Off-Grid Street Lighting
Tom Lombardo posted on May 12, 2013 | 12940 views

It costs a lot of money to build a road … even more if you want to add wires to power the streetlights from the grid. Urban Green Energy (UGE) has a solution: an off-the-grid streetlight.

UGE recently installed 120 streetlights on a stretch of highway in PingQuan, China. What’s special about these lights? They’re powered by a combination of solar and wind. Complementary systems derive the most energy because when the solar resource is low (e.g. in the winter), it’s often windy. On the other hand, it’s more likely to be sunny on calm summer days. When your photovoltaic panels are in the dark, the wind turbines pick up the slack. And when the wind slows down, it’s likely that the solar panels will produce. (That’s the theory, at least.) What about calm nights? The light fixture includes a battery that holds enough energy for up to five days of autonomy.

Each UGE light consists of two highly-efficient LED bulbs, two solar panels, a vertical axis helical wind turbine, and a 150Ah battery. One LED bulb produces over 3100 lumens of light while using 56W of electricity. (By comparison, you would need two 100W incandescent bulbs or one 70W high-pressure sodium lamp for the same light output.) Each solar panel generates 235 Watts (peak) and the wind turbine generates 200W at a wind speed of 12 m/s (about 27 MPH). That’s a pretty high wind speed, especially considering its low latitude. But keep in mind that on a busy highway there’s a lot of turbulent wind generated by the traffic. 

Just running some conservative numbers, let’s say you can achieve a somewhat consistent 6 m/s wind. Wind power operates on the inverse-cube law, so cutting the wind velocity in half reduces the power by a factor of 8. That 200W turbine is generating a paltry 25W at this speed. If that occurs for 10 hours per day, we can generate 250 watt-hours of energy each day.

With a solar resource estimate of 4 Peak Sun Hours (PSH), each solar panel would generate 940 Watt-hours per day, so the pair gives 1880 Watt-hours per day. Combined with the wind resource, the system can generate roughly 2 kWh per day. A 56W bulb running 12 hours per day uses 672 Wh/day. Two bulbs requires 1344 Wh. This leaves around 700 Wh available to charge the batteries.

The math works out; the lights will be on when you need them. But I think the helical wind turbine serves more of an aesthetic purpose than anything else. With the above numbers, the turbine generates 12% of this system’s total energy. Based on my calculations, the system would work perfectly well without the turbine. But hey, it looks nice, doesn’t it?

Image and video: Urban Green Energy

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