Solar Panel Potential Calculator

What would the sun actually deliver here?

Solar quotes begin with one number: how much radiation a site receives, on average, over a year. This tool fetches twelve months of ERA5 satellite radiation for your exact coordinates, averages it into peak-sun-hours (kWh per square metre per day), and turns that into a labelled production estimate for your system size — an 80% performance ratio covering the real-world losses of inverters, temperature and wiring — plus its value at whatever electricity price you enter.

The assumptions are printed, not buried: flat, south-facing (in the northern hemisphere) panels, climate-level radiation, no local shading. That last one is the honest boundary — a chimney, a walnut tree or a neighbouring tower can cut real output in ways no satellite average can see, and the page names certified shade studies as the escalation when money is committed. Within those bounds the estimate is exactly the right screening instrument: compare two roofs, sanity-check a quote, or size expectations for a cabin. It sits in the sun family beside sunrise, golden hour and daylight tools — the same sky, finally put to work.

Worked examples

• Equinox day length — runs ≈ 12h 07m at the Equator, 12h 08m at 45° and 12h 14m at the polar circle — latitude, not calendar, sets the swing.
• Golden hour — lengthens toward winter as the sun's path shallows: the −4°→+6° window that is ~70 minutes at equinox can exceed two hours near solstice at mid-latitudes.
• Timezone vs solar time — diverge by over an hour in much of western Europe in summer; stating both keeps shared sunrise plans honest.

The clockwork sky: sun, moon and the politics of time

Solar times are computable to about a minute from first principles: Earth's orbit and tilt give the sun's declination each day, your latitude sets the hour angle at which the sun crosses any chosen altitude, and the equation of time reconciles the sundial with the clock. Official sunrise uses a zenith of 90.833° — the sun's disc centre slightly below the horizon — because atmosphere refracts light over the rim. Inside the polar circles the formulas return their honest extremes: midnight sun and polar night, no fabricated times.

Time zones are the political overlay. A coordinate has no clock of its own; the IANA tz database encodes humanity's answers, down to daylight-saving quirks, and modern browsers resolve them natively. The divergence between solar and wall-clock time — vast in places like western China or summer-evening Spain — is a policy choice you can see in the numbers, and comparing several zones at once turns that fact into a practical meeting window.

The Moon completes the picture with simpler geometry: phase is the Sun–Earth–Moon angle, global at any instant, cycling every 29.53 days. Photographers care about the sun's altitude bands (golden hour is the warm window around ±a few degrees), gardeners about day length, planners about both. Every one of these quantities is local math — no service required — which makes the sky the most privacy-friendly dataset of all.

Tips & common mistakes

Convert solar times to local clock times deliberately: the sun keeps astronomical time, while governments keep political time, and the gap between them is large in many countries. State both when sharing results.

For photography, plan around sun altitude, not clock time: golden hour is an altitude band, so its clock time migrates with the seasons even at a fixed place — the calculator's windows handle that for you.

When comparing day length across a year, remember the curve is your latitude's signature: near-equatorial sites hover at twelve hours while high latitudes swing wildly. Choose expectations by latitude, not by calendar folklore.

Planning life around an honest sky

Solar arithmetic is the rare everyday science that is both exact and accessible: given a date and coordinates, sunrise, sunset, day length and the photographer's altitude windows follow from first principles to about a minute. The skill is not in the math but in the labels. State the zenith convention (official sunrise includes refraction), state the timezone handling (UTC plus the location's political clock), and the result becomes reproducible by anyone, anywhere — which is the entire point of publishing a number.

The Moon and the calendar complete a planner's sky. Phase is global geometry with local orientation; day length is latitude's signature; timezone overlap grids turn a distributed team's pain into a visible rectangle of shared daylight-hours. Used together, these tools replace folklore ('it gets dark early in winter') with a curve, a window and an invite that works for every participant — quiet infrastructure for photography, agriculture, logistics and ordinary punctuality.

How professionals use this

• Publish solar times with their convention (90.833° zenith) and both clocks (UTC + local zone).
• For shoots, plan by sun altitude windows, then convert to local time — never the reverse.
• Use the annual daylight curve, not single days, to set expectations for a new latitude.
• For global meetings, choose the overlap window from the grid and rotate the pain quarterly.

