Costs, savings and the maths
This page explains how Power Insight puts a price on power, for readers who want the formulas behind the cost and savings sensors. For the short version, see How it works.
Cost of electricity (COE)
The cost of electricity is a blended per-kWh price across your whole energy mix — what one kWh actually costs you right now, given how much is coming from the grid vs. your own devices. Multiply it by power and you get a cost rate (currency per hour); integrate that over time and you get a total cost.
There are two ways to price your own devices:
- Standard uses the live grid import price for everything — it answers "what would this power have cost if I'd bought it from the grid?"
- Levelized prices each device by its own lifetime cost per kWh (see below).
LCOE (Levelized Cost of Electricity)
LCOE spreads a PV system's total lifetime cost across all the energy it produces over its life:
LCOE = lifetime_cost / lifetime_production (currency per kWh)
It answers "what does a kWh of my own solar really cost, once I account for what
the system cost me?" You provide lifetime_cost and lifetime_production per
device; Power Insight derives the LCOE. Levelized sensors only exist for devices
that have these values.
LCOS (Levelized Cost of Storage)
LCOS is the battery equivalent of LCOE — the lifetime cost of the battery spread across the energy it stores/delivers over its life. A battery's levelized sensors use its LCOS in place of an LCOE.
LCOS is computed with the same cost / throughput formula as LCOE, where the
throughput is the energy the battery discharges over its life. That energy
is metered at the battery's AC port, so round-trip losses are already netted
out of it — which is why Power Insight asks for no efficiency figure.
The correction factor
Levelized values are recorded over time (in the accumulated totals). If you later change a device's lifetime cost or production, its LCOE/LCOS changes — but you don't want history to become inconsistent.
Power Insight solves this with a correction factor:
correction_factor = current_lcoe / default_lcoe
Because the factor is constant, multiplying the recorded base totals by it retroactively and exactly rescales all the displayed levelized values to the new cost basis. A total that mixes energy from several devices — a battery charged from two PV systems, say — keeps a share per device, so each share is rescaled by its own device's factor.
The correction reaches the device's whole history on purpose. LCOE and LCOS are lifetime averages, so a revised lifetime cost or production is the right price for energy already recorded too — whether the first estimate was off, a repair added to the cost, or the device produces less than expected. Two things follow:
- The long-term statistics show the correction as one step in the hour you made the edit; earlier statistics are not rewritten.
- Replaced hardware is a new device. New panels or a new battery have a lifetime of their own: add them as a new device and remove the old one rather than editing its lifetime values.
When a device is removed, its final corrected contribution is frozen into a ledger so the combined totals never drop, and its share in other devices' totals keeps its last factor.
This is why the reconfigure page warns:
If you change the lifetime cost or lifetime production values, Power Insight applies a correction factor that retroactively rescales this device's already-recorded levelized values to stay consistent.
Export compensation
Export compensation is what you are paid per kWh exported to the grid. It drives:
- Export compensation rate (currency/h) = current export power × the rate.
- Total export compensation = that rate integrated over time.
How savings and financial return are calculated
Power Insight tracks three related but distinct financial quantities:
Cost savings — the money you save by not importing power you would otherwise have bought. Your own generation (PV, battery discharge) covers some of your load; the savings are the grid price of that avoided import, minus the operating cost of the device that provided it:
cost_savings = avoided_import_cost − operating_costs
For PV the main operating cost is standby consumption at night. For batteries it is the cost of the energy used to charge them, adjusted for round-trip losses.
Export compensation — the revenue you earn from power exported to the grid. This has its own dedicated sensors (see Export compensation).
Financial return — the combined picture: savings plus export compensation.
financial_return = cost_savings + export_compensation
Use cost savings when you want to know how much you avoided spending. Use financial return when you want one number that includes everything your devices are earning for you.
Why is my levelized financial return lower than my levelized savings?
In the levelized version, every kWh a device produces carries its lifetime cost (LCOE for PV, LCOS for a battery) — the kWh it exports included. So the levelized financial return also subtracts what the exported energy cost to produce:
levelized_financial_return = levelized_cost_savings
+ exported_kWh × (export_compensation − LCOE)
When your feed-in tariff is below the device's LCOE/LCOS, each exported kWh loses money and the financial return ends up below the savings. That is not an error: it tells you self-consumption pays for the device while exporting does not. If you never export, the two are equal.
Example. A PV system with an LCOE of 0.10 sends 1 kWh into the home and exports 1 kWh; the grid price is 0.30 and the feed-in tariff 0.08.
| Total | Calculation | Value |
|---|---|---|
| Levelized cost savings | 1 × (0.30 − 0.10) | 0.20 |
| Levelized financial return | 0.20 + 1 × (0.08 − 0.10) | 0.18 |
The standard (non-levelized) values treat your own generation as free, so there the financial return is never below the savings.
Why does my battery have negative cost savings?
Any device can show negative cost savings if it doesn't earn enough to cover its costs. Batteries specifically always show negative cost savings while charging, because Power Insight tracks the cost of the energy going into the battery. That cost is "paid back" as positive savings when the battery later discharges and offsets a grid import. Over a full charge/discharge cycle the battery's net contribution is what matters.
How totals are counted
Total sensors integrate a rate (currency/h) over time using a left-Riemann method — each stretch of time is counted at the rate that held through it — and persist their running total in Home Assistant's recorder so it survives restarts. While a rate is unavailable (a meter has dropped out) the total pauses, and it resumes when the meter reports again; the time in between is not counted. There is no staleness timeout: a sensor that is still available is trusted, even if it has not reported for a while. What a device earned before Power Insight counted it can be carried over from its app, in the device's Already accumulated section (see Carried-over history).