Chapter 2-4 Electronic Devices / Sustainable Society Prout Village Third Edition

 ○Rare Metal-Free Home Appliances

Many home appliances also use significant amounts of rare metals. Therefore, like smartphones, they are not sustainable and require redesign. The following table summarizes the depletion years of rare metals used in home appliances.

Appliance Category	Main Rare Metals Used	Purpose	Approximate Depletion / Supply Difficulty Year (AD)	Comments
TV (LCD / OLED)	Indium, Gallium	Screen, light emission, touch function	Around 2050	Competes with smartphones and PCs
Refrigerator	Neodymium, Gold, Copper	Motor, circuits, wiring	2035–2050	Magnets are the biggest challenge
Washing Machine	Neodymium, Copper, Nickel	Rotating motor, control circuits	Around 2040	Long lifespan design is important
Microwave Oven	Gold, Tin, Tantalum	Circuit board, component fixing, capacitors	Around 2045	Miniaturization makes recovery difficult
Air Conditioner	Neodymium, Copper, Aluminum	Fan motor, refrigerant circulation	2040–2055	Mass production drives demand
Vacuum Cleaner (Cordless)	Lithium, Cobalt, Neodymium	Battery, motor	2035–2045	Battery is the main limiting factor
Personal Computer	Tantalum, Gold, Indium, Tin	Electronic circuits, memory, display	2035–2050	Contains many types of rare metals
Smartphone	Indium, Tantalum, Cobalt, Lithium, Gold	Screen, circuits, battery, camera	2035–2045	Average lifespan of 2–4 years is unsustainable
Rice Cooker / Oven	Copper, Gold, Nickel	Heating coil, control circuits	2040–2060	Reducing electronic parts can improve sustainability
Speaker / Audio Equipment	Neodymium, Gold, Palladium	Magnets, wiring, contacts	2035–2045	Increased rare metal use for better sound quality
LED Light (Lighting)	Indium, Gallium, Rare earth elements (e.g., Europium)	Light-emitting elements, phosphors, contacts, semiconductor substrates	2035–2050	Highly efficient but uses many rare metals; low recovery rate

Home appliances found in Japanese households have become unsustainable. Therefore, Prout Village aims to create Mid-tech-oriented home appliances designed for sustainability, assuming the use of local resources and manual repair and regeneration.

●Rare Metal-Free Refrigerator

Component	Alternative Method / Material	Description
Cooling Method	Absorption refrigeration (Ammonia + Water + Heat source)	No compression motor needed, resulting in fewer failures. Uses heat (firewood, solar heat, biogas, etc.), minimizing dependency on electrical infrastructure and reducing electricity consumption at the village level. Approx. 4–10°C (refrigeration), around －10°C (with freezing function).
Refrigerant	Ammonia	Natural refrigerant replacing fluorocarbons. Requires no rare metals and can be recovered and reused after use.
Power Source	Magnesium battery / Hydroelectric power / Solar thermal water heater / Firewood / Biogas	Operates with thermal energy and renewable electricity.
Insulation Material	Wood + Sawdust + Carbonized cork + Hemp cloth	Natural materials with no rare metals used, ensuring insulation performance.
Structural Material (Body)	Recycled wood / Aluminum / Recycled iron	Uses locally sourced materials to build a durable and highly recyclable body.
Control Device	Mechanical temperature controller / Simple thermal expansion thermostat	Simple structure without electronic control. Easy to repair and maintain within the village.
Lighting	Carbon filament incandescent lamp	Uses carbon filament made from bamboo and cotton materials. Provides natural warm light inside. Replaceable and regenerable for several hundred to 1000 hours.

Reasons Why the Rare Metal-Free Refrigerator Is Sustainable

1. It can also use methods that hardly consume electricity.

・Uses heat (firewood, solar thermal water heater, biogas, etc.) as an energy source, thus does not depend on electrical infrastructure.

・Requires manual adjustments every few hours.

