Concentrated Solar Power

Concentrated solar power uses curved reflectors to focus sunlight onto a small area, reaching 300-1,500°C depending on the concentration ratio, which is enough for steam generation, soldering, brazing and melting metal with no fuel. A satellite TV dish fitted with mirror tiles is the most practical high-concentration device to build from salvage, while a parabolic trough needs to track the sun in only one axis.

While flat plate collectors reach 60-90°C — enough for hot water — many applications demand higher temperatures. Concentrated solar power (CSP) uses curved reflectors to focus sunlight onto a small area, achieving temperatures of 300-1,500°C depending on the concentration ratio. This enables steam generation, metalworking (soldering, brazing, melting), water distillation, and even powering a steam engine — all with zero fuel.

Concentrating Optics

The principle is simple: a curved mirror focuses parallel sunlight (from the sun, which is effectively at infinite distance) onto a single point or line.

Parabolic Trough

A curved, trough-shaped reflector focuses sunlight onto a pipe running along the focal line:

Concentration ratio: derive it from your own trough. For a pipe receiver it is the aperture width divided by the pipe’s circumference, C = W ÷ (πd). A 1 m wide trough on a 5 cm pipe is 1 ÷ (π × 0.05) = about 6×, not the 30-80× an earlier version of this line gave. 30× on a 5 cm pipe needs a 4.7 m aperture — commercial scale; the industrial LS-3 trough is 5.76 m wide on a 70 mm tube, which is about 26×. A salvage trough a metre or two across is a single-figure concentrator, and its working temperature follows accordingly
Applications: Generating steam, heating oil for cooking, pasteurizing water at scale
Advantages: Only needs to track the sun in one axis (east-west), simpler mechanism
Construction: Bend sheet metal or plywood into a parabolic cross-section, cover with reflective material
Size: 1-3 meters wide, as long as needed (each additional meter adds more energy collection)

Parabolic Dish

A bowl-shaped reflector focuses sunlight onto a single point:

Concentration ratio: 100-1,000x (temperature: 300-1,500°C)
Applications: Metalworking (melting, soldering, brazing), high-temperature chemistry, Stirling engine drive
Advantages: Highest temperatures of any solar technology
Disadvantages: Must track the sun in two axes (azimuth and elevation). Focus is a point — useful only for small targets
The satellite dish conversion is the most practical post-collapse approach (see below)

Fresnel Reflector

Multiple flat mirror strips arranged to approximate a parabolic curve:

Concentration ratio: 10-40x
Advantages: Flat mirrors are easier to salvage than curved ones. Can be large-scale
Disadvantages: Less precise focusing, lower temperature
Ideal for: Community-scale water heating, pre-heating for steam generation

Concentration Ratio & Temperature

The concentration ratio determines achievable temperature:

Ratio	Approximate Max Temperature	Reflector Type
1x (flat plate)	80-100°C	No concentration
5-10x	150-200°C	Flat reflector boost
30-80x	250-400°C	Parabolic trough
100-300x	400-800°C	Small parabolic dish
500-1,000x	800-1,500°C	Large precision dish

Read the device column as the commercial version of each design, not as what you will build. A salvage trough a metre or two wide on a 5 cm pipe comes out at about 6×, which puts it on the first row of this table rather than the trough row — useful heat, not process heat. The trough row describes something several metres across. Likewise a hand-tiled dish lands nearer 100-300× than 500-1,000×, because the limit is how accurately the tiles are aimed.

Building Reflectors from Salvage

Satellite Dish Conversion

The most practical high-concentration solar device you can build:

Find a satellite TV dish — common on abandoned buildings. Sizes from 60 cm to 3 meters
Clean the dish surface thoroughly
Apply mirror tiles: Cut small mirror pieces (2-5 cm squares) from salvaged mirrors. Glue them to the dish surface with silicone adhesive or epoxy, fitting as closely as possible
Alternative: Cover with reflective Mylar film (emergency blankets, balloon material) stretched smooth
Find the focal point: Hold a piece of wood at increasing distances from the dish while aiming at the sun. The focal point is where the reflected light concentrates to the smallest, brightest spot
Mark the focal length — this is where you will mount your target (pot, metal piece, boiler tube)

A 1.5 m dish is 1.77 m² of aperture, and its concentration is simply that area divided by the area of the spot you actually achieve — which is set by how accurately the tiles are aimed, not by the dish’s size.

