Calling all solar experts

[pas63]

I have 3 Renogy 100 watt solar panels wired in series. The first thing that has me scratching my head is the input on the MPPT. I'd expect to see 100 watts max at 3x voltage. Right now, with a load on the system (lights, shower sump, fridge) I see it fluctuating between 105-130+ watts and voltage around 62v. On the output I am seeing it in float at around 9 amps at roughly 14.1v.

I am using 6v golf cart batteries. The MPPT is a Victron 75/30The MPPT is set to output 30 amps max, absorption is set to 14.8v, float 14.4v and equalize 15.5v

Questions
1) How am I seeing far more that the expected 100 watts?
2When I look at my battery monitor I see 2-3 amps outgoing. If I turn on the battery charger I will probably see far more than 8 amps input, why am I not seeing more from the solar?
3) I assume all the recommended charge voltages are for a battery with no load? What about a battery under load? How do you configure charge voltages for that?
4) Why am I only seeing 8-9amps going into the batteries? Math tells me a single 100w panel should output up to 12-13 amps. Shouldn't 3 x 100 be expected to output 30-35 amps?

[rslifkin]

3x 100w panels in series is good for 300 watts. Watts add regardless of series vs parallel. The difference is in amps and volts. So if your panels get 100 watts as 5 amps at 20 volts for maximum output (made up but valid numbers), in series you'd have 5 amps at 60 volts for peak output from 3 panels (5a x 60v = 300w). In parallel, you'd have 15 amps at 20 volts for peak output (15a x 20v = 300w).

[pas63]

Originally Posted by rslifkin

3x 100w panels in series is good for 300 watts. Watts add regardless of series vs parallel. The difference is in amps and volts. So if your panels get 100 watts as 5 amps at 20 volts for maximum output (made up but valid numbers), in series you'd have 5 amps at 60 volts for peak output from 3 panels (5a x 60v = 300w). In parallel, you'd have 15 amps at 20 volts for peak output (15a x 20v = 300w).

I get all the above, that wasn't my question. The question was - if I have 3 - 100 watt panels in series I'd expect to see no more than 100w at 3x the voltage. How am I seeing input to the MPPT of up to 240 watts at roughly 3x the voltage?

[seandepagnier]

please re-read post #2 until it makes sense and answers question in post #3

Originally Posted by pas63

Math tells me a single 100w panel should output up to 12-13 amps. Shouldn't 3 x 100 be expected to output 30-35 amps?

Try doing math again.

[GoodShipLolipop]

Originally Posted by pas63

2When I look at my battery monitor I see 2-3 amps outgoing. If I turn on the battery charger I will probably see far more than 8 amps input, why am I not seeing more from the solar?

3) I assume all the recommended charge voltages are for a battery with no load? What about a battery under load? How do you configure charge voltages for that?

Other questions have already been answered, so I'll take a stab at these. Do note that I'm not an expert, and might be wrong, but this is how I understand things.

2: The battery is a "low impedance" source, so it will tend to provide more of the energy than higher impedance sources. Think about it like pipes. You've got two pipes feeding into a bucket, and one of them is WAY wider than the other. Even if you turn them both on full blast, the wide pipe will supply most of the water.

3: I don't think the battery needs a different voltage if it's being simultaneously charged and discharged, but somebody should really fact check me on that one just to make sure you don't ruin something.


Edit: I may have misunderstood question #2?

[pjShap]

Originally Posted by pas63

I get all the above, that wasn't my question. The question was - if I have 3 - 100 watt panels in series I'd expect to see no more than 100w at 3x the voltage. How am I seeing input to the MPPT of up to 240 watts at roughly 3x the voltage?

As rslifkin explained, watts do NOT stay the same. In series, total amps will be the same as a single panel. Voltage is multiplied by the number of panels in series. Watts is volts times amps, so watts will also be about 3 times higher. That's why you use multiple panels- to get more power.

[Pete7]

Originally Posted by pas63

On the output I am seeing it in float at around 9 amps at roughly 14.1v.

Batteries are full. The 9A is likely what you are using with lights etc. Batteries will only accept what they want, not what the MPPT can output. Just as well or you would boil the batteries dry.

