[0:00] in a previous video we made some of our
[0:02] Christmas lights rechargeable and one of
[0:04] the viewers suggested why not make them
[0:06] solar powered as well now I made the
[0:08] obvious joke of creating an infinite
[0:10] energy machine with the lights power in
[0:12] the solar cell which then power the
[0:14] light which then power the solar cell
[0:16] you get the idea eventually it would
[0:18] explode but it got me thinking is it
[0:21] even possible in the Scottish winter to
[0:23] run the lights off solar power now
[0:25] contrary to popular belief it is
[0:27] actually quite sunny in Scotland the
[0:30] only problem is being quite far north
[0:32] our winter days are pretty short you can
[0:35] see this from the calculator here
[0:36] Edinburgh is around 56 degrees north so
[0:40] around this time of year the sun rises
[0:41] about 9 A.M and sets about 3 P.M but you
[0:45] can see that during the summer it’s
[0:46] rising at about 3 30 am and setting it
[0:49] about 8 PM we do get really long days in
[0:52] the summer but in Winter pretty short
[0:55] using this next calculator we can work
[0:57] out what the best tilt for our panel is
[0:59] the sun is so low that we need to be
[1:01] almost pointing at the Horizon for
[1:04] maximum power reading off the graph we
[1:06] should get around two kilowatt hours per
[1:08] meter Square so I thought it was worth a
[1:11] go and ordered some small solar panels
[1:13] off Amazon using the two kilowatt hour
[1:16] per meter Square value with the size of
[1:18] our little cells we’ll have around 4.55
[1:21] Watt hours of sunshine our panels should
[1:24] be around 20 efficient so we’ll get 0.91
[1:28] Watt hours
[1:29] in theory assuming we get 5 volts from
[1:32] our solar panel the maximum we’ll be
[1:34] able to get is around 200 milliamp hours
[1:36] now I have to say this feels very
[1:39] optimistic and pretty unlikely but let’s
[1:42] run some experiments and see I have
[1:44] hacked up the code for my DIY battery
[1:46] discharge tester so it just monitors
[1:48] voltage it’s based around the esp32
[1:51] which is quite handy as it’s a wireless
[1:53] device so I can stick it outside on the
[1:55] balcony and pull readings off it
[1:57] remotely I really don’t want to be
[1:58] standing outside because it is pretty
[2:01] cold this should give us fairly optimal
[2:03] conditions as the balcony faces South
[2:05] and there’s not much in the way rather
[2:08] than measuring the open circuit voltage
[2:10] of the solar panel I thought it might be
[2:12] more realistic to measure it under load
[2:14] so I’m feeding it into a voltage divider
[2:16] made up of two 220 ohm resistors this
[2:20] will give us about 10 milliamps when the
[2:21] solar panel is outputting 5 volts we do
[2:24] need the voltage divider as the esp32 is
[2:27] a 3.3 volt device so we need to get our
[2:29] voltage into that range
[2:32] I’ve left the panel on our South racing
[2:34] balcony and recorded the output of the
[2:35] solar panel at this point I’d just like
[2:38] to say thanks to PCB way for powering
[2:40] the YouTube channel over the past couple
[2:42] of years there probably wouldn’t be a
[2:44] channel without them and there certainly
[2:45] wouldn’t be any pcbs for projects check
[2:48] out a link to them in the description
[2:49] they do a really good job
[2:52] the results look kind of promising even
[2:55] with our weak sunshine and shadows from
[2:57] the trees and the occasional Cloud there
[2:59] are previous where we might actually get
[3:01] enough voltage and current to charge a
[3:02] lithium cell we might at least be able
[3:05] to harvest enough power to run some LED
[3:07] light strings for a couple of hours at
[3:08] low brightness
[3:10] calculating the current based off this
[3:12] voltage and our fixed resistors and
[3:14] integrating the area under the curve I
[3:16] think we managed to get about 33
[3:18] milliamp hours it’s not much but it’s
[3:21] better than nothing
[3:22] I’ve got one of these tp4056 charging
[3:25] boards and I’ve removed the charge
[3:26] indicator LEDs so that we don’t waste
[3:29] any power hopefully this board won’t
[3:31] have the same issue that one of my other
[3:32] boards had where it was draining the
[3:34] battery when it wasn’t charging check
[3:36] out the video that should be in the top
[3:37] corner right now if you’re interested in
[3:39] that investigation it was pretty fun
[3:42] I’ve also taken one of my Savage lithium
[3:44] cells and discharged it completely we’ll
[3:47] hook this up to the charger board and
[3:48] leave it in the window for a day
[3:50] unfortunately after making all these
[3:52] great claims about Scotland Being Sunny
[3:54] the weather forecast for the next few
[3:56] days was pretty dire even measuring the
[3:59] open circuit of one of the cells gives
[4:01] us a pretty bad result this won’t charge
[4:03] anything but with two cells in series we
[4:06] get a reasonable voltage and adding
[4:08] another two in parallel means that we
[4:10] might actually be able to get some power
[4:12] after a day on the windowsill we’ve got
[4:14] some results there was no sun at all but
[4:17] we have managed to raise the voltage of
[4:18] the cell by a very tiny amount but it is
[4:21] a very tiny amount so I’ve discharged
[4:24] the battery again this time I’ve tried
[4:26] to get it to exactly three volts and
[4:28] we’ve got a pretty reasonable day
[4:29] forecast I’m trying it with just a
[4:32] single cell and we’re getting quite a
[4:33] good voltage even with it under load
[4:35] connected to the charger it’s quite a
[4:37] nice day so hopefully we’ll get some
[4:39] good results and some sunshine
[4:41] well the sun is pretty much down and
[4:44] looking at the voltage coming from the
[4:45] cells we might as well call this
[4:46] experiment done we managed to raise the
[4:49] voltage by a whopping 0.2 volts over the
[4:52] day which is definitely better than the
[4:54] last time but according to my battery
[4:56] discharge test we only managed to get a
[4:58] measly 10 milliamp hours into the
[5:00] battery not a great result at all but
[5:03] probably about right given that the
[5:04] solar cell is on the windowsill indoors
[5:07] and the weather has been a bit worse
[5:09] than normal not a great deal of sun
[5:11] really so I think maybe we could double
[5:13] this on a good day and get 20 milliamp
[5:15] hours so I’m going to call this
[5:17] borderline possible we could definitely
[5:19] run our LED string at a lower current
[5:21] and on a good day get a couple of hours
[5:23] of run time all in all a pretty
[5:25] interesting experiment but I think for
[5:27] now I’ll stick to charging my lights via
[5:29] USB thanks for watching I’m going to
[5:32] take a break now for Christmas and I’ll
[5:33] see you all in the new year