1, Yes, the kettle takes a little longer...
2, There is a reduction in consumption, because there is a relation between Volts, Resistance and Current, hence power consumption. Probably 10% reduction, because of the change from 250v to 220v.
3, I am not sure what payback that works out to,
1, Thats cos its using the same total energy but at a lower power rate. 1L of water will always take the same TOTAL energy to get from the cold temp to boiling. In fact its using slightly more energy due to a longer time with thermal losses, but thats really quite small.
2, In general there is no reduction. The rate of consumption is lower but the total used is the same. Remember V = I x R ? Change one & the others change to keep the status quo.
3, Never is as close as you are going to get.
All of the above is for domestic billing.
Businesses get billed by peak demand / load so they do have a reason to reduce peak consumption, so a slower boiling kettle thats still uses the same kWh to boil might have only peaked at say 1.8kw & not the 2kw rating due to the reduced V so they get billed for the lower peak. Going up one peak demand band can have huge cost implications.
I know when I used to moon light at a road side cafe (Happy eater lol) we had to turn all the electric stuff (griddles, fryers ect) on one at a time & wait till one was hot till turning on the next. That kept the peak low unless we were very unlucky & they all came on on the stats at the same time.
