Solar panel wattage calculator
Ten 400 W panels at 5 peak sun hours form a 4 kW array that yields 20 kWh a day and 7300 kWh a year before any losses. Check a rooftop quote by multiplying three numbers you already have. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Panel wattage
- 400
- Panel count
- 10
- Peak sun hours
- 5
- Array watts
- 4,000
- Array kw
- 4
- Daily kwh
- 20
- Annual kwh
- 7,300
Solar panel wattage is the nameplate DC rating printed on a photovoltaic module, but what homeowners, installers and students actually need is energy: how many kilowatt-hours that array will produce in a typical day and over a year. This solar panel wattage calculator takes three finite numbers you already have from a datasheet and a site estimate — panel wattage in watts, how many panels sit in the array, and average daily peak sun hours — and returns daily and annual kilowatt-hours from the textbook product of array kilowatts times sun hours times three hundred sixty-five. Zero wattage, zero panels or zero sun hours returns zero kilowatt-hours.
The solar energy formula and what each term means
The energy a photovoltaic array can deliver on a typical day is the product of three quantities. Each module has a nameplate DC wattage, the power it would produce under standard test conditions of one thousand watts per square metre and a cell temperature of twenty-five degrees Celsius. Dividing that wattage by one thousand converts it to kilowatts so that multiplying by hours yields kilowatt-hours rather than watt-hours.
The panel count scales a single module up to the whole array: ten four-hundred-watt modules are four kilowatts of DC nameplate. Peak sun hours are not clock hours of daylight; they are the equivalent number of hours at one thousand watts per square metre that would deliver the same insolation the site actually receives on an average day. A location with five peak sun hours therefore supplies five kilowatt-hours of ideal DC energy for every kilowatt of nameplate.
Annual energy is that daily figure times three hundred sixty-five, the calendar-year constant this calculator uses so two callers never disagree about leap days. A ten-panel array of four-hundred-watt modules at five peak sun hours therefore yields twenty kilowatt-hours per day and seven thousand three hundred kilowatt-hours per year. The calculator does not model inverter clipping, soiling, temperature derate, tilt, azimuth or shading: those belong in a detailed performance study.
What you get is the textbook screening energy you can audit by multiplying three numbers. Change wattage, count or sun hours and the kilowatt-hours move in lockstep. This page is not a panel-count sizer that starts from a monthly utility bill, and it is not a generic watts-to-kWh converter for an appliance that runs on a clock: those answer different searches about how many modules to buy or how long a load ran, not about how much energy a given array and climate can produce.
Who screens solar quotes with this figure
Homeowners screening a rooftop quote use a deterministic solar panel wattage calculator to turn a datasheet wattage, a proposed module count and a climate table of peak sun hours into daily and annual kilowatt-hours they can put next to last year’s utility bill, instead of quoting a slogan about free sunshine. Campaign pages that ask visitors to compare a rooftop array with a small hydro plant can send the same three numbers the visitor already typed and show annual kilowatt-hours without inventing a derate. Failed validation does not consume balance.
Keep requests small, pin the rounded fields in tests, and you get a reproducible photovoltaic energy product without standing up a weather-station historian of your own.
What you can do with it
Rooftop quote screening
Turn a datasheet wattage, a proposed panel count and a climate table of peak sun hours into daily and annual kWh you can put next to last year’s utility bill.
Classroom photovoltaic problems
Let students submit watts, count and peak sun hours and check the textbook product (W/1000)×N×PSH without flipping a 365 factor by hand.
FAQ
How is solar panel energy calculated from wattage, count and sun hours?
Annual kilowatt-hours equal that daily figure times 365. Ten 400 W panels at 5 peak sun hours therefore yield 20 kWh/day and 7300 kWh/year.
Are peak sun hours the same as hours of daylight?
No. Peak sun hours are equivalent hours at 1000 W/m² that match the site’s average insolation. A long summer day with weak sun can have fewer peak sun hours than a shorter, clearer day.
What happens if wattage, count or sun hours is zero or negative?
