My Power Station completed an installation of an off-grid photovoltaic (PV) system at Gecko Rock, near Touwsriver, Western Cape, South Africa.
Summary:
- 1.6 kilowatt photovoltaic array with 24 Volt 675 Amp Hour battery bank and 1,200 watt inverter charger with generator backup
- 8 kwh of battery backup
- 8 kwh of average daily solar production from the photovoltaic array
- the system has been sized to operate: a DSTV decoder, satellite phone system and satellite data system used 4 hours a day and on standby 20 hours a day; LCD TV set; Lighting; Laptop; 220 Volt energy efficient refrigerator; small hi-fi system, playing an ipod; digital projector from time to time. The system should be able to manage much greater outputs than this and has been sized to allow for conferences and training courses to be held at Gecko Rock
Installation Team (left to right in the group photo at the top of this page):
- Antony Stone from Big Bang Stunts and Effects: Camera
- Steven Mulder from Intricate Steel: Welding, Dual Axis Trackers; Metal Work
- David Lipschitz from My Power Station: Sales, Design and Team Leader
- Peter Burden from SolarSells: Design and Electrician
Overview:
- System Type: Off-grid solar-electric
- Location: Gecko Rock, 25 km South South East of Touwsriver, Western Cape, South Africa
- Solar Resource: approximately 5 average peak sun-hours
- Photovoltaic Array Size: 1.62 kW (1,620 watts)
- Nominal Voltage Batteries: 24 Volts
- Nominal Voltage Array: 72 Volts
- Array Voltage at Max Power: 108.6 Volts
- Array DC Current at Max Power: 15 Amps
- Battery Amp Hours: 675 Ah (amp hours) at 20-hour discharge rate. Multiplied by 24 Volts and allowing for a 50% maximum depth of discharge = 8.1 kWh in the batteries for overnight and overcast periods
- Record Low Temperature: unknown; we have allowed for Minus 15 degrees Celsius (during day light (operating) hours)
- Average Low Temperature: 2.2 degrees Celsius in July
- Average High Temperature: 28.6 degrees Celsius in February
- Average Daily Production: 8.1 kWh
- Average Electricity Available after taking account of efficiencies (or inefficiencies): Allow 7% for inverter loss; 20% loss for battery charge/discharge from photovoltaic array; and 2% voltage drop on the cabling: 8.1 kwh * 0.93 & 0.8 * 0.98 = 5.9 kwh per day of usable electricity (daily average over the entire year)
PV System Components:
- 9 Tenesol TE1700 at 24 Volt nominal: 180 Wp STC, 36.2 Vmp, 5 Imp, 44.4 Voc, 5.4 Isc (133.2 Volts open circuit for the array (at zero amps, i.e. first thing in the morning) and 16.2 Amps Short Circuit current for the array)
- Array: 1 “string” of 3 “panels” with 3 “modules” in each panel. Total 9 Modules, 1,620 Watts total
- Array installation: Dual-axis (manual) trackers designed by SolarSells, and enhanced, built and installed by Intricate Steel
- Inverters: 1 x 24 Volt Victron 1200 Watt multi-plus Inverter/Charger allowing 24 Volt DC to 220 Volt AC conversion of electricity and allowing automatic synchronisation of a generator input into the system to supplement the batteries in the case of long cloudy periods
- Solar Charge Controllers: 1 x 80 Amp Outback FM80 MPPT (maximum power point tracking) controller. The FM80 allows array sizes up to 2,000 Watts when charging at 24 Volts. The FM80 allows one to use a higher output voltage PV array with a lower voltage battery, such as charging a 24 VDC battery with a 72 VDC array. This reduces wire size (and cost) and power loss from the PV array to the battery/inverter location and maximises the performance of the PV system
- Batteries: Deep Cycle: 12 x 6 Volt Trojan T105′s in 24 Volt nominal configuration, i.e. 3 banks (in parallel) of 4 batteries (in series) making 24 Volts nominal and 675 Amp Hours capacity. Each 6 volt battery weighs 28 kg making a total battery bank weight of 336 kg. We expect the batteries to last about 8 years with an average discharge of 20% and a maximum discharge of 50%. The batteries have a 2 year free replacement guarantee assuming they are looked after and “watered”, i.e. the battery de-ionised water is checked and filled as required. We can tell how the batteries have been used by looking at the information on the Victron Battery Status Monitor. The Trojan batteries are designed in the USA and assembled in Cape Town
- Generator: 5 kw Honda
- System performance metering: Victron Battery Status Monitor BM 600 for DC performance and battery monitoring; Efergy e2 Electricity Monitor for AC performance and historical AC kwh tracking
- 2 Earth spikes and open earthing cabling allowing all metal work to be earthed. System and Equipment negative grounding. We have used USA NEC Article 690 rules as far as possible as there aren’t standards for PV systems in South Africa yet.
