Today, renewable energy projects connected to the interconnected network, with powers of the order of tens of megawatts, are more and more numerous in sub-Saharan Africa. And financing these investments requires a reliable amortization schedule. In the context of photovoltaic systems connected to the interconnected electricity grid, the quintessence of damping is the amount of energy injected into the grid. Thus it is fundamental to know the parameters of this network and their variation. This paper presents an evaluation of the impact of power grid disturbances on the performance of a solar PV plant under real conditions. The CICAD photovoltaic solar plant, connected to the Senelec distribution network, with an installed capacity of 2 MWp is the study setting. An energy audit of the plant is carried out. Then the percentage of each loss is determined: voltage drops, module degradation, inverter efficiency. The duration of each disconnection is measured and recorded daily. The corresponding quantity of lost energy is thus calculated from meteorological data (irradiation, temperature, wind speed, illumination) recorded by the measurement unit in one-minute steps. The observation period is three months. The total duration of disconnections related to the instability of the e lectrical network during the study period is 46.7 hours. The amount of energy lost is estimated at 22.6 MWh. This represents 2.4% of the actual calculated production.
Photovoltaic (PV) solar energy, having the sun as its primary source, is very appropriate for the production of electrical energy in some countries such as Senegal with a high solar potential (varying between 1850 and 2250 kWh/m2/year [
Since 2016, an acceleration in the commissioning of PV plants has been noted. With the connection and injection of: Bokhol (20 MWp), Malicounda (22 MWp), Kahone (20 MWp), Ten Merina (29.5 MWp), Santhiou Mekhe (29.5 MWp), Sakal (20 MWp) and Diass (20 MWp in test phase), the PV power connected to the Senelec interconnected grid has increased from 2 MWp to 164 MWp between 2016 and 2019 [
Thus, based on the meteorological data and the energy produced by the plant, recorded over a period of three months, we will evaluate the losses due to the grid.
In this document, we first present the CICAD solar power plant as well as the methodological approach adopted. Then, the evaluation of the amount of energy lost as well as the corresponding duration will be presented in the results and discussion section.
Based on the daily reports from the Abdou Diouf International Conference Center (CICAD) power plant, the meteorological data recorded and additional physical measurements carried out in the PV field, all the losses, the number and duration of interruptions as well as the quantity of energy produced day by day are aggregated. The working method adopted, consists in first making an energy audit of the plant in order to identify all the existing losses. Then determine the percentage of each type of loss on production. Finally, the total duration of the disconnections and the corresponding amount of energy during the study period are evaluated.
The Centre International de Conference Abdou Diouf (CICAD) Solar PV power plant is the first PV power plant interconnected to the Senelec power grid. It is located in Diamniadio (30 Km from Dakar
The CICAD plant is composed mainly of the following elements:
- A photovoltaic field.
- 116 boxes or junction boxes.
- Fuse grouping boards.
- Two inverters branded GAMESA of 1 MW each.
- A 2 kVA transformer.
- Cables.
- Parameter monitoring system (SCADA).
- Protection equipment.
- A meteorological station.
The performance of a PV plant decreases over time due to a degradation process of the PV system, especially the PV panels. Also, the inverters, transformer, connectors, and protection system can be affected by degradation [
The evaluation of the system losses of the power plant is necessary to control the amortization plan and the follow-up evaluation of the investment. It also allows to evaluate the quality of the Senelec distribution grid in the area.
