5 ms·
Methodology is flawed. If you switch from burning oil in ice engines to electric you use at least 50% total energy less. So they overestimate area needed.
by llukas 7y ago
Methodology is flawed. If you switch from burning oil in ice engines to electric you use at least 50% total energy less.
So they overestimate area needed.
- gtirloni 7y agoWhat's that due to? Less energy lost to dissipation?
- Gibbon1 7y agoThermodynamic cycles and engineering constraints. ICE engines are about 30% efficient at best. Operationally they're usually a lot worse. Where modern combined cycle power plants are pushing towards 60%. A big part of the difference is that stationary plants use multiple stages to wring the last bit of energy out of the fuel. Where piston engines use one stage. They also suffer from mechanical and thermal losses due to their small size. Small size means higher internal surface area to volume and higher operating speeds. Contributes to higher friction and thermal losses. Friction in an ICE is actually significant.
- llukas 7y agoCarnot cycle limiting maximum ICE efficiency to ~40% (can be obtained if you're big electric power plant) vs 95% electric engine efficiency. For practical purposes, ICE has way lower efficiency than 40% and electrics lose some due to the transmission and battery recharge.
- Robotbeat 7y agoFor the same kind of reason solar panels only access about 15-20% of the energy that hits them.
- Robotbeat 7y agoI was serious. Solar cells are like solid state heat engines in that they’re fundamentally limited by Carnot Efficiency (which is theoretically high for solar cells as the effective temperature of sunlight is high). If we’re going to use “primary energy” and not useful electrical or mechanical energy, then we’d need to include the energy of sunlight falling on the solar panels, which is about 5 times the useful electrical energy produced. And just like actual heat engines, solar cells are improving. The best cells have achieved 47% efficiency in the lab, comparable to a high performance combined cycle natural gas plant (note that thermal power plants often cheat a bit by listing the efficiency in terms of the low heating value of a fuel, ie the heat produced not counting condensing the water vapor out).
- adrianN 7y agoElectric cars need about 15-20kWh/100km. A liter of gasoline has about 9kWh of energy. The average car needs about seven liters per 100km, so around 60kWh/100km. Similar improvements can be had for heating. You get a little less than 1J of heat in your room per Joule-equivalent of fuel you burn, but with an electric heatpump you get 3-5J of heat per Joule of electric energy.
- ksec 7y ago>Methodology is flawed The end product of those efficiency is still Twh. I don't see how the Methodology is flawed.
- llukas 7y agoYou're burning 1kg of gasoline with 46MJ/kg energy at 20% efficiency gives you 9.2MJ of work done. Do you need to replace 46MJ energy embodied in gasoline with 46MJ worth of electricity? No. Electric engine has 95% efficiency so you need 9.68 MJ of energy.