Guide · Build it yourself

DIY heliostat: can you build one yourself?

Yes - a sun-tracking mirror is a classic maker project, and a first prototype that turns with the sun is within reach if you are comfortable with electronics, mechanics and a little code. The hard part comes after that: keeping the light on the same spot all day, in every season, through wind and rain, without dazzling anyone. Here's what a DIY heliostat needs, where projects usually get stuck, and when a finished device is the better choice.

What a DIY heliostat needs

Every heliostat, home-built or factory-made, combines the same building blocks:

• A reflective surface. A flat or slightly convex mirror. Glass mirrors reflect well and stay flat, but they are heavy and can break; acrylic mirrors are light and less fragile, but they bend easily and distort the light spot. Never a concave mirror - more on that below.
• A two-axis mount. One axis turns the mirror horizontally (azimuth), the other tilts it (elevation). It has to be stiff and free of play, because every wobble at the mirror arrives twice as large at the target.
• Motors and gearing. Stepper motors or geared DC motors with a high reduction ratio. A self-locking gear such as a worm drive helps the mirror hold its position in the wind without drawing power.
• A controller and a clock. A microcontroller or a small single-board computer with an accurate real-time clock. It calculates the sun's position and drives the motors.
• Power and housing. A weatherproof enclosure, outdoor-rated cables and connectors, and a power supply suitable for outdoor use. If mains voltage is involved, leave the connection to a qualified electrician.

How the tracking works

The sun's path is predictable, so its position can be calculated from the date, the time and your geographic coordinates with published solar position algorithms. A heliostat then needs one more step: to keep the reflection on a fixed target, the mirror must face exactly halfway between the direction of the sun and the direction of the target. The controller recalculates that angle every few seconds or minutes and moves the motors to match.

Some builders add light sensors that correct the aim in a closed loop. That helps against mechanical drift, but clouds, haze and stray reflections confuse simple sensors. Most projects therefore rely on the calculation and use sensors, if at all, only for fine-tuning.

Calibration: where most projects get stuck

Making the motors move is the easy part. The calculation assumes the device knows exactly how it is standing: where true north is (a compass points to magnetic north, which can be several degrees off), whether the base is level, where each axis sits at zero, and where the target is in relation to the mirror. Small errors add up, and a mirror doubles every angle error: one degree of error in the mirror's angle moves the light spot by about 35 cm at a distance of 10 m.

Typical symptoms: the spot lands on target in the morning but wanders off by the afternoon, or it works in summer and misses in winter. Fixing that means measuring, correcting offsets and checking again over days and seasons. Many DIY heliostats stop right here, as a working demo that needs regular re-aiming by hand.

Weather, wind and mounting

A heliostat lives outdoors all year. Rain, condensation, frost, UV light and dust wear down electronics, bearings and the mirror coating. A mirror also catches the wind like a sail, so even a moderate gust puts real force on the mount and its fixing points.

Plan a stable base or a fixing you have checked properly, a storm strategy (for example parking the mirror flat), and regular checks of screws and joints. A mirror that comes loose from a balcony, roof or wall is a danger to anyone below.

Glare and safety are your responsibility

Whoever puts up a mirror decides where sunlight goes, including where it must not go. If the reflection sweeps across a neighbour's window, a street or a footpath, it can dazzle people, and for drivers that is dangerous. A DIY heliostat can also send light in unplanned directions: while it moves, after a power cut or when the software crashes.

So before the first test, work out where the reflection can land at every point of its movement, run the first trials with the mirror covered or facing a wall, and check local rules: rules on glare toward neighbours or traffic can apply.

Never use a concave mirror. A concave mirror, such as a magnifying make-up mirror or a dish-shaped reflector, creates a focal point. There, sunlight can scorch wood, melt plastic or set fabric alight. To light a room you need a flat or slightly convex mirror, which produces a broad area of light instead.

Build it or buy it?

Building a heliostat yourself makes sense if the project is the point: you enjoy mechanics, electronics and code, you accept that calibration and weatherproofing will take many weekends, and you are ready to take full responsibility for where the reflection goes.

A finished device makes more sense if what you want is the light itself: sun on a desk, in a north-facing room or on a shaded terrace, day after day, without re-aiming anything by hand. That is what the ohoya Heliostat is built for. It sits outside, tracks the sun automatically using on-device computation and redirects daylight through a window or onto an outdoor seating area. You choose the target in the app, and glare protection is built in. The mirror is slightly convex and creates no focal point. Where you place it still matters: the siting notes are part of the installation.

Frequently asked questions

Can you build a heliostat yourself?

Yes. A basic two-axis mirror that follows the sun is a realistic project if you are comfortable with electronics, mechanics and programming. The hard part is precise calibration, weatherproofing and wind resistance, so that the light stays on target reliably for years.

What kind of mirror should I use for a DIY heliostat?

A flat or slightly convex mirror. Glass reflects best and stays flat but is heavy and breakable; acrylic is lighter but bends and distorts the light spot. Never use a concave mirror: it creates a focal point that can scorch or ignite materials.

How does a DIY heliostat know where the sun is?

It calculates the sun's position from date, time and location with a published solar position algorithm, then points the mirror halfway between the sun and the target. An accurate clock and careful calibration of north, level and zero positions matter more than the algorithm itself.

What about glare toward neighbours and traffic?

Plan for it before the first test. A home-built device can send the reflection in unplanned directions while moving or after a fault. Make sure it can never reach neighbouring windows, roads or footpaths, and check local rules, which can apply to glare.

When is a finished heliostat the better choice?

When you want the light rather than the project. A finished home heliostat should track the sun automatically, let you set the target and keep the reflection out of the directions you exclude. The ohoya Heliostat is available as a refundable reservation - not a purchase. Deliveries are planned for the EU from H1 2027 and for the US after FCC certification.