Solar Energy

This section covers the fundamentals of solar energy. From this we can determine how much energy is available over an area to be used for heat or electricity.

Motivation

To use the sun effectively as a source of energy, we have to know how it moves through the sky and what energy is available. From this knowledge we can place photovoltaic panels, building windows, or heat collectors correctly.

References

Renewable and Efficient, Gil Masters

Questions we will be able to answer

Where is the sun at any time?
How much radiation does it produce?
Where do I put solar panels or windows?
Will my solar devices be blocked by trees or homes?
Which direction should they face?
How much will they produce now? this month? this year?

Solar Fundamentals

This section covers the sun, the solar system, and the atmosphere in order to understand the radiation striking the earth.

The journey of a photon

Created in the core of the sun
Millions of years to bounce out to surface of sun
Zips to earth in about 8 minutes
Passes through the atmosphere
Strikes a solar panel and dislodges an electron in the PV panel
Electron is collected and delivered to the grid

Electromagnetic Spectrum

Blackbody Spectrum

Solar Spectrum

The Solar System

Radiation units

Power per unit area (watts per square meter) (W/m $^2$ )
Power = Power per unit area $\times$ area
Energy = Power $\times$ Time

Atmospheric depth

Atmospheric absorption

Air mass ratio
$I_B = Ae^{-km}$
$I_B$ - insolation at earth's surface (W/m $^2$ )
$A$ - insolation in space (W/m $^2$ )
$k$ - optical depth (no units)
$m$ - air mass ratio (no units)

Air mass ratio

There are some standard air mass ratios we use
AM0 is "in space"
AM1 is for noon-day sun
AM1.5 is the standard test condition that resembles year round
insolation

Earth sun distance

$d=1.5 \times 10^8 \left(1 + 0.017 sin\left(\frac{360(n-93)}{365}\right)\right)km$

$n$ is the day of the year
Is this close to circular?

Theory vs Practice

I'll demonstrate mathematical expressions for solar radiation
In practice you will use tables or software applications that
calculate these values
I want you to be able to go back in 10 years, pick up this book, and
figure it out again.