An economic case for small scale solar-wind-augmented agriculture in exurban localities

Charles Thangaraj

doi:10.12688/f1000research.127506.1

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Method Article

An economic case for small scale solar-wind-augmented agriculture in exurban localities

[version 1; peer review: 1 not approved]

Charles Thangaraj

PUBLISHED 04 Apr 2023

Author details Author details

Department of Mathematics and Computer Science, University of St Thomas, Houston, TX, 77006, USA

Charles Thangaraj
Roles: Conceptualization, Investigation, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing

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This article is included in the Energy gateway.

This article is included in the Agriculture, Food and Nutrition gateway.

This article is included in the Enhancing water, energy, and food security in an era of increasing demand, degradation, depletion and climate change collection.

Abstract

Background: In addition to energy security and independence, infrastructure development, food production, agricultural resource management, and food security are increasingly becoming principal concerns for local and global affairs with public policy deliberations for economic, environmental, and new business initiatives. Furthermore, the COVID-19 pandemic has exposed the frailty of global supply chains and hastened the acceptance of remote work culture, motivating an urban exodus to exurbs and nearby rural communities. Globally, climate change has led to food scarcity and food supplies have been weakened by ongoing hostilities, commodity inflation, and political nationalism in banning exports. A potential solution for this is distributed small scale agriculture; which can increase food self-reliance, lower global demand, and can help achieve more equitable food availability.
Methods: This paper presents a framework for designing an automatable farm for exurban locations with new population growth, identifying and quantifying the bounds on additional long-term economic benefits on an assumptive framework based model. The framework is based on localized, small scale modified pumped storage and gravity fed irrigation, where solar and wind provide the energy requirement. An economic case is made by contrasting capital cost to estimated reduction in food wastage and revenue from excess energy generation.
Results: Using multidimensional US agricultural, energy, and economic data, a non-conventional economic analysis estimates that a 20% reduction in food wastage (due to use of exurban agriculture) over 10 years equates to USD $31.8 billion. This capital applied to exurban agriculture can be recovered in 10 years, plus setting up the infrastructure for long term agriculture and or local energy production for local consumption or export for additional revenue.
Conclusions: Exurban agriculture, located closer to demand centers, leads to reduction in overall agriculture energy needs, improving food security and wastage. Additional energy production can generate revenue or reduce local grid-energy demand.

Keywords

Agri-business, energy and demand offset, food security, exurb economics

Corresponding author: Charles Thangaraj

Competing interests: No competing interests were disclosed.

Grant information: The author(s) declared that no grants were involved in supporting this work.

Copyright: © 2023 Thangaraj C. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

How to cite: Thangaraj C. An economic case for small scale solar-wind-augmented agriculture in exurban localities [version 1; peer review: 1 not approved]. F1000Research 2023, 12:363 (https://doi.org/10.12688/f1000research.127506.1) First published: 04 Apr 2023, 12:363 (https://doi.org/10.12688/f1000research.127506.1) Latest published: 04 Apr 2023, 12:363 (https://doi.org/10.12688/f1000research.127506.1)

1. Introduction

Energy demand is generally considered to be relatively price inelastic. Which is to say that irrespective of price per unit of energy, the demand remains relatively unchanged; except during artificial periods of abnormal demand. On the supply side, intentional surplus production is generally counterproductive to profitability and intentional scarcity leads to loss of market share or markets all together. The delicate global supply-demand equilibrium is achieved via special economic and trade measures. Simply put, global energy trading is not a simple marketplace where open market economics can prevail. However, within a single political entity or partnership governed by common rules, open market principles and markets exist. Understanding this basic fact of our globalized economy is crucial to discussing energy usage and demand offset.

According to Webber (2019), in the US 10% of all energy consumed is for the entire food supply chain i.e., 1% in calorific content and 9% expended as energy for processing, storing, refrigeration, transportation, and cooking etc. Therefore, in 2021, the total energy consumption for food in the US was roughly 9.7 quadrillion British thermal units (Btu). Of which upwards of 40% or 3.9 quadrillion Btu is lost due to food waste according to Gunders (2012). To quantify that loss, it is equal to USD $21.6 Billion per year (3.9 quadrillion Btu * USD $5.54/1 Million Btu) in natural gas equivalent as of July 6, 2022. Geographically, food waste occurs closer to areas where consumption is also high. Consequently, dense urban and suburban areas have the highest food demand.

A 2020 study from Tufts University (Kurtz et al., 2020) found that local food production is feasible and a potential solution for food availability optimization. However, the study also found that not all urban regions are suitable for local food production. While the study’s conclusions are based on sound data, it is also based on traditional farming techniques and land use practices. This paper, however, explores the idea of mixed use of exurban lands i.e., both for agriculture and non-agricultural use. Also, the focus is on small scale farms that can be well integrated into exurban or even suburban landscapes, thus bringing the farm closer to the urban centers and reducing the farm-to-fork energy consumption and food waste. In addition to energy reduction due to proximity (lower transportation needs), the idea of further reducing energy demand by powering farm operations through wind and solar augmentation, is explored, analyzed, and justified.

The remained of this paper is organized in the following sections. The basic structure, dimensions, and features of the smallest unit field for the proposed exurban farm is described in Section 2. Section 3 discusses the capital needs, operational aspects, energy storage and offsetting capabilities of a unit farm; followed by comments and concluding remarks in Section 4.

2. Proposed design

The proposed exurban farm is described and illustrated in this section. The basic unit of exurban agricultural parcel is defined as a unit field (UF) and described in Section.

Each UF is served by two towers and three tanks for irrigation and other operations. The tower design and tank layout are presented in Sections 2.2 and 2.3, respectively. Sections 2.4, 2.5, 2.6, and 2.7, presents wind and solar energy augmentation, demand offsetting, space utilization improvements, and local food benefit aspects, respectively.

2.1. Land parceling

Figure 1A shows the parameterized (variable x) dimensions for a UF. Where T1 and T2 are the two towers located along the center line of the UF. Let us consider the following two cases for the UF i.e., x is 50 and 100 meters.