This article used to give two numbers that contradict each other

It claimed 200-500× concentration in one place and a spot “no larger than 2-5 cm” in another. Those cannot both be true. At 200× the spot is 1.77 ÷ 200 = 0.0088 m², which is 10.6 cm across, and at 500× it is 6.7 cm. A genuine 2-5 cm spot on a 1.5 m dish would be 900-5,600×.

Measure your own: focus the dish on a sheet of something that chars, and the diameter of the scorch mark is your spot. Then C = 17,700 ÷ (spot area in cm²). Hand-glued mirror tiles typically give 8-12 cm and so a few hundred times concentration, which is still enough to melt aluminium (660 °C) and boil water in seconds. Tighter spots need the tiles aimed to within a fraction of a degree, which is slow, careful work rather than a matter of covering the dish.

Polished Sheet Metal

If mirror glass is unavailable:

Polish aluminum sheet with progressively finer abrasive (sandpaper, then polishing compound, then metal polish)
A well-polished aluminum surface reflects 80-90% of sunlight (vs 95% for glass mirror)
Form into a parabolic shape over a wooden or sand mold

Accuracy & Focus Testing

The tighter the focus, the higher the temperature:

Use a piece of white paper or wood to find the focal spot
A well-made dish should focus sunlight into a spot no larger than 2-5 cm diameter
Irregularities in the dish surface spread the focus — each misaligned tile wastes energy
Re-adjust tiles that are reflecting off-target. Even a 5° misalignment on one tile sends its light completely outside the focus

High-Temperature Applications

Metalworking

CSP can replace a forge for many tasks:

Soldering (230-350°C): Focus sunlight on the joint with a small dish. Flux and solder flow normally
Brazing (600-900°C): Requires a larger dish or trough. Position the work at the focal point
Melting aluminum (660°C): A 1.5-meter dish easily melts aluminum for casting
Melting copper (1,085°C): Requires a well-made 2+ meter dish or very accurate smaller dish
Forge welding / steel heat treatment (800-1,100°C): Achievable with precision dishes but challenging to control compared to a coal or charcoal forge

Advantage over fire-based metalworking: No fuel consumption, no smoke, no bellows needed. Can operate for hours with zero input except sunlight.

Steam Generation

Focusing sunlight on a water-filled tube or boiler:

A parabolic trough 2 m × 1 m is a 2 m² aperture, so about 2,000 W in full sun. Raising water 80 °C to the boil at a realistic 60% end-to-end efficiency is 1,200 ÷ (4,180 × 80) = roughly 13 litres an hour; actually turning water into steam costs 335 + 2,257 = 2,592 kJ/kg, which is about 1.7 kg of steam an hour. An earlier version of this line claimed 20-40 litres an hour, which needs 93% efficiency at the low end and nearly twice the available sunlight at the high end
Steam can drive a small steam engine for mechanical power or electricity generation
For continuous operation, a sun-tracking system is essential (see below)

Water Purification

Solar distillation at concentrated temperatures:

Focus on a dark vessel containing contaminated water
Water boils rapidly (much faster than a flat-plate solar still)
Condense the steam in a separate, cooled container
Produces pure distilled water at 5-20 liters per hour with a 2+ meter trough

Tracking Systems

Why Tracking Matters

The sun moves 15° per hour across the sky. A parabolic dish pointed at the sun at noon is 30° off-target by 2 PM — with a high-concentration system, this means zero useful output. Tracking is essential.

