Electricity + Control November 2017

PLANT MAINTENANCE, TEST + MEASUREMENT

Performance of 500 kWp PV Plant – One Year After Jaco Bergh, Brand Engineering

An assessment of the performance which can typically be achieved by a PV plant after the first year of operation.

A 500 kWp Photovoltaic (PV) plant, operating in the Northern Cape, is assessed after be- ing in operation for over a year. The aim of this assessment is to provide a simplistic approach to determine the performance which can typically be achieved by a PV plant after a certain period of operation. The plant was commissioned by spe- cialist electrical contractor, Brand Engineering SA, a company which has carried out the highest num- ber of utility scale solar Renewable Energy (RE) installations in South Africa. The plant is rated at 450 kW / 502 kWp and therefore with an ac to dc ratio of 89,6%. It con- sists of 18 x 25 kW String Inverters which convert dc power from 1 620 x 310 W PV panels into ac power at 400 V, stepped up to 11 kV and fed into the client’s MV network. SANS 50010 [1] provides guidance for a more complicated approach but in principle uses the fol- lowing core equation: In this particular case the energy saving should be equal to or exceed the upfront guaranteed Yield and Performance Ratio value. The baseline period energy use of the client on the network is not dis- cussed in this report but the demand exceeds the output of the PV plant at all times. No +/- adjust- ments have been taken into account, but an exam- ple of this could be network downtime by others.

The plant starts generating at 07:00 in the morn- ing, peaks around 13:00 and stops generating at 19:00 (see Figure 1 ).

Take Note!

Analysing the data as- sists in planning, design- ing, pricing and operat- ing PV plants. RE in the form of solar is the answer to future energy requirements. Owing to the issue of base power, in the fore- seeable future RE will still have to be mixed with other forms of en- ergy to make financial sense.

1

3 000 2 500 2 000 1 500 1 000 500 0

2

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Yield (kWh)

Figure 2: Typical daily yield over a period of one month.

100 000 90 000 80 000 70 000 60 000 50 000 40 000 30 000 20 000 10 000 0

Energy Saving = (baseline period energy use) – (reporting period energy use) +/- adjustments

Jul-16

Jun-16

Apr-17

Jan-17

Oct-16

Feb-17

Sep-16

Mar-17

Nov-16

Dec-16

Aug-16

May-16

Yield (kWh)

Figure 3: Yield generated in the first year of operation.

The plant generated approximately 950 000 kWh (950 MWh) during the first year of operation with a performance ratio in excess of 83% (see Figure 3 ). Discussion Yield assessed in this report is measured at the output terminals of the Inverters. Energy for this particular plant is also metered at LVac (input of transformer) and MVac (point of connection). The plant outperformed the guaranteed yield by ap- proximately 10%. The guaranteed yield at the time was calculated by a software package against a P90 (90%) probability. The yield output was even higher than the predicted P50 probability. It can further be calculated that this plant gen- erated on average 5,2 kWh per day for every kWp

Results

450 400 350 300 250 200 150 100 50 0

01:00

02:00

03:00

04:00

05:00

06:00

07:00

08:00

09:00

10:00

11:00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

19:00

20:00

21:00

22:00

23:00

00:00

Figure 1:Typical power curve on a clearWinter’s day.

24 Electricity + Control

NOVEMBER 2017