・Minimizes electricity consumption even at the village (Municipality) level.

2. No compressor or motor → fewer breakdowns.

・Conventional electric refrigerators often fail due to motors, pumps, or circuit boards.

・Absorption refrigeration has almost no moving parts, making it highly reliable.

3. No rare metals required (by design).

・Refrigerants are natural substances such as ammonia and water.

・Ammonia has a boiling point of －33.3°C and high latent heat, enabling efficient heat absorption.

・The body, insulation, and structure can be built from wood, recycled metals, and natural fibers.

・Eliminating electronic controls makes a completely rare metal-free design possible.

4. Long lifespan.

・With proper maintenance, can last 20–30 years or more.

・Many gas-type camping refrigerators have remained in use for over 20 years.

5. Easy to repair.

・Simple structure allows for repair without specialized knowledge.

・Spare parts can realistically be produced within the village.

6. High recyclability.

・Most materials are reusable or recyclable.

・Refrigerants like ammonia can also be recovered and reused.

●Rare-metal-free earth tube cooling

An earth tube is installed by digging a trench about 1.5 to 2.5 meters deep in the ground and embedding pipes. The air at a constant temperature underground passes through the pipes and is sent indoors, serving as cooling in summer and as heating support in winter.

Temperature changes when using earth tubes (around Tokyo)

Season	Example outside air temperature	Underground temperature (depth 1.5–2.5 m)	Approximate temperature of air taken into the room	Effects / Remarks
Summer	Max 35–38℃	About 15–18℃	About 18–22℃ (cooling of 10–15℃)	Depending on humidity and ventilation amount, differences close to 20℃ are possible. Usable day and night.
Winter	Min －5–0℃	About 15–18℃	About 10–15℃ (warming of 10–20℃)	Large temperature difference makes it effective as heating support.

Material comparison table for earth tubes

Material name	Sustainability	Characteristics	Notes / Remarks
Ceramic pipe (high-temperature fired pipe)	◎ Very high (semi-permanent use possible)	High durability / historic use in ancient sewage systems	Heavy and expensive / processing and construction labor-intensive
Unglazed clay pipe	◎ Very high (natural, locally sourced possible)	Excellent moisture absorption and release, good affinity with soil	Slightly low strength / airtightness requires attention / easy to repair
Bamboo pipe (processed)	○ Relatively high (renewable resource)	Lightweight / good ventilation / inexpensive	Requires preservative treatment / low durability / suitable for short-term or temporary use

Design proposal

Element	Recommended composition
Earth tube diameter	150–200 mm
Length	15–25 m (preferably installed on the shady side)
Number	2–4 tubes (ensure intake routes from different directions)
Material	Unglazed clay pipe or high-temperature fired ceramic pipe (+ crushed stone layer for insulation and drainage)
Fan	DC blower fan + solar panel (20–30W) / air outlet installed at the center
Airflow	Intake from ground → cooling through tube → into room center → exhaust from high windows or chimney (combined with gravity ventilation)

●Rare‑Metal‑Free Absorption‑Chiller‑Based Air‑Conditioning System

Item	Details
Energy Source	Magnesium batteries, micro‑hydro, solar thermal, firewood, or other locally renewable heat energy
Cooling / Heating Method	Absorption chiller (ammonia + water) that delivers both cooling and heating from heat energy
Refrigerant	Ammonia + water (natural refrigerant with very low environmental impact)
Rare‑Metal Use	Virtually none ― no motors or semiconductors, so resource load is extremely low
Electricity Demand	Only a tiny amount for any pump or control device (small wind power is sufficient)
Sustainability	Very high ― no fossil fuels, minimal resource load, ideal for a circular, regional society
Size / Installation	Optimized for high‑airtightness homes such as straw‑bale houses; high insulation allows efficient, low‑energy operation
Maintenance	Periodic checks of the refrigerant loop and combustion unit; simple structure keeps technical burden low
Safety	Careful handling of ammonia is essential; proper knowledge and training are mandatory
Comfort	Comfort can be enhanced with basic electrical controls; despite absorption‑cycle limits, provides ample cooling and heating
DIY / Municipal Operation	With training, residents or Municipalities can build and run the system; perfectly fits a local‑resources, local‑production model

●Rare-metal-free underfloor hot water heating
During the day, solar energy is collected to heat the water in a storage tank. The hot water circulates through pipes to warm the floor heating system and heat the room. On cloudy or rainy days, electricity heats the storage tank water to warm the room. The heating element does not use rare-metal nickel-based nichrome wire but instead uses copper or iron wire.

Item	Description
Solar hot water heater	A device that collects sunlight and heats water. Often installed on roofs or walls.
Hot water circulation	Heated hot water is sent through pipes to the underfloor heating system.
Underfloor hot water heating	Hot water flows through pipes under the floor, gently warming the entire room.
Indoor heating effect	Radiant heat raises the perceived temperature, creating a warm and comfortable environment starting from the feet.
Energy efficiency	Utilizes natural solar energy, reducing electricity and fuel consumption.
Electric heating (cloudy/rainy days)	Electric heater warms the storage tank water. Heating elements use copper or iron wire without rare metals, powered by electricity.

●Rare-metal-free solar thermal panel air heating

Item	Description
Solar thermal collection	Black heat-absorbing surface absorbs sunlight and warms the air inside the box-shaped panel.
Blower fan	Warm air is sent through ducts into the room. The warm air is directed onto the inner earthen walls of a strawbale house so that the walls store heat and slowly release it at night for nighttime heating. Ideal wall thickness is 20–30 cm.
Indoor air circulation	Warm air spreads throughout the room, raising the room temperature.
Control device / temperature sensor	Automatically manages fan operation to prevent overheating and optimize efficiency.
Ventilation / exhaust openings	Removes indoor moisture and stale air and brings in fresh air.

●Summary of Cooling and Heating Equipment

Purpose	Pathway	Usage Time
Cooling①	Earth tube	Morning, noon, night
Cooling②	Solar hot water heater → Absorption chiller (ammonia + water)	Morning, noon (Earth tube prioritized)
Heating①	Solar hot water heater → Hot water underfloor heating	Morning, noon, night
Heating②	Electricity → Hot water underfloor heating	Night on rainy or cloudy days
Heating③	Solar thermal panel air heating	Morning, noon
Heating④	Heat storage in strawbale house earthen walls from air heating	Night
Hot water supply & living heat source	Solar hot water heater → Bath, hot water supply, washbasin	Morning, noon, night

For residential cooling, the earth tube is considered the first priority. For heating, the combination of solar hot water underfloor heating and solar thermal air heating with forced air circulation is planned.

When using an absorption chiller with ammonia, the piping is installed near the room ceiling.

The following table shows the total size of the solar hot water heater and tank for a residence with a 12 m diameter, two floors, and a family of six. The equipment with a total width of about 11 m and height of about 2 m is installed around the residence. This accounts for about 29% of the circumference (approx. 37.7 m).

For space efficiency, the solar hot water heater is installed as the roof of a small carport.

Heat Flow in the Solar Thermal System

Step	Flow Description	Equipment / Location	Role / Key Points
1	Sunlight hits the solar hot water heater panels	Roof/wall panels	Heats antifreeze or water with solar thermal energy
2	Heat transfer fluid (antifreeze etc.) is sent to heat exchanger	Indoor heat exchanger	Transfers heat from fluid to tank water
3	Heat exchanger heats the storage tank water	Indoor storage tank	Stores heat for hot water underfloor heating
4	Heat exchanger also heats the domestic hot water tank water	Indoor domestic hot water tank	Stores hot water for bath, washbasin, and kitchen
5	Heated water circulates through underfloor heating pipes	Underfloor piping / indoor	Radiant heat gently warms the entire room
6	Domestic hot water is supplied through supply piping	Kitchen, bath, washbasin	Meets daily hot water needs
7	Electric heater (copper or iron wire) provides auxiliary heating	Heat exchanger or storage tank	Maintains and supplements heat on cloudy days or at night

Solar Thermal Hot Water System + Tank Configuration

Item	Main Use	Approximate Capacity	Temperature Range	Approximate Size (Diameter × Height)	Installation / Notes
Solar hot water heater	Heat source for heating, cooling, hot water supply	Heat output about 10–12 kWh/day (for 6 people)	Max around 90°C	One panel approx. 1.5m × 2.0m × 6–7 panels (approx. 15㎡)	South-facing, tilt 30–45°. Installed as small carport roof
Storage tank (for heating)	Hot water underfloor heating	200–500 L	About 40–60°C	φ50–70cm × height 120–160cm	Indoor insulation required / placed near floor
Domestic hot water tank	Hot water for bath, washbasin, kitchen	300–500 L	About 50–70°C	φ60–80cm × height 150–180cm	Indoor or outdoor shaded area (insulation required)
Water supply tank	Storage of rainwater, spring water for daily use, laundry	1,000–2,000 L+	Room temperature	φ100–150cm × height 130–200cm+	Outdoors, directly under gutters / filtration recommended
Cooling storage tank (optional)	Heat source for absorption chiller night cooling	100–300 L	Approx. 60–90°C (heat side) / 5–15°C (cool side)	φ50–60cm × height 100–150cm	Near cooling equipment / insulation and shading required

●Rare Metal-Free Washing Machine

Item	Description / Example Materials
Power Source	- Locally sourced renewable energy- Mechanical assistance via hand crank or foot pedal
Motor Structure	- Brushed motor with iron core and copper winding (no permanent magnets)- Induction motor- Equipped with clutch and gear mechanism for manual drive
Electronic Control	- Low-power microcontroller (uses ceramic capacitors and components with reduced rare metal content)- Can be paired with mechanical timer to control spin duration
Body / Exterior	Recyclable steel plate, aluminum, weather-resistant natural wood, recycled bioplastics
Wash Tub / Agitator	Made of stainless steel or durable recycled plastic. Designed to withstand centrifugal force during spin cycles
Gears / Bearings	Mechanical gearbox with iron and brass gears and bearings. Includes clutch for switching between manual and electric drive
Wiring / Electrical Materials	High-purity recycled copper wire. Insulation made from biodegradable resin or silicone-based material
Detergent Compartment / Plumbing	Natural rubber gaskets, stainless steel or copper pipes
Spin-Drying Function	- High-speed rotation (600–1000 rpm) using iron + copper motor- Auto-stop via mechanical timer- Balancing mechanism- Equipped with safety brake
Manual Drive Option	- Operated via hand crank or foot pedal- Equipped with clutch to switch or combine electric and manual modes
Safety Features	Low-voltage design, mechanical overload protection, centrifugal balance adjustment, shock protection measures
Maintenance	Easy replacement of brushes, bearings, and wear parts. Repairable at local workshops in the community

●Rare Metal-Free Rice Cooker

Item	Description / Example Materials
Power Source	- Locally available renewable energy
Heating Method	- Electric resistance heating using nichrome wire or other non-rare-metal materials- Manual ignition with firewood or biomass heat also possible
Control Method	- Mechanical timer (e.g., spring-wound) to control heating duration- Simple temperature regulation using thermal fuses or bimetal switches
Inner Pot (Cooking Vessel)	- Durable stainless steel (contains no rare metals)- Ceramic- Earthenware or other natural materials
Exterior	Recycled steel plate, aluminum, natural wood
Safety Devices	- Mechanical overheating protection (thermal fuses, bimetal relays)- Leakage breaker (non-electronic options available)
Maintenance	- Designed for easy disassembly and cleaning by the user. Parts are easily replaceable.

