UE 07: PV

Question 1

What is the azimuth angle?

Answer 1

Azimuth angle

• The deviation from the optimal orientation of PV modules on a roof
• It is one of the factors that determines the yield of the photovoltaic system
• The optimal orientation is south
• Azimuth angle = 0 –> south
• Azimuth angle = -90° –> east
• Azimuth angle = 90° –> west
• Azimuth angle = +/-180° –> north

Question 2

True or false?

When installing PV-modules on the roof these are the steps you go through:

Step 1: Determination of the global radiation, given the orientation and pitch angle of the roof
Step 2: Shading analysis
Step 3: Selection of the PV module
Step 4: Determine the number of modules
Step 5: Energy yield forecast
Step 6: Determination of the share of own consumption
Step 7: Determination of the degree of self-sufficiency (autarky)
Step 8: Increasing the share of own consumption

Answer 2

True!

Question 3

True or false?

When installing PV-modules on the roof these are the steps you go through:

Step 1: Determination of the global radiation, given the orientation and pitch angle of the roof

• Use the azimuth angel as well as the tilt angel to determine the annual sum of global radiation [kWh/(m^2a)]* using a given graph

Answer 3

True!

Question 4

True or false?

When installing PV-modules on the roof these are the steps you go through:

Step 2: Shading analysis

For each obstacle:

• Determine the elevation angle alpha of potential obstacles which could cause shading on the PV system: tan(alpha) = height/distance
• Use the elevation angle alpha as well as the azimuth angle range of the obstacle to determine times of an average day per month in which the obstacle causes shading on the PV system using the solar orbit diagram.
• For each month calculate the direct radiation generator, the total radiation generator as well as the radiation losses
  –> Direct radiation generator [kWh/m^2]
  = (Unshaded sunshine hours / Total sunshine hours) * direct radiation
  –> Total radiation generator [kWh/m^2]
  = Direct radiation generator + Diffuse radiation
  –> Radiation losses [kWh/m^2]
  = Globale radiation - total radiation generator
  –> Radiation losses [%]
  = (Globale radiation - total radiation generator) / globale radiation

(Globale radiation = direct radiation + diffuse radiation)

Answer 4

True!

Question 5

True or false?

A solar orbit diagram visualizes the position of the sun depending on its elevation angle and azimuth angle for a given location (e.g. Berlin, longitudes + latitudes)

Answer 5

True!

Question 6

What is the fill factor FF of a solar cell?

Answer 6

Fill factor FF of a solar cell

• Measure of the quality of the solar cell
• Usually ranges between 0,5 and 0,82
• FF = P_max / P_T = I_MP * V_MP / I_SC * V_OC

Question 7

What is the efficiency of a solar cell?

Answer 7

Efficiency of a solar cell

n = generated power / Power of incident sunlight = P_max / P_in

Question 8

True or false?

When installing PV-modules on the roof these are the steps you go through:

Step 3: Selection of the PV module

• Select a specific type of PV module

Answer 8

True!

Question 9

True or false?

When installing PV-modules on the roof these are the steps you go through:

Step 4: Determine the number of modules

• Calculate the total number of PV modules based on the total generator area [m^2]
• Calculate the total installed capacity [kW]
• Calculate the total price of all PV modules [€]

Answer 9

True!

Question 10

True or false?

When installing PV-modules on the roof these are the steps you go through:

Step 5: Energy yield forecast

• Determine
  –> total generator area [m^2]
  –> annual theoretical energy yield [kWh/a]
  = global radiation [kWh/(m^2*a)] * total generator area [m^2])
  –> annual ideal energy yield [kWh/a]
  = annual theoretical energy yield [kWh/a] * n_module
  –> annual real energy yield [kWh/a]
  = annual ideal energy yield [kWh/a] * (1-losses)
  (losses include losses due to shading as well as other real world loss factors)
  –> full load hours [h]
  = “work_real” / “installed capacity”
  = annual real energy yield [kWh/a] / installed capacity [kW]

Answer 10

True!

Question 11

True or false?

When installing PV-modules on the roof these are the steps you go through:

Step 6: Determine the share of own consumption

• Determine
  –> PV power output [kW_p/MWh]
  = installed_PV_capacity [kW_p] / annual_electricity_consumption [MWh]

–> Usable storage capacity [kWh/MWh]
= installed_storage_capacity [kWh] / annual_electricity_consumption [MWh]

• Use both parameters and a given diagram to determine the share of own consumption

Answer 11

True!

Question 12

1) What is the share of own consumption?

2) What is the degree of self-sufficiency?

Answer 12

1) Share of own consumption

• How much of my own generation is used for self-used electricity (= self consumption + storage charges)?
• In reality this parameter has to be simulated or be calculated using empirical values!
• Theoretical calculation (do not apply directly!)
  –> share_of_own_consumption
  = self_used_electricity / self_generated_electricity
  –> self_used_electricity = self_consumed_electricity + storage charges

2) Degree of self-sufficiency

• How much of my own consumption is self-used electricity (= self consumption + storage charges)?
• In reality this parameter has to be simulated or be calculated using empirical values!
• Theoretical calculation (do not apply directly!)
  –> degree_of_self-sufficiency
  = self_used_electricity / annual_electricity_consumption

Question 13

Explain the following situation:

a) The share of own consumption is about 80 %.
b) The degree of self-sufficiency is about 15 %.

Answer 13

a) The share of my own consumption is about 80 %.

• 80 % of my own electricity generation is used for my own consumption (= self-consumption + storage charges)
• 20 % of my own electricity generation is supplied into the public power grid

b) The degree of self-sufficiency is about 15 %.

• 15 % of my total annual electricity consumption is covered through my own electricity generation
• 85 % of my total annual electricity consumption is covered through the public power grid

Question 14

What possibilities are there to increase the share of own consumption for a given PV-system?

Answer 14

Goal: increasing the share of own consumption

• Generation
  –> Install a PV tracking system to further align the generation pattern with the given consumption pattern by increasing the number of hours in which the system generates electricity
• Consumption
  –> Further align the consumption pattern with the given generation pattern by adopting the consumption behaviour
• Battery storage
  –> Increase the storage capacity to further balance out the generation and consumption pattern

(- Theoretical calculation (do not apply directly!)
–> share_of_own_consumption
= self_used_electricity / self_generated_electricity
–> self_used_electricity = self_consumed_electricity + storage charges)

Question 15

What possibilities are there to increase the share of self-sufficiency for a given PV-system?

Answer 15

Goal: increasing the share of self-sufficiency

• Consumption
  –> Decrease the total annual consumption
  –> Further align the consumption pattern with the given generation pattern (self_used_electricity increases)
• Generation
  –> Increase the total annual generation (self_used_electricity increases)
  –> Further align the generation pattern with the given consumption pattern (self_used_electricity increases)
• Battery storage
  –> Increase the storage capacity to further balance out the generation and consumption pattern (self_used_electricity increases)

(- Theoretical calculation (do not apply directly!)
–> degree_of_self-sufficiency
= self_used_electricity / annual_electricity_consumption)