DIY Solar Buffer Tank Heating - Pufferspeicher Heizstab Rechner
2026-03-31 #Blog | #Solar | #DIY
We had 4 older LiFePO4 batteries, a second-hand inverter, 8 solar panels and some used MPPT trackers lying around. So the idea was born: build a DIY solar system to heat up our buffer tank (Pufferspeicher), reduce pellet consumption and have some fun along the way.
The setup
The system uses a heating rod (Heizstab) — originally a 3-phase unit, now wired to run on a single phase at around 1.3 kW — to heat an 800L hygiene buffer tank. The solar panels feed through the MPPT trackers and the LiFePO4 batteries provide storage for heating after sunset. It’s a DIY playground, all built from parts we already had.
In summer this produces enough hot water for 4 persons and the pellet boiler stays off from spring to autumn.
The calculator
To plan the energy flow, I built a small calculator tool: the Pufferspeicher Heizstab Rechner. It has three tabs:
- Aufladung — How much energy goes into the buffer tank per day
- Entladung Sommer — Summer discharge and hot water usage
- Übergangszeit — Transition season calculations
Single HTML file, no dependencies, vanilla JS. MIT licensed.
| Live Tool | GitHub Repo |