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Adaptive energy saving street lighting system in Évora

In the scope of the InovGrid Project the utility EDP Distribution (DSO), retrofitted the historical area of Évora city with a more energy efficient LED lighting system that is adaptive to traffic activity, including cars and pedestrians. 

Short description of the technical lighting system

  • EDP Distribution
  • Portuguese electric utility
  • in the scope of Évora InovCity (InovGrid Project)
  • replaced High Pressure Sodium in conventional luminaries with ferromagnetic ballasts with LED luminaires including sensors (thermal, sunlight, movement and pole stability).

This case study demonstrates, with actual collected data, savings in public lighting by using LED luminaires instead of HID lamps. It also tackles one of the main reasons of energy waste in street lighting by illuminating at nominal flux when there are no cars or pedestrians. Furthermore, it shows LEDs as an innovative, more efficient and perfectly adaptable street lighting solution with the new standards of widespread communication networks and artificial intelligence.

In addition to energy savings and less light spillage (due to LED´s directionality), the existence of an intelligent grid has allowed the Municipality and the Distribution System Operator to gain a better knowledge of the street light usage, improving service and maintenance activities. This shows there is an enormous potential of energy reduction in public lighting by replacing HID with LED technology, which can be enhanced with continuous development of LEDs and smart grids.

These new LED luminaires include PLC (Power Line Communication) and real time centralized management of all the street lighting. The street lighting luminous flux is adaptive and adjust down and up according to traffic information given through sensors, without jeopardizing security, comfort and functionality. The sensors measure:

  • Junction temperature of the LEDs, which makes it possible to keep the temperature below the maximum temperature limit and thus not jeopardising the lifetime of the LED.
  • Natural light and thus the need for artificial lighting.
  • Movement of cars and pedestrians regulating the luminous flux accordingly.
  • Pole stability/integrity in relation to strong winds or car crash.
  • Status of the luminaire concerning if there is need for maintenance.

Lessons Learned

So far a decrease of around 68% in the monthly energy consumption has been measured.

The LED lighting system integrated in an intelligent grid allows the Municipality and the Distribution System Operator to gain a better knowledge of the street lighting usage and adapt to the activity with improved service and maintenance activities.

The energy savings potential regarding mercury vapour lamps: There are approximately 25.6 MW installed, with an average of 87 W per lamp. If we add 11W as an average power for ballasts, we get an average of 98 W per luminaire. Replacing it with a 50 W LED (4000 lumens) we would save approximately half of the actual consumption = 50% of 4200h * 25.6 MW = 53 GWh/year. If control by sensors are added, the savings is estimated to be 50% larger.

84% of the existing around 3 million street lighting lamps in Portugal are HPS lamps with a total load around 250 MW. Using the same rational as above, the saving potential for high pressure sodium lamps is around 500 GWh/year.

EDP is about to set up criteria for procurement of LED luminaires. EDP is also on the verge of disseminating a Public Lighting Manual prepared in collaboration with ISR-University of Coimbra. The manual will explain and support the clients/customers.