Apartment building in Thessaloniki, 4 floors, 12 apartments. The roof is taken up by other owners’ solar tanks, or has restrictions from the general assembly, or the third-floor tenant simply doesn’t want to spend 6 months on approvals for a hot water tank. In practice, a solar water heater in an apartment building is hard, even when it’s technically feasible.
What the real options are
1. Solar water heater on the roof (classic)
Requires:
- Building assembly approval (majority vote, often 51%)
- Free roof space with southern orientation
- Piping running from the roof down to the apartment (through a lightwell, mechanical room, or externally)
- Waterproofing at roof penetrations
In practice: feasible mainly in new-build apartments designed for it, or in older ones with a willing assembly.
2. Solar on the balcony
Flat collectors mounted on the balcony railing. Option for west- or south-facing apartments.
- Pros: individual system, no assembly approval (for private balconies), no roof penetrations
- Cons: aesthetics, lower output because the collector is vertical and small, harder pipe routing
3. AXINAR SolBox, PV Panel on the Balcony + Existing Water Heater
This is the most practical apartment solution. A 300 to 400W PV panel is placed on the balcony or the facade, connects to the AXINAR SolBox (DC controller), and feeds the element of the existing electric water heater.
- No general assembly approval required (the panel is inside the apartment envelope)
- No utility connection required (does not produce AC for the grid)
- No inverter required
- No plumbing changes
- Works year-round with reduced output on cloudy days
The water heater stays the same. Electricity cost drops significantly, since hot water is 25 to 40% of a household’s power bill.
4. Heat pump water heater
A standalone unit that draws heat from ambient air (or from a non-air-conditioned space) and transfers it to water. Good coefficient of performance (COP ~3), but:
- Takes up space (kitchen, bathroom, exterior wall)
- Has noise (~50 dB)
- Draws power from the grid
- Significantly higher purchase cost
Comparison for apartment buildings
| Solution | Assembly approval | Work on common areas | Works in clouds |
|---|---|---|---|
| Solar on the roof | Yes | Yes | With backup element |
| Solar on the balcony | Probably | No | With backup element |
| AXINAR SolBox (PV on balcony + existing water heater) | No | No | Reduced |
| Heat pump water heater | No | No | Yes, from grid |
Practical guidance for apartments
If you have a south- or west-facing balcony
The sun reaches you almost all day. A 400W PV panel laid flat or on a railing bracket, connected to AXINAR SolBox, gives enough energy for hot water for a 2 to 3 person household. The panel doesn’t need exact southern orientation (a 30° offset left or right only costs 10 to 15%).
If you have a north-facing balcony
Hard for PV. A heat pump water heater is a better fit.
If you’re in a penthouse with roof access
The easiest combination: a PV panel on the roof (small footprint, no piping), DC wiring to the water heater inside the apartment.
SolBox works with a balcony PV panel, without grid connection, and without work in the common areas. No general assembly vote required.
- Light version for 1 to 2 person apartments
- Family version for 3 to 4 people
- Installation without touching the plumbing
- Works with your existing water heater
Request a quote
Send us a photo of the balcony, orientation, and water heater type. We’ll suggest the right solution.
See also: SolBox: Complete guide to converting a water heater, Comparison of PV water heater vs solar vs heat pump.
