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Solar Panel Output Calculator

DeveloperMath

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INPUT

Auto Process

Number of Panels *

Panel Wattage *

STC rated wattage per panel (typically 300–450W)

Peak Sun Hours per Day *

Average peak-sun-hours for your location (3–7 in most regions)

System Losses *

Combined losses from inverter, wiring, shading, soiling, temperature (default 15%)

Electricity Rate *

Your cost per kWh from the utility (used for savings estimate)

Daily Usage

kWh

Optional — your household's average daily consumption for battery sizing and offset %

OUTPUT

Client Side

Period	Energy (kWh)	Savings ($)
Daily	-	-
Weekly	-	-
Monthly	-	-
Yearly	-	-
25-Year Lifetime	-	-

System Summary

System Size

CO₂ Offset (yearly)

Battery Size (1-day backup)

Requires daily usage input

Daily Consumption Offset

% of your daily usage covered by the system

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Guide

Solar Panel Output Calculator

Estimate the real-world energy output of a solar panel array in daily, monthly, and annual kWh, along with projected savings, CO₂ offset, and a battery size recommendation. Unlike vague AI-generated estimates, this tool accounts for system losses and panel degradation over a 25-year lifetime so you get a realistic picture instead of a nameplate-only number.

How to Use

Enter the number of panels you plan to install and the rated wattage of each panel (typically 300–450W for modern modules).
Set the peak sun hours per day for your location. Most regions fall between 3 and 7 hours; check a local solar insolation map for a precise figure.
Adjust the system loss percentage. The default 15% covers inverter conversion, wiring resistance, shading, soiling, and thermal losses — industry standard for most grid-tied systems.
Enter your utility electricity rate in dollars per kWh so the calculator can estimate your savings.
Optionally enter your household’s average daily consumption to see what share of it the array would cover and the recommended battery capacity for a one-day backup.

Features

System loss modeling – Applies a configurable derating factor for inverter, wiring, soiling, and temperature losses instead of reporting an inflated nameplate number.
25-year lifetime projection – Includes 0.5% per year panel degradation so lifetime kWh and savings reflect what the array will actually deliver.
Savings estimate – Multiplies generated energy by your local electricity rate to produce daily, monthly, yearly, and lifetime dollar figures.
CO₂ offset display – Converts annual output into kilograms of CO₂ avoided using a standard grid emissions factor.
Battery sizing – Recommends a usable battery capacity for one full day of backup, accounting for depth-of-discharge headroom.
Consumption offset percentage – Shows what fraction of your household’s daily usage the system will cover, and flags any expected surplus that can be exported to the grid.

 FAQ

What are peak sun hours?

Peak sun hours are a measure of solar energy density that condenses a full day of varying sunlight into an equivalent number of hours at 1,000 W/m². A location with 5 peak sun hours per day receives the same total energy as five hours of direct overhead sunlight, even though the actual sunshine is spread across the whole daylight window. Peak sun hours depend on latitude, weather patterns, and seasonal tilt, and they are the single biggest driver of how much energy a panel will produce.
Why do solar arrays have system losses?

A photovoltaic system cannot deliver 100% of its panels' nameplate rating because energy is lost at every stage of the chain. Inverters convert DC to AC with roughly 95–98% efficiency, wiring and connectors introduce small resistive losses, dust and pollen soil the glass, partial shade cuts output sharply in unshaded strings, and high module temperatures reduce silicon efficiency. The combined derating — often called the performance ratio — is typically 10–20% under real conditions.
How fast do solar panels degrade over time?

Crystalline silicon panels lose a small but steady fraction of their output each year due to UV damage, thermal cycling, and potential-induced degradation. The industry consensus is roughly 0.5% per year for modern modules after the initial year, which is why most manufacturers guarantee at least 80% of the original nameplate power at 25 years. Older or lower-quality panels may degrade closer to 0.8–1.0% annually, shrinking long-term production.
How is battery backup capacity sized?

Usable battery capacity is sized to cover the critical load you want to run for a chosen number of days of autonomy. Because lithium-ion batteries should not be fully discharged, designers divide the daily load by a depth-of-discharge factor — commonly 80% — to get the nameplate capacity needed. Round-trip efficiency losses of a few percent per charge-discharge cycle are usually added on top, which is why real installations size batteries slightly larger than the raw daily consumption figure.