Thomas Maxime

2012

2

Solar energy

• Promising technology

• Latitude and temperature

True North Power, Ontario

• Azimuth trackers

• Wind & solar

• Customers’ concerns

• Need to assess different configurations

I) State of the art1) Passive and active trackers2) One axis and double axis trackers3) Limits of the technology

II) Solar radiation modelTwo solar models: Orgill and Pérez

III) Computation of the solar model1) Solar data2) Different simulations3) Modification of the model

IV) Results of the simulation1) Slope and azimuth of double axis tracker2) Radiation on panel

V) Discussion

VI) Conclusion

3

1) Passive and active solar trackers

Passive

• Gas under partial pressure

• Memory of shape of an alloy

• Temperature dependant

• Bad with changing weather

4

Active

• Time-based: from solar equations and modeling

• Experimental: optical sensors

• Optimization

• Not weather dependant

The identical tubes are filled with gas

2) Single and double-axis trackers

Single-axis

• Different configurations

• Fixed slope

• Rotation 2° every 8min

• Around 28% energy gain

5

Double axis

• Rotation of two axis: azimuth+slope

• Energy gain>40% around sunrise and sunset

• Around 32% energy gain

3) Limits of the technology

Possible improvement of azimuth tracker

• Monthly hand-tilting = 3.1% energy gain

• One hour step = 99.75%

• Two hour step = 98.80%

• Two step tracker = 95%

6

• Double axis = 5-6% gain against 2-3% consumption of total energy due to addition of a motor

• Costs and maintenance

• Cloudy days: diffuse radiation only

of continuousazimuth tracking

Continuous Two step

Fixed tilt

7

Ipanel = Idiffuse + Ibeam + Ireflected

8

Orgill model

Iground

+Solar equations +Latitude+longitude

Idiffuse

+Ibeam

Pérez model

Idpanel

+Ibpanel

+Ireflectpanel

Ipanel

Idiffuse

+Ibeam

+Panel’s slope and azimuth

First step model

Second step model

Measured total radiation on horizontal surface: Iground

1) Solar data• Queen’s University, Kingston • One minute measurement of solar horizontal radiation for 2011• 44.225°N 76.495°W

2) Different simulations• Fixed South facing panel with optimum slope• Azimuth tracker with ∆az=1° and optimum slope• Double-axis tracker with ∆az=1° and ∆β=[1,2,5,10°]• Perfect continuous tracker θ=0°

9

3) Modification of the model• Problem at sunrise and sunset, assumption: Ibeam=0 and Idiffuse=Iground

• Two cases: Pérez model + Liu & Jordan for Zenith angle > 85° or Pérez model all the time

10

Orgill model

Pérez model

Pérez model

Liu & Jordan model

Zenith angle > 85°Zenith angle ≤ 85°

OR

Ipanel

Ipanel

1) Slope and azimuth of double axis

11

Δaz=Δβ=1°

2) Radiation on panel

12

Pérez + Liu & Jordan when Zenith angle>85°Continuous 100,00% 132,54%

Two axis with ∆az=1°

1° 99,99% 132,53%

2° 98,87% 131,04%

5° 98,78% 130,92%

10° 98,48% 130,52%

One axis ∆az=1° fixed slope 50° 97,14% 128,75%

Fixed slope 0° south 34° 75,45% 100,00%

• Two-axis tracker increases energy gain from 28.75% to 32.53% compared to fixed panel facing south

• Only 1.73% gain of two-axis over one-axis with Δβ=2°

• Maximum gain of 2.85% with a very accurate tracking

13

Use of Pérez + Liu & Jordan

• Received radiation for Zenith angle>85° represents only 1.96% of total radiation on horizontal surface on earth.

• Comparison with 5 other sites in the USA with 43°<latitude<45.5° and 70°<longitude<83°

Syracuse, New York

Rochester, New York

Concord, New Hampshire

Burlington, Vermont

Massena, New York

• Fixed panel: consistent slope of 34°

USA sites Queen’s University

Two-axis tracker 32.9% 32.53%

Azimuth tracker 28.8% 28.75%

Energy gain over fixed south facing panel

Queen’s University:44.225°N 76.495°W

14

Uncertainty of the solar model

• 6.7% difference between use of Pérez or use of Pérez + Liu & Jordan for continuous tracking

• High resolution data: error around sunrise and sunset & 5W/m² measurement precision

• Geography of the site: top of a mountain? Shadow?

Feasibility of addition of a second axis

• 2.85% energy gain of two axis over azimuth tracker against 2% motor consumption. Need of battery?

• 2.85% with very accurate tracking. Use of the motor

• Additional costs and maintenance

15

Is it worth adding a second axis?

• Small energy gain

• Big uncertainty in solar models

• Additional costs

Solar tracker = optimized PV panels

• Gain of a few percent

• Better in sunny weather

• No need for perfect tracking

16