(Equation 1a)

x = 50 m = \Rightarrow {UF}_{area} = 5000 m^{2} or \approx 1.25 acres

(Equation 1b)

x = 100 m = \Rightarrow {UF}_{area} = 20000 m^{2} or \approx 5 acres

Figure 1. Proposed land parceling scheme of a unit field (UF) where T1 and T2 are the two towers located along the center line of the UF.

(A) A unit field (UF) with parameterized dimensions.

(B) A unit field (UF) with regions of influence shown.

The smallest average farm size in any US state according to the United States Department of Agriculture Farm Labor Survey (USDA FLS, 2022) is 55 acres. Hence, the case described by Equation 1B (i.e., when x = 100) for a UF area of ≈5 acres, offers a reasonable multiple (10-11) to represent the smallest average US farm size. Therefore, this case will be considered as the standard UF dimensions for analysis throughout the rest of this work. Area of influence is defined as the region of a UF an individual tower is expected to serve, this is illustrated in Figure 1B. If the land available is larger than a single UF, then multiple UFs can be fit into the available land as shown in Figure 2 for analysis purposes.

Figure 2. A random field containing multiple unit fields (UFs) with varying orientations.

2.2. Tower design

There are two identical towers per UF. These towers are placed on circular concrete pads with a radius of (x/20). Each tower will have an above ground steel structure that will be angled to support a water storage tank. The tower base will consist of an underground concrete structure with built in water tank and contains usable space for additional utilities, if desired. The conceptual top view and side view of such a tower is shown (not to scale) in Figures 3 and 4, respectively.

Figure 3. Top view of a unit field (UF) tower design.

Figure 4. Side view of a unit field (UF) tower design.

The two tanks will play a significant role in irrigating the influence area, provide drinkable water to any life stock and for use as a pumped storage energy harvesting/demand offset system (more in Section 3). The steel structure also can serve as mounting frame for:

• anchoring and securing any shading applications if livestock are raised along with food crops
• water faucets for life stock drinking solutions
• irrigation sprinklers or for drip irrigation distribution plumbing
• solar panels and or wind generators

2.3. Storage tank design

In every UF there are two towers; T1 and T2. At tower T1 there are two tanks, TT1 as the top tank at T1 and BT1 as the bottom tank at T1. Similarly, at tower T2, TT2 is the top tank at T2 and BT2 is the bottom tank at T2. In addition to these, there is a deep buried common tank (CTk) which will be located centrally to both the towers (T1 and T2). Figures 5 and 6 show the top and side views of the tank locations, respectively. Figure 6 also shows the water head definitions used in potential energy offset capability calculations done in Section 3.

Figure 5. Top view of a unit field (UF) tank locations.

Figure 6. Side view of a unit field’s (UF’s) tank locations.

2.4. Wind solar augmentation

The towers can be equipped with wind and solar power generation systems to en- able grid energy offsetting. Here the focus is on using multiple relatively inexpensive vertical or horizontal axis wind turbines (VAWT or HAWT) along with similarly in- expensive flexible mount solar photovoltaic panels (PV). Using multiple inexpensive units can improve serviceability and improve long term reliability, however other components such as power conditioners can become more complex and thus expensive. Consequently, achieving a balanced mix of sub-units will be critical. Also, a critical concern for using wind generation, particularly in suburban or exurban locations is its impact fatality of wild and specifically avian life. A simple solution is to use a mesh surround or shroud to shield the spinning parts from direct bird or wildlife hits, as illustrated in Figures 7 and 8.

Figure 7. Front and top view of a covered horizontal axis wind turbine (HAWT).

Figure 8. Front and top view of a covered vertical axis wind turbine (VAWT).

Peak efficiency and maximizing energy generation are not the key motivators in this application, rather, a lowering capital and maintenance costs, increasing replace-ability and serviceability, and reducing downtime cost of the subsystems are paramount. Therefore, any losses that may result as a consequence of including wild-life protection features should be considered reasonable and acceptable. Figure 9A shows the top view of an UF tower where two sets of wind generators are used to capture winds in both perpendicular (north-south and east-west) directions. Winds at any angles can be captured by a VAWT, however when a HAWT is desired (due to simplicity) it should be mounted on a swivel to capture winds in any directions. When photovoltaic panels are included, they can be easily mounted on the top surface of the top tank, as shown in Figure 9B.

Figure 9. Possible energy generator schemes at each unit field (UF) tower.

(a) Top view of a tower showing wind generators and wind capture directions.

(b) Top view of a tower showing wind generators, wind capture directions and photovoltaic panels.

2.5. Energy demand offsetting

Energy demand offsetting can be achieved with in an UF when the energy requirements for operations within the UF is met partially or fully with energy that has been generated or (previously generated) and stored within the UF for later use. The primary and key feature the UF based farming proposes is the use of simple water storage tanks to store the excess energy production. The proposed scheme is therefore a modified pumped (potential energy) energy storage scheme where the energy generated is minimally conditioned and used directly to power pumps to pump water from the deep common CTk to each of the bottom tanks (BT1 and BT2). Then once they are full, it will continue to pump from the bottom tanks to the top tanks (TT1 and TT2) respectively. When the top tanks are full, gravity assist is used to irrigate, supply drinking water, or for other utility purposes. A small battery backup can be included for remote operation communication system, but batteries are not used for bulk energy storage.

The proposed scheme has the following distinct advantages;

• Irrigation is a normal and necessary farm operation powered entirely by local energy generation.
• Drinking use, particularly filtering, purification, and or heating/cooling is also a normal and necessary farm operation powered by local energy generation.
• Even without wind or solar generators, when connected to the electric grid, UF tanks can serve as one way distributed grid storage to buffer any generation surplus (constant load for solar and wind producers) and help regulate the grid metrics. There is no need to idle generations facilities or use dump loads to dissipate generation surplus, which has both short and long term maintenance and economic benefits.
• Unlike battery storage, there is no cyclic storage capacity loss. That is, the tanks can be filled and emptied infinitely without any loss of capacity, multiple times a day.
• Unlike battery storage, operating temperature range, cold and heat tolerance is much higher.
• Unlike battery storage, there are no toxic or hazardous chemicals involved.
• Unlike battery storage, replacement cost and end of life cost are minimal.
• Unlike battery storage, life cycle cost, environmental impact and carbon footprint for the entire system during construction, operation and decommissioning are smaller.

