An introduction to the basics of electricity and solar systems in Mauritius


Intro by Dietmar

After reading the interesting and inspiring thesis of Onyedika Atuchukwu on a Hybrid System for a rice factory processing plant in Nigeria that is connected to an unreliable grid, I discussed with him if we could do a project on the basics of electricity and an introduction on solar systems in Mauritius to get better acquainted with the subject. You are most likely consuming electricity at the moment you are reading this in one way or the other. Whether it is from your phone’s battery or your desktop PC connected to the CEB grid, having the lights on, the air con running etc. Electricity plays an important role in our daily lives. Sometimes when I hire an electrician to fix something, I realise my short comings on this subject and I wished, I knew more on this topic. Just like when reading my CEB bill, what does kilowatt hour (kWh) mean? How is the price calculated? How much might a solar system cost? How long might it take until I would have fully amortized the costs? How interesting is it for example for a beach villa that is operated as a holiday rental unit? These are some of the topics that we have addressed in this project. Please bear in mind that this project is only an introduction to these themes, the topic of electricity is vast and solar systems can be complex and have various variants on how these can be setup. What not to expect in this project is an analysis of local existing solar systems nor solar farms that are present in Mauritius. Links to projects and companies are not endorsements, these are for information purposes only. You are welcome to contribute questions and information around this topic in the comments section.

Onyedika recently finished his Bachelor degree in the study field of Electrical Power Systems Engineering at the The African Leadership University in Mauritius.

Without further ado, let’s dive into the topic of electricity and solar energy with Onyedika.

Photo by Dennis Schroeder / NREL from WikiMedia
Dennis Schroeder – NREL Photographer / Public domain | For illustration purposes.

Power System Overview

You turn on the switch and the power come on. Have you wondered how the power travelled to that point of use? This is made possible by (Electrical) Power Systems. Conventional power systems involve the generation, transmission and distribution of electricity, and it does not usually involve situating electrical power plants close to habitation because of the disturbances they might present. Kosmadakis and his colleagues [1] defined conventional power systems as those which include power generation from fossil fuels. Fossil fuel examples are coal, natural gas, oil, etc. In contrast, renewable power systems include generation from solar, wind, hydro (water), geothermal, biomass, etc.

Electricity in Mauritius

According to the Mauritius (CEB) Central Electricity Board’s production overview website, the island of Mauritius had a nominal installed power capacity of 876.76 MW in 2018 of which CEB has a share of 56.85% and the rest taken up by Independent Power Producers (IPPs), Small Scale Distributed Generation (SSDG) and Medium Scale Distributed Generation (MSDG). In the same year, 2,827.6 GWh of energy was consumed. According to the 2017 Energy Observatory Report [2], 2,558.6 GWh was consumed in 2016 and 2,618.1 GWh in 2017. The Renewable Energy Roadmap [3] projects consumption to reach 3,097 GWh in 2020, 3,345 GWh in 2025 and 3,775 GWh in 2030. Of the 2,827.6 GWh of electricity used in 2018, 1,307.8 GWh (46.25%) was generated by power plants owned by the CEB. The rest was provided by IPPs, SSDGs and MSDGs whose generations were mostly from bagasse and imported coal. In the Renewable Energy Roadmap 2030 for the Electricity Sector, it was stated that 79.3% of electricity in 2018 was generated from non-renewable sources mainly fuel oil, gas and coal. 20.7% came from renewable sources that included bagasse, hydro, wind, solar and landfill gas.

Explanation of terms

  • Power Plant: This is a complex/facility where electricity is generated from different energy sources.
  • Bagasse: This is the usually dry fibrous/pulpy residue after the juice from sugar cane is extracted.
  • Installed/Nominal capacity: This the intended maximum output of a facility, in this case, a power plant.
  • Independent Power Producers: These are non-utility (not owned by CEB) organisations which own electricity generation facilities. Since CEB is the sole agency in charge of transmission, distribution and sale of electricity to the public in Mauritius, these IPPs have to sell their generated electricity for the public to the CEB for the public’s consumption.
  • What is the difference between GW and GWh? The smallest unit of power is Watts, written as “W”. Power can be understood as an instant output (or input). 1000 units of Watts (W) make a Kilowatt (kW); 1000 units of Kilowatt make a Megawatt (MW); 1000 units of Megawatt make a Gigawatt (GW) and 1000 units of Gigawatt make a Terawatt (TW). In essence, 1 TW is 1,000,000,000,000 W (one trillion Watts).
  • Since power is an instant output, the sum of the power at different instances gives energy. Generally, energy is the product of power and time, so if a constant 20 W is used for 5 seconds, then the energy consumed in that period is 100 Joules (J). However, in electricity calculations, it is preferred to represent energy in W and h for Watts and hour respectively. Therefore, even though 20 W of electricity for 45 seconds normally would be 900 J, in electricity calculations, it will be presented as 20W*45/(60*60)h=0.25 Wh. And 20,000 W (20 kW) of electricity for 100 hours, which ordinarily would be 2,000,000 J, will be presented as 20,000W*100h=2,000,000Wh=2,000kWh=2 MWh.

