The Mainichi answers common questions readers may have about the summer power-saving measure dubbed a "negawatt" exchange.

Question: What is a "negawatt" exchange?

Answer: It is a system where power saved by corporations or others -- through measures such as raising air conditioner temperature settings or turning off unnecessary lights -- is considered as power generated and bought by power companies, who are effectively paying reward money. The name "negawatt" is used in reference to the amount of power saved.

Tokyo Electric Power Co. (TEPCO) and Kansai Electric Power Co. are introducing negawatt exchanges for the first time this summer as part of efforts to keep down peak daytime power usage. They have been used in the United States since the late 2000s to ease power crunches in the summer and winter.

Q: How is a negawatt exchange set up?

A: For example, an energy management business handling power saving measures for office buildings, factories or commercial facilities could sign a contract with TEPCO and decide on an energy saving goal for peak consumption times. The energy management business would recruit power users with contracts of 50 kilowatts or more, such as office buildings, to participate in a negawatt exchange, and the energy management business would introduce a system to closely check the power users' consumption. If users' consumption increased, the energy management business would provide detailed advice on how to cut it, such as "raise the air conditioning temperature by another degree Celsius" or "lower the lighting by the windows a little further," getting the users to keep down their energy usage.

If the power users met their power saving goals, the energy management business would receive reward money from the power company, which it would distribute to the users. The system's attraction for users is two-fold: helping them cut their power bills plus the chance at reward money. However, if power-saving measures are insufficient and users fall far short of energy management businesses' goals, those businesses may be fined by the power company for breach of contract.

Q: How much effect on power demand is there?

A: TEPCO has estimated a maximum saving of 400,000 kilowatts this summer -- around 0.7 percent of maximum power demand -- but if negawatt exchanges become widespread, TEPCO estimates a maximum saving in fiscal 2014 of 1.4 million kilowatts, or 1-2 percent of maximum power demand. TEPCO has said that if there is a risk of a sudden power outage from extremely hot weather, a 1-percent saving from negawatt exchanges will be very important. (Answers by Kenji Wada, Business News Department)