SPIS Toolbox - Evaluate Geophysical Parameters
Several geophysical parameters can be used to assess SPIS markets. This module highlights 3 that are crucial to the viability of SPIS applications as discussed in Chapter 1: Land cover-land use, solar irradiation and precipitation (under water availability). If the state of these three parameters is unfavourable in the area under assessment, SPIS is unlikely to be practical. An additional 4 parameters that are key to the market assessment for SPIS are also identified – these do not affect the viability of SPIS; they affect the success of SPIS adoption on a case by case basis. The 7 parameters are expounded on below.
LAND COVER/ LAND USE
Land Cover refers to the physical and biological cover over the surface of the earth including water, bare surfaces, forests, and artificial structures among others. Land use on the other hand refers to how people utilize the land whether for recreation, agriculture or wildlife habitats among others.
Land cover/land use is one of the fundamental parameters to be considered during the identification of potential markets for SPIS as it helps determine feasible locations for agriculture from which other parameters may be considered. Land cover is measured either through direct field observations or through remote sensing techniques involving the analysis of satellite and aerial imagery. Based on the land cover analysis, land use data can be inferred through ancillary data. The data assists decision makers and stakeholders in cross-cutting sectors to understand the dynamics of a changing environment and ensure sustainable development.
Land cover data typically consists of eight classes including wetlands, water bodies, urban, shrubs, grassland, forests, bare land and agricultural land. These may, however, be classified into varying classes depending on the source of data. The FAO framework for land suitability for instance, divides land into four classes ranging from highly suitable land for agriculture (S1) to currently not suitable land (S4). For the 8 classes listed above, ‘agricultural land’ can be classified as highly suitable (S1) and ‘grassland’, which requires land clearing and levelling, as moderately suitable (S2). ‘Shrub land’ and ‘bare land’, which require higher initial investment for land preparation can be classified as marginally suitable (S3) while ‘forest’, ‘water’, ‘urban’, and ‘wetlands’ can be categorized as not suitable (S4).
In assessing market potential for SPIS for a given country or region, stakeholders need to assess the irrigation viability of their target location from a land cover-land use perspective. For example, areas that are mostly classified as S1 land would have higher potential for SPIS compared to those that are highly urbanized or classified as wetlands.
It should be noted that desktop analysis of land cover/land use data through application of remote sensing techniques should be followed by ground truthing to ascertain the land cover/land use in the selected regions prior to investment.
OUTCOME/PRODUCT
- Classification of land based on agricultural suitability
- Selection of optimal sites to promote solar powered irrigation
DATA/REQUIREMENTS
- Land use - land cover data
- Land suitability classification frameworks (e.g. FAO)
PEOPLE/STAKEHOLDERS
- Land Surveyors
- Remote sensing analysts
- Government land ministries
IMPORTANT ISSUES
It is always important to follow up desktop analysis of landcover with actual on-ground visits to the selected areas. Satellite and aerial images are typically very accurate however if one is not using up to date datasets it becomes important to verify the selection.
SOLAR IRRADIATION
Solar irradiation is a key factor in gauging the market potential of SPIS within a region. It refers to the amount of energy incident per unit area on the earth’s surface in units of watts hours per square meter. PV systems use Global Horizontal Irradiation (GHI) which is the total amount of radiation received from above by a horizontal surface. GHI consists of both Direct Normal Irradiation (DNI) – the amount of solar radiation received per unit area by a surface that is always held perpendicular to the incoming rays and; Diffuse Horizonal Irradiation (DHI) – the amount of radiation received per unit area by a surface that does not arrive on a direct path from the sun, but has been scattered by molecules and particles in the atmosphere.
Solar radiation can be categorized into four classes: levels less than 2.6kWh/m2 are classified as low solar radiation while solar irradiance between 2.6-3kWh/m2 is moderate solar radiation; irradiance of between 3-4kWh/m2 is high solar radiation and irradiance higher than 4kWh/m2 is very high radiation. It is important to note that the classification is used for purposes of distinguishing the efficiency of systems as advances in solar technologies have allowed for the set-up of systems in almost all areas that receive radiation. In areas of low radiation, system efficiency will be compromised due to lower panel output. Additionally, set up of solar panels in regions of low solar radiation could lead to high set up costs resulting from the use of a greater number of panels to generate the same output as regions with higher insolation. It is therefore noted that, because of technological advances, solar irradiation is more of an economic consideration than a question of technical feasibility.
OUTCOME / PRODUCT
- Classification of regions based on GHI or PV system output
- Identification of optimal sites for SPIS
DATA REQUIREMENTS
- Global horizontal irradiation data
PEOPLE / STAKEHOLDERS
- Solar PV system installers
- Meteorological service providers
- Solar equipment suppliers
IMPORTANT ISSUES
- There are various other factors that affect the functionality of a PV system in addition to solar irradiance. Two of the most important include temperature and aspect which are further expounded on in the ambient temperature and topography sections of the module.
WATER AVAILABILITY
This parameter investigates the amount and quality of water available for irrigation at a potential SPIS area. Irrigation water requirements depend on the balance of the crop water demand against the water availability.