| Site Name | CICAD solar plant |
|---|---|
| Area | 2.2 hectares |
| Number of modules YL295P-35b | 6960 |
| Coordinates | 14˚33'44"North, 16˚47'13"West, Elevation: 0 m |
| Tilt Azimut | 6˚ |
| South orientation | 24˚ |
| Sizes | Values |
|---|---|
| Nominale power (P) | 295 W |
| Optimal voltage (Vopt) | 35.6 V |
| optimal Current (Iopt) | 8.29 A |
| Open circuit voltage (Voc) | 45 V |
| Current short-circuit (Isc) | 8.99 V |
| Reference temoerature | 25˚C |
| BT decoupling protections | Type B.1 (ex type 2.1) | Type B.2 (ex type 2.2) | Automatic disconnector DIN VDE 0126 |
|---|---|---|---|
| Detection of HTA single-phase faults | Not done | Note done | Note done |
| Detection of BT polyphase faults | Minimum instantaneous V 85% Vn | Minimum instantaneous V 85% Vn | Minimum instantaneous V 80% Vn |
| Separate grid operation | Minimum instantaneous V 85% Vn | Minimum instantaneous V 85% Vn | Minimum instantaneous V 80% Vn |
| Maximum instantaneous V 115% Vn | Maximum instantaneous V 115% Vn | Maximum instantaneous V 115% Vn | |
| Minimum of f instantaneous 49.5 HZ | Minimum of f instantaneous 49.8 HZ | ||
| Maximum instantaneous f 50.5 HZ | Maximum instantaneous f 50.2 HZ |
| DC Input Values | |
|---|---|
| Recommended rated power | 1200 kWp |
| Max. Direct Current | 1800 A |
| Direct Current Voltage range | 570 - 1000 V |
| DC MPPT Voltage range | 570 - 910 V |
| No. Of DC Inputs | 12 |
| Start of production | 0.5% Pn approx. |
| AC output values | |
| No. of phases | 3 |
| Rated AC power | 1000 kW |
| Maximum AC power | 1100 kW |
| Rated AC voltage | 360 Vrms |
| AC voltage range | −15%/+10% |
| Output frequency range | 47.5…53/57…63 Hz |
| Degradation type | Cause | Consequence |
|---|---|---|
| Corrosion | Moisture Penetration | Increased leakage current performance loss |
| Delamination | Loss of adhesion between the encapsulant and the cells | Increased light reflection Water penetration in the structure |
| Discoloration | UV rays combined with high temperatures and water | Decrease of the generated power |
| Hot spot | Cell shading | Energy loss transformed into heat |
| Orientation and tilt | Insufficient surface Panel sagging | False forecast Decrease of the energy capture by the modules |
| Voltage drop | High current; Low section | Energy loss |
| Joule effect | Cables heating | Energy Loss transformed into heat |
| Conversion loss | Inverter efficient | Low power loss |
| No grid | Electrical parameters not compatible with those of the grid | Open circuit operation of the PV generator |
The amount of energy lost is obtained by subtracting the theoretical energy of the plant from the actual energy obtained during an hour of time. The meteorological and electrical parameters are measured and known for the determination of the theoretical energy that should produce the plant. It will remain only to deduct the losses of energy due to the disconnections by instability of the electric network. Thus we distinguish:
- The efficiency of the inverter which is the ratio of the output power of the inverter on its input power.
η o n d = P a c P d c (1)
ηond: Inverter efficiency.
Pac (kW): Alternating power inverter.
Pdc (kW): Inverter continuous power.
- Voltage drops which are losses due to the connection cables at the junction box and the electrical tables.
Δ U = ρ ∗ L ∗ I S ∗ U (2)
- The form factor is one of the most important values for evaluating the efficiency of a photovoltaic system.
F F = P max V o c ∗ I s c (3)
P max = V o p t ∗ I o p t (4)
It is equal to 0.8 for plants with normal operation [
In order to determine the coefficients for the various losses accurately, we used the peak data for each month over the three month study period (January, February, and March). The data are measured and recorded in one-minute steps.
- The loss coefficient at the inverter is represented by the letter K1. The conversion efficiency is a measure of the losses incurred during the conversion from DC to AC. These losses are due to several factors: the presence of a transformer, magnetic losses and associated copper losses, and self-consumption of the inverter.
- Voltage drop coefficient K2
The voltage drop coefficient K2 expresses the connection cable losses. The voltage drop must be calculated for each cable of the PV array, each cable of the PV junction boxes, and for the cable of the inverter. The cumulative voltage drop of the cables between each string and the inverter is then calculated.
ΔUa: Voltage drop of the cables connecting the junction box to the inverter.
ΔUb: Voltage drop of the cables connecting the PV panels to the junction box.
K 2 = 100 % − 0.271 % = 99.7 %
- The tilt coefficient, this value is related to the angle of inclination, orientation and fixation of PV modules. It is measured using the solar disk in the Dakar region. The CICAD PV solar power plant has a PV module tilt of 6˚C and an orientation of 24˚C south. The tilt coefficient (K3) is therefore 0.99.
