Compare two fictional proposals delivering the same 2000 kWh of useful electricity per year for 3 years. A (solar with storage) has initial embodied emissions 5000 kg CO₂e and operating emissions 0.04 kg CO₂e per delivered kWh. B (a generator service) has initial emissions 1000 kg CO₂e and operating emissions 0.4 kg CO₂e/kWh. The supplied rates include operating losses; ignore replacement and disposal only for this first calculation. Find total emissions over the stated horizon and the equal-emissions time. Then recommend how the decision should account for this constraint: cloudy periods need reserve capacity, while delivered fuel requires boat journeys. Do not assume these fictional factors describe actual products.

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Over 3 years: A 5240 kg CO₂e, B 3400 kg CO₂e. Equal-emissions time 5.5556 years. B has the lower modelled total; adoption also depends on the stated service and stakeholder constraints. Both proposals deliver the same useful service, so their operating emissions can be compared on a common boundary. Over 3 years the delivered energy is 2000 × 3 = 6000 kWh. Add initial and operating contributions. A gives 5000 + 6000 × 0.04 = 5240 kg CO₂e; B gives 1000 + 6000 × 0.4 = 3400 kg CO₂e. A starts with 4000 kg CO₂e more embodied emissions but saves 720 kg CO₂e each year of operation. Dividing gives an equal-emissions time of 5.5556 years under the constant-rate assumptions. A carbon ranking is only one decision input: cloudy periods need reserve capacity, while delivered fuel requires boat journeys. Discuss who receives the benefits, who pays upfront, and whether either proposal reliably delivers the promised service before choosing. Make the recommendation conditional on verified service life, repair and replacement needs, disposal and representative operating factors. The stated calculation intentionally omits those effects, so it cannot establish the full life-cycle impact or guarantee that the ranking survives changed assumptions.

Power for an island workshop

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