Suspect solar panels stunt growth of community crèche

February 26th, 2015, Published in Articles: Energize

 

The opening of a community crèche as reported in October 2014 (www.ee.co.za/article/shaping-future-roots.html), was greeted with great expectations. The crèche is regarded as a major benefit the community and as a successful social upliftment programme. The performance of the main solar power system has been less than encouraging, and has affected the functioning of the crèche, as well as placing the future expansion at risk. Mike Rycroft was requested to assist and this article covers the findings of the investigation.

Most solar power system suppliers in this country can be relied on to supply quality and reliable systems, and although some are questionable, the industry in the form of SESSA via the industry ombudsman and other initiatives, has put much effort into ensuring that customers get what they pay for and what they ask for. Companies that don’t provide good service do however exist, but one would not expect even the worst of these to take advantage of a charity organisation providing social services to the community.

The organisation running the crèche reported that the system was unable to carry the load over a full 24 hour period, with numerous failures when running on batteries at night.

Initial survey

The system as encountered on first inspection consists of:

  • 6 x 300 W (labelled) ECCO solar panels
  • Outback FM 80 battery charge regulator
  • 4 x 100 Ah 48 V Royal gel battery strings
  • 5000 W inverter.

Documents provided showed the load to be estimated at 987 W maximum with 3,5 kWh average daily consumption. The load consists of daytime use, driven directly from solar, and night-time use powered by the battery bank.

Initial observations

The elevation of the solar panels is too high for optimum power output over the whole year. The angle appears to be about 40° [Fig.1]. The optimum for this area is 25 to 30° above horizontal. The solar array faces west of north which could affect energy output. These two factors should not affect the operation to the extent reported.

Fig.1: The elevation of the solar array is higher than optimum for this area.

Fig. 1: The elevation of the solar array is higher than optimum for this area.

The solar panel array should produce an average of more than 6 kWh per day on sunny days, and a minimum of half that on heavily overcast days. This should be adequate to drive the load. The batteries were in a heavily discharged condition, judging by the charging voltage observed. The battery is cycling between full discharge and a low partial charge condition, (PSOC) which is known to cause deterioration of the battery capacity and the ability to recharge or accept charge.

One string of batteries had already failed, and had been removed from the battery bank. The array was not producing anywhere near the current output required to charge the battery fully, as well as to provide the daytime load requirements. Other solar arrays on the site were working satisfactorily. A comparison with the size of the other solar arrays on site which were functioning effectively, lead to a questioning of the actual capacity of the ECCO solar array.

Investigation

System output

The months following installation have been characterised by daily rain and thunderstorms, a fact that possibly was not taken into account when sizing the array. It is difficult to assess the performance based on instantaneous values the weather and level of irradiance varies.

However, the charge controller was equipped with a logger which recorded the daily kWh produced as well as maximum current and voltage levels.
Fig. 2 shows the readout of the recorder on the day in question plus the previous day. Poor weather had a great effect on daily production , as seen from the 2,36 kWh produced on day one, a heavy storm day.

Fig. 2a: Instantaneous recorder values.      Fig. 2b: Full day recording.

Fig. 2a: Instantaneous recorder values.                                  Fig. 2b: Full day recording.

Table 1 lists the recorded data for a 21 day period.

Table 1: Records for a 21 day period.
Day kWp kWh Array peak voltage (V) Ahr Max battery voltage (V) Min battery voltage (V)
1 0,71 3,3 74 64 57,1 40,5
2 0,75 4 75 78 55,3 40,5
3 0,75 3,8 77 75 55,6 40,5
4 0,54 1,2 78 23 57,6 47,8
5 0,73 3 75 59 53,2 46,2
6 0,85 2,5 74 50 52,4 40,5
7 0,64 4,4 75 86 52,1 40,6
8 0,81 2,7 74 54 54,8 40,5
9 0,64 1,7 74 32 57,6 47
10 0,69 3,7 76 72 53,8 46,3
11 0,81 3,3 73 66 51,8 43,4
12 0,64 4,4 77 87 51,7 40,5
13 0,85 2,6 79 50 57,1 44
14 0,76 3,8 76 78 51,3 40,6
15 0,8 4,2 79 80 56,9 46,3
16 0,59 3 76 56 57,6 46,5
17 0,63 3,4 74 67 53,6 40,6
18 0,8 4 75 78 53 40,6
19 0,72 3,8 76 73 57,4 43,9
20 0,61 3,2 77 58 57,6 48,4
21 0,81 3,7 77 69 57,6 46,4

The maximum recorded power output over this period is 0,85 kW, well below the expected value for 300 W panels. The minimum recorded is 0,54 kW, with a daily output of only 1,2 kWh, indicating a very cloudy day. The maximum Ahr delivered was 87, approximately 21% of the battery capacity. Subtracting the daily load from this shows that the maximum charge would probably be in the region of 10 to 15% of the battery’s capacity.

