Testers wanted: NIBE S-series + PV — validate the Solar PV surplus feed on a site that has both

[HuggeK]

FTW can now feed live solar surplus to a NIBE S-series heat pump's own
Solar PV input (registers 2107/2109) over the pump's on-prem Local REST
API — the pump then soaks the surplus into heating and hot water using its
own owner-tuned logic. The mechanism is built, reviewed-ready and
hardware-validated as far as one site can take it. What we cannot produce
ourselves is a site that has both an S-series pump and PV — and that is the
half that matters most.

Looking for: one or more testers with an S-series pump (S735/S1155/S1255 or
similar, myUplink-era firmware with the Local REST API in installer menu 7.5)
AND real PV production on the same site.

What is already proven

On a real S735 (no PV on site), the full write chain has been run end-to-end
(findings on #537):
the pump accepts the write (modified), the value read back from register
2109 tracks exactly what FTW wrote, the driver's dead-man's switch clears a
stale feed on its own, and a hard crash mid-feed is cleaned up by the next
boot's orphan sweep. Every write is clamped to an operator-set max_w
ceiling, and the whole path is off by default behind three separate gates.

What only a PV site can answer

• Does the pump do something sensible with a real, moving surplus? Our
  test site had register 2107 (the owner's Solar PV master switch) off, so
  the value was accepted but ignored. With 2107 on, the pump acts on it —
  compressor scheduling, hot-water boosts, offsets — and nobody has watched
  that happen under FTW yet.
• The pump's own timeout for a silently stopped feed is undocumented; we
  clear proactively, but knowing the pump-side behaviour would let the
  driver state it instead of guessing.
• Register 2108 (own consumption): gross vs net — whether "include own
  consumption" changes what the pump expects 2109 to mean on a real site.

What testing involves

• Enabling the Local REST API on the pump's own screen (installer menu 7.5 —
  no myUplink account or app needed) and setting it to read/write
  (7.5.15), plus turning on the Solar PV input (2107) when ready.
• Running the write-capable build: driver from
  device-drivers#46, UI
  switch from #769 — once merged,
  it is one toggle in Settings → Devices plus a maximum-watts field.
• Starting with a small max_w and watching: the feed value, the pump's
  reaction, and the two telemetry series FTW records for exactly this
  (hp_solar_pv_feed_w — what FTW wrote, and the register 2109 read-back).
• A wrong value degrades to wasted comfort, never to unsafe operation — the
  pump's own firmware stays in charge of everything that matters.

If you have the hardware and are willing, reply here or on
#537. We can help with setup and
will take telemetry in whatever form is convenient.

🤖 Generated with Claude Code