Crop water demand may generally be defined as the amount of water needed for a plant to live and grow and is measured in milimeters per day, month or season. It is affected by various factors including:
- Climatic conditions including temperature, humidity and windspeeds. Consequently, water needs for one crop will vary with varying climatic conditions, with the highest demand seen in areas that are hot, dry, windy and sunny;
- The type of crop affects its water demand, both in the short term (daily water demand) and the longer term (seasonal water demand);
- The stage of growth for a particular crop also affects its water demand. For instance, a mature maize plant may demand more water than one at the shooting stage. Local data on crop water needs is often available with agricultural extension offices. The Water requirement tool under the SAFEGUARD WATER Module as well as resources provided by the FAO may also be used in estimating water demand.
Water availability for crop growth is dependent on three main sources: precipitation, ground water and surface water resources.
Precipitation, the amount of rainfall received in an area, has a direct influence on the need for irrigation within an area. If the amount of precipitation received within a region is enough to meet the water demands of the crops grown, irrigation is not necessary; when precipitation volumes are not adequate, water supply through irrigation from ground or surface water resources becomes critical for crop growth. The adequacy of precipitation may be evaluated by comparing the effective rainfall against the crop water demand using the SAFEGUARD WATER – Water Requirement Tool.
Effective rainfall – this looks at the amount of water from rainfall received within an area that is available for utilization by crops. This volume is affected by various factors including soil texture and structure, climate, topography and the depth of crops’ root zone among others. These factors consequently affect the rate of surface run-off and water percolation / infiltration beyond the root zone. The amount of rainwater retained in the root zone of plants that can be used by plants is referred to as effective rainfall. Most countries have developed tools to determine effective precipitation. However, in the absence of data (e.g. lack of prevailing soil type, rainfall reliability and topography data), the FAO provides rough estimates for effective rainfall per rainfall received.
Ground and surface water sources – the need to tap into these resources to meet the water deficit from rainfall introduces the market potential for SPIS. However, it is important to note that factors such as water source proximity and yield, aquifer recharge rates, water quality, water permits or rights required for abstraction among others must be taken into consideration when identifying and designing SPIS for specific areas. Water source yield, for example, has a direct influence on the type of irrigation method selected. In situations of inadequate water supply, sensitive soils or poor quality water (sedimentation, salinity and water hardness) appropriate methods like drip and sprinkler irrigation are preferred. Surface irrigation is preferred if the irrigation water contains large amounts of sediment which may clog the drip or sprinkler irrigation systems. This is expounded on in the DESIGN module.
OUTCOME / PRODUCT
- Classification of regions based on crop water demand vs effective rainfall.
- Identification of ground and surface water sources.
DATA REQUIREMENTS
- Monthly Precipitation data
- Data on surface water bodies and ground water aquifer systems
- Water licensing and abstraction rights
- Water source flow rates
- Crop water demand
PEOPLE / STAKEHOLDERS
- Meteorological Service Providers
- Water resource management authorities and abstraction licensing authorities
- Agricultural advisors and extension officers
- Irrigation boards and organisations
IMPORTANT ISSUES
- Desktop analysis of precipitation and ground and surface water sources should be followed by verification of data from the relevant government bodies (e.g. national meteorological centres and water resources management authorities) prior to investment.
- Determination of crop water requirements can be done using the WATER REQUIREMENT TOOL in the Safeguard water module.
- Adoption of SPIS should ensure sustainable abstraction of water from identified water sources. The SAFEGUARD WATER module provides information on water resource management and sustainable water abstraction and provides a water resource management checklist.
TOPOGRAPHY
Topography describes the elevation and the relief features on the earth’s surface. Relief features include both natural and man-made landforms such as roads, hills, valleys, railways among others. Key topographical features in evaluating market potential for SPIS are slope and aspect.
Slope is a measure of the change of elevation over a certain distance. It answers the question of how steep an area is and is a determining factor for the type of irrigation system to promote. This in turn determines the cost and labour requirement (e.g. erosion control practice and water conveyance channels). For instance, surface irrigation is more suitable in undulating areas and is cheaper compared to sprinkler and drip irrigation which are more suited on steeper or unevenly sloping land. Therefore, coupling steep lands with a factor like low access to finance (discussed in Chapter 3) would lead to weak market potential for SPIS.
Aspect describes the direction which a slope faces. It is especially relevant for systems located in higher latitudes and rarely affects systems close to or along the equator. Aspect influences the amount of solar radiation that the slope receives as well as the daily range of temperature and the relative humidity on the slope.
Generally, more direct sunlight tends to fall on the south and southwest slopes while North aspects of slopes are more shaded in the northern hemisphere. The converse is true in the southern hemisphere where more direct sunlight tends to fall on the north and northwest slopes.
Topographic analysis for potential SPIS sites can be determined through use of topographic maps that depict the physical configuration of the earth’s surface using contour lines as wells as symbols for man-made and natural features. Users can also use Digital Elevation Models (DEMs) that are specialized databases that represent the relief of a surface between points of known elevation. DEMs can be used on Geographical Information System (GIS) platforms. This should be followed by a ground-truthing exercise to determine the exact slope and aspect of the area of interest.
