There is ton of overnight capacity but it’s mostly non renewables right now, which drives up your CO2 emitted per mile.
We really need, in California at least, to ramp up workplace charging, otherwise we’re going to have a lot of unused solar :-/.
We really need, in California at least, to ramp up workplace charging, otherwise we’re going to have a lot of unused solar :-/.
As part of the same topic, I think we’re going to see PV-covered EV cars in the not too distant future; not because they don’t need charging (they’re about 10% of your instant needs on the move), but because adding PV reduces the pressure on the grid, and will significantly reduce the need to install power lines to sunlit car parks.
Home, multi-storey, and hotel/motel parking will still almost certainly still need power.
But this is about what I expect soon-ish, and “soon-ish” both continues the cost decline of PV (including thin flexible panels that would make them suitable for more than just the Cybertruck), and also makes it likely that every roof suitable for PV will already have it (because exponential growth).
With current efficiency PV systems, the math requires a fairly large surface like the entire flatbed of a Cybertruck to actually generate a meaningful charge.
This also requires the vehicle be parked somewhere its going to get a good amount of sun, excluding parking garages, a lot of urban areas, etc.
Model 3 is about 5m by 2m, and is apparently rated for 241 Wh/mile
4m * 2m * 1kw/m^2 * 50% * 20% = average power 800 W
(50% because the panels are flat, 20% because cell efficiency)
241 Wh/mile * 60 miles/day = average usage 602 W
I’m not sure what fraction of the day people drive for given that I’m not a driver, but I’m eyeballing 5-10%. I acknowledge professional drivers — taxis etc. — can’t possibly rely on PV alone, that PV can only supply a fraction of what they need (my 10% guesstimate), but I still think this should help with the general public. Or are my assumptions way off?
Further answer - The consensus from people who know this better than you & I, have these cars, and in some cases have tried.. is basically - it won’t charge much, and it’s way more expensive than the electricity it is going to generate.
Note there are AC-DC inverter losses of 10-20%. plus input->battery charge losses which are non-linear and very bad at the low end. For example a Tesla won’t even take a charge if the input is below the ~300-500W range in good weather. In cold weather say Northeast US winter, the floor is closer to a 1kW input as there is a heating system to get the battery put to temperature for charging that is going to eat almost all of that.
https://forums.tesla.com/discussion/93521/solar-panels-on-th...
https://forums.tesla.com/discussion/150998/charge-tesla-w-so...
2) In good weather you are probably looking at post-inverter input to charger at 700W, with charger losses meaning about 400-500W making it to the battery. So that is, in an efficient Tesla about 2 miles of range for every hour of peak sun. Depending on your location, orientation and time of year you might expect peak sun hours of 3-6 hours/day. So grand total 6-18mi/day of range added making a lot of happy assumptions and not moving your car during lunch. This amount of charge per day could be acquired in 1-2 minutes at a supercharger and worth about 30-75cents. Or charge at a L2 charger in your own garage in 12-36 minutes.
(Or, equivalently, multiply the power from the PV by time to get daily energy output).
The “won’t take a charge below 1 kW” is definitely a killer, if it’s a limit of the batteries themselves and not the charging circuit logic.
4m length * 2m width * 1kw/m^2 insolation * 50% loss due to the panel area being calculated by ground area and it not tracking the sun and therefore not getting peak output * 20% cell efficiency = average power 800 W
My BOTE calculation above should use 25% instead of 50% for day-night average of PV panels horizontal to the ground. Can’t edit now, though. 25% is the planet-wide average for day-night and seasonal variation because that’s the ratio of the surface area of the Earth to the area of a disk intersecting the same flux of sunlight at 1AU (4πr^2 : πr^2).
With that correction, that’s 400 watts average over 24 hours (as in: no not merely the peak at noon); which means 24 h * 400 W = 9.6 kWh per day.
If you drive 60 miles per day, and each mile consumes 241 Wh of energy, then you consume 14.41 kWh of energy per day.
