Solar panel output

[amiklic1]

Since I don't have any comercial built solar panels, I would like someone to post the comment about this.

I use few 50 watts panels to charge my batteries. Now, we are talking of JUST ONE! Others are disconnected from the system for the testing purpose.

First, about the panel:

It consists 36 WB 29 cells from Plastecs. They are rated 1.8 to 2.0 Amps and 0.57 to 0.6 Volts.

If I calculate from that, I can get:

Voc would be 20.52 to 21.6 Volts

I (?) would be 1.8 to 2.0 Amps.

So, that panel is rated 37 to 43 Watts.

Is that right?

I can see commercial built panels have max power voltage of 17 Volts. Would the current be higher if I put the panel to 24 Volts battery?

[Flux]

I am no expert on solar panels, but yours seem very close to most commercial ones.

The take the rating at the point that gives maximum power. In your case it is also likely to be near 17v.

The standard rating is at an insolation power of 1000W/sq M. you probably won't be able to measure this and in some climates you may having trouble ever seeing it.

They load them to the point where the product of volts and amps is a maximum and use that point as maximum power.

With 36 cells you will not get any output into 24V unless the battery was flat.

The 17v point is chosen to handle a fully charged 12v battery with a bit of line loss and with some panel heating, that tends to reduce output.

You would likely have a rating of about 35W.

Flux

[iFred]

You can calculate about 18-20% of the total rated output of any panel. That's the total power you can anticipate on. Sounds dismal but at least it works. It also depends on the type of charger used and the wiring etc..

[richhagen]

While the voltage curve and power curve at different current levels can vary with the specific design of the cell, in general the voltage won't likely drop more than a volt and a half to two volts between the voltage open circuit and the voltage at maximum power.  Below is a graphic I happened to have uploaded for a previous post.  Notice the graph at the top left.  





If you look at the top curve of the three that form arches, it shows the power output verses voltage at 1000 watts per square meter of illumination.  that is approximately the equivelant of being under full sun.  You can see that the voltage doesn't drop much between open circuit voltage, where the loop looking line intersects with the y axis towards the bottom right of the graph, and the voltage at peak power, where that same curve is at its peak.  

If your panel behaves similarly, based on the numbers you provided, you would likely see around 21 volts open circuit, and a little better than 1.8 amps short circuit.  The peak power would likely be at about 1.8 amps and 19.5 volts or so which would give you a peak power of about 35 Watts.  This is just a ballpark estimate.  Rich Hagen

[farmerfrank]

Don't be confused about the open current voltage. OCV is exactly that, measured with no current flowing. If the terminals are shorted the voltage can drop quite a bit. Thats why the wattage can not be calculated using OCV.

farmerfrank

[farmerfrank]

Hello Fred. How you been?

[zyewdall]

Commercial solar panels designed for charging 12 volt batteries almost all use 36 cells in series.  They used to make ones with 30 or 33 cells, but those don't have enough voltage during hot weather, and sometimes they won't charge the battery at all.  Ones for a 24 volt battery usually have 72 cells in series.

With regards to 1000 watts/sq meter.  You can exceed this by 20% or so in Colorado (high elevation and clear skies).  In the eastern US, you will rarely see it because of high haze and humidity levels.

[richhagen]

If you short the output, the voltage will drop to zero.  The open circuit voltage rated cell current are the best data we have available to us to use for estimating the power.  They were the only data provided.  The power rating can be estimated if the cells behave like typical silicon solar cells, which is what I did above.  The results are however, just a ballpark estimate as mentioned above.  Rich