ENB120 Electrical Energy and Measurements GFW/13 DC CIRCUIT DESIGN CHALLENGE

Fred the Farmer wants to use renewable energy on his farm to power his hot water system. He has bought a solar panel, a wind generator and a hydroelectric generator. The solar panel acts principally as a current source, while the wind and hydroelectric generators are voltage sources. [Note: solar panels and generators are actually more complex than this, but assume that they behave this way for this assignment]. He has connected all of the three sources in parallel with the hot water system, but is not convinced that this is the best way. Note that the hydro generator is some distance away and is connected to the other components over cables with resistance of 1Ω. He has asked you to analyse the system, and to provide a recommendation for an improved design.

+

c Ω

d Vb A

WindGenerator

SolarPanel

+

f Ω

g V

HydroGenerator

a Ω

e Ω

Hot WaterSystem

1 Ω

1 Ω

Oddly, the parameters of these three sources and the hot water system can be derived from your student number. The parameters of the elements are determined using your student number as follows:

( ) 101 1Digit ×+=a ; 5 2Digit +=b ; ( )10

1 3Digit +=c ; 101) 4(Digit ×+=d ; 1 5Digit +=e ;

( )10

1 6Digit +=f ; 101) 7(Digit ×+=g ;

Example: For student number 4726715, a = 50; b = 12; c = 0.3; d = 70; e = 8; f = 0.2; g = 60. [Do not use these values, they are an example only. Derive values from your own student number.]

Explanations of steps used are essential, and will be carefully accounted for in assessment. Best marks are awarded to numerically correct solutions, but partial credit will be given to partially complete solutions or incorrect solutions where errors have carried through the calculations. State any and all assumptions that you make.

Take Home Exam • Perform this take home exam on your own. Tutors (including peer tutors) and academic

staff are not able to help you with this assessment item. • Your submission coversheet must include the statement that you have performed this

work without the help of others.

(a) Draw a circuit diagram of the system described above. Where possible, simplify the

diagram by noting series and parallel resistances. (2 marks)

(b) Using a circuit analysis technique of your choosing, calculate the power balance of the

system. Show all working. Comment on the effectiveness of power transfer from the solar panel and generators to the hot water system.

(4 marks)

(c) Use circuit simulation software to verify your calculations in (b). Show screen shots of the software that verify your results.

(2 marks)

(d) When the sun is not shining, the solar panel produces no current. When the wind is not blowing, the generator produces no voltage. Use circuit analysis to show the effect of three situations: (i) no sun; (ii) no wind and (iii) no sun or wind. Show all working. Use circuit simulation software to verify your calculations, supported by screen shots.

(6 marks)

(e) Show how diodes can be used to improve the effectiveness of the system during periods of no sun and/or wind. Quantify the efficiency gains made from your design using circuit simulation software – no manual circuit analysis is required for this part. Look online for an appropriate diode to use in this application. Ensure that your diode model in the circuit simulation is equivalent to the real diode that you have chosen.

(5 marks)

(f) Suggest a way of rewiring the system that will increase the overall efficiency and reliability. Note the cabling from the hydro generator cannot be changed, nor can the generator be moved closer. A different hot water system with a different resistance may be used, but changes must be justified. Quantify the efficiency gains that you have made, showing all working from your full circuit analysis. Use circuit simulation software to verify your calculations, supported by screen shots.

(6 marks)

Total: (25 marks)