20W Solar Panel / 21W Bulb – A Perfect Match? (part 1)

so here I've got a 20 watt solar panel and this is a polycrystalline type conceal the higgledy-piggledy crystal structure there on the surface it's a 36 cell panel and actually probably more importantly this it's an absolutely glorious cloudless day so we can have sunshine all day perfect for conducting solar power experiments and to go with my 20 watt solar panel I have this which is a 21 watt bulb 12 volt 21 watt out of a car have wired a little wire harness on it so I can connect it up this is a car brake light bulb so on the face of it these should be a perfect match a 21 watt bulb and a 20 watt solar panel so let's see if we can lock up light up the bulb so I've angled the solar panel directly towards the Sun and connecting up the bulb there it is and it's on it lights up so it works but it's not terribly bright is it in fact it's really quite dim so that does appear to be a problem connecting a 21 watt bulb to a 20 watt solar panel so I've rigged up a couple of digital voltmeters digital multimeters and connected them through this little block here which enables me to measure current and also volts so let's have a look at what we've got without the bulb connected on the Left we've got volts so the open circuit voltage of this panel is twenty point five volts and of course there's no current flowing at the moment because we have no circuit because the plug isn't connected to anything so let's connect up the bulb and see what we get now it's the connector there's the one for the bowl right so once again just a dim glow on the bulb so on the right which is the ampere meter the current meter we've got 1.17 amps and on the Left we've only got five point six volts so that immediately explains why this bulbs isn't very bright 5 point 6 volts on a 12 volt bulb it's only running 1/2 voltage so why is it that this 20 watt solar panel doesn't just miraculously detect that it's a 12 volt bulb and shove 12 volts through it well solar panels are pretty dumb and it just isn't going to do that in fact solar power very fussy about the load that you connect in order to get the full power wattage out of the panel now there's a little clue here on the back of the panel it says smart solar polycrystalline photovoltaic module working voltage 18 volts now we had nothing like 18 volts we had five-and-a-half thoughts working current 100 500 milliamp so that's 1.05 amps and we heard about we have moon that actually we had about 1.1 something so certainly the voltage is way out and we need to have a look at why well the sun's come around a little bit now and we're getting a bit more power through the bulb we've got five point nine three volts on the voltmeter 1.2 one amps on the ammeter so let's calculate what we're getting in terms of watts power into that bowl five point nine three one point two one so let's go to the calculator 5.9 three times 121 so we're only getting 7.2 watts now this is a 20 watt solar panel so to only get 7.2 watts it's a bit disappointing and what's going on here is that there's a mismatch between the bulb as a load and the solar panel and the sort of load that it requires we're going to need to do some maths to work out what's causing that mismatch so we'll cover that in part two

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