A Novel Algorithm for Solar Potential Estimation

in Complex Urban Scenes

Partha Acharjee Virtual Environment Lab (VEL)

University of Texas at Arlington

email: partha.acharjee@mavs.uta.edu

Dr. Venkat Devarajan Professor, Electrical Engineering

University of Texas Arlington

2 Solar potential estimation || Virtual Environment Lab (VEL) 3/22/2017

Motivations and Challenges

Estimation of annual solar potential over an area using airborne LiDAR data.

• Help to identify the possible location of the solar panel installation.

• Give an estimated amount of solar potential received annually.

• Provide a confident economical decision for households.

Challenges:

Motivations:

• Estimate solar potential for both rooftops and facades.

• 3D representation of 2.5D airborne LiDAR data.

• Faster algorithm speed for large scale application.

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LiDAR data

3D city modeling Build patches Calculate sun position TMY data

Diffuse radiation model

1) Calculate sky view factor

2) Calculate diffuse radiation on patches

Direct radiation model

1) Calculate shadow map

2) Calculate solar intensity on patches

Global radiation on roof-tops

and facades

Proposed algorithm

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Patch representation

Solar potential estimation || Virtual Environment Lab (VEL)

From 2.5D LiDAR elevation data, patches were created to represent all planes.

• Four adjacent points were selected as patch vertices.

• Each vertical patches was divided into 64 small patches.

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Patch representation

Patches are shown without vertices Patches are color codded by elevation

Solar potential estimation || Virtual Environment Lab (VEL)

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Astronomical model for sun position

The position of the sun at a specific place on a specific time can be calculated using

the astronomical model,

Here, 𝜑 is the latitude, and the hour angle 𝐻 and the declination angle 𝛿 can be

calculated from the longitude and the local time.

Therefore, algorithmically we can say,

𝑠𝑜𝑙𝑎𝑟𝐸𝑙𝑒𝑣𝑎𝑡𝑖𝑜𝑛, 𝑠𝑜𝑙𝑎𝑟𝐴𝑧𝑖𝑚𝑢𝑡ℎ = 𝐴𝑠𝑡𝑟𝑜𝑛𝑜𝑚𝑖𝑐𝑎𝑙𝑀𝑜𝑑𝑒𝑙{𝐿𝑎𝑡𝑖𝑡𝑢𝑑𝑒, 𝐿𝑜𝑛𝑔𝑖𝑡𝑢𝑑𝑒, 𝐿𝑜𝑐𝑎𝑙 𝑇𝑖𝑚𝑒}

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South East

Jan

Feb

Mar

Apr

May Jun

Sun position on the sky

South East

Jul Aug

Sep

Oct

Nov

Dec

The position of the sun in different hours on the first day of each month over the year.

• The sun tilted towards the south most of the year.

• During the middle of the year, the sun travels close to the zenith.

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Typical meteorological year data

Amount of solar radiation received by a flat plane in per square meter is shown

for two months at different time of the day.

National Solar Radiation Database holds solar and meteorological data for locations

over United States.

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Solar radiation models

• An algorithm to map shadows

• Calculate angle between the surface normal and the sunbeam

• Calculate sky view factor

• Calculate area from patch vertices

• DNI and DHI are available from TMY data

Both direct and indirect sunlight can be the source of solar potential on a surface.

Direct radiation model Diffuse radiation model

• Shadow or not

• Angle between surface normal and sunbeam

• Direct Normal Irradiance and Surface area

• Observable portion of the sky

• Diffuse Horizontal Irradiance

• Surface area

Global Solar radiation

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Ray lines of sunlight

N

S

E W

Sunlight has the parallelism properties, which means all rays are parallel, and a single

solar azimuth and elevation angle are enough for the location.

Sunray lines are shown for 0 degrees and 330 degrees solar azimuth from the top.

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Ray tracing on the ground

Elevation of each point on the ray line was used to calculate shadow limit.

Ray line on the ground

Reference sunbeam

Sunbeam

Shade Light

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Shadow limit and Shadows

Sun elevation 15 degree

Sun elevation 60 degree

Shadow limits are shown in left figures, and patches under shadow are shown in right.

Solar potential estimation || Virtual Environment Lab (VEL)

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Intensity from direct sunlight

Sun elevation 30 degree

Sun elevation 45 degree Sun elevation 60 degree

Sun elevation 15 degree

Solar potential from direct sun light are shown for four different solar azimuth.

Solar potential estimation || Virtual Environment Lab (VEL)

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South East

Diffuse radiation model The sky was evenly segmented, and sky view factor determined how many of those

are in the line of sight from the surface.

• Obviously, vertical planes have sky view factor <=0.5

• Surfaces close to the tall objects have smaller sky view factor.

Solar potential estimation || Virtual Environment Lab (VEL)

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July

September

December

April

Wh/m2/day

W

E

N S

Solar potential in different months

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kWh/m2/year

September

W

E

N S

E

W

S N

Annual solar potential

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Solar potential on facades over the year

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Solar potential: Rooftop vs facade

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Future work

Solar potential estimation || Virtual Environment Lab (VEL)

• Apply on large-scaled projects and investigate

the computation time.

• Include solar panel tilt.

• Make the code available for public use, and

make it compatible with publicly available

LiDAR and solar data.

20 3/22/2017

Thank you

Solar potential estimation || Virtual Environment Lab (VEL)