Connecting 12V Solar Panel to 12V Battery: Should I?

[jabers]

I'm working on a project where I charge a 12 volt battery with a 12 volt solar panel. Links for the battery and solar panels are below. My question is how I should connect the two. The main thing I can find is that I don't want the solar panel draining the battery. I plan to put a diode from the positive terminal of the solar panel to the positive terminal of the battery. My first specific question is should I use a 1N001 diode or a 1N5820 diode or something else? The only problematic difference I see is the average rectified output current limit. For the 1N001 it seems to be 1 amp and for the 1N5820 it is 3 amps. The max output on the solar panel is 1.78 amps.

My second specific question is, should I be doing more? I have found several more complex circuits but I don't understand their advantages for my purposes. If I can do something to increase efficiency I would like to try. An example is directly below.

http://www.den-uijl.nl/electronics/solar.html

Solar Panel
http://www.solarpanelstore.com/solar-power.small-solar-panels.solartech.spm030p_bp.info.1.html

Battery
https://www.amazon.com/dp/B001DL7D1O/?tag=pfamazon01-20

 

[berkeman]

I didn't look at the links yet. You need to put a SEPIC DC-DC converter between the solar panel and the battery. Google SEPIC DC-DC Converter to learn more. Then tell us why you need this converter between the panel and the battery...

 

[OmCheeto]

I'm working on a project where I charge a 12 volt battery with a 12 volt solar panel. Links for the battery and solar panels are below. My question is how I should connect the two.

I've looked at your links, and you can hook them directly together with no intermediate circuitry. This does though require that you continuously monitor battery voltage such that you never exceed 14.4 volts.

The main thing I can find is that I don't want the solar panel draining the battery. I plan to put a diode from the positive terminal of the solar panel to the positive terminal of the battery. My first specific question is should I use a 1N001 diode or a 1N5820 diode or something else? The only problematic difference I see is the average rectified output current limit. For the 1N001 it seems to be 1 amp and for the 1N5820 it is 3 amps. The max output on the solar panel is 1.78 amps.

I discussed this in another thread. Full of experiments!

My second specific question is, should I be doing more?

That all depends or what you are trying to accomplish. If you want an unmonitored charging system, then your first link looks like a good start. Though I question the values the author uses for minimum and maximum cutoff voltages. I would cut off the battery at no less than 12vdc.

I have found several more complex circuits but I don't understand their advantages for my purposes.

We don't really know what your purposes are. A solar panel charging a battery can be replaced with a rock in your garden, if that is it's only purpose. If we knew more about what you planned on powering with the system, then we could be a bit more helpful.

If I can do something to increase efficiency

There are actually many types of efficiencies.

Your solar panel listed below comes out to $4.20/watt. You can buy solar panels for less than a dollar a watt. Economically, it would be more efficient to purchase a larger, more cost effective panel. Same thing with your battery. I paid twice as much for a battery with 5 times the capacity of the one you listed.

Solar panels degrade when exposed to sunlight. I would think it would be more efficient to shield the panel once the battery was charged, rather than simply electrically isolating it. I have 4 portable 50 watt solar panels. I keep them inside when not in use. Solar panels left in the sun, generally have a lifespan of 30 years. I expect mine will last 100 years or more. I don't take them out very often. But when I do, and battery reaches 14.4 volts, I throw a towel over them.

I would like to try.

An example is directly below.

http://www.den-uijl.nl/electronics/solar.html

Solar Panel
http://www.solarpanelstore.com/solar-power.small-solar-panels.solartech.spm030p_bp.info.1.html

Battery
https://www.amazon.com/dp/B001DL7D1O/?tag=pfamazon01-20

 

[davenn]

Hi jabers

the initial description of the charger circuit tells you about the diode and how they replaced it

the first 2 listed features are also really important.
in that you cannot just continue to "pump' power into the battery from the solar panel
as you will just cook the battery and kill it

was there anything else in the first 2 sections in that charger link you are unsure of ?

cheers
Dave

 

[berkeman]

I'm still too time challenged (translation -- lazy) to read the links. Is this some super solar panel whose output voltage stays at 12.7 volts on overcast days?

 

[OmCheeto]

I'm still too time challenged (translation -- lazy) to read the links. Is this some super solar panel whose output voltage stays at 12.7 volts on overcast days?

Nothing super required. That's just the way they work. The no load voltage from jaber's panel is listed at 21 vdc. My ≈20 year old panels, with no load, put out ≈16 vdc on a cloudy day, and ≈20 vdc on a sunny day. Solar panels are marginally functional, except when locked in a dark closet.

From my link, my 50 watt panels put out a maximum of ≈0.2 watts, on a cloudy June morning.

 

[sophiecentaur]

It totally depends upon what level of performance you want. If you pick a small enough panel to allow you just to connect it straight, then your battery may not charge fast enough to supply your load.
You first need to specify how many Ahrs per day you will need, then how much money you have to spend (or the area available for the panels). I have been toying with the idea, myself, in order to supply power for a fridge on my boat (sailing) without running the engine more than perhaps one hour a day. Getting the 'right' answer is hard, I think.

@OmCheeto
"marginally functional" doesn't run a fridge motor (lol). The open circuit voltage is of no interest if you want to take some current from a panel.
I would be interested in some details of your set up. What load have you been supplying over the 20 years? I'd bet you could get significantly better from modern panels (and for a fair bit less cost too).
There have been a lot of Bosch panels on the market, recently - going cheap. I am tempted but I have other jobs to do which are more pressing.

 

[jabers]

Thank you all for the replies.

You need to put a SEPIC DC-DC converter between the solar panel and the battery.

