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92 lines
3.2 KiB
Markdown
92 lines
3.2 KiB
Markdown
# nrel_spa
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[](https://pub.dev/packages/nrel_spa)
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[](https://github.com/acamarata/nrel-spa-dart/actions/workflows/ci.yml)
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[](LICENSE)
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NREL Solar Position Algorithm for Dart and Flutter. Calculates solar zenith, azimuth, sunrise, sunset, and solar noon for any location and time. Pure Dart, zero dependencies.
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Based on Reda & Andreas (2004), NREL/TP-560-34302. Accurate to ±0.0003 degrees.
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## Installation
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```yaml
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dependencies:
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nrel_spa: ^1.0.0
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```
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## Quick Start
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```dart
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import 'package:nrel_spa/nrel_spa.dart';
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void main() {
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final result = getSpa(
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DateTime.utc(2024, 3, 15, 17, 0, 0),
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40.7128, // latitude (NYC)
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-74.0060, // longitude
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-5.0, // UTC offset (EST)
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);
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print('Zenith: ${result.zenith.toStringAsFixed(4)}°');
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print('Azimuth: ${result.azimuth.toStringAsFixed(4)}°');
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print('Sunrise: ${result.sunrise.toStringAsFixed(4)} h');
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print('Solar Noon: ${result.solarNoon.toStringAsFixed(4)} h');
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print('Sunset: ${result.sunset.toStringAsFixed(4)} h');
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}
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```
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## Custom Zenith Angles
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Calculate rise/set times for any solar depression angle (twilight, prayer times, etc.):
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```dart
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final result = getSpa(
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DateTime.utc(2024, 3, 15, 12, 0, 0),
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40.7128, -74.0060, -5.0,
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customAngles: [96.0, 102.0, 108.0], // civil, nautical, astronomical
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);
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for (final angle in result.angles) {
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print('Rise: ${angle.sunrise}, Set: ${angle.sunset}');
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}
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```
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## API
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### `getSpa(date, latitude, longitude, timezone, {...})`
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| Parameter | Type | Default | Description |
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| --- | --- | --- | --- |
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| `date` | `DateTime` | required | UTC date and time |
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| `latitude` | `double` | required | Degrees (-90 to 90) |
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| `longitude` | `double` | required | Degrees (-180 to 180) |
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| `timezone` | `double` | required | Hours from UTC |
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| `elevation` | `double` | 0 | Meters above sea level |
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| `pressure` | `double` | 1013 | Atmospheric pressure (mbar) |
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| `temperature` | `double` | 15 | Temperature (Celsius) |
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| `deltaT` | `double` | 67 | TT - UT1 (seconds) |
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| `customAngles` | `List<double>` | [] | Zenith angles for rise/set |
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Returns `SpaResult` with `zenith`, `azimuth`, `sunrise`, `solarNoon`, `sunset`, and `angles`.
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## Architecture
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A direct port of the NREL Solar Position Algorithm (Reda & Andreas 2004) to Dart. The implementation follows the original algorithm's 142 intermediate calculations exactly. Custom zenith angles are computed in a single pass alongside the primary solar angles using the same ephemeris state.
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## Compatibility
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Dart SDK 3.7.0+. Works in Flutter, Dart CLI, and server-side Dart. Zero dependencies.
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## Related
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- [pray_calc_dart](https://github.com/acamarata/pray-calc-dart) - Islamic prayer times (uses nrel_spa)
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- [nrel-spa](https://github.com/acamarata/nrel-spa) - JavaScript/TypeScript version (npm)
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## Acknowledgments
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> Reda, I. and Andreas, A. (2004). Solar Position Algorithm for Solar Radiation Applications. NREL/TP-560-34302. [DOI: 10.2172/15003974](https://doi.org/10.2172/15003974)
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## License
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[MIT](LICENSE). See LICENSE for NREL third-party notice.
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