Try This Real McKinsey-Style Case: The Renewable Energy Pilot in San Andreas
- Jun 6
- 10 min read
If you've ever wanted to know what a real McKinsey case actually feels like, here's one.
We designed this case ourselves. We spent 6+ years each at McKinsey, both as consultants and as case interviewers, and we built it to mirror the difficulty, length, and pacing of a real first-round McKinsey interview. The case has been used in our YouTube channel as a full mock interview, and it's the same kind of case that sits inside our paid Udemy course.
The honest pitch on what this post is: it's the case prompt, the exhibits, and a walkthrough of how a strong candidate would approach each question. Written in a way so that you can actually try it before reading the solutions.
So here's how to get the most out of this:
Grab a pen & piece of paper
Read the case prompt / questions
Under each question we indicate the solution in blue for each question starts
Go through the case from start to finish, skipping the blue sections. Then, go throught it again and compare your solution with the blue sample solution and explanations.
If you would like to see the solution for each section right away, do so. But we recommend to take the time to solve each question yourself. A worked example that you've already wrestled with is worth ten cases that you've only read.
We also have this case on our YouTube channel with a detailed solution and insider tips. Especially when checking the solution, watching and listening to a candidate acing the case is much more useful than just reading it:
If you are ready for the case, let's go.
The Case Prompt
Our client is a mid-sized utility company in Spain. They produce electricity, and they do that primarily with natural gas power plants. Given the recent turbulences in the natural gas market, they want to invest in renewable energy. The CEO, however, isn't sure what to invest in. In a first stage, he wants to run a pilot program in San Andreas, an island just off Spain's Mediterranean coast. There he wants to gain experience and build a first successful business case, so he can convince the shareholders of further investments. And for that, he came to us. Specifically with the question: which exact type of renewable energy project should he invest in? How would you help him?
That's the briefing.
Stop here. Set a timer for 2 minutes. Try to summarise the situation back, ask 2–3 clarifying questions you'd want answered before structuring, and then take a minute or two to lay out a structure. Then come back.
Question 1: How Would You Structure the Problem?
A few things a top candidate would clarify before structuring:
What does success look like to the CEO? Answer: the project needs to deliver a return, and it needs to be executable in a way that's repeatable elsewhere in Spain.
Are there budget or timeline constraints? Answer: no.
Which energy sources are in scope? Answer: hydro isn't viable on the island; the CEO wants to stick to onshore wind and solar.
Notice what's happening with those clarifying questions. Each one materially changes how a candidate would structure the problem. That's the bar: questions that narrow the solution space, not questions that signal you're paying attention.
How a Top Candidate Would Structure It
Here's the structure our candidate built in the live mock interview, slightly compressed:
First level: Wind. Solar. Then a cross-cutting "business model" bucket for considerations about the business model and financing ideas.
Second level (for each energy source): Financial factors + non-financial factors.
For wind the financials come down to power generated (turbines × performance × wind conditions) times the selling price of electricity, minus depreciation, maintenance, and land lease. The non-financials are the hard part: permits, environmental approvals, neighbour resistance (the "not in my backyard" phenomenon, in short: NIMBY), and the logistics of getting large turbines onto an island.
For solar the financials look similar — power generated (modules × performance × sunshine hours) times the selling price, minus depreciation and the lease of the land. The non-financials are lighter than for wind: less visible, less invasive, easier to install.
And the third bucket — the "business model" — captures things like residential rooftop rental models, power purchasing agreements (PPAs) direct to a community or company and green bonds.
The Feedback Insight You'd Pay $300 a Coaching Hour For
The reason this structure works isn't that it's clever. It's that it's specific to the case.
If you walked into the same interview and reached for a generic profitability framework — revenue minus cost, four buckets of revenue drivers and three buckets of cost drivers — you'd technically be correct, and you'd bore your interviewer to death within 90 seconds.
Custom structures, weaving in light industry knowledge (the NIMBY phenomenon, PPAs, residential rooftop rental, green bonds), tell the interviewer two things in one move: you can think clearly, and you have business common sense. That second one is what separates the candidates who pass the first round of interviews from the ones who don't.
Question 2: Read the Exhibit. Where's the Best Opportunity?
Alright, great. Now, our team has done some research into the potential for solar and wind, and summarized it on this exhibit. What you see here are the 3 districts of San Andreas. Las Venturas, San Fierro, and Los Santos. We also have weather data on wind and solar, as well as the capacity data for wind and solar. Based on this information, how would you assess the potential for wind and solar on San Andreas? Can you interpret this for me?