So this is a voltage regulator that can output a larger voltage than is imputed? I plan to use a 5v voltage regulator, 7805, on the other side of the battery to control a microcomputer. I also plan to power this 12v pump,

https://www.amazon.com/dp/B002XM5G70/?tag=pfamazon01-20

I don't plan on using the pump for more than an hour a day, probably much less, and the other things that need to be powered have a much lower current requirement.

Covering the solar panel is a great idea. I will definitely use that for the times when I know its not in use. However I do want to be able to set up the panel and leave it for a month or a couple weeks without watching it. This has been very helpful, I understand my issues a lot more. My main problem with the circuit I found is that I don't understand how it all works. Ill be going through it today but does anyone know what the separate section of the diagram is for? The one that says Vbat? The link is below.

http://www.den-uijl.nl/electronics/solar.html

Also should I use a DC_DC converter in between the 12v battery and the 12v pump or will the dc voltage battery output be consistent enough?

 

[OmCheeto]

It totally depends upon what level of performance you want. If you pick a small enough panel to allow you just to connect it straight, then your battery may not charge fast enough to supply your load.
You first need to specify how many Ahrs per day you will need, then how much money you have to spend (or the area available for the panels). I have been toying with the idea, myself, in order to supply power for a fridge on my boat (sailing) without running the engine more than perhaps one hour a day. Getting the 'right' answer is hard, I think.

@OmCheeto
"marginally functional" doesn't run a fridge motor (lol).

By marginally functional, I meant that with no load, the panel will float charge a battery on a cloudy day.

The open circuit voltage is of no interest if you want to take some current from a panel.
I would be interested in some details of your set up. What load have you been supplying over the 20 years?

I use them when and where I need them. I don't power anything in my house with them unless the main power goes out. Then I can power lights and my laptop via a 400 watt converter and 1200 watt-hour deep cycle battery.
Their most common use is to run bilge pumps in my boat, and keep the battery charged, as my outboard motor has no alternator.
I also used them once in an emergency when the alternator idler pulley on my vehicle broke off one day. 3 x 50 watt panels were sufficient to power the electrical needs of my car for the 13 mile trip home.
So there is no "set up". I can use one, two, or all three, depending on my energy requirements. (My fourth panel failed a few years back. Zero output.)

I'd bet you could get significantly better from modern panels (and for a fair bit less cost too).

I inherited my panels when my father passed away about 6 years ago. He was living off the grid somewhere in northern Arizona. I have been eyeing the newer panels though. I have a 16 foot cabin cruiser that I would like to power with solar. 6 x 250 watt panels would provide me with 2 hp and cost about $1500. I'm not sure how fast it will go, but I will soon be no longer in a hurry.

There have been a lot of Bosch panels on the market, recently - going cheap. I am tempted but I have other jobs to do which are more pressing.

The refrigerator is actually my next project. If I had a larger boat, I would purchase a Sun Frost refrigerator-freezer. Their smallest unit only consumes 140 watt hours a day, but is quite spendy, and quite large.

 

[OmCheeto]

Thank you all for the replies.

So this is a voltage regulator that can output a larger voltage than is imputed? I plan to use a 5v voltage regulator, 7805, on the other side of the battery to control a microcomputer. I also plan to power this 12v pump,

https://www.amazon.com/dp/B002XM5G70/?tag=pfamazon01-20

I don't plan on using the pump for more than an hour a day, probably much less, and the other things that need to be powered have a much lower current requirement.

Covering the solar panel is a great idea. I will definitely use that for the times when I know its not in use. However I do want to be able to set up the panel and leave it for a month or a couple weeks without watching it. This has been very helpful, I understand my issues a lot more. My main problem with the circuit I found is that I don't understand how it all works. Ill be going through it today but does anyone know what the separate section of the diagram is for? The one that says Vbat? The link is below.

http://www.den-uijl.nl/electronics/solar.html

It sounds like your system will work. Unfortunately, my electronics is very rusty, and I can't help you with this circuit. My circuit would be very rudimentary, almost Neanderthal in comparison. If I were not concerned with panel degradation, I would simply hook up a 14.1 volt zener diode:

The USB thingy being replaced with your 12v battery.

Also should I use a DC_DC converter in between the 12v battery and the 12v pump or will the dc voltage battery output be consistent enough?

You can hook them together without a converter.

 

[sophiecentaur]

If you really want the most out of your PV panel, you need to buy (or make) a Switched Mode Maximum Power Transfer regulator, which arranges the current out of the cells to be optimal and charges the battery AQAP. But they can cost a lot to buy.
In it's way, engineering low power supplies is quite a sophisticated business.
I really wonder whether it's is worth while 'scrounging' a small amount of energy from PV cells during low light periods. Whatever you do with the volts, in order to put (some) charge into a battery, the actual VA produced is very low. The standard way to optimise performance is to use MPT, which does nothing in low light. Also, intelligent regulation will maximise the life of your storage battery; they really don't benefit from long periods of overcharging.
This maintenance season, I looked at my Rutland wind turbine and replaced the bearing. You get low levels of AC at very low rotation speeds but the rectifiers impose a floor on the speed at which any current is available, then it requires some volts in hand to be charging the battery. I was considering some sort of Joule Thief circuit to obtain some power out at low wind speeds but I reckon the same thing applies as with PV: it's very much diminishing returns and (obviously) it takes 10 hours of low speed wind to do the same job of 1 hour of higher wind (or 10 minutes of engine). In my case, if there is no wind, and I am on the go, I will be using the engine. A Yachtie may point out that a whole day's gentle sailing with a light wind will not be turning the turbine significantly (triangle of velocity vectors and all that) but I am not a blue water sailor so that situation is very rare.