TiltSync: Solar Panel Alignment With Your Phone

A solar panel produces the most when it faces the sun squarely, so its tilt and direction matter. The usual starting point is a tilt close to your latitude, facing true south in the northern hemisphere, but working out the number is only half the job. You still have to set a panel to that angle on a roof, a ground mount, or a campsite, usually with a level, a protractor, and a compass app open in another hand.

I used apps for this. My favorite was abandoned by its developer and eventually stopped working, and the other one I relied on filled up with ads. I don’t want a popup ad while I’m on the roof trying to line up a panel. I also wanted to understand the algorithms these tools use to pick an angle, rather than trusting a number I couldn’t explain.

So I built TiltSync. It turns a phone into the alignment tool: lay the phone on the panel, and it shows the current tilt and heading against the target for your location, with haptic feedback that guides you in without watching the screen. It has no ads.

Android testers wanted: TiltSync is available on iOS, and the Android version is in closed beta. I need Android testers to help get it onto Google Play. Request Android beta access and include the email you use for Google Play. I’ll add you to the test and send joining instructions. Once invited, opt in, try the app, share feedback, and remain opted in continuously for at least 14 days.

Google currently requires eligible new personal developer accounts to complete a closed test with at least 12 continuously opted-in testers for 14 days before applying for production access. Meeting that threshold allows an application; it does not guarantee approval or an automatic public launch.

If the link doesn’t open your mail app, email cameo-kayak.5j@icloud.com with the subject “TiltSync Android Beta Access”. More details are on the TiltSync site.

How it works

TiltSync reads three of the phone’s sensors:

• Accelerometer for the panel’s tilt, with the phone lying flat on the panel.
• Magnetometer for the direction the panel faces.
• Location for your latitude, which sets the target tilt and whether the panel should face south or north.

The main screen combines a compass card with a tilt indicator and shows the current and target values side by side. Dedicated tilt-only and compass-only views are there when you want to adjust one thing at a time. Each reading turns red, yellow, or green as you get closer, and the haptic feedback grows stronger as you approach the target, so you can make the adjustment by feel.

AR Sun Path, added in version 1.1.2, draws the sun’s path across the camera view: today’s arc, plus the June and December solstices and the equinox.

Choosing a target

There isn’t one right angle; it depends on what you’re optimizing for, so TiltSync lets you pick:

• Set it and forget it: Year-Round, the default, gives one fixed angle for the best production over the whole year at your location.
• A few days of camping with a travel panel: Daily calculates the best angle at solar noon for that date, so the target stays the same all day.
• Winter matters most, for example a system that has to keep running through short days: Seasonal steepens the panel by 15° for winter (and flattens it by 15° for summer), and Winter Priority asks NREL’s PVWatts for the angle that does best in the weakest month.

Under those modes, you can choose which of seven tilt calculation methods sets the base angle. The simplest sets the tilt equal to your latitude. Others adjust for diffuse light or use empirical fits from research, such as the Landau formula (latitude × 0.76 + 3.1°), and PVWatts Live asks NREL directly. The TiltSync site explains how each one works and where it comes from.

Two other settings came from user feedback. Time-of-use rates let you enter what your utility charges at different hours; TiltSync then suggests a direction that weights the panel toward the expensive hours, for example a little west for an afternoon peak. Invert compass 180° flips the compass so it reads correctly when you’re holding the phone toward the sun or have it lying screen-down on the panel.

Offline by default

The calculations run on the phone, and there’s no account. Your last location is cached so the app starts without waiting for a GPS fix.

One feature is optional and online: PVWatts Live, which is off by default. When you turn it on in Settings, TiltSync sends your location to the National Renewable Energy Laboratory’s PVWatts service and uses its tilt recommendation instead of a local formula. Winter Priority uses the same service. If the request fails, TiltSync falls back to a local calculation.

Limitations

• The compass reads magnetic north. The target direction is true south (or true north in the southern hemisphere), and TiltSync doesn’t yet correct for the difference, called magnetic declination. Near the middle of the US the difference is small; in the Pacific Northwest or New England it’s around 15°. Until that’s fixed, adjust for your local declination using NOAA’s calculator.
• Metal can throw off the compass. Steel racking or a metal roof can deflect a phone’s compass, and I haven’t yet tested how much a panel’s frame does. The tilt reading isn’t affected. Compass Only mode lets you stand behind the panel and hold the phone away from it. Testing on metal frames is next.
• Accuracy hasn’t been measured yet. In my use the readings have seemed accurate, but I haven’t checked them against a reference instrument. I want a repeatable way to show that before making accuracy claims.

Next steps

• iPhone: Download TiltSync from the App Store.
• Android: Request closed-beta access with the email you use for Google Play. Once the invitation arrives, opt in and stay opted in for at least 14 days.

The source is on GitHub.