Open-source off-grid power, water purification, and homestead systems built entirely from hardware store materials.
We've got dreams of a homestead where we can live off grid — and that means solving three problems: store power, purify water, and do it all without a monthly bill. Everything here is designed to be built by one person in a garage with a 3D printer, a propane torch, and a trip to Home Depot. No specialty lab equipment. No Nafion membranes. No $200/liter vanadium electrolyte.
Can we pull it off with table salt, scrap iron, and PVC cement? Yeah. We got this.
| Project | Status | Description |
|---|---|---|
| Flow Battery | Active | All-iron redox flow battery — stores energy in liquid electrolyte |
| Membrane | Active | DIY ion exchange membranes from ground resin beads + PVC cement |
| Electrode | Active | "Popcorn Ball" intumescent carbon foam electrode — our novel contribution |
| Electrolyte | Active | Ferrous chloride from scrap iron + hydrochloric acid |
| SEM Cell | Planned | Salt Electro Mining — make your own HCl and NaOH from table salt |
| ED Water | Planned | Electrodialysis water purification — $100 vs $4,000 conventional |
| Store | Planned | Kit sales and e-commerce |
A flow battery stores energy in liquid electrolyte, not in solid electrodes like lithium. The liquid is pumped through electrochemical cells where the reactions happen. Separate the power (cell size) from the energy (tank size) — want more runtime? Get bigger tanks. Want more watts? Add more cells. They're independent.
Both sides use the same base electrolyte: ferrous chloride (FeCl₂) dissolved in hydrochloric acid.
- Positive side: Fe²⁺ ↔ Fe³⁺ + e⁻ (iron stays dissolved, changes oxidation state)
- Negative side: Fe²⁺ + 2e⁻ ↔ Fe⁰ (iron plates as metal during charge, dissolves during discharge)
- Cell voltage: ~1.2V open circuit, ~1.0-1.1V under load
- Round-trip efficiency: 70-80%
| Feature | All-Iron | Vanadium | Lithium |
|---|---|---|---|
| Electrolyte cost | Free (scrap iron + salt) | $150-200/liter | N/A (solid) |
| Toxic materials | No | Yes (V₂O₅) | Yes (cobalt, fluoride) |
| Membrane crossover | Self-healing | Capacity loss | N/A |
| Cycle life | Unlimited | 10,000+ | 500-2,000 |
| Fire risk | Zero | Low | High |
| DIY difficulty | Hardware store | Specialty chemicals | Don't try it |
The self-healing property is key: since both sides use the same iron electrolyte, if ions cross the membrane, they just end up where they started. No permanent damage, no capacity fade from crossover. Vanadium flow batteries lose capacity when the membrane leaks. Ours doesn't care.
Two identical 3D-printed ASA boxes glued face-to-face onto a flat membrane electrode assembly (MEA). No gaskets, no bolts through the cell, no complex frame geometry. The box IS the flow chamber, current collector housing, and structural support.
┌─────────────────────────────────────────┐
│ ASA Box (popcorn-coated walls) │
│ ┌───────────────────────────────────┐ │
│ │ Coarse activated charcoal fill │ │
│ │ ┌─────────────────────────────┐ │ │
│ │ │ SS Screen (soot-blackened) │ │ │
│ │ │ ┌───────────────────────┐ │ │ │
│ │ │ │ Popcorn Ball Electrode│ │ │ │
│ │ │ └───────────────────────┘ │ │ │
│ │ └─────────────────────────────┘ │ │
│ └───────────────────────────────────┘ │
├─────────────────────────────────────────┤
│ CATION DIODE FILM (ion gate) │
│ landscape fabric + SAC resin + PVC │
├─────────────────────────────────────────┤
│ ┌───────────────────────────────────┐ │
│ │ Popcorn Ball Electrode │ │
│ │ ┌─────────────────────────────┐ │ │
│ │ │ SS Screen (soot-blackened) │ │ │
│ │ └─────────────────────────────┘ │ │
│ │ Coarse activated charcoal fill │ │
│ └───────────────────────────────────┘ │
│ ASA Box (popcorn-coated walls) │
└─────────────────────────────────────────┘
- ASA, not PLA: PVC cement chemically welds to ASA (MEK/THF dissolves the surface). PLA does not bond — cement just sits on top and peels off. Every seal, coating, and bond in this system relies on PVC cement fusion.
- Both boxes are identical: One STL file. No left/right, no sorting, no labeling.
