This one has a brilliant built-in hook because CSP sounds like ordinary solar power until you realise it is basically a steam power station with an enormous field of mirrors.
I have always associated solar power with panels.
Flat rectangles on roofs.
Rows of them sitting in fields.
Sunlight hits the panel.
Electricity comes out.
Simple enough.
Then I came across Concentrated Solar Power.
At first, I assumed it was just a more efficient version of the same thing.
It isn’t.
Concentrated Solar Power doesn’t usually turn sunlight directly into electricity.
It uses thousands of mirrors to focus sunlight onto one place until it becomes hot enough to run something remarkably familiar.
A steam turbine.
In other words…
It is a conventional thermal power station where the furnace has been replaced by the Sun.
The misconception
When people hear solar power, they generally think of photovoltaic panels.
Photovoltaic cells convert sunlight directly into electricity.
Concentrated Solar Power, usually shortened to CSP, takes a completely different approach.
It collects heat.
Large mirrors track the Sun throughout the day and concentrate its energy onto a receiver.
That heat is then used to warm a working fluid.
The fluid produces steam.
The steam spins a turbine.
The turbine drives a generator.
Something spins around.
Electricity comes out.
Once again, the final part is not especially exotic.
The extraordinary bit is how the heat gets there.
Building an artificial suntrap
A CSP plant requires an enormous area of direct sunlight.
Not daylight.
Not brightness.
Direct, uninterrupted sunlight.
That distinction matters.
Cloud cover that merely reduces the output of photovoltaic panels can seriously disrupt a concentrating solar plant because the mirrors need a clear path to the Sun.
Thousands of mirrors must continuously adjust their position as the Sun moves across the sky.
Each one reflects sunlight towards a carefully controlled target.
Individually, a single mirror does very little.
Collectively, they can produce temperatures of several hundred degrees Celsius.
Some designs reach much higher.
The solar field effectively turns a wide area of weak sunlight into a much smaller area of intense industrial heat.
The main designs
There are several ways to concentrate sunlight.
Solar power towers
This is probably the most spectacular design.
Thousands of computer-controlled mirrors, known as heliostats, surround a central tower.
Each mirror tracks the Sun and reflects light towards a receiver at the top.
From a distance, the receiver can appear to glow.
The concentrated sunlight heats a fluid, often molten salt, which can then be used immediately or stored for later.
It looks less like a power station…
And more like something designed to communicate with aliens.
Parabolic troughs
Parabolic trough plants use long, curved mirrors shaped like channels.
The mirrors focus sunlight onto a pipe running along the centre.
A heat-transfer fluid flows through the pipe and carries the collected energy to a steam-generation system.
Rather than thousands of mirrors focusing on one tower, each trough concentrates sunlight along a line.
Linear Fresnel systems
These use rows of flatter mirrors to reflect sunlight onto an elevated receiver.
They can be cheaper and mechanically simpler than parabolic troughs, although they may collect energy less efficiently.
Parabolic dishes
Dish systems resemble enormous mirrored satellite dishes.
They focus sunlight onto a receiver mounted at the focal point.
Some drive small Stirling engines directly rather than producing steam for a large central turbine.
Where does the fuel come from?
CSP has no fuel supply chain in the conventional sense.
There are no mines.
No wells.
No forests.
No pipelines.
No ships delivering fuel.
The energy arrives as sunlight.
The real supply chain sits inside the equipment needed to capture it.
That includes:
- Glass manufacturing
- Mirror coatings
- Steel support structures
- Tracking motors
- Control systems
- Heat-resistant pipework
- Turbines and generators
- Molten salt production
- High-temperature pumps
- Thermal insulation
- Grid infrastructure
The sunlight may be free.
The machinery required to collect it certainly is not.
The real advantage: storing heat
One of the most interesting features of CSP is that it can store energy as heat.
This changes the argument around solar power.
Photovoltaic panels stop producing useful electricity when the Sun goes down unless they are paired with batteries or another storage system.
A CSP plant can collect heat during the day and store it in large insulated tanks.
Many modern systems use molten nitrate salts.
The salt is heated by the solar field and stored in a hot tank.
When electricity is needed, that heat produces steam and drives the turbine.
The cooler salt then moves into a second tank before being reheated the following day.
This means a CSP plant can continue generating electricity after sunset.
The mirrors may have stopped working.
The power station has not.
That ability to separate the collection of energy from the generation of electricity is one of CSP’s strongest advantages.
Geography gets the final vote
Like geothermal power, CSP depends heavily on location.
It works best in places with:
- Strong direct sunlight
- Very low cloud cover
- Large areas of relatively flat land
- Low atmospheric moisture
- Good grid connections
- Access to water or dry-cooling technology
That naturally favours desert and semi-desert regions.
