Electrical & Solar Calculator
Explore voltage, current, AC power, energy use and solar panel estimates. Pick a calculation, follow the diagram and see the formula behind your result.
For learning and preliminary estimates. These conceptual diagrams are not wiring plans. Results do not establish safe cable, breaker, motor or solar installation specifications.
Choose a quantity. See how it is calculated.
Select a family, then the specific calculation you need.
Inputs use the units shown on each field. Drafts stay only while this page is open.
Four examples, with the working shown
Hypothetical inputs demonstrate the difference between electrical power, running current and daily solar energy.
Balanced three-phase load
A load draws 15 A at 415 V line-to-line with a power factor of 0.8. Calculate real electrical input power.
8.6256 kW · not mechanical shaft output
Assumption: balanced sinusoidal RMS values. No motor efficiency is applied.
Motor shaft output to current
An 11 kW shaft-output motor runs at 415 V, power factor 0.85 and 90% efficiency.
20.0043 A · steady running estimate
The motor mode uses efficiency once. It does not estimate starting current or select a breaker.
Solar panels to daily energy
Ten 550 Wp panels give 5.5 kWp DC nameplate. Assume 5 peak sun hours and an 80% combined output factor.
22 kWh/day · illustrative, not guaranteed
The output factor includes the inverter and other assumed losses. This is not a weather-based simulation.
Daily energy use from power
A device uses an average real input of 3.5 kW for six operating hours in one day.
21 kWh · for the stated day
Use average input power during operation. A maximum or nameplate rating may differ from the actual average.
Start with the question, then choose the formula
Identify what is given, what is unknown and which assumptions apply. Find your case in the table to see the required inputs, calculation family and mode.
| Your case | Known values to prepare | Family and calculation | Choose |
|---|---|---|---|
| Find voltage from current and resistance. | Current in A; resistance in Ω. | DC & unit basicsVoltage · Ohm’s law | |
| Find current for an ideal resistive load. | Voltage in V; resistance in Ω. | DC & unit basicsCurrent · Ohm’s law | |
| Find DC power for a battery load. | DC voltage in V; DC current in A. | DC & unit basicsDC power · W and kW | |
| Calculate balanced three-phase input power. | Line-to-line RMS V; RMS line A; PF. | AC power & motorsThree-phase AC power | |
| Estimate motor running current from a shaft rating. | Output kW; line-to-line RMS V; PF; efficiency %. | AC power & motorsThree-phase motor current | |
| Compare line and phase current in a star load. | Line-to-line RMS V; equal branch resistance in Ω. | AC power & motorsStar (Y) resistive load | |
| Compare line and phase current in a delta load. | Line-to-line RMS V; equal branch resistance in Ω. | AC power & motorsDelta (Δ) resistive load | |
| Find resistance of one conductor. | Resistivity in Ω·mm²/m; length in m; area in mm². | Conductors & circuitsConductor resistance | |
| Estimate a DC resistive voltage drop. | Supply V; current A; complete loop resistance Ω. | Conductors & circuitsDC resistive voltage drop | |
| Find series RLC impedance at one frequency. | R, XL and XC, all in Ω. | Conductors & circuitsSeries RLC impedance | |
| Find power factor from meter readings. | Real power kW; apparent power kVA. | AC power & motorsPower factor · kW / kVA | |
| Calculate energy used over operating hours. | Average real input kW; hours/day; days. | Energy & solar panelsEnergy use · kWh | |
| Estimate daily energy from an existing panel count. | Panel count; panel Wp; PSH; combined output factor %. | Energy & solar panelsSolar panel output estimate | |
| Estimate panel count for a daily energy target. | Daily kWh target; PSH; combined output factor %; panel Wp. | Energy & solar panelsSolar panel count estimate |
Opening a mode keeps any draft already entered there. Review the diagram, enter the labelled units and show the numeric substitution in your working. Equipment selection and installation design remain outside this tool.
Read the units before comparing results
Similar-looking ratings describe different quantities. Keep these distinctions with your calculation.
kW, kVA and power factor
kW is real power. kVA is apparent power. Their non-negative ratio gives power factor magnitude; it does not tell you whether a load is leading or lagging.
kW and kWh
kW describes a power rate. kWh describes energy over time. A constant 3.5 kW average input for six hours uses 21 kWh. A rated device may draw a different average input during normal use.