- No gaskets or O-rings: PVC cement chemical bonds + landscape fabric overhang = zero leak paths.
- Terminals in the sealed zone: Threaded holes in the box wall overlap the mesh in the glued/sealed zone — screws bite into the stainless screen but never penetrate the electrolyte cavity. Zero leak path at the terminals.
- Open pocket with charcoal fill: No serpentine maze channels. The charcoal granules create micro-turbulence and provide massive electrode surface area. The charcoal IS the flow distributor.
| Parameter | 50mm Test Cell | 300mm Production |
|---|---|---|
| Active area | 25 cm² | 900 cm² |
| Estimated power per cell @ 50mA/cm² | ~1.25W | ~49W |
| Estimated power per cell @ 80mA/cm² | — | ~79W |
| Materials cost per cell | ~$0.72 | ~$5-8 |
| Print time (0.2mm layers) | ~10 min | ~45-60 min |
| Both sizes print on | VzBot 400 (400mm bed) | VzBot 400 |
Power estimates are based on cell chemistry and dimensions at theoretical current densities. Real-world performance will be documented on the YouTube channel as we test.
Phase 1 target: 4 cells at 50mm = self-sustaining stack that powers its own pump and charges a phone. Total BOM: ~$150.
This is our novel contribution to the DIY flow battery space. Traditional approaches use expensive carbon felt ($20-50/sheet) or graphite plates. We use cornstarch, Elmer's glue, PVC cement, and ground ion exchange resin — mixed, painted on, and torched.
The cornstarch puffs into intumescent carbon foam (like Night Hawk in Light's Starlite material), creating a porous, conductive electrode with three self-correcting porosity mechanisms:
- Emulsion drying — Elmer's (water-based) mixed into PVC cement (MEK-based) creates an immiscible emulsion. MEK flashes off first, water evaporates later, leaving pores.
- Intumescent torching — Cornstarch carbonizes and puffs into foam. The expanding carbon layer insulates the membrane from heat (same principle as fire-retardant coatings).
- Acid dissolution — Whatever didn't carbonize (unreacted starch, Elmer's) dissolves when the cell fills with acid electrolyte, creating additional flow channels.
Over-torch = more carbon. Under-torch = more dissolves. Either way you get a porous, conductive electrode. Can't lose.
The electrode forms directly on the membrane surface — intimate chemical bond through PVC cement, zero interface gap. This is fundamentally better contact than pressing a separate carbon felt sheet against a membrane.
Full recipe and process: electrode/
We call our ion exchange membranes diode films because they work exactly like a diode in electronics — they let specific things through in one direction and block everything else. Just like a diode is a one-way valve for electrical current, a diode film is a one-way valve for ions.
There are two types:
- Cation diode film — passes positive ions (H⁺, Fe²⁺, Na⁺, Ca²⁺), blocks negative ions and electrons. Think of a turnstile that only lets people with a blue wristband through. Made from SAC resin (the beads that sink in brine).
- Anion diode film — passes negative ions (Cl⁻, SO₄²⁻, NO₃⁻), blocks positive ions and electrons. Same turnstile, but now it only lets red wristbands through. Made from SBA resin (the beads that float in brine).
Both are made from the same bag of mixed bed DI resin beads — the exact same beads used in water softener systems. Separate the two types with a brine float, grind them up, mix 50/50 with PVC cement, paint onto landscape fabric. Based entirely on Rowow's open-source technique. This replaces Nafion ($500-1,000/m²) with a diode film that costs about $0.10 per cell from hardware store materials.
Full fabrication process: membrane/
Buy muriatic acid at Home Depot ($8/gallon). Drop scrap iron in it. Wait 24 hours. You have battery electrolyte.
Or make the acid yourself from table salt and electricity using a SEM (Salt Electro Mining) cell — same Rowow membrane, graphite electrodes, saturated brine, 12V DC. The byproduct (NaOH/lye) is worth $170-330 per batch.
Full details: electrolyte/ | sem-cell/
Same Rowow diode film technique, but now we use BOTH types — alternating cation and anion diode films in an electric field. Positive ions get pulled through the cation films one direction, negative ions get pulled through the anion films the other direction, and clean water is left behind. Combined with activated charcoal channels and UV sterilization: complete drinking water system for $100-150 vs $1,500-4,000 conventional.
