Solar Self-Sufficiency Calculator

Estimate solar coverage, battery impact, grid use, and yearly savings with an hourly profile model.

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Essentials

Build your scenario

Annual electricity usekWh/yrUse the annual total from your electricity bill.Solar array sizekWpUse the array's rated DC capacity.Expected annual yieldkWh/kWpUse a site estimate that already includes orientation, shading, and system losses.Household usage profileChanges when electricity is used, not the annual total.Usable battery capacitykWhEnter usable, not nominal, capacity. Use 0 for no battery.Grid import price/kWhThe price avoided when solar supplies the home.Export credit/kWhUse 0 if exported electricity receives no credit.

Advanced assumptionsEfficiency, costs, currency

Battery round-trip efficiency%Combined charging and discharging efficiency.Installed system costOptional. Enables simple whole-system payback.Battery costOptional. Enables simple incremental battery payback.Display currencyChanges labels only; no exchange-rate conversion is applied.

Decision evidence

See when the estimate changes

Annual totals can hide winter grid dependence.

Solar generation vs household use

Monthly model totals in kWh

Solar
Use

View monthly values

Month	Solar	Use	Grid import

Does the battery help?

Same solar and usage scenario

8 kWh battery

No batteryWith battery

Self-sufficiency——

Grid import——

Estimated net bill——

Modeled annual bill difference—Before battery purchase, financing, degradation, and replacement costs.

Where the energy goes

Conservation view of the modeled year

Household use—

Solar generation—

Money view

Simple annual comparison, not a quote

Grid-only baseline: —
Net bill after export credit: —
Modeled annual benefit: —
Simple system payback: —
Simple battery payback: —

Excludes fixed charges, taxes, tariff tiers, financing, degradation, maintenance, incentives, and replacement costs.

Planning range

Scenario sensitivity, not a confidence interval

Lower and higher cases change yield and demand by 10%. They show direction, not outcome probability.

Browser-local calculationInputs and results stay on this device unless you choose to copy, share, or print them.

Hourly profile modelSynthetic timing and battery state improve comparisons but do not replace site weather or engineering data.

Read methodology

Calculator ready.

How to use the estimate

Start with annual electricity use, array size, and an expected annual yield in kWh per installed kWp. Then choose the household profile that best reflects when electricity is used. Compare the same scenario with and without a battery before entering optional purchase costs.

The expected annual yield is deliberately a single site input. Use a reputable site-specific estimate such as the European Commission's PVGIS tool or an installer model, and make sure it already includes orientation, tilt, shading, and system losses. This avoids multiplying rough loss factors twice.

What the calculator cannot know

Real solar performance depends on site weather, roof layout, module temperature, inverter sizing and clipping, export limits, battery power limits, degradation, outages, tariffs, taxes, incentives, and installation quality. Treat the result as a scenario comparison, not a quote, engineering design, or production guarantee.

Model boundary

The model distributes the entered annual generation and demand across 8,760 synthetic hours using a temperate-season solar shape and one of three household load profiles. Each hour sends solar to the household first, then charges the battery, exports remaining surplus, and uses stored energy before importing from the grid. Battery state carries between hours and months, and round-trip conversion loss is included.

This is more timing-aware than a single annual self-use assumption, but it is not historical weather or smart-meter data. The battery model does not limit charge or discharge power and does not simulate reserve settings, outages, degradation, or replacement. The lower and higher planning cases change yield and demand by 10%; they are sensitivity scenarios, not confidence intervals.

The energy-flow sequence follows the same basic hourly accounting described in the European Commission's PVGIS documentation: solar serves the load, surplus can charge storage, and deficits can draw from storage before grid energy is counted. UsefulAtlas uses synthetic profiles and the annual yield you provide; it does not call PVGIS or upload an address.

What to ask a solar installer

What annual production estimate and weather period are you using?
How much shading loss did you assume?
What battery capacity is usable, not just nominal?
Are charge/discharge power and battery reserve settings modeled?
Which electricity price and export credit did you use?
How do the results change with my actual hourly smart-meter profile?

Common questions

Is this solar calculator a quote or a guarantee?

No. It is a planning calculator for comparing scenarios. Real production and savings depend on roof layout, weather, tariffs, export rules, installer design, and local conditions.

Why does a battery not always make the result better?

A battery only helps when there is enough surplus solar, enough evening or nighttime demand, and enough usable storage capacity. Battery losses and seasonal production limits can reduce the benefit.

What does self-sufficiency mean here?

Self-sufficiency estimates the share of annual electricity use covered by solar used directly or through the battery. It does not mean the home is fully off-grid.

Where should the annual solar yield come from?

Use a site-specific annual energy estimate in kWh per installed kWp from a reputable solar resource or installer. The value should already reflect orientation, tilt, shading, and system losses so those effects are not counted twice.