●Rare Metal-Free Vacuum Cleaner

Item	Description / Example Materials
Power Source	- Locally sourced renewable energy
Motor Structure	- Brushed motor with iron core and copper wire (no permanent magnets)- Induction motor also possible
Electronic Control	- Low-power microcontroller (with reduced rare metal content)- Simple on/off switch- Can be combined with mechanical timer for basic control
Main Body / Exterior	Recycled steel plate, aluminum, weather-resistant natural wood
Suction Head / Brush	Roller brush made from recycled fibers, sealed with natural rubber gaskets. Replaceable and repairable locally
Hose / Piping	Natural rubber hose and gaskets. Designed for durability
Dust Container	Stainless steel. Easy to open, close, and clean
Suction Fan	Fan driven by motor with iron and copper winding. Supports high-speed rotation. Wear parts can be replaced
Safety Features	Overload protection, low-voltage system, overheat prevention, mechanical braking system
Maintenance	Brushes, filters, and bearings can be replaced. Local repair support available

●Rare Metal-Free Speaker

Item	Description
Drive System	Analog amplifier + speaker unit (preferably vacuum tube amplifier)
Amplifier Design	- Fully rare metal-free vacuum tube amplifier, or a rare metal-free transistor amplifier design- Manually repairable wiring and components
Speaker Unit	- Full-range mid-frequency unit with paper cone (special acoustic-grade paper diaphragm) and ferrite magnet- No use of rare earth magnets like Alnico or neodymium
Enclosure	- Resonance cabinet made of locally sourced wood (e.g., bamboo, thinned wood, strawboard)- Nails and adhesives should prioritize natural materials
Power Supply	Designed for low-voltage operation around DC 12V (compatible with renewable energy)
Functionality	- No Bluetooth or other wireless functions (to avoid rare metals)- Wired input only (RCA / mini-plug), for simplified structure
Repair / Restoration	- Can be disassembled with a single screwdriver- Easy-to-replace components (wiring, units, power supply)
Usage	For village-wide announcements, local events, music playback, language and educational purposes

●Rare Metal-Free Light

Item	Description
Name	Incandescent lamp (carbon filament type with glass bulb)
Light Source	Electric illumination using carbon filament
Materials Used	Glass bulb, carbon fiber filament (bamboo or cotton), copper wiring, ceramic or wooden socket
Use of Rare Metals	None (completely rare metal-free)
Lifespan	About 500–1,000 hours (replaceable and restorable)
Power Supply	Renewable energy
Brightness / Illuminance	Soft warm light; multiple lamps or supplementary lighting may be needed for reading or tasks
Manufacturing / Repair	- Handmade within the Municipality- Can be manufactured and repaired in small local workshops
Usage	Residential areas, shared spaces, lamp stands, and low-light zones

Thus, each product can be designed with near-zero to extremely small amounts of rare metals, resulting in an extremely low risk of resource depletion even if deployed on a global scale for a population of 10 billion.

Item	Description
Rare Metal Usage	Each product can be designed with near-zero to minimal rare metal content. Even on a global scale, the risk of resource depletion remains extremely low.
Renewability	Most components can be repaired or regenerated within the local region. Optimal for a locally-sourced infrastructure.
Waste & Environmental Impact	Plastics are not used, and electronic components are minimized, eliminating landfill waste and microplastic emissions.
Feasibility of Global Implementation	Both materials and structural designs are highly sustainable and adaptable to local contexts, avoiding resource depletion and geopolitical dependency.

Many home appliances use motors, and considering durability, efficiency, and design flexibility, induction motors and ferrite magnet motors are viable options, while small and simple appliances can also use brushed DC motors. All of these motors are rare-metal-free, do not depend on scarce resources, and can be used sustainably. By selecting appropriately among these three types of motors, it is possible to design home appliances that are sustainable and independent of scarce resources.

High-tech technologies such as smartphones, PCs, AI, and EVs are based on a temporary bubble of energy and resources, representing a singular structure that can be said to disappear along with resource depletion.