

The thing to be careful of is a lot of these are polarity specific and break the traditional AC convention. The active live goes into the terminal on the bottom marked +, switched live out the top.
There are similar white versions available that only go to 60v iirc and some of these are polarity insensitive (no + marking)

They're quite neat, DIN rail mountable and you can fit 4 in a 3 unit standard domestic box.

For convenience I'd use one for the solar module, one for the solar controller, one for lights, one for 12v sockets, and additional for large loads.

In the case of "Which is more positive the solar controller or the battery?", the solar controller is the higher voltage and a current source however the battery is the greater threat in terms of available instantaneous current should the controller fail closed, so the battery is wired to the + contact.

Solar PV Panels for my Shed

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