Plug-In Solar Calculator
This plug-in solar calculator is in final testing and will be available soon.
When it launches, it will estimate how much electricity a small plug-in solar system could generate at your location, and compare that hourly solar estimate with household electricity use to show how much might be used directly and how much could become surplus.
It keeps panel capacity and inverter output separate: a system with 1,200 W of panels and an 800 W inverter will not be treated as if it only had 800 W of panels.
Generation estimate, not a permission check
Generation estimates do not establish whether a system size or product is permitted where you live.
The interactive calculator is coming soon
The generation model is built and is being finalised before launch. In the meantime, the sections below explain what the calculator estimates, why panel capacity and inverter output are kept separate, and why household timing matters. For the rules that apply where you live, start with your country.
Why can more panels still help with the same inverter?
Panel wattage and inverter output describe different parts of the system.
The panels determine the rated DC generating capacity available.
The inverter limits the maximum AC output it can supply.
So:
1,200 W of panels + 800 W inverter
is not calculated as:
800 W of panels
The calculator models the full panel capacity and applies the inverter limit as solar conditions change.
When available solar production is below the inverter limit, additional panel capacity can increase output.
When the inverter reaches its maximum output, the AC output stops increasing beyond that limit.
This limiting is commonly called clipping, but the calculator does not claim to measure exact clipping duration or clipping losses from hourly data.
Why does household electricity use matter?
Solar is most directly useful to the household when electricity is being used at the same time that the panels are generating it.
Two homes can have identical solar systems in identical sunlight and generate the same amount of solar electricity.
If one home uses more electricity during solar-producing hours, it can use more of that solar directly.
If the other uses most of its electricity at a different time, more of the solar may become surplus.
That is why the calculator compares solar generation with household demand hour by hour rather than asking you to guess a self-consumption percentage.
What does self-consumption rate mean?
Self-consumption rate is the share of generated solar electricity used directly by the household.
If a system generates 500 kWh and 350 kWh coincides with household demand:
350 ÷ 500 = 70% self-consumption
This is different from solar coverage.
What does solar coverage mean?
Solar coverage asks what share of the household's entered electricity demand is supplied directly by solar.
A household can therefore have a high self-consumption rate while solar still covers only a modest share of its total electricity use.
Solar coverage is only shown when you provide annual or monthly household electricity use.
It is not shown for a steady-load scenario.
What does potential surplus mean?
Potential surplus is solar generation above estimated household demand during the same hourly interval.
It does not mean:
- the electricity will definitely be exported
- the grid will necessarily accept it in the same way everywhere
- you will receive a payment for it
The treatment of surplus depends on the system and the rules and arrangements where you live.
What difference does shade make?
Shade can reduce solar generation substantially, but a simple description such as "some shade" does not tell us when the shade occurs or how much sunlight it blocks.
A neighbouring building shading a panel in the morning is different from a tree shading it in the late afternoon.
For that reason, the calculator does not turn "some shade" into a hidden fixed loss percentage.
If you report nearby shade, the result remains a base estimate and is marked with a warning that real generation may be lower.
How accurate is the estimate?
The solar estimate uses geographic solar-resource data and an hourly PV performance model rather than a simple fixed number of "sun hours".
It is still an estimate.
- Typical weather
- The calculation represents a typical weather year, not a forecast for next year. Actual generation changes from year to year as weather changes.
- Nearby shade
- Nearby trees, walls, balconies and buildings are not modelled from a qualitative shade description.
- Hourly modelling
- Solar production and household electricity demand can change within an hour. Shorter variations are smoothed by the hourly model.
- Household timing
- Annual or monthly electricity-use totals do not show exactly when appliances are used. The general household timing pattern is therefore an assumption, not measured consumption.
- Standard PV assumptions
- The calculator uses generic PVWatts module, inverter and system-loss assumptions rather than modelling one manufacturer's equipment.
- Mounting approximation
- The airflow choice approximates the effect of mounting on panel temperature. It cannot describe every physical mounting arrangement.
- One direction and tilt
- All panel capacity entered is assumed to share one direction and one tilt.
- No battery
- Battery storage is not modelled.
- No financial model
- Electricity tariffs, export payments, system prices, payback and ROI are not part of this shared calculator.
- No legal judgement
- The calculation does not establish whether the system or product is permitted where you live.
No installation assessment
The calculator does not assess:
- balcony structure
- railing suitability
- mounting safety
- socket suitability
- circuits
- fixed electrical installations
How the estimate works
Solar generation model: PVWatts V8.
The model uses your:
- location
- panel DC capacity
- inverter AC output
- direction
- tilt
- mounting/airflow choice
to produce an hourly typical-year solar estimate.
Panel capacity and inverter output are modelled separately.
Shade: nearby-object shade is not assigned a hidden percentage from the qualitative shade question.
Household overlap: where annual or monthly household-use modelling is available, the calculator compares hourly solar generation with an estimated hourly household-use pattern.
Time basis: solar and household use are compared in local standard-time hourly intervals. Daylight-saving clock changes are not applied to the synthetic typical year.
Weather variability: PVWatts' public calculator can show historical weather-year variability for some locations, but this calculator does not reproduce that range. No arbitrary ± percentage is added.
Generation is not a permission check
The calculator is shared across markets.
It does not silently change your system to match a local legal limit.
If you enter a larger system, the calculator can estimate its generation within the calculator's technical input range.
That does not establish that the configuration is permitted where you live.
United States
State laws, product requirements, output limits and utility processes can differ.
United Kingdom
The current Great Britain plug-in solar framework has its own product and output requirements.
Use the energy result to look at costs and savings
This calculator deliberately stops at electricity.
It does not assume:
- your electricity tariff
- export payment
- SEG eligibility
- US utility compensation
- system cost
- payback period
Those questions depend on where you live.
United States
Use your estimated annual generation, directly used solar and potential surplus with: