Power Alert: An Innovative System to Control Residential Loads Under Peak Conditions Using National TV

Abstract

The Western Cape region of South Africa experienced severe power supply problems between February and August 2006. The reason for this was that Eskom, the electricity supply utility, lost one of its nuclear supply units. Forecasts predicted a winter shortfall of 300 MW for the region out of an average supply of about 4000 MW. It was clear that if something could not be done to reduce demand, power outages would be experienced. The main concern was the evening peak between 18:00 and 21:00, due to the high evening load. Eskom sent out a request for proposals to energy solution providers and ESCOs to come up with solutions to the crisis. The problem was that there was not enough time to implement solutions like residential hot water control systems in the 625,000 households of the Western Cape. The total residential load was around 1,200 MW. Energy Cybernetics, an energy solution provider, came up with the solution to use the national TV broadcaster to inform the public on the status of the electricity supply network between 18:00 and 21:00 on weekdays. Energy Cybernetics and Yardstick implemented the project for Eskom. It was called power alert. Power alert made use of real-time total electrical load data obtained from Eskom’s national control centre to identify when the electrical supply was under strain. Predictive modeling was also used to determine the total electrical demand for the Western Cape based on real-time data, historical data, and predicted weather conditions. The real-time predictive modeling was then used to predict the demand of the Western Cape 30 minutes, 60 minutes, and 24 hours in advance. An online computer system and application was also developed that connected the power alert control centre to the broadcasters control centre. This provided the power alert control centre with the capability to change any message to be broadcast within fi ve minutes. The real-time predictive modeling was used to predict the total electrical demand and consequently the expected level of strain. The level of strain was then prioritized according to four status levels. The status levels were: • Green—Indication that there was no strain on the electrical supply of the Western Cape.• Orange—Indication that there was strain on the electrical supply.• Red—Indication that there was increasing strain on the electrical supply and that load shedding was imminent.• Brown—Indication that there was signifi cant strain on the electrical supply and that load shedding was in progress. Based on the strain level experienced at that time, the public was asked to switch off certain appliances, thereby relaxing the strain on the network and preventing power outages. Power alert was deployed within three weeks and was in operation from April 2006 until the nuclear power station came again online during August. No further power outages were experienced during this period except for two short occasions: one when there was a transmission line failure, and two when Eskom lost a second unit on the nuclear power station. The power station tripped on a Thursday evening and it was too late to inform the public. Power outages were experienced for the whole next day until the fi rst power alert message was fl ighted on Friday afternoon at 18:00. The demand then started to drop and continued to drop further as more messages were broadcast. No additional power outages were experienced from 18:30 onwards until the unit came back on line on Sunday. Independent measurement and verifi cation results showed that power alert achieved impacts of up to 180 MW when red and brown messages were broadcast. Power alert achieved a total savings of more than 19,000 MWh over this period. The total cost to implement and operate power alert was about US$3 million, resulting in an average peak reduction cost of US$156 per MWh or 15.6 c/kWh. With all the initiatives, Eskom reduced the demand in the Western Cape by more than 400 MWs over a period of three months. The project has been a huge success, and Eskom decided to roll power alert out nationally as well as to other regions. Because the project will reach a bigger audience, the expected cost for the national power alert will come down to US$56 per MWh or 5.6 c/kWh. Eskom is also looking at expanding power alert to the commercial and industrial sectors. This will be done by “hard wiring” the power alert control center to non-essential loads in these sectors and controlling them when the networks come under pressure.