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72 lines
2.7 KiB
Markdown
72 lines
2.7 KiB
Markdown
# nrel-spa
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[](https://www.npmjs.com/package/nrel-spa)
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[](https://github.com/acamarata/nrel-spa/actions/workflows/ci.yml)
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[](./LICENSE)
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[](https://github.com/acamarata/nrel-spa/wiki)
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Pure JavaScript implementation of the NREL Solar Position Algorithm (SPA). Computes solar zenith angle, azimuth, sunrise, sunset, and solar noon for any location and date. Zero dependencies, synchronous. Validated to produce identical results to the original NREL C reference implementation.
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## Installation
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```bash
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npm install nrel-spa
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```
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## Quick Start
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```javascript
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import { getSpa, calcSpa } from 'nrel-spa';
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const date = new Date('2025-06-21T00:00:00Z');
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// Raw fractional hours
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const raw = getSpa(date, 40.7128, -74.006, -4); // New York, EDT
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console.log(raw.sunrise); // 5.417
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console.log(raw.solarNoon); // 12.965
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console.log(raw.sunset); // 20.509
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// Formatted HH:MM:SS strings
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const fmt = calcSpa(date, 40.7128, -74.006, -4);
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console.log(fmt.sunrise); // "05:25:03"
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console.log(fmt.solarNoon); // "12:57:56"
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console.log(fmt.sunset); // "20:30:35"
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```
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CommonJS:
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```js
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const { getSpa } = require('nrel-spa');
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```
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Pass a `zenith angles` array as the sixth argument to `getSpa`/`calcSpa` for civil (96°), nautical (102°), or astronomical (108°) twilight times.
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## TypeScript
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```typescript
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import { getSpa, calcSpa, formatTime, SPA_ZA_RTS } from 'nrel-spa';
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import type { SpaOptions, SpaResult, SpaFunctionCode } from 'nrel-spa';
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```
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## Documentation
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Full API reference, algorithm notes, and twilight calculation guide: [GitHub Wiki](https://github.com/acamarata/nrel-spa/wiki)
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## Related
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- [solar-spa](https://www.npmjs.com/package/solar-spa): WASM build of the same algorithm, async, for high-throughput batch work
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- [pray-calc](https://www.npmjs.com/package/pray-calc): Islamic prayer times built on nrel-spa
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## Acknowledgments
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The core algorithm is a JavaScript port of the NREL SPA by Ibrahim Reda and Afshin Andreas:
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> Reda, I., Andreas, A. (2004). "Solar Position Algorithm for Solar Radiation Applications." Solar Energy, 76(5), 577-589.
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## License
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MIT (TypeScript wrapper and build tooling). The core algorithm in `lib/spa.js` is a port of NREL's SPA C source, subject to its own terms. See [LICENSE](./LICENSE).
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## Telemetry
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This package supports optional, anonymous usage telemetry via [`@acamarata/telemetry`](https://github.com/acamarata/telemetry). It is **off by default**. See [TELEMETRY.md](https://github.com/acamarata/telemetry/blob/main/TELEMETRY.md) for what is collected and how to enable or disable it.
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