05/12/2025
🤔 Question : How much does it really cost to cook rice for a family of 4 over a 75-year lifetime – using LPG, Induction, Rice Cooker, or Solar + Backup?
We’re not talking about this month’s bill.
We’re asking:
> “If a family of four cooks rice once a day, every day, for 75 years – what is the total fuel cost under different cooking methods?”
Below is the full breakdown with numbers.
1️⃣ Core Assumptions
👨👩👧👦 Family size: 4 people
🍚 Rice: cooked once per day
⏳ Life expectancy: 75 years
📆 Total cooks:
75 × 365 ≈ 27,375 rice cooks
Prices today
🔥 LPG cylinder: ₹1,000 for 14.5 kg
Energy in 14.5 kg LPG ≈ 185 kWh
→ LPG fuel cost ≈ ₹5.4 per kWh
⚡ Electricity: ₹10 per kWh
Inflation assumption
LPG price grows at 7% per year
Electricity price also grows at 7% per year
Time horizon: 75 years
This roughly matches how both have behaved over the last ~50 years in India (in nominal terms).
2️⃣ How much energy is needed to cook rice?
For a family of 4, one cook:
We assume about 0.4 kWh of useful heat must reach the food
(rice + water + pot losses).
But stoves and pots are not 100% efficient.
How much fuel you actually burn depends on efficiency.
3️⃣ Efficiency assumptions (with reasoning)
🔥 a) LPG + stainless steel pot → ~50% efficient
Steel is a poor thermal conductor.
A lot of heat escapes around the pot and into the kitchen air.
We assume ~50% of flame energy actually goes into cooking.
To get 0.4 kWh useful:
> Fuel energy needed = 0.4 ÷ 0.50 = 0.8 kWh (fuel) per cook
Cost per cook = 0.8 × ₹5.4 ≈ ₹4.32 per cook
🔥 b) LPG + aluminium pot → ~60% efficient
Aluminium conducts heat much better than steel.
More of the LPG flame reaches the rice.
We assume ~60% efficiency.
To get 0.4 kWh useful:
> Fuel energy = 0.4 ÷ 0.60 ≈ 0.67 kWh (fuel)
Cost per cook = 0.67 × ₹5.4 ≈ ₹3.60 per cook
⚡ c) Electric rice cooker → ~80% efficient
Resistive heating plate + closed vessel.
Heat losses are less than LPG, but not zero (sides, lid, “keep warm” mode).
Assume ~80% efficiency.
To get 0.4 kWh useful:
> Electricity = 0.4 ÷ 0.80 = 0.50 kWh
Cost per cook = 0.50 × ₹10 ≈ ₹5.00 per cook
⚡ d) Induction cooktop → ~90% efficient
Heat is generated directly in the pot base.
Very little waste to surrounding air.
Assume ~90% efficiency.
To get 0.4 kWh useful:
> Electricity = 0.4 ÷ 0.90 ≈ 0.44 kWh
Cost per cook ≈ 0.44 × ₹10 ≈ ₹4.44 per cook
☀️ e) Solar cooker + rice cooker backup
On sunny days, rice is cooked in a box-type solar cooker.
Fuel cost = ₹0 (sunlight is free)
But cooker has hardware + maintenance cost.
On non-sun days, we use the electric rice cooker as backup.
Assumptions:
Use solar cooker 150 days/year
Use rice cooker backup 215 days/year
Over 75 years:
Solar cooks = 150 × 75 = 11,250
Backup cooks = 215 × 75 = 16,125
Solar hardware & maintenance:
1 solar cooker life: 25 years
Over 75 years → 3 cookers
Cost per cooker (incl. minor fixes): ₹15,000
→ 3 × 15,000 = ₹45,000
Extra maintenance allowance: ₹500/year × 75 = ₹37,500
→ Total solar capital + maintenance = ₹82,500 (in today’s rupees)
We treat this as fixed (no inflation).