Zero is accepted and the calculator returns zero kilowatt-hours.
Does the result include inverter, heat or shading losses?
No. It is the textbook energy before losses: inverter clipping, dirt, temperature, tilt, orientation and shading are left out. Treat it as a screening figure and leave those details to a full performance study.
Can I enter a 370.5 W module or 4.75 sun hours?
Yes. Fractional values are accepted, so you can type the exact datasheet rating or climate figure without rounding first. A planning count such as 12.5 equivalent panels is accepted as well.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/eco/solar-panel-wattage \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"panel_wattage":400,"panel_count":10,"peak_sun_hours":5}'const res = await fetch("https://api.kit.forhosting.com/eco/solar-panel-wattage", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"panel_wattage": 400,
"panel_count": 10,
"peak_sun_hours": 5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/eco/solar-panel-wattage",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"panel_wattage": 400,
"panel_count": 10,
"peak_sun_hours": 5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/eco/solar-panel-wattage", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"panel_wattage":400,"panel_count":10,"peak_sun_hours":5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"panel_wattage":400,"panel_count":10,"peak_sun_hours":5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/eco/solar-panel-wattage", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"panel_wattage": 400,
"panel_count": 10,
"peak_sun_hours": 5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "eco.solar_panel_wattage",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Any negative or non-finite input fails with invalid_input instead of inventing energy.
The solar energy formula and what each term means
Written as one product, daily_kwh equals (panel_wattage divided by 1000) times panel_count times peak_sun_hours.
Input contract, units, aliases and error behaviour
Fractional values are allowed so a 370.5 watt module or a 4.75 peak-sun-hour climate do not need rounding first, and a planning count such as 12.5 equivalent modules is accepted. Missing fields, empty strings, booleans, objects, Infinity, NaN and tokens that are not plain decimal or scientific numbers fail the same way because they are not finite numbers. Zero wattage, zero panels or zero sun hours is accepted and returns zero daily and annual kilowatt-hours, because an empty rack or a night with no equivalent sun really does produce no energy. Numbers are rounded to twelve decimal places so goldens and clients compare byte-for-byte across runtimes. Send a JSON object with three required finite numbers: panel_wattage, the DC nameplate of one module in watts; panel_count, how many identical modules sit in the array; and peak_sun_hours, the average daily equivalent full-sun hours at the site. Each field also accepts a numeric string and a short list of aliases (panel_watts, wattage, watts, panel_w, module_watts, W, count, panels, n_panels, number_of_panels, qty, sun_hours, psh, peak_hours, daily_peak_sun_hours, insolation_hours, hours) so spreadsheets and forms do not have to rename columns. Any negative panel_wattage, panel_count or peak_sun_hours is rejected: a negative nameplate or a negative sun hour is not a physical array, so the task fails with invalid_input that names the field. On success the response echoes the resolved panel_wattage, panel_count and peak_sun_hours, reports array_watts and array_kw for the whole string, then daily_kwh, annual_kwh, days_per_year equal to 365, a compact formula string, and the method label solar_panel_wattage. There is no network lookup, no random draw, and no dependence on the current date: the same three numbers always produce the same JSON.
Where a solar panel wattage API earns its keep
Installers who already log string layouts can post one task per candidate array and store daily_kwh beside the site identifier without opening a spreadsheet of 365 factors. If you later need a derated figure, multiply daily_kwh by a performance ratio you already trust; this endpoint stops at the nameplate times peak-sun-hours product on purpose, so the kilowatt-hours stay an honest function of the three numbers you sent.
Integration use cases
Campaign and journalism widgets
Show visitors the yearly energy of a rooftop array from the three numbers they typed, using the same module the API bills so the live figure never drifts.
Technical questions
What units does the solar panel wattage calculator expect?
Send panel_wattage in watts, panel_count as a non-negative count of modules, and peak_sun_hours as average daily equivalent full-sun hours. The response reports daily_kwh and annual_kwh.
What does the solar panel wattage calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.