Embedded Files
Winter is beautiful for astronomy, until 15 cm of snow sits on the observatory!
In our case, snow accumulation on the roof could prevent the observatory from opening safely and even worse, when the roof opens, chunks of snow or ice could fall directly onto the telescope.
After dealing with this fear for a while, we decided to install a simple roof heating system. The goal was not to keep the roof warm all winter, but simply to melt snow and ice quickly when needed.
After one winter of testing, the system works well. In this article we’ll describe how it works and what we learned.
Quick Specs
Quick Specs
Roof surface: 2 x 2.1 m²
Heating cable: 12 m / 360 W per half
Heating density: ≈ 240 W/m²
Clearing time: 15–20 minutes
Energy per cycle: ~0.12 kWh
The Observatory Roof Design
The Observatory Roof Design
Our observatory has a split roof architecture: two halves slide apart when opening.
The southern roof section slightly overlaps the northern one to ensure good waterproofing when the roof is closed.
Each half-roof is 1.6 m wide and about 1.3 m long, giving roughly:
2.1 m² per half roof
4.2 m² total roof surface
The roof panels are made of 1.5 mm aluminum sheet, with no thermal insulation.
The roof is not a simple slope. Instead, it uses four segments with different angles:
15°
45°
75°
90° (vertical edge)
Each of the first three segments is about 400 mm long, and the vertical edge is about 180 mm.
The reason for this unusual geometry is simple: telescope clearance.
When a telescope moves, it describes what I like to call a “clearance sphere”. The roof shape was designed to minimize the building height while still allowing the telescope to move freely in every direction.
Choosing the Heating Cable
Choosing the Heating Cable
For heating we use a DOJA constant-power heating cable:
Length: 12 m
Power: 360 W
Voltage: 220–230 VAC
This corresponds to roughly 30 W per meter.
We use a constant power cable rather than a self-regulating one because the system is only used occasionally. When it runs, we simply apply full power.
Power Density
Power Density
Currently the cable heats about 1.5 m² of roof surface.
That gives:
360 W / 1.5 m² ≈ 240 W/m²
This turns out to be a very good value for melting snow and ice on metal surfaces.
Later I plan to extend the cable to 18 m, increasing power to 540 W per half-roof, which keeps the same power density across the entire surface.
Installing the Cable
Installing the Cable
The cable runs across the roof in horizontal back-and-forth lines, spaced roughly 25 cm apart.
To ensure good thermal contact with the aluminum sheet, the cable is fixed using:
3M aluminum tape (reference 1436 - 50 mm width)
Before applying the tape, we cleaned the aluminum thoroughly with isopropyl alcohol. This step is essential for good adhesion. No glue gun was needed in my case — the aluminum tape holds the cable quite well.
Electrical Installation
Electrical Installation
The heating system is powered through a dedicated circuit:
10 A circuit breaker (GE G61 B10)
230 V AC supply
1.5 mm² shielded cable
The heating cable connections use spade crimp connectors, which are enclosed inside a small electrical junction box for safety.
Because the roof structure is aluminum, proper grounding of the roof is absolutely essential.
Control System
Control System
Instead of full automation, I chose a simple manual control system.
The heater is controlled by my IPX800 automation controller, with three buttons:
Heat for 15 minutes
Heat for 60 minutes
Stop heating
Each button also displays a progress bar, which makes it easy to see how much heating time remains.
This approach has two advantages:
The system cannot run indefinitely by mistake
It keeps the design simple and reliable
Since snow only occurs 5–10 times per year, manual activation is perfectly acceptable.
Real-World Performance
Real-World Performance
The system has already been tested in real winter conditions.
Typical conditions:
Temperature: down to –12 °C
Snow thickness: 10–15 cm on the upper segment
Results:
Snow or ice melts in about 15–20 minutes.
The roof clears quickly and can then be opened safely.
A Lesson Learned
A Lesson Learned
During the first installation I made a mistake.
I did not install heating cable on the final vertical segment of the roof, assuming that melted water would simply run off.
What actually happens is this:
Snow melts on the heated roof
Water flows downward
It reaches the unheated vertical section
The water freezes immediately!
The result was large ice stalactites hanging from the roof.
The solution is simple: the vertical edge must also be heated so the water can drip freely to the ground.
I will extend the cable in the future to solve this.
After all, we are the Disastronomers, aren't we?
Energy Consumption
Energy Consumption
Although the heater is relatively powerful, it runs only briefly.
Typical heating cycle:
360 W
20 minutes
Energy used:
≈ 0.12 kWh
Even heating the entire roof with 1080 W would only use about:
0.36 kWh per cycle
So the actual operating cost is very small.
Just a reminder!
Final Thoughts
Final Thoughts
After testing this system, we can say that roof heating is a very practical solution for snowy observatory locations.
A few key takeaways:
Around 200–250 W/m² works well for snow melting
Always heat the lowest edge of the roof
Keep the control system simple and fail-safe
Ensure proper electrical grounding
The system is simple, reliable, and makes winter observing much easier.
And best of all, it only takes about 20 minutes to clear the roof and get back to observing the night sky.
Page updated
Google Sites
Report abuse