Solar Cells

Question 1

For what kind of missions are solar cells suited?

Answer 1

earth satellites and space probes for all plants up to Jupitar

Question 2

What are the ranges of the power outputs of the pv cells?

Answer 2

a few watts up to tens of kW

Question 3

In the electric power versus use duration plot, what does the plot for solar arrays look like

Answer 3

curves around from bottom middle to middle right, occupying a quadrant

Question 4

What’s the base material resistivity of solar cells?

Answer 4

10^-3 - 10^-2 Ohm cm

Question 5

What are semi conductor junctions doped with to make p and n type junctions? What are there electrical compositions?

Answer 5

p type: boron doped, electron deficiency

n type: phosphorous doped, electron excess

Question 6

What happens to IR photons incident on the single cell solar cell? What about UV photons?

Answer 6

IR: passes through without interaction (transparent)

UV: dissipate as heat within the cell reducing efficiency

Question 7

Describe the structure of a basic triple junction solar cell and the materials used

Answer 7

• n-junction is always closest to the sun as p-junction on top of cells suffer more degradation from radiation damage
• shortest wavelength cells are closest to the sun
• the materials are GaInP, GaAs, Ge
• conductors between the layers are called tunnel junctions

Question 8

What is the profile of the Absorption versus wavelength for a triple junction cell

Answer 8

• peak in the visible (90% EQE)
• a ridge peak from 700 to 900 nm (90 % EQE)
• a slow rise from 900 to 1600 nm then sharp fall off ( 60 to 80 % EQE)

Question 9

What is the current state of the art triple junction solar cell?

Answer 9

GaInP/GaInAs/Ge

Question 10

How thick is the state of the art solar cell?

Answer 10

150 microns +/- 20 micron

Question 11

How to calculate power output of 1000 cell with efficiency 28 % (BoL SotA)

Answer 11

Solar flux x area x efficiency x 1000

Question 12

What are the three benefits from the CdTe thin film PV cell developed by Swansea

Answer 12

• High specific power (W/kg)
• Radiation hard
• Flexible so glass can be rolled allowing for different storage methods meaning larger cell arrays can be carried

Question 13

What is the main property of the CdTe that makes it a promising technology from a power perspective?

Answer 13

It is lightweight compared to silicon and triple junction

Question 14

What is cover glass manufactured from?

Answer 14

Quartz, sapphire or cerium-doped silica

Question 15

what is the job of the cover glass?

Answer 15

Provide some protection against radiation and micrometeorite damage

Question 16

Between the cover glass adhesive and the pv cell, what else is on the stackup diagram

Answer 16

Anti-reflective coating about 0.6 micron thick

Question 17

What do back-surface radiators do?

Answer 17

reflect unabsorbed radiation back through the cell to reduce cell heating

Question 18

On the output current versus cell voltage what features indicate the following:
- Maximum power output
- Optimum load resistance

Answer 18

• Maximum power output is the area which is bound by the maximum power point
• Optimum load resistance is the gradient that joins the origin to the maximum power point

Question 19

Considering the IV plot of the solar cell, what is the role of the PCU?

Answer 19

Keep the array operating at maximum power using a max power point tracking system

Question 20

at grazing angles, what happens to the cell’s reflectivity? how does the pwoer produced fall off?

Answer 20

• It tends towards 1
• the power falls of as cos theta

Question 21

What happens to the maximum power point as the cell temperature increases?

Answer 21

It decreases

Question 22

What are the consequences of a solar cell leaving eclipse? How is this handled?

Answer 22

The solar cell is at its most efficient as it is at its coolest after leaving eclipse. By disconnecting portions of the array until it warms up again, current surges can be avoided. More prominent after GEO

Question 23

What particles cause displacement damage in the crystal structure of semiconductor materials?

Answer 23

Ions, neutrons, high-energy photons and electrons

Question 24

What happens to the electrical properties of the solar cell when is is affected by displacement damage? What happens to the gain?

Answer 24

• more defects
• decreased carrier lifetime
• decreased carrier mobility

lower current gain, non-ionising damage

Question 25

is displacement damage cumulative or single event?

Answer 25

cumulative with exposure (dose)

Question 26

How is radiation hardness calculated and how is it different between silicon and GaAs?

Answer 26

efficiency_irradiated / efficiency_init

• Silicon is less resilient to efficienct changes over time

Question 27

What do the GEO and LEO plots look like for Si and GaAs cells?

Answer 27

Falloff is worse for GEO with both cell falling from max sharply at during the first years of operation and then flattening out Si -> 55 %, GaAs -> 75 %

Small falloff for LEO with Si worse but going flat quick with Si at 90 % and GaAs at 95 %

Question 28

How are solar panels protected against reverse bias zener breakdown?

Answer 28

Diodes (need more info)

Question 29

What causes thermal cycling on the solar cells? What effect does that have on the cell

Answer 29

• Entry and departure into eclipse
• higher failure rates as the different materials in the cell expand contract at different rates and rupture

Question 30

How are solar panels deployed?

Answer 30

Either as wings or body-mounted