Wp, kWp and solar yield
Wp and kWp describe a panel or array’s rated DC power under test conditions. A daily energy estimate adds solar-resource and loss assumptions; it does not turn the nameplate into a guaranteed AC output.
Know the boundary of the model
Use the working to understand a relationship, then check the conditions that a short formula cannot represent.
AC and conductor assumptions
- Three-phase modes assume a balanced load.
- Star/delta modes use equal resistive branches.
- Conductor resistance uses your chosen resistivity and temperature assumption.
- Voltage drop uses complete loop resistance for a DC resistive model.
Solar estimates need local context
- Enter peak sun hours appropriate to the location and season.
- Use one combined factor for the losses you include.
- Panel count is rounded up mathematically.
- Night-time supply, batteries, roof layout and inverter constraints are not modelled.
Equipment selection is separate
- No breaker rating or cable ampacity is selected.
- No fault current, earthing or shock-protection assessment is performed.
- Diagrams show concepts, not terminal connections.
- Use a qualified professional for installation decisions.
Check the relationships and assumptions
These references explain the underlying physics or provide a more detailed solar estimate. They do not certify this calculator.
Formula references
Follow a reference for the relationship behind a result. These links do not imply certification or endorsement.
- OpenStax · resistivity and resistancePhysics reference · length, area, material and temperature.
- OpenStax · series RLC circuitsPhysics reference · resistance, reactance and impedance.
- Fluke · power factorMeasurement reference · real kW and apparent kVA.
- Kentucky electrical study guide · PDFTheory reference · DC and three-phase relations. Local installation requirements still need separate review.
- PVWatts · detailed solar modellingSolar resource · use location and system details for a more detailed estimate.
Related calculation tools
Open a separate tool for a different quantity, or browse the full calculation directory.
Use related tools for separate quantities; they do not complete an electrical installation design.
Questions about electrical and solar estimates
Which calculations are included?
Choose from 18 modes: Ohm’s law voltage, current and resistance; DC power; single-phase and three-phase power; three-phase line and motor current; balanced resistive star and delta loads; conductor resistance; DC resistive voltage drop; series RLC impedance; power factor; energy use; two solar estimates; and W/kW/MW conversion.
Why are line voltage and phase voltage different?
For an ideal balanced star load, phase voltage equals line-to-line voltage divided by √3. For a delta load, each branch sees line-to-line voltage. The star/delta modes here assume three identical resistive branches.
Should I enter motor output kW or input kW?
The motor mode takes mechanical shaft output kW and divides by efficiency to account for electrical input. The separate three-phase line-current mode takes electrical input kW directly. Do not apply efficiency twice.
Does a solar panel’s watt rating equal its daily energy?
No. Panel watts describe rated DC power under test conditions. Daily kWh depends on solar resource and losses. The solar modes use your peak sun hours and a combined output factor; they do not retrieve weather or predict a specific installation’s yield.
Are peak sun hours the same as daylight hours?
No. Peak sun hours express daily solar irradiation as equivalent hours at 1 kW/m². Use a suitable location- and season-specific value. The 5-hour example is a hypothetical assumption, not a local forecast.
Can this choose my breaker, cable or solar inverter?
No. These formulas do not select protective devices, cable ampacity, earthing, solar string voltage or inverter compatibility. A simple current multiplier is not a complete design method. Have equipment and installation decisions checked by a qualified electrical professional using applicable requirements.
Does the tool save or send my inputs?
The calculator script keeps values in page memory and does not upload or persist them. Font files and other WordPress scripts may make network requests. WhatsApp opens an external service with the report values you choose to share. Reset clears the active calculation; reloading clears all calculator drafts.
How do downloads and examples work?
Each Load example button fills a hypothetical case, calculates it and scrolls to the tool or mobile result. Download TXT saves the current report. Print / PDF opens a printable report; PDF saving depends on the browser’s print options. Editing an input clears the previous result until you calculate again.