I've been considering suitable areas for emplacement of lot of solar panels. Many of you are familiar with the Land Art Generator Initiative and the global map they have used to demonstrate how much of various portions of the earth's surface would be needed to satisfy global total energy demand. My approach differs; one of such differences is that I am considering solely electricity production.
My methodology centers on land dual use. There are many valid arguments against using vacant land for large-scale PV farms. It might take away agricultural land; it might destroy - or at least ineluctably alter - a desert or "wasteland" ecosystem; it could be considered a visual blight; and so on.
But much area already is used. Residential and commercial rooftops; parking lots; aqueducts; highways. This exercise looks at one subset of highways: the USA Interstate Highway System. I chose this for a number of reasons, most importantly because it was the easiest to obtain size information.
The thesis is that a road's areal footprint could be dual-purposed - an array of PV panels could be constructed above the roads. Reasons for this are powerful: the land already has been sequestered under Rights-of-Way terms; it is immediately accessible by roads (that's a joke, son, but this also makes for an easier time in connecting such systems to a nationwide electrical grid); driving along a covered road is safer, in that sun glare and weather effects (rain & snow) would be mitigated by a properly-constructed panel array.
Below are my calculations - I ask for others' review of same and request any challenges or corrections.
Raw data: at present, the Interstate System is:
*length: 77 x 10^6 m long.
*width of lanes is mandated at 4m in rural ares; 3m in urban; 2 lanes per direction is the minimum; 3 is more common and many routes have far more. For calculations I have allotted 25m as a mean width of lanes by themselves
*width of shoulders also varies rural, urban and mountainous; I have agglomerated them to 10m
*width of median strip is a minimum of 11m rural; 3m urban. I have used 10m
*Right-of-Way strip varies enormously; to bring the sum to a round number I have allotted another 15m to the total.
25+10+10+15 gives us a usable mean width of 60 meters.
77 x 10^6 * 60 = 4.6 x 10^9 m^2. As an aside, this is equivalent (rounded) to 1,800 mi^2, or 1.1mm acres.
Aside: How many panels is that?
*In 2015, a run-of-the-mill PV panel is 2m^2 in area. Using round numbers, our highway system thus can be covered with approximately 2.3 X 10^9 panels. With a nameplate capacity of about 250 watts, that is a peak output potential of 580 X 10^9 watts.
Back to power generation - in other words, how many kWh might be generated?
Using a nationwide annual average of 5kWh/m^2/day**, and a round-number panel efficiency of 20%, we arrive at 1kWh/m^2/day (gotta love these rounded numbers), or 365kWh/m^2/yr.
For a total of 365 * 4.6 x 10^9 = 1700 x 10^9kWh/yr ---> 1700 x 10^6MWh/yr. At present, the US is generating approximately 4000 x 10^6MWh/yr***.
CONCLUSION:
These calculations suggest that with today's technology, approximately 40 percent of the United States's entire electricity production could be accounted for by over-highway solar panels.
Critical data sources:
** nrel.gov/gis/il_solar_pv.html
***Electricity Data Browser
My methodology centers on land dual use. There are many valid arguments against using vacant land for large-scale PV farms. It might take away agricultural land; it might destroy - or at least ineluctably alter - a desert or "wasteland" ecosystem; it could be considered a visual blight; and so on.
But much area already is used. Residential and commercial rooftops; parking lots; aqueducts; highways. This exercise looks at one subset of highways: the USA Interstate Highway System. I chose this for a number of reasons, most importantly because it was the easiest to obtain size information.
The thesis is that a road's areal footprint could be dual-purposed - an array of PV panels could be constructed above the roads. Reasons for this are powerful: the land already has been sequestered under Rights-of-Way terms; it is immediately accessible by roads (that's a joke, son, but this also makes for an easier time in connecting such systems to a nationwide electrical grid); driving along a covered road is safer, in that sun glare and weather effects (rain & snow) would be mitigated by a properly-constructed panel array.
Below are my calculations - I ask for others' review of same and request any challenges or corrections.
Raw data: at present, the Interstate System is:
*length: 77 x 10^6 m long.
*width of lanes is mandated at 4m in rural ares; 3m in urban; 2 lanes per direction is the minimum; 3 is more common and many routes have far more. For calculations I have allotted 25m as a mean width of lanes by themselves
*width of shoulders also varies rural, urban and mountainous; I have agglomerated them to 10m
*width of median strip is a minimum of 11m rural; 3m urban. I have used 10m
*Right-of-Way strip varies enormously; to bring the sum to a round number I have allotted another 15m to the total.
25+10+10+15 gives us a usable mean width of 60 meters.
77 x 10^6 * 60 = 4.6 x 10^9 m^2. As an aside, this is equivalent (rounded) to 1,800 mi^2, or 1.1mm acres.
Aside: How many panels is that?
*In 2015, a run-of-the-mill PV panel is 2m^2 in area. Using round numbers, our highway system thus can be covered with approximately 2.3 X 10^9 panels. With a nameplate capacity of about 250 watts, that is a peak output potential of 580 X 10^9 watts.
Back to power generation - in other words, how many kWh might be generated?
Using a nationwide annual average of 5kWh/m^2/day**, and a round-number panel efficiency of 20%, we arrive at 1kWh/m^2/day (gotta love these rounded numbers), or 365kWh/m^2/yr.
For a total of 365 * 4.6 x 10^9 = 1700 x 10^9kWh/yr ---> 1700 x 10^6MWh/yr. At present, the US is generating approximately 4000 x 10^6MWh/yr***.
CONCLUSION:
These calculations suggest that with today's technology, approximately 40 percent of the United States's entire electricity production could be accounted for by over-highway solar panels.
Critical data sources:
** nrel.gov/gis/il_solar_pv.html
***Electricity Data Browser