- The form factor coefficient K4 is the average of the calculated form factor values divided by 100.
| Year | Month | Time | Irradiance (W/m2) | Ambiante Temperature Ta (˚C) | Module temperature Tm (˚C) | Open circuit voltage max Vocm (V) | Short circuit current max Iscm (A) |
|---|---|---|---|---|---|---|---|
| 2017 | Janu | 12 h 53 mn 13 | 783 | 34 | 59.309 | 36.460 | 6.894 |
| Feb | 12 h 57 mn 29 | 937 | 27 | 57.286 | 36.751 | 8.250 | |
| March | 12 h 56 mn 39 | 906 | 29 | 58.284 | 36.607 | 7.977 |
| PAC (W) | 421 | 520 | 670 |
|---|---|---|---|
| PDC (W) | 413 | 510 | 657 |
| Efficiency (K1) | 98.1% | 98.1% | 98.1% |
| Utable (V) | Itable (A) | Ibox (A) | ΔUa (V) | ΔUb (v) | Cables losses |
|---|---|---|---|---|---|
| 678 | 47.55 | 9.51 | 0.11% | 0.16% | 0.27% |
K 4 = 100 − ( averageofFF ) 100 (5)
K 4 = ( 100 − 0.75 ) / 100 . K 4 = 0.99
- Calculation Power injected into the grid (Pinj)
The electrical power at the output of the inverter is the module power multiplied by the different loss coefficients of the PV system.
P i n j = P f i e l d ∗ K 1 ∗ K 2 ∗ K 3 ∗ K 4 (6)
The field power is the power of all the photovoltaic modules in the plant. It is obtained by multiplying the power of a module by the total number of solar panels [
P f i e l d = P p v ∗ N m (7)
Pfield: PV field power; Nm: number of modules
The module power Ppv represents the measured module power. It is obtained from the measured values of the open circuit voltage, the short circuit current and the form factor [
P p v = V c o ∗ I c c ∗ F F (8)
The coefficients of the different losses are calculated, the duration of the disconnections noted as well as the meteorological parameters. We can calculate the amount of energy lost during the whole observation period and their percentage on the global production.
| Headings | Unit | Inv1 | Inv2 | TOTAL |
|---|---|---|---|---|
| Grid absence (lost hours) | h | 0:44 | ||
| Production duration | h | 7:16 | ||
| Sunshine duration based on weather | h | 8:00 | ||
| Number start | 5 | |||
| Peak of the day | KW | 910 | 917 | 1827 |
| Gross production | KWh | 4612 | 4637 | 9 249 |
| Date | Disconnection periods | Irra diance (W/m2) | Estimated Power (kW) | Grid absence duration | Lost energy (kWh) | ηpv (rendement) | K1 | K2 | K3 | K4 |
|---|---|---|---|---|---|---|---|---|---|---|
| 01/02/2017 | 9 h 17/9 h 25 | 215 | 365.897 | 0.133 | 48.786 | 3.194 | 0.980 | 0.970 | 0.900 | 0.992 |
| 12 h 10/12 h 24 | 768 | 1222.582 | 0.233 | 285.269 | 10.671 | 0.980 | 0.970 | 0.900 | 0.992 | |
| 12 h 46/12 h 53 | 276 | 465.970 | 0.117 | 54.363 | 4.067 | 0.980 | 0.970 | 0.900 | 0.992 | |
| 01/03/2017 | 10 h 02/10 h 08 | 476 | 786.072 | 0.100 | 78.607 | 6.861 | 0.980 | 0,970 | 0.900 | 0.992 |
| 01/04/2017 | 16 h 24/16 h 27 | 369 | 615.979 | 0.083 | 51.332 | 5.377 | 0.980 | 0.970 | 0.900 | 0.992 |
| 01/05/2017 | 9 h 38/9 h 44 | 430 | 714.914 | 0.100 | 71.491 | 6.236 | 0.980 | 0.970 | 0.900 | 0.992 |
| 01/06/2017 | 8 h 25/8 h 32 | 169 | 289.556 | 0.117 | 33.782 | 2.524 | 0.980 | 0.970 | 0.900 | 0.993 |
| 14 h 32/14 h 39 | 753 | 1203.390 | 0.117 | 140.395 | 10.482 | 0.980 | 0.970 | 0.900 | 0.994 | |
| 01/07/2017 | 9 h 58/10 h 05 | 522 | 860.147 | 0.117 | 100.351 | 7.487 | 0.980 | 0.970 | 0.900 | 0.994 |
| 10 h 22/10 h 28 | 630 | 1025.490 | 0.100 | 102.549 | 8.920 | 0.980 | 0.970 | 0.900 | 0.995 | |
| 10 h 38/11 h 15 | 684.87 | 1107.906 | 0.617 | 683.208 | 9.631 | 0.980 | 0.970 | 0.900 | 0.996 | |
| 01/08/2017 | 9 h 00/9 h 05 | 123 | 212.506 | 0.083 | 17.709 | 1.846 | 0.980 | 0.970 | 0.900 | 0.997 |
