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Get the most Power out of your Solar ElectricPanels: Electric Resistance, Cell Temperature,

Shading Effects and Panel Orientation

Voltage Drops in Solar Panel SystemsThe current (amps) and power output (watts) of photovoltaic solar

panels are approximately proportional to the suns intensity. At a

given intensity, a solar panel's output current and operating

voltage are determined by the characteristics of the load. Many

materials naturally provide an electric resistance to the flow of

electrical current. If that load is a battery, the battery's internal

resistance limits the modules operating voltage. This is also

known as voltage drop.

A solar panel rated at 17 volts will yield between 12 and 15 vo lts

when used in a battery backup system. Because wattage (or

power) is the product of volts multiplied by the amps, the module

output is reduced. For example, a 50-watt solar panel working at

13.0 volts will products 39.0 watts (13.0 volts x 3.0 amps = 39.0

watts).

To reduce these voltage drops we utilize MPPT charge

controllers. All charge controllers will regulate the amount of

voltage to the battery bank within acceptable limits. This keeps

the battery from being undercharged or overcharged and

prolongs battery life. Additionally, an MPPT charge controller

optimizes the voltage of the system array to maximize power

output. This can result in a boost of system performance by as

much as 30%. Larger solar modules can be used with this MPPT

technology without the associated battery voltage drop. This is

ultimately more economical on a per watt basis.

Solar System Sizing Worksheet - Learn the basics of

electricity and figure out how to size your system to meet

all your needs.

What Are the Different Types of Solar Panels?

Solar Power map - Usable solar power throughout

different parts of the USA

FAQ about solar power

AC solar panels

An I-V curve shows all of a solar panels possible operating points

(current/voltage combinations) at a given cell temperature and

light intensity (irradiance). I is the amperage/current. Increases

in cell temperature will slightly increase a solar panels current

while significantly decreasing voltage

Maximum power in watts is shown at the knee of the curve. Most

I-V curve charts use optimal operating cell temperature of 25C

(77F). To calculate the true power generated from a

battery/array system without a charge controller, check the

amperage produced during operating battery voltage (12, 24 or

48 volts) and actual cell temperatures.

PV solar panels are very sensitive to shading.Many brands of PV solar panels do not tolerate shading, even

from the branch of a leafless tree. Shading obstructions may be

from soft or hard sources.

If a tree, roof vent, chimney or any other item is blocking the suns

rays from a distance, the shadow is diffuse or dispersed. A bit of

dust directly on the panel surface will also cause soft shading.

These soft sources reduce the amount of light reaching the solar

panels cells and can significantly reduce power output.

Shading obstructions are considered hard when objects are in

direct contact with the glass, completely blocking the suns rays.

Bird droppings, broken tree branches and wayward frisbees are

examples of hard shading that can affect a panels performance.

Partial hard shading of one cell in a photovoltaic panel can create

a power drop as much as 50%. Because all the cells in a panel

are connected in a ser ies string, all the cells will be affected,

ultimately reducing the panel output by about the same

percentage.

Panel OrientationTo compare the energy output of your array to its optimum value,

you will need to know the actual tilt angle (which may be the slope

of your roof if your array is flush-mounted) and the directional

angle of your array. If your solar array tilt is within 15% of thelatitude angle, you can expect a reduction of 5% or less in your

system's annual energy production. If your solar array orientation

is greater than 15 degrees off either angle the latitude angle

and/or the east/west angle, the reduction in your system's annual

energy production may fall by as much as 15% from its peak

available value. During the winter months at higher latitude, the

reduction will be greater, as much as 25% or more.

Optimal Tilt Angle

At any given instant, an array will generate maximum output when

pointed directly at the sun. The optimal tilt angle is perpendicular,

or 90 degrees, to the suns rays at true solar noon. True solar

noon is when the sun is at its highest during its daily east-west

path across the sky. This is also known as 0Azimuth.

0

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Tech Tip: Finding Solar

During Daylight Savings

by Wil Burlin

When the U.S. is using Dayli

Savings Time, solar noon is

at 1 pm by the clock. If at 1 p

stake is driven into the groun

shadow is created that points

and south. The stake will beexact solar south end of the

shadow.

While you could use a sexta

measure the sun's height ab

horizon like the sailors used

stake and clock method will g

close enough as to not make

of a difference. A Green Bere

neighbor of mine told me his

"At solar noon, put a block of

on the glass of the solar pan

Rotate and ti lt the rack until t

no shadow on the glass, the

your perfect adjustment."

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Solar Panels need to be positioned just right to

maximize power harvesting.

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7/30/2019 Maximizing Your Solar Panels' Output

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Examples of partial cell shading that reduce solar panel power by

half.

When a single cell is fully shaded by hard sources it can pull

power from the remaining cells throughout the series string, again

likely resulting in a 50% power loss. If the bottom row of cells is

fully hard shaded, as can happen with accumulated snow on

ground-mounted panels, this can result in a complete power loss.

If enough cells are hard shaded the panel can become a drain on

an entire system, or on one string of panels within the system.

To reduce this shading effect, roof-mounted panels wired in the

same string of a system should be installed on roof sections that

face the same directions and set at the same tilt angle. Most

manufacturers use bypass diodes that allow current to flow in only

one direction to reduce the effects of shading, but they often

cannot prevent the effects completely. When shading cannot be

avoided (or you do not have enough space to position all solar

panels in the same direction), you'll want to consider using:

The SolarEdge System SolarEdge PowerBox optimizers

allow solar panels to operate independently by maximizing

energy throughput of each and every module individually.

Because SolarEdge Power Box optimizers automaticallymaintain a fixed string voltage, the SolarEdge inverter can

work at optimal e fficiency.

Micro inverters In a system using micro-inverters, each

panel has its own inverter, eliminating system power

drains. Each panel can still be ind ividually affected by

shading. See Enphase inverters and AUO AC solar

panels.

To capture the maximum amount of solar radiation over the

course of a year, the tilt angle should be adjus ted seasonally.

During spring and fall the angle should be approximately equal to

a site's latitude at solar noon. To optimize winter performance, the

solar array can be tilted 15 degrees more than the latitude angle,

and to optimize summer performance, 15 degrees less than the

latitude angle.

Optimal Direction Angle

True solar south is the optimal direction for maximizing the power

output of your PV solar panels. Using a compass or a magnetic

declination chart does not give you true solar south. See tech tip

(top right of page) to find true solar south. The closer you get tothe north and south poles the more the earths magnetic field

skews your compass readings. Other geological magnetic forces

can affect the compass needle as well. Remember playing with

magnets and a compass in science class?

A magnetic declination map will not give you "true solar south". See

tech tip to the right.

If a south-facing roof is unavailable, an east or west-facing

surface is the next best option. SolarEdge and Microinverter Solar

Power Gridtied Systems allow for your solar panels to be facing

more than one direction, while centralized gridtied inverter

systems allow for only one orientation.

Local Climate Effects

Typical weather patterns may change your optimal panel

orientation. For instance, those on the West Coast with early

morning fog may want to adjust their array towards a southwest

angle to take advantage of the clear skies later in the day.

Panel Mounting

The type of solar panel mounting that can offer the greatest

flexibility is top of pole mounting. This type of mounting allows you

to take advantage of the optimal panel angles for your climate,

latitude and site conditions.

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