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Calculating solar specs for personal use


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34 minutes ago, Stanley Rogers said:

Hi, is my calculation correct? I couldn't find an app to do calculations so I'm trying it in excel... 

 

image.png.9e48fc6327e6d8b79b12c7535033d9f9.png

 

Yes this is correct. 2S(2*37.5V)6P(6*8.7A) is the short version of your connections. 

Edited by Scorp007
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32 minutes ago, Stanley Rogers said:

Hi, is my calculation correct?

Yes, are the Voltage and Current ratings based on max-power or open/short circuit values for the panels in question?

If you use the open circuit Voltage and short circuit Current, then you'd be looking at the max numbers under normal conditions, if you have temperature going very low with still lots of direct sunlight then the Voltage can be higher as well as the current, but probably not enough to be a problem, unless you're sailing very close to the MPPT's limits...

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15 minutes ago, Kalahari Meerkat said:

Yes, are the Voltage and Current ratings based on max-power or open/short circuit values for the panels in question?

If you use the open circuit Voltage and short circuit Current, then you'd be looking at the max numbers under normal conditions, if you have temperature going very low with still lots of direct sunlight then the Voltage can be higher as well as the current, but probably not enough to be a problem, unless you're sailing very close to the MPPT's limits...

I have to differ. Under normal conditions you will never get Voc and Isc at the same time. Using Vmp and Imp will give a better indication. 

Yes on cold days the the V and I will be higher. 

I stand to be corrected :)

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52 minutes ago, Scorp007 said:

give a better indication

but not the maximum numbers possibly to be encountered...

12 minutes ago, Piper said:

I think its more like this  

Yes, I was not concerned or looking at the power, only the Voltage and current calculations, but you are right @Stanley Rogers did not calculate the power correctly and I didn't bother to check that one, the Voltage is most important, to prevent the MPPT/PWM from letting out the magic smoke, the current less so, since the MPPT/PWM should draw as much current as it can utilise and if its properly designed, won't go beyond what it can safely consume, but, I suppose a bad design without limits on the current can also blow the magic smoke out, if the current available is more than it can safely handle. The power is just the indication of what can be expected peak power production wise, assume the other two values are within the limits of the MPPT/PWM's handling capabilities, but... and here's the curve ball, 75V, check, 52-odd A, check, assuming the unit can only handle 40A but is designed well enough that it will limit the current as such, then the power calculation should be 75 * 40 for a 3kW peak... just thumbsucking the 40A to make the point that the peak power calculated may be off from what the power handling equipment may be able to consume... so @Stanley Rogers, how did you multiply 75 with 52.5 and end up with 1950? what broken spreadsheet from the 1st half of last century are you using 🙂

Edited by Kalahari Meerkat
grammatik
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1 hour ago, Kalahari Meerkat said:

@Stanley Rogers but... and here's the curve ball, 75V, check, 52-odd A, check, assuming the unit can only handle 40A but is designed well enough that it will limit the current as such, then the power calculation should be 75 * 40 for a 3kW peak... just thumbsucking the 40A to make the point that the peak power calculated may be off @Stanley Rogers

A difficult call without knowing what inverter. There are even 24V 3kW inverters that can take up to 5000W of panels. It might have a 100V MPPT which is the reason for 2S connections. 

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4 hours ago, Scorp007 said:

@Stanley Rogers

Some kind of funny error on the Watts as pointed out. 

 

Oh. I thought that wattage in series stays the same while in parallel adds up (325W x6). That was my main concern, probably cause I was misinformed.

 

Anyway, it's just for personal use while I learn about solar systems. 

 

Thx!

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5 hours ago, Stanley Rogers said:

 

Oh. I thought that wattage in series stays the same while in parallel adds up (325W x6). That was my main concern, probably cause I was misinformed.

 

Anyway, it's just for personal use while I learn about solar systems. 

 

Thx!

That's how we all start somewhere. Watts=V*A

Just multiply the volts and amps as you had calculated it. :)

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