Workshop Notes

SOCIETY OF AFRICAN EARTH SCIENTISTS WORKSHOP NOTES 

CONTENTS
1. SOLAR PHOTOVOLTAIC ENERGY SYSTEM INSTALLATION
2. SOIL AND WATER CONSERVATION IN AFRICA

 SOLAR PHOTO VOLTAIC ENERGY SYSTEM INSTALLATION 

Photoelectric Effect

When electromagnetic radiation falls onto the surface of a metal, it is observed that electrons may be ejected.  This phenomenon is called the photoelectric effect.

   The effect was first observed in 1887 by a German scientist named Heinrich Hertz .

In 1899 J. J. Thompson proved that electrons were being emitted due to the action of electromagnetic radiation.

   Then in 1905 Albert Einstein won the Nobel Prize for explaining that electromagnetic radiation (for instance, common sunlight) is formed by packets of energy called photons. To understand this is it helps to think of these “packets” as containers (having no mass) which carry energy from the source (the sun) to the metal surface.

Introduction to Electricity

Consider two points, respectively the positive and negative terminals of a battery, connected by a copper wire.  An electric current flows through the wire when there is an electrical potential difference between the two points.
   A simple electric circuit illustrated below includes a battery, a fuse and a solar charge controller.  To locate

Figure 2. Simple circuit consisting of battery, fuse and charge controller

the fuse to protect our solar charge controller, we place it on the positive wire leaving the positive terminal of the battery and leading to the solar charge controller, as this is the direction of the electric current. This is the case for any electrical device we wish to protect: the fuse is always located at the wire leading from the positive battery terminal to the device, as shown below. In our installation of a 24v solar photovoltaic system, we place a 20 amp fuse on the wire leading from the positive terminal of the battery to the charge controller. The 20 amp (A) charge controller is protected by a 20A fuse, which will break the circuit if a current greater than 20 A travels from the battery towards the controller.

   We move on to define basic concepts of electricity which will be of relevance in our solar electricity installation.

i)                    Electric Charge - The build-up of electricity. In nature we witness an electric charge as a lightning strike. A battery stores an electric charge.  Batteries will be a key component in our solar setup, as we wish to store up the energy we collect from solar panels. Electric charge is measured in coulombs,

ii)                   Electric Current - This is the flow of an electric charge. Electric current is measured in amps (A).

iii)                 Electric Potential – Refers to the potential difference in electrical energy between two points, such as the positive and negative terminals of a battery. It is measured in volts (v).

iv)                 Relationship between volts, amps, ohms and watts-hours

a.       Voltage (v) is a measure of potential difference

b.      Resistance (R) is a bit like friction - it is the natural opposition to an electron flow found in a material. It is measured in ohms.

c.       As already noted above, current (I) is a measure of the flow of electrons /electric charge in a circuit. It is measured in amps (A).

d.      Power (P) measures the rate at which electrical energy is converted into work (whatever that work is: boiling a kettle, operating a drill, etc.). It is measured in watts (W).

e.      Energy (E) refers to the capacity for work is  power x time and measured in joules (1 watt/s), but usually shown as watts-hours or kilowatt-hours.

Important relations to note are that

V = I R                                             (1)

P = V I              = I² R                      (2)

How a Solar Panel Works

A solar panel consists of a grid of many singular solar cells. Each cell consists of two semiconductor layers called P- and N-type semiconductors, which are joined by conductive wiring.  The N-type upper layer (blue colour layer, in above figure) is pure silicon that has been mixed with negatively charged phosphorous and so has an excess of electrons; whilst the lower layer (green layer above)  is pure silicon that has been mixed with positively charged boron, leading to a deficit in electrons (or holes). By “doping” or adulterating the pure silicon with respectively negatively or positively charged elements, a potential difference is created between the two semiconductor layers so that one layer is relatively positively (or negatively) charged in respect to the other. When light falls onto the solar cell, the potential difference creates an electric field in the gap between the two semiconductor layers, and a current flows from one layer of the solar cell to the other, causing a positive charge to flow from the positive to the negative terminal. The gap between the two layers is called the p-n junction. The electric current actually flows in the opposite direction to the electrons.  Conceptually, the travel of negatively charged electrons from the negative to the positive terminal is equivalent to the travel of a positive charge from the positive to the negative terminal.