Fig. 3: Daily Ahr delivery and minimum battery voltage.

Fig. 3: Daily Ahr delivery and minimum battery voltage.

Fig. 3 shows the Ahr output of the regulator and the minimum battery voltage in graphical form.

The regulator is programmed only to record values when there is an output from the solar array, and the minimum battery voltages recorded is very likely to be the battery voltage at the start of the day. Minimum battery voltages of around 40 V, which indicate a fully discharged battery, occur regularly, (red bars in Fig. 3) showing that the battery had discharged fully during the previous night .There is a visible relationship between the Ahr delivered the previous day, and the minimum battery voltage, although this has been distorted by the use of portable generator to charge the batteries on several days.

Solar panels

An attempt was made to obtain data on the ECCO panels. Normally the internet is a vast source of information, and almost anything can be found there, but in this case, in spite of using several search engines, not a single item of meaningful data on this product could be found. No brochures, data sheet, images or other references exist on the web. The only hit obtained was that of a company trying to sell panels with this name on an internet auction site. The site contained a notification that the company had been blacklisted.  This led to further suspicions as to the validity of the label on the panels. Data sheets of reputable 300 W panels were obtained for comparison. The initial impression was that the ECCO panels were much smaller and could not be 300 W panels as labelled ( Fig. 4).

Fig. 4: Panel label indicating a capacity of 300W.

Fig. 4: Panel label indicating a capacity of 300W.

This was confirmed when the site was revisited. Comparison between the size of a reputable panel and the ECCO panel is given in table 1 [1].

The wafer size of 120 x120 mm alone indicates that this is not a 300 W panel. I would hesitate to give an accurate capacity but would estimate it at about 150 W.

Faults

In addition the panels show extensive signs of delamination, as can be seen from Fig. 4. This affects the operation of the panel and will reduce the output. It is unusual for a panel to show delamination after only a few months in service and this suggests the following possibilities:

  • The panels are not new.
  • The delamination occurred during manufacture and the panels were sold as “seconds” or substandard panels into the informal market. The random shape of the delamination suggests a manufacturing defect rather than in- service deterioration.
Table 2: Comparison between panels.
Dimensions ECCO Reputable panel
Length (m) 1,58 1,956
Width (m) 0,8 0,992
Area (mm2) 1,264 1,94
Cell (wafer) size (mm) 120 x 120 156 x 156

The label on the panel clearly contains information which does not match the panel and the panels have serious faults which affect performance to the extent that even the expected output for that size panel would not be achieved. Most Solar panels carry a guarantee of 20 years. No information was available on what guarantee was given on these panels.

Fig. 5: Delamination observed on the panels.

Fig. 5: Delamination observed on the panels.

Load determination

Initial load determination did not appear to take into account the efficiencies of the charger, the battery, and the inverter. The crèche operates from 07h00 to 17h00, a total of ten hours daily. The initial load determination as provided is shown in Table 3.

Table 3: Load calculations as supplied.

Table 3: Load calculations as supplied.

There are some miscalculations (yellow cells) and incorrect estimates (green cells) in this table. Revised load calculations taking into account efficiencies is shown in Table 3:

  • Inverter efficiency is assumed to be 85%
  • Battery round trip efficiency is estimated to be 85%
  • Charge controller efficiency is approx. 95% (specified on the data sheet)

Weekday loading

The crèche is in operation from Monday to Friday. The day and night weekday loading is given in Table 3. ten hours of usage for the classrooms is used as the maximum use of classroom and kitchen lights on a cloudy winter day. During summer the figure of five hours or less may be applicable, but the system should be sized for the maximum drain.

Weekend loading

The crèche is closed on weekends and the only load is the alarm system and the lights at night.  Daytime load is given in Table 4a. The weekend night load consists of the lights and the alarm system. Night load is given in Table 4a. The weekend load is considerably lower than the weekday load and this should allow the battery to recover and build up charge over the weekend. The night load amounts to 2,9% of the inverter’s capacity. At this load the inverter efficiency could be as low as 60%. The recalculated figure is much higher than the original estimate, and also does not include the occasional 500 W load.

Day loads
Application Power (W) Qty Run hours Total power (W) Total energy (Wh)
Classroom 1 and 2 lights 200 1 10 200 2000
Office lights 50 1 10 50 500
Kitchen lights 25 1 10 25 250
Printer 63 1 1 63 63
Alarm system day 14 1 12 14 168
Totals 352 2981
Adjusted for inverter efficiency of 85% 3507
Adjusted for charge controller efficiency of 95% 3692
Table 4: Revised load calculations.
Night loads
Application Power (W) Qty Run hours Total power (W) Total energy (Wh)
20 W flood lights 22,5 6 12 135 1620
Alarm system night 14 1 12 14 168
Totals 149 1788
Adjusted for inverter efficiency of 85% 2104
Adjusted for battery efficiency of 85% 2475
Adjusted for charge controller efficiency of 95% 2605
Total adjusted load (Wh) 6297

The actual load figures need to be verified, especially the day load in the classrooms, (run hours – assumed to be ten on a rainy day), which is the major day load item. If the crèche is to be expanded an accurate load figure is needed.