2.6. Improving space utilization

The proposed UF based approach to farming is mainly focused on exurban cultivation, although it can be applied to suburban and even urban agriculture (UA) under the right conditions such as land availability and zoning laws permitting. At the present, UA has gained support among non-governmental organizations (NGOs), community developers, urban planners, and politicians, as several examples both in formal academic and informal online literature can be found. Some examples are (Precker, 2021; Siegner et al., 2018; UGC, 2017; McCauley, 2021; Sustainability, 2019). However exurban agriculture (EA) concept as its own entity is not well developed and it is lumped together with UA.

Notwithstanding the minutia, an UF based approach to EA will improve land utilization by;

• Encouraging mixed use of lands for both traditional farming and energy offsetting and load stabilization applications.
• Reclaiming contaminated land or land not suitable for agriculture, for food cultivation using more (than traditional) energy and labor intensive green house/hydroponics based techniques where the farm is mostly or fully energy self-sufficient.
• Repurposing off-grid wet and coastal lands to become energy self-reliant aqua- phonics farms for oysters, seafood and fish.

2.7. Local food and economic benefits

A food desert (FD) is defined as a neighborhood that lacks supermarkets, grocery stores, or other local food outlets offering healthy and affordable options (Dutko, Ploeg, and Farrigan, 2012). Criteria for designating food deserts include low-income and low-access census tracts, where food establishments are more than one urban or 10 rural miles away. Figure 10 shows the areas in the US designated as food deserts using this criteria (USDA FARA, 2010). When inspecting Figure 10, it is clear that FD (Rhone, Williams and Dicken 2022) are spread through the US. Large area FD in the southwest and western regions also coincide with low population density regions but are sufficiently close to densely populated urban regions. This means there is an abundance of cultivatable exurban land available and is underutilized for food production. According to Kaili (2021) economic opportunity zones (OZs) are located throughout the US, however there is only a 30% overlap between OZs and FDs regions. This means there are federally administered programs that can assist in setting up new businesses in these overlapped regions. For example, a newly setup downtown food co-op or a community restaurant can source all of their produce from a just-outside-the-OZ exurban farms. Such partnership will help address both food insecurity through local farming and economic insecurity through local jobs creation. Sustained access to nutritious food would likely result in better health outcomes (Gundersen and Ziliak, 2015), high school completion rates and regional economic outlook (USHHS, 2030).

Figure 10. US regions identified as food deserts in 2019.

This figure has been reproduced with permission from (USDA FARA, 2010).

3. Capital, operation, and energy analysis

Estimating the capital needed to set up a new farm with or without using the proposed UF approach, is generally considered difficult. Mainly due to opportunity cost for the capital used towards farm setup and the expected return from the farm both cannot be predicted accurately and the price for land varies based on location. However, we can attempt to quantify the present worth of the cost of energy saved using the proposed UF design approach over a period of time. This amount would serve as a baseline for setting the boundaries for investment in long term infrastructure i.e., setting up an UF.

As land is not considered a depreciating asset, we will not consider the cost of land in capital investment calculations. All the rest of the UF equipment such as towers, tanks, wind, solar generators and power electronic systems, irrigation systems, pumps, and motors are considered to be 10 year depreciating asset (as classified by the US tax agency, the internal revenue service - IRS) and so the calculations will be done over a 10-year period. Interest rate and inflation rate will be fixed for the entire duration and the calculations done on a monthly basis. Fixed interest and inflation rates are used to simplify the calculations, and it is a standard technique in economic analysis. Monthly time interval is chosen as most consumer and or small business (small farms) level economic activity is represented in monthly time frames (rents, loan payments etc.). The calculations are shown below in steps #1 through #6.

Step #1: Assumptions

(Equation 2a)

Number of periods (p) = 10 \times 12 = 120 months

(Equation 2b)

Cost of capital : interest rate (i) = 6 %

(Equation 2c)

Rate of inflation (f) = 2 %

Water head from Figure 6.

(Equation 2d)

h 1 = 8, h 2 = 10 = \Rightarrow h = 18 meters

Step #2: Estimating irrigation water usage and tank sizing

According to the UDSA’s 2017 Census of agriculture, total irrigated acreage and water use per acre are 55.9 million acres and 1.5 acre-foot, respectively (USDA AgCensus, 2019). Acre-foot is the amount of water required to cover one acre to a depth of one foot. This is equivalent to 43,560 cubic feet or 325,851 gallons of water for one acre of land. In Figure 11, using data from Chiarelli et al., (2020), the relative water usage per acre of cultivated land is shown. It can be inferred that crops intended for food relatively consumed close to the average. Thus, average water usage is assumed for calculations.

Figure 11. Global water usage per acre by crop type (Chiarelli et al., 2020).

Total available area in a UF is;

(Equation 3)

A_{uf tot} = 100 \times 200 = 20000 m 2

Total cultivatable area in a UF is, A_{uf tot} - (area lost to tower concrete pads) here X = 10 m.

(Equation 4)

A_{uf cul} = A_{uf tot} - (2 \times (π \times {(X / 10)}^{2})) = 19842.9 m^{2} or 4.9 acres

Total water consumption for an UF will be,

(Equation 5)

W_{uf tot} = 4.9 \times 1.5 = 7.3 5^{'} acre - f t^{'} or 2395004 gal

If the irrigation is done over a period of 300 days/year, the water consumption per day for an UF is;

(Equation 6)

W_{uf daily} = 2395004 / 300 = 7984 gal / day or 30.2 m^{3} / day

The tower tanks (TT1, TT2, BT1, and BT2) should at minimum have a radius of 2.5 meters and height of one meter, for a cylindrical tank shape. A wider tank shape will be beneficial for stability purposes and also for providing surface are for the photovoltaic panels. Therefore, the tank volume with these dimensions is;

(Equation 7)

V {ol}_{tt tb} = π \times (2 . 5^{2}) \times 1 = 19.63 m^{3}

When the top two (TT1 and TT2) tanks are full the entire UF can be irrigated and then the excess can be used for life stock drinking, cleaning, or for other utilities. The tank dimensions are well within the radius of the concrete pad size for the towers. The total overhead storage capacity is;

(Equation 8)

V {ol}_{tt tot} = 2 \times 19.63 = 39.26 m^{3}

The buried common tank (CTk) should at minimum have a radius of 3.6 meter and a height of one meter.

