1. Power Systems Design -II
Introduction to Space Systems and Spacecraft Design
Space Systems Design

2. Power Systems or EPS Power Systems Design II 2
Introduction to Space Systems and Spacecraft Design
Space Systems Design

3. Power Systems Design II3
Introduction to Space Systems and Spacecraft Design
Space Systems Design

4. Look at the parts of the EPS
Power Systems Design II
Look at the parts of the EPS 4
Introduction to Space Systems and Spacecraft Design
Space Systems Design

5. Take Solar Panel Power Systems Design II 5
Introduction to Space Systems and Spacecraft Design
Space Systems Design

6. 5. 6. 1350 Power Systems Design II 6
Introduction to Space Systems and Spacecraft Design
Space Systems Design

7. What do we need from the solar panel?
Power Systems Design II
What do we need from the solar panel?
What are the attributes of a solar panel?
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels.
Lets go back and look at the solar cell. 7
Introduction to Space Systems and Spacecraft Design
Space Systems Design

8. Lets go back and look at the solar cell.
Power Systems Design II
Lets go back and look at the solar cell.
This dual junction cell
Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm 8
Introduction to Space Systems and Spacecraft Design
Space Systems Design

9. Solar cell has an I-V curve like this
Power Systems Design II
Solar cell has an I-V curve like this
This dual junction cell
Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm 9
Introduction to Space Systems and Spacecraft Design
Space Systems Design

10. Looked at the solar cell.
Power Systems Design II
Looked at the solar cell.
This dual junction cell
Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm
What are the attributes of a solar panel?
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels. 10
Introduction to Space Systems and Spacecraft Design
Space Systems Design

11. Need to select a battery to design for solar panel voltage
Power Systems Design II
Need to select a battery to design for
solar panel voltage
What are the attributes of a solar panel?
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels. 11
Introduction to Space Systems and Spacecraft Design
Space Systems Design

12. Power Systems Design II Rechargeable12
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Space Systems Design

13. Use a lithium ion battery
Power Systems Design II
Use a lithium ion battery
Li Ion batteries = 3.6 v nominal
Design Criteria for charging Li Ion battery:
Need 10-15% more voltage to charge than the nominal voltage.
Here we would need solar panel voltage of ~ 4.0 – 4.2v to charge this battery.
Design Criteria solar panel:
Number of cells = Max voltage/cell voltage.
Take minimum number of whole cells.
# cells = (4.2v/string)/(2.2v/cell)
= 1.9 or 2 cell for a string voltage of 4.4v 13
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14. Power Systems Design II14
Introduction to Space Systems and Spacecraft Design
Space Systems Design

15. Use two lithium ion batteries
Power Systems Design II
Use two lithium ion batteries
Li Ion batteries = 7.2 v nominal
Design Criteria for charging Li Ion battery:
Need 10-15% more voltage to charge than the nominal voltage.
Here we would need solar panel voltage of ~ 8.0 – 8.3v to charge this battery.
Design Criteria solar panel:
Number of cells = Max voltage/cell voltage.
Take minimum number of whole cells.
# cells = (8.3v/string)/(2.2v/cell)
= 3.77 or 4 cell for a string voltage of 8.8v
Lets be conservative and use 5 cells for 11v. 15
Introduction to Space Systems and Spacecraft Design
Space Systems Design

16. Now we have: Two Li Ion batteries = 7.2 v nominal
Power Systems Design II
Now we have:
Two Li Ion batteries = 7.2 v nominal
5 cells for 11v to charge with. 16
Introduction to Space Systems and Spacecraft Design
Space Systems Design

17. What is packing factor? What are the attributes of a solar panel?
Power Systems Design II
What is packing factor?
What are the attributes of a solar panel?
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels.
Got
Got 17
Introduction to Space Systems and Spacecraft Design
Space Systems Design

18. Packing Factor Packing Factor = Total Cell Area/ Total Panel Area
Power Systems Design II
Packing Factor
Total Cell Area
Total Panel Area
Packing Factor = Total Cell Area/ Total Panel Area 18
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Space Systems Design

19. Cell type 2 Fixed solar panel size Cell type 3
Power Systems Design II
Packing Factor
Cell
type 1
Cell type 2
Fixed solar panel size
Cell type 3
What do you do if given a fixed size panel on which to put solar cells and you have these different size solar cells? 19
Introduction to Space Systems and Spacecraft Design
Space Systems Design

20. Power Systems Design II
Packing Factor
What do you do if given a fixed size panel on which to put solar cells and you have these different size solar cells? 20
Introduction to Space Systems and Spacecraft Design
Space Systems Design

21. How do you mount these 5 cells on this panel?
Power Systems Design II
11v
Now we have:
5 cells for 11v where the string has all of the cells hooked in series
Total Panel Area
How do you mount these 5 cells on this panel? 21
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Space Systems Design

22. OK! NO! How do you mount these 5 cells on this panel?
Power Systems Design II
How do you mount these 5 cells on this panel?
OK!
NO!
Visually we can see a very poor packing factor. 22
Introduction to Space Systems and Spacecraft Design
Space Systems Design

23. Oh Oh! What if the cells were bigger?
Power Systems Design II
What if the cells were bigger?
Oh Oh!
Now you have only 4.4v in the string. 23
Introduction to Space Systems and Spacecraft Design
Space Systems Design