Table 4a: Daytime weekend load.
Day loads
Application Power (W) Qty Run hours Total power (W) Total Energy (Wh)
Alarm system 14 1 12 14 168
Totals 14 168

Adjusted for inverter efficiency of 85%

198

Adjusted for charge controller efficiency of 95%

208
Table 4b: Night-time weekend load.

Night loads

Application Power (W) Qty Run hours Total power (W) Total energy (Wh)
20 W flood lights 22,5 6 12 135 1620
Alarm system night 14 1 12 14 168
Totals 149 1788

Adjusted for inverter efficiency of 85%

2104

Adjusted for battery efficiency of 85%

2475

Adjusted for charge controller efficiency of 95%

2605

Total adjusted weekend load (Wh)

2813

Inverter

A 6 kW inverter is specified in the quote but the inverter supplied is a 5 kW unit. The inverter is oversized for this application, with a maximum daytime load of 352 W (excluding the 500 W occasional load) and a night time load of 149 W. The problem with oversizing is that the efficiency of the inverter drops rapidly at loads below 10% of its maximum (example given in Fig. 6), and under these load conditions may be lower than 60%, considering the type of inverter supplied. This increases the drain on the batteries at night.

Fig. 6: Typical inverter efficiency curve [3].

Fig. 6: Typical inverter efficiency curve [3].

Battery size and charging cycle

The battery is considered to be oversized for this application. The capacity amounts to 20 kWh, which is sufficient to run the site continuously for a period of at least 3 days. Oversizing the battery makes it difficult to bring it to a fully charged state with the current available from the solar array, and it is currently cycling at a very low charged state. Deep cycle batteries are designed to operate under partial state of charge regimes (PSOC) but not at an extreme low level as is the case here. This is not good for the battery and depending on the inverter cut-out voltage may be the cause of load dropping. The use of three strings only, giving 15 kWh, or even two strings giving 10 kWh, which is more than adequate for the crèche’s current and future needs, would give better performance.

Fig. 7 Battery partial state of charge operation [4].

Fig. 7: Battery partial state of charge operation [4].

Running a battery in a semi discharged state leads to sulphation of the active material which makes it difficult to recharge the battery [3]. Sulphation is the formation of nearly insoluble (electrochemically partially active) lead sulphate crystals (PbSO4), which during re-charging of lead-acid batteries are difficulty to convert into the charged active mass, i.e. they cannot be converted into spongy lead and porous lead-oxide (PbO2). This leads to a capacity reduction and in addition an increase in the internal resistance. A high charge acceptance i.e. charging rate capability, is an important requirement in the solar power sector and sulphation is one mechanism which degrades the charge acceptance.

Sulphation is accelerated under the following conditions:

  • Cycling in partial state of charge cycle. (PSOC)  (especially with deficient charging and at a low state of charge)
  • Discharging with small currents

Fig. 4 shows the effect of PSOC with an efficient battery. Note the comments that cycling below 20% state of charge leads to a lower efficiency and higher rate of degradation. Also that the same applies to cycling between 100% and 80% charge. Correct sizing of the battery is essential to ensure battery life.

The inability of the battery to hold its charge, even with supplementary charging from a portable generator, and extra charging over weekends, indicates that sulphation is very likely to have taken place.

Summary

The main problem is the solar panel array, which does not match that specified in the quotation, in size or quality. The panels appear to have been delivered with defects. The loads need to be accurately determined, and the size of the battery needs to be better matched to the load requirements and the charging capability of the array.

Happy ending

The supplier agreed to replace the existing PV panels with genuine 300 W panels from a reputable supplier, and the battery will probably be replaced at the same time. A more accurate survey of actual energy requirements will be taken some time in the future.  The panels have been replaced and the system is reported to be working satisfactorily.

References

[1]    Renesolar specification sheet: Virtus II module.
[2]    R Perez: “Off grid inverter efficiency”, Home power 113, July 2006.
[3]    J Dambrowski: “The challenges for charging techniques with lead acid batteries”, Deutronic Elektronik GmbH, Adlkofen, Germany, March 2009.
[4]    Ultrabattery: “High efficiency in partial state of charge use”, http://ultrabattery.com/wp-content/uploads/sites/2/2013/06/ECOG-03.1A-high-efficiency-psoc-800.png

Send your comments to: energize@ee.co.za

 

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