Solution
Paragraphs highlighted in green indicate diagrams or tables that can be shared in the “Case exhibits” section.
Paragraphs highlighted in blue can be verbally communicated to the interviewee.
The following structure provides an overview of the case:
I. Background
At this point the interviewee should understand the situation and structure the problem solving strategy.
Share Drawing with interviewee.
Part 1:
How much power is needed?
Mr. Friday needs in the area of ~5000 MWh of power (1000 x 5000 kWh, which is roughly the European average for a household)
What are the options for Mrs. Robinson?
Mrs. Robinson could build up renewable generation with a suitable transmission and storage system, mainly: Wind power onshore, Wind power offshore, Hydro power, Solar PV, Concentrated solar power, Biomass
What does she need to consider in her decision making generally?
- Need to consider invest per capacity, output (demand), price and O&M cost
- Need to consider technology risks
- Need to consider whether Mrs. Robinson could just install an interconnector from neighboring island
Part 2:
What factors could influence the technology decision (except for CAPEX required)?
Mrs. Robinson should consider external factors influencing the output and the stability/risk of systems
- Wind power onshore: How much wind is there? How many hours per year?
- Wind power offshore: How much wind is there? How to solve foundation issue? Where is site exactly/accessibility? Need transmission.
- Hydro: Are there suitable sites: Rivers, waterfalls, tidal power, etc. ?
- Solar PV: Is there sufficient sunlight? Can use diffuse light. Which technologies feasible: Thin film / conventional mono-crystalline silicon? [deep knowledge – nice-to-have only]
- Concentrated solar power: Direct sunlight available? E.g. in desert. Need transition cable. (Has storage solution integrated.)
- Biomass: Sufficient fuels available in a sustainable way?
II. Analysis
Part 3:
Suppose now that Mrs. Robinson’s engineering suppliers on the neighboring island only make a reasonable offer on wind power technology.
How should she decide between offshore and onshore systems given the following information?
Share Table 1 with interviewee.
In order to solve the questions, the interviewee should perform calculations.
Analysis & calculations
Running hours (hrs/year)
= 24h * 365d * Load factor
= 5,256 (Offshore) // = 2,190 (Onshore)
→ Approx. running hours: 5,000 (Offshore) // = 2,000 (Onshore) [rounded for easier calc.]
Capacity needed
Capacity installed(kW)
= Demand / Running hours * 1,000
= 1,000 (Offshore) // = 2,500 (Onshore)
Analysis & calculations
Price (EUR/MWh)
= Price in ct/kWh * 1000 / 100
= 100 (Offshore) // = 100 (Onshore)
Earnings
Revenues (EUR/year)
= Price * Demand
= 500,000 (Offshore) // = 500,000 (Onshore)
Invest (EUR)
= Capacity * Sum of CAPEX
= 2,000,000 (Offshore) // = 2,500,000 (Onshore)
Depreciation (EUR/year)
= Invest / Time horizon [linear]
= 200,000 (Offshore) // = 250,000 (Onshore)
Profit after depreciation (EUR/year)
= Revenue - Depreciation
= 300,000 (Offshore) // = 250,000 (Onshore)
Part 4:
Suppose now that Mrs. Robinson finds out about potential differences in O&M cost. How does this impact on earnings?
Share Table 2 with interviewee.
Analysis & calculations
Cost of O&M (ct/kWh)
= Cost in ct/kWh * 1000 / 100
= 50 (Offshore) // = 20 (Onshore)
Cost of O&M (EUR/year)
= Cost in MWh * Demand = [Output]
= 250,000 (Offshore) // = 100,000 (Onshore)
Earnings
Cost of O&M (EUR/year)
= Revenue - O&M Cost - depreciation
= 50,000 (Offshore) // = 150,000 (Onshore)
Following the calculation you can share Table 3 with interviewee.
III. Conclusion
What is your recommendation for Mrs. Robinson?
The interviewee should make a top-down summary of findings and most critical areas. He or she should also make a reference to the risks of maintenance in offshore windparks (hard during some times of the year, need ships etc.).
