Consumer Energy Report is now Energy Trends Insider -- Read More »

By Robert Rapier on May 12, 2008 with 13 responses

Replacing Gasoline with Solar Power

Executive Summary

If you don’t want to run through the calculations, here is the summary. I attempted a thought experiment in which I calculated whether it would be feasible to use solar power to generate enough energy to offset all U.S. gasoline consumption. My conclusion is that it will take about 444,000 megawatts of electrical generating capacity. Current U.S. generating capacity is over 900,000 megawatts, but there isn’t a whole lot of spare capacity in that number.

To generate 444,000 megawatts with solar PV would require just under 1,300 square miles (a 36 mile by 36 mile square) of just PV surface area. To generate that much power with solar thermal – including supporting infrastructure – would require 4,719 square miles (a 69 mile by 69 mile square). A large area, but not impossible to envision us eventually achieving this.

——————–

Introduction

Having made an attempt to calculate the number of square miles to replace current U.S. electricity consumption via solar PV or solar thermal, I have been challenged to do the same exercise for replacing our gasoline usage. (In fact, I was told by someone that they had never seen this kind of calculation done, so I told them I would do it). I have no idea how this calculation is going to turn out, but I suspect it is going to be similar to the previous calculation for replacing electrical consumption. My guess is less than 100 miles by 100 miles. Note that this is a thought experiment, in which I try to get an idea of what it would take to achieve this.

First, some caveats. There are still technical obstacles that prevent this scenario from being realized. Those are, 1). Battery range is still too low (The plug-in Prius is only going to be able to go 7 miles on battery power).; and 2). Solar power can’t be adequately stored. However, that’s not the purpose of the exercise. The purpose is to satisfy my curiosity: If we were going to try to replace gasoline with solar power, are the land requirements prohibitive?

I am only going to do this calculation for gasoline, as I think it is unlikely that electricity will ever power long-haul trucks or airplanes.

How Much Do We Need?

The U.S. currently consumes 389 million gallons of gasoline per day. (Source: EIA). A gallon of gasoline contains about 115,000 BTUs. (Source: EPA). The energy content of this is equivalent to 45 trillion BTUs per day. The average efficiency of an internal combustion engine (ICE) – that is the percentage of those BTUs that actually go into moving the vehicle down the road – is about 15%. (Source: DOE). Therefore, the energy that goes toward actually moving the vehicles is 6.7 trillion BTUs per day.

The efficiency of electric infrastructure can be broken down into several steps. According to this source, the respective efficiencies for the transmission lines, charging, and the vehicle efficiency are 95%, 88%, and 88%, for an overall efficiency (after the electricity is produced) of 74%. To replace the gasoline BTUs that go toward moving the vehicle with electricity is going to require 6.7 trillion/0.74, or 9.1 trillion BTUs. To convert to electricity, we use 3,413 BTUs/kilowatt-hour (kWh). Thus, 9.1 trillion BTUs/day is equal to 2.7 billion kWh/day. That’s how much energy we need. To convert this to power, we need to multiply by 1 day/24 hours, and that gives us 111 million kilowatts, or 111,000 megawatts (MW) of power generation required.

Looking back at my Solar Thought Experiment, I calculated 2,531 square miles to replace our peak electrical demand of 746,470 MW (746 GW). However, the current calculation is a different sort of calculation than what I did previously. The previous calculation attempted to have enough installed solar PV to meet peak demand. In the case of replacing our transportation fuel, I need enough panels to produce the required transportation energy in 8 hours or so while the sun is shining. To be conservative, we can assume 6 hours, which means we will actually need four times the 111,000 MW, or 444,000 MW.

Using Solar PV

From the previous essay, I used a conservative value of 12.5 watts per square foot as the generating capacity of an actual GE PV panel. To get 444,000 MW is going to take an area of 35.5 billion square feet, which is 1274 square miles. This is an area of just under 36 miles by 36 miles. However, this is just the surface area required to generate the electricity. It does not include area required for supporting infrastructure.

Using Solar Thermal

Doing the same calculation based on the solar thermal output from Running the U.S. on Solar Power, the expectation was that 0.147 megawatts could be produced per acre. This did include all of the land associated with infrastructure. If we use that number, we find that to generate 444,000 MW is going to take a little over 3 million acres, or 4,719 square miles. This is a square of just under 69 miles by 69 miles.

