Answer:
Excludable and rival in consumption.
Step-by-step explanation:
A good is defined as excludable if people can be prevented from using it.
A good is also considered to be rival if the consumption of the good by one person results in a reduction in consumption of another person.
In this scenario on hot summer days generation of electricity is stretched to the limit. So it is finite in supply and if one person uses it, another will have reduced consumption (rival).
Electric companies asking people to cut back on their consumption means that electricity is excludable. People can be prevented from using it.