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Home EV chargers sold per year in Australia (interviewer-led, with data)

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

Target length:

1. Read the prompt aloud

Read it slowly, then pause. Let the candidate ask questions before they structure.

An Australian maker of home electric-vehicle (EV) chargers asks: in five years, how many home chargers will be sold in Australia each year, and what will that be worth? Use the household table below. A charger costs the household about AUD 1,800 installed.

Format note: Interviewer-led: the interviewer gives the household table, answers your clarifying questions with the ownership assumptions, and asks for the estimate step by step.

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: New installations only, or replacements too?
Answer: Both. A home charger lasts about 10 years.
If asked: Can people in apartments install one?
Answer: Only if they have a private parking space. The table shows the share of each dwelling type with off-street parking.
If asked: What EV ownership should I assume?
Answer: In five years, about 12 percent of households with off-street parking own an EV, and that share is rising by about 2.5 points a year. About 80 percent of those owners install a home charger.

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.

A home charger needs off-street parking, so my hypothesis is that detached houses drive almost all demand, and that yearly sales in five years are a few hundred thousand units, worth a few hundred million Australian dollars.

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.

Yearly chargers = new installs + replacements
- Households that can install: households x share with off-street parking, by dwelling type
- New installs: rise in EV ownership that year x install rate
- Replacements: installed chargers / 10-year life
- Value: units x AUD 1,800

Exhibit 1

Reveal to candidate: when they ask for this data, say "Open Exhibit 1" (they press "Show exhibit 1" on their screen).

Australian households by dwelling type (illustrative)

Australian households by dwelling type (illustrative)
Dwelling type	Households (millions)	With off-street parking (%)
Detached house	7	90
Townhouse or terrace	1.4	60
Apartment	1.6	20

So-what

Detached houses hold about 6.3 million of the 7.46 million households that can install a charger, so they drive the market.

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: Households that can install
What a strong candidate does: Read the table: 90 percent of 7.0 million detached houses, 60 percent of 1.4 million townhouses, and 20 percent of 1.6 million apartments have off-street parking. Detached houses are about 85 percent of the total, which supports the hypothesis.
Households with off-street parking (millions): 7 × 0.9 + 1.4 × 0.6 + 1.6 × 0.2 = 7.46
Step 2: Installed chargers in five years
What a strong candidate does: 12 percent of those households own an EV, and 80 percent of them install a charger.
Installed home chargers (millions): 7.46 × 0.12 × 0.8 = 0.7162
Step 3: New installs that year
What a strong candidate does: Ownership rises about 2.5 points a year, and 80 percent of the new EV households install.
New installs per year (millions): 7.46 × 0.025 × 0.8 = 0.1492
Step 4: Replacements
What a strong candidate does: The installed base divided by a 10-year life. This is a simplification: the base is growing fast, so in five years most chargers will still be young and fewer will need replacing. Treat about 70,000 as an upper figure.
Replacements per year (millions): 0.71616 ÷ 10 = 0.07162
Step 5: Total units
What a strong candidate does: New installs plus replacements: about 220,000 chargers a year.
Chargers per year (millions): 0.1492 + 0.071616 = 0.2208
Step 6: Value
What a strong candidate does: About 220,800 chargers at AUD 1,800 each is about AUD 400 million a year.
Market value (AUD a year): 220,816 × 1,800 = 397,468,800
Step 7: Sanity-check against an outside anchor
What a strong candidate does: Australia sells roughly 1.2 million new cars a year. The new EV households implied here are about 187,000 a year, or about 16 percent of new-car sales. That is a plausible EV share five years out, so the estimate is not far off.
Implied new EV households as a share of new cars (%): 7.46 × 0.025 ÷ 1.2 × 100 = 15.54

The recommendation to listen for

At the end, say: "The CEO walks in. What is your recommendation?"

About 220,000 home chargers a year in five years, worth about AUD 400 million a year at AUD 1,800 installed. First, about 7.5 million households can install a charger, most of them in detached houses. Second, new EV households add about 150,000 installs a year. Third, replacements add up to about 70,000 a year; because most chargers will still be young, the true number is likely lower, so the total sits between about 150,000 and 220,000 units. The biggest uncertainty is the 12 percent ownership figure. If it is 10 percent, the installed base and replacements fall by a sixth, so the next step is to test the answer with a low and a high ownership case.

Risks a strong answer names: EV ownership may grow faster or slower than 2.5 points a year; Apartment buildings may add shared chargers, which changes who buys; Replacements may be well below 70,000 a year while most chargers are still young.

Next steps: Rerun the estimate at 10 and 15 percent ownership; Check the install rate with two electricians who fit chargers.

Strong versus weak

A strong answer

Used the table instead of inventing numbers, split new installs from replacements, and checked the implied EV sales against new-car sales, an anchor outside the table.

A weak answer

Multiplied all 10 million households by the EV share, ignoring that apartments without parking cannot install, and forgot replacements.

Score the candidate

Score each criterion from 1 to 5. A 2 or a 4 sits between the descriptions.

Structuring

1: No clear structure, or a memorized framework that does not fit the problem.
3: A sensible structure, but with some overlap, a gap, or no clear priority.
5: A structure built for this problem, with no overlap and no gaps, a stated hypothesis, and a clear first step.

Math

1: Frequent errors, no units, or needed heavy help to finish.
3: Right answers but slow or messy working, or one error caught late.
5: Accurate and clearly narrated, with units, a sense check, and what the number means.

Exhibit reading

1: Read the chart aloud without finding the number that matters.
3: Found the key number but gave only part of the so-what.
5: Pulled the right number quickly and said what it means for the case.

Synthesis

1: Summarized what was done, with no clear answer.
3: Gave an answer, but with weak reasons or no next step.
5: Answer first, then two or three reasons with numbers, the main risk, and next steps.

Communication

1: Hard to follow: long silences, no signposting.
3: Clear most of the time, with some rambling.
5: Calm and concise, signposted each step, and checked in with the interviewer.

Total

0 out of 25

Score all five criteria to see the band and the feedback template.