Electricity Generation in Mauritius

The CEB generates electricity from four thermal power plants: Nicolay (Port Louis), Fort George (Mer Rouge), Fort Victoria (Cassis) and St. Louis (Pailles); as well as ten hydropower stations: La Nicoliere F.C (Nicoliere), A.I.A (Reduit), La Ferme (La Ferme), Midlands (Midlands), Magenta (Henrietta), Tamarind Falls (Henrietta), Le Val (Riche en Eau), Champagne (Mahebourg), Ferney (Mahebourg), Cascade Cecile (Surinam). While the hydropower plants are powered by water in motion, the thermal power plants run on heavy fuel oil (HFO) and jet fuel, both of which are non-renewable fossil fuels. Comprehensive information on both the CEB and IPPs operated power stations in Mauritius can be found at Power Stations in Mauritius and Rodrigues, though not up to date.

Electricity Transmission and Distribution in Mauritius

Since electricity is generated far away from the points of consumption, the electricity needs to be transmitted to locations where they are needed, and after transmission, the electricity is distributed at those localities. Consider transmission as the aeroplane that moves passengers from some place overseas to SSR International Airport, Mauritius, and consider distribution as the taxi or public bus that takes the passengers to their destinations in Mauritius.

The size of an aeroplane compared to the size of a taxi car can also be related to the transfer of electricity. In Mauritius, the power outlet where one plugs in their TV set or washing machine supplies 230 Volts (V), but according to the CEB, the transmission network in Mauritius operates at a voltage level of 66 kV which is more than 250 times of what one receives at their home power outlet. 1000 units of V make 1 kV and you might be wondering how “V” relates to “W”. Current, measured in Ampere (A) is the third parameter needed to understand the relationship. Voltage measured in “V” is the electrical force that drives a current, and current is the rate of flow of electric charge. Voltage is the cause and current is the effect. This YouTube video explains the difference between the three parameters.

More information on the differences can also be found at the Diffen website. Power, measured in Watts (W) is the product of voltage and current. This means that if one is receiving 230 V at their power outlet, and a TV set that draws (requires) 0.4 A is plugged in and turned on, the TV set immediately starts drawing 92 W, and if it operates for 2 hours, it uses 184 Wh of electricity. Mathematically, Power (W) = Voltage (V) x Current (A), and Energy (kWh) = Power (kW) x time (h).

Electricity can be generated at different voltage levels by power plants but because the transmission network in Mauritius requires a voltage level of 66,000 V (66 kV), which is typically higher than the output voltage levels of electricity generators, the voltage level of the generated power is stepped up (increased) with the use of power transformers. Transformers in basic terms increase or decrease (transform) the voltage level in the process of electricity transfer. Ignoring losses during power transformation, the power before and after voltage transformation remains the same. For the power to remain the same, as the voltage increases, the current decreases and that is very important and beneficial to power transmission. There are certain losses that occur during power transmission which is very dependent on the current level of transmission. So, making the transmission current level as low as possible minimizes the losses. An illustration of this is like counting the sum of Rs 36,000 made of Rs 2,000 notes and comparing that to counting the same sum but comprising Rs 10 coins. Ultimately, Rs 36,000 was counted but more energy would be expended when counting the avoidable 3,600 coins. So, consider the size of the commercial aeroplane as the transmission voltage level, and consider the size of the taxi car as the distribution voltage level.

According to the CEB, these 66 kV transmission lines terminate at 22 kV substations where the voltage level of the power is stepped down from 66 kV to 22 kV and the resulting current increased by a factor of 3. The electricity at 22 kV voltage level also travels some distance to consumption locations or substations where they are further stepped down to 6.6 kV. Ultimately, before the power gets to homes, the voltage level is stepped down to 400 V line-to-line voltage. This is the same as 230 V line-to-neutral or phase voltage. Electric power is transmitted through three phases to minimize losses. This is why the electricity poles you find along the highway have at least three lines/cables running through them. There is usually a fourth wire, known as earth/ground/shield wire, which serve as protection against lightning. When the voltage between any two phases of a three-phase line is measured, the resultant value is known as the line-to-line voltage. On the other hand, when the voltage between any one phase and the neutral of the system (0 V) is measured, the value is called phase voltage and is always less than line voltage. In electricity distribution, different phases are connected to different buildings such that the electricity demand in the phases are balanced.

Generally, line-to-line voltage (VLL) = phase voltage (Vph) x √3. The line-to-neutral 230 V voltage is what the power outlet at home supplies. Hence, while you use the power at home or place of work, some generator most likely far away from you is generating that power using energy resources that may or may not be environmentally-friendly. The generation, transmission and distribution of electricity are illustrated in the figure below.