Originally Posted by pas63

The MPPT is a Victron 75/30The MPPT is set to output 30 amps max

Can you confirm the Victron model number please.

[pas63]

Originally Posted by Pete7

Batteries are full. The 9A is likely what you are using with lights etc. Batteries will only accept what they want, not what the MPPT can output. Just as well or you would boil the batteries dry.


Can you confirm the Victron model number please.

It is a 75/30. I your point on batteries accepting only what they can hold,but I just turned the charger back on and it started dumping 10amps vs the amp and bit the solar was inputting.

[Kelkara]

Originally Posted by pas63

It is a 75/30. I your point on batteries accepting only what they can hold,but I just turned the charger back on and it started dumping 10amps vs the amp and bit the solar was inputting.

Originally you said that the solar was producing 9A, but that the battery was still discharging at 3A ... meaning you have a total of 12A of loads, and the battery is not charging at all but discharging, and all the solar can do is help the battery power the loads.

When you turn on the shore power charger you can not only supply the remaining 3A of load, but also start charging the battery (up to the maximum capacity of the charger). If you're only getting 10A from the charger, then the batteries are only accepting 7A (with 3A supplying the remaining load that the solar couldn't). Whether that is a lot or a little depends on how big the batteries are and how fully charged.

Now you are saying that there is only 1A of solar ... what has changed?

I think your biggest problem is that you don't have enough sunshine for your solar to deliver its full potential.

[redneckrob]

Originally Posted by pas63

I get all the above, that wasn't my question. The question was - if I have 3 - 100 watt panels in series I'd expect to see no more than 100w at 3x the voltage. How am I seeing input to the MPPT of up to 240 watts at roughly 3x the voltage?

watts=volts*amps I think you're conflating watts with voltage and amperage from what you're saying. In series you'd expect the amperage to stay the same and the voltage to triple. In parallel the voltage would stay the same and the amperage would triple. In either case, your wattage=volts*amps would triple. To see 300 watts you would need to be at optimal azimuth (south facing) and tilt (approximately 30 degrees in FL, for example) at full sun and standard test conditions, meaning the panel temp would need to be 25 degrees C. You're probably seeing a lot less than 300 watts because some of those aren't optimal, and keep in mind when you wire panels in series, any shading on one panel pulls all the panels down to the shaded panel's output. On a boat you would almost always want to wire in parallel.

[guyrj33]

@pas63
I respectfully suggest you do some reading about electricity, since we're talking about 12 volt systems you may find this book useful.
https://www.landfallnavigation.com/w...caAqy7EALw_wcB

As you read through the book work to understand that current(amps), voltage(volts) and power(watts) are separate and are related by the equations
Power = Current * Voltage.

[RobAndSally]

Solar panel that is rated at 100Watts will not deliver 100 watts unless brand new, angled and pointed directly at the sun. So 100-130 watts that is being read out on the controller is valid. This would be the individual panel voltage x 3 since they are in series. So lets say 130 watts @65 volts = 2 amps coming from the panels to the controller.

The output (9 amps @ 14.1 volts = 9x10 + 9x4.1 = 126.9 Watts) is consistent with your input. As others have said, the 9 amps is outbound going wherever the load is, be it the battery charging or DC loads.

The difference between the 130 watts and 126.9 watts is the loss in the controller. I was just using easy to calculate numbers, and if they were valid the efficiency of your controller would be 126.9/130 * 100 = 97.6% efficiency.

Solar is awesome, nothing like renewable energy until the lighting strikes!

With kind regards,
Rob

[CatNewBee]

Originally Posted by pas63

I have 3 Renogy 100 watt solar panels wired in series. The first thing that has me scratching my head is the input on the MPPT. I'd expect to see 100 watts max at 3x voltage. Right now, with a load on the system (lights, shower sump, fridge) I see it fluctuating between 105-130+ watts and voltage around 62v. On the output I am seeing it in float at around 9 amps at roughly 14.1v.

