1. .. Track APT – Energy Planning and Appropriate Power Technology at The 2007 ngNOG Workshop on Network Technology, Power and Policy at Bayero University, Kano on November 18 – 22, 2007 by Rev. Ukaegbu Ogwo (MD/CE, Solartime Electric Ltd.)

2. DAY 1  ngNOG APT Track 4 –  Solar Power

3. Photo-voltaic (PV) Module

4. Introduction  The phenomenon of converting sunlight into electrical energy was first used in the space industry in the 1960’s.  These first modules were exceedingly expensive, costing as much as $1000 (N130,000.00) per watt.  However by 1970 more solar modules were produced for use on the earth surface than in space. Since then the use of solar modules has steadily increased until today when there is a boom in the industry with a watt costing less than $5 (N650.00).

5. Types of Solar Modules  Crystalline or Polycrystalline, silicon cells each produce about 0.5 volts (a little less for amorphous silicon)  Thin Film, or Amorphous silicon modules  Unisolar modules

6. Crystalline & Unisolar

7. Location of your Array  The roof will seem logical as the best place to locate your array. However rooftop mounted modules are difficult to clean. Dust particles, after a little sprinkle, leave the PV module surface spotted thus shielding the modules from optimum sunlight penetration.

8. Pole Mounted Solar Array

9. The Flip Side of Pole Mounted PV’s

10. .  The solar array needs to be as close as possible to the building in a location where it can receive full, unimpeded sunlight for 3 hours on either side of noon.  Trees, bushes or other obstructions that cast a shadow on any part of the array will greatly reduce the energy output.

12. Solar Array for Water Borehole

13. Due South  Arrays should always point due South at 15 degrees angle tilt to the horizontal for those in the tropics.  If the best spot to locate the array is farther than 50 feet, you might consider designing a 48 volts system.  This will greatly reduce the size of the wire needed to carry the current to the house with a minimum line loss.

14. Irradiance  Irradiance is a measure of the sun’s power available at the surface of the earth and it peaks at about 1000 watts per square meter.  With typical polycrystalline cells efficiencies of 14-16% are recorded. This means a generation of 140 – 160 watts per square meter of solar cells placed in full sun.  This full sun is expressed in “Full Sun Hours” or “Equivalent Sun Hours.” - ESH

15. .  5ESH is 5 hours of sunlight at an irradiance level of 1000 watts per square meter. Different parts of the world receive different amounts of sunlight.  Southern parts of Nigeria receive an average of 5ESH’s, the Middle belt averages 6ESH’s while up North – Maiduguri, Sokoto and Katsina areas average 7ESH’s.  This translates to less amount of solar array for the same load sizes as you move from the South to the North of Nigeria.

16. .  Thus, though the initial cash outlay for solar power installation is quite high relative to fuel generators, it is cheaper to run solar power in the North than in the South.  Since the lifespan of the modules is up to 40 years (usually with a warrantee of 20 years) the numbers work out much cheaper on the long run.  The solar isolation zone map will give you a general idea of the ESH for your location. Most African countries enjoy 12 hours of sunlight per day, but only average 4-6 ESH’s.

17. Wiring the PV’s  Most common modules are wired for 12 volts operation. There are also many large modules that will be wired for 24 volts from the factory or that is field adjustable for 12 to 24 volts.  All the modules you buy will have the diagram detailing how to wire them in parallel and in series.  Since every brand of module is set up a little differently, there would be no point going into specifics here. Knowing the basics will be helpful before you order the modules.

18. .  In a 12 volts system, all the modules are wired in parallel – positive to positive, and negative to negative.  Thus without increasing the voltage, the amperage of each individual module adds to the amperage of the array.

19. .  In a 24 volts system, each pair of modules is wired in series – positive to negative and vice versa – doubling the voltage (12 to 24). Then each series string is wired in parallel to increase the amperage.  Likewise in 48 volts systems, every 4 modules are wired in series. The important point to know is that only modules of identical wattage should be wired in a series string, since the amperage of the string will be equal to the amperage of the weakest module.

20. Electrical Terms and Calculations  The building blocks of an electrical vocabulary are voltage, amperage, resistance, watts and watt-hours.  Electricity can simply be thought of as the flow of electrons (amperage) through a copper wire under electrical pressure (voltage) and is analogous to the flow of water through a pipe.

21. .  If we think of copper wire in an electrical circuit as the pipe, then voltage is equivalent to pressure and amperage is equivalent to flow rate.  To continue with our electricity to water analogy, a battery stores energy much as a water tank stores water.  Since a column of water 2.31 feet tall produces 1 psi at the base, the taller the water tower, the higher the pressure you get at the base.

22. .  As you can see from the picture below, the mushroom shape design of a water tower allows it to provide a large volume of water to end users at between 40-60 psi.  Once drained below 40 psi, which occurs near the neck of the tower, continued water usage will rapidly deplete the water supply at an ever decreasing pressure.  Although a 12 volt battery is not physically shaped like a water tower, it has most of its stored electricity available between 12 volts to 12.7 volts.