Illustration of electricity generation, transmission and distribution
Figure 1: Illustration of electricity generation, transmission and distribution

Effect of Fossil Fuels

According to National Geographic, fossil fuels when combusted release greenhouse gases (GHG) including carbon dioxide which trap heat in our atmosphere and contribute significantly to global warming and climate change. The effect of global warming can be seen in pictures on this web page on Fossil Fuels by National Geographic. More information on climate change can also be accessed at the United Nations Climate Change web page. The United Nations Environment’s 2019 Emissions Gap Report shows that greenhouse gas emissions need to be reduced by 7.6% in each year of this decade in order for the world to be on track towards limiting global temperature rise to close to 1.5 ° C. NASA’s Earth Observatory website notes that a 1° C change in global temperature is significant as it requires a huge amount of heat to warm all the areas of the earth including oceans, atmosphere and land, and cause an increase by 1° C. According to the World Meteorological Organization (WMO), 2019 was the second warmest year on record, following after 2016, and this calls for more deliberateness towards tackling global warming and climate change. Several interventions by different countries and regions have been initiated to that regard. European Commission president Ursula von der Leyen last December presented a deal, which was agreed to by European Council national leaders, that aims to make the European Union carbon neutral by 2050. This would involve reducing greenhouse gas emissions in the EU by at least 50% relative to the 1990 levels by 2030.

Reducing greenhouse gas emissions can be achieved through several means. The European Union pledged to reduce their GHG emissions in 2020 by 20% relative to the 1990 levels and that involves committing to having 20% of gross final energy consumption (GFEC) from renewable energy sources. In addition to using more renewable energy sources to mitigate climate change, National Geographic highlights other actions which include using less coal, oil and gas-based energy sources, capturing carbon dioxide from the smokestacks of coal or natural gas plants to prevent new emissions, planting more trees to absorb carbon dioxide from the atmosphere, and using complex machines to capture carbon dioxide from the atmosphere, amongst others. With the increasing need for energy, generating energy from clean and renewable sources solves both the challenges of providing energy and making the earth more sustainable.

The Deputy Prime Minister of Mauritius, Hon. Ivan Leslie Collendavelloo noted in the Renewable Energy Roadmap 2030 for the Electricity Sector that the target of 35% renewable energy in the Mauritius electricity mix can be achieved with an additional 396 GWh by 2025. Renewable energy contribution is projected to reach 25% this year with solar energy taking up 8% of the 25% in 2020, 10.2% of 35% in 2025 and 11.8% of 35% in 2030. Solar in these cases is the sum of residential, commercial and utility energy contributions. The installed capacity of renewable energy sources is expected to grow from 394.4 MW in 2020 to 519.2 MW in 2025, and 610.4 MW in 2030 for the 35% target of renewable energy contribution to the electricity mix.

Renewable Energy (Solar PV)

There are several means of generating energy sustainably which include solar photovoltaics (PV), concentrated solar power (CSP), wind turbine, wave energy technology, hydro turbine, geothermal, etc. The solar water heating (SWH) technology common in Mauritius is also a renewable means of generating energy in the form of hot water rather than heating with the costly and non-renewable based sources. The facts that manufacturing processes for these clean energy technologies need to be more sustainable, and hardware as much as possible should be recycled or upcycled at the end of their service life, are worth noting.

Solar PV technology converts solar radiation from the sun to electricity using semiconductors through a process known as the photovoltaic effect. One of the merits of solar PV technology is its modularity which means that the capacity can be across a wide range of size although it is more cost-effective as the size increases. Such energy source not only makes a user and consumer an active player in making the world more sustainable but also saves the energy user costs in the long term. Generation of energy using solar PV technology involves different equipment that is largely dependent on the architecture of the system. Because the sun is not always available at a point and the variation of solar irradiance during the day, it is necessary to combine solar PV generation with other energy sources like the grid (CEB), wind turbine, combustion engines, etc. or storage systems like battery energy storage.

For a typical household in Mauritius which wishes to offset their energy cost (amount paid to CEB for energy consumed), it can install a grid-connected solar PV system. This does not require battery storage as the solar PV system supplies partial or total power for the household when the sun is available, with any deficit sourced from the grid and any excess sent to the grid. For total independence from the power grid (off-grid) using solar PV, an appropriately-sized storage system is required, and in whichever case an emergency energy source (the grid or a backup generator) is necessary. Battery storage systems come in different technologies differentiated by their chemical composition. Some of these battery technologies are lead-acid, lithium-ion, sodium sulphur and nickel-cadmium. The most used types for solar PV applications are lead-acid and lithium-ion with the latter being more financially demanding because of its better characteristics. This Youtube video discusses three types of battery technologies that are applicable to solar storage systems and how they can be connected.

In developing an off-grid solar PV system, several components are needed, some of which are also used for other solar PV configurations. Some of these components include solar panels (modules), charge controller, inverter and battery storage units.

The solar panel(s) convert the irradiation from the sun into DC power which can be used to charge the battery units or used immediately after conversion to AC power.

The output from the solar panels, when used to charge battery units, passes through a charge controller which regulates the charging and discharging of the battery units. Charge controllers prevent overcharging as well as over-discharging of battery storage units [4]. The output from the charge controller can also be used to power DC loads.

