Solarposition.org

Hai Phong · Vietnam · 20.73° N · 107.05° E

Solar position in Cát Bà

Sun position, daylight and the best solar panel angle for Cát Bà — computed for 20.73° N, 107.05° E, 24 m above sea level.

Sunrise today05:50103° ESE
Sunset today17:20257° WSW
Best panel angle15°year-round, facing south
Off-grid angle36°best for the darkest month

The sun right now

Azimuth180.0°
Elevation57.2°
At solar noon, 11:35Open on the sun map

Sun in Cát Bà today

Sunday, 25 October 2026 · local time UTC+7

EventTimeDirection / height
Astronomical dawn04:36sun 18° below horizon
Nautical dawn05:0212° below
Civil dawn05:286° below
Sunrise05:50103° ESE
Golden hour ends06:20sun 6° up
Solar noon11:3557.2° high
Golden hour starts16:50sun 6° up
Sunset17:20257° WSW
Civil dusk17:436° below
Nautical dusk18:0912° below
Astronomical dusk18:3518° below
Day length11 h 30 min

Sun path diagram for Cát Bà

Where the sun stands in the sky: the centre is straight overhead, the outer ring is the horizon. Numbers mark local clock hours.

15°30°45°60°75°N30°60°E120°150°S210°240°W300°330°June solstice6789101112131415161718EquinoxDecember solstice7891011121314151617Today
  • June solstice
  • Equinox
  • December solstice
  • Today

On the June solstice the sun reaches 87.3° at solar noon in Cát Bà; on the December solstice only 45.9°. Sunrise swings from 64° ENE in June to 115° ESE in December — a 50° arc along the horizon.

Sunrise, sunset and sun height by month

Values for the 21st of each month, local clock time including daylight saving time.

MonthSunriseSolar noonSunsetDay lengthNoon elevation
January06:3012:0317:3511 h 05 min49.4°
February06:1812:0517:5211 h 35 min58.7°
March05:5511:5918:0312 h 08 min69.5°
April05:2811:5018:1212 h 44 min81.1°
May05:1211:4818:2413 h 12 min89.5°
June05:1111:5318:3513 h 24 min87.3°
July05:2111:5818:3413 h 13 min89.7°
August05:3211:5518:1712 h 44 min81.4°
September05:4011:4417:4912 h 09 min70.0°
October05:4911:3617:2311 h 34 min58.6°
November06:0511:3717:0911 h 05 min49.4°
December06:2311:4917:1510 h 53 min45.9°

A year of daylight in Cát Bà

Each column is one day of 2026. Bright: sun above the horizon; soft: civil twilight; line: solar noon. Steps are daylight saving time changes.

00:0003:0006:0009:0012:0015:0018:0021:0000:00JanFebMarAprMayJunJulAugSepOctNovDec

Best solar panel angle in Cát Bà

Fixed array facing south (azimuth 180°). Energy per kWp from NASA POWER monthly climate, including clouds, temperature and snow reflection.

15°collects the most energy over a year: 1155 kWh per kWp.

36°gives the most in the darkest month — the one an off-grid system is sized for.

40%50%60%70%80%90%100%0°10°20°30°40°50°60°70°80°90°Best year-round 15°Best worst-month 36°70°Yearly energyWorst-month energy
  • Yearly energy
  • Worst-month energy
TiltkWh/kWp per yearShare of best yearJanuary kWh/kWp/dayBest ÷ worst month
0°112497%1.932.1×
15° year-round best1155100%2.161.8×
21° = latitude1150100%2.221.7×
30°112698%2.281.6×
36° off-grid best109895%2.291.5×
45°103990%2.281.6×
60°90278%2.161.6×
70°78868%2.021.7×
90°55048%1.612.1×

A fixed array in Cát Bà produces the most over a year at 15°. The design month for an off-grid system is January: at 36° it makes 2.29 kWh per kWp a day, 6% more than at 15°, and costs 5% of the yearly total. Why steep panels win winter.

Off-grid solar in Cát Bà at 70°

Daily energy of 1 kWp by month. Bars: panels at 70°. Line: panels at 15° (year-round best).

