AVIATION'S NEW ERA
Chapter 11. Solar Power
Photovoltaic cells have been the power supply of choice for HAPS/HALE aircraft in prototypes by NASA, Boeing, and Airbus. Additional metrics of performance emerge when applications expand to aircraft that approach being consumer products and when the solar power is relied on the mitigate global warming. These additional metrics include: a) cost relative to lowest-cost alternatives, b) the EROI (Energy Return on Investment), and c) power ratio as the amount of power produced versus the amount of power needed to sustain the photovoltaic cells in 24/7 flight.
Cost of Solar Power – The cost of solar power varies considerably based on location, time scale for payback, and person doing the estimating. What is more reliable, is the ability to estimate how the key factors that impact the cost vary with an application on a Towed Platform. These factors and the impact are estimated by the following bullets:
The cumulative impact factors range from 2.7 to 18. These higher productivities decrease costs and reduce risks. The US Department of energy estimates commercial photovoltaic electrical power in 2020 as $0.09 per kWh with $0.04 being both a 2030 commercial goal and a 2020 estimate for utility power (See 2030 Solar Cost Targets | Department of Energy).
Installation and maintenance costs would approach negligible values for Towed Platforms since the platforms could be fabricated at the same location as the photovoltaic cells, minimal structure is required for use on the Towed Platform, there is no cost for real estate, and there is minimal cost for cleaning and vegetation control. Thus, a reasonable base case cost for 2022 is $0.05 per kWh. When divided by the above cumulative impact factors, the cost of 2022 solar on the Towed Platform is <$0.02 per kWh to <$0.01 per kWh for the best applications. This is relative to the cost of liquid fuels and is major savings.
EROI – The EROI is the [Energy Delivered] / [Energy Required to Deliver that Energy]. For solar power, the denominator includes the energy needed to produce the photovoltaic cells, to deliver the panels to location, and to install and maintain the solar panels.
Estimated EROI for photovoltaic cells range from 1.0 to 10. Many factors can lead to the failure to realize optimistic values for systems where returns are often estimated on time scales up to 30 years. Also, when including battery storage, the EROI is typically cut in half. This author believes that realized EROI are more in the range of 1.2 to 2 for appropriate applications.
When including battery storage, the EROI is typically cut in half. This places a high value on direct solar with energy stored as altitude for aircraft.
The cumulative impact factors identified in the previous section increase productivity, and thus proportionally increase the EROI. Also, energy input is reduced due to direct production of Towed Platform structures near the production of the photovoltaic cells. The result is a reliable EROI of 4 to 10 that is destined to markedly increase with improved photovoltaic cells.
Power Ratio for Towed Platform Application – The following base case specifications are used to estimate the power ratio for a towed platform that is a flying solar panel of minimal structure. Here, minimal structure is a polymer sheet that has high tensile strength to be stretched on a frame. The design of the platform is for weight per area to be equal and opposite of lift per area; alleviating essentially all stresses on the surface from steady-state flight.
Attainable power generation from a Towed Platform is 300-600 W/kg; which is a range between photovoltaic cells supported on a standard honeycomb array (150 W/kg) and the thin film photocell array (1000 W/kg) (see https://www.spectrolab.com/photovoltaics.html ). The required thrust power (per kg) is acceleration (9.8 m/s2) times velocity (m/s) divided by L:D. At an L:D of 50:1 (i.e. half of 100:1 goal) and speeds of 360 and 720 km/h; the thrust power requirements are 20 and 40 W/kg; the provided power is 10X that needed (>4X is a toned-down factor) to tow the platform. Since both weight and lift are evenly distributed, little structure is needed for flight; a structured shuttle aircraft can be used to take the platform to flight/altitude. The Towed Panel’s loading (mass per m2) is much lower than needed to attain the highest of L:D.
The claim is that a Towed Solar Platform will produce more than 4X the power needed to sustain its 24/7 flight when operated at reasonable conditions. The Towed Solar Platform is essentially a power supply that can be scaled to any power need.
Extreme Solar – In Towed Platform applications, Solar Power emerges as the low-cost power supply with costs projected to continue to decrease as technology improves. Of particular relevance is the stacking of photovoltaic layers in the higher-radiation environments above 60,000 ft.
The extended implications are that Towed Platforms emerge as such a low cost that nothing can complete, and that Towed Platforms become platforms for industrial fabrication and energy harvesting. Dedicated platforms could venture toward polar regions where 24/7 sun is available, leading to further reductions in solar power costs.
Example Towed Platform industries include hydrogen production, ammonia production, and atmospheric decarbonization. The first two only rely on water and nitrogen as feed stocks, both of which are available in the atmosphere. The last recovers carbon from the atmosphere and makes it available as a feed stock which greatly extends the range of chemicals that can be produced. Also, batteries could be charged and delivered and energy beams could deliver the energy to locations on Earth’s surface.
Additional Information – A starting point for additional information on these topics in Wikipedia under the topics of EROI and solar power.
