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pdavis

Help designing a tiny solar system (self.solardiy)

submitted 10 months ago by MossyHabitat to c/solardiy

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For several years I've used a Raspberry Pi Zero for sensors, camera & door motor control which opens & closes a chicken coop door. The Rpi & controller is 5v, the motor is 12v. This has been powered by around 50' of extension cord, but the elements are beginning to weather the cord & we also need to move the chickens further away from our mains. I think it is time to implement solar. I aspire to assemble a PV, battery, & converter system which:

Uses an off-the-shelf 12v PV panel (30w or so)
Uses LiFePO cells for heat resiliency & stability
Provides both 12v & 5v power
Isn't proprietary; uses standard, easily-sourced components... unless it meets specs perfectly & isn't terribly expensive.
Minimal power draw; at most 2 amps @ 12v for 10 seconds twice daily.

Does anyone have suggestions regarding this configuration, know of a post, blog, or video which does something similar, or is willing to ID components you'd recommend for this project?

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[–] [email protected] 3 points 10 months ago* (last edited 10 months ago) (1 children)

Do you have stats on how many watt hours you collect from the 100w panel in the Dec/Jan (assuming you’re in the northern hemisphere),

You can model average insolation (and use that to extrapolate average harvest) by month using tools like PVwatts. Here's a walkthrough.

Using Bowling Green, KY as an example since it's on the 37th. 100w of flatmounted panel on an MPPT solar charge controller would average:

Solar wattage	100
Month	Daily Wh Avg
Jan	168
Feb	249
Mar	331
Apr	426
May	513
Jun	598
Jul	555
Aug	506
Sep	396
Oct	305
Nov	201
Dec	156
Average	367

Derate those yields by ~18% if using PWM. <-- rule of thumb, not gospel

if we are on the west coast instead, here's Santa Cruz, California:

Solar wattage	100
Month	Daily Wh Avg
Jan	206
Feb	286
Mar	386
Apr	519
May	582
Jun	642
Jul	605
Aug	542
Sep	447
Oct	349
Nov	245
Dec	183
Average	416

and how those stats vary on overcast days vs sunny?

The figures above are daily averages, including normal weather patterns and are how we size our systems. But for the sake of curiosity/understanding, my observations have been that if my clear-day harvest is X then overcast is 0.6X, bright overcast is 0.7X and dark/rainy is 0.05-0.10X. Cloud-edge effect and other reflective phenomena can result in harvest >1X.

While it does freeze here (occasionally down to 0° F) the battery will be inside the chicken coop where the temp has always remained above freezing.

A battery warming solution could be implemented for $20 (warming pads, 12v temp controller).

[–] [email protected] 1 points 10 months ago* (last edited 10 months ago)

Not OP but this is really neat. Thanks.

Over the past few days my system has been severely under performing in relation to these calculations. For January it says 290 Wh per day, but I'm only seeing 50. I do have a lot of trees, so probably some shading... maybe even a lot of shading.

Jan	290.3
Feb	392.9
Mar	387.1
Apr	400.0
May	387.1
Jun	400.0
Jul	419.4
Aug	387.1
Sep	400.0
Oct	322.6
Nov	300.0
Dec	290.3