I was asked recently if it was possible to use solar power in street lighting. As always new developments in technology makes what was once not possible feasible. In this case developments in high intensity discharge and led bulbs that use less power and stll provide equivalent luminousity as standard street lamps makes it feasible. However is it practical ?
Practicallity
1. A 20 watt HID or LED lamp will require 200 watts hours (Wh) for 10 hours of lighting. So we need solar panel or panels that can produce more than 200 Wh a day. The next problem is to mount this panel or panels on pole we attach the street lamp to. Here the considerations of the height. strength of the pole and effects of wind sheer on the panels have to be taken into account.
2. On location where the panels are sited is vital to it's effectiness in producing power. If it is sheltered or shadowed these factors must be taken into account.
3. Next problem to solve is power storage. As sunlight is variable from day to day there will be days when power produced is less than the 200 Wh required. On these days we will have to depend on stored energy on days when we have excess to make up the slack.
4. A 40 ah battery stores about 500 Wh. If the worst day power production is 100 Wh this battery should provide enough for 5 days of uninterrupted lighting. Of course larger batteries will provide more uninterrupted days.
5, The problem with larger batteries is that they have to be mounted on the pole. A mid pole mount brings into question aestatics and wind sheer factors. In ground mount is not practical because of damp and flooding risks, An in pole mount is best but limits the size of batteries that can be used.
6. Instead of lead acid batteries we could use lithium ion. However a 40 ah 12 volt lithium ion battery would cost $1200 compared to a restored and reconditioned lead acid battery at $60.
So we see that what is feasible is not always practical. The ability to solve the practical problems is what divides those who succeed and the also ran.
