What do these numbers mean?

[Ian_H]

Hi All
I am planning on having solar fitted on my PVC in January. I had originally asked for 2 x 150W panels, but having seen these panels on a similar van I think they are a bit too big and will interfere with mounting a roof rack for transporting a canoe. Looking at the next size down (125W), they would probably do the job BUT the numbers on the suppliers web site have confused me, as the 125W panels seem out of kilter with the others, producing a higher voltage. Could someone with more knowledge have a look at the attached table and advise whether dropping down from 150W to 125W panels is likely to have other implications than just the expected drop in panel output from 300W total to 250W?
Many thanks
Ian

 

[Lenny HB]

The 125 w panel is a domestic panel rather than a 12v panel either will work fine provided the controller you use is suitable for the votage.

 

[RogerIvy]

Remember to take into account the brackets.
You could use aluminium rectangular tubing (50mm x 25mm with 1.5mm wall) to mount directly under the panel. We’ve done quite a few of these very successfully (preparation is very important even though the surface area is more than adequate even for a panel fitted sideways).

 

[autorouter]

The numbers are correct, but the units in the column headers are misleading. Columns 2 & 3 should be 'Watt-hours per day (Wh)' and 'Amp-hours per day (Ah)'. The 'Charge Controller' column should show amps (A) not amp-hours (Ah), which a suitable Amps rating for the charge controller.

The 150W panel will produce 150W at full spec (Vmp x Imp): 18.8V x 7.98A = 150W. Over the whole day it will produce a charge of 47.88Ah, so if the voltage is 18.8V that's 18.8 x 47.88 = 900Wh.

The 125W panel will produce 125W at full spec (Vmp x Imp): 31.9V x 3.92A = 125W. Over the whole day it will produce a charge of 23.52Ah, so if the voltage is 31.9V that's 31.9 x 23.52 = 750Wh.

These voltages are on the input side of the solar controller. The controller regulates the voltage to a value suitable for charging the batteries.

Note that the amps in the column Imp (Amps at max power) is on the input side, but the controller is rated by the amps on the output side. Because the voltage is lower (about 14.5V) the amps is higher.