Step-by-step masterclass

1. 1. Fix the convention before sharing — State the zenith (official 90.833°) and both clocks (UTC + local zone); a sunrise without its conventions is an argument waiting to happen.
2. 2. Plan photography by altitude — Golden hour is the −4°→+6° band; its clock time migrates seasonally, so schedule from the window, then convert.
3. 3. Use the annual curve for expectations — One date misleads; the year-long daylight curve is a latitude's signature and the right object to compare cities by.
4. 4. Let the grid choose the meeting — For distributed teams, read the overlap rectangle from the 24-hour grid and rotate the pain quarterly — fairness made visible.
5. 5. Treat polar answers as answers — Midnight sun and polar night are correct outputs, not errors; the calculator says so plainly instead of fabricating times.

Solar geometry is universal; clocks are not. Spain runs solar-late, western China dramatically so, and DST rules differ by polity — which is why every solar result here carries UTC beside local time, letting any reader re-anchor the fact in their own political frame.

Related questions people ask

Quick glossary

Declination

The sun's latitude-equivalent angle, ±23.44° across the year.

Equation of time

The sundial-vs-clock correction from orbit eccentricity and tilt.

Civil twilight

Sun between 0° and −6°: usable outdoor light without lamps.

Synodic month

The 29.53-day new-moon-to-new-moon cycle behind phases.

Hour angle

The sun's angular distance from solar noon; the engine behind rise/set times.

Blue hour

The −4°→−6° band after golden hour; twilight's cool companion.

Living by the sky: putting solar literacy to work

Solar literacy pays off in unglamorous, compounding ways: the photographer who plans by altitude windows instead of clock time stops losing light to season; the gardener who reads the daylight curve sets expectations by latitude, not by folklore; the distributed team that chooses its meeting slot from the overlap grid rotates pain instead of accumulating resentment; the traveller who checks polar behaviour avoids booking 'midnight sun' in a week the geometry never promised. None of this requires expertise — the arithmetic is exact and local — only the habit of carrying conventions along: which zenith, which clocks, which date. The sky keeps perfect books; the skill is quoting it with its units attached, and knowing the two doors (almanacs for science, terrain-aware tools for mountains) where everyday formulas hand over to specialists. There is also a quieter benefit to keeping this literacy in-house: because every computation runs locally, the tools become a classroom. Change a latitude and the daylight curve responds instantly; change a date and the golden-hour window migrates; add a second city and the overlap grid redraws. That immediacy turns parameters into intuitions in a way static tables never manage, which is why these pages invite play — drag the inputs, watch the geometry answer, and let the conventions (zenith, clocks, vintage) become habits rather than footnotes. A reader who has watched the polar circle snap day length to twenty-four hours understands something a definition alone cannot teach, and that understanding is the durable output of the whole exercise.

• Add solar windows to trip notes as altitude ranges; convert to local time only at the end.
• For teams, publish the overlap grid quarterly — DST changes move the rectangle more than anyone expects.
• Garden planning: pair hardiness zone with the daylight curve; crops respond to both clocks.

Honest limits & when to escalate

Solar arithmetic's limits are small but real: the official zenith encodes average refraction, not today's atmosphere; coordinates are rounded to your input's precision; and terrain is absent unless you add height yourself — a mountain rises the sun late and the formulas won't know. Time adds the political layer: zones and DST are human law, and western edges of big zones (Spain, western China) make solar noon wander hours from clock noon. Every output here therefore carries its convention and both clocks, because an unanchored sunrise time is an argument, not a fact.

Lunar and seasonal outputs carry their own gentle limits: phase from the synodic approximation is hours-precise, which outruns every planning need but not ephemeris science; day length is geometric daylight, not sunshine, and clouds belong to climate's department. Escalation is rare and well-defined — astronomical almanacs and ephemerides for science, terrain-aware apps for mountain photography, and the tz database maintainers whenever a government invents a new DST rule at 48 hours' notice, as they delight in doing.

• Science-grade ephemerides → astronomical almanacs/JPL horizons.
• Mountain sunrise/sunset → terrain-aware horizon adjustments.
• Legal daylight definitions → jurisdictional statutes (they vary!).
• PV engineering → measured irradiance, not reanalysis averages.

Data & methodology note

ERA5 shortwave radiation via Open-Meteo archive; 12-month average; 0.8 performance ratio; flat-panel assumption. Solar times use the NOAA algorithm with the 90.833° official zenith; lunar phase uses the synodic cycle. Timezone geometry comes from the open tz database resolved locally in your browser.

Category context: Sun & Moon — Sunrise, sunset, day length and lunar phases for any place and date. This page is one of the sun & moon tools on MapForge; the related-tools links below and the header's Tools menu connect every sibling instrument.