Solar powered all sky camera.

[cjdawson]

I'm planning a my astronomy project for 2023.  This is going to be a solar powered all sky camera based on a Raspberry PI 4 (8Gb model) with a ZWO ASI 462MC camera.    I'm thinking about the rest of the bulid, and have decided that the Dewcontrol 12v heater ring should work well.

Here's a list of the things that I've been thinking about for this project, so ensure it's success.

 

1. Controller - Raspberry Pi 4 (8Gb Model)  (Already have)

2. Camera - ZWO ASI 462MC  with standard lens (Already Have)

3. DewControl 12v dew heater (on order)

4. Relay that will be PI controlled, (Have some already, but likely to order a different one later, I have duel relays, but will only need a single)

5. Temperature and humidity sensors.   (want to calculate the dew point and keep the camera dew free)

6. Battery

7. Solar controller (already have one)

8. Solar panels. (have 50w panel, will this be enough)

9. SSD or MicroSD?

 

My plan is to have the camera, PI and heater all run from the battery, and have the battery charged by solar power. 

For the OS, I know that there's an all sky project on Github that I'll be using for the camera control part of things, that's going to do most of the work.  The PI will connect to my home network via Wifi, the build in wifi on the PI should be good enough, especially as it'll be in a plastic enclosure.

I'm not sure what size battery I'd need to be able to set this up and leave it running.  Most likely a 10Ah 12V battery should do the job?      I'm thinking of getter a 12v to USB C adapter to run the PI on.  That should provide enough power without worrying about under volting the PI.

The real question here is will a 10Ah battery be enough to keep the PI running 24/7, and will a 50W panel be enough to keep the battery alive through the winter?

 

Would be interested in others experiences as it would be helpful in allowing me to come up with a solution that is going to be up to the job.

[vlaiv]

1 hour ago, cjdawson said:

The real question here is will a 10Ah battery be enough to keep the PI running 24/7, and will a 50W panel be enough to keep the battery alive through the winter?

Probably not.

PI4 alone on idle draws about 2.8W of power according to this:

https://linuxhint.com/power-consumption-raspberry-pi/

With camera and dew heater - you can easily hit 10W of power consumption total (not sure what is the wattage on that dew heater), and 10Ah battery will provide you with ~120Wh (in reality less than that as you don't want to run your battery flat), so you have something like 12h of operation on a single charge. That will do for the night, but larger issue is recharging that battery during the day.

I'm running full scale solar array on my house and in December, stats are as follows: - less than x1 installed power rating in Wh on average. I have 10.6KW array and on a sunny day it manages to produce 12-14KWh, but on cloudy day - it produces only 2-3KWh - and I'm at 45 degrees latitude.

This means that on average, 50W panel will produce less than 5Wh of power - so it will take something like 24 days to fully recharge that battery. As a contrast, on a sunny summer day, when you point the array at the sun directly, it will take something like 3-4h to charge that battery fully.

If you want to run trouble free - I'd increase size of battery to say 50Ah (this will give you 5 nights autonomy) and to be able to charge that you'll need at least one full sized panel of  ~700W if not two.

[cjdawson]

The heater is 2.8 Watts, I know that the PI's power supply needs to be 15watts max.   So when running at full power, we talking about 18Watts of power.

I suppose, the best idea would be to split to project into several parts.

 

1. The All sky Camera, Dew Control and sensing.

2. The power bank

3. The recharging solution

 

This way I can build the camera itself and get that working.    This would be powered by anything 12V, no requiring anything specific.    This will allow me to take measurements of the power consumption, so that I can then size the battery, based on real world usage.     This would then allow me to properly size the charging part without over or under doing it.   All it needs to be able to do is put enough charge into the battery to get through the night in the winter.   During the summer, it should be able to top off the battery.   Though, I wouldn't want to discharge too far.

[vlaiv]

5 minutes ago, cjdawson said:

 All it needs to be able to do is put enough charge into the battery to get through the night in the winter. 

You can already do some basic calculations based on where you are located.

https://www.pvfitcalculator.energysavingtrust.org.uk/

This is for full scale solar array - it it will give you idea of what you can expect (you could scale things by 100 so instead of using 50W  - put in 5KW array and see what sort of energy you'll get on average during December/January).

Another way of doing it is by simple spreadsheet.

Nominal output of panel (say 50W) - is possible if incident light is at 90 degrees to panel surface and sun is at zenith on a clear day.

You can calculate the loss due to air mass in the same way we do it for stars - in magnitude change and from magnitude change you can get power factor. Further - you need to account for angle (use cosine of incident angle). Make calculations for each hour on average depending on your install angle.

Resulting number will be available power on a sunny day, but you need to account for number of sunny hours during the month.

Here is breakdown of production from 10.6KW array in December here (not yet over, so it show only up until today):

So it ranges between 15KWh at peak down to below 3KWh of daily production - with average being less than 10KWh.

This is for unoptimized angle (or rather suited for whole year round). You should get better performance if you optimize your angle for winter production, but it won't wary by much.

50W panel should therefore produce ~45Wh of power on average daily. Sorry I made mistake in above calculation - it won't take 24 days to fully charge 10Ah / 12V battery - but rather 10 times less - but still over two and a half days (120Wh / 45wh per day = 2.666... days).