Sustainable Energy Exam

What are the renewable energy sources

Solar, wind, biomass, hydroelectricity, ocean energy, geothermal.

What are Intermittent Renewables?

Wind, solar PV, wave energy

What are