| 15 h 48/15 h 57 | 613 | 999.317 | 0.150 | 149.898 | 8.675 | 0.980 | 0.970 | 0.900 | 0.997 | |
| 01/09/2017 | 12 h 01/12 h 16 | 470.63 | 781.559 | 0.250 | 195.390 | 6.780 | 0.980 | 0.970 | 0.900 | 0.998 |
| 15 h 10/15 h 17 | 334.13 | 564.211 | 0.117 | 65.825 | 4.891 | 0.980 | 0.970 | 0.900 | 0.999 | |
| 15 h 22/15 h 29 | 282 | 479.438 | 0.117 | 55.934 | 4.153 | 0.980 | 0.970 | 0.900 | 0.999 | |
| TOTAL | 2.55 | 2135 |
The special case of
We note during the period from January 02 to 09, 2017, there were several disconnections due to the instability of the electrical grid, During the period from January 2 to 9, 2017, there were several disconnections due to the instability of the electricity network, with a peak of lost energy of 879 KWh recorded on January 7, 2017. The causes of grid instability are of several types among which we can mention: automatic load shedding due to lack of production, fault tests, grid incident, etc. The total duration of generation interruptions during this period is 2.55 hours and the corresponding lost energy estimated at 2.1 MWh.
Based on the complete summary of the three months studied, we present in
| Month | Grid instability duration (hour) | Energy injected (kWh) | Lost Energy (kWh) | Real calculated energy (kWh) | % Ratio Elost/Ereal |
|---|---|---|---|---|---|
| January | 22.1 | 278,167 | 20,156 | 298,323 | 6.75% |
| February | 12.3 | 291,451 | 921 | 292,372 | 0.31% |
| March | 12.3 | 334,619 | 1432 | 336,051 | 0.42% |
| Total | 46.7 | 904,237 | 22,509 | 926,746 | 2.4% |
It can be seen that the monthly producible during the first quarter of the year is around 3 Gwh. But the lost energy rates for the months of February and March are almost nil (0.3%) unlike the month of January which recorded a rate of 7%. This difference is explained by the high duration of network instability during the month of January, which corresponds to an inverter disconnection duration equivalent to 22 hours.
An evaluation of the amount of energy not produced as a result of grid disconnections is presented in this study. The different technical energy losses are determined and classified into four types: aging of the photovoltaic modules, tilt of the photovoltaic modules, voltage drops and inverter efficiency. The factor of each type of loss is taken into account in the evaluation of the amount of energy produced by the photovoltaic field. The first results obtained after the study of three months of operation of the disconnections of the CICAD power plant, due to the instability of the Senelec distribution grid are:
- The amount of energy lost is estimated at 22.509 kWh.
- The percentage of energy lost is 2.4% of the total calculated energy that the plant was to produce.
- The total duration of the disconnections is equal to 46.7 hours.
However, it is very difficult to quantify the unproduced energy with precision. Finally, it should be noted that it is very rare to find research that gives results on the energy lost due to the instability of the electrical grid.
In the future, studies on longer periods and on larger power plants would be very relevant as well as work on the causes of disconnections.
The authors declare no conflicts of interest regarding the publication of this paper.
Ndiaye, A., Aidara, M.C., Mbaye, A. and Ndiaye, M.L. (2023) Study of the Impact of Grid Disconnections on the Production of a Photovoltaic Solar Power Plant: Case of Diamniadio Power Plant. Journal of Power and Energy Engineering, 11, 16-25. https://doi.org/10.4236/jpee.2023.116002