When the output from the solar panels is used to power AC loads, it passes through an inverter which converts DC power into AC power. While a transformer steps an AC voltage level up or down, an inverter changes power in DC (Direct Current) form to AC (Alternating Current) form. In AC flow, electrons which cause current flow switch direction depending on the frequency of operation while in DC flow, the electrons flow only in one direction. More on the differences can be found at the Diffen Website. The important point to note is that the power from the wall sockets at home or office are in AC form.

Electricity Consumption and Billing

Sample CEB Electricity Bill for Tariff 120
Figure 2: Sample CEB Electricity Bill for Tariff 120

From the bill, it can be seen that 171 kWh of electricity (electrical energy) was consumed from 8th October to 5th November which is a total of 29 days. The average consumption per day becomes approximately 6 kWh which however does not give any knowledge of the energy consumed on the day with the maximum consumption. For a real design, proper energy analysis of the building or complex is necessary for a properly sized solar PV system. The consumption charges can be calculated using the table shown in the image below.

Breakdown of Electricity Tariff Costing
Figure 3: Breakdown of Electricity Tariff Costing

For the considered electricity bill, it belongs to Tariff 120 and that determines the cost calculation shown in the table below.

Tariff 120 Cost Calculation
Units per month (kWh)Units of kWhCost per kWh (Rs)Total Cost (Rs)
First 25253.1679
Next 25254.38109.5
Next 25254.74118.5
Next 25255.45136.25
Next 100716.15436.65
Total171
879.9
Table 1: Electricity Consumption Cost Calculation

The process of getting the consumption charges as stated in the electricity bill can be seen from the table above. The energy consumption, as well as the solar radiation at a location, play a vital role in designing a solar PV based energy system. According to an assessment performed by Ramgolam and Soyjaudah [5], averaged daily irradiation ranged from 3.25 kWh/m2/dayto 5.04 kWh/m2/day across locations in Mauritius. Also, according to a map developed by Ryan Shea which was based on a study performed by the University of Mauritius, the solar irradiation in Mauritius was from 3.5 kWh/m2/day to 5 kWh/m2/day. These energy values give a picture of the abundance of raw solar radiation at particular meter-square locations before considering the inefficiencies presented by solar panels and other equipment that make up the solar PV system.

Battery Sizing

Even though the average daily energy demand from the bill above was approximately 6 kWh, for this section an energy demand of 9.6 kWh is assumed and used for the calculations following. A deeper understanding of the loads and consumption pattern, as well as the number of days the battery bank is expected to act as backup, are required for a more realistic sizing of a battery bank for an off-grid application. The knowledge of the value of the highest energy demand from a range of days is also important in battery sizing. An illustration of how different loads contribute to the daily energy consumption is shown in the table below.

Sample total energy calculation
Table 2: Sample total energy calculation

While the assumed usable capacity of the battery system being designed is 9.6 kWh, the actual capacity of the battery system must be higher than the usable capacity because of a battery feature known as Depth of Discharge. Battery depth of discharge simply means how much a battery can be discharged as a percentage of the overall capacity of the battery. Lead-acid batteries typically have their depth of discharge at around 50%; this means that for an estimated usable capacity of 9.6 kWh, the actual capacity of the battery system should be 19.2 kWh. If the depth of discharge of the battery storage system was 60% (40% remaining), then the actual battery capacity would be 16 kWh. Consider this 12 V, 200 Ah battery unit on Alibaba, the capacity of each unit is 2400 Wh (12 V * 200 Ah) which is equivalent to 2.4 kWh. For a 19.2 kWh capacity, 8 of such battery units are required. Solar PV and battery sizes can be oversized with respect to the daily load in order to provide security (backup) for days with less sunshine.

Basic Solar Panel Sizing

With the battery capacity decided for storing energy sufficient for one day, the capacity of the solar panel is chosen. There are three main types of solar PV panel technologies namely mono-crystalline silicon, poly-crystalline and thin film, in the order of their decreasing efficiency. This YouTube video from Duet Justus did a good job of explaining the different types of solar panels and the different ways of wiring the panels as the designer desires.

Roughly noting, the capacity of the solar panels will be dependent on the usable capacity of the battery storage since the battery is not expected to be discharged below the usable capacity (or charged beyond the actual capacity). A proper study of the solar radiation at the location together with the elevation of the location is required to determine the capacity of the solar panels. The European Commission’s PVGIS tool helps in the basic analysis of a location. According to the tool, for a random location in Mauritius with coordinates -20.276, 57.570 (Belle Rive) and 14% system losses, the average daily output per 1 kWp installed capacity of a free-standing (fixed position) system with optimized slope and azimuth of 20° and -143° respectively, was 4.365 kWh/kWp/day. This value is with respect to the monthly averages. That implies that when 1 kWp of solar panels are installed, the energy that can be extracted in a day would be around 4.365 kWh on average. The monthly averages from the PVGIS tool ranged from 3.73 kWh in June to 5.01 kWh in December. kWp stands for Kilowatt peak and is the unit for maximum or installed capacity. If the solar PV system is made up of four 250 W solar panels, then the system has a capacity of 1 kWp; if there are nine 150 W solar panels, then the capacity of the system is 1.35 kWp. For better understanding, the “p” stands for “peak” and represents the maximum/installed capacity.

If the usable battery capacity is 9.6 kWh and the average output at the location is 4.365 kWh per kWp, then the required solar PV capacity is 9.6/4.365 is 2.2 kWp. Various solar PV module sizes can be combined to get exactly 2200 Wp (2.2 kWp) system, but for simplicity, this could be ten 220 W solar panels (10 * 220 W = 2200 W = 2.2 kW.) The system can then be described as a 2.2 kWp, 19.2 kWh system. These analyses are merely theoretical as more intensive analyses of the location and system components are required to design a technically and economically viable solar PV based power system. Solar panels and battery storage units do not make up solar PV systems alone. The desired operation of the system determines the type of inverter that can be used.

A good and basic tool that can be used for solar panels and battery sizing exercises is the altE Store Online Off-Grid Calculator. For a 9.6 kWh daily energy demand, 1-day backup power and 6 sun hours, the resultant battery capacity was 23 kWh and the required solar panel capacity was 2.08 kWp, which are all estimates. The altE website also offers tools for grid-tied solar electric system calculator, electricity load calculator, wire and cable sizing calculator amongst other tools.

Inverters

There are several types of inverters but three will be discussed which are PV inverters, battery inverters and hybrid inverters. In a nutshell, PV inverters, which exist as either string inverters or microinverters, convert the DC power from the solar PV panels into AC power that is used directly by the AC loads or sent to the grid. Microinverters are attached behind individual solar panels to give a better performance; however, it makes initial costs higher. Battery inverters convert DC energy stored in batteries to AC power/energy, and they also can convert AC power into DC power for battery charging. Hybrid inverters also called multi-mode inverters perform the functions of converting DC power from solar panels to AC power to serve AC loads or supply to the grid for grid-tied connections, charging battery units with either the regulated DC power from the solar panels or the rectified power (AC to DC conversion) from the grid, and converting the stored energy in the battery to AC power/energy to serve AC loads, quite a lot. Battery inverters and hybrid inverters, due to their functions, are usually equipped with inbuilt charge controllers that regulate the charging and the discharging of the battery storage units. The pros and cons of these inverter types can be found at Solar Choice. The desired configuration in the system determines the choice of inverter and coupling that is implemented and sometimes can be vice versa based on certain constraints.

System Coupling and choice of inverter

System coupling can simply be described as the form of power (AC or DC) that ultimately links all the components in a power system. The effect of the coupling of the system on the choice of inverter is illustrated in the two diagrams following.

AC coupled system using PV and battery inverter
Figure 4: AC coupled system using PV and battery inverter

For the AC coupled system, The DC power from the PV panels are converted to AC power by the PV inverters and is supplied to the AC loads. AC loads are any electricity demanding equipment (item in general) that requires AC power. DC loads are items that require DC power; rechargeable battery units require DC power for their charging which they can also deliver when required. AC power (electricity) can also be converted to DC power (electricity) which is used to charge the battery system.

When the PV power is not sufficient, the battery discharges with its DC power converted to AC power by the battery inverter. When both the PV power and battery power cannot meet the AC load, then the backup generator or the grid can be made to supply the deficit. The function of the Automatic Transfer Switch (ATS) is to switch between the backup generator and the grid automatically and to ensure that the backup generator and the grid are not supplying power at the same time. This is especially useful for regions/countries where the grid is not always available.

The AC bus bar is the point where different AC power sources meet. It is ensured that all power getting to a bus bar is of the same voltage level, frequency and phase sequence. If electricity is considered as water, an AC bus bar can be likened to a joint where the water from different water pumps meet and supply a common point. However, for water, it can flow at different speeds from the different water pumps and there won’t be an issue at the joint.
Someone can decide to have the backup generator, the grid and the solar PV to all be connected to the ATS. What that means is that only one of them can supply at any time. That is why the solar PV power is sent directly to the bus bar so that any output from it is always utilized (remember it is first priority). The grid and the backup generator cannot be supplying backup power at the same time, hence why an ATS is needed for them. If you connect four sources to an ATS, you can only use one of such sources at a time. The battery was connected as it is because it also needs to be charged (and not just supplying power).

With respect to figure 4, the power from the solar PV and the battery are the primary power. Whenever the power from the solar PV (and battery if available) is sufficient to power the available load and there is a grid outage, the power supply to the load is not disturbed because neither the grid nor the backup generator is supplying power to the load. However, at any time the load is supplied by both the solar PV (and battery if available) and the grid (because solar PV and battery are not sufficient), and the grid goes off, power supply to the load is terminated until there is enough power to supply to the system, which can be the generator coming online, and the ATS switching from “the grid” option to “the generator” option.

To prevent power cuts, the battery system is sufficiently sized such that it can supply any possible level of power that can be demanded, while supported/charged by the solar PV power (when available), the grid (when available and needed), and backup generator (when needed).

