Enrichment · STEM Explorations · Energy

Watts on the label,
kilowatt-hours
on an ordinary day.

Type the panel rating, how many panels and the peak sun hours where they sit. The estimator gives the energy for a day, a month and a year, and how much of your use it would cover.

Estimate the outputWhat you get

The solar output estimator

The worked example is made up: six 400 W panels on a greenhouse roof with 4.5 peak sun hours. Nothing you type leaves this browser.

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What you get

Enrichment · STEM ExplorationsFree

What you finish with
System size, energy a day, week, month and year, the capacity factor, the share of your use covered and its value. It prints as a summary and downloads as a spreadsheet.
Who it is for
STEM and environmental science students, school green teams and science fair students, and families thinking about solar.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The STEM Explorations space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Type the panel rating from its label and the number of panels.
  2. Look up peak sun hours for your place and type them.
  3. Keep 14% losses unless you know better.
  4. Add your daily use and electricity price.
  5. Read the energy and print the summary.

Estimate the output

How the estimate works

Power times time, less the losses.

The worked example: a greenhouse roofSystem size2.4 kW6 × 400 W× 4.5 sun hours10.8 kWhat full rating× 86% after losses9.29 kWha day× 3653,390 kWha yearThe worked example: a greenhouse roofSystem size2.4 kW6 × 400 W× 4.5 sun hours10.8 kWhat full rating× 86% after losses9.29 kWha day× 3653,390 kWha year
A panel’s watt rating is its output in full test sunlight. Peak sun hours turn a day of changing light into hours of that full sun, and losses take their share.

Watts and watt-hours

A panel’s rating, such as 400 W, is its power in standard test sunlight of 1,000 watts per square metre. Energy is power times time, so a 2.4 kW array in full sun for one hour makes 2.4 kWh. Real sunlight varies through the day; peak sun hours compress it into the equivalent hours of full sun, which is why 4 to 6 is typical across most of the United States.

Losses and seasons

Wiring, the inverter, heat (panels lose output as they warm), dust and partial shade all cut output; NREL’s PVWatts calculator uses 14% as its default. A single average hides the seasons: summer days can make twice what winter days do. For a real installation, PVWatts runs your address, tilt and direction against hourly weather data.

Sources

  1. National Renewable Energy Laboratory. PVWatts Calculator and Dobos, A. P. (2014), PVWatts Version 5 Manual, NREL/TP-6A20-62641 (nrel.gov).
  2. National Renewable Energy Laboratory. National Solar Radiation Database (NSRDB) and solar resource maps (nrel.gov).
  3. U.S. Department of Energy, Solar Energy Technologies Office. Solar photovoltaic system basics (energy.gov).
  4. International Electrotechnical Commission. IEC 61215: standard test conditions for crystalline silicon PV modules (iec.ch).

The worked example is made up. This is an educational estimate, not a design or a quote. Your figures stay in this browser. Support: team@caveatacademic.com.