Amps Amps Amps

[MikePower]

So I am putting together a solar system and I am making 18v 60watt 3.5amp panels. I am trying to figure out if I should hook them up in series or parallel!

I understand what each does, increase amps vs volts, but I dont understand how I should calculate for the conditions.

I read that you need to produce 1.5x more volts than what you are charging. If this condition is true then I shouldnt need to hook them up in series. How does increasing my amps affect my charging potential? I guess on the flip side, when do I want to increase my voltage?

Sorry if these are basic questions!

[EnviroNut]

yes, the solar panels need to be a higher voltage than the batteries so the current flows from one to another.

in regards to the amps affecting the charging, it really doesn't.

Watts = Volts x Amps

In your particular case, we assume (3) 60 watt panels @ 18V and 3.5Amps, so we have:

3.5 Amps x 18 volts = 63 Watts each x 3 panels = 189w total panel output

Regardless if the solar panels are hooked in series or parallel, they will still only produce 189w. It's the job of the charge controller to take the incoming wattage from the panels and use that wattage to properly and efficiently charge the batteries.

when it comes to a solar panel system, the higher the voltage, the more efficient a system becomes. Also higher voltage systems can support greater loads with less wiring (and wiring protection) costs.

And to touch up on charge controllers. There are two major types of solar charge controllers:

PWM (Pulse Wave Modulation--basically On/Off/On/Off--The simple (less costly, less capable, typically used on smaller systems)... This requires your panels to be ~2 volts or so above the battery charging voltage. So--charge the batteries to 15.5 volts (for equalization), and the solar panels have to be ~17.5 volts or higher. If you put two 18 volt panels in series, you will get 36 volts output--which might ruin the PWM controller, and will be wasted on the battery (which will clamp the voltage to 15.5 volts).

MPPT (Maximum Power Point Tracking)--a switch mode power supply--which almost behaves like the DC equivalent of a variable transformer... If the Panel voltage is high (and current low), the MPPT charge controller converts the power to battery voltage (lower voltage, higher current)--and the MPPT controller can do it pretty efficiently.

So, depending on the type of controller (PWM--use 18 volts for a 12 volt battery bank -- or -- MPPT--use any panel voltage from 18 volts to ~98 volts for a "standard" large MPPT controller--60-80 amp size).

The typical battery itself--they start around 12 volts (near dead) and is "bulk charged" to ~14.2-15 volts, then the controller will cut back to around 14.2 volts for a few more hours, then back to ~13.8 volts when the battery is fully charged (bulk, absorb, then float stages).

So, with an MPPT controller, why choose 18 volts vs 96 volts...

If the panels are close and or subject to some shading, then placing the panels in parallel will be a) slightly more efficient at lower voltages; and b) if you have shading problems, parallel panels may drop less power than a series string when slightly shaded. Be aware, solar panels need full sun to generate power. Shading (morning/afternoon, or partial) dramatically kills their output.

Choose the higher voltage (typically ~96-98 volts max) when there is no shading problems, and the panels are a long distance from the battery shed + charge controller. Because the voltage is ~5x more, the current in the wires from the array to the charge controller will be 1/5 as much--so you can use dramatically smaller wire (and cheaper) for the long runs (and/or use heavier wires to reduce voltage drop and improve efficiency).

whew, my fingers need a break

[MarineLiner]

What a complete explanation made ever

i give my biggest appreciation.
very important more over toward my idea of "DC-AC240v Solar Electric System". thanks alot.

[MikePower]

Wow- Thanks for all that great information.


My conclusion of what I just read, and correct me if I am wrong.

If I use a PWM controller, I should hook my panels up in parallel so I dont damage the controller. Thus the increased amps are of no use to charging capability.


If I use an MMPT contoller and have my panels in full sun all time, I should hook my panels in series. The controller will then efficiently drop the volts down and incrcease the current thus charging the batteries quicker.


So you would use PWM if you where charging batteries with one solar panel(18v 60w). You would use MMPT is you had multiple panels.


When choosing an MMPT do I have to calculate how much current is being inputed or how much is being created vs the controllers rating?

Thanks for all the help. I am slowly peicing together a solar system to run my well pump.

[EnviroNut]

You'll have to read the specifications of the charge controller... But, basically the rating would be based on the output current at the battery bank voltage.

For instance, a 60 amp controller charging a 12 volt battery bank at 15 volts:

60a*15v=900 watts maximum solar panel rating (approx numbers)

For the same 60 amp controller charging a 48 volt battery bank at 60 VDC:

60a*60v=3,600 watts maximum solar panel rating

To see what the panel/string current is... Look at the Vmp/Imp of the panels...

Vmp/Voc adds for panels in series (current remains the same).

Imp/Isc adds for panels in parallel (voltage remains the same).

Or, remember the P=I*V equation...