Grid-tied solar PV structure without battery does not require a battery storage system, and power is drawn from the grid when needed, for example at night. The solar PV system can also be sized such that it can produce surplus electricity that can be sent to the grid. It is assumed the grid is reliable in this case. A household can also be set up such that it only draws power from the grid with the assumption that the grid is reliable, and then sells all solar PV generated power to the grid (CEB). In the case where the household decides to also use the power from the solar PV, a suitable inverter for grid tied operation is used which controls the utilization of the power from the grid as the output from the solar PV reduces; there would be no power cut as this occurs. Power cut would be expected to occur when the grid power fails. For load systems having critical/sensitive electrical equipment and an unreliable grid, the risk of power cut is reduced by sourcing power from suitably sized battery storage system. The battery storage system would then be charged by the solar PV output as the first preference, the grid when available and necessary, or a backup generator if necessary.

Solar PV structure with battery can be on or off-grid depending on preference. Here a battery storage system is required to store energy and supply when needed. The grid is also assumed to be reliable here. In the case where the grid is not reliable, a backup generator is needed.

Operation of hybrid inverter
Figure 5: Operation of hybrid inverter

In this case, the hybrid inverter is the brain and heart of the operation. It takes input from PV panels, the battery storage system, the grid and the generator and ensures the AC loads are met. It also does the function of charging the battery storage system as required. The system can be designed in such a way that only solar PV charges the battery when there is more power output from the solar PV than is needed, or both solar PV and the grid, or even all three –solar PV, grid and generator.

There are other ways to design solar PV/hybrid systems based on the particular system requirement and each design involves more details than have been explored in this writing. Some of these can be seen at Energy Informative. Chamburn Radha, a solar energy enthusiast and DIY designer based in Mauritius describes how he designed and installed his off-grid solar system with battery storage in this Instructables post.

Residential Solar PV Cost

Residential/domestic solar PV system costs are considered more expensive than the grid. Setting up a solar PV based power system is capital intensive but operating and maintaining the system is at little or no cost. A good comparison of the grid power and an off-grid solar PV system gives more insight into the costs. Ryan Shea in his report noted that residential solar PV is more expensive than utility-scale solar PV. For the cost analyses, the cost of the off-grid solar PV system based on the 2.2 kWp capacity is compared to the cost of using the power from the grid according to CEB’s Tariff 120.

According to the report by Maxwell Stamp PLC from an assessment of solar PV in Mauritius which was highlighted in the Renewable Energy Roadmap 2030 for the Electricity Sector, the capital cost of residential solar PV in Mauritius is estimated to be $2,250/kW. They also added that the installation of battery for full power back-up (off-grid) would add another cost of between $1,500/kW and $2,800 kW. The $1,500 value is assumed for this analysis. The total cost for an off-grid solar + PV system becomes $3,750/kW. For a 2.2 kW system, it becomes $8,250 = RS 301,125 ($1 = Rs36.5). The savings from using a solar PV + battery system is used to determine how long it would take to recover the capital cost of the system.

For an average daily energy demand of 9.6 kWh, the energy demand for a month (30 days) becomes 288 kWh. The cost of this energy according to the CEB’s Tariff 120 is calculated below.

Energy cost calculation for 288 kWh
Table 3 Energy cost calculation for 288 kWh

With a monthly consumption charge of Rs1,709.45 by the CEB for a 288 kWh consumption, the yearly cost of electricity is estimated to be Rs20,513.4. It would, therefore, take about 15 years to recover the initial capital of Rs301,125. The cost of replacement of components like battery units was not considered. A more cost-effective option is using a grid-connected system thereby eliminating the need for a battery storage system.

Solar PV Cost for High-Energy Consumers

Let’s consider a beach villa in Mauritius composed of 3 bedrooms, 3 bathrooms, 1 kitchen and 1 living room. The appliances in the villa are tabulated below with typical daily energy demand in the summer computed. *Above average usage scenario assumed for AC units.

Consumption for high energy demanding villa
Table 4: Consumption for high energy demanding villa

The table shows that the daily energy demand for the sample villa is 61.425 kWh. This equates (30*61.425) 1,842.75 kWh per month. Using the 120 Tariff electricity pricing rate, the consumption charge is calculated as below.

Energy cost calculation for 1,842.75 kWh
Table 5: Energy cost calculation for 1,842.75 kWh

The monthly consumption charge amounts to Rs15,334.17 which for a year becomes roughly Rs184,010. With an average output of 4.365 kWh/kWp/day got from the PVGIS tool, the required solar PV capacity to fully cover the daily load of 61.425 kWh would be 14 kWp (61.425/4.365). Using the $3,750/kW capital cost rate for solar PV + battery system discussed earlier, the total capital cost for a 14 kWp solar PV + battery system becomes $52,500 which is equivalent to Rs1,916,250. This would take 10.5 years (Rs1,916,250/ Rs184,010) to recover.

