kVAh metering for environmentally conscious utilities

Today even the domestic load (consisting of washing machines, water pumps, refrigerators, air conditioners and so on) is seen to have a low power factor. It is therefore time to review this kWh tariff.

A tariff system should be designed with the following objectives.

  • Consumer pays for the capital and running cost of energy generation, transmission and distribution.
  • Consumer pays for his own consumption and not for his neighbour’s consumption (especially when the neighbour has a low power factor load).
  • Improvement in efficiency.

The kWh tariff cannot be justified in each of the above cases.

The cost of power generation can be split into:

  • the capital cost;
  • the fuel cost;
  • the losses.

The generation capacity of a power plant, as well as the capacities of the transmission and distribution lines, are governed by the current carrying capacity and are therefore given in kVA. The capital cost, therefore, has to be computed in terms of total (apparent) energy kVAh. The cost of fuel is primarily related to the active energy (kWh) generated. The copper losses are proportional to the square of the current. Therefore the losses in generation, transmission and distribution are primarily governed by kVAh. The efficiency of the plant is also less when running at capacities lower than rated, which occurs at low power factors – another reason why losses are governed by kVAh.

Of the three factors contributing to the cost of energy, only the fuel cost is governed by kWh. Yet, at the load end, the consumer is only concerned about paying for the energy consumed in kWh. Most consumers are not aware that the appliances which lower the power factor are responsible for both the under-utilisation of the power plants and increased losses, and therefore lower efficiency of electrical generation and transmission equipment. It is this lack of awareness that results in unintentional inefficient use and therefore wastage of energy. It is also responsible for increased tariff rates.

A change to a kVAh tariff is beneficial to everyone. The non-defaulting consumer is happy that the kVAh tariff is cheaper than the kWh tariff. The electricity utility can benefit through the collection of more revenue from consumers having low power factor loads. Most importantly, the tariff is environmentally friendly due to improved efficiency. With the introduction of the kVAh tariff, consumers would also take the initiative in correcting the power factor, using compensating capacitors at their end.

Today it is possible to measure kVAh instead of kWh using static meter technologies. Microprocessor based technology has given us an edge whereby a static meter that measures total energy can be offered at the same price as a static meter that measures active energy. This is true even in the domestic whole current energy meter category, where the cost of a static kVAh meter can be as low as US$40. For the industrial category, the maximum demand and time-of-day metering can also be incorporated at a nominal extra cost.

For purposes of simplicity the tariff for domestic and small agricultural loads (less than 10 kVA) can be based on a single parameter – kVAh. Such a tariff can be supported by simple single phase and 3-phase static kVAh meters respectively. In the case of heavy industrial loads, even the auxiliary tariff parameters such as time-of-day consumption and maximum demand should be based on kVAh, and not on kWh as is normally the case today.

The kVAh tariff is under review by a number of electric utilities in countries where there is an acute shortage of power, and the need for reduction of losses is seen as being of particular importance.