(Equation 9)

V {ol}_{CT k} = π \times (3 . 6^{2}) \times 1 = 40.72 m^{3}

Step #3: Estimating potential energy storage capacity

The total water head available was shown in Figure 6 and the values assumed for h1 and h2 in Equation 2d. Energy needed to raise 39.26 m3 of water from the common tank CTk to the two bottom tanks BT1 and BT2 are;

(Equation 10)

{En}_{CT k to BT} = m \times g \times h = 39260 \times 9.80665 \times 10 = 1070 Wh or \approx 1 kWh

where; m is the mass of water in kilograms, g is the acceleration due to gravity in m/s² and h is the height water is raised in meters. Similarly, energy needed to raise 39.26 m3 of water from the bottom to the top tanks is;

(Equation 11)

{En}_{BT to T T} = m \times g \times h = 39260 \times 9.80665 \times 8 = 856 Wh or \approx 0.86 kWh

Total energy storage capacity assuming an 80% pump efficient (η = 0.8) is;

(Equation 12)

{En}_{T ot} = \frac{1}{η} \times ({EN}_{BT to TT} + {En}_{CTk to BT}) = 2408 Wh or \approx 2.4 Wh

Step #4: Estimating size and cost of wind and solar generators

The total energy needed to irrigate a fully gravity fed UF a day is 2.4 kWh (Equation 12). If drip irrigation or pressurized irrigation are used, then the energy needed will be higher. Let us assume an irrigation overhead γ of 25%, and power electronics (for wind and solar energy conditioners and converters) efficiency η_pe of 90%, these are reasonable values sources from several manufacturer’s product documentation.

(Equation 13)

{En}_{gen target} = 2408 \times γ \times \frac{1}{η_{pe}} = 535 Wh or \approx 0.54 k Wh

Let us assume that pressurized irrigation is used and the duration of irrigation is one hour i.e., the tanks are already full and only the irrigation pumps are operating. This means that the solar and wind generators have to generate at a minimum 535 W of power, combined. Also, the time taken to fill the tanks can be several hours (but must be done within 23 hours). Therefore, with a generating capacity of 535 W, the tanks can be filled in 2.4 kWh/0.54 kW = 4.5 hours. The tank can be filled and ready to irrigate every single day if needed, completely free of any demand on the grid. Therefore, the total energy to irrigate an UF with pressurized irrigation is;

(Equation 14)

{En}_{irrigation daily} = 2408 \times (1 + γ) \times \frac{1}{η_{pe}} = 3210 Wh or \approx 3.21 kWh

Step #5: Estimating grid energy demand offset

If an UF is irrigated for 300 days a year, then the total energy demand on the grid would be;

(Equation 15)

{En}_{T ot annual} = 300 \times 3210 = 963200 Wh or \approx 963.2 kWh

At USD $0.15/kWh this means a total annual energy cost for an UF of;

(Equation 16)

{En}_{cost annual} = 963.2 \times 0.15 = $ 144.5

(Equation 17)

{En}_{cost annual peracre} = 144.5 / 4.9 = 29.5 $ / acre

According to UDSA’s 2017 Census of agriculture, (USDA AgCensus, 2019), energy cost per farm on average was USD $15,289 for a total of 231,474 farms irrigating a total of 55.9 million acres.

(Equation 18)

{En}_{USDAcost annual peracre} = 15289 \div \frac{55, 900, 000}{231474} = 63.3 $ / acre

This higher USDA figure is due to energy + transmission costs typically assessed by electric utilities and it included pumping from wells and pressurized irrigation systems. It is consistent with the estimates presented in this paper.

Step #6: Estimating capital for setting up an UF

Using the estimate from USDA (Equation 18) and assuming the usage if uniform over the year, the monthly cost of energy for a UF is;

(Equation 19)

{En}_{USDAcost monthly perUF} = (63.3 \times 4.9) \div 12 = $ 25.85

Assuming the cost of electricity keeps with inflation and less than the interest rate, the present value of the cost of grid power can be calculated as;

(Equation 20)

{PV}_{grid power} = \frac{A_{1}}{(i - f)} \times [1 - {(\frac{1 + f}{1 + i})}^{p}]

where; i, f, p are defined in Equation 2 and A₁ is En_{USDAcost monthly perUF} from Equation 19. Substituting the correct values results in;

(Equation 21)

{PV}_{grid power} = $ 2549.8

For an UF or an UF sized farm, irrespective of the cost and source of energy used to operate it;

• the cost of land is fixed
• the cost of water for irrigation and farm use is fixed
• the cost (some not all) of water storage tank(s) is fixed
• the cost of irrigation sub-systems are all fixed

Thus, the equivalent present worth of the cost of purchasing grid power for a 10-year period, is sufficient (and greater than) the immediate cost of setting up wind and or solar generation systems. Even at twice the required generation capacity i.e., 1 kW (≈ 2× Equation 13), the cost of generating equipment needed is well under USD $2,500, at the time of writing this paper.

However, the cost of materials and installation of the tanks, support structures, pumps, and concrete, should also be considered. Here the analysis is more nuanced. These structures have multiple purposes, they can be used for irrigation, for shading, as open barns, watering areas, and nursery etc. Therefore, the added cost of installing these structures should be considered as marginal or additional expenses to standard farm setup costs, which is difficult to estimate without detailed knowledge of the type and location of the standard structures.

