Taking a car of 2 tons weight and 2 m� front area as an example, running with pneumatic tyres on asphalt concrete roads on a levelled surface on a wind still day. To accelerate it to 100 km/h within 12 seconds, you need 57.2 kW net, to overcome inertia, rolling resistance and aerodynamic drag. You have to cater for the drivetrain losses, too, so you might need some 82.6 kW gross. And, of course, you need power for your air conditioning, power steering, windshield wipers, &c. Of course, that's just for a couple of seconds, and if running smoothly at 50 km/h, you need only 3.71 kW net for rolling resistance and aerodynamic drag (without climbing or wind forces, of course), at 90 km/h 10.6 kW net, at 120 km/h, 20.1 kW net. Plus the drive train losses, plus the power for the auxiliary systems. On average, a diesel car in Germany is running 17,500 km per year, and there is a VW Golf with a nominal consumption of 4.2 litres/100 km (56 mpg) - normally a real-life consumption will be about 25% higher, say, 5.3 litres/100 km (44.8 mpg). So we're talking 918.75 litres diesel per year, IOW, 983 kWh. An electric engine might be 60-100% more efficient, so 614 kWh might suffice (disregarding all the losses in charging/discharging the batteries - so add another 20% - and alternating/rectifying -so add another 10-15%. Of course, as the specific energy and energy density of the batteries is much smaller than of the diesel, you might end up with a heavier and bulkier vehicle, so this might add to your consumption ...). Solar constant above Earth's atmosphere is about 1,350 W/m�, in mid-latitudes due to absorption, scattering and reflection by the air mass about 930 W/m�, due to water vapours, aerosols, photochemical smog, and the effects of temperature inversion, about 870 W/m� on average. As the surface of a globe is four times the surface of a disk, you will have on average 1/4 of this. And as, for physical reasons (blackbody radiation, radiative recombination, spectrum losses) 33.7% are the theoretical maximum efficiency of a solar cell. The 24% achieved might be very close to the practical real-life limit. To get our 614 kWh per annum, you might need about 1.34 m� of this quality (24% efficiency). It will be somewhat more as the cells won't be perpendicular to the insolation all the time ... -- Michael -----Original Message----- From: xxxxxx@simplelists.com [mailto:xxxxxx@simplelists.com] On Behalf Of Jeffrey Schwartz Sent: Wednesday, October 07, 2015 3:17 PM To: tml Subject: Re: [TML] Re: Understanding batteries and solar and motors. Although consider that you don't drive a car continuously. I'm in Florida, we average 4 "peak output" hours of sunlight a day. Lets say I have 3 square meters on top of my car, and go with the 390w/sqm That's around 4.7kwh solar input per day... or about 6 HP/hours per day. I ran the Torque app on my car, and cruising on the interstate I only draw about 2-3 HP to cover wind resistance. I very briefly pull more as I accel to 70. Start/Stop rush hour traffic, I pull 30hp or so for a few seconds, then coast. Around town, it's a similar thing. I suspect that the average driver could get along on this. On Wed, Oct 7, 2015 at 8:40 AM, Knapp <xxxxxx@gmail.com> wrote: > So we are looking at 650 watts per square meter * .6 which is 390 > watts as the current max and future max might be something like 600 > watts per square meter which still leaves a car or boat very underpowered. > > "The car motors are rated to a peak power of x watts. They don't need > to run at peak output otherwise you couldn't get the rated range figures." > > Is this because of air and road friction or does the motor loose > efficiency at peak output. > > -- > Douglas E Knapp, MSAOM, LAc. > > ----- > The Traveller Mailing List > Archives at http://archives.simplelists.com/tml > Report problems to xxxxxx@travellercentral.com To unsubscribe from > this list please goto http://archives.simplelists.com ----- The Traveller Mailing List Archives at http://archives.simplelists.com/tml Report problems to xxxxxx@travellercentral.com To unsubscribe from this list please goto http://www.simplelists.com/confirm.php?u=R5i9xKRvwtSYrbOxd8whsOxqIcKnDVY1