Exhibit 1:
How a Top Candidate Would Approach It
This is a math + interpretation question. Don't grind through it head-down. Step back, do the multiplication, then synthesyze into a single sentence the CEO would care about.
Solar potential by district:
Las Venturas: 5 × 1,200 = 6,000 MWh
Los Santos: 1 × 900 = 900 MWh
San Fierro: 10 × 600 = 6,000 MWh
Total solar: ~12.9 GWh
Wind potential by district:
Las Venturas: 40 × 1,200 = 48,000 MWh
Los Santos: 10 × 600 = 6,000 MWh
San Fierro: 10 × 1,200 = 12,000 MWh
Total wind: ~66 GWh
That's a roughly 5x gap. The synthesis writes itself:
San Andreas has plenty of sun, but solar capacity is almost fully utilised — there's only about 13 GWh of unused potential. Wind has 5x the headroom, with the bulk of it in Las Venturas. So our recommended focus is wind, and Las Venturas specifically.
The Feedback Insight
The trap on this question isn't the math. It's stopping at the math.
Plenty of candidates do the calculations correctly, recite the numbers back, and pause. The interviewer is left to draw the conclusion themselves. That's a soft fail. Not a wrong-answer fail, but a "this person needs hand-holding" fail. You tell the interviewer that you are not thinking of the "so what".
The candidate who passes finishes with the synthesis: here's what the numbers mean, here's where we go next. That's the consultant move. Always close a numerical analysis with a one-sentence "so what."
Question 3: Which Wind Park Configuration Is Most Powerful?
We’ve done some further research and the team came up with different wind park configurations. The options differ in the wind turbine models used, and the number of wind turbines that can be financed. The question is, which of these options produces is the most powerful. You can find the equation to calculate the power at the bottom. After finding the most powerful option, please roughly calculate the power for this option.
Exhibit 2:
How a Top Candidate Would Approach It
This question is designed to reward 80/20 thinking. A weak candidate calculates all three options end-to-end. A strong candidate looks for shortcuts.
Option 1 vs Option 2:
Same wind speed. Option 1 has 20% more turbines. Option 2 has a 20% larger rotor — and the rotor is squared in the equation. A 20% larger rotor produces 44% more power per turbine, which beats the 20% extra turbine count.
Option 1 is off the table. No calculation needed.
Option 2 vs Option 3:
Same rotor diameter. The question becomes: does the higher wind speed (8 vs 6 m/s) compensate for halving the number of turbines (5 vs 10)?
6³ = 216
8³ = 512
512 is more than 2× larger than 216. So a single turbine in option 3 produces more than 2 turbines in option 2 would. Option 3 wins.
The interviewer then asks for the actual power of one Option 3 turbine (i.e., the most powerful one). Roughly:
D² × V³ = 120² × 8³ = 14,400 × 512 ≈ 14.4M × 0.5 ≈ 7.2 megawatts per turbine.
The Feedback Insight
Look at what just happened. The candidate eliminated Option 1 with zero math. Then they did two cube calculations and were done.
That's the consultant mindset: what's the minimum work needed to answer this question? Most candidates default to "calculate everything precisely." Don't. You're a consultant in this interview, not a scientist. Round. Compare. Eliminate. The directional answer is enough to make the decision, and the time you save buys you composure for the next question.
This pattern (i.e., shortcuts, common sense, 80/20) shows up in every case McKinsey gives. Drill it.
And this is not just important for your McKinsey interview:
Understanding what truly matters and being efficient when finding solutions will not only help you in your McKinsey interview but also later in your professional career.
Question 4: How Would You Get the Locals on Board?
So now, after some further investigation, we realized that the business case for this operation is extremely positive. The only problem that we see is resistance by the people who live near such wind turbines. Maybe you can take some time and tell me some ideas how we could get people on board with the wind turbines.
How a Top Candidate Would Approach It
The interviewer flips the case: the business case is excellent, but the only obstacle is resistance from people who live near wind turbines. How would you address that?
This is a brainstorming question. There's no right answer. What's being tested is whether you can structure ideas under pressure.
The top candidate breaks it into two buckets: financial incentives and non-financial incentives.
Financial:
Direct compensation to residents living near turbine locations.
Cheaper electricity for households in the affected districts.
Investment in local infrastructure — sponsoring a school, a sports club, a community centre.