Another option is installing solar PV without battery and sourcing any deficit from the grid. For this analysis, the system is considered to not provide any excess that can be sent to the grid. In practice, it requires careful study of the load pattern of the villa and matching that with the possible solar output at the location. Assuming that a 7 kWp system would not be able to produce more power than the load at any point but can supply half of the energy need, the cost of the 7 kWp solar PV only system becomes $15,750 (2250 x 7) using the $2,250/kW cost rate reported by Maxwell Stamp PLC. In Rupees, the capital cost becomes Rs574,875. The energy sourced from CEB (the grid) is halved (1,842.75/2 = 921.375 kWh) such that the new consumption charge becomes Rs7,253.71 as shown below.

Energy cost calculation for 458.6 kWh
Table 6: Energy cost calculation for 458.6 kWh

With this second setup, Rs8,080.46 (15,334.17 – 7,253.71) is saved monthly which is equivalent to Rs96,965.51 yearly. It would therefore take 6 years (Rs574,875/ Rs96,965.51) for the savings from using a solar PV only system to cover the capital cost of the solar PV only system which is a better option cost-wise. The same operation can also be applied to the low-energy demand residential solar PV illustration.

There is also the option of selling excess electricity to the grid from a solar PV only system as mentioned by Go Solar, a solar PV power system developer that has installed several PV systems in residential houses through the phase 1 of the Mauritius Small Scale Distributed Generation (SSDG) Scheme.

Solar Calculator
https://www.altestore.com/howto/solar-calculators-c36/

Solar PV + Battery Table

Solar PV + Battery
Energy Consumed (kWh)Cost of Grid Energy (CEB Bill)Approx. Solar System CostAmortisation Period (years)
75MUR 307.00MUR 78,393.4721.28
100MUR 443.25MUR 104,524.6319.65
150MUR 750.75MUR 156,786.9417.40
200MUR 1,058.25MUR 209,049.2616.46
250MUR 1,409.25MUR 261,311.5715.45
300MUR 1,804.25MUR 313,573.8814.48
350MUR 2,242.75MUR 365,836.2013.59
400MUR 2,681.25MUR 418,098.5112.99
500MUR 3,558.25MUR 522,623.1412.24
550MUR 3,996.75MUR 574,885.4511.99
600MUR 4,435.25MUR 627,147.7711.78
800MUR 6,189.25MUR 836,197.0211.26
1000MUR 7,943.25MUR 1,045,246.2810.97
1500MUR 12,328.25MUR 1,567,869.4210.60
1800MUR 14,959.25MUR 1,881,443.3010.48
2000MUR 16,713.25MUR 2,090,492.5510.42
2500MUR 21,098.25MUR 2,613,115.6910.32
3000MUR 25,483.25MUR 3,135,738.8310.25
3500MUR 29,868.25MUR 3,658,361.9710.21
4000MUR 34,253.25MUR 4,180,985.1110.17
4500MUR 38,638.25MUR 4,703,608.2510.14
5000MUR 43,023.25MUR 5,226,231.3910.12
5500MUR 47,408.25MUR 5,748,854.5210.11
6000MUR 51,793.25MUR 6,271,477.6610.09
6500MUR 56,178.25MUR 6,794,100.8010.08
7000MUR 60,563.25MUR 7,316,723.9410.07

Solar PV Only

Solar PV Only
Energy Consumed (kWh)Cost of Grid Energy (CEB Bill)Approx. Solar System CostSavings (50% Solar 50% Grid)Amortisation Period (years)
75MUR 307.00MUR 23,518.04MUR 173.2511.31
100MUR 443.25MUR 31,357.39MUR 254.7510.26
150MUR 750.75MUR 47,036.08MUR 443.758.83
200MUR 1,058.25MUR 62,714.78MUR 615.008.50
250MUR 1,409.25MUR 78,393.47MUR 812.258.04
300MUR 1,804.25MUR 94,072.16MUR 1,053.507.44
350MUR 2,242.75MUR 109,750.86MUR 1,338.256.83
400MUR 2,681.25MUR 125,429.55MUR 1,623.006.44
500MUR 3,558.25MUR 156,786.94MUR 2,149.006.08
550MUR 3,996.75MUR 172,465.64MUR 2,390.006.01
600MUR 4,435.25MUR 188,144.33MUR 2,631.005.96
800MUR 6,189.25MUR 250,859.11MUR 3,508.005.96
1000MUR 7,943.25MUR 313,573.88MUR 4,385.005.96
1500MUR 12,328.25MUR 470,360.82MUR 6,577.505.96
1800MUR 14,959.25MUR 564,432.99MUR 7,893.005.96
2000MUR 16,713.25MUR 627,147.77MUR 8,770.005.96
2500MUR 21,098.25MUR 783,934.71MUR 10,962.505.96
3000MUR 25,483.25MUR 940,721.65MUR 13,155.005.96
3500MUR 29,868.25MUR 1,097,508.59MUR 15,347.505.96
4000MUR 34,253.25MUR 1,254,295.53MUR 17,540.005.96
4500MUR 38,638.25MUR 1,411,082.47MUR 19,732.505.96
5000MUR 43,023.25MUR 1,567,869.42MUR 21,925.005.96
5500MUR 47,408.25MUR 1,724,656.36MUR 24,117.505.96
6000MUR 51,793.25MUR 1,881,443.30MUR 26,310.005.96
6500MUR 56,178.25MUR 2,038,230.24MUR 28,502.505.96
7000MUR 60,563.25MUR 2,195,017.18MUR 30,695.005.96

