3. Cost Analysis and Bill of Materials (BOM)
A target cost of $100 per unit at scale (high-volume manufacturing) drives every aspect of the design. Below we break down the Bill of Materials into major components with rough cost estimates based on current prices (assuming production of tens of thousands of units, which brings significant economies of scale). All costs are in USD. The BOM and cost analysis demonstrate that the design can indeed be produced at low cost, using mostly commodity components and simple manufacturing processes.
Electrochemical Reactor Components
This includes the electrodes (Bi, Ag/AgCl), support structures, chamber, and any pump/valves.
Bismuth Electrode
Bismuth metal powder or sheet (~10–20 g) pressed or coated on a conductive substrate (graphite foil or stainless mesh). Bi is about $15/kg in bulkpubs.rsc.org, so 20 g costs $0.30. Including substrate and fabrication, estimate $2.
Silver Chloride Electrode
A few grams of silver (for a coated wire or mesh). Silver is about $0.80/g; we might use ~5 g ($4). However, reclaimed silver or silver chloride can be cheaper, and at scale this cost might drop. We budget $5 for the cathode including mounting.
Chamber & Housing
Injection-molded or vacuum-formed plastic parts for the chambers, plus O-rings, seals, and the main enclosure. In mass production, a set of plastic parts of this size might cost only a few dollars. We allocate $5.
Pump/Valves
A small DC water pump (e.g. 6 V brushless pump used in appliances or solar fountains) can cost $3–$5 in quantity. Alternatively, two solenoid valves (to alternatively flush water) might be $5 each. We aim to use a single small pump ~$4 and some simple flap valves (pennies each). $5 total for fluid handling.
Gas Capture System
A one-way valve or membrane cap and some tubing if needed to channel CO₂. Off-the-shelf one-way valves (plastic) are maybe $1, and tubing negligible. $1.
Reactor Subtotal: $18
Power Subsystem
Includes the energy harvesting (solar, etc.), battery, and power electronics.
Solar Panel
A small photovoltaic (PV) panel in the 10–20 W range. At scale, solar panels cost on the order of $0.2–$0.5 per Wattalibaba.com. A 20 W panel could be $4–$10. Let's budget $10 (this could be lower with bulk ordering or using surplus panels).
Battery
A lithium iron phosphate (LiFePO₄) battery, ~20–30 Wh capacity (e.g. 12 V, 2.5 Ah, or a single 3.2 V cell of 8 Ah with a boost converter). Such batteries in bulk might cost $5–$10. We allocate $10 for the energy storage.
Power Electronics
A small MPPT charge controller chip or module ($2), DC-DC converter components ($2), PCB and assembly for these power circuits ($2). Roughly $5 for the power management electronics.
Power Subtotal: $25
Control & Sensors
Microcontroller & PCB
A microcontroller (few $) and a 4-layer small PCB with passive components. At high volume, an assembled control board could be $5 (similar to the cost of simple microcontroller dev boards in bulk).
Communication Module
LoRa radio chip or module, or similar sub-GHz radio. LoRa modules are about $5–$10. We'll say $5. (If satellite communication is needed, it would be an optional add-on costing much more – Iridium modems can be $100s – so not included in base cost).
Sensors
pH Sensor: $5
There are solid-state ISFET pH sensors or even cheap glass electrode modules. A durable marine pH probe might be $20+ which is too high, but a miniaturized solid-state sensor integrated on PCB could be a few dollars. We budget $5 (perhaps using a chip like the SeaFET in quantity or a simpler approach).
Temperature Sensor: $1
A digital temperature sensor (e.g. a digital temp sensor).
CO₂ Sensor: $0
A dissolved CO₂ sensor is expensive (optodes can be $100s), so the base design might exclude a dedicated CO₂ sensor and rely on pH.
Other Sensors: $0-2
Voltage, current shunts for monitoring power, etc.: a few small components, $1–2 total.
Control & Sensors Subtotal: $16
Casing & Miscellaneous Hardware
Plastic outer enclosure (if separate from reaction chamber parts), any mounting brackets (could be plastic or cheap metal), screws, potting epoxy, connectors, etc. In bulk, these mechanical odds-and-ends might sum to $5 per unit.
Casing & Misc Subtotal: $5
Total Cost Summary
Cost Per Ton of CO₂ Removed
If a unit costs $100 and can remove on the order of 0.1–0.2 tons of CO₂ per year (a rough estimate given energy constraints, see Section 4), and it has a lifetime of say 5 years, the capital cost per ton would be:
$100 ÷ (0.1 tons/year × 5 years)
$100 ÷ (0.2 tons/year × 5 years)
This rough calculation aligns with our earlier statements and literature targets of around $100–$200/tonspectrum.ieee.org. Operating costs are minimal since it's solar-powered and has no fuel cost; maintenance costs are also intended to be minimal. So the levelized cost of CO₂ removal could approach $100/ton in the field, making it economically promising especially as carbon credit markets mature.
Manufacturing Considerations
Each component of the BOM has been chosen for low cost and high availability. By leveraging components used in consumer electronics (solar garden lights, sensor nodes, etc.), we ensure that manufacturing can be scaled without exotic supply chain needs. The design purposefully avoids precious metals (only a tiny bit of silver) and minimizes specialized materials. The highest cost single item is the solar panel, which has seen steady cost reductions over the years. If units are deployed in high-wind or wave areas where solar alone is less effective, we might include a small wind turbine or wave energy device instead – but those currently are more expensive per watt than solarreddit.com, so the baseline uses solar for cost reasons.
Assembly Cost Considerations
The $100 target includes some assumptions about assembly. The assembly can be semi-automated: the PCB can be assembled by machine (SMT placement), the plastic housing can be robotically welded or screwed, and even electrode fabrication can be batched (e.g., coating Bi onto many substrates at once). Labor is minimal per unit. We have allocated a margin for testing – each unit might be dunk-tested for leaks and run briefly to ensure it works, which adds a small cost. If this is done in a low-labor-cost region or highly automated factory, it doesn't add much.
Economies of Scale
Even at lower volumes, the cost should not exceed $150, and with further optimization and mass manufacturing (millions of units), the cost could potentially drop below $50 by leveraging economies of scale (for example, custom-designed system-on-chip integrating microcontroller and LoRa, bulk deals on solar cells, etc.).