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really basic solar question...  RSS feed

 
C. Hunter
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(but google is giving me too much crap to find the info I need after 20 minutes of sorting advertising from info.)

Can someone explain the whole why of wiring panels in parallel vs series? I've been watching the solarhomestead videos and he's got his set up in series (I think?) and I know that's something to do with 12v vs higher voltage, correct?

Trying to learn all the things. Think my head may explode.
 
chad duncan
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When you wire multiple power supplies in series, their voltages are added together. So two 12 volt @10 amp power supplies wired in series would give you a 24 volt system with 10 amps available.
When you wire multiple power supplies in parallel, their amperage is added together. So two 12 volt @10 power supplies wired in parallel would give you a 12 volt system with 20 amps available.

You lose less power to the resistance in the wires when you run at higher voltages.
 
Gerard Foret
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Here's the why:

While solar panels are rated in watts of output, watts is actually a product of voltage x amperage. Where voltage is pressure and amperage (or current) is flow. Think of your wiring as pipe to handle this flow.
So, think about water in a pipe and I want to fill a 5 gallon bucket from an 10 foot elevated (volts/pressure) water source containing 20 gallons of water (watts) . I can use a large pipe ( higher amps/current/flow) and fill the bucket in a certain amount of time. Or, I can elevate the water source to 20 ft (increase pressure/voltage), use a smaller pipe (lower amps/current/flow, and fill the bucket in the same amount of time. In this example the higher pressure (voltage) allows me to use a smaller pipe and still get the same amount of work done. Copper is expensive. By using higher voltage I can reduce my wire size and save money. The same theory applies to battery bank voltage. Notice on inverters that their efficiency goes up when using 24 or 48 volt inverters vs. 12 volt inverters.

Secondly, especially in longer wire runs, higher voltages experience less voltage drop than lower voltages. Since the current is lower (and the voltage/pressure is higher), there is less reaction to the electrical resistance of copper wiring, meaning more juice from the panels getting to your controller (or from your battery bank to your inverter).

Lastly, higher voltage allow for longer cell strings in the battery bank. There was a recent heated discussion about the importance of reducing parallel strings to improve battery bank health and safety, meaning it is safer and healthier for a battery bank to contain 4-12 volt batteries in series and operate at 48 volts than it is to have 4-12 volt batteries in parallel and operate at 12 volts.



C. Hunter wrote:(but google is giving me too much crap to find the info I need after 20 minutes of sorting advertising from info.)

Can someone explain the whole why of wiring panels in parallel vs series? I've been watching the solarhomestead videos and he's got his set up in series (I think?) and I know that's something to do with 12v vs higher voltage, correct?

Trying to learn all the things. Think my head may explode.
 
Gerard Foret
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chad duncan wrote:
You lose less power to the resistance in the wires when you run at higher voltages.
 
Charles Tarnard
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Everything said above is correct, so if you understand those posts but not this post, then ignore this post.

Voltage is a measure of potential, or differential. With each 12v cell you have a difference of 12v from terminal to terminal.

When you put the terminals in series, you are increasing the differential from the most negative point to the most positive point (in other words, adding them up). In this case the cell with the lowest current capacity (the panel with the least sunlight, the battery that is weakest) limits the whole set in amount of current they can deliver.

When you put the cells in parallel, all the positive terminals are on the same point and all the negative terminals are on the same point so the difference across all the cells has to be the same as the difference across any one cell. In this case each cell can deliver current across the terminals in the same way so current capacity can be added up.

Hope that wasn't totally confusing.

 
Gerard Foret
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This is correct as well. The goal is watts (work that can be done) and higher voltage systems do that the most efficiently. On small systems it's of little consequence other than battery health and safety. My small barn system (250w) is 12 volts (single 12v deep cycle). My 1kw system running refrigeration is 24 volts (4-6v Crown 235 in series). On large, multi-kw systems 24 volts or higher is the norm. Another reason for this is the charge controller(s) can only handle X amps in charge capacity, and a parallel bank requires a much higher charge current than a series bank for proper charge rate. Both deliver the same watt/hrs of work minus inefficiencies.

Charles Tarnard wrote:Everything said above is correct, so if you understand those posts but not this post, then ignore this post.

Voltage is a measure of potential, or differential. With each 12v cell you have a difference of 12v from terminal to terminal.

When you put the terminals in series, you are increasing the differential from the most negative point to the most positive point (in other words, adding them up). In this case the cell with the lowest current capacity (the panel with the least sunlight, the battery that is weakest) limits the whole set in amount of current they can deliver.

When you put the cells in parallel, all the positive terminals are on the same point and all the negative terminals are on the same point so the difference across all the cells has to be the same as the difference across any one cell. In this case each cell can deliver current across the terminals in the same way so current capacity can be added up.

Hope that wasn't totally confusing.

 
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