Non-financial:
A two-pronged PR campaign: debunk the myths (turbines causing cancer, killing birds, changing the local weather) with partnerships from biologists and doctors; and make the positive case (climate, lower electricity prices, energy independence).
Appoint local champions — find the residents who are open to the project and use them to anchor community support.
Involve residents in the decision-making process. Where there are equally good turbine sites, let the locals have a say.
When the interviewer pushes for more ideas (and they will), the candidate stays calm and offers one more: leverage local pride. Find a successful neighbouring project and frame San Andreas as the next community that can do it.
The Feedback Insight
The "can you think of anything else?" prompt isn't always criticism. Sometimes the interviewer wants to see how you handle being pushed.
The wrong move is to apologise, get defensive, or start second-guessing what you already said. The right move is what the candidate did: pause for a beat, draw on personal experience, offer one more reasonable idea. Calm under pressure is the muscle. The ideas themselves matter less than the composure.
The Synthesis: The Final Recommendation
So now, the CEO is coming. In about 2 minutes. Would you be so kind and summarize the situation?
How a Top Candidate Would Close
Based on our analysis, we recommend the CEO focus the pilot on wind power in Las Venturas, with five large wind turbines. We're recommending this for three reasons. First, while San Andreas is sunny, the existing solar capacity is almost exhausted. Only about 13 GWh more could be produced, and solar would still need to be complemented overnight. Second, wind has substantial unused potential. In Las Venturas alone, we identified 40 MW of free capacity, equating to roughly 48 GWh of additional output. Third, the largest turbines — Option 3 — produce more power than ten of the next-biggest option, driven by higher wind speeds at greater rotor height. As immediate next steps, we'd suggest two workstreams. First, validate the logistics — confirm the large turbines can be transported onto the island and erected safely. Second, begin a PR campaign to address anticipated local resistance.
The Feedback Insight
Three patterns to take from how the candidate closes.
1. Three supporting reasons. Not two. Not five. Three.
This is a consulting classic at this point. Three is the magic number: enough to sound substantiated, few enough to hold attention. The interviewer expects it.
2. Recommendation, then reasons, then recommendation again.
The candidate opens with the verdict ("five large wind turbines in Las Venturas"), gives the three reasons, then closes with the same verdict ("for these reasons, five large wind turbines in Las Venturas"). That bracketing makes the recommendation land. The CEO walks out of the room knowing what to do.
3. Next steps.
Especially in front of a partner-level interviewer, ending with next steps is gold. Partners are always thinking about phase two of an engagement. Showing that instinct — here's what we'd do tomorrow — signals you'd be useful on a project, not just a smart consultant ready for grunt work in the team room.
What This Case Actually Tested
If you scroll back through what the strong candidate did across the four questions, the pattern is clear. Strip the renewables away and what's actually being tested is four specific skills:
Question 1 tests structured thinking.
Can you turn a vague business problem into a clean and structured issue tree with 2-3 layers of sub-categories, customized to the case?
Question 2 tests data interpretation.
Can you do the math without grinding and land with a synthesis?
Question 3 tests 80/20 judgement.
Can you think 80/20 and find shortcuts to avoid calculating things you don't need?
Question 4 tests composure.
Can you brainstorm under pressure in a structured manner and stay calm when pushed?
Synthesis tests top-down communication.
Can you brainstorm under pressure in a structured manner and stay calm when pushed?
If you can do those five things at a high level, you'll pass a McKinsey case. Most candidates can do one or two of them well. The candidate in this case did a perfect job at all five. The sample solution is what "stellar performance" actually looks like.
The Bottom Line
Reading a worked case is useful. Actually trying one yourself is what builds the skill.
If you did the case before reading the solutions (even badly), you got more out of this post than someone who only read the walkthrough. If you didn't, go back and try the next case you find with that same pause-before-reading discipline. That habit really helps you make the most out of your case interview preparatation.
Another critical part of your preparation is volume. One case is a start. 5+ cases at McKinsey-level difficulty, each followed by a structured review of what a top candidate would have done differently, is what gets you interview-ready.
Our Case Interview Mastery course on Udemy gives you 7 McKinsey-style cases with detailed model solutions and interviewer feedback, taught by us, two former McKinsey interviewers. Each case comes in three formats — do-it-yourself, sample solution, and a feedback version where we pause and explain why each move was made.
The renewable energy case above is also our YouTube channel. Hearing the case is much better than just reading it in this post, so feel free to check it out:
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