To continue with the capital analysis, an unconventional approach would be to consider the cost of energy lost due to food wastage. Energy loss was estimated in Section 1 to be equal to USD $21.6 Billion per year in natural gas energy cost equivalent. Now, assume a portion of this loss is reduced due to local farming using UFs, let this loss reduction be 20%. That would imply an additional capital (monies not spent) availability of roughly USD $4.32 Billion in natural gas energy cost equivalent per year. The present value of total capital availability using the interest rate from Equation 2b, over a 10-year period is equivalent to USD $ 31.8 Billion. If this capital is made available as annualized capital infusion, loans or grants via some form of governmental program. For example, an initiative to promote 1,000,000 new exurban UF farms to solve food insecurity and reduce wastage, where each farm gets a voucher for USD $31,800 to be used and redeemed as capital investments are made within the 10-year period. Such an infusion of capital can completely reshape the national food landscape, realizing its many hidden health and economic benefits.

3.1. Additional local economic benefit

The calculation presented in Section 3 mainly focuses on irrigation to estimate tank sizing and making the economic case for solar wind augmentation at the smallest minimum dimensions, generation and storage capacities. However as mentioned earlier, infrastructure such as towers, concrete pads, irrigation lines etc. are fixed cost capital assets, irrespective of installed generation capabilities. Therefore, an UF or a collective of neighboring UFs can realize additional revenue by;

• Installing additional and operating photovoltaic panels and or wind generators to produce excess energy that can be directly exported to the grid operator for additional revenue
• Installing additional photovoltaic panels and or wind generators to produce excess energy that can be used to service loads with in the UF(s) such as living accommodations, grid backed refrigeration units, sterilization and food processing equipment etc; reducing overall grid demand, lowering operating costs and improving revenue of agri-businesses
• Leasing the tank surface areas for third party virtual net-metering energy companies
• Leasing the tank top for 5G network installations
• Operating a private EV charging stations powered (partially or fully) by on premises wind and solar generation

All of the above mentioned activities inherently involve additional labor requirements for maintenance, operation and repair services. Thus, directly improving the farm economics and indirectly improving derived demand and local economic activity.

3.2. Enabling hydrogen economy and local production opportunities

In 2021, 28% of the total energy used was for transportation of people and goods according to the U.S. Energy Information Administration (USEIA, 2022). Of the total transportation energy mix, biofuels accounted for a mere 5%. Which further breaks down as ethanol’s share around 4%; biodiesel, renewable diesel, and other biofuels making up the remaining 1%. Therefore, transport fuels are a major part of the total energy use mix and any reduction in the demand for fossil fuel derived transportation fuels will have a positive environmental and economic benefit.

The US Department of Energy (DOE), lists hydrogen H₂ as an excellent choice for use as transportation fuel (USDOE H2, 2022). H₂ has roughly 2.8 times the energy dense per kg weight of regular gasoline. However, due to its low volumetric efficiency (energy contained per unit volume), a centralized production model utilizing large storage containers (at very high pressure) and long distance transportation and distribution to end users (which is energy intensive); at the moment seriously limits the use of H₂ as a mass transportation fuel.

At the same time, H₂ is an excellent candidate fuel when its transportation and distribution is removed from the supply chain. This means H₂ must be produced close to where it is needed and consumed. That is, H₂ must be produced where it is needed almost on demand. Consequently, the US DOE recognizes the following as feasible pathways for local green H₂ production (USDOE,2022).

• H₂ from Electrolysis: by splitting water into hydrogen and oxygen. Where the electricity is produced by excess solar or wind generation.
• H₂ from Renewable Liquid Reforming: by reacting a renewable liquid fuel, such as ethanol, with high-temperature steam to produce hydrogen gas.
• H₂ from Biomass Fermentation: by converting biomass into sugar rich feedstock for fermentation to produce H₂ gas.
• H₂ from Biomass Gasification: by combining biomass with high-temperature steam and oxygen in a pressurized gasifier to generate H₂ gas.

Of these techniques, electrolysis is the most commonly used for low-volume H₂ production. Making this pathway the most suitable for small scale production such as in the case of an UF. Also, this technique is relatively simple with least raw materials and equipment needed. However, it is more energy intensive and utilizes only one aspect of solar radiation i.e., photon intensity for H₂ production. A commercial example of such an electrolysis based H₂ production turn-key system is found here, (MRE LLC, 2022). Academically, a 2020 study quantified the benefits of using both solar and solar-heat for H₂ production and found that the addition of heat improves the overall production volume and system efficiency (Gul and Akyuz, 2020).

Renewable liquid reforming can also utilize energy from wind, solar photon intensity, and solar thermal energy to generate the electricity and heat needed in areas where alcohol production is readily available. While ethanol can be used directly as a transportation fuel, it had a limited shelf life due to its hydrophilic nature. Additional processing is required to extend its shelf life. Conversion of feedstock alcohol to H₂ not only extends the shelf life and also improves energy density (per kg or per gallon) for use as a transportation fuel. The specific energy (energy per unit mass) of ethanol is approx. 25 MJ/kg, regular gasoline is approx. 46 MJ/kg and H₂ is approx. 130 MJ/kg.

Electrolysis and liquid reforming pathways both do not directly use or consume low-grade agricultural waste or biomass. Food waste is a major problem both for energy loss during production and transport phases, and during its final or post-consumption phase in terms of landfill use, decomposition and methane (landfill gas) escape into the atmosphere. Food waste can be considered biomass and it can be separated from landfill waste and used as feedstock for H₂ production. Doing so further reduces overall energy wastage in the food cycle, in addition to the reduction realized through local farming.

Therefore, up-cycling local food refuse, waste, farm refuse and byproduct (collectively biomass) and using it as the feedstock for biomass fermentation (Satinover et al., 2020) or gasification (Meramo-Hurtado et al., 2020) processes is an excellent way to minimize waste and capture otherwise wasted latent energy as useful transportation fuel. Furthermore, these processes can use the energy generated from wind, solar photon intensity, and solar thermal for H₂ production. The produced H₂ can then be used as transport fuel locally. Or a collective of local farms can join together to become an off-grid H₂ producing center capable of satisfying and off-setting some regional transportation fuel needs. Such centers would greatly be benefiting their local environment and economy.

