rooster63 Posted January 12, 2021 Share Posted January 12, 2021 On our new van there is solar panel fitted and looking at the control panel it is feeding juice into the batteries.(only a tiny amount as van not in direct sun) There aren't any instruction manuals so just wondering if there is any way of telling how many watts it is rated at. Is there anyway of telling? On a sunny day what amperage would you expect to see and how do I know if that is feeding much juice into the batteries? Does the formula Watts= Volts x Amps apply? So if I multiplied the number of amps registering on the control panel by 12 would that give me the wattage? Link to comment Share on other sites More sharing options...
colin Posted January 12, 2021 Share Posted January 12, 2021 Couple of things. Is it a standard fitment to van, if so what van have you got. There may well be a label on rear of panel. Failing that if you measure the panel, then you can compare that to outputs of similar size panels. Link to comment Share on other sites More sharing options...
plwsm2000 Posted January 12, 2021 Share Posted January 12, 2021 If you cannot read the label (and the supplier doesn't know), then you can calculate a very approximate power rating from the dimensions of the panel. As a rough guide, measure the length and width (in cm), subtract 5cm from each (to account for the frame and space between cells) and then multiply the two numbers (length - 5cm) x (width - 5cm). This gives the approximate area of the cells. For a low/moderate quality monocrystaline panel, divide the above result by a "fudge factor" of 56 to get the approx. wattage. For higher quality panels that generally have a higher efficiency, this fudge factor is more like 48. These are just approximate numbers but should give you a result that is close to 10% of the actual rating. Just as an example, this (low cost) panel [url=] https://www.photonicuniverse.com/en/catalog/full/476-120W-monocrystalline-solar-panel-with-5m-cable.html [/url] measures 118cm x 67cm so (118-5)x(67-5) / 56 =125W. It is not unusual for manufacturers to underrate their panels when new as they know they degrade over time. After say 5 years, they can still guarantee 80% (or what ever) of their specified rating. "Watts = Volts x Amps" is only useful if you have a MPPT controller (not a PWM controller). Even then, the MPPT controller will have some inefficiency and the power you get out will be around 95% of the solar power input (panel Volts x Amps). For a PWM controller, the power output is more like 14V x the solar panel current. The 14V is just the battery voltage when on charge so is just a nominal figure. The excess panel voltage gets wasted with a PWM controller Link to comment Share on other sites More sharing options...
spirou Posted January 12, 2021 Share Posted January 12, 2021 I would just look at panels of similar size. Link to comment Share on other sites More sharing options...
weldted Posted January 12, 2021 Share Posted January 12, 2021 Slide your phone under and take a picture of the label it’s usually near the edge. Our 2019 Burstner came with a 100 watt panel and a 10 amp controller Link to comment Share on other sites More sharing options...
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