For example 3,600 watts of panels, with Vmp = 18 volts, assuming 48 volt battery bank, so need 5 or more panels in series (5x18v=90volts):

P=I*V > I=P/V=3,600 watts / 90 volts = 40 amps for controller input current...

Of course, the above numbers are approximate. Vmp changes with temperature, Vbatt changes with state of charge, temperature, and amount of current going into/out of battery. Solar panels tend to output less than "rated" current on hot days, hazy days, etc. There is a ~5-10% energy loss through the controllers and wiring...

There are some, not obvious, issues--so make sure you have done all of the calculations and checks (max power, Voc Max, Vmp min, Isc, etc.) before you start buying components.

For example, there is a problem with a 48 volt battery bank and using solar panels with Vmp>48 volts... One panel's Vmp is not high enough voltage (under 60 volts + 2 volt drop)... And two or more panels in series Voc is higher than the Vmax controller's rating on cold days.

Lower Vmp/Voc panels are ok (and even the 48 volt panels are good panels)--it is just the combination that can cause problems.

[MarineLiner]

...... For instance, a 60 amp controller charging a 12 volt battery bank at 15 volts:

60a*15v=900 watts maximum solar panel rating (approx numbers)

For the same 60 amp controller charging a 48 volt battery bank at 60 VDC:

60a*60v=3,600 watts maximum solar panel rating

Vmp/Voc adds for panels in series (current remains the same).
...
Or, remember the P=I*V equation...

For example 3,600 watts of panels, with Vmp = 18 volts, assuming 48 volt battery bank, so need 5 or more panels in series (5x18v=90volts):

P=I*V > I=P/V=3,600 watts / 90 volts = 40 amps for controller input current...

[Sampson77]

Are you meaning "A solar system that puts out 240VAC"?

Yes those do exist, but they are not made up of 240VAC panels or 240V batteries.

A set of DC panels are connected together and feed into a charge controller.
The charge controller charges the batteries. The batteries may be set up for 12V, 24V, 36V, 48v, depending on the model of inverter.
The inverter takes power from the batteries and produces 240VAC for your needs.

As long as you don't consume more than the panels can supply everything will be great.

now, taking this more literally i'll say that no you won't find a 240v pv as you'll need to get many pvs in series to come up with that voltage.

as to the 240v battery system i'll say no again as controllers at present do not operate in the voltage range for charging a battery bank that high in voltage.

[MarineLiner]

...
Yes those do exist, but they are not made up of 240VAC panels or 240V batteries.
The batteries may be set up for 12V, 24V, 36V, 48v, depending on the model of inverter.
The inverter takes power from the batteries and produces 240VAC ...

... as controllers at present do not operate in the voltage range for charging a battery bank that high in voltage.

[JuanEvans]

The question that isn't asked is why?

Anything is possible,, you could string panels together up to the max series string to get to 240 vdc.

You COULD also string batteries together in series endlessly to get what ever voltage you wish. Why you would wish to do so remains a mystery.

(My guess is you wish to run some 240 loads without an inverter)

[MikePower]

So if finding a charge controller that handles 240vdc is hard, whether it be high price or availability, would you say that most larger solar systems either run their panels in parallel or have multiple charge controllers?

[MarineLiner]

Inverter without voltage step-up

Thank you and sorry for my poor english.
First, i thought, all household appliances work at AC 220v. So why not making solar electric system around that common voltage. By no step-up process needed, means no power lost for it. Then, wire from solar panel output can carry more amperes current compared with lower voltage. Thanks again.

[Pylonman]

So I am putting together a solar system and I am making 18v 60watt 3.5amp panels. I am trying to figure out if I should hook them up in series or parallel!

I understand what each does, increase amps vs volts, but I dont understand how I should calculate for the conditions.

I read that you need to produce 1.5x more volts than what you are charging. If this condition is true then I shouldnt need to hook them up in series. How does increasing my amps affect my charging potential? I guess on the flip side, when do I want to increase my voltage?

Sorry if these are basic questions!

Good question
But, just remember, those homemade panel watt ratings are really for marketing. Those are peak ratings and you should use a MPPT charge controller to pull as much juice out of them as you can. I know from personal experience, that the summer time, my three so called 63 watt panels all tied together produced 12.67 volts at 10 amps peak (with load). I just checked them on the Oct 6th and was getting 12.XX volts at 2.93 amps. A lot depends on the angle of sun and the materials you use. So, if you're going the DIY route, build a few more panels than you intended.

[newmoon]

help!!

I need immediate help!!! I have a solar panel which provides only 60milli ampere, but the requirement is 200 milli ampere. Is there anything i can do

[Naptown]

I need immediate help!!! I have a solar panel which provides only 60milli ampere, but the requirement is 200 milli ampere. Is there anything i can do

get three more?

[Sunking]

I need immediate help!!! I have a solar panel which provides only 60milli ampere, but the requirement is 200 milli ampere. Is there anything i can do

This is a joke right?