Components of a Solar Electric Energy System

The key components of a solar electric energy system demonstrated in the workshop are

• ·         Solar panels
• ·         Batteries
• ·         Solar charge controller
• ·         Pure sine wave power inverter

Having a pure sine wave inverter in place of a simple inverter ensures that computer or other sensitive electronic equipment is protected from fluctuations in voltage. The arrow in the diagram below indicates the AC (alternating current) output from the power inverter to power household appliances.

(Not to scale)

The above figure gives an outline of a 24v solar photovoltaic system installation consisting of:-

1. Two 12v and 150 W solar panels arranged in series to give a 24v solar panel array.
2. Two 12v deep cycle batteries  arranged in series to create a 24v battery bank
3. A 2000W, 24v pure sine wave power inverter
4. A 20 amps, 12v / 24v solar charge controller
5. Accessories including, wiring, fuses and battery terminal clamps.

The materials listed above for our solar electric system can be purchased at UK prices for under £1400 pounds sterling as at August 2013. Cheaper options are available to the buyer by, for instance,  going without some of the capacity provided by  4 batteries in LIST A  below, and instead making do with 2 batteries. Solar enthusiasts can purchase the bare necessities to begin with and add more capacity to their solar electric system as available funds dictate, by acquiring more battery capacity and/or adding solar panels to the array to generate more power.

We consider the details of installation for each of the four main components.

Figure5. Two 12v, 150W solar panels connected in series

Solar Panels

Solar panels can be arranged in an array by connecting in series or in parallel.  Which arrangement we choose will depend on the capacity and voltage we wish to maintain for our system.

Example: 24v series array formed by 2 x 12v solar panels

Series array - allows the panels to run at a higher voltage

   A series connection between two solar panels is made by connecting the positive terminal of one panel to the negative terminal of the other panel.  Two 12v solar panels connected in series will give a 24v solar panel array. Similarly, three 12v solar panels in series would give a 36v array; whilst four connected in series would give us a 48v solar panel array.

Parallel array - more panels in parallel increases capacity whilst voltage remains the same

A parallel connection between two solar panels is made by connecting the positive terminal of one panel to the positive terminal of the other (or negative terminal to negative terminal). Two 12v solar panels connected in parallel will give us a 12v solar panel array. Similarly, three or four or any number of 12v solar panels connected in parallel will give us a 12v array of solar panels. Adding solar panels to the array in parallel will increase the capacity of the array whilst maintaining the same voltage.

Figure 6. A 24v battery bank consisting of 2x12v batteries in parallel (close together on the right),
connected in series to a single 12v battery (standing apart on left)

Batteries

Just like the solar panels, batteries can be arranged in series or parallel to increase or maintain voltage in accordance with system requirements.

Figure 7. A 24v battery bank consisting of 2x12v batteries connected in series

Figure 8. A 48v battery bank consisting of 4x12v batteries connected in series

Figure 9. A12v battery bank consisting of 2x12v batteries connected in parallel

Figure 10. A 12v battery bank consisting of 4 x 12v batteries connected in parallel

Figures 11a and b. A 12/24v, 20 amp, solar charge controller

Charge Controller

The charge controller controls the current into and out of the batteries and helps to protect them, preventing them from overcharging or discharging completely. Positive and negative terminals of the controller are connected with respective positive and negative terminals of the solar panel array and the battery bank.

Figures 12a and b. Pure sine wave 2000W, 24v power inverter

Power Inverter

The inverter converts the direct current (DC) from the batteries into alternating current (AC) which is required for household appliances.  The respective positive and negative terminals of the inverter are connected to the respective terminals of the battery bank. A round pin plug attached to a plug board  plugs into the inverter to make AC available to run household appliances.

Solar Cabling / Wiring

Calculating Area and Thickness Required for Solar Systems Cabling

Cable thickness (Area in sq. mm) = 20(length x I x 0.04)/V

where "cable thickness" is an expression for the cross-sectional area in sq. mm, I is the current in amps,

V is voltage in volts.