An example techno-analysis for a small to medium scale farm is presented in (Janke et al., 2020). They show that sharing production among farms can reduce H₂ production costs by up to 28% and when local delivery vehicles were modified to run on H₂, overall cost further reduced by 35%. Strengthening the case for local H₂ production and consumption in agriculture, similar to the UF based approach proposed in this paper.

Biomass fermentation/digestion pathway to H₂ production can be further improved by the use of Microbial electrolysis cell (MEC) technology, where a selected electrochemically active bacteria oxidize organic matter to generate CO2, electrons and protons. MEC require external energy in the form of an electric current as an input to force ion movement in solution to produce H₂. This current can be supplied by solar or wind energy generators making the process more energy neutral. The main challenges to use MEC technology are the reactor design and the need for membranes. Although, membrane free designs have been developed and are being tested currently; with large scale commercialization is still a few years away (Kadier et al., 2016; Dange et al., 2021). However, small scale reactors have been shown to be effective and can be readily incorporated into a distributed small scale farms for H₂ production. Therefore, multiple successful demonstration of distributed small scale adoptions can bring about quicker large scale commercial adoption. Moreover, a favorable lending scheme or governmental assistance would also encourage commercial large scale adoption of such technologies earlier than when market economics could meaningfully support such adoptions.

Potential future work

This paper presented a design methodology and framework for approaching ex- urban agriculture. The reader would notice that the proposed approach has not been implemented or tested. Doing so would require capital that the author does not currently possess. Moreover, local business and governmental support is also vitally needed. In order to obtain these and to begin the next phase of this research i.e., to setup and test the proposed approach, a publicly read, peer reviewed, and well flushed out proposal is essential. This is the desired fundamental outcome for the phase one theoretical work presented in this paper. The feedback obtained will guide the direction of subsequent work and to establish research partnerships, particularly in developing regions with acute food insecurity.

4. Conclusion

Energy and food security are increasingly becoming principal concerns which can threaten economic and national security. With the COVID-19 pandemic exposing existing food supply chain weaknesses, pandemic driven exurban population growth, and ever increasing energy and food demands, local urban, suburban, and exurban agriculture have gained importance as a potential solution to both reducing grid energy demand and servicing local food needs via local production. In this paper, a modular land parcel i.e., unit field, based approach to exurban agriculture was presented. The unit field included a modified pumped storage design to reduce grid energy demand for standard farm operations by wind and solar augmentation.

The saving in energy costs over a 10-year period was shown to be economically equivalent to capital investment in solar and wind generation systems, even at minimal system size. When considering the cost of energy savings due to reduction in food waste over 10 years, it was determined that one million new farms could receive capital infusion of USD $31,800 to cover initial setup costs. Furthermore, additional avenues for revenue generation with and without new investments and capable of being operationalized in a short time, were also identified. Looking further into the future where new and renewable transportation fuels will be needed, several pathways which utilize the excess energy produced by the unit fields and the biomass generated locally to produce H₂ were also identified. The produced H₂, when used as transportation fuel, locally generates additional benefit both to the producers and the local energy and labor markets.

Data availability

All data underlying the results are available as part of the article and no additional source data are required.

References

Chiarelli DD, Passera C, Rosa L, et al.: Global Gridded Dataset of Crop-specific Green and Blue Water Requirements.2020. Publisher Full Text
Dange P, Pandit S, Jadhav D, et al.: Recent Developments in Microbial Electrolysis Cell-Based Biohydrogen Production Utilizing Wastewater as a Feedstock. Sustainability. 2021; 13(16): 8796. Publisher Full Text
Dutko P, Ploeg MV, Farrigan T: Characteristics and Influential Factors of Food Deserts. United States Department of Agriculture, Economic Research Service; 2012. Report Number 140.
Gul M, Akyuz E: Hydrogen Generation from a Small-Scale Solar Photovoltaic Thermal (PV/T) Electrolyzer System: Numerical Model and Experimental Verification. MDPI Energies; 2020. Reference Source
Gunders D: Wasted: How America Is Losing Up to 40 Percent of Its Food from Farm to Fork to Landfill. Natural Resources Defense Council; 2012. Reference Source
Gundersen C, Ziliak JP: Food Insecurity And Health Outcomes. Health Aff. 2015; 34(11). Publisher Full Text
Healthy People: U.S. Department of Health and Human Services, Office of Disease Prevention and Health Promotion.2030. Reference Source
Janke L, McDonah S, Weinrich S, et al.: Techno-Economic Assessment of Demand-Driven Small-Scale Green Hy- drogen Production for Low Carbon Agriculture in Sweden. Front. Energy Res. 2020. Publisher Full Text
Kadier A, Simayi Y, Abdeshahian P, et al.: A comprehensive review of microbial electrolysis cells (MEC) reactor designs and configurations for sustainable hydrogen gas production. Alex. Eng. J. 2016. Publisher Full Text
Kurtz JE, Woodbury PB, Ahmed ZU, et al.: Mapping U.S. food system localization potential: The impact of diet on foodsheds. Environmental Science & Technology; 2020. Publisher Full Text
Kaili L: OZs Could Be The Place-Based Solution We Need To Tackle USDA Food Deserts. Sorenson Impact Center, University of Utah; 2021. Reference Source
Meramo-Hurtado SI, Puello P, Cabarcas A: Pro- cess Analysis of Hydrogen Production via Biomass Gasification under Computer- Aided Safety and Environmental Assessments. ACS Omega. 2020; 5(31): 19667–19681. PubMed Abstract | Publisher Full Text | Free Full Text
McCauley DJ: Urban Agriculture Combats Food Insecurity, Builds Community. Reference Source
Millennium Reign Energy LLC: Reference Source
Office of Energy Efficiency & Renewable Energy: Hydrogen Production. US Department Of Energy; 2022. Reference Source
Precker M: Food insecurity’s long-term health consequences. Reference Source
Rhone A, Williams R, Dicken C: Low-Income and Low-Foodstore-Access Census Tracts, 2015–19, EIB-236. U.S. Department of Agriculture, Economic Research Service; June 2022. Reference Source
Satinover SJ, Rodriguez M, Campa MF, et al.: Performance and community structure dynamics of microbial electrolysis cells operated on multiple complex feedstocks. Biotechnol. Biofuels. 2020; 13: 169. Publisher Full Text
Siegner A, Sowerwine J, Acey C: Does Urban Agriculture Improve Food Security? Examining the Nexus of Food Access and Distribution of Urban Produced Foods in the United States: A Systematic Review. Sustainability. 2018; 10(9): 2988. Publisher Full Text
USDA: FARA. Reference Source
USDA: Farms and Land in Farms 2021 Summary. Reference Source
USDA: Census of Agriculture. Reference Source
USEIA: Energy Explained. Reference Source
Hydrogen and Fuel Cell Technologies Office: DOE National Clean Hydrogen Strategy and Roadmap. Reference Source
Urban Growers Collective: Reference Source
Warshawsky D, Vos R: Governing at Scale: Successful Local Food Initiatives in the World’s Cities. Sustainability. 2019; 11(24): 7226. Publisher Full Text
Webber ME: Power Trip: The Story of Energy. Basic Books; 2019. ISBN-13: 978-1541644397.

