nrel-spa/bin

bin/README.md

This folder contains the C reference executable (spa_cli) and the JavaScript test harness (test.js) to compare your JS port of the NREL Solar Position Algorithm (SPA) against the original C implementation.

Prerequisites

• Node.js (v14+) installed on your machine.
• C compiler (e.g. gcc) supporting C99.

Files

• spa_cli.c – C CLI wrapper to parse command-line arguments into the SPA structure and output Sunrise, Solar Noon, Sunset in HH:MM:SS format.
• spa.c, spa.h – The NREL SPA reference source (download separately).
• test.js – Node.js script that runs 10 diverse test cases through both spa_cli and your JS port (getSpa) and prints a side-by-side comparison.

Setup

1. Download the NREL SPA source

   cd bin
   curl -O https://midcdmz.nrel.gov/spa/spa.c
   curl -O https://midcdmz.nrel.gov/spa/spa.h
   

2. Copy or create spa_cli.c Place the spa_cli.c file (provided alongside this README) into this folder.

3. Compile the C executable

   gcc -std=c99 -O2 -o spa_cli spa.c spa_cli.c -lm
   

   • Do NOT include spa_tester.c for this purpose. The custom spa_cli.c handles all required argument parsing and output.

4. Install Node.js dependencies From the project root (one level up):

   npm install
   

   This ensures your JS port (index.js and dist/spa.js) is available.

Running the Tests

Inside the bin/ folder, execute:

node test.js

You should see a table with each city/date, and matching Sunrise, Solar Noon, and Sunset times from both the C reference and your JS implementation.

Example output:

Location         | Date       | C Rise   | JS Rise  | C Noon   | JS Noon  | C Set    | JS Set
-----------------------------------------------------------------------------------
New York Summer  | 2025-06-21 | 05:25:03 | 05:25:03 | 12:57:56 | 12:57:56 | 20:30:35 | 20:30:35
...

Notes

• If you update your JS port (index.js), rerun node test.js to verify that drift remains within a second.
• Ensure spa_cli is executable (chmod +x spa_cli) and located in the same directory as test.js.

Results

Results from my personal tests when comparing original C version to this JS version is below:

% node test.js
Location         | Date       | C Rise   | JS Rise  | C Noon   | JS Noon  | C Set    | JS Set
-----------------------------------------------------------------------------------
New York Summer  | 2025-06-21 | 05:25:03 | 05:25:03 | 12:57:56 | 12:57:56 | 20:30:35 | 20:30:35
New York Winter  | 2025-12-21 | 07:16:41 | 07:16:41 | 11:54:19 | 11:54:19 | 16:31:56 | 16:31:56
London Summer    | 2025-06-21 | 04:43:07 | 04:43:07 | 13:02:22 | 13:02:22 | 21:21:37 | 21:21:37
London Winter    | 2025-12-21 | 08:03:52 | 08:03:52 | 11:58:42 | 11:58:42 | 15:53:32 | 15:53:32
Tokyo Summer     | 2025-06-21 | 04:25:52 | 04:25:52 | 11:43:00 | 11:43:00 | 19:00:22 | 19:00:22
Sydney Winter    | 2025-06-21 | 07:00:12 | 07:00:12 | 11:56:56 | 11:56:56 | 16:53:52 | 16:53:52
Reykjavik Mids   | 2025-06-21 | 02:55:10 | 02:55:10 | 13:29:38 | 13:29:38 | 00:03:54 | 00:03:54
Cape Town Summer | 2025-12-21 | 05:31:55 | 05:31:55 | 12:44:28 | 12:44:28 | 19:57:01 | 19:57:01
Quito Equinox    | 2025-03-20 | 06:17:54 | 06:17:54 | 12:21:10 | 12:21:10 | 18:24:25 | 18:24:25
Tromso Polar     | 2025-12-21 | N/A      | N/A      | N/A      | N/A      | N/A      | N/A