Fourteen lessons, three briefs. Can you design a plant that beats the competition?
There's no multiple choice here. You get a brief and a set of tests — efficiency, emissions, cost, materials, physical limits — and every law of the course pulling against the others.
How an energy-systems engineer thinks
Every brief in the studio is answered by the same chain of questions, each one a lesson:
- What is the product? Electricity is pure exergy; heat at 70 °C is mostly not (Lesson 7). A design that confuses them wastes fuel.
- Where does the heat come in, and at what temperature? The mean temperature of heat addition sets the ceiling (Lessons 5 and 8). A gas turbine takes heat in far hotter than any steam boiler (Lesson 9).
- Where does it go out? As cold as the environment allows — a condenser near the cooling-water temperature (Lesson 12) — unless the rejected heat is the product (Lesson 8's cogeneration).
- What do the materials allow? Steam above about 620 °C, turbine gas above about 1850 K, and steam wetter than 88% at the turbine exit are all off the table (Lessons 8 and 9).
- What about the exhaust? Too cool a stack and acids condense; too hot and you throw fuel away (Lessons 12 and 13).
- What does it cost, and what does it emit? Fuel price, carbon content and the carbon price, all divided by the efficiency (Lesson 13).
The studio
Choose a brief, then shape your plant. The block diagram shows your plant and its headline numbers; the test report on the right tells you what fails, why, and which lesson holds the fix. Your designs are saved in this browser.
Design reviews
Stuck? These reviews describe one route through each brief. Try on your own first: the struggle is where the understanding forms.
Going deeper
Grid power station: why combined cycles took over
The default design is a 1950s-style coal plant: 100 bar, 500 °C, a warm condenser. It fails almost everything. Push it as far as the materials allow — 280 bar, 620 °C, reheat, a feedwater heater, a 32 °C condenser — and it climbs past 40%, but no coal plant can reach the 55% efficiency, the 380 g CO₂ limit or the cost target. Burning gas in the same boiler helps the carbon, not the efficiency.
Switch to a combined cycle. A pressure ratio around 18–22 and a turbine inlet temperature near the 1850 K limit give a gas turbine of about 40%, with exhaust near 850–900 K. Under it, a steam cycle at moderate pressure — 60–80 bar — keeps the turbine exhaust dry enough, and a condenser just above 30 °C finishes the job. You should land near 59–60%, about 340 g/kWh and around €74 per MWh. That is, almost exactly, why most new fossil plants of the past thirty years are combined cycles.
Going deeper
City heat and power: the condenser becomes the boiler
District heating needs water at 90 °C, so the steam must condense at 95 °C or more: a back-pressure turbine. That costs electricity — a steam plant exhausting at 95 °C makes only about 28% — but nearly all the rest of the fuel energy reaches the city as heat, so the fuel utilisation is excellent.
The electrical and exergetic tests are what rule the steam plant out. Heat at 70 °C is only about 15% exergy, so a plant whose output is mostly heat has a low exergetic efficiency, however well it uses the fuel's energy. A combined cycle with a back-pressure steam turbine fixes both: the gas turbine makes high-exergy electricity first, then its exhaust raises steam that is expanded and condensed into the district-heating water. Ask for a cool stack — the heat-recovery boiler's pinch will decide how cool it can really get — and you should see more than 50% electrical efficiency and a fuel utilisation near 90%.
Going deeper
Town heat pump: it's all about the lift
On a −5 °C design day, an air-source heat pump must lift heat from about −11 °C (the evaporator runs colder than the air) to 65 °C or more: a huge lift, a pressure ratio above 8, a hot compressor and a COP of about 2.5. It can't meet the 13 MW grid limit, and it barely beats gas boilers on carbon.
Change the source. River water at 4 °C gets you close but just misses the carbon target; a ground loop at 10 °C cuts the lift by about 15 K and gets there. Keep the supply temperature at the 60 °C the old radiators need — no higher. Choose a good compressor (80% or better) and add a few kelvin of subcooling, which increases the cooling effect per kilogram of refrigerant for free. The COP rises to about 3.5, the grid draw falls under 12 MW, and the CO₂ drops below half of what the gas boilers emitted — and it will keep falling as the grid decarbonises, which no boiler can do.
- Energy is conserved (Lessons 2 and 4): every device and cycle is a set of first-law balances.
- Entropy is not (Lessons 5 and 6): the second law caps every engine, refrigerator and heat pump, and irreversibilities generate entropy.
- Exergy says which losses matter (Lesson 7): combustion and big temperature differences destroy most of it; condensers reject little of it.
- Cycles (Lessons 8–10) are engineered around those three facts: hot heat in, cold heat out, small temperature differences everywhere.
- Properties, mixtures, reactions and equilibrium (Lessons 3, 11–14) supply the numbers — and the reasons flames never quite finish.
That's the course. You can now read any energy system — a car engine, a refrigerator, a power station, a planet — as a ledger of energy, entropy and exergy. Go and find the biggest destruction of exergy around you, and think about how you would fix it.