Renewable Energy Systems (Solar)

1 - I have never seen a single panel that is made for a 12V system to be wired under 12v at load
2 - I never said your using the same amount of cells to make a 30Ah panel. I said now if it was wired to put out 30Ah then you would get
3 - You have to remember if you use the cells that are only up 0.5v your forgetting that the voltage drops under load. Prefabbed panels have a volt output of around 17v and under load it goes to 12v. So leaving the voltage of the custom panel at 0.5v is a waist of money. Hence why you need your panels to be 12v at load

solar is still to young to be very effective but they still work im mass quantities .

Yes they are still young to be very effective but if you put say lights on a battery bank and go from there then its not as bad. Solar you have to get the lower power draw items off the grid first then if you want combine it all or w/e to take a higher draw item off the grid.

Toolage 87 said:

2 - I never said your using the same amount of cells to make a 30Ah panel. I said now if it was wired to put out 30Ah then you would get

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How can you compare them then? You are comparing a different number of unspecified cells. By my calculations you would need exactly 25 times the number of cells to wire up a 12v,25A system as compared to a 12V,1A system. The charge time is different because you are getting more energy out of the system because you used more cells.

Toolage 87 said:

Solar cells of the kind and size will not always produce the same amount of output.

Each cell puts out x amount of volts and x amount of amps.


The charge controllers can only handle x amount of amps, watts and volts going though it. If you wire enough solar cells that are 0.5v each to give you 12v at load in series but not in parallel that meens it will take longer to charge your battery bank. Let me do some numbers as a example.

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This is what i'm getting at. If each cell puts out x volts and x amps, then it puts out x*x watts. Therefore total wattage is only dependant on area (or number of panels - all with equal area) and not on wiring configuration. Different wiring configurations will give you a different number of volts or amps, but the total watts will be the same.

Toolage 87 said:

3 - You have to remember if you use the cells that are only up 0.5v your forgetting that the voltage drops under load. Prefabbed panels have a volt output of around 17v and under load it goes to 12v. So leaving the voltage of the custom panel at 0.5v is a waist of money. Hence why you need your panels to be 12v at load

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I'm not advocating using any particular voltage or amperage. I agree you will want to wire it up to some certain specification to be comparable with your equipment. I still think the total energy output is proportional to the area regardless of how it is wired though.

The watts wouldn't be the same due to the fact that when the panels are under load the voltage drops thus also dropping the amount of watts produced going into the battery bank.

Toolage 87 said:

The watts wouldn't be the same due to the fact that when the panels are under load the voltage drops thus also dropping the amount of watts produced going into the battery bank.

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And the voltage drop won't be proportional to a different configuration?

If I wire 2 cells in series I should theoretically get 1V and 1A, agreed?

If I wire 2 cells in parallel I should theoretically get 0.5V and 2A, agreed?

Are you saying if I connect each of these to a load and measure the total wattage I will get a different value because of a non proportional voltage drop?

guy incognito said:

And the voltage drop won't be proportional to a different configuration?

If I wire 2 cells in series I should theoretically get 1V and 1A, agreed?

If I wire 2 cells in parallel I should theoretically get 0.5V and 2A, agreed?

Are you saying if I connect each of these to a load and measure the total wattage I will get a different value because of a non proportional voltage drop?

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I truly think that you would get less watts output with a 0.5v setup then a 1.0v setup. I do not think that the voltage drop due to load would be the same between a 0.5v and a 1.0v config

Toolage 87 said:

I truly think that you would get less watts output with a 0.5v setup then a 1.0v setup. I do not think that the voltage drop due to load would be the same between a 0.5v and a 1.0v config

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The load drop won't and can't be the same. Just for a clearer example say you did 200 cells instead of just 2. The in series set would be 100V, and still just 1 amp. The set in parallel will still only be 0.5V, but will now be 200 amps.

100V X 1A = 100 watts
0.5V X 200A = 100 watts

The maximum voltage drop across the parallel cells would be 0.5 V. There is no where else for the voltage to drop to. There will be a small voltage drop across all 200 parallel cells. Say it drops 0.1V. Now you have 200 cells in parallel, at 0.4V and 200 amp = 80 watts.

When they are in series you are seeing a cumulative voltage drop. All the voltages add up (0.5 V + 0.5 V + 0.5 V.....= 100 V), so a small drop in voltage across each cell is added up. So each cell drops 0.1V as in the previous example, and now you have a total voltage drop of 20 V across all the cells in series. so you have a circuit at 80V and 1 amp = 80 watts.

