Wrong figures

In Your Letters in the September 2019 issue, John Waldron wrote in to respond to a query we had about hybrid vehicles using solar panels and the figures that John predicted would be gained from fitting them. Unfortunately, we interpreted John’s figures wrongly, so he wrote in again to explain our error.

John writes: “In my email to you (‘Panel Beating’ CM Sept 2019), I notice that my ‘kwhr’ was published as ‘Kw/hr’. Now kwhr is a measure of capacity, while kw/hr is a measure of how many kilowatts are used per hour – not the same thing! As an analogy: a 12-volt lead acid car battery may be sold as having a capacity of 60Ah (ampere hours) – this means it could produce a current of 1 amp for 60 hours or 10 amps for 6 hours, etc. This same battery could be marked as having a capacity of 0.72kwhr as wattage = amps x volts, thus 12 x 60 = 720 watts or 0.72 kw.

“As an aside this shows the large difference in the capacity of the lead acid battery compared to the Zoe traction battery, which is 40kwhr.” Glad to set the record straight.