UE 07: PV Flashcards
What is the azimuth angle?
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
What steps do you go through when installing PV-modules on the roof?
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, total peak power and total costs 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
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
What do you do?
Step 1: Determination of the global radiation, given the orientation and pitch angle of the roof
- Use the azimuth angle as well as the tilt angle to determine the annual sum of global radiation [kWh/(m^2*a)] using a given graph
What is missing?
When installing PV-modules on the roof these are the steps you go through:
Step 2: Shading analysis
Step 2.1)
- For each obstacle: Determine the “…” which could cause shading on the PV system: “…”
- Use the “…” as well as the “…” to determine “…” using the “…”.
Step 2.2)
For each month calculate the “…”
–> Direct radiation generator [kWh/m^2]
= “…”
–> Total radiation generator [kWh/m^2]
= “…”
–> Radiation losses [kWh/m^2]
= “…”
–> Radiation losses [%]
= “…”
Globale radiation = “…”
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 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 all obstacles to determine times during 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 absolute and relative 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”
What is missing?
A “…” visualizes the position of the sun depending on its elevation angle and azimuth angle for a given location (e.g. Berlin, longitudes + latitudes)
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)
What is missing?
Fill factor FF of a solar cell
- “…”
- Usually ranges between 0,5 and 0,82
- FF = P_max / P_T = I_MP * V_MP / I_SC * V_OC
“Measure of the quality of the solar cell”
True or false?
Efficiency of a solar cell
n
= Generated power / Power of incident (‘einfallendem’) sunlight
= P_max / P_in
True!
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
- Afterwards: Price [€/kW_p], Power [kW_p/module], Efficiency per Module [%] and Dimensions (m^2) are given!
True!
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 [€]*
True!
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]
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]
What is missing?
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]
= “…” - Usable storage capacity [kWh/MWh]
= “…” - Use both parameters and a given diagram to determine the share of own consumption
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
What is missing?
When installing PV-modules on the roof these are the steps you go through:
Step 7: Determine the degree of self-sufficiency
Determine:
- PV power output [kW_p/MWh]
= “…” - Usable storage capacity [kWh/MWh]
= “…” - Use both parameters and a given diagram to determine the share of own consumption
Step 6: Determine the degree of self-sufficiency
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
1) What is the share of own consumption?
2) What is the degree of self-sufficiency?
1) Share of own consumption
- How much of my own generation 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!)
–> 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
Explain the following situation:
a) The share of self-consumption is about 80 %.
b) The degree of self-sufficiency is about 15 %.
a) The share of my self-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
What possibilities are there to increase the share of own consumption for a given PV-system?
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)
What possibilities are there to increase the share of self-sufficiency for a given PV-system?
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 by e.g. increasing the installed capacity or installing a PV-tracker (self_used_electricity increases)
–> Further align the generation pattern with the given consumption pattern by changing the consumption behaviour (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)
What is missing?
How does a solar cell work? - Non-irradiated status
- When p-doped and n-doped “…” come into contact, “…” is formed.
- In n-“…”: excess of “…”
- In p-“…”: excess of “…”
- The electrons diffuse from the “…“-region into the “…“-region.
- The holes diffuse from the “…“-region into the “…“-region.
- Positive space charge zone: where electrons have diffused into the p-region, positively ionized dopant atoms remain.
- Negative space charge zone: where holes have migrated into the n-region, negatively ionized dopant atoms remain.
How does a solar cell work? - Non-irradiated (‘bestrahlt’) status
- When p-doped and n-doped semiconductors come into contact, a pn junction (‘Schnittstelle’), also called space charge region, is formed.
- In n-semiconductor: excess of free electrons
- In p-semiconductor: excess of free holes (‘Elektronenfehlstelle’)
- The electrons diffuse from the n-region into the p- region.
- The holes diffuse from the p-region into the n-region.
- Positive space charge zone: where electrons have diffused into the p-region, positively ionized dopant atoms remain.
- Negative space charge zone: where holes have migrated into the n-region, negatively ionized dopant atoms remain.
How does a solar cell work? - Non-irradiated status
Draw the p- and n-doped visualization.
Compare: UE 07 slide 18
Carrier concentration (log scale) over x
Neutral region
- p-doped
- Holes: high
- Electrones: low
- Diffusion force of holes –>
- E-field force on holes –>
Space charge region
- Electron excess
- Protone excess
- E-field <–
Neutral region
- n-doped
- Holes: low
- Electrones: high
- Diffusion force of electrones <–
- E-field force on electrones <–
How does a solar cell work? - Irradiated status
Draw the visualization.
Compare: UE 07 slide 19
Solar heat / Solar thermal energy
What is the solar contribution margin/coverage?
Solar contribution margin = (Solar heat supply / Heat demand *) 100 %
What percentage of the total heat requirement (e.g. for hot water or heating) is covered by the solar thermal system.
How does solar thermal energy with solar collectors work in residential buildings?
Explain the basic principle.
Goal: Provide domestic hot water + space heat
During sunny hours:
1) Sunlight hits the collectors (usually flat-plate or evacuated tube).
2) The fluid inside (water + antifreeze) is heated.
3) A pump circulates this fluid through a heat exchanger.
4) The heat is transferred to water in a storage tank.
5) The cooled fluid returns to the collector
During not-sunny hours:
- If solar energy is insufficient, a backup heater (gas, oil, or electric) kicks in to ensure comfort