OUTCOME/PRODUCT
- Determination of slope and aspect of potential SPIS markets
- Selection of suitable irrigation systems based on the topography of the potential SPIS market
DATA REQUIREMENT
- Topographic Maps
- Digital Elevation Models(DEMs)
PEOPLE/STAKEHOLDER
- Lands and Survey Authorities
IMPORTANT ISSUES
- Care must be taken when designing irrigation systems on steep slopes as such areas are prone to erosion and runoff.
CROPS AND LIVESTOCK
An overview of the prevailing types of crops and/or livestock in the country or region of interest serves to understand which SPIS are most suitable and is also indicative of the market potential for SPIS technology. This is particularly relevant for SPIS system suppliers and entities seeking to promote adoption of SPIS by farmers. This information can be sourced from government ministries in charge of agriculture, global research studies on cultivated areas, FAO databases on crop cultivation among others.
Additionally, stakeholders interested in promoting or setting up SPIS schemes can use agro-ecological zones (AEZs) to determine the most suitable crops to be cultivated and animals to be reared in an area. AEZs define areas based on combinations of soil, landform and climatic characteristics and match suitable crops and animals to regions. The zones can also be used to determine the potential yields of the main crops grown within the zone thus helping with income projections of the target market. As discussed under Finance in Chapter 3, access to finance is a key parameter in evaluating a market’s potential for SPIS.
The Global Agro-ecological Zones (GAEZ) portal by FAO and the International Institute for Applied Systems Analysis (IIASA) provide a comprehensive online portal with details on land resources, agro-climatic resources, suitability and potential yield, actual yield and production and yield and production gaps. Stakeholders interested in SPIS can refer to this or similar tools to determine important characteristics that influence the type of crops or livestock in an area.
OUTCOME/PRODUCT
- List of crops grown and animals reared in selected countries or regions
- AEZ classification for selected areas
- Potential crop/livestock yield within the area of interest
DATA REQUIREMENT
- Global AEZ by FAO and the International Institute for Applied Systems Analysis
PEOPLE/STAKEHOLDERS
- Ministry of Agriculture
AMBIENT TEMPERATURE
As the name suggests, this parameter looks at the temperature of the areas surroundings. This has two main effects on SPIS potential:
- affects the efficiency of SPIS and
- affects the crops and livestock found in an area.
On efficiency of SPIS, temperature is a key factor in the design of pumping systems as it affects the functionality and life span of solar PV equipment. The flow of electricity and the voltage output of solar panels depend linearly on the operating temperature of the panels. Lower temperatures produce reduced resistance to electricity flow resulting in higher voltage outputs; higher temperatures increase resistance and subsequently lead to lower voltage outputs. High ambient temperatures also affect the performance of the system’s inverter by reducing its frequency which in turn reduces its efficiency and the flow rate of the pump.
Due to the variability of climate in different regions, most panels do not operate under ideal temperature conditions. To correct this, panels in hotter regions of the world are often designed with cooling systems to keep the panels within certain temperatures. Additionally, PV systems in different temperature environments must be sized to ensure that the output voltage is not too high, which could damage the equipment.
The range of crops and livestock that are suitable in an area is often affected by ambient air temperature. Analysis of thermal regimes using agro-ecological zoning discussed in the previous section can reveal crops and livestock suited to a region based on its temperature. This may then inform the need for SPIS for the said region.
OUTCOME/PRODUCT
- Determination of ambient temperatures in potential SPIS markets
- Selection of suitable solar technology based on temperature regimes
- Determination of suitable crops and livestock based on temperatures
DATA REQUIREMENT
- Global AEZ by FAO and the International Institute for Applied Systems Analysis
PEOPLE/STAKEHOLDERS
- Meteorological service providers
IMPORTANT ISSUES
- Panel selection should be done with ambient air temperature in mind to maximize efficiency of the system and to ensure adequate voltage output.
DEMOGRAPHICS
An understanding of demographic characteristics including population density, age, migration levels and patterns and household income provide additional information when making decisions on potential SPIS markets. These characteristics can be used as proxy indicators of poverty levels, labour availability, prevailing agricultural practices, urban settlements among others.
This parameter cannot be used standalone, but in combination with other parameters can assist in a deeper understanding of social dynamics and cultural conditions for a target region. For example, as earlier mentioned, coupling topography with poverty levels could help infer market potential. Also, analysis of population density and land cover-land use data could highlight densely populated areas or urban settlements which could be a factor in determining the viability of a potential SPIS market. SPIS sites cannot be in densely populated urban settlements however they could be located close to such areas as they provide market for produce.
Evaluating demographic characteristics such as household income alongside business parameters such as financing and incidences of poverty can serve to highlight the capability of households to take up SPIS systems.
OUTCOME/INCOME
- Correlation of demographic characteristics with SPIS geophysical and business parameters to identify relevant issues in determining potential SPIS markets
DATA REQUIREMENTS
- Census Reports
- Satellite imagery on global population
PEOPLE/STAKEHOLDERS
- Government Ministries including Ministries of labour and migration
- Statisticians