The voltage drop is different only because of the number of cells wired in series. The total energy output is the same. If it's not the same (as you claim) then where does the energy go to?

guy incognito said:

The load drop won't and can't be the same. Just for a clearer example say you did 200 cells instead of just 2. The in series set would be 100V, and still just 1 amp. The set in parallel will still only be 0.5V, but will now be 200 amps.

100V X 1A = 100 watts
0.5V X 200A = 100 watts

The maximum voltage drop across the parallel cells would be 0.5 V. There is no where else for the voltage to drop to. There will be a small voltage drop across all 200 parallel cells. Say it drops 0.1V. Now you have 200 cells in parallel, at 0.4V and 200 amp = 80 watts.

When they are in series you are seeing a cumulative voltage drop. All the voltages add up (0.5 V + 0.5 V + 0.5 V.....= 100 V), so a small drop in voltage across each cell is added up. So each cell drops 0.1V as in the previous example, and now you have a total voltage drop of 20 V across all the cells in series. so you have a circuit at 80V and 1 amp = 80 watts.

The voltage drop is different only because of the number of cells wired in series. The total energy output is the same. If it's not the same (as you claim) then where does the energy go to?

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The energy is wasted because the charge controllers aren't 100% efficient thus your not gonna get 100% of the volts, amps and watts from your panel setup. The other thing is the more wire length that the power has to go though from the panel to the charge controller also causes a voltage drop. The type of wire you use to will make a difference.

You also have to remember that just because your solar panel could produce up to x amount doesn't meen they will. The cells aren't 100% efficient either. You have to take into account that after every year the panels produce x amount of power less.

I found a thing stating that the best properly designed solar panels can only convert up to around 40% of the sun light that hits the cells. Another thing that I've read some where 4 months back is that the temperature of the cells will also effect the power production.

Toolage 87 said:

The energy is wasted because the charge controllers aren't 100% efficient thus your not gonna get 100% of the volts, amps and watts from your panel setup. The other thing is the more wire length that the power has to go though from the panel to the charge controller also causes a voltage drop. The type of wire you use to will make a difference.

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Agreed. Difference in types of wire (though theoretically you should be able to set up series or parallel circuits using the same wire making this a non issue) and different lengths (not as controllable because its a different physical configuration) will provide different real world voltage drops.

Is there just a single charge controller between the cells and the battery?

Toolage 87 said:

You also have to remember that just because your solar panel could produce up to x amount doesn't meen they will. The cells aren't 100% efficient either. You have to take into account that after every year the panels produce x amount of power less.

I found a thing stating that the best properly designed solar panels can only convert up to around 40% of the sun light that hits the cells. Another thing that I've read some where 4 months back is that the temperature of the cells will also effect the power production.

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Agreed that the cells aren't 100% efficient, but that should effect each cell regardless of whether it is in series or parallel. If the cell can only produce 80% of the stated voltage, then it should do so regardless of how it's wired.

I also agree that the age, amount of sunlight, and temperature can affect the total power production, but for comparison purposes all these variables need to be controlled. So in essence the 2 examples I brought up would have to be made using the exact same components, with the exact same age, and tested under the same temperature with an equal amount of light being uniformly supplied to each set of panels. Then any differences in output should be dependent only on the efficiency of the charge controllers.

Does the overall efficiency of the charge controller changed based on the voltage or amperage?

As far as I know you can on;y have 1 charge controller per battery bank so if you wanna run just regular house lights on 1 system you would have to have battery bank and a charge controller for that one. As far as I know its only the voltage that is effected.

I just found out by looking at specs of some charge controllers that so far they have a Min. voltage to operate 9V that meens your solar panels must be at around 9v to use those charge controllers

Just a small update here for some that are still watching this or curious.

I figured out that the best way to find solar panels that are the best for producing power is to calculate how much a solar panel produces per 1 square foot area.

1 - Take the dimensions if they are in inches then divide it by 12 and that will give you the foot (do this for both Width and Length)
2 - Next do L*W to get the square footage the solar panel takes up.
3 - Take the wattage of the solar panel then divide that by the square footage to get how many watts are in each square foot.

Here's an example
Panel - 245w
Length - 65.4"
Width - 39"

1 - Length = 65.4"/12"= 5.45 Feet long , Width = 39"/12"=3.25 feet wide
2 - Length = 5.45 Feet long * Width = 3.25 = 17.71 Square Feet
3 - 245 watts / 17.71 Square feet = 13.83 watts per square foot