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Department of Mathematics and Computer Science, University of St Thomas, Houston, TX, 77006, USA

Charles Thangaraj
Roles: Conceptualization, Investigation, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing

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No competing interests were disclosed.

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The author(s) declared that no grants were involved in supporting this work.

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Thangaraj C. An economic case for small scale solar-wind-augmented agriculture in exurban localities [version 1; peer review: 1 not approved]. F1000Research 2023, 12:363 (https://doi.org/10.12688/f1000research.127506.1)

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Reviewer Report 08 Sep 2023

Ogheneruona Diemuodeke, University of Port Harcourt, Choba, Rivers, Nigeria

Not Approved

https://doi.org/10.5256/f1000research.140024.r194318

The manuscript is on an important research area, which focuses on food availability and reduction in energy intensity of agrifood production. However, the part of content seems to me like craftwork. The manuscript could be improved by considering the following: ... Continue reading

The manuscript is on an important research area, which focuses on food availability and reduction in energy intensity of agrifood production. However, the part of content seems to me like craftwork. The manuscript could be improved by considering the following:

The author could free space for the engineering design of all the equipment considered in the study, namely wind turbine, solar PV, power electronics etc.
Present the wind and solar resource assessments of the studied area. The author could use literature to support the resource availability.
The water needs analysis of the studied area to support the irrigation system.
Is UF_area different from A_{uf tot}?
Regarding Equation 4, is the area covered by the buried tank considered a cultivatable area?
Regarding Equation 5, where does 1.5 come from? If it is from water needs analysis, it should be explicitly presented.
A potential leader would like to know the function of the buried tank. This should be presented explicitly along the justification in terms of energy storage and irrigation methods.
Equation 10 should clearly show the conversion factor from Joule to Watt-hour.
Equation 12, 2.4 Wh should read 2.4 kWh.
One wonders how 535 Wh suddenly became 535 W (approx. 0.54 kW). The author should be reminded that energy (Wh) is different from power (W).
The Section for hydrogen looks abrupt and does not connect with the research question, including the problem statement, of the study. Why do we need the hydrogen Section?

In general, the manuscript lacks the focus and rigour of a scientific paper. In addition, there were cases of measuring the volume of air with a syringe. The author could extend the work by computing emission reduction via the reduction in energy density of the agrifood.

Is the rationale for developing the new method (or application) clearly explained?

Partly
Is the description of the method technically sound?

No
Are sufficient details provided to allow replication of the method development and its use by others?

No
If any results are presented, are all the source data underlying the results available to ensure full reproducibility?

No
Are the conclusions about the method and its performance adequately supported by the findings presented in the article?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Renewable energy, climate change mitigation technologies and deep decarbonisation.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

CITE

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Ogheneruona Diemuodeke, University of Port Harcourt, Choba, Nigeria

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Reviewer Report

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08 Sep 2023 | for Version 1

Ogheneruona Diemuodeke, University of Port Harcourt, Choba, Rivers, Nigeria

8 Views Cite this report Responses(0)

Not Approved

The manuscript is on an important research area, which focuses on food availability and reduction in energy intensity of agrifood production. However, the part of content seems to me like craftwork. The manuscript could be improved by considering the following:

The author could free space for the engineering design of all the equipment considered in the study, namely wind turbine, solar PV, power electronics etc.
Present the wind and solar resource assessments of the studied area. The author could use literature to support the resource availability.
The water needs analysis of the studied area to support the irrigation system.
Is UF_area different from A_{uf tot}?
Regarding Equation 4, is the area covered by the buried tank considered a cultivatable area?
Regarding Equation 5, where does 1.5 come from? If it is from water needs analysis, it should be explicitly presented.
A potential leader would like to know the function of the buried tank. This should be presented explicitly along the justification in terms of energy storage and irrigation methods.
Equation 10 should clearly show the conversion factor from Joule to Watt-hour.
Equation 12, 2.4 Wh should read 2.4 kWh.
One wonders how 535 Wh suddenly became 535 W (approx. 0.54 kW). The author should be reminded that energy (Wh) is different from power (W).
The Section for hydrogen looks abrupt and does not connect with the research question, including the problem statement, of the study. Why do we need the hydrogen Section?

In general, the manuscript lacks the focus and rigour of a scientific paper. In addition, there were cases of measuring the volume of air with a syringe. The author could extend the work by computing emission reduction via the reduction in energy density of the agrifood.

Is the rationale for developing the new method (or application) clearly explained?

Partly
Is the description of the method technically sound?

No
Are sufficient details provided to allow replication of the method development and its use by others?

No
If any results are presented, are all the source data underlying the results available to ensure full reproducibility?

No
Are the conclusions about the method and its performance adequately supported by the findings presented in the article?

