This document serves as the technical master specification for the Keystone Project's energy architecture. The system utilizes a bifurcated thermal management strategy: High-Grade Generation via Stirling engines for baseload power and Low-Grade Active Thermal Lifting via vapor-compression heat pumps to maximize solar efficiency. The central 4,000-gallon thermal battery acts as the primary energy buffer and distribution hub.
- Source: Thermal Wood Gasifier / Biogas Burner.
- Primary Hardware: Qnergy Stirling Engine Modules (hermetically sealed free-piston units).
- Mechanism: Thermal-to-Electric conversion. High-temperature exhaust (800°C+) from either the gasifier or the biogas burner is buffered in a common refractory-lined sand bed (the "Sand Battery") to feed the Stirling hot-head.
- Role: Baseload electrical generation during low-solar periods (winter) and high-grade thermal supply for the water-based thermal battery.
- Source: PV/T Solar Array.
- Primary Hardware: VFD-controlled Vapor-Compression Heat Pumps (R290/R744).
- Mechanism: Active Thermal Lifting. The system uses surplus electricity to "lift" low-grade heat (30°C–45°C) from the PV/T loop into the 4,000-gallon battery (50°C–70°C+).
- Role: Maximizes PV electrical output by cooling cells and salvages low-grade solar heat for domestic use and space heating.
The 4,000-gallon thermal battery (see heating-thermal-battery-plan) is the energy heart of the homestead. Stability is maintained via a strict Hierarchy of Disposition:
| Priority |
Strategy |
Action |
| 1. Useful Work |
Load Shifting |
Route energy to VHRS (climate control), greenhouse, or domestic hot water. |
| 2. Storage |
Thermal Buffering |
Increase tank temperature (up to 90°C) to store surplus energy. |
| 3. Recovery |
Stirling PowerGen |
If tank > 85°C and electrical batteries < 90%, drive Stirling engines to convert thermal energy back to electricity. |
| 4. Emergency |
Dump Manifold |
If tank > 95°C, divert energy to external air-to-water heat exchangers (dummy load). |
- Modulation: All motors, pumps, and compressors must utilize Variable Frequency Drives (VFDs) for precise energy transfer matching.
- Precision: 3-way mixing valves must use PID control to maintain stable hydronic temperatures and avoid thermal oscillations.
- Fail-Safes: Valves must be configured to "fail-safe" positions (e.g., bypass loops) to protect the Stirling hot-heads and gasifier integrity during power loss.
- Monitoring: Real-time COP (Coefficient of Performance) calculation for heat pumps and electrical yield for Stirling modules via ESP32-based telemetry.
- Homestead Server: A dedicated, low-power server located in the primary Mechanical Shed. It hosts the homestead dashboard, the Community Token Ledger node, and the n8n automation engine. It must be connected to the redundant battery-backed power circuit.
¶ 4. Engineering Standards
- Working Fluid: Helium for Stirling-cycle machines (low molecular weight, inert).
- Refrigerants: R290 (Propane) or R744 (CO2) for heat pumps to maximize environmental compatibility and high-lift COP.
- Mechanical Integrity: Stirling units must be oil-free and dry-running to prevent carbonization/varnish in high-heat zones.
- Standardization: Use of uniform modules (e.g., Qnergy PG-series) for parts interchangeability.
- Phase 1: Install the 4,000-gallon battery and core hydronic piping.
- Phase 2: Integrate LTL via PV/T and initial heat pump modules for climate control.
- Phase 3: Commission HTL via Wood Gasifier and Stirling Engine integration.
- Ongoing: Continuous PID tuning and automation refinement.