# How to calculate required battery charge for 300 miles

1. Aug 18, 2010

### jacstar

Need help - my brain is mush and the longer I look at it the more I don't understand it...can someone please tell me if this calculation is correct:

1. The problem statement, all variables and given/known data

A car is run for 400 hours per year, with a total mileage of 10,000 a year.
The car uses diesel and consumes 2,000 litres a year.
A litre of diesel costs £1.10 and holds 38.7MJ of primary energy.

If the engine is 20% efficient overall, how much energy would need to be stored in 95% efficient batteries to give a range of 300 miles on full battery charge?

2. Relevant equations

n/a

3. The attempt at a solution

Background Calcs:
Convert MJ to J: 38700000J
Total Joules (J x 2000 litres): 77400000000J
Convert 400 hours to seconds: 1440000s

Energy 77400000000 J
Time 1440000 seconds
= Power 53750 Watts
53.75 kW
1 watt = 0.001341022 horsepower
Convert W to hp: 72.07993734 hp

Primary energy (1 year): 400h*53.75kw=21.5MWh
Energy to 95% efficient batteries: 21.5 x 100/20 x 100/95 = 113.2MWh
Therefore 300 miles: 300/10000*113.2=3.4MWh

Thanks guys

+ :zzz: + = me
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Aug 18, 2010

### Zryn

Does the battery replace the diesel or the engine?

Either way, look at it from the point of view of a flow of units. For example, taking distance traveled & diesel used and energy in diesel, and then calculating energy per distance (MJ/mile) should give you a good grounding for calculating the energy required to travel some more distance.