A COMPOUND PARABOLIC CONCENTRATOR FOCUSES SUNLIGHT WITHOUT TRACKING THE SUN
A solar concentrator that sits still because it accepts light from a whole range of angles at once, drawn with string instead of maths.
by NightHawkInLight
EnergyScience
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COMPAREE VERDICT
A compound parabolic concentrator accepts light from many angles at once and funnels it all onto a central target, so it can be bolted down and left alone while an ordinary parabola needs a tracker and a motor. NightHawkInLight shows the geometry and builds one on camera, using a string construction to trace the ideal reflector curve directly onto the material — no maths, no CAD, no template to print. Because it accepts off-axis light it also collects scattered light on overcast days, not just direct beams, and he films the focal area with a thermal camera outdoors to show the hot spot. This is for someone who wants to understand the optics and adapt the shape to their own scale and purpose — a pond heater, a kiln, a cooker — rather than follow a fixed plan. The one thing most likely to go wrong is expecting a drop-in design: you get the method and the reasoning, but you decide the dimensions, the reflective material and what you are pointing it at. If you want a parts list and a cut file, this is not it. If you want to know why the shape works and how to lay it out with string and a straight edge, it is exactly right.
IN THE REPO
GOOD TO KNOW
- —This is a filmed method, not a repository — no CAD file or parts list, but the description links an online CPC plotting tool and simulations.
- —The construction is demonstrated step by step on camera: the reflector curve is traced with a string construction, simulating how rays reflect.
- —No licence is stated because there is no repository; the video is standard YouTube terms.
- —What IS present: full geometry explanation, thermal camera verification footage, outdoor comparison between two finished concentrators.
- —What is NOT present: dimensions for a specific application, reflective material supplier, any mounting or attachment hardware.
- —You will have to decide reflector size, material thickness and what you are heating based on your own use case.
Parts to buy
5 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Videos
Creator’s build video
Full geometry walkthrough, string construction demonstration, outdoor thermal camera footage of the focal hot spot.
More builds like this
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Watch the video through once to understand the string construction before you start tracing (The string traces the reflection path — if you miss how it works, the curve will be wrong.)
- 2.Decide your acceptance angle and target size based on what you are heating(The video shows the principle; you choose the dimensions for your own use case.)
- 3.Lay out the string construction on your reflector material and trace the curve(String, pencil, straight edge. No calculation needed if you follow the method.)
- 4.Cut, mount, orient it towards the sun's path and leave it alone(The whole point is that it sits still.)
KNOWN ISSUES
- Expecting a parts list or a cut file — this is a method video, not a repository. You decide the scale and materials.
- Not understanding the string construction before you start tracing. If the string is not simulating the reflection path correctly, the curve will not focus.
- Choosing a reflector material that cannot hold the curve or loses its shine outdoors. The concentration only works if the surface follows the traced shape accurately.
- Do not expect a burning-glass hot spot. In the video's cloudy-day test the target reached about 91 °F; on a sunny day it will be hotter, so mount the target securely and keep flammable material away from it until you know what your build reaches.
- Building a large concentrator for high-temperature work without planning how to aim it safely and keep it clear of anything flammable.
- Ignoring that scattered light means this works under cloud, but the focal temperature is much lower — adjust expectations if you are not in direct sun.
Is there a repository or a downloadable file?
No repository or CAD file. The geometry is explained and demonstrated on camera with a string construction, and the video description links an online Desmos tool for plotting CPC curves around a tube absorber, plus further reading.
What reflective material should I use?
Use the material shown in the video as your starting point. Whatever you choose has to hold the traced curve accurately and stay reflective outdoors, so test a small piece in the sun before building a large one.
How hot does the focal point get?
Hot enough to be useful, not a burning-glass focus: in the cloudy-day test the target pipe inside the compound parabola reached about 91 °F with the air at 60 °F, 20 °F warmer than a regular parabolic trough next to it. A compound parabola spreads light over the whole target rather than to a pinpoint, and the exact temperature depends on the size, the reflective material and how sunny it is.
Do I need to track the sun at all?
No active tracking is needed. A compound parabola accepts light from a range of angles, so within its acceptance angle it keeps concentrating as the sun moves. You pick that angle when you lay out the curve, and you orient the trough towards the sun's path (south in the northern hemisphere).
Does it work on an overcast day?
Yes, because it collects scattered light from the whole acceptance angle, not just a single direct beam. The focal temperature will be lower, but it still concentrates.
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Discussion1
FROM THE COMPAREE TEAM
A compound parabolic concentrator gathers sunlight from a wide range of angles, so it works without tracking the sun and still collects scattered light on cloudy days. What would you point one at?
NightHawkInLight
NightHawkInLight makes long-form science and making videos, explaining the principles behind builds rather than just showing the steps. The channel has been running for over a decade and the focus is always on understanding how something works so you can adapt it yourself.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM1mo agoedited
Practical notes from our verification: this is a method video from NightHawkInLight, not a released design, so there is no repository or project page with files. The video teaches the string construction — using a string to trace the ideal reflector curve — and the description adds the useful extras: an online Desmos tool for plotting CPCs around tube collectors, a separate simulation by Matthew Pritchard, and links to review papers and a non-imaging optics reference. The single biggest decision is not the reflector material, it is choosing your own scale and target based on what you are actually heating — the video gives you the principle, you choose the dimensions. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.