012345January: 2.02 (70°)2.0JanFebruary: 1.94 (70°)1.9FebMarch: 1.74 (70°)1.7MarApril: 1.96 (70°)2.0AprMay: 1.91 (70°)1.9MayJune: 1.80 (70°)1.8JunJuly: 1.79 (70°)1.8JulAugust: 2.00 (70°)2.0AugSeptember: 2.48 (70°)2.5SepOctober: 2.84 (70°)2.8OctNovember: 2.95 (70°)3.0NovDecember: 2.48 (70°)2.5Dec15°
MonthSun hours, flatSun hours at 70°kWh/kWp/day at 70°at 15°Mean temp.
January2.402.412.022.1616.8 °C
February2.702.331.942.3318.2 °C
March2.892.131.742.3820.5 °C
April3.972.421.963.1723.7 °C
May5.042.401.913.8627.0 °C
June5.132.271.803.8528.6 °C
July5.052.271.793.8028.8 °C
August4.662.522.003.6028.6 °C
September4.553.082.483.6827.8 °C
October4.093.482.843.4925.5 °C
November3.423.572.953.1022.3 °C
December2.692.952.482.4818.2 °C
Year3.89 avg2.65 avg788 kWh1155 kWh

Sizing example. To run a 1 kWh-per-day load through March on LiFePO4 batteries (charge controller, battery and inverter losses included) you need about 680 Wp of panels at 70°, versus 550 Wp at 15°. Here the lower tilt is the better winter choice — the sun stays high enough. Size your own system.

Row spacing in Cát Bà

Distance between rows of 2 m long panels (slope length) so that no row shades the next between 10:00 and 14:00 solar time on the winter solstice.

2.7 mrow pitch at 70°

2.5 mrow pitch at 15°

Row spacing calculator

How Cát Bà compares in Vietnam

Against the other 306 places in Vietnam with climate data, for a fixed array at its best angle.

198thof 307 places in Vietnam for sunshine: 3.89 peak sun hours a day on flat ground.

−13%solar energy a year compared with the average place in Vietnam: 1,154 against 1,320 kWh per kWp.

+38 mindaylight on the longest day, compared with Ho Chi Minh City: 13 h 24 min against 12 h 46 min.

15°best year-round tilt here; across Vietnam it runs from 9° in Vĩnh Châu to 21° in Dien Bien Phu.

Of the 307 places in Vietnam, Phú Quý gets the most sun (5.45 peak sun hours a day) and Thị Trấn Thất Khê and one other place the least (3.61); Cát Bà ranks 198th. In its darkest month, March, 1 kWp of off-grid panels at 70° makes 1.74 kWh a day here, against 1.53 kWh on average in Vietnam. The shortest day lasts 10 h 53 min, −37 min compared with Ho Chi Minh City.

The sunniest places in Vietnam

Solar forecast for Cát Bà, next 48 hours

Expected output of 1 kWp at 70°, computed from the ICON-EU weather model of the Deutscher Wetterdienst (DWD), Europe.

Loading the latest forecast…

Questions about the sun in Cát Bà

What is the best solar panel angle in Cát Bà?
For a fixed array facing south, the best year-round tilt in Cát Bà is 15°, worth about 1155 kWh per kWp a year. An off-grid system that has to get through January does better at about 36°.
What time is sunrise and sunset in Cát Bà today?
On 25 October 2026 the sun rises at 05:50 and sets at 17:20 local time (UTC+7), giving 11 h 30 min of daylight. Solar noon is at 11:35.
How many peak sun hours does Cát Bà get?
On a flat surface 3.9 hours a day averaged over the year, from 2.4 in January to 5.1 in June. Panels tilted at 70° receive 2.1 sun hours a day in March.
How high does the sun get in Cát Bà?
At solar noon the sun stands 87.3° above the horizon on the June solstice and 45.9° on the December solstice.
Is Cát Bà a good place for solar panels?
With 3.9 peak sun hours a day on flat ground, Cát Bà ranks 198th of 307 places in Vietnam for sunshine. A 1 kWp array at the best angle (15°) makes about 1,154 kWh a year here, 13% less than the average place in Vietnam.

Places near Cát Bà

All places in Vietnam

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Sun positions: NREL Solar Position Algorithm. Climate: NASA POWER monthly climatology (NASA Langley Research Center). Forecast: Deutscher Wetterdienst, ICON-EU (CC BY 4.0), processed. Places: GeoNames (CC BY 4.0). Time zones: IANA. Sources and licences.