Backup fuel:
Rice cooker cost per cook = ₹5.00 (today’s basis)
4️⃣ Lifetime cost without inflation (today’s money only)
Number of cooks: 27,375
LPG + steel pot
> 27,375 × ₹4.32 ≈ ₹1,18,260
LPG + aluminium pot
> 27,375 × ₹3.60 ≈ ₹98,550
Induction
> 27,375 × ₹4.44 ≈ ₹1,21,545
Rice cooker
> 27,375 × ₹5.00 ≈ ₹1,36,875
Solar + rice cooker backup
Solar hardware + maintenance = ₹82,500
Backup rice cooker cooks: 16,125 × ₹5 = ₹80,625
Total : ₹82,500 + ₹80,625 ≈ ₹1,63,125
These are all in today’s rupees, assuming no price rise.
5️⃣ Now apply 7% annual inflation for fuels (LPG & electricity)
We now assume:
LPG price grows 7% per year
Electricity price grows 7% per year
Period: 75 years
Over 75 years, if you sum the rising yearly costs, the total ends up about 30.3 times higher than the “no-inflation 75-year total”.
So:
> Nominal lifetime fuel cost ≈ (No-inflation lifetime fuel cost) × 30.3
Important:
This 30.3× applies to all LPG and electricity usage, but not to the solar hardware cost (which we keep fixed in this model).
6️⃣ Lifetime nominal cost with 7% inflation (75 years)
🔥 LPG + steel pot
No-inflation lifetime: ₹1,18,260
> 1,18,260 × 30.3 ≈ ₹35,83,278
Rounded: ≈ ₹35–36 lakh
🔥 LPG + aluminium pot
No-inflation lifetime: ₹98,550
> 98,550 × 30.3 ≈ ₹29,86,065
Rounded: ≈ ₹29–30 lakh
⚡ Induction cooking
No-inflation lifetime: ₹1,21,545
> 1,21,545 × 30.3 ≈ ₹36,82,814
Rounded: ≈ ₹36–37 lakh
⚡ Rice cooker only
No-inflation lifetime: ₹1,36,875
> 1,36,875 × 30.3 ≈ ₹41,47,313
Rounded: ≈ ₹41–42 lakh
☀️ Solar cooker + rice cooker backup
Split into:
1. Solar hardware + maintenance:
Fixed in today’s rupees = ₹82,500
2. Backup rice cooker fuel:
No-inflation lifetime = ₹80,625
With 7% inflation → 80,625 × 30.3 ≈ ₹24,42,938
Total nominal cost over 75 years:
> Solar hardware (₹82,500) + Backup fuel (~₹24,42,938)
≈ ₹25,25,438
Rounded: ≈ ₹25–26 lakh
7️⃣ Final comparison (family of 4, rice once a day, 75 years, 7% annual price rise)
Approximate total nominal lifetime costs:
🔥 LPG + aluminium pot:
👉 ₹29–30 lakh
🔥 LPG + steel pot:
👉 ₹35–36 lakh
⚡ Induction:
👉 ₹36–37 lakh
⚡ Rice cooker only:
👉 ₹41–42 lakh
☀️ Solar cooker + rice cooker backup:
👉 ₹25–26 lakh
(All figures are rough, scenario-based, and depend heavily on the assumptions.)
8️⃣ What does this actually mean?
1. Today, if you look only at current prices (no inflation), LPG + aluminium looks cheapest, and solar looks expensive.
2. Over 75 years with 7% annual price rise on both LPG and electricity:
The fuel costs balloon massively.
The methods that rely 100% on fuel (LPG / Induction / Rice cooker) become very expensive.
The solar cooker, which has a fixed front-loaded cost, starts to win on cumulative cost – even though each unit is expensive to buy.
3. This is only for rice once a day.
If you also move dal, sabzi, reheating, etc. to solar on sunny days, the fuel savings become even larger.
🎯 Summary in one line
> Assuming (₹1,000 LPG, ₹10/kWh, 7% annual price rise, 75-year lifetime, 4 people, rice once a day), LPG + aluminium is cheapest in the short term, but Solar Cooker + Rice Cooker backup becomes the lowest total-cost option over a full lifetime in nominal rupees — because it avoids decades of compounding fuel inflation.