It's All Sunshine and Heliostats

There’s nothing like sunshine to brighten up your day. Its warm glow has an immediate and noticeable effect on your mood, making everything feel lighter and more hopeful. But during the wintertime, sunshine can be a rare sight. That is especially true for those who find themselves cooped up indoors for most of the day. Unless windows are in the right positions, the winter sun may never even touch the interior of the home, leaving rooms perpetually dim and reliant on artificial light.

Redditor Erqos recently pointed out that there is another option — if you don’t mind putting in some work. Erqos created a small ESP32-controlled heliostat that can be used to bring sunlight into any space in your home, no matter what the actual position of the sun in the sky is at any given time.

Inspired by the town of Rjukan, Norway — which installed giant mirrors on a mountainside to redirect sunlight into its shadowed town center — Erqos set out to build a compact, dual-axis heliostat suitable for everyday home use. The prototype, already fully functional, uses a 20-centimeter mirror mounted on a scaled-down pan-tilt frame driven by two linear actuators.

The system is powered by an ESP32-S3 microcontroller, which fetches real-time sun-position data from an online astronomy API. By pulling precise azimuth and altitude values for its exact GPS coordinates, the device computes how the mirror must tilt and rotate to reflect sunlight into a fixed target — in this case, Erqos’s daughter’s living room. Every minute, the ESP32 recalculates the ideal orientation and makes tiny corrections to track the sun’s slow drift across the sky.

To achieve this level of precision, the actuators are driven in extremely small increments using low-power PWM pulses, producing mirror adjustments of fractions of a degree. An onboard IMU confirms the mirror’s orientation with an impressive resolution of 0.001 degrees, ensuring the system locks onto the correct angle despite small disturbances.

All of the electronics — including the 24-volt power supply, ESP32 microcontroller, and relays used to reverse actuator direction — are neatly arranged inside a waterproof DIN-rail cabinet. According to Erqos, roughly 95% of the control software was generated with the help of AI, using an iterative prompting strategy.

For households craving a little winter sunshine, Erqos’s DIY heliostat may quite literally offer a bright new solution.