Rotating Shadowband Pyranometers

Rotating Shadow Band Monitor at Toyah, TX

Computing Incident Solar Power on a Panel Surface To compute the incident solar power on a panel surface, we assume that the panel captures all of the diffuse horizontal (DH) power, plus the fraction of (GH – DH) that is perpendicular to the panel surface.

)cos()cos(

)(incidentzenith

sunincident

DHGHDHP

W/m2. (10)

The above value, in W/m2, is then multiplied by the panel surface area to yield total incident solar power incidentP . Multiplying by panel efficiency yields maximum expected electrical

power output.

tiltpanel

Line perpendicular to horizontal plane

tiltpanel

Horizontal plane

Figure 6. Panel Tilt Angle

Line perpendicular to panel surface

Edge of panel

zyxsun aaaa ˆcosˆsinsinˆcossinˆ zenithsun

azimuthsun

zenithsun

azimuthsun

zenithsun .

Considering Figure 6, the unit vector perpendicular to the panel surface is

zyxpanel aaaa ˆcosˆsinsinˆcossinˆ tiltpanel

azimuthpanel

tiltpanel

azimuthpanel

tiltpanel

The dot product of the two unit vectors is then

azimuthpanel

tiltpanel

azimuthsun

zenithsunincident cossincossinˆˆcos panelsun aa

azimuthpanel

tiltpanel

azimuthsun

zenithsun sinsinsinsin tilt

panelzenithsun coscos .

Combining terms yields

azimuthpanel

azimuthsun

azimuthpanel

azimuthsun

tiltpanel

zenithsunincident sinsincoscossinsincos

tiltpanel

zenithsun coscos .

Simplifying the above equation yields the general case,

tiltpanel

zenithsun

azimuthpanel

azimuthsun

tiltpanel

zenithsunincident coscoscossinsincos . (9)

AVERAGE DIRECT NORMAL INSOLATION MAP LEGEND

COLOR KEY

per day (kWh/m2-day)

per YEAR (MJ/m2) (quads/100 mi2)

<3.0 <3,940 <1.0

3.0 - 3.5 3,940 - 4,600 1.0 - 1.1

3.5 - 4.0 4,600 - 5,260 1.1 - 1.3

4.0 - 4.5 5,260 - 5,910 1.3 - 1.5

4.5 - 5.0 5,910 - 6,570 1.5 - 1.6

5.0 - 5.5 6,570 - 7,230 1.6 - 1.8

5.5 - 6.0 7,230 - 7,880 1.8 - 1.9

6.0 - 6.5 7,880 - 8,540 1.9 - 2.1

6.5 - 7.0 8,540 - 9,200 2.1 - 2.3

>7.0 >9,200 >2.3

0

1

2

3

4

5

6

0 5 10 15 20 25 30 35 40 45

V(panel) - volts

I - a

mp

s

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

0 5 10 15 20 25 30 35 40 45

V(panel) - volts

P(p

an

el)

- w

att

s

Nameplate Test Results for 30 Watt Solar Panel Shown in Class, Nov. 10, 2014

Elements of a Small Off-Grid 24 Volt Solar System

(Installed by Mack Grady at Gary Grady’s cabin, 15 miles north of Silverthorne, CO, in the Gore Range. 9200’

elevation)

Cabin originally had only a 120Vac generator to power house wiring and water pump about 1 hour each day. There was no battery system.

150W Pairon a good day, 1kWH

Watch out for

shadows

Essential Load!

Straddles the Roof for Best Azimuth AngleSeparate grounding cable for

lightning protection goes straight down to single-point ground rod

Use outdoor-rated UV wiring

Box for DC connections and breakers

PV battery charge

controller

1100W Inverter

AC box and breakers for

inverter output feed a separate set of inverter-

powered outlets in the cabin

DC lightning arrestor

Ground wire connects all metal boxes

to the single-point ground rod

Battery charger from

portable generator

DC breaker from panels to controller

DC breaker from controller to batteries

DC breaker

from batteries to

inverter

DC breaker from battery charger to

batteries

Battery charger from portable

generatorPV battery

charge controller

1100W Inverter

DC lightning arrestor

Inverter on/off switch goes to kitchen

Inverter output to AC breakers

Cables to battery breaker

Four 6 Volt, L6 Batteries in Series (24 Volt System)

in a Homemade Vented Box

Battery temperature sensor goes to PV charge controller

Two-person testing of the 30 Watt solar panel

Step 1 – Student A adjusts the test setup to face the sun and minimize the pin shadow.

Step 2 – Student B holds the probe