Full details: ed-water/
| Material | Where | What It Does | Cost |
|---|---|---|---|
| Mixed bed DI resin | Amazon | Ground into powder for membranes + electrodes | ~$25/5lb |
| PVC cement (clear) | Amazon | Universal binder — welds ASA, bonds membrane, seals tubing | ~$6/16oz |
| SS window screen 18 mesh | Amazon | Current collector, electrode backbone | ~$15 |
| Activated charcoal | Amazon | High surface area electrode fill | ~$8/lb |
| Landscape fabric (non-woven) | Amazon | Membrane reinforcement + gasket + insulator | ~$15 |
| ASA filament 1.75mm | Amazon | 3D printed cell boxes | ~$22/kg |
| Cornstarch | Grocery | Intumescent carbon electrode ("popcorn balls") | ~$2 |
| Elmer's white glue | Walmart | Sacrificial pore former in electrode emulsion | ~$3 |
| Muriatic acid 31% HCl | Amazon | Electrolyte acid (or make your own via SEM) | ~$8/gal |
| Scrap mild steel | Garage | Iron source for electrolyte | Free |
| Table salt | Grocery | SEM cell feedstock for acid + lye production | ~$1/lb |
| Graphite powder | Amazon | Conductive filler | ~$12/lb |
As an Amazon Associate I earn from qualifying purchases.
Full BOM with all links: flow-battery/bom/50mm-test-cell.md
This project wouldn't exist without the open-source work and inspiration of these people. We credit them by name because that's how open source should work.
- Rowow — Invented the open-source ion exchange membrane technique that makes this entire project possible. Ground resin beads + PVC cement = working membrane from hardware store materials. GitHub | Website
- Night Hawk in Light — His intumescent coating and Starlite demonstrations directly inspired our "popcorn ball" electrode method. The puffing carbon foam that protects the membrane from torch heat? That's his principle applied to electrochemistry.
- Cody's Lab — Pyrolysis and materials science inspiration for our carbonized 3D-printed electrode work.
- FBRC — Open-source flow battery community and design files.
- Chemisting — Daniel's detailed documentation of DIY flow battery builds.
- Cayrex2 — 5-part vanadium flow battery build series showing what's possible.
YouTube: ChipMonkeys Off Grid
Follow the entire journey from first test cell to a full off-grid power system. Every build step documented. Every failure shown. Every file free.
Everything is open source — build it yourself from the files here. Or buy a kit with pre-measured, pre-ground materials and save yourself the prep time:
- Materials Kit ($35) — Pre-measured resin, charcoal, fabric, PVC cement, cornstarch, and glue
- Pre-made MEAs ($12 each) — Cast, torched, ready to glue into your boxes
- Assembled Cells ($40) — Printed, sealed, leak-tested — just add electrolyte
- Electrolyte Concentrate ($25/gal) — Ready to dilute and use
- Complete Starter Kit ($99) — Everything in one box. 4 cells, electrolyte, pump, wiring. Build in an hour.
This project involves acid, solvents, open flame, and gas generation. Respect the chemistry.
- Acid (pH 1-2): Chemical-resistant nitrile gloves and splash-proof goggles. Baking soda nearby for spill neutralization. Rinse skin contact immediately with water.
- PVC cement fumes: MEK and THF solvents. Always work in ventilated area or outdoors. Don't breathe this stuff.
- Chlorine gas (SEM cell only): The anode produces chlorine. Run SEM cells outdoors ONLY. If you smell "swimming pool," move upwind immediately.
- Hydrogen gas: Released during charging and iron dissolution. Never seal a cell or container airtight. No flames near the electrolyte.
- Torching electrodes: Outdoors on a fire-safe surface. Keep an extinguisher handy. The torch step takes seconds, not minutes.
Dual License — Personal Free / Commercial 10% Royalty
Personal use is free. Build it, modify it, teach a class, fork the repo — no license needed.
Commercial use requires a license. If you sell kits, components, or products based on these designs, you pay a 10% royalty on revenue. Free to sign up. Self-reported quarterly. All royalties go back into the project. Apply at monkeybusinessmanager.com/offgrid/license.
See LICENSE for full terms.
Build one. Break one. Tell us what happened. Open an issue or pull request. See CONTRIBUTING.md for details.
We run a community electrode challenge — submit your 3D-printable electrode geometry STL and we'll test it on the YouTube channel. See electrode/community-designs/.
ChipMonkeys Inc. — Indiana C-Corp