Small-Scale Solar Power

Solar Power Rangers

Project Definition

• Small Scale, non-photovoltaic, 20 Watts at 12 V continuous.

• Competition: Photovoltaic

• Applications: 3rd world countries, disaster relief

Our Approach

Collection

Conversion

Storage

Design vs Prototype

• Design for the final product

• Prototype key components of the design to assess concept feasibility

• Final Result: two distinct products

Final Product

Parabolic Trough

• Features– Why?– End-plates– Reflecting Material– Heat Transfer

Mechanism

Why a Trough?

• Trough– Mature technology– Ease of construction– ONE degree of freedom/tracking

• Set once per day according to date and global position

• Dish– Relatively young technology– More difficulty in physical realization– TWO degrees of freedom/tracking

End-plates

• Features– Parabolic– Open-ended

Alignment

Reflective Film

• Southwall/ReflecTech– Southwall film is

enhanced with environmental inhibitors to protect the silver from oxidation and PSA for easy application

– Nominal reflectance = 94%

*Courtesy Southwall Technologies

Evacuated Glass Solar Tube

• Apricus Tubes– Dewar’s flask

configuration– Al-N/Al coating– Absorptance > 92%– Non-wicking heat

pipe• 30° Elevation

Trough Recap

• Provides heat focusing method• Utilizes developed and proprietary

products• Nominal efficiency expectancy

– 94% reflectance x 92% absorptance = 86.5% efficient

– Results of tests in conclusion

Stirling Engine: Rationale

• No phase change required• Effective over wide range of energy

inputs

Stirling Engine:Virtual Model

Stirling Engine: Virtual Demonstration

Stirling Cycle

• Assuming Qin = 267 W, achieve Wout = 67 W– This means 40 W electrical

• Minimize DT across heat sink– Proper choice of fin dimensions

• Maximize power delivered to flywheel– Proper sizing of linkages

• Maximize efficiency of cycle– Appropriate engine sizing

T∞

Tb

Heat Sink• Number of fins N

and thickness t• Expected DT = 13 oC

Cylinder

• Dimensions D, L, S

S = 0.833 L

L = 12 in

D = 5 in

Links• Link lengths r2, r3

r2 = 6 in

r3 = 8 in

Tavg = 65.2 N-m, w = 9rpm

P = 61.4 W

Stirling Engine:Feasibility

• Nominal Case– h = 26%– Qin = 267 W >> Wout = 69.5 W

Prototype

Calorimeter

• Measures thermal power output• Ideal calorimeter has zero heat loss

– Insulated thermos with lid• Convection inside calorimeter

– Measure T after stirring water

Stirling Engine

• Bought versus build yourself• Engine Issues

– Tolerances– Seals– Thermal Expansion

Embedded Intelligence Logic

Engine Rotating?

ΔT ≥ 20 °C

NO

Light LEDYES

YES

NO

Lessons Learned

• Solar Collection Test Results

• Desired Power ≥ 175 W/m2

• Average efficiency of 78%• Trough vs. Dish, revisited

Date Conditions Power (W) Power per Area (W/m2)

11 April Partly Cloudy 48.16 147.24

14 April Clear 62.67 191.60

14 April Clear 60.81 185.91

Average 57.21 174.91

Lessons Learned, cont.• Engine configuration

– Binding due to moments– Alternatives?

Image from Wikipedia

Rhombic DriveBasic Crank-Slider

Conclusions

• Feasible– Will be able to meet power requirements

• Continuing Development• Not competitive for small scale

applications– High manufacturing cost– System placement– System complexity

Questions

The Solar Power Rangers are:Phillip Hicks,

Kevin Kastenholz, Derek Lipp, Paul Nistler,

and Rachel Paietta