Disclaimer: These tables are only examples and not to be taken as is. Values computed are based on reference figures for the year 2019/2020. Costs can vary and there are also maintenance costs from time to time to consider. Ideally if interested for a more precise costing one should contact a solar company that does such installations who will analyse your home setup. The information presented in the second table is based on the assumption that half of the energy requirement is sourced from the solar PV system (without battery), and the other half is sourced from the grid. This means that when the system is operational, only the cost of half of the energy demand which is sourced from the grid is paid. That is unlike when the system has a battery storage system and is off-grid, therefore no energy is sourced from the grid, hence the full cost of energy is saved.

Power Cuts

The system with a sufficiently sized battery storage system as the main source of power should be able to carry the load without power cuts. This battery storage system is primarily charged by solar PV. The grid (grid-tied) or a generator can act as backups that charge the battery on days when the sun does not produce enough energy. With this architecture, power is drawn from the battery which is charged in the following order of preference: Solar panel, grid, diesel generator.

For a grid-tied system without battery storage, once the grid goes off and the grid power was part of the supply at that instant, there is power-cut so this is avoided if power cuts are not tolerated. This can be avoided by incorporating battery storage that has enough power and energy for the system of electrical loads.

When the grid goes off, power shouldn’t be sent to the grid. Inverters for grid-tied operation have that capability. It is like using a small generator to power a whole community which is not feasible; the generator will breakdown.

Beyond saving with solar

There are some practices that one can enact to save energy costs. One of them is using energy-saving/efficient appliances. Rather than using the conventional incandescent light bulbs, opt for energy-saving bulbs like the one shown below.

Incandescent bulb vs LED (Energy-saving) bulb
Figure 6: Incandescent bulb vs LED (Energy-saving) bulb

A 9 W LED light bulb can light a room better than a 60 W incandescent bulb, and for any period the 9 W light bulb is used 85% of energy is saved. Beyond light bulbs, when buying home appliances like fridges, dishwashers, washing machines, televisions, etc., check for their performance through their energy efficiency label. An appliance with a higher efficiency level will save more energy (electricity) when compared to another of similar capacity but with less efficiency level. Consider the energy efficiency label for two different capacities of refrigerators.

Figure 7: Energy-saving refrigerators

While the product on the left consumes more energy due to its larger capacity, it is more efficient than the product on the right when their capacities are considered. The product on the left with an energy efficiency rating of A++ has annual energy consumption rate per unit volume of 0.82 kWh/annum/litre (without consideration of the freezer compartment). The 0.82 value was got from 309/376. For the product on the right, it is 0.97 kWh/annum/litre (285/293). These higher efficiency appliances make use of inverter technology which makes the appliances’ energy consumption proportional to the work required to be done, rather than the maximum energy consumption anytime the appliance operates – for the non-inverter type appliances. There are plans to make the energy efficiency scale A (most efficient) to G (least efficient) from 1st March 2021, by the European Commission.

Another way to save energy is to power off the appliances when not in use. Use of sensors can also be beneficial as seen with lighting systems that are controlled by motion sensors which makes electricity consumption to only occur when required.

Solar PV Power System Developers in Mauritius

There are several solar PV power system developers in Mauritius, and some of them are Synnove Energy, Go Solar, GreenYellow, Meeco, SmartSolar. Gosolar has a checklist to know if a 3.5 kWp solar PV system is suitable for your home and also gave a 6-steps guide on how one can start producing their own electricity, SmartSolar offers free roof surveys and provides information on Tax Relief and Cashback possibilities, and Synnove Energy offers some amount of money for referrals.

References

[1] G. Kosmadakis, S. Karellas, and E. Kakaras, “Renewable and conventional electricity generation systems: Technologies and diversity of energy systems,” in Lecture Notes in Energy, vol. 23, 2013, pp. 9–30.

[2] Ministry of Energy and Public Utilities, “ENERGY OBSERVATORY REPORT 2017,” 2018.

[3] Ministry of Energy and Public Utilities, “RENEWABLE ENERGY ROADMAP 2030 FOR THE ELECTRICITY SECTOR,” 2019.

[4] V. Salas, “Stand-alone photovoltaic systems,” in The Performance of Photovoltaic (PV) Systems: Modelling, Measurement and Assessment, 2017, pp. 251–296.

[5] Y. K. Ramgolam and K. M. S. Soyjaudah, “Assessment and validation of global horizontal radiation: a case study in Mauritius,” Int. J. Green Energy, vol. 16, no. 14, pp. 1317–1328, 2019, doi: 10.1080/15435075.2019.1671407.


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