Ask HN: Building an Overengineered Chicken Coop with Hybrid Energy Harvesting
The Problem: We decided to hop onto the "egg prices are high" bandwagon and buy into the importance of always having eggs as we have bakers in the family who must bake whenever it suits them. We have 6 chickens arriving in September, and I’m estimating that about 4-6 will make it to the coop as hens. Like any reasonable person, I thought "I should automate the chicken hatch so I don't have to go outside twice a day." Your typical solar + battery setup would work fine in the summer, but I was curious about supplementing it with thermoelectric generators (TEGs) for winter energy capture. Chickens are little 105°F heat engines that cluster together at night, especially in winter when solar energy is weakest. With a metal roof and some TEG’s, could I capture enough energy to run all of my coop things?
The actual requirements: Door control, temperature monitoring, water/feed level alerts, and egg detection. No grid connection, but within BLE distance. All sensor data flows into Home Assistant for convenience.
Estimated power budget analysis: • Door servo: ~0.5Wh daily (10W for 10 seconds, twice daily) • ESP32 + sensors + BLE transmission: 1-20Wh daily (depends on transmission frequency) • Total: 1.5-20.5Wh daily Energy sources: • Small solar panel (10W): 10-60Wh daily (seasonal variation) • TEG array on coop roof: 2-40Wh daily (winter peak, summer ~zero)
Hardware Foundation I’m considering ESP32 for door automation, then extend it with sensors and integrate everything with Home Assistant for monitoring/alerts. Sensors: • Temperature/humidity (DHT22) in the coop • Door position (reed switches) • Water level (float switches in barrels—keeping it simple) • Food level (load cell under feeder) • Egg detection (load cell in collection tube + weight logic) Power System Questions: • Multiple TEG modules mounted on interior roof surface—but how many? 4-8 small units vs 2-3 larger ones? • How should I mount the TEG modules properly to a metal roof, which would be insulated on the inside? Heat sinks on the exterior? • Can a solar charge controller handle both solar + TEG inputs simultaneously? • Is 12V LiFePO4 (50-100Ah) overkill for this power budget? I need something that can be stable and handle a week over 100 degrees and winters as low as the 20’s.
Software Strategy Adaptive power management based on available energy: • High power: BLE transmission every hour (overkill?) • Medium power: Every 6 hours • Low power: Daily + emergency alerts only Using BLE instead of WiFi should cut power 10-20x per transmission (0.1-0.2Wh vs 1-1.5Wh). Does this math seem right?
Thermal Engineering Assumptions Here's where I'd really appreciate feedback: • Ceiling insulation to trap warm air near TEGs • TEGs between interior roof and exterior heat sinks • Assuming ~20-40°F differential in winter (chickens warming interior vs 40-50°F outside) • Coop volume: 3x5x4 feet for 4-6 chickens. Vertical space is being used
Am I missing something obvious about heat transfer or thermal bridging?
The goal is a completely autonomous system that runs for months without intervention, scaling its monitoring frequency intelligently based on available power. Of course, I'll be out there for the eggs most of the time, but will want to know if something isn't working.