Interviewer view · keep this screen to yourself
Standard: SunRoof Homes: rooftop solar in a western Indian state
You run the case. Read the prompt, answer questions from the notes below, and share data only when the candidate asks for it or gets stuck. Score at the end.
Case timer
00:00
1. Read the prompt aloud
Read it slowly, then pause. Let the candidate ask questions before they structure.
First, estimate how much rooftop solar capacity homes in a large western Indian state could install. Then: SunRoof Homes, a solar installer, asks whether homeowners will find the economics attractive, and what could change that.
Format note: Difficulty: Standard. Format: market-sizing opener, then a business question. Industry: Energy. Region: India. Interview length: about 30 minutes. The company is fictional and all figures are illustrative.
2. Answers to clarifying questions
Give these answers only if the candidate asks. If they ask something not listed, give a sensible answer or say it does not matter here.
If asked: Homes only?
Answer: Yes, homes in one large western state with about 15 million households (illustrative).
If asked: Which homes can install panels?
Answer: Mainly independent houses with their own roof, about 40 percent of households.
If asked: What system size?
Answer: About 3 kW per home.
If asked: For the business question, what does a system cost and save?
Answer: A 3 kW system costs about INR 1,80,000 installed, before the central PM Surya Ghar subsidy of INR 78,000 (check the current rules). It runs at about 4 full-sun hours a day, and each kWh used replaces grid power at about INR 7.
If asked: What does SunRoof earn?
Answer: About INR 25,000 of gross margin per system, and it can install about 20,000 systems a year.
3. The hypothesis a strong candidate states
Listen for an early, testable guess like this one. It does not need to match word for word.
Rooftop solar is limited by who owns a suitable roof and can pay upfront. My hypothesis is that the realistic market is a few hundred thousand homes, and that homeowner payback decides how fast it grows.
4. A model structure
Compare the candidate's structure with this one. A different split can be just as good if it is clean and fits the problem.
- Size the market, then test the homeowner's payback
- Households x share with own roof x share who buy
- Capacity = homes x kW per home
- Key: Homeowner payback
- Installer profit
5. The working, step by step
Each step shows how a strong candidate works it out. Share a new fact from it only when the candidate asks or is stuck, and let them do the math: the result in the dark box is what they should reach.
Step 1: Homes with their own roof
What a strong candidate does: 40 percent of 15 million households.
Independent houses: 15,000,000 × 0.4 = 6,000,000
Step 2: Likely buyers in the next few years
What a strong candidate does: Assume 10 percent can pay and want it.
Buyer homes: 15,000,000 × 0.4 × 0.1 = 600,000
Step 3: Capacity
What a strong candidate does: 3 kW each, converted to gigawatts (1 GW is 1,000,000 kW).
Capacity (GW): 600,000 × 3 ÷ 1,000,000 = 1.8
Step 4: Yearly generation per home
What a strong candidate does: 3 kW for about 4 full-sun hours a day.
Generation (kWh a year): 3 × 4 × 365 = 4,380
Step 5: Yearly saving
What a strong candidate does: Each kWh replaces grid power at about INR 7.
Saving (INR a year): 3 × 4 × 365 × 7 = 30,660
Step 6: Homeowner payback
What a strong candidate does: A system costs about INR 1,80,000. After the central PM Surya Ghar subsidy of INR 78,000 for a 3 kW system (check the current rules), the homeowner pays INR 1,02,000.
Payback (years): 102,000 ÷ (3 × 4 × 365 × 7) = 3.33
Step 7: Curveball: export rules change
What a strong candidate does: Interviewer: "The state regulator proposes moving homes from net metering to net billing, paying INR 3.5 per kWh exported. About half of generation is exported." Payback becomes:
Payback under net billing (years): 102,000 ÷ (3 × 4 × 365 × (0.5 × 7 + 0.5 × 3.5)) = 4.44
Step 8: Installer contribution
What a strong candidate does: SunRoof earns about INR 25,000 of gross margin per system and can install about 20,000 a year.
Gross margin (INR a year): 20,000 × 25,000 = 500,000,000
The recommendation to listen for
At the end, say: "The CEO walks in. What is your recommendation?"
The state has room for roughly 1.8 GW of home rooftop solar, and the economics are attractive but sensitive to export rules. First, after the central subsidy a homeowner earns back the cost in about 3.3 years, which should sell well. Second, if the state moves to net billing and pays half the retail rate for exported power, payback stretches to about 4.4 years, which will slow sales. Third, SunRoof can protect demand by sizing systems so more power is used at home (for example with timers for water pumps and air conditioning) and by offering monthly-payment plans. At 20,000 installs a year it earns about INR 50 crore of gross margin.
Risks a strong answer names: Export-rule changes; Subsidy amounts and rules may change; Installation quality problems damage the brand.
Next steps: Model payback for different system sizes and home-use shares; Partner with a lender for monthly-payment plans.
Strong versus weak
A strong answer
Sized the market in clear steps, then shifted to the homeowner's payback and tested the rule change.
A weak answer
Gave a capacity number without steps and never looked at what the buyer earns.
Score the candidate
Score each criterion from 1 to 5. A 2 or a 4 sits between the descriptions.
This case has no exhibit. Score Exhibit reading on how the candidate used the data you gave them: did they pick out the number that matters and say what it means?
Total
0 out of 25
Score all five criteria to see the band and the feedback template.