Spain.
Morocco.
The Middle East.
Northern and southern Africa.
Parts of the United States.
Australia.
The UK is not an obvious candidate.
We have daylight.
We sometimes even have sunshine.
What we do not have is enough consistently strong direct sunlight to make large CSP projects particularly attractive.
A cloudy day in Nottinghamshire is irritating for rooftop solar.
For a field of precision mirrors attempting to focus sunlight onto a tower…
It is more of a fundamental problem.
The hidden water problem
Solar energy sounds as though it should require very little water.
That is true for photovoltaic panels during operation.
CSP is different.
Because many plants operate like traditional steam power stations, they may require water for:
- Producing steam
- Condensing steam after the turbine
- Cooling equipment
- Cleaning mirrors
Unfortunately, the places with the best solar resource are often the places with the least available water.
That creates an awkward trade-off.
Wet cooling is usually more efficient.
Dry cooling uses far less water but can be more expensive and may reduce plant efficiency, particularly during very hot weather.
CSP therefore has to solve a slightly absurd engineering problem.
Build a water-dependent thermal power station…
In the middle of a desert.
Insurance and operational risk
CSP avoids many traditional fuel risks.
It introduces a collection of its own.
Mirror damage
A commercial CSP plant may contain tens of thousands of mirrors.
Each one must remain correctly aligned and sufficiently clean.
Risks include:
- Hail
- High winds
- Sandstorms
- Dust
- Mechanical damage
- Tracking failure
- Degradation of reflective coatings
A small alignment error repeated across thousands of mirrors can significantly reduce output.
Extreme heat
The receiver, pipework and storage systems operate at very high temperatures.
Thermal expansion places repeated stress on equipment.
Seals degrade.
Pumps wear.
Pipework moves.
The system must survive continuous heating and cooling cycles for decades.
Molten salt freezing
Molten salt is useful because it can store enormous quantities of heat.
It also has an inconvenient habit.
If its temperature falls too far…
It solidifies.
Frozen salt inside pipework can block circulation and potentially damage equipment.
Critical pipework therefore requires insulation and trace heating to keep the salt above its freezing point.
The storage medium itself becomes an operational risk.
Fire and heat-transfer fluids
Some CSP plants use synthetic oils as heat-transfer fluids.
These can operate at high temperatures and may be combustible.
Leaks around pumps, valves or pipework create fire and environmental risks.
Business interruption
A photovoltaic solar farm is highly modular.
One failed panel has almost no effect on the wider site.
CSP is more centralised.
A major failure involving the tower receiver, heat exchanger, turbine or molten salt system can reduce or stop generation across the entire plant.
The power station may be solar.
The business interruption exposure looks much more conventional.
Wildlife and environmental risk
The environmental impact of CSP depends heavily on the design and location.
Large solar fields require significant areas of land.
Construction can disturb desert habitats that may appear empty but support highly specialised ecosystems.
Power-tower designs introduce another unusual risk.
The concentrated solar flux near the receiver can injure birds passing through the most intense areas.
Mirror fields can also alter drainage, habitat movement and local land use.
Low-carbon does not mean impact-free.
It means the impacts are different.
The early adoption problem
CSP also faces a commercial risk that has affected several emerging energy technologies.
The technology works.
The more difficult question is whether it can compete.
Photovoltaic solar panels have become dramatically cheaper.
Battery storage has improved.
Wind generation has expanded.
That places CSP in a difficult position.
Its ability to store heat and generate electricity after sunset is valuable.
But the plant itself is mechanically complex.
Thousands of moving mirrors.
High-temperature fluids.
Pumps.
Heat exchangers.
Steam systems.
Turbines.
A developer could spend billions constructing a highly sophisticated CSP plant only to discover that solar panels paired with batteries have become cheaper before the investment has been recovered.
The plant would still work.
It may simply no longer be the most competitive way to solve the problem.
That is not engineering failure.
It is technology risk.
The strategic lesson
Concentrated Solar Power is one of those technologies that becomes more impressive the longer you look at it.
It takes something diffuse and ordinary…
Sunlight falling across empty land…
And turns it into industrial heat.
That heat can be stored.
Released when required.
Used to create steam.
Used to spin a generator.
The basic process is surprisingly traditional.
The collection system is anything but.
CSP is not simply solar power with bigger mirrors.
It is an attempt to build a conventional power station whose fuel arrives from the sky every morning.
And perhaps that is the most interesting thing about it.
After looking at coal, gas, nuclear, biomass, hydro and wind, the machinery at the centre of electricity generation often remains remarkably familiar.
Heat something.
Move something.
Spin something.
Generate electricity.
Concentrated Solar Power simply does the first part with an extraordinary amount of glass.
Gareth Winterman