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PV and battery: technical scenarios

A simplified hourly model of a typical day: how much PV output is used on site, what a battery changes, and whether a battery of a given power and capacity can cover one power peak. A technical basis for thinking, not a design or a forecast — the calculation runs only in your browser.

Scenario A — PV self-consumption

One typical day with the same consumption and generation, compared without and with a battery.

Roughly in Central Europe: a winter day about 0.5–1.5, a clear summer day about 4–6. Depends on site, orientation, tilt and weather.
About 8–9 h in winter, 15–16 h in summer. The model spreads generation symmetrically around 12:00.
Capacity 0 = no battery. Efficiency covers losses on both charge and discharge.
Without batteryWith battery
PV generation [kWh]——
Direct use of PV [kWh]——
Charged into the battery [kWh]——
From the battery to the load [kWh]——
Grid import [kWh]——
Grid export [kWh]——
Battery losses [kWh]——
PV self-consumption [%]——
Load covered without the grid [%]——

The day hour by hour: consumption and PV generation

consumption PV generation

Scenario B — can a battery cover a power peak?

One peak above a chosen limit, simplified as a rectangle: a constant excess power for the given duration.

Uses the battery entered in scenario A (power, capacity, efficiency).

One such peak—
Battery power needed
— kW
Energy above the limit
— kWh
Usable capacity needed
— kWh
Battery power sufficient
—
Battery capacity sufficient
—

Find your maximum and how it relates to your capacity with: 15-minute demand → · Reserved capacity utilisation →

Considering PV or a battery?

A technical analysis of interval data shows how consumption and peaks really behave — and whether, and at what size, PV or a battery makes technical sense.

Technical analysis→Energy→

How the model works

The model calculates the 24 hours of one typical day:

  • consumption is spread according to the chosen profile,
  • PV generation = size × yield per kWp, spread as a half sine over the solar day,
  • PV covers the load first, surplus charges the battery (within its power and capacity) and the rest is exported,
  • when PV is not enough, the battery covers the load and the grid covers the rest,
  • the day is repeated until the midnight state of charge settles, so the battery does not start the day artificially empty or full.

What the model does not account for

It is a simplification for comparing scenarios. The model does not include:

  • the actual site, orientation, tilt and shading of the panels,
  • weather and the variation of days over the year,
  • the real profile of your consumption (only the chosen shape),
  • battery degradation, depth of discharge and lifetime,
  • the control strategy, the inverter and grid connection constraints.

A decision on PV or a battery needs measured interval data and a technical assessment of the specific site.

Note

This tool is an indicative technical model. It is not a PV design, a yield forecast, battery storage sizing, or an economic calculation of savings or payback, and it does not replace an assessment of the grid connection conditions.

An exact assessment must be based on measured data, a site survey and a design by a qualified designer.

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