A Spreadsheet Works — Until It Doesn't
A year of Fluvius quarter-hourly data quickly adds up to 35,000 rows for a single connection with one register — a formula recalculating that per client gets slow and error-prone past a few dozen clients. A copy-paste formula error, a forgotten filter, a sheet accidentally overwritten: risks that grow with the number of clients and how often you reuse the sheet.
What a Sheet Can't Maintain on Its Own (Live Pricing, PV/Battery Signals)
Calculating a dynamic tariff against real, historical quarter-hourly prices needs a live connection to a price source — not a snapshot you refresh manually. Detecting signals such as a suspected PV installation or battery from the usage pattern itself is in principle buildable in a spreadsheet, but needs maintenance that grows with every new client and every new insight.
Same Calculation, Different Place: One File per Client Instead of One File per Installer
The calculation approach doesn't change: usage data, simulation, final financial recommendation — the same steps a good spreadsheet already follows. What changes is where that work happens: one client file per client, a Fluvius import that processes itself, and a final recommendation built from that same file instead of a separate document — no sheets drifting apart between clients.
When a Sheet Still Does the Job
For a single, one-off calculation, a spreadsheet remains a perfectly reasonable choice — there's no reason to switch for one client. The point where a purpose-built workbench pays for itself is repetition: multiple clients, the same steps, over and over.