A huge electric bill in prospect?

[Cursitor Doom]

Hi all,

A pal of mine is hosting one of the TT Zero teams for this year's competition. This is a race for the newish category of zero-emission electric bikes. They're developing very rapidly currently and are at present capable of putting out 160bhp for 37.75 miles (one lap) at least (on a good day anyway). Some online calculator I've tried states this is equal to about 120kW but that seems like an awful lot to me and surely cannot be right. I was just wondering what sort of electric bill he can expect (after they've gone home, obviously). They made several overnight charge-ups during testing and he said his breakers were repeatedly tripping out. Anyone care to do the maths? You'll have to allow for efficiency as well, of course, since the 160bhp is the power OUT. I'll pass on the result when I see him again tomorrow (assuming it's not too horrible, that is, as he has a heart condition).

cheers, cd.

[Andy Burns]

Assume 20 minute laptime to achieve average speed of 118mph as reported elsewhere (spherical cows and all that) your 120kW is right assuming the horsepower is right, so about 40 kWh per lap, allow 75% efficiency from meter to tyre maybe, manx rates seem to be 16.75p/unit plus VAT (presumably 5% same as here) so about £7 per fill-up ...

[spuorgelgoog]

Depends on which breaker was tripping.

Assuming lots of things like a steady sustained load and a breaker tripping exactly on rated current,

32 Amp socket ring circuit = 7.680 kW load at 240 volt. 7.680 kW for 8 hours overnight charge = 61 kWh 61 kWh @ say 12p / kWh (depends on electricity tariff) = £7.30

Unless I've misplaced a decimal point somewhere.

Owain

[Tim Streater]

Yes, 160HP is 120kW, near enough (the distance is irrelevant).

[Cursitor Doom]

Thanks for that, Andy. Not that it makes any difference to speak of but Manx juice costs 16.01p /unit and VAT is the same. I'll inform him accordingly.

[Andy Burns]

Irrelevant to the power, but not the energy ...

[John Rumm]

1 hp = ~750W, so that sounds about right.

What makes you think its unrealistic? With the right battery technology you can suck amps out of them at a ferocious rate.

The power out tells you nothing much of any use directly. Ideally we need to know the energy density of the battery pack for an accurate answer.

ok a wild stab in the dark: (figures could be out by a significant margin!(

Well let's say the bike is competitive, and it can lap in 20 mins. If it were running at full power for say 50% of the lap (don't know if these things have any energy capture from regen breaking?) That would give a total energy output of say 120 * 0.5 * 20/60 = ~20kWh

That would suggest a battery capacity of something in the order of 30kWh

(by comparison the latest Nissan Leaf boasts a 24kWh battery) - so that may be a bit of an over estimate for something that fits into a bike (unless it has a side car for the battery!).

Still 24kWh would equate to anything from five to ten quid a charge depending on how efficient the charging process is.

[Tim Streater]

Correct, but the OP seemed to think that 160HP as 120kW was wrong. He may have asked other questions too, but I wasn't answering those due to not having the information required to do so or enough interest to go find it.

[Cursitor Doom]

Sorry, Andy. I did mean to include the 20 minutes bit but fortunately you had the nous to fill that blank in. Unlike some people.

[Cursitor Doom]

You've never seen a TT race, clearly. ;-)

[...]

Not known - yet. However, we can now deduce it from the 7 quid per charge figure by subtracting the units used this time from a normal bill from the same period last year. AOTBE of course.

[Jonno]

Cursitor Doom scribbled

A tt zero fact sheet

[harry]

Ball park figures. I have an electric car. The battery size is 16Kwh (weighs almost a ton)and is far bigger than any b ike. This will take me about 80 miles. So a bike is likely to have around a quarter of this (let's say). So a bike is likely to need say 4 Kwh per charge. So each charge up would cost around £0.75

Battery chargers come in various sizes, if they had fast chargers than mayb e his breakers would trip.

My car has a slow charger (2.2Kw) and would take 8 hours from complete depl etion.

[harry]

Drivel. All is down to battery size. Which we can only guess. Tripping is down to how big/fast the battery charger is. Again we can only guess. Nothing else is relevant.

[harry]

A lot of people here don't know the difference between power and energy. Bad education.

[Andy Burns]

The TTzero bikes are limited to 300kg

I presume the bike is designed to run out of juice as soon after it crosses the line as is possible.

You seem to be thinking about a toy scooter, not something that did this last year ...

[dennis]

Are you sure its not a milk float? The whole bike with a 14kWHr battery is a quarter of a ton.

The bike does 120 miles.

[Andy Burns]

It's a single 37¾ mile lap, the superbikes refuel every other lap, how many years before the electric bikes can do two 130mph laps on a charge?

[Dave Liquorice]

No but I know enough about motorsport to know that the GO and STOP controls are digital, just two states full on or off.

Only on the open to the public roads around here, which reminds me I must get the dashcam out of the car and see what it caught of a bike hurtling around a RH bend (for them) at not much more than 30 deg up from the horizontal. If I'd been a second or so earlier his head would have been pretty much inline with my headlight...

Does your pal use any electricity for space heating and is the billing period monthly or quarterly. Space heating can be very seasonal, if this time last year just happened to be cold it could mask the energy given to the bikes.

My workings would be worst case, others more realistic but if you have the bike spec and get the maximum battery capacity. You'd get simpler maths and a better guide to how much energy is likely to have been used.

• =

Effciency guesstimate at 80% in (but probably better) 80% out (probably worse due to the high discharge rates). Two lots of 80% gives an overall effciency of 64%, call it 60%.

= ( / 60) * 100

= *

[Adrian]

Do you, Harry? I don't think you've mentioned it before.

The battery in Harry's i-MIEV is actually 200kg, and the car is a ton and a half.

Anyway, how did he escape from my bozobin?

[Andy Burns]

With one predictable exception, maybe they could have a TT triple-A class for harry?