# A+ Answers

Consider a crystalline PV module with the following output parameters mentioned at STC (Standard Test Conditions) conditions by the manufacturer.

Pmax = 300 W

Voc = 40 V

Isc = 8 A

NOCT = 40°C

Temperature coefficient of power = -2 W/°C

If the ambient temperature falls to 15°C while the irradiance is 1000 W/m², what is the cell level temperature in ºC, as per the NOCT model?

AQ5.1.2 PV MODULES

What is the new power output of the PV module in watts, under the ambient temperature of 15°C and 1000 W/m² irradiance?

AQ5.2.1 MAXIMUM POWER POINT TRACKERS

With respect to a PV module’s I-V and P-V curves, and the module’s operating point, consider the following statements:

- a) When the operating point of the PV module is on the MPP (maximum power point), Pmpp<Voc×Isc.
- b) For a given irradiance and temperature condition, and a uniformly illuminated (all solar cells receive the same illumination) module with perfectly functional solar cells, there is one and only one MPP defined for the PV module.
- c) Assume that a simple fixed load of pure resistance R is connected directly to the PV module, and no MPPT device is connected to this setup. Under such a scenario, the operating point of the PV module will always coincide with the MPP, irrespective of the illumination conditions.
- d) The curvature of the I-V characteristics of a module around the region of MPP can be looked upon as a result of the non-ideal resistances of the solar cells that make up the module.

Which of the above statements are true?

AQ5.2.2 MAXIMUM POWER POINT TRACKERS

Consider the following statements related to the field of MPPT techniques:

- a) The PV output is never steady at the MPP.
- b) Inclusion of a pilot solar cell can improve the PV module’s yield.
- c) The hardware complexity is high for implementing this design.
- d) The output of the PV module is maximum only if load resistance = VmppImpp.

Consider the following conditions at the PV output:

- i) An MPPT device implementing Fractional Open-Circuit Voltage method.
- ii) An MPPT device implementing Incremental Conductance method.

iii) No MPPT device connected; solar module directly connected to the load.

- iv) An MPPT device implementing Perturb and Observe method.

Which of the following matches the statements a) through d) with the right PV output conditions in i) through iv)?

AQ5.3.1 INVERTERS

Which of the following statements is NOT true about solar inverters?

A stand-alone inverter is supposed to work as an AC voltage source for a specified range of AC loads.

An ideal grid-tied inverter has its operational voltage and frequency synchronized with those of the grid

A bimodal inverter can power backup loads even if the grid-connection is disrupted.

An ideal grid-tied inverter works as a perfect voltage source, and changes the grid voltage and frequency to match its own.

AQ5.4.1 BATTERIES

(1 point possible)

Consider a lead-acid battery with 500 Ah capacity and a rated voltage of 12 V.

What is the total capacity of energy in watt-hours that can be stored in the battery?

AQ5.4.2 BATTERIES

Assume that the battery is completely empty. The battery is now charging at a C-rate of 0.20C. What is the charging current in amps that is going into the battery?

AQ5.4.3 BATTERIES

How much time in minutes will it take for the battery to go from 0% SOC to 100% SOC, assuming a constant C-rate of 2C? You may assume a linear rate of charging.

AQ5.4.4 BATTERIES

If the battery is charged at an average constant voltage of 13 V, and discharged at an average constant voltage of 11.7 V, what is the voltaic efficiency of the battery in %? :

AQ5.4.5 BATTERIES

If the coulombic efficiency of the battery is 95%, what is the roundtrip efficiency of storage in % for the battery? Assume the same voltaic efficiency as you calculated above.

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