Manual Sun Tracking

The simplest approach:

Mount the reflector on a pivot (azimuth) and tilt (elevation) mechanism
Adjust every 15-30 minutes throughout the day
Adequate for cooking and small metalworking tasks that need periodic attention anyway

Gravity-Driven Clock Tracker

A mechanical tracker requiring no electricity:

Use a clock mechanism (salvaged from a large clock or built from gears) to rotate the reflector at 15° per hour
A weight-driven clock escapement provides the motion
Calibrate for your latitude and adjust for seasons
Historically used in heliostats (sun-tracking mirrors) for lighthouses and solar furnaces

Seasonal Adjustment

The sun’s elevation changes with seasons:

Summer solstice: Highest noon elevation (90° minus your latitude plus 23.5°)
Winter solstice: Lowest noon elevation (90° minus your latitude minus 23.5°)
Adjust the tilt of your trough or dish seasonally (every 2-4 weeks is sufficient)
Mark the correct tilt angles on the mount for quick adjustment

Practical Example: Solar Forge Station

A complete solar metalworking station for a community workshop:

Reflector: 1.8-meter satellite dish covered in mirror tiles (salvaged from bathroom mirrors, cut with glass cutter)
Mount: Steel pipe on a concrete base with azimuth bearing (lazy susan bearing from furniture) and elevation pivot (bolt hinge)
Work platform: A fireproof surface (steel plate on brick) positioned at the focal point, adjustable via threaded rod for fine focus
Tool rack: Tongs, flux, solder, brazing rod — all within arm’s reach of the focal point
Shade screen: A sheet of plywood or metal with a small window, positioned so the operator can see the work without staring at the reflected glare

Daily workflow:

Morning (9-10 AM): Adjust dish for morning sun angle. Pre-heat metal stock at the edge of the focal zone (warm-up reduces thermal shock)
Peak hours (10 AM - 2 PM): Perform high-temperature work — brazing, aluminum casting, steel heat treatment
Afternoon (2-4 PM): Lower-temperature tasks — soldering, lead melting, wax melting for lost-wax casting
Track the sun every 20-30 minutes (manual adjustment takes 15 seconds once you learn the rhythm)

Output: On a clear day, a 1.8-meter dish provides roughly 1.5 kW of concentrated thermal power — equivalent to a small propane torch, running for free, all day.

Scaling Up: Community Solar Steam

For a Phase 4 village, multiple parabolic troughs can generate steam for mechanical power:

Array: 4-6 troughs, each 3m x 1.5m, focused on a single insulated pipe carrying water/steam
Steam temperature: 200-300°C at 5-15 bar pressure
Applications: Drive a small steam engine (1-5 kW mechanical), run a grain mill, power a workshop lathe, or generate electricity through a steam-driven alternator
Storage: Route steam through a thermal mass (rock bed or insulated water tank) for 2-4 hours of operation after sunset

This approach was demonstrated at the SEGS plants in California (Kramer Junction and Daggett, built from 1984, 354 MW of parabolic troughs) and at Frank Shuman’s Maadi solar plant in Egypt in 1913, which pumped irrigation water with parabolic troughs — the technology is proven at much larger scales. (An earlier version of this line credited Solar One and Solar Two. Those were also in California and also solar thermal, but they were power towers: a field of flat heliostats focused on a single tower-mounted receiver, Solar Two on molten salt. A different design, aimed at a much higher concentration than any trough reaches.)

Common Mistakes

Using flat mirrors without curvature: Flat mirrors only achieve ~5x concentration. For metalworking temperatures, you need a parabolic curve
Cheap adhesive on mirror tiles: Silicone in direct sun degrades. Use high-temperature RTV silicone or epoxy rated for 200°C+
Ignoring eye safety: Concentrated sunlight at 500x will permanently blind you in milliseconds. Never look at the focal point. Wear welding shade 12-14 glasses when working near the focus
Undersized support structure: A 2-meter dish in 30 km/h wind experiences significant force. Guy the mount or weight the base heavily

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