The reality is that we would use a combination of the solar PV and solar thermal. We have a lot of available rooftops that can create electricity with solar PV, and there are large tracts of land in sunny Arizona and Nevada that can create electricity with solar thermal.

Conclusions

Clearly, a lot of area is required, but it isn’t impossibly large. Of course to achieve this, a couple of big problems need to be resolved. First, battery life needs to improve somewhat before people are going to embrace electric transport. According to this ABC News story, the average commute is 16 miles one-way, but the range of the plug-in Prius is only expected to be 7 miles. The Aptera, on the other hand, claims a range of 120 miles. Maybe we just need to change the way we think about what we drive. (On the other hand, not a lot of commuters are going to climb into an Aptera if they have to share the road with large SUVs).

Second, and the bigger issue, is that we still don’t have a good way to store excess solar power. We need to have a good storage mechanism so electric cars can be charged at night from solar electricity produced during the day. One idea for this that I have seen floated is to use peak solar energy to electrolyze water, and then store the hydrogen in centralized locations. The hydrogen would then be burned at night to run centralized electrical generators. Not the most efficient method for storing solar energy, but technically workable.

Finally, the current electrical grid couldn’t handle such a large increase, but the model I envision would generate and consume the electricity locally.

Note

I had delayed posting this for almost a week, because I was sure there was an error in the calculations. I finally found one (I had turned a kilowatt into a watt), but let me know if you find other errors or incorrect assumptions.

  1. By BilB on May 4, 2010 at 8:49 am

    Did you do a direct vehicle fuel consumption for electricity? Or did you realise that internal combustion engines (working fleet) are 35% energy conversion efficient whereas electric vehicles (properly designed) are 90%+ (running) efficient. ie require a third of the energy charge to power them the same distance on electricity alone.

    [link]      
  2. By BilB on May 4, 2010 at 9:18 am

    Improvements in electric vehicles from VW

    http://www.gizmag.com/volkswagen-milano-taxi-electric-vehicle/14891/?utm_source=Gizmag+Subscribers&utm_campaign=88dc79d9cd-UA-2235360-4&utm_medium=email

    On CSP power and costing SolarPaces have a figure for a 8000 to 9000 hour per year full capacity system at 4.3 billion euros per gigawatt. That is a compound system that uses extra solar fields to charge eutectic salts to provide for full capacity night time output and non period output.

    The general solar field figure is 50 megawatts per square kilometre. Your calculation there came to 36, so there is a discrepency to find a reason for.

    We are designing a PV system (I think that I have already noted this in your area) that will put 10Kw capacity on house and small business premesis rooves. This system will deliver 19,200 Kwhrs per year (+other energy) in Sydney. This is a very different construction to normal PV and does not disfigure the appearence of buildings. Where such a system is suitable it will provide all of the electricity for a family of 4 plus the energy required to run 1 car (the above VW) with a charge every day and a half (186 miles range times 3 per week). Once the units are paid for the energy thereafter is free. The point of the comment is that there are solid energy systems on the way using todays technology. I do not see the people to need to significantly reducing their life style unless they are massive energy wasters.

    Replacing gasoline with electricity with solar will be no big deal, and could well happen for many sooner than previously thought.

    [link]      
  3. By Justin Fischer on September 23, 2010 at 1:38 pm

    To convert this to power, we need to multiply by 1 day/24 hours, and that gives us 111 million kilowatts, or 111,000 megawatts (MW) of power generation required.

    Won’t this be off by a factor of three or four since the sun doesn’t shine 24 hours per day?

    [link]      
  4. By Justin Fischer on September 23, 2010 at 1:41 pm

    Disregard my last. I didn’t read far enough.

    [link]      
  5. By Oct on October 7, 2010 at 5:02 pm

    I would be interested to see what the average capital investment per person would be to collect and store that amount of solar.

    Is this greater than or less than the cost of the average new car?

    [link]      
  6. By Richard Gammell on October 8, 2010 at 7:58 am

    Good morning Robert,

    Yes, in most cases gasoline can be replaced be solar energy!!
    I would say that a solar panel area of about 240 sq/ft to 320 sq/ft per car is needed to propel it 40 miles per day.
    We have a solar powered electric vehicle “SOLARCAR”, which has been powered by wind and solar energy since January 1, 2010. All mileage and wattage have been documented. This demonstrates that solar energy can replace gasoline as a transportation fuel.
    For more pictures of 3100 pound SOLARCAR go to my Facebook page.

