If there is an answer to this question, this is the place to find it.
I want to work out two things.
If I switched the entire vehicle population of City X to EV from petrol what information would I need to collect to work out and how would the calculatons look?
a) How much carbon I can save
b) What generating capacity will I need to cater to recharging demand
OK, now for my baseline assumptions and an indication of the sorts of information I can get access to.
a) Number of cars in the city
b) Average yearly distance per car
c) Possibly / Maybe total amount of petrol sold in the city per year
Assume for the sake of the argument that the power is coming from a dedicated nuclear power station that is used ONLY for charging the EV, and that everywhere there is a parking lot, there is a charging station so the load is somewhat distributed but will still have peak periods.
Do also assume that there is some sort of a method for load balancing for evening / overnight charging.
So how?
If you want to know why - I am considering a “what if” magazine article putting the idea forward of switching from petrol to all electric for a very tightly controlled car population that in terms of usage patterns is very amenable to full EV
God, I’m no mathmetician so hopefully somebody, you know, smart steps in, but for simplicity, I’d use an idealized ‘average’ car and take that fuel efficiency. Then, I’d use average miles driven per year from some source. Then, I’d use the average fuel source (some combination of diesel, gasoline and perhaps ethanol). That average fuel source would also have to have the ‘carbon emissions per gallon’ teased out. Ideally, that carbon usage would be a ‘well to wheels’ number, but that may be difficult to get to. All that would lead you to the average carbon emissions per person.
Distance per year x Miles per gallon x carbon per gallon = carbon per year.
Then, you’d need to get the watts per mile for your average electric car and the carbon emitted per watt for your city. That would get you the carbon emitted for your electric car
Distance per year x Miles per watt x carbon per watt.
There are probably a lot of other advantages that would minimize carbon emissions that I haven’t thought of like powering your car at night when power prices are low, but I’ll leave that to others.
For the record I postulating an idea where the IC engine car population is taken off the road and replaced by a fleet of full electric battery powered cars. The electricity to be generated by a nuclear power station (no point in just shifting carbon emissions right) so I would like to get a feel for how big the power station would need to be, and what sort of peak generating capacity it would need
Yep, the carbon emissions side is not such a problem - I can get the average km per year per vehicle without a problem, and its not beyond the realm of possibility to also get a figure for the total amount of petrol sold in a year.
Its part two of the equation that I am more worried about - what sort of generating capacity would I need to cater to the peak demand? And how would this calculation look?
I know for a fact that I can’t just say (for example) that capacity = total energy consumption in a year / number of hours in a year = megawatt hours generating capacity…this is the hard part that would need input from someone like **Una **
One nuclear plant can’t do what you want to do - they need to be refueled. And that’s several weeks of derates and outages every cycle. Really, you need at least 3 units - so that whenever one is in refueling, there are 2 available so that you have 1 ready to back the other in case of an outage.
This is why we use a grid instead of just using one plant to serve any particular load.
And once you’re in the grid, you can’t really say “I’m only going to use carbon free electricity.” You get the electrons that you get. You could get a PPA from a carbon free generating source or you could buy carbon offsets, but chances are the electricity you actually get would be from a coal plant.
As far as what capacity you need to serve a load - well, that depends on your load factor. Load factor equals energy divided by peak demand times 8,760.
-peaks during the day
Different types of loads have different types of load factors - industrial is typically the highest. Load factors also change over the seasons - shoulder months tend to be the lowest, while summer or winter will be the hihest depedning on what part of the country you’re in.
The real way to power PHEVs is by charging them at night so that you can use off-peak power. The price of power varies quite a bit over the course of the day, depedning on the season. The peak is considered the 5 by 16 running from hours ending 7 through 23 while the off-peak runs hours ending 24 through 6. There are also 1 or 2 superpeaks during the peak depending on the season and geography - usualy around 8am and 5pm, as heating or cooling ramp. The ‘valley’ in-between these periods can also see low prices as utilities have to deal with trying to ramp down gen or dump energy.
Instead of trying to model building a plant to serve the energy, you might be better off trying to model a PPA for 7x8 blocks and carbon offsets to go along with it.
Huh? Would you mind trying again in English please?
But to be clear - I am not trying to model an actual “real world” situation, I am trying to model what could be achieved in some form of closed system ideal world.
The reason I want to restrict to generation for the cars only is that I don’t want to try and account for varying demand due to high season, low season, weather etc etc. And can please help to explain the abbreviations…
PPA =?
Whats a “7 x 8 block”?
PHEV = ?? (EV I assume is Electric Vehicle, PH = Petrol hybrid?)
And why times 8760, what does this represent?
sorry for my ignorance - this would be an article for a motoring magazine, so i am not looking for a super robust technical model, more of a back of envelope calculation that can stand up to casual scrutiny, even if it can be made more complete and robust
7 x 8 block is 8 hours per day, 7 days per week - it represents the off-peak, 11 pm to 7 am
PHEV - Plugin Hybrid Elelctric Vehicle, although I guess you’re actually going for full electric, not hybrid
8760 is the number of hours in a non-leap year
The problem with a closed system is you need 3 times as much capacity as your peak demand because of refueling and outages - you also have a lot of minimum output and ramp speed problems
Could the excess output be fed back into the grid? The reason I want to base the calculation on Nuclear is I don’t want some form of “pollution shift” complicating the article - i.e I don’t want the argument raised of “well yeah fine, but you’re just moving the pollution from the exhaust pipe to the powerplant smoke stack”
For
Vehicle population 500,000
Average distance per year 20,000km
Average fuel consumption: 10 km/l
Total fuel consumption then equals 1,000,000,000 litres
So how much electricity would you need to generate in total do you think to account for this? (assuming uniform demand across all 8760 hours in a year) - taking into account any transmission losses (assume a 50km transmission distance)
Would we need to account for some form of “charging efficiency”? In other words does 1 kw electricity = 1 kw of stored charge in the battery?
Would need to reach some form of kilowatts (or should that be megawatt hours?) of needed consumption right?
I am also assuming that with these sorts of figures, there isn’t enough current capacity in the system to handle it - so a new power station would need to be built, this one I don’t actually know…
OK, so yuo have two things here - Power and Energy. Power is an instaneous measuremetn made in kW or MW. Energy is measured over time in kWh or MWh. It’s pretty stright forward - 5 MW of power for 2 hours is 10 MWhs.
I have no idea how much electricity hybrid cars will actually need to do their business. However, I can tell you that the heat content of 1 Billion liters of gasoline is about 33 million mmbtus. This is where I go out on a limb - an internal combusiton engine is similar to a Combustion Turbine plant. A combustion turbine plant turns mmbtus into MWhs at about a rate of 12 to 1. So, under that assumption, your gas usage is equivalent to an energy usage of approximately 2.75 million MWhs. I don’t know what kind of assumptions to make about battery storage, so I’m going to ignore them rather than make something up. Tranmission losses will assumed to be about 3% - this is normal enough. That means your going to need about 2,835,000 MWhs or energy. Spread that over 8760 hours in a year and you’ll have a demand of 323 MW with a load factor of 1.00.
Now, you need to determine what kind of assumptions about how variable the load factor really is, what kind of system backups you, how you woudl deal with ouages and so on. Also, 300 or 400 MW is probably too small for an effective nuclear unit - there usually over 1,000. Bu this might get you pointed in the right direction.