Normally, we know the voltage and current (amps) of our system by the specifications of the

equipment we intend to install.

The cable thickness formula enables us to design a wire thickness that will safely carry the current for our solar electric system without risk of over-heating and causing fire. 

From the formula we obtain the cable cross-sectional  area, A. given by

A = pi x (D²)/4

    = (3.14) x (D²)/4

where D is the diameter of the wire, and we assume pi = 3.14. Hence

D =    Square root (4A / 3.14 )

Your wiring must be at least this diameter to meet minimum requirements.

WORKSHOP REFERENCE AND SOLAR ELECTRIC SYSTEM MATERIALS

1. 1. Luque, Antonio & Steven Hegedus, Handbook of Photovoltaic Science and Engineering - 2nd Edition, Wiley, 2010
2. Reference:  Boxwell, M., Solar Electricity Handbook 2013 Edition, Greenstream Publishing, 2013.
3. SAES youtube guide to installation of 24v system:https://www.youtube.com/watch?v=pLOa-3-q0o0
4. 
   
5. Materials  lists are given for both a 24v home solar electric system (List A)  and a 12v home system (List B). 
6.        SAES Solar Photovoltaics Installation demo 30 June 2023: https://youtu.be/00Bn5fCjByA
7. 
   

LIST A  - 24V SOLAR ELECTRIC SYSTEM COMPONENTS

item	Rounded Price £  [as at summer 2014]
used in demo Solar cable 4mm single core (1x 18m length) (preferably use 9 mm of braided wiring)	27.00
Solar testing device and holster	16.00
Solar controller 20A 12v/24v with LCD	130.00
2 x Polycrystalline solar panel  150W, 12V	500.00
Battery leads x	39.00
Sunshine Power inverter 2000W, 24V, pure sine wave	340.00
4xDeep Cycling 100AH, 12V leisure battery*	400.00
6x Battery terminal clamps (w/Nut)	40.00
1x Fuse holder	6.00
20A, fuse	3.00

LIST B  - 12 V SOLAR ELECTRIC SYSTEM COMPONENTS

item	Rounded Price £ [as at summer 2014]
used in demo Solar cable 4mm single core (1x 18m length)     (preferably use 9 mm of braided wiring)	27.00
Solar testing device and holster	16.00
Solar controller 20A 12v/24v with LCD	130.00
1x Polycrystalline solar panel  150W, 12V	250.00
Sunshine Power inverter 1500W, 12V, pure sine wave	249.00
2xDeep Cycling 100AH, 12V leisure battery**	200.00
2 x Battery terminal clamps (w/Nut)	14.00
1x Fuse holder	6.00
20A  fuse	3.00

* 2 batteries will suffice for the system to operate, but 4 listed for better capacity if funds allow.
** A single battery will suffice for the system to operate, but 2 are listed for better electrical storage capacity.

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SOIL AND WATER CONSERVATION  IN AFRICA

- a workshop  covering traditional and modern methods  of soil and water conservation

Introduction

This workshop addresses improving the continent’s food yield and clean water provision  through a focus on low cost methods for reducing the continent’s loss of soil, water and soil fertility and increasing clean water provision for drinking and sanitation by means of groundwater recharging and water harvesting.
   Three quarters of Africa’s farmland is severely affected by land and soil degradation due to soil erosion. Water erosion due to rain washes away both the soil and the nutrients within the soil. As well as conserving soil and soil fertility water conservation is crucial. About 1.1 billion people in the world live without access to clean water. One third of this total live in Africa. So it is estimated that 30-40% of Africans have no access to clean water.
   The workshop proposes various approaches to meeting these needs though modern and traditional approaches to soil and water conservation including  the retention of groundwater and rainwater harvesting. 

Land Degradation

Land degradation can be defined as the loss of the productive quality of the land to sustain life. Land degradation refers to the worsening quality of the land whereby soil is  lost due to the natural agents such as wind and  water ( predominantly rainfall and overland flow
   Nutrients in the soil are  lost through being washed out by the rainfall and overland flow. Runoff  or overland flow is water  that flows over the land surface once the rainfall no longer infiltrates the soil  (once  the soil has become saturated). 