    We also have developed a solar generating system that takes the place of most job-site gasoline generators. We are trying to market the system but banks are not being any help.

    There are some news clips (below), stories and pictures can be seen on our website, http://www.canadiceconstruction.com there have been a total of 28 over the past 2 years.
    You are right on thinking that gasoline can be replaced with solar and wind energy……we are doing it now in, of all places, Western, New York!!

    In addition, we also have a 29 acre parcel of property currently being subdivided into 5 lots. I would like to partner with other companies to build an off-grid Solar Wind Hydrogen Community. Our property is located on Rt. 15A and is in close proximity to the land that New York State has just purchased from the City of Rochester. When this project goes, it will be one the first, if not THE first, such community in the nation and a model of things to come. I would like to see the following incorporated into the project:
    1. Solar and Wind energized homes and buildings.
    2. Direct charging of electric vehicles from solar and wind energy (the Volt).
    3. Hydrogen production from solar and wind energy (for Fuel Cell cars).
    4. Lots of conservation measures.
    5. Geothermal Heating.
    6. Carbon capturing coal furnaces and wood stoves.

    Here are the news clips:

    http://www.youtube.com/watch?v=beaZVAKlnDQ
    WKBW TV (ABC) out of Buffalo, NY 8/5/08

    http://www.youtube.com/user/canadiceconstruction#p/a/u/2/Y0N9DNIq1_U
    WGRZ TV (NBC) out of Buffalo, NY 8/21/08

    http://www.youtube.com/watch?v=fSamGenpgnM
    WBNG TV (CBS) out of Binghamton, NY 2/20/09

    http://news10now.com/southern-tier-news-1115-content/top_stories/487926/county-route-73-bridge-opens-in-lindley
    News 10 Now TV out of Corning, NY 11/17/2009

    http://www.youtube.com/watch?v=xazJ-Lmecvc
    WROC TV (CBS) out of Rochester, NY 12/20/08

    http://www.youtube.com/watch?v=2E3I4OkVHuk
    Afghanistan combat veteran and congressional candidate Matt Zeller (NY-29)

    [link]      
  7. By Dave S. on October 8, 2010 at 11:07 am

    The aria of PV panels required to replace our gasoline use, 35.5 billion square feet, works out to be about the average aria of a parking space times the number of passenger vehicles in the U.S.

    [link]      
  8. By Ronald Brak on October 10, 2010 at 9:30 pm

    If you are replacing gasoline with solar electricity, then I guess this means you are replacing a lot of gasoline burning cars with electric and plug in hybrid cars. The batteries in these cars could store a large amount of energy. But even without electric cars, solar generated electricity generally would not require storage until it became a large portion of total electricity production. Just what portion of electricity could be practically generated from solar depends on costs and grid characteristics. The amount of land required can be reduced by installing solar capacity on roofs. Point of use solar saves users paying retail electricity prices and reduces transmission losses.

    [link]      
  9. By Rob Ryan on October 11, 2010 at 11:40 am

    I am only going to do this calculation for gasoline, as I think it is unlikely that electricity will ever power long-haul trucks or airplanes.

    While I agree that airliners and long haul trucks will not run on batteries, I do think that the energy for them will ultimately, at least in part, come from electricity. Possibilities include hydrolysis to produce hydrogen, and thermo-chemical processes powered by electricity to produce liquid fuels.

    [link]      
  10. By preciseenergy on June 6, 2011 at 5:07 am

    Really we can replace every non-renewable source with some renewable energy so that we can save our future.

    [link]      
  11. By Alison Young on June 16, 2014 at 9:27 am

    your post is too good and very informative, as well. So thanks for the sharing.
    http://www.skyhighenergy.com/

    [link]      
  12. By Re-Port on October 29, 2015 at 2:53 am

    The solar power and carbon dioxide fuel be used to replace gasoline?

    [link]      
  13. By Nicholas Bohn on May 9, 2016 at 4:47 pm

    Would LOVE to see an updated version of this for 2016.

    [link]      
Register or log in now to save your comments and get priority moderation!