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Comment by walrus01 | Hacker News Reader

If the people who created this are here in the thread, some questions on the power system...

1. What is your baseline calculation for Wh per day produced by the PV panel?

2. More precise specifications on the PV panel?

3. What is the calculated load in Wh per day? How much of this is dependent on data traffic level? (eg. Does it go into a sleep mode?)

4. Have you calculated this for sunlight levels in mid winter, off grid, at latitudes 48 and above? The Wh produced in a day, week or month by that size panel somewhere like North Vancouver, BC, will be really low from November to February due to short day lengths and winter weather.

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The hardware section mentions:

> disaster.radio nodes are capable of functioning in most moderately sunny locations

I live in Northern Europe (54N) and wanted to use an old phone as a time lapse camera in a remote location without power or internet (hence the phone rather than something like a Raspberry Pi). The battery when fully charged would last ~3 days, so I just needed a solar panel big enough to keep it topped up.

I figured a 20W solar panel would be sufficient, as most phones use way less than that when charging. In my initial testing in direct sunlight this panel was barely able to keep the battery % the same, let alone charge it. I'm not sure whether I just needed or a bigger panel, or it was just the 20W solar panel I got from eBay not really being 20W. If anyone has any experience with this I'd still like to do the project :-)

That will almost certainly need a much bigger panel. If a phone is a 3W constant load, that's 2232Wh in a month, except in summer there is no way a nominally 20W cheap PV panel will keep up with that from October to March at latitude 54. Combination of short daylight hours and overcast weather so rarely any direct sunlight.

The 20W rating is at what is called standard test conditions, basically equivalent to direct sunlight in the Arizona desert.

You'd probably want at least a nominal 180W panel and a basic 25 Euro PWM PV charge controller.

The rating for a panel is the absolute best case where it has full direct sunlight and the panel is cold. Most of the time you will be getting less than the rated power.

In Germany, the solar panels in commercial installations produce about 10% of their peak wattage averaged over a year. I guess these are installed in locations with good insolation. So at best you could assume some 2W on average from your 20W panel. But if it didn't even work in direct sunlight, the panel was probably broken.

In theory, couldn't you boost the input light by using a couple of mirrors (one capturing light below the panel, one above the solar-incident light shining down at a Summertime angle?) or some carefully position Fresnel-style lensing?

Is polarisation of the reflected light an issue?

I am the current maintain of the firmware for this project. Recently, I've been doing development for it using the LILYGO TTGO ESP32 dev board (V2.1_1.6) https://www.aliexpress.com/item/32915894264.html?spm=a2g0o.p... Therefore, power consumption specs should be similar to this board.

We are working on a new board design with an integrated solar panel and two LoRa radios, but I am less involved in that part of the project, so I can't answer all your questions on the power system. Perhaps this link will help, though it has not been updated for the ESP32, https://github.com/sudomesh/disaster-radio/wiki/Power

Currently, it does not have a sleep mode, I recall there being some concerns with waking up from sleep mode back when I was dev'ing with the ESP8266, not sure if that has changed on ESP32, have not re-approached the idea it since switching to ESP32.

We did have some do some tests with an off-the-shelf 15W solar panel and a super-cap, it seemed to work well. Check out their report, https://sudoroom.org/pipermail/disasterradio/2019-December/0...

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