Backyard Aquaponics
A place to discuss aquaponics

Apparently lead acid batteries discharge a bit when they are just sitting around.

And there are also losses when you charge one.

I'm looking at a solar design for a very low power system, and was wondering if there was a disadvantage to running a big battery.

I already have a 200amp hour deep cycle battery, but I want to power the system from as small a solar panel as I can and I'm wondering if I would be better off with a smaller battery due to self discharge, and also losses in charging.

1. Are there losses in charging that go up with larger batteries?

2. do larger batteries self discharge at a faster rate than smaller ones?

3. anything else that you think it is that I'm really trying to ask

Once the battery is floating you wont have any troubles. The current draw from the battery should fall fairly close to 0. (Maybe 0.1A or so)

If telepower can run on solar then i am sure your system will work Just remember to size you solar panel to run you equipment and still have enough excess to charge the system.

so if I'm trying to run a system on a really low power budget, charging a large battery from a small panel wont have any greater losses than charging a smaller battery?

I already have the battery, but I want to get the smallest solar panel I can get away with, so don't want to waste any collected power. As a result I'd buy a smaller battery if that was going to be more efficient. My battery I have now is total overkill for the kind of power budget I'm looking at, so I think I could get away with a lot less battery if it would be better to spend the money on solar cells.

I dont imagine the additional losses you would see in a bigger battery would even be noticed. If you already have a bttery use that for sure. The losses certainly wouldnt justify buying a new battery. Assuming the one you have is in decent health that is. I would imagine that the ability to hold the battery voltage higher on a bigger one would far out weigh any losses you would see internally in any case.

I think you would be better of with the biggest battery you can. You want to run as long as possible without the solar cell. If you have a few cloudy days in a row the last thing you want is a small battery not having the capacity to last.

and this...

when I'm trying to work out my solar cell requirements, does a 50watt panel supply half as much as a 100 watt one. ie is the relationship linear with losses in things like charging, and inverters? Or is the loss a %

ie will I just need to work out a loss budget, + a use per day budget + a reserve budget for how much solar panel I need, or are the losses twice as big for a system twice as large?

ok thanks

There are a huge amount of factors that will dictate the amount of power you get from you cell. Things like where in SA you are, the temperature of the day, shade etc etc. Shade is a big one because unless you have some of the newest tech available in panels, a small amount of shade will significantly reduce the amount of power produced. Google will tell you more but a quick search i just did had this pop up which might help you get started.

http://www.solarchoice.net.au/blog/how-much-energy-will-my-solar-cells-produce/

It is only basic info and for domestic PV setups, but will give you an idea. When you are looking at sizing up your system you will need to look at it over 24 hours in winter (shortest daylight hours).

One thing you could possibly do to reduce your solar panel size is make a simple solar tracker with a picaxe

I'm all over that

I've always been interested in making a heliostat and is going to be a "Thing" for 120 things in 20 years at some stage. In fact it was nearly the second "thing" after aquaponics, but I got distracted, I think by solar water heating.

I thought I'd make one originally to put some light into my office, then as extra winter light for the grow house, and lately as a solar tracker, or even to add light to a panel (though heat is a concern)

You will lose approximately 0.5% of the battery capacity per day due to self discharge.
So, yes, the bigger the battery the bigger the losses.
If you had a small panel and a big battery your panel would not be able to charge it.

Also bear in mind (when sizing the system) that you are unlikely to get the full claimed Watts except under absolutely perfect conditions, so aim higher with the Wattage of the solar panel requirements.

I have a very small panel (unregulated), 2W and about 24 volts unloaded.
You have to be a little careful with lead-acid when they are fully charged, you should trickle charge at 13.8 volts which with an unregulated panel you can't do.

Yep you will definately need a regulator. I have seen kits in supercheap etc that come with the panel and regulator. Although i imagine you could have it cheaper elsewhere.

This website might give you a better idea as to the self discharge rate of you particular battery.

http://www.windsun.com/Batteries/Battery_FAQ.htm

Hmmm re: 0.5%

more decisions to make. I hate trade-offs. Capacity vrs efficiency*.

Can I just create a situation where I only need to pump say 1/4 of the time, then if the voltage is high, dump the power by pumping more? I can do that with a PICAXE, I think the 14 pin chips have an internal referance voltage thinggy that you can compare other voltages to, so switching on the pump should be easy enough if the battery is charged, so I can dump excess in a positive way. (presuming I get the numbers right and actually have excess)



*What Would Brian Boitano Do?

Thanks...so much to learn

Absolutely.
Or.
So many options..
Charge a set of NiCads for an overnight LED growlight, etc. etc. etc.
I want to make an underwater thingy that wanders around the tank at night disturbing settled solids and getting them circulating again, like one of those auto swimming pool filter heads, all solar powered of course

And, yeah, many of the bigger PICS have multi-channel A to D's but you'll need a potential divider to measure 13.8V.
I know how much you love potential dividers

I wouldnt go out and buy a new battery. If you bought a 100AH battery you would only get at best a 0.25% saving. You will have bigger things to worry about than that 0.25% saving if you are running your power system that tight. Aside from all that wasted energy in producing the new battery



That would be a far better option for excess power. The last thing you want to do is use all the power in your battery one day and have a overcast one the next.