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Electric energy: what's smarter?

image credit: kW demand and kWh capacity
Rafael Herzberg's picture
Rafael Herzberg 154,873
Consultant energy affairs Self employed

Rafael Herzberg- is an independent energy consultant, self-employed (since 2018) based in São Paulo, Brazil* Focus on C level, VPs and upper managers associated to energy related info, analysis...

  • Member since 2003
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  • Jul 26, 2020
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Energy: what's smarter?

Let us consider two medium sized households.

One is equipped with 2 conventional electric instant showers of 5 kW each and the other with a 100 liter electric tank heater of 1.5 kW.

To heat the water consumed, both require the same amount of energy. 150 kWh/month.

The difference between them is only the power demanded from the electric utility's grid.

The one with electric (instant) showers, the demand is 10 kW for the showers plus 1 kW for the rest of the loads, resulting in 11 kW.

The other with the tank heater demands 1.5 kW plus 1 kW for the rest of the loads, resulting in 2.5 kW.

Both pay exactly the same monthly bill to the concessionaire, since the tariff is only charged in $ /kWh of energy consumed.

For the concessionaire, however, there is a huge difference - as meeting a demand of 11 kW requires an investment 4.4 times that of 2.5 kW.

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Bob Meinetz's picture
Bob Meinetz on Jul 26, 2020

Rafael, in the U.S. meeting 11 KW of demand involves a one-time investment of about $1,500, and is paid by the homeowner. But here, there's no reason to heat water with electricity - it's cheaper, more efficient, and less emissions-intensive to use a natural gas-powered water heater.

Most U.S. electricity is currently generated by burning natural gas to create heat, then boiling water to make steam, then using steam to generate electricity, then using electricity to create heat again - inefficient, bad for the environment. But one day advanced economies will generate all electricity with nuclear power. Cars will all be electric; massive solar/wind farms, and natural gas pipelines, will be quaint anachronisms. That day can't come soon enough.

Rafael Herzberg's picture
Rafael Herzberg on Jul 27, 2020

Hi Bob,

This one-time investmet by the home owner is associated with the connection to the local power grid. 

If you take into account the whole power value chain including generation, transmission and distribition (up to the closest electric utility's substation) the invesment is at a minimum USD 1 000/kW.  This includes generating plants, step up substations, transmission lines and step down substations.

For a 11 kW load the investment was USD 11 000. That's what I am talking about!

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