# Saving money with electricity (basic)

Concepts addressed: electrical power and analytical skills.
An advanced version of Saving Money with electricity is also available.

Scenario:

I got a gaming computer for my birthday and I use it to play Fortnite with my friends. When I go to sleep I leave it on, but it’s not doing anything (idle). Assuming I sleep for 8 hrs every day…

1. How many hours of Fortnite would I be able to play with the energy I waste during one night?
2. How much money do I waste over a year by not turning my computer off?
3. The EU uses 220V electric systems while the US uses 120V. Compare their energy consumption for 3 hrs of gaming.

Data:
Computer while gaming: 400 W
Computer at idle: 100 W
Household voltage: 120V (US) || 220V (EU)

Useful calculators:

Question 1 hints:

Hint 1
You don’t need to calculate the idle consumption at night.
Hint 2
Power is energy per unit of time. Twice the power means that you use the same amount of energy in half the time.

Question 2 hints:

Hint 1
1kWh = 3600000 J. If you cannot search online use 0.25 cents/kWh as the price of electricity.
Hint 2
time * power = energy
energy * price = cost

Question 3 hints:

Hint 1
Don’t overthink it. Sometimes the extra information is not needed.

Solutions (WARNING: results may vary depending on price of electricity) :

Question 1
The result is that you game 2 hrs with the energy your computer uses on idle overnight.
Question 2
You spend 35.06USD/year by leaving your computer idle at night.
`Using the average price for electricity in the US ( 0.12USD/kWh)`
Question 3
They are the same.

Step-by-Step solutions (WARNING: results may vary depending on price of electricity) :

Question 1
The energy consumed is proportional to the time of usage. We can use this fact to simplify things:

power_gaming * time_gaming = power_standby * time_standby
time_gaming = (power_standby * time_standby) / power_gaming = 100W * 8h / 400W = (8/4) h = 2 h

The result is that you game 2 hrs with the energy your computer uses on idle overnight.
Question 2
You can use the average price for electricity in the US (0.12USD/kWh), and multiply it by the power used on idle and the hours it will be on standby over a year:
total_cost = 0.12USD/kWh 0.100kW * 8h/day * 365day/year = 35.06USD/year
Bonus points if you use the real price of electricity in your region.
Question 3
Since we have the total power consumption of the computer in each state, the voltage used to power them is not relevant. They are the same.

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