# Allowing the energy flow INTO the solar panel (photovoltaic), what happens?

I was watching this video https://www.youtube.com/watch?v=HZf-sm3UXX0&feature=youtu.be&t=3m4s as I was willing to learn how to test my solar array, from 3m4s he's testing the Amps provided by the solar panel simply by using the multimeter and WITHOUT any kind of external load. If I would have a simple battery connected this way it will most likely blow up or experience really high temperatures on the battery case.

Well ... this means that the current is wasted inside the solar panel ? That amperage is converted in heat inside the solar panel ? If the power wasn't used at all then the multimeter won't show a flow of amps.

If YES, this means that I can thaw my solar panels in the winter if I provide them with power ? For example after a snowy day could I just provide power to solar panels in order to clean them up of snow and ice ?

Thanks!

There's two things here:

• short circuiting the panels to measure current
• back-feeding current in the "wrong" direction (such as from a battery)

The first is apparently a normal way of measuring current output for small panels. Provided the meter can take it, it's for a short duration, and the total current isn't expected to be at levels with severe arcing, it's fine. So don't try it on a whole 4kW array.

Note that the total heating is limited by the sun: there's no way for the panel as a whole to get hotter due to electrical self-heating than a black sheet of the same size! Although you may cause localised heating at joints.

The second is bad for panels, as you're reverse-biasing them. Most systems with batteries will contain an ordinary diode to prevent this.

You raised the possibility of heating the panels to self-clean them, which is interesting but I suspect very inefficient.

• Data point, 2 years on: The "reverse diode" is often less necessary that it may appear. I always use one, but - When Vpanel is > Vbattery the diode is unneeded. As PV panel is ~~= a luminance controlled current source , Vpv_oc is usually close to Vmp. eg a say 12V panel with Vmp of 18V and Voc of say 20V+ will not fall to Voc < 14V or so until light is down to maybe 1% of max (say 1000 lux or less). At this stage the back current is in the order of the Isc at that light level so maybe 1% of max. ... Commented Aug 16, 2019 at 8:21
• ... As light falls further Isc will fall to near zero quite rapidly. SO back drain will be small and largely confined to the period as light falls from say 1% to 0.01% of full. || [I have been involved with using 100;s of thousands of small PV panels (< 1 Watt). Despite this I was not aware of the low back flow issue until after substantial involvement. I've never formally characterised it . I yet may do BUT - I use a diode :-) Commented Aug 16, 2019 at 8:24
• @RussellMcMahon that implies you could remove the need for a diode by means of a small lamp pointed at the panels overnight to keep the Voc up... :) Commented Aug 16, 2019 at 8:26
• A few years ago I worked on a prototype for an intelligent [tm] home solar system. My task was hardware and embedded systems hardware interface. I used a 300 Watt panel to simulate a larger array and the software guys scaled it up and played various games with the data. Occasionally in the dead of night I wanted a small output from the system to check various things. I could have added power at the PV interface but chose to illuminate the panel (just outside my workshop door) with a suitable LED lantern. VERY LOW output. Met need. | Commented Aug 16, 2019 at 10:37
• I found that 2 to 3 hours before sunrise while visually it was still nearly pitch black (say <= 0.1 lux) the panel voltage started to rise. Over the next hour or so it was a fairly flat slowly increasing pedestal then, as the sky started to lighten it would start to rise more (visibly) exponentially. I'm not 100% sure it was the sun - eg there is a motorway about a mile away well screened by trees and at the light levels involved there MAY have been other sources - but I'm reasonably certain it was the sun. One of these days, when time allows [tm](again) ... . Commented Aug 16, 2019 at 10:37