Small scale (rooftop) solar PV system capacity sizing in Tamilnadu

Blog Type: Installation & Integration

Solar Array Capacity

The capacity of a solar PV array (in kW_p, kilowatt-peak) depends90% energy consumption of the building on and the shade-free rooftop (or other) area available.

Assumptions

−   Theroof(orelevatedstructure)arearequirementperkWofsolarPVmodules is about12m².

−   In Tamil Nadu the typical average annual energy generation per installed kW of solar PV capacity is 1,500 kWh. (This number assumes a system capacity utilization factor of 18% and average grid availability of 95% during the daytime).

As per the Tamil Nadu solar net-metering policy, electricity generated from a Solarrooftop/SolarsystemandinjectedintotheTANGEDCOgridshallbecapped commercially at 90% of the electricity consumption by the eligible consumer at the end of a 12 month settlement period which is from August to July. Excess energy generated beyond the 90% cap shall be treated as lapsed and will notbe credited for the purpose ofnet-metering.

With these assumptions, the recommended capacity of the solar modules array of a proposed grid-connected solar PV system can be calculated with the following three steps.

Step1:Calculatethemaximumsystemcapacityonthebasisoftheshade- free rooftoparea.

Formula:Capacity=shade-freerooftoparea(insquaremeters)dividedby 12.

Example:

The shade-free rooftop area is 60 m².

ThemaximumsolarPVcapacitythatcanbeinstalledonthisrooftoparea would be 60 / 12 = 5kW_p

Step2:Calculatethesystemcapacitybasedonannualenergyconsumption. Formula:Capacity=90%ofannualenergyconsumption(inkWh)dividedby 1,500.

Example:

The (estimated) annual energy consumption is 15,000 kWh

ThesolarPVsystemcapacitybasedonannualenergyconsumptionwouldbe (90% x 15,000) / 1,500 = 9kW_p

RecommendedCapacity:Takethelowestoftheabovetwocapacity calculationresults.

In this example: 5 kW_p

Solar Grid Inverter Capacity

TherecommendedsolargridinvertercapacityinkWshallbeinarangeof95%- 110%ofthesolarPVarraycapacity.Intheaboveexample,thesolararray

capacitywascalculatedtobe5kW.Thesolargridinverterrequiredforthisarray would be in a range of 4.75 – 5.50 kW. In Tamil Nadu for systems above 4 kW, three phase solar grid inverters shall be used (three single phase inverters or a single three phaseinverter).

As per the solar net metering orders of the Tamil Nadu Electricity Regulatory Commission (TNERC) of 13-11-2013, crediting of energy for the purpose of net-metering is limited to 90% of the consumed energy during a 12 month settlement period. The maximum recommended solar PV capacity for grid-connected solar PV systems is therefore a capacity that produces not more than 90% of the annual energy consumption of the building.

The Installer shall supply the followingdocumentation for Net Metering:

1. a) System description with workingprinciples.

1. b) System single linediagram.

1. c) Solar PV arraylay-out.

1. d) Routing diagram of cables andwires.

1. e) DatasheetsandusermanualsofthesolarPVpanelsandthesolargrid inverter.

1. f) A system operation and maintenancemanual.

1. g) Name,address,mobilenumberandemailaddressoftheservicecentre to be contacted in case of failure orcomplaint.

1. h) Warranty cards.

1. i) Maintenanceregister.