Running the numbers: Harrisburg’s smart lighting investment
When the state of Pennsylvania crafted a recovery plan for the bankrupt city of Harrisburg, money was obviously tight. The state and the city were at odds, and the federal government had made Harrisburg the first and only city in U.S. history to be charged with securities fraud. All of this made Harrisburg an unlikely candidate for groundbreaking smart infrastructure, but nonetheless the state approved a 12% increase in the city’s budget for new LED street lights, enabling Harrisburg to add a wireless sensor to each light.
Harrisburg city engineer Wayne Martin said the total cost of the smart lighting system was $591,992.50, broken down as follows:
- $66,229.50 for three gateways
- $501,500 for 4,250 telecells
- $6,825 for software
- $17,438 for startup and training
Martin said the smart lights saved the city $85,000 before the first light was even switched on. The connected lights do not use photocells, which Martin said cost $10 each. With $5,000 lights in the city that came to $50,000 in savings. The sensors also meant that city workers did not have to visually check to make sure each streetlight had been replaced with an LED light. Martin thinks that process would have consumed 50 eight-hour days for one crew, costing $34,000 at $85 an hour. He attributes another $1,000 in savings to gas he didn’t have to buy for that crew to drive around, putting the total savings at $85,000 upfront.
Annual savings total $23,932, according to Martin’s estimates. He said the city pays for its electricity for the lights based on a tariff formula: 4300 hrs x wattage of the light x cost per kilowatt hour. The connected lights have enabled Harrisburg to report actual usage to third party electricity suppliers, and this has decreased the cost per kilowatt hour from $.05457 to $0.0363, a savings of $0.01827 per kilowatt hour. Multiplying that number by the 1,309,948 kilowatt hours used by the city during a year gives Martin his $23,932 in annual savings.
Of course it will take years for those annual savings to approach the $591,992.50 that Harrisburg invested, but Martin said the city is also saving about $60,000 a year on maintenance. Some of that is attributable to the sensors, but he doesn’t know how much. City workers no longer have to drive the streets looking for broken lights, and when lights do stop working, they get fixed faster than before. At the same time, LED lights intrinsically last longer than traditional lights. This also reduces maintenance costs, and this benefit is independent of the wireless controls.
The LED lights have cut the city’s lighting electricity bills in half, and Harrisburg has seen a drop in its crime rate since they were installed. The sensors are integral to keeping the LED lights fully functional, and Martin believes that their benefits far outweigh the cost. In addition, the light fixtures are able to accommodate other types of sensors that may be added in the future, meaning that their ultimate value may still be unknown.