The Hydrological Cycle

   The processes of degradation strip the land of its nutrients and worsen  poverty among African peoples. Causes of land degradation include the physical process of erosion either by wind or by water.  This process is principally determined by climate, particularly rainfall in tropical climates or in the case of dry arid zones, where wind erosion is more important.
   Key to the understanding of how climate brings about land degradation is  an appreciation of the hydrological cycle.

Soil degradation – a reduction in soil fertility caused by soil erosion  (loss of soil matter) and exploitative cropping. 
   So soil degradation has key features:

• Impoverishment of vegetation cover - loss of vegetation cover is often caused by both wind and water and also over-use of the land by people and livestock. Also poor  or unsustainable farming methods are likely to deplete soil fertility and further degrade the land. 
• Desertification - Continued degradation of the land will cause the soil to become so denuded of vegetation and unproductive as to cause desertification which can only be reversed with enormous effort.  Severely degraded land  becomes denuded of all vegetation and leads to desertification.  Desertification is not an absolutely irreversible process. Desert land can be reclaimed back with the assistance of irrigation to re-establish the growth of vegetation.    If sufficient vegetation can be returned, moisture willreturn to the atmosphere and drought  will decline.

Certain erosion processes are highly selective in the way they strip the soil of its nutrients.4 stages of severity of soil erosion are identified: Splash erosion, sheet erosion, rill erosion and gully erosion, in order of severity of soil loss.

Severe land degradation leads to desertification

1) Splash erosion –  occurs when soil particles are dislodged by the direct impact of rainfall. The level of splash erosion is  determined by physical characteristics of rainfall, such as  energy, intensity and the duration of the rain.

Rainsplash and runoff erosion

Rainsplash erosion

Rainsplash erosion

2) Sheet erosion – as the term suggests, involves the flow of shallow runoff over the surface of the soil. It is the most highly selective process in that it strips the soil of its nutrients more effectively than other processes. The pattern of sheet erosion shows how miniature streams are cut into the soil surface by the runoff (or overland flow). In sheet erosion, because of the shallow depth of flow, soil particles can be dislodged by the impact of raindrops and carried away by the flow, so that this process actually involves a combination of splash and runoff erosion. In deeper flow, the cushion provided by the water depth protects the soil from erosion by direct raindrop impact.

Sheet erosion pattern

3) Rill erosion – is the next most severe erosive process. At  the sheet erosion stage we can already see from the tracks left by the shallow sheet of surface flow  that the flow is beginning to cut little fine streams of flow into the soil surface and some of these will widen to form rills.

Rill Erosion in Kenya

4) Gully erosion – some of the rills created widen and deepen  to form channels which are now transporting substantial quantities of  overland flow eventually becoming gullies.

Gully erosion in Kenya

Gully erosion

Gully erosion

Soil erosion is exacerbated by certain conditions which increase the erosive power of the water.  On hilly slopes the greater the slope degree, the greater will be the velocity of the water flow over the land and this  will increase the erositivity of the flow ,especially as the velocity increases to such an extent as to turn the flow from a smooth laminar flow to turbulent flow which is far more destructive and erosive.

Rainfall erositivity – this refers to the capacity of rainfall to cause erosion and this is dependent on the physical characteristics of rainfall:  energy, intensity and duration. The first two of these are affected by raindrop size.

Soil erodibility – a measure of the vulnerability of the soil to erosion.

Topography – generally, the steeper and longer the slope, the greater the rate of erosion.

Vegetative cover – this is usually the most important factor of all. Where soil is completely covered by vegetation, erosion is virtually eliminated.

Crop management and  conservation practices - also have a significant impact on erosion

Quantification of Land Degradation

Various methods have been devised to quantify the rate of erosion or land degradation.  Traditionally mainstream erosion science has relied on the Universal Soil Loss Equation (which I will not care to state at this stage) as a mathematical model of soil loss due to erosion. However, this has obvious drawbacks as there is doubt that an equation based on years of data collected in the United States of America will be applicable or relevant to African conditions.  In recent years an alternative mathematical equation  called the  “Soil Loss Estimation Model”, developed in Zimbabwe has been developed.  Other  more  rigorous (so I feel)  mathematical models have been developed in recent years which are based on the so called “mass balance equation” which essentially is an application of the principal of conservation of mass and energy. This area of study is very heavily mathematical  employing the principles of physics and fluid mechanics and will not be covered by this workshop except in passing mention.

Marginalisation

In the 1992 report of the International Fund for Agricultural Development, the term marginalisation refers to a process through which rural people lose autonomous control over their land and are forced to split their efforts to survive over more than one economic  sector. Actually, marginalisation appears to go beyond this,  to what  the agricultural engineer,  Amilcar  Cabral, described as the  control of the African means  or modes of production. This processes marks  a key reason for Africa’s impoverishment, where African labour is diverted from self subsistence to working for the colonial (and now neo-colonial) overlords on their native land.  Africans dispossessed of their land are forced to sell their labour at a low price, often to the very usurpers of their land. In the modern era, this phenomenon continues in the form of Africans who once owned  and lived from their land being forced to work on  land-grabbed farms for very little remuneration, as no other means of livelihood is available.  

 A study in 1992 by the International Fund for Agricultural Developments established the enormous value of traditional African systems of soil and water conservation, showing that in some instances traditional methods gave rise to better soil erosion  and soil fertility protection and  greater food yield s (by as much as 30% over modern methods) for such  crops as cowpeas,  sorghum and millet, etc. This has led steadily along with other studies to the greater adoption of indigenous soil and water techniques  as part of an integrated  modern   approach  to soil and water conservation in Africa. The most popular techniques are described below.

It is now more widely appreciated Africans have  been striving to conserve their soil, water and soil fertility for thousands of year by various indigenous techniques. Some of the many  techniques are described below:-

Shifting cultivation

Shifting cultivation techniques are an ancient practice in Africa aimed at moving cultivation from one plot to another with the intention of allowing the vacated plot to “lie fallow”  or regenerate  for some years , enabling the vegetation to regenerate before the land is at some point re-cultivated. Miracle (1967) has identified a remarkable number of systems of shifting cultivation in Africa. He identified 12 systems in the Congo Basin alone, all ecologically sound.  However the pressure of increasing urbanisation and population have taken their toll and  now traditional fallow periods have been reduced or in many cases abandoned altogether with no rest for the regeneration of the soil. The IFAD  1992  report identifies  a range of indigenous soil and water conservation techniques. These include:  stone lines (bunding), trash lines, ridges, furrows, pitting systems, mounds or bunds with green manure worked into them,  terraces (including stone and bench terraces)

Terracing

Terracing slows  down the velocity of the water by removing the land steepness at step intervals; thereby making overland flow less erosive.


Terracing increases the infiltration of water into the soil. Terracing therefore conserves soil as well as water

•      Terracing enables the cultivation of land on steep slopes and even escarpments (e.g., the Dogon of Mali)

Terracing in Cameroon

•    Spectacular forms of indigenous terracing exist such as the examples we find in Cameroon’s  Mandara Mountains and in Sudan

Terracing in Cameroon

•      Indigenous terraced systems are major economic assets as  they protect land down stream from degradation  as well as preserving cultivated land on the slopes.  Their maintenance is the  most cost effective strategy for land conservation, as these structures exist and only need to be maintained.

Bench Terrace

Terracing in Cape Verde

Terracing in Ethiopia

Stone Terracing in Niger

Terrace Construction - central Africa

Terrace construction

Pitting systems slow down the velocity of the flow and collect both water and nutrients

Planting pits in Mali

Planting Pits - Mali

Planting pits

Stone Bunds

Once again these have the effect of  slowing down the water flow. They also serve to collect soil.

Stone bund construction

Stone lines at approx. 20-30 m intervals

Stone Bunds - Niger

Stone bund construction

Vetiver Grass Erosion Protection

In the workshop so far the emphasis has been on traditional methods of soil and water conservation that have been used in Africa for hundreds, if not thousands of years. Vetiver grass has been extensively tested in Africa for at least the past 40 years and has been found to be highly effective in controlling erosion and retaining soil nutrients.

So the use of vetiver may be classed as a modern erosion protection measure falling under the heading of biotechnology”. Although vetiver grass is new to the African continent (originating from India), it is used in what are actually traditional soil conservation measures (such as hedging and terracing of slopes).

Vetiver grass hedge

In Nigeria, vetiver grass has been tested   extensively  since the 1970s, and found to be effective. In the 1980s many  Nigerian federal highway construction projects specified the use of vetiver erosion protection for roadsides and road embankments.  This erosion protection measure was potentially  beneficial for the soil and water conservation of the surrounding area, because controlling the erosive power of runoff from the road through sufficient grassing of slopes served to protect the local environment downstream of road embankment slopes. Unfortunately, many contractors were in the habit of omitting the vetiver protection and this has led to more widespread road and  local land degradation.

Vetiver hedging - Ethiopia

The reason that vetiver is so effective in soil and water conservation is due to its massive root system, which can extend to several metres depth into the soil. This serves to bind together the surrounding soil, making it highly erosion resistant, whilst the foliage traps sediment and slows the velocity of erosive overland flow.  The deep root system also serves to increase the soil capacity to absorb and hold water and therefore vetiver plays a crucial role in helping the more rapid recharge of groundwater; which is important near water wells  and springs in maintaining the community water supply.

vetiver 

Vetiver root system

Geotextiles

Other modern methods other than the use of vetiver include the use of geotextiles. These are synthetic & natural materials used mainly in non-agricultural engineering structures  such as roads and riversides, bridge abutments and roadside drainage structures to protect against erosion, and are made of materials such as jute and synthetic fibres .

Geotextiles can be highly useful at roadsides on escarpments and on other steep slopes to prevent dangerous landslides. However, they are expensive.  They limit erosion as they protect against rainfall impact and inhibit runoff, and also assist the establishment of vegetation in taking root and holding the soil together

Geotextile made from jute (a plant fibre)

Slope stabilisation using geotextiles

Roadside slope protection using geotextiles

Water Harvesting

•      Water harvesting, the collection of water directly from rainfall or from runoff (overland flow) promises to be an efective means of helping to meeting Africa’s water needs.

•      A recent UN report (2006) estimates that Africa has the capacity to meet the clean water needs of 1.5 times the Earth’s population through water harvesting.

•      It is estimated that both Ethiopia and Kenya have the capacity of meeting the clean water needs of 6-7 times their populations purely through employing rainwater harvesting techniques.

Roof construction for rainwater harvesting

Runoff rainwater harvesting

Runoff rainwater harvested with downstrean pan construction

•      Reading List

•      Morgan, R.P.C, Soil Erosion & Conservation, Wiley, 2009 edition.

•      Soil and Water Conservation in Sub-Saharan Africa, IFAD, Rome, 1992

•      A link on “Groundwater and Rural Water Supply in Africa”: http://www.iah.org/downloads/occpub/IAH_ruralwater.pdf

•      Cabral, A., Return to the Source – Selected Speeches, Monthly Review Press/Africa Information Service, N.Y. and London, 1973

•      UN link on rainwater harvesting:  http://www.un.org/apps/news/story.asp?NewsID=20581&Cr=unep&Cr1=water#.UKjJWOQ3Ya4

•      Udealor, A and PO Nwadukwe, On-farm evaluation of the effect of Vetiver Grass (Vetiveria zizanoides) hedgerow on the soil loss and yields of the components of Yam/Maize/Cassava intercropping system in Southeast Nigeria, Nigerian Journal of Soil Science, Vol 17 (2007).

•      Babalola, O. , et al, Use of vetiver grass for soil and water conservation in Nigeria, http://www.vetiver.org/NIG_SWC.pdf

•      Edem, I.D., et al, Effect of vetiver on infiltration characteristics of kaolinitic alfisols of Ibadan, South Western Nigeria, http://iosrjournals.org/iosr-javs/papers/vol1-issue2/J0124549.pdf