They're already popping up in the development stage [0]. 12 km/hr peak solar charging sounds really quite good, and I like the overall design. The company was founded by students who won the World Solar Challenge [1] in 2015, it's pretty neat to see them taking that experience and running with it.
I'm guessing you'll get no more than 400W of power on-car solar. I'm guessing 1-2 rooftop panels with a sub-optimal angel.
A Model 3 uses 0.24 hWh per mile.
That's 13 miles of range from baking in the sun for 8 hours? Best case?
There is also the cost savings in scaling. The cost for a solar system comes down even more when a business can install a whole row of solar panel covered parking, either offer EV charging as a perk or charge for charging, and use the rest of the electricity to power normal electric operations. For the driver, buying the electricity as needed from home or work panels would always be cheaper per total watt usage than buying in-car roof panels, since again, the specialty nature of them means they will always be more expensive and less efficient than their stationary mounted counterparts. You can never scale up car roof solar because you can never install move than one car roof’s worth at a time. You also can’t ignore the inverter power loss that is much worse at the lower power a car roof system would have.
Then of course you have the downsides of long term sun damage to your vehicle to get that minimal charge, instead of protected under a solar panel covered parking or in a garage with solar mounted on top. You have the higher rate of damage by being installed on a moving vehicle instead of a stationary object on a building or parking structure roof. You have the lower rate of return, since panels are rated for 20-25 plus years and most vehicles don’t stay on the road that long. You have the downside of sub optimal charging angle and all the time the vehicle spends in a parking garage during the day, as opposed to a stationary panel that is pointed at the sun 365 days a year. At the end of the day, it will always be cheaper and more efficient to have stationary solar panels.
Given that most people charge their EVs overnight/during work anyway, car roof panels would only really provide value during “road trip” situations, where you are driving close to or beyond at full charge per day. Since you are only getting at best 10-15 additional miles over an entire day in the sun (and more realistically less than 10), it would do very little to reduce range anxiety. And that is not even calculating how much the additional weight of the panels would reduce range.
It sounds good on paper but it is highly unlikely to translate to a real world benefit.
Are they? Does that include the manufacturing process?
Example calculation: https://uploads.volkswagen-newsroom.com/system/production/up...
Here is a quite comprehensive analysis:
https://www.nature.com/articles/s41893-020-0488-7.epdf
Edit: you might have better luck with this link;
https://www.nature.com/articles/s41893-020-0488-7.epdf?refer...
https://en.wikipedia.org/wiki/Life-cycle_greenhouse_gas_emis...
I do like your emphasis on marginal effects. As renewables and BEVs grow it will be a balancing act to pick the most marginally effective resources for emissions abatement. California may soon reach a point where an additional dollar invested in solar doesn't abate as much CO2 as the same dollar invested in transmission, storage, or wind -- even if solar has the lowest instantaneous generation cost.
Is this generally true, or does it depend on geography (e.g. being near the coast)? Where I am in the midwest, it seems that the air normally gets very calm after sunset.
"The Relationship between Wind Generation and Balancing-Energy Market Prices in ERCOT: 2007–2009"
https://www.nrel.gov/docs/fy11osti/49415.pdf
See Figure 5. Hourly generation reaches a minimum from about 1:00 to 5:00 PM and reaches its maximum around 1:00 AM.
Offshore wind output changes less from short term day-night cycles, and generally achieves a higher capacity factor. It is also more expensive to build than onshore wind and no large projects have yet been built for the US, though several are on the drawing board.
Remember that hydro power doesn’t care about time of day and wind is often able to generate more overnight than during the day.
Further time of use rates can be tweaked as usage & generation requires. Maybe with a lot of EVs in the future & solar installed we encourage people to charge mid-day at work or sunrise->commute start & commute end->sundown, this doesn’t work great in winter but also electric use is lower in winter so maybe it nets out.