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Solar system power help requires...

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Soon I am finally thinking of buying solar system.

Not that big only 600w max.

So I was thinking of buying 4x 150w panels.

I am confused how to connect them.
Series or parallel... I have researched a lot on this topic but in the end I always got confused.

The next thing is charge controller.
One costs $30 the other around $200
Pwm vs mppt

I will be using 12v 150 ah battery which requires about 15 amp current to charge.

If I were to connect my PV in series, that would give me around 18.9v x 4 = 75v with 8 amps.

Now if I were to use this setup with mppt controller.. Would the charging current be enough to charge my battery? How much current would I get anyway at peak sun hours?

And if I connect PV in parallel I would get 12v and 36 amps... I know it would require thicker cable.. But if I were to connect this setup to mppt then how much output current would I get?

And how much current if connected to pwm cc.?

The load I will be running is mostly ac so I will be using DC to ac inverter 230v 50hz. I know there will be losses in the conversation that is why I want to squeeze every last bit of power the solar PV can offer.

So basically I am asking to to tell me what can I do with my 4x 150 w panels?

Any detailed explanations would be appreciated as long as it is understandable.

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Rich D.

Active Member
1) The manufacturer of the charger should provide the needed information. If they are not forthcoming with the solar panel data required, maybe they are not so good with the solar panels themselves?
Maybe you found a great deal or have them already. So #1 wouldn't help.

2) Have you considered series/parallel wiring? This is where two cells are connected in series, and then it is parallel connected to the other two (which are also connected in series). Using the numbers you gave, you'd get 37.5 volts and 16 amps. The voltage and current should still be pretty good at non-peak solar conditions. You might still get say...20 volts and 10 amps early/late in the day. At peak, 37.5 volts should be plenty to charge a 12 volt battery!

Depending on the charger, parallel with all panels may be the most efficient. A charger should limit the current and drop the voltage to the battery, and a cheaper/poorer design may just use resistance to dissipate the excess voltage/current. I imagine the better charger could be much more efficient since they *might* have spent extra money on components and quality and used an efficient switching system.

Also, I believe the spec calling for 15 amps to charge is a maximum allowable current. Anything more than that can't be done or would cause damage to the battery. I never heard of a battery that can't be trickle charged - or charged with a lower current for a longer time period. In fact that is usually the most reliable way to charge a battery and preserve it's service life. Of course with a 150 AH battery, 15 amps is kind-a' like a trickle charge in that it is a relatively low current. Roughly, that would take more than 15 hours to get a full charge, possibly a lot more since the sun isn't often stationary at high noon.


Thanks for your reply...

I was thinking of going with all panels in parallel and using a 12v 40A pwm charge controller.. It is my first system so i don't want to spend much on it..
Considering pv's are 80% efficient, so with 600Wp i should probably get about 450W to 500W at peak sun.

450/18.9 = 23 amps in 12v 150ah battery and my inverter will be connected to it during day time to run ac load...

I could also wire them in series and using mppt charge controller, output from this is going to be around 14 or 15v @ 32 amps and it would take a 40A or more rated charge controller to handle it. Only this mppt charge controller is going outside of my budget. I don't want to spend that much for this test setup.. maybe in future..
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Well-Known Member
Set 1 of your solar panels outside is full sun test it with your volt meter. It will probably be about 17 to 18 volts DC most are. Loaded it will be about 15 to 16 volts connected to the battery. Lead acid car batteries are self regulation the deader it is the more amps it pulls, the closer it gets to full charge the less amps it pulls. I don't know what battery you have if it is not self regulating then you need current limiting. Test your solar panel on a cloudy day also on a very dark over cast rainy day to see what power reading you get.

I would not wire solar panels in series unless you plan to connect enough to run a device at a different voltage. My solar panels are 17.5 volts 7 in series will run a 100 watt 120 volt light bulb all day with no battery. I can run 1 light bulb in my work shop all day when the sun goes down my light goes out. Everything runs on AC light bulbs are the only thing that will run on AC or DC.

I have not found a really good use for my solar panels yet. I have 9 panels that produce 135 watts at 17.5 volts DC.


Well-Known Member
Most Helpful Member
A panel that puts out 18 to 22V open-circuit will have a Maximum Power loaded voltage of around 14 to 15V, which is just about the charging voltage for a nominal 12V lead-acid battery, so buying a solar battery charger regulator that claims to be "MPPT" is totally a waste of money. You do need to have a "regulator" between the panel(s) and the battery to limit the voltage as the battery reaches full charge. Note that charging voltage is typically ~14.6V during charging, and only ~13.5V during maintenance (floating) after the battery reaches full-charge. Solar battery chargers are programmed to do that, independent of being "MPPT" or not.

The first thing to do is to look at the data sheet for your battery to determine what is the maximum allowed charging current for that battery. Then buy just enough panels to produce no more than that maximum current when the panels are wired in parallel. Fewer panels will just take longer to recharge. More panels than are implied by the maximum charging current acceptance of the battery just overheat and damage the battery during charging...
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