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Solar Energy - Book: Photovoltaic Solar Energy summary
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Photovoltaic Solar Energy, chapters 1-6 course: Solar Energy Sustainable energy technology University of Twente
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Photovoltaic Solar EnergyChapter 1: Introduction to photovoltaics
Properties of light:
Energy contained by a photon, E:
hc
E=
λ
E=hv
The energy of light is discontinuously distributed in space, and which can be produced and absorbed
as complete units.
Air mass coefficient = the ratio of the direct optical path length of solar irradiance through the Earth’s
atmosphere, Lθ, relative to the path length with the zenith as an origin, called the zenith path length,
L.
L 1
AM =
Lθ cosθ
Solar irradiance depends on:
Moment of the day and year; thus the related sun positions (effect of the optical path length
through the atmosphere)
The composition of the atmosphere
Weather, including cloud formation and the precipitation
Snell’s law = the different propagation of light in two different isotropic media results in refraction at
the interface of these media
sin θi n2
=
sin θt n1
From Snell’s law it can be derived that when light propagates from a medium with a higher refraction
index to a medium with a lower refractive index (hence, n 1>n2), total internal reflection occurs for
incidence angles greater than the critical angle, θcrit, leading to refraction into the medium with the
higher refraction index.
n1
θcrit =arsin
n2
The law of refraction states that if light hits an interface between two media with a different
refractive index, the angle of reflection, θr, is equal to the angle of incidence, θi.
1
,Chapter 13: Supporting methods and tools
Levelized cost of electricity (LCOE) = gives a levelized (average) cost of electricity generation over the
life of the asset. It can be used to compare alternative technologies when different scales of
operation, investment, or operating time periods exist.
Total life cycle cost
LCOE=
Total lifetime energy production
Drivers of a system LCOE:
1. Cost of capital = effectively the level of interest rate required to finance a system, has a
substantial influence on economics, equal in important to the system cost or performance.
Since essentially all of the energy from a system is prepaid in the form of the system price,
the cost to finance that asset is critical. The average cost of financing is linked to the real
and/or perceived risk of the asset.
a. Off-take risk = risk that the system electricity sale price and/or volume will be lower
than planned
b. Performance risk = risk of lower than expected cash flows due to weather conditions
or system technical issues
c. Property risk = risk of property damage/loss.
2. System life/residual value = high performance from PV panels with more than 20 years of
outdoor exposure. No fundamental barrier to operating more than 30 years. Systems will
likely operate for 40-80 years with periodic refurbishments.
3. Plant energy production = expressed in kilowatt hours generated per rated kilowatt peak of
capacity per year (kWh/kWp). It depends on:
a. System performance
b. Local climate
4. Annual O&M/Opex = includes the operations and maintenance of the plant, the cost to
administer the project, such as accounting and tax reporting, property insurance, land lease
as applicable, site security and property or revenue taxes that may apply.
5. PV plant cost = how to reduce the system cost.
Four main types of collective initiatives:
Collective buying initiative = the initiatives to co-ordinate potential purchasers are taken by
PV suppliers, regional and local governments, companies for their own employees, or
environmental organizations. Costs and risk may be reduced.
Community shares = multiple users, lacking the proper on-site conditions for solar energy or
the financial capacity to invest in a full individual PV system on their own house, purchase a
portion of their electricity from a facility located off-site. Costs and risk may be reduced.
Third party ownership = PV companies own and operate customer-sited PV systems and
either lease PV equipment or sell PV electricity to the building occupant. Potential
advantages for people are the (partial) absence of investments costs and that they do not
have to worry about the technological aspects and risks.
Local renewable energy cooperatives = the cooperative conducts several utility-related
activities, such as the collective purchase of green energy, the local production of renewable
energy, supply to the local community, financing of or participating in renewable energy
projects, and supporting energy saving within the community.
2
,The diversity of people’s involvement with PV in housing:
Four steps for conducting an LCA:
1. Goal and scope definition
2. Life cycle inventory
3. Life cycle impact assessment
4. Interpretation
The life cycle stages of photovoltaics:
1. The production of raw materials
2. Their processing and purification
3. The manufacture of solar cells, modules, and balance of system (BOS) components
4. The installation and operation of the systems
5. Their decommissioning, disposal, or recycling
The life cycle Cumulative Energy Demand (CED) = the sum total of the (renewable and non-
renewable) primary energy harvested from the geo-biosphere in order to supply the direct energy
and material inputs used in all its life cycle stage.
Energy Payback Time (EPBT) = the period required for a renewable energy system to generate the
same amount of energy (in terms of equivalent primary energy) that was used to produce (and
manage at end of life) the system itself.
Energy Return on Investment (EROI):
Where T is the period of the system operation.
Greenhouse Gas (GHG) emissions & Global Warming Potential (GWP) = the overall GWP due to the
emission of a number of GHGs along the various stages of the PV life cycle is typically estimated using
an integrated time-horizon of 100 years, using CO 2 equivalence.
Electricity and fuel use during the production of the PV materials and modules are the main sources
of the GHG emissions for PV cycles, and specifically the technologies and processes for generating
the upstream electricity play an important role in determining the total GWP of PVs, since the higher
the mixture of fossil fuels is in the grid, the higher are the GHG (and toxic) emissions.
3
, PV education Chapter 2: Properties of light
Photovoltaics = the direct conversion of light (photo) to electricity (-voltaic).
Depending on the situation, a photon may appear as either a wave or as a particle and this concept is
called ‘wave-particle duality’.
High energy photon for blue light (short wavelength).
Lower energy photon for red light (long wavelength).
Low energy photon for infrared light.
The important characteristics of the incident solar energy are:
The spectral content of the incident light
The radiant power density from the sun
The angle at which the incident solar radiation strikes a photovoltaic module
The radiant energy from the sun throughout a year or day for a particular surface
Photon energy: 3.0675 eV.
Relationship between the energy of a photon (E) and the wavelength of the light (λ):
1 eV = 1.602*10-19 J
Photon flux = the number of photons per second per unit area:
The photon flux is important in determining the number of electrons which are generated, and hence
the current produced from a solar cell.
For the same light intensity, blue light requires fewer photons since the energy content of each
photon is greater.
At a given wavelength, the combination of the photon wavelength or energy and the photon flux at
that wavelength can be used to calculate the power density for photons at the particular wavelength.
Power density = photon flux * energy of a single photon
Spectral irradiance, F = most common way of characterizing a light source. It gives the power density
at a particular wavelength.
Total power density emitted from a light source:
4
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