Photovoltaic cells have been the power supply of choice for HAPS/HALE aircraft in prototypes by NASA, Boeing, and Airbus. Additional metrics of performance emerge when applications expand to aircraft that approach being consumer products and when the solar power is relied on the mitigate global warming. These additional metrics include: a) cost relative to lowest-cost alternatives, b) the EROI (Energy Return on Investment), and c) power ratio as the amount of power produced versus the amount of power needed to sustain the photovoltaic cells in 24/7 flight.
Cost of Solar Power – The cost of solar power varies considerably based on location, time scale for payback, and person doing the estimating. What is more reliable, is the ability to estimate how the key factors that impact the cost vary with an application on a Towed Platform. These factors and the impact are estimated by the following bullets:
- Increased solar radiation at 20,000 to 80,000 ft altitude (factor of 1.2 to 2).
- Above trees and clouds (factor of 1.5 to 3, based on location).
- Travel with (against) sun during the day (night) (1.5).
- Optimal orientation to maximize sunlight (1.5 to 2).
The cumulative impact factors range from 2.7 to 18. These higher productivities decrease costs and reduce risks. The US Department of energy estimates commercial photovoltaic electrical power in 2020 as $0.09 per kWh with $0.04 being both a 2030 commercial goal and a 2020 estimate for utility power (See 2030 Solar Cost Targets | Department of Energy).
Installation and maintenance costs would approach negligible values for Towed Platforms since the platforms could be fabricated at the same location as the photovoltaic cells, minimal structure is required for use on the Towed Platform, there is no cost for real estate, and there is minimal cost for cleaning and vegetation control. Thus, a reasonable base case cost for 2022 is $0.05 per kWh. When divided by the above cumulative impact factors, the cost of 2022 solar on the Towed Platform is <$0.02 per kWh to <$0.01 per kWh for the best applications. This is relative to the cost of liquid fuels and is major savings.
EROI – The EROI is the [Energy Delivered] / [Energy Required to Deliver that Energy]. For solar power, the denominator includes the energy needed to produce the photovoltaic cells, to deliver the panels to location, and to install and maintain the solar panels.
Estimated EROI for photovoltaic cells range from 1.0 to 10. Many factors can lead to the failure to realize optimistic values for systems where returns are often estimated on time scales up to 30 years. Also, when including battery storage, the EROI is typically cut in half. This author believes that realized EROI are more in the range of 1.2 to 2 for appropriate applications.
When including battery storage, the EROI is typically cut in half. This places a high value on direct solar with energy stored as altitude for aircraft.
The cumulative impact factors identified in the previous section increase productivity, and thus proportionally increase the EROI. Also, energy input is reduced due to direct production of Towed Platform structures near the production of the photovoltaic cells. The result is a reliable EROI of 4 to 10 that is destined to markedly increase with improved photovoltaic cells.
Power Ratio for Towed Platform Application – The following base case specifications are used to estimate the power ratio for a towed platform that is a flying solar panel of minimal structure. Here, minimal structure is a polymer sheet that has high tensile strength to be stretched on a frame. The design of the platform is for weight per area to be equal and opposite of lift per area; alleviating essentially all stresses on the surface from steady-state flight.
Attainable power generation from a Towed Platform is 300-600 W/kg; which is a range between photovoltaic cells supported on a standard honeycomb array (150 W/kg) and the thin film photocell array (1000 W/kg) (see https://www.spectrolab.com/photovoltaics.html ). The required thrust power (per kg) is acceleration (9.8 m/s2) times velocity (m/s) divided by L:D. At an L:D of 50:1 (i.e. half of 100:1 goal) and speeds of 360 and 720 km/h; the thrust power requirements are 20 and 40 W/kg; the provided power is 10X that needed (>4X is a toned-down factor) to tow the platform. Since both weight and lift are evenly distributed, little structure is needed for flight; a structured shuttle aircraft can be used to take the platform to flight/altitude. The Towed Panel’s loading (mass per m2) is much lower than needed to attain the highest of L:D.
The claim is that a Towed Solar Platform will produce more than 4X the power needed to sustain its 24/7 flight when operated at reasonable conditions. The Towed Solar Platform is essentially a power supply that can be scaled to any power need.
Extreme Solar – In Towed Platform applications, Solar Power emerges as the low-cost power supply with costs projected to continue to decrease as technology improves. Of particular relevance is the stacking of photovoltaic layers in the higher-radiation environments above 60,000 ft.
The extended implications are that Towed Platforms emerge as such a low cost that nothing can complete, and that Towed Platforms become platforms for industrial fabrication and energy harvesting. Dedicated platforms could venture toward polar regions where 24/7 sun is available, leading to further reductions in solar power costs.
Example Towed Platform industries include hydrogen production, ammonia production, and atmospheric decarbonization. The first two only rely on water and nitrogen as feed stocks, both of which are available in the atmosphere. The last recovers carbon from the atmosphere and makes it available as a feed stock which greatly extends the range of chemicals that can be produced. Also, batteries could be charged and delivered and energy beams could deliver the energy to locations on Earth’s surface.
Additional Information – A starting point for additional information on these topics in Wikipedia under the topics of EROI and solar power.