Flexible solar panels for ANPR
We’ve been using flexible solar panels for our security and ANPR cameras for over 2 years. Here are a few lessons we learned.
We used two slightly different versions of solar panels:
- White: 15cm x 84 cm, 18v, 20W
- Black: 15cm x 75cm, 18v, 18W
Both panels had very similar performance of about 12W … 15W under normal summer sun conditions. The manufacturers always claim some hypothetical wattage under some ideal tropical midday sun. It always works out to be less than that because:
- haze, smog and dust reduce the amount of light hitting the panel
- the installation angle is not always optimal (must be 90° to the sun)
- the panel accumulates a layer of dirt and salts overtime
- the coating gets more opaque from UV and ozone damage
Why choose flexible panels for ANPR and traffic counting
The main reason is the ease of use. They are very light (100g or so) and easy to install. We used 3 strong UV-stable cable ties to hold them firmly in place even in the strongest of winds. None flew away or even got loose.
The other reason is the camouflage. Those black panels don’t look like solar panels at all and attract minimal attention. Installing a metal frame with a rigid solar panel is OK for a permanent site, but doing it for a few weeks of traffic monitoring on a temporary site adds extra cost and time that can be used elsewhere.
A single 18W panel installed vertically was more than enough to power a security camera or a lightly used ANPR camera all year around. That statement holds true for a reasonably sunny location like Auckland, New Zealand with its 2000hrs of annual sunshine hours. Check your local average sunshine hours to compare.
Our ANPR cameras run at below 5W during maximal use (recording speed, detecting vehicles, reading number plates and uploading data to the cloud). In theory an 18W panel can power 3 of them, but the sun is not always on.
The panel charges the battery when the sun is out and the electronics of the ANPR cam draw the power from there. The 18W output has to average out over night time, a cloudy day or even a wet cloudy week when almost no energy comes from the sun.
From experience, we recommend at least 18W nominal power panel for light ANPR use (a few vehicles per day) and twice that for heavier or constant use.
Some flexible solar panels have a special textured surface to improve light absorption from different angles like in this picture. Others may even claim to have a special nano-coating. We do not dispute the manufacturers’ claims about improved efficiency in any way, but from our experience there was no difference between the same size panels for the purpose of powering a 4G ANPR camera.
The white panel pictured at the top of this article was purchased from a local marine equipment supplier. It felt sturdy and had a good spring to it. We liked the quality, but the white backing stood out too much and we opted out for using completely black panels purchased directly from a manufacturer.
Those black panels started getting brittle and opaque after about a year in the sun. The laminate at the front was cracking from a slightest bend, which was the reason for us to remove some of them.
That was a quality issue, not a “blackness” issue. A quality product can be manufactured with either type of backing.