On the Reliability of Small-scale Solar system: Design of a stand-alonesystem in rural countries

Abstract: Over  one  billion  people  in  the  world  do  not  have  any  sort  of  access  to  electricity  service  and suffer  fromenergy poverty.  A large share of people who don’t have access to electricity live in the Sub-Saharan, African region, and are spread in rural and remote locations.  Connecting these people to the national grid is a great challenge in terms of cost and time.  Thus, off-grid is the suitable solution to limit the energy poverty in rural areas, especially when the location is far from the grid.  The use of renewable energy resources is gaining more  attention  and  more  off-grid  systems  are  operated  and  installed  since  they  supply  environmentally- friendly and cost-effective energy.  However, designing reliable off-grid systems based on renewable energy is challenging due to the stochastic nature of these resources.  This project focuses on how to design reliable and cost-effective stand-alone systems based on renewable energy sources.  A literature study has been conducted in order to gain knowledge about the different off-grid systems, which in turn has been needed to understand the different components that should be included in the various types of these systems.  The literature study was also conducted for the purpose to understand the different design alternatives and approaches.After gaining knowledge about off-grid systems,  a case study was selected about a stand-alone photo-voltaic (PV) system in Zambia.  The selected case study analysis a sustainable energy project that has been implemented in a rural community located in the southern part of Zambia called Chalokwa.  This study is a result of a collaboration between a volunteer-run organization called KiloWatts for Humanity (KWH), Dr. Henry Louie from Seattle University and the Reliability Centered Asset Management “RCAM” department at KTH. The selected system is a mini-grid system, which consists of 2.4 kW PV array and 10 kWh battery bank.The selected method that was defined by Dr.  Henry Louie and according to IEEE standards [20], [21], was used to study the existed design of the system and, further, suggest new design alternatives that could be implemented when the system needs to upgrade.  The system needs to upgrade when the battery bank reaches its end of life which is assumed, in this study, to be 5 years.  Two Scenarios were created, the first Scenario tests the selected design methodology on the initial system in the current time.  Furthermore, the second Scenario implements the same methodology to suggest new design alternatives that could be suitable for future expansion of the system, assuming that the consumption continues to increase by 5 % each year throughout the next 5 coming years.  The design result of the studied system in the first Scenario consists of 19 kWh battery capacity and 2.6 kW PV array capacity.  Moreover, the second Scenario resulted in two suggested design alternatives.  The first alternative design consists of 19 kWh battery capacity and 3.12 kW PV array, while the second alternative design consists of 19 kWh battery capacity and 3.36 kW PV array capacity.Furthermore, the results of the different alternative designs were tested in an energy management algo- rithm in MATLAB environment.  This step was considered to be important in order to test the performance of the system and calculate the deficit and the surplus of the different alternative designs, in order to compare the reliability of each design alternative.  The total deficit represents the unmet demand during the studied time period, which is used later to estimate the Loss of Power Supply Probability (LPSP). The LPSP is used later to evaluate the availability of the different alternative designs of the system.The LPSP of the initial system was measured to be 13.8%.  Furthermore, the LPSP of the design that is suggested in the first Scenario is 6%.  Moreover, the LPSP of the second Scenario was measured to be 11% and 4 %, for the first alternative design and the second alternative design respectively, assuming that the consumption increases by 5 % each year in the next 5 coming years.The reliability results showed that the second alternative design of the system,  which consists of 3.36 kW PV array and 19 kWh battery bank capacity would provide the best reliability.  This is the case if the system consumption continues to increase by 5 % per year in the future, and if higher reliability than the current system is required. However, if the system consumption remains constant, then the design alternative suggested in the first Scenario is optimal, which consists of 19 kWh battery bank capacity and 2.6 kW PV array.In reality, the cost should be weighed against the reliability in order to make the smartest design decision and rather implementing more systems and help many people to get access to electricity than investing inonly one system with high reliability.