Physics trivia

Electricity billed

The tariff system of flags makes additions to the electric energy bill based on the difficulties of its generation. The color of the flag stipulates the form of charging for electricity.

The flag tariff system underwent significant reductions that may reflect a decrease in the energy bill
Electricity plays a fundamental role in our daily lives, running all the appliances we need, such as irons, showers, computers, etc. The electricity bill has been highlighted in the media in recent months because the generation of energy, mainly due to problems such as lack of rain, has become more expensive.

The electricity used on a daily basis is mostly produced by hydroelectric plants, hence the dependence on rains, which are necessary to keep the levels of water reservoirs full, but there is also the generation of energy through thermoelectric, wind and nuclear plants spread across the parents. In Brazil, there is a hydrothermal energy production and transmission system formed by companies from the South, Southeast, Midwest, Northeast and North regions that work together in the distribution of electricity throughout the country. The so-called national interconnected system, SIN, produces approximately 98% of the energy distributed.

At the beginning of 2015, the charging of the energy bill started to be done by the tariff flag system, which charges the population for energy according to the difficulty in its production. Sometimes there is a need to connect the thermoelectric plants to generate the necessary energy, as the cost of this form of generation is higher, the bill paid by the population also becomes higher. The table below shows the form of collection through the tariff flags that have been used within the SIN since 2015.

The state of Roraima is the only one outside the SIN, so its collection will not be based on tariff flags.

GREEN Favorable conditions for power generation. There is no increase in the account
YELLOW Less favorable conditions for power generation. Increase of R$ 2.50 for each 100KWh consumed
RED Unfavorable conditions in production and need to connect thermoelectric plants. Increase of R$ 4.50 for every 100KWh consumed

As of February 2016, due to the improvement in the amount of rainfall, mainly in the Southeast region, the collection system suffered a decrease in its values, but it will continue under the red flag regime, which now has two collection levels depending on the amount of thermoelectric plants still connected.

GREEN There is no increase in the account
YELLOW Increase of R$ 1.50 for every 100KWh consumed
RED 1 Increase of R$ 3.00 for each 100KWh consumed
RED 2 Increase of R$ 4.50 for every 100KWh consumed

The determination of electrical energy consumption is made from the electrical power of the appliances connected to the socket and the time of use of them. We can calculate the energy consumed through the product of the electrical power of the device by the time of use, thus, we can write the equation E = P x Δt.

As an example, imagine a family of four that consumes 300 kWh monthly of electricity. After the lowering of the billing price, and assuming that the energy supply company charges R$ 0.45 for each Kwh used, what would be the value of the energy bill for the situation of each flag?

GREEN Flag: 300 Kwh x 0.45 = R$ 135.00

YELLOW Flag: (300 Kwh x 0.45) + 4.5 = BRL 139.50

RED Flag 1: (300kWwh x 0.45) + 9.00 = BRL 144.00

RED Flag 2: (300 Kwh x 0.45) + 13.5 = BRL 148.50

Imagine each member of that family taking two baths a day of approximately 15 minutes. If the power of the shower used is 3000W, power of a conventional shower, what is the energy consumption of this equipment only considering that all showers were in winter mode?

To calculate the time, 8 baths of 15 min will be considered, totaling 120 min, which correspond to 2h per day, therefore, 60h per month. Since energy is the product of power and time, we have:

E = 3000 W x 60h = 180,000 Wh or 180 Kwh.

This energy consumption is too high to represent just one appliance and can correspond to the total consumption of a house with one or two people!

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