24. Got a cube? Put other cells on another face?
Power Systems Design II
Got a cube? Put other cells on another face?
Can’t do. All cells for a single string must be on same face. 24
Introduction to Space Systems and Spacecraft Design
Space Systems Design

25. Where are we now in the solar panel design?
Power Systems Design II
Where are we now in the solar panel design?
What are the attributes of a solar panel?
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels.
Got
Not got, but
understand
Got
Assume we could mount the 5 cells on a panel, what is total power for the cells selected? 25
Introduction to Space Systems and Spacecraft Design
Space Systems Design

26. How much power from these cells?
Power Systems Design II
How much power from these cells?
5 cells for 11v
One cell area = 76 x 37 mm = 2812 mm^2
Total cell area = 8*2812 = mm^2 = 2.25 x10-2 m^2
We have watts/m^2 from the sun in space
Direct power = (1350 w/m^2) x (2.25 x10-2 m^2)
= 34.4 watts
Converted power = direct power x cell efficiency
= 34.4 w x 0.22 eff
= 7.5 watts
11v
For this dual junction cell
Has an efficiency of ~ 22%
Open circuit voltage ~ 2.2v
Size – 76 x 37 mm 26
Introduction to Space Systems and Spacecraft Design
Space Systems Design

27. Where are we now in the solar panel design?
Power Systems Design II
Where are we now in the solar panel design?
What are the attributes of a solar panel?
Total output power of solar panel.
Voltage of solar panel.
Maximum packing factor.
Efficiency of the solar cells.
Operating temperature of the panels.
Got
Got
Not got, but
understand
Got
Now we can assume to start:
panel is at 90 degrees with sun – max power
operating temperature 20 degrees.. Centigrade – 22% eff
Don’t forget, temperature counts a lot. 27
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Space Systems Design

28. Power Systems Design II Start here Tuesday for Idaho28
Introduction to Space Systems and Spacecraft Design
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29. Power Systems Design II
Now that we have beat our way through the solar panel design lets go look at the some more parts of the EPS. 29
Introduction to Space Systems and Spacecraft Design
Space Systems Design

30. Power Systems or EPS What is this? Power Systems Design II 30
Introduction to Space Systems and Spacecraft Design
Space Systems Design

31. Power Systems or EPS Back bias diode Panel 1
Power Systems Design II
Power Systems or EPS
Back bias diode
When panel 1 is shaded, the back bias diode keeps the current from flowing backwards through panel 1, when panel 2 is generating a voltage across it.
Panel 1
Panel 2 31
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Space Systems Design

32. Power Systems or EPS What is this? R V Power Systems Design II 32
Measure current by measuring voltage across a low resistance precision resistor 32
Introduction to Space Systems and Spacecraft Design
Space Systems Design

33. Power Systems or EPS Power Systems Design II 33
Introduction to Space Systems and Spacecraft Design
Space Systems Design

34. Power Systems or EPS Power Systems Design II 34
Introduction to Space Systems and Spacecraft Design
Space Systems Design

35. Power Systems Design II35
Introduction to Space Systems and Spacecraft Design
Space Systems Design

36. Power Systems Design II36
Introduction to Space Systems and Spacecraft Design
Space Systems Design

37. Expanded subsystem control
Power Systems Design II
Expanded subsystem control 37
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Space Systems Design

38. Expanded subsystem control
Power Systems Design II
Expanded subsystem control 38
Introduction to Space Systems and Spacecraft Design
Space Systems Design

39. What does a charge regulator do?
Power Systems Design II
What does a charge regulator do?
Controls voltage from PV to battery
Controls rate of charge
Prevents overcharging
Can “boost” or “buck” PV voltage to match battery needs. 39
Introduction to Space Systems and Spacecraft Design
Space Systems Design

40. Expanded subsystem control
Power Systems Design II
Expanded subsystem control 40
Introduction to Space Systems and Spacecraft Design
Space Systems Design

41. Power Systems Design II
Consider:
When high current occurs in a subsystem, it could be from latch-up. What to do? Cycle power. Where do you do this – hardware controlled in the EPS. 41
Introduction to Space Systems and Spacecraft Design
Space Systems Design

42. Consider the satellite’s attitude control for solar power generation.
Power Systems Design II
Consider the satellite’s attitude control for solar power generation. 42
Introduction to Space Systems and Spacecraft Design
Space Systems Design

43. Power Systems Design II
Satellite Orbit
Parallel Sun Rays
Eclipse
Sun
Earth 43
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Space Systems Design

44. Power Systems Design II Gravity Gradient Stabilized
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45. N Power Systems Design II Passive Magnetic Stabilized S N S N S N S N45
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46. Power Systems Design II Inertially Stabilized46
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47. Power Systems Design II47
Introduction to Space Systems and Spacecraft Design
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48. Power Systems Design II48
Introduction to Space Systems and Spacecraft Design
Space Systems Design

49. Some Solar Notes Power from sun in orbit ~ 1350 watts/meter2
Power Systems Design II
Some Solar Notes
Power from sun in orbit ~ 1350 watts/meter2
Power from cells on ground ~ 35% less than in space
Can get some power form albedo – earth shine ~ 35% 49
Introduction to Space Systems and Spacecraft Design
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50. Power Systems Design II50
Introduction to Space Systems and Spacecraft Design
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51. Power Systems Design II
Need to consider the power requirements of all of the subsystems and when they are used to build a power budget. 51
Introduction to Space Systems and Spacecraft Design
Space Systems Design

52. Questions? Power Systems Design II 52
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