I am using 6v golf cart batteries. The MPPT is a Victron 75/30The MPPT is set to output 30 amps max, absorption is set to 14.8v, float 14.4v and equalize 15.5v

Questions
1) How am I seeing far more that the expected 100 watts?
2When I look at my battery monitor I see 2-3 amps outgoing. If I turn on the battery charger I will probably see far more than 8 amps input, why am I not seeing more from the solar?
3) I assume all the recommended charge voltages are for a battery with no load? What about a battery under load? How do you configure charge voltages for that?
4) Why am I only seeing 8-9amps going into the batteries? Math tells me a single 100w panel should output up to 12-13 amps. Shouldn't 3 x 100 be expected to output 30-35 amps?

Yes, No.

Forget the solar for a moment. You are familiar with batteries? OK, a start battery is rated 800A CCA (cold cranking amps). Why do you not see 800A when turning on a light? Simple answer: resistance. Each electrical thing has a resistance, it is Volts divided by Amps.

Resistance defines the current that flows across a circuit, no matter if charging or discharging.

Now back to your panels, 3 * 100Wp (Watt peak!) is always 300Wp (Watt peak!), regardless of wiring in parallel or in series. In Series you have Imp at 3x Vmp, in parallel you have 3x Imp at Vmp, means a 14V panel has 7A roughly at MPP, 3 panels in series CAN deliver 42V at 7A, in parallel they CAN deliver 14V at 21A. That simple. They do this only if there is a load, that can either burn 300W at 42V (7A, 6 Ohm) OR 300W at 14V (21A, 0.66 Ohm). if you put on a higher resistance (smaller load) you get only a fraction of the current, if there is no load at all, there is no current and no power draw, REGARDLESS of the system capability, just like your battery, no load, no current, no charge / discharge.

Your MPPT charge controller just keeps the panels at MPP and transforms high voltage low amps to low voltage high amps, but only IF there is a load that can take the current.

So to measure the performance you must turn on a load, that exceeds the Wp of the system, you need a load over 300W to burn that incomming energy and measure the solar current, if you turn on a load of 400W, 300W would come from the solar and 100W from the battery (at noon, brite sky, cold panels for peak power).

[sesmith]

Originally Posted by pas63

I have 3 Renogy 100 watt solar panels wired in series. The first thing that has me scratching my head is the input on the MPPT. I'd expect to see 100 watts max at 3x voltage. Right now, with a load on the system (lights, shower sump, fridge) I see it fluctuating between 105-130+ watts and voltage around 62v. On the output I am seeing it in float at around 9 amps at roughly 14.1v.

A renogy 100 watt rigid panel has an open circuit voltage of 21.2 v and a short circuit current of 6.1 A. Optimum operating voltage is 17.7 V and operating current is 5.7 A. Your 3 panels in series will produce no more that rated current.

You show 105-130 watts input at 62V (so about 2A current) in from the solar panels to the controller. Output is 9A at 14.1V. That is about 127 watts output from the controller. So that makes sense cause it matches the input. If it's really in float, I'm a little surprised you are seeing that much. You're panels will only produce what the battery can take regardless of sun conditions.

Voltage and power add in a series circuit, so your max power for the 3 panels is theoretically 300 watts. In reality, it will be less (often much less).

[Wotname]

To add to this mostly correct post, see the red additions.

Originally Posted by sesmith

A renogy 100 watt rigid panel has an open circuit voltage of 21.2 v and a short circuit current of 6.1 A. Optimum operating voltage is 17.7 V and operating current is 5.7 A. Your 3 panels in series will produce no more that rated current.

The output is also temperature dependant on the panel temperature - cold panels will deliver more power than hot panels.

You show 105-130 watts input at 62V (so about 2A current) in from the solar panels to the controller. Output is 9A at 14.1V. That is about 127 watts output from the controller. So that makes sense cause it matches the input. If it's really in float, I'm a little surprised you are seeing that much. You're panels will only produce what the battery can take regardless of sun conditions.

This assumes there are no other loads on the system except for battery charging. For example, if the battery will only accept say 3A in float but there is a 4A load elsewhere, then the panels will be delivering 7A (from the MPPT). If the load is say 10A, then the panels will provide 9A and the battery supplies 1A.

Voltage and power add in a series circuit, so your max power for the 3 panels is theoretically 300 watts. In reality, it will be less (often much less).