Partly

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Renewable energy, climate change mitigation technologies and deep decarbonisation.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

Respond to this report

Responses (0)

[1] Chiarelli DD, Passera C, Rosa L, et al.: Global Gridded Dataset of Crop-specific Green and Blue Water Requirements.2020. Publisher Full Text

[2] Dange P, Pandit S, Jadhav D, et al.: Recent Developments in Microbial Electrolysis Cell-Based Biohydrogen Production Utilizing Wastewater as a Feedstock. Sustainability. 2021; 13(16): 8796. Publisher Full Text

[3] Dutko P, Ploeg MV, Farrigan T: Characteristics and Influential Factors of Food Deserts. United States Department of Agriculture, Economic Research Service; 2012. Report Number 140.

[4] Gul M, Akyuz E: Hydrogen Generation from a Small-Scale Solar Photovoltaic Thermal (PV/T) Electrolyzer System: Numerical Model and Experimental Verification. MDPI Energies; 2020. Reference Source

[5] Gunders D: Wasted: How America Is Losing Up to 40 Percent of Its Food from Farm to Fork to Landfill. Natural Resources Defense Council; 2012. Reference Source

[6] Gundersen C, Ziliak JP: Food Insecurity And Health Outcomes. Health Aff. 2015; 34(11). Publisher Full Text

[7] Healthy People: U.S. Department of Health and Human Services, Office of Disease Prevention and Health Promotion.2030. Reference Source

[8] Janke L, McDonah S, Weinrich S, et al.: Techno-Economic Assessment of Demand-Driven Small-Scale Green Hy- drogen Production for Low Carbon Agriculture in Sweden. Front. Energy Res. 2020. Publisher Full Text

[9] Kadier A, Simayi Y, Abdeshahian P, et al.: A comprehensive review of microbial electrolysis cells (MEC) reactor designs and configurations for sustainable hydrogen gas production. Alex. Eng. J. 2016. Publisher Full Text

[10] Kurtz JE, Woodbury PB, Ahmed ZU, et al.: Mapping U.S. food system localization potential: The impact of diet on foodsheds. Environmental Science & Technology; 2020. Publisher Full Text

[11] Kaili L: OZs Could Be The Place-Based Solution We Need To Tackle USDA Food Deserts. Sorenson Impact Center, University of Utah; 2021. Reference Source

[12] Meramo-Hurtado SI, Puello P, Cabarcas A: Pro- cess Analysis of Hydrogen Production via Biomass Gasification under Computer- Aided Safety and Environmental Assessments. ACS Omega. 2020; 5(31): 19667–19681. PubMed Abstract | Publisher Full Text | Free Full Text

[13] McCauley DJ: Urban Agriculture Combats Food Insecurity, Builds Community. Reference Source

[14] Millennium Reign Energy LLC: Reference Source

[15] Office of Energy Efficiency & Renewable Energy: Hydrogen Production. US Department Of Energy; 2022. Reference Source

[16] Precker M: Food insecurity’s long-term health consequences. Reference Source

[17] Rhone A, Williams R, Dicken C: Low-Income and Low-Foodstore-Access Census Tracts, 2015–19, EIB-236. U.S. Department of Agriculture, Economic Research Service; June 2022. Reference Source

[18] Satinover SJ, Rodriguez M, Campa MF, et al.: Performance and community structure dynamics of microbial electrolysis cells operated on multiple complex feedstocks. Biotechnol. Biofuels. 2020; 13: 169. Publisher Full Text

[19] Siegner A, Sowerwine J, Acey C: Does Urban Agriculture Improve Food Security? Examining the Nexus of Food Access and Distribution of Urban Produced Foods in the United States: A Systematic Review. Sustainability. 2018; 10(9): 2988. Publisher Full Text

[20] USDA: FARA. Reference Source

[21] USDA: Farms and Land in Farms 2021 Summary. Reference Source

[22] USDA: Census of Agriculture. Reference Source

[23] USEIA: Energy Explained. Reference Source

[24] Hydrogen and Fuel Cell Technologies Office: DOE National Clean Hydrogen Strategy and Roadmap. Reference Source

[25] Urban Growers Collective: Reference Source

[26] Warshawsky D, Vos R: Governing at Scale: Successful Local Food Initiatives in the World’s Cities. Sustainability. 2019; 11(24): 7226. Publisher Full Text

[27] Webber ME: Power Trip: The Story of Energy. Basic Books; 2019. ISBN-13: 978-1541644397.

An economic case for small scale solar-wind-augmented agriculture in exurban localities

Abstract

Keywords

1. Introduction

2. Proposed design

2.1. Land parceling

(Equation 1a)

(Equation 1b)

Figure 1. Proposed land parceling scheme of a unit field (UF) where T1 and T2 are the two towers located along the center line of the UF.

Figure 2. A random field containing multiple unit fields (UFs) with varying orientations.

2.2. Tower design

Figure 3. Top view of a unit field (UF) tower design.

Figure 4. Side view of a unit field (UF) tower design.

2.3. Storage tank design

Figure 5. Top view of a unit field (UF) tank locations.

Figure 6. Side view of a unit field’s (UF’s) tank locations.

2.4. Wind solar augmentation

Figure 7. Front and top view of a covered horizontal axis wind turbine (HAWT).

Figure 8. Front and top view of a covered vertical axis wind turbine (VAWT).

Figure 9. Possible energy generator schemes at each unit field (UF) tower.

2.5. Energy demand offsetting

2.6. Improving space utilization

2.7. Local food and economic benefits

Figure 10. US regions identified as food deserts in 2019.

3. Capital, operation, and energy analysis

(Equation 2a)

(Equation 2b)

(Equation 2c)

(Equation 2d)

Figure 11. Global water usage per acre by crop type (Chiarelli et al., 2020).

(Equation 3)

(Equation 4)

(Equation 5)

(Equation 6)

(Equation 7)

(Equation 8)

(Equation 9)

(Equation 10)

(Equation 11)

(Equation 12)

(Equation 13)

(Equation 14)

(Equation 15)

(Equation 16)

(Equation 17)

(Equation 18)

(Equation 19)

(Equation 20)

(Equation 21)

3.1. Additional local economic benefit

3.2. Enabling hydrogen economy and local production opportunities

4. Conclusion

Data availability

References

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