23. Water/Electricity analogy

24. .  When drained below 12 volts, little amperage remains and the battery voltage will decrease rapidly.  In a simple system, a power source like a solar module provides the voltage which pushes the amperage through a conductor (wire) and on through a load that offers resistance to the current flow which in turn consumes power (watts).

25. .  Power is measured in watts and is the product of voltage and amperage. Energy is power (watts) used over a given time frame (hours) and is measured in watt- hours or kilowatt-hours (1 kilowatt-hour equals 1000 watt-hours).  For example, a 100 watt light left on for 10 hours each night will consume 1000 watt- hours or 1 kilowatt-hour of energy.

26. .  A kilowatt-hour is the unit of energy measurement that the utility company bills you for each month.  Electrical appliances are rated in terms of how many watts (or amps) they draw when turned on.  To determine how much energy a particular appliance uses each day, you need to multiply the wattage by the number of hours used each day.

27. A Watt is a Watt…is a Watt  Now that you know the formula for power (watts = volts x amps), be sure to remember that different voltages (ie: 12, 24, 48) do not necessarily mean any change in power.  For example, 6 amps at 12 volts is the same amount of power as 3 amps at 24 volts or 1.5 amps at 48 volts. It is still 72 watts. A watt is a watt is a watt.

28. .  For our purposes, changes in operating voltages do not change overall power. A 24 volt battery bank of 300 amp hours is equivalent to a 12 volt battery bank at 600 amp hours.

29. POWER GENERATION - SOLAR (PV)  Let's consider solar as a generating source first.  Remember that light striking the silicon cells within a module excites the electrons in the silica molecules, causing them to move down the conductive tabs and out the wires of the solar module.

30. .  In a typical solar module, this electricity will leave the module at between 16 and 18 volts at no load.  The voltage and amperage of each module is determined by the size and number of "cells" or thin slices of silicon that make up the module.

31. .  An I-V curve as illustrated below is simply all of a module’s possible operating points, (voltage/current combinations) at a given cell temperature and light intensity.  Increases in cell temperature increase current slightly, but drastically decrease voltage.  Maximum power is derived at the knee of the curve.

32. I-V Curve

33. .  Check the amperage generated by the solar array at your battery’s present operating voltage to better calculate the actual power developed at your voltages and temperatures.  So now you can see why a 50 watt solar module doesn't put 50 watts of power into your battery.

34. .  So, taking our sample system's daily requirement of 34 ah, how much PV (solar) would we require in a typical African country with an annual average of 5 kWh-meters (sun hours)?  34 ah / 5 sun hours = 6.8 amps  We need a module, or collection of modules that will provide 6.8 amps at max current.

35. . . A Kyocera 120 watt module will do nicely. Or we could use two 60 watt modules wired in parallel.  This sizing would guarantee performance on an average. But since the 5 kWh-meters or sun hours was an average, we know that some months were probably better and others were worse.  If we need to guarantee maximum performance, we should size to the worst average weather conditions.

36. .  Modules should be installed in completely un-shaded areas - remember that the cells are wired in series and even partial shading can cut your module's power in half.  Pole mounted modules are popular in Africa, but if your array exceeds four modules, you will probably want to use a ground or roof mount. You can buy ready- made mounting structure at Solartime, or have it made locally.

37. .  Remember that north of the equator your modules should tilt at 15 degrees south, and in the south, face north.  Tilt your modules at not less than 15 degrees, and up to your actual latitude. The 15- degree minimum tilt ensures that water and dust run off the module.  You can also adjust to latitude minus 15 degrees in the rainy season and latitude plus 15 degrees in the harmattan, but never below 15 degrees.

38. .  Use a compass or magnetic declination chart to find true north.  Remember to earth (ground) your racks and connect your modules with toothed or burred washers that will dig into the module frame and create a good electrical connection so that they can share your rack's ground.

39. Combiner Box  For large arrays of several series strings (for example, 4 series strings of 4 modules each in a 48 volt system) you should use a PV array combiner that will allow you to fuse or break each string and combine it efficiently into a 2 wire output.

40. .

41. Sizing your system  Below is a model for determining the size of array required to power the load shown  9.643KWH Load Capacity

42. Load Sizing Load QuantityWattsConnect ed Load HoursTotal Watt Hours System Loss Watt- Hours Require d Light PC’s 3434 15 100 45 400 3838 135 3200 1.15 155 3680 Fan Refrigera tor 1111 50 200 50 200 5 24 250 4800 1.15 288 5520 Total 6958385 9643

43. Calculate the # of PV’s rqrd.  Using 120W PV’s there will be  Ipv=Pmax =9643VAH = 80.36A Vdc 24V x 5ESH The nominal current of the 123W; 17V Sharp solar module is 7.1A. Therefore there will be  80.36A= 11.3 ~ 12 streams of 24VDC 7.1A solar modules = 12 x 2 = 24nos. for 5ESH (Equivalent Sun Hour) =24nos. 123W Sharp 17V, 7.1A solar modules.

44. The End  Thank You.