Goodmorning!
I was thinking about powering an ESP32 with a solar panel.
I already have a 5V Solar panel.
I was thinking of connecting this to the solar panel:
and power my project with an ESP32
This is not a simple task. Some things you need to know:
How much power can the solar panel supply?
What is minimum number of daylight hours in the middle of winter?
How many days of no sunlight (cloudy /rain) will you need to run the device off battery for?
What is the power draw of your ESP32 when awake?
What is the power of your ESP32 when asleep?
What minimum sleep wake duty cycle do you need?
Does that battery pack protect your batteries from over discharge (assuming they are lithium).
Does that battery pack supply a regulated output voltage, and if so, what efficiency?
I know these battery shields. What exactly is your project?
To get any reasonable power out of small panel, you need solar charger. Otherwise the charger tries to draw more than panels Impp causing the voltage to collapse.
Something like this:
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I was thinking of a simple ESP8266 D1 mini to monitor outside air quality and temperature.
I tried powering it only with a 5000mAh powerbank and it lasted about 24 hours.
Then I also tried charging the power bank alone with the 10W 5V solar panel and it charged in about 5 hours (more or less).
I live in Italy and the sun is always there.
That’s 2A, quite big panel . If you set regular charger to max 1A, it should work quite well.
If you have any chance of keeping such a project running year round you will need to make use of deepsleep.
The major problem will be that particular battery shield. Below a certain current draw the shield will shut down and only provide power again when you press the tactile button on the side. Also if the shield shuts down due to battery going low and protection jumps in you will have to remove the batteries and reinsert. The shield has no power path
I started back 4 years ago with a D1 mini but ditched it as it was still using too much enerty with it’s voltage regulator. I moved to ESP12F and powered it from the 3.3V on the shield. That worked for longer but I’m up about 54 degrees north so not as much sunshine and I only had a 11x8cm solar panel.
Don’t believe the 10W power advertised by the seller unless you have measured it yourself.The temperature sensor is relatively easy but air quality sensor might be too much of a power drain depending on what you choose.
I’m assuming you want the project to be relatively small
Italy has good sunshine but it can also be cold. The lithium cells don’t hold their charge as well when cold and potentially can be damaged by charging in a sub zero temp.
I use this freezer thermostat to stop my batteries charging if below freezing.
So much this.
I went through a ridiculous number of solar panel refunds and returns until I got an actual 5V 5W (peak) panel.
I used to use an ESP to monitor my mailbox. A 5V 5W panel and one 2200Ah LiPo cell was fine for that as 99.9% of the time the device was asleep. Only waking for a short time once a day to check in or when the mailbox flap was opened.
You want to use deep sleep to get reasonable run times 
I ditched the battery shield for a MCP73871 which has a power path and use a 450mAh cell with a 90x30mm(time will tell if this is enough for a powerpath) solar panel that provides a peak current of 60mA which is 0.33 W to power my battery charger. I have to use deepsleep with very short awake times and powering on the temp/humidity sensor just before wifi comes on. I’ve put about 2 feet distance between panel with sensor and the ESP with the cell as when in direct full sunshine the ESP would crash when temp went into the 30s.
It’s tricky to test it. In italy on winter sun is too low. At summer it’s too hot, you need to cool the panels to standard temp.
Size can give some indication if panel Wp is totally fake or not.
10Wp poly panel should to be at least 700cm2, like 20x35cm.
Saw this on ebay. Only a third the surface are you suggested. Things don’t add up. It is monocrystalline though. LOL
Buyer beware
0.6A at 5V gives 3W…
yup! Can’t trust anyone.
Maybe that 3m usb-cable is harvesting 7W from 100MHz radio transmissions playing AC/DC 
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This is my solar panel:
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It’s 175x120mm (it’s typeC with no adapter)
It is normally used for IP cams
~2W panel, I have one like that connected to my Reolink cam. Does the job for it.
I want ti use it for an ESP32
Post #4 charger not possible?
Maybe… but what does it need to charge? What kind of battery can power my ESP 24 hours?
I thought that, since a power bank kept my ESP running for about 24 hours, and since the panel recharged my power bank in a few hours, I thought that by installing a battery of about 10,000 mAh I could use my ESP without problems.
At first I considered installing a simple power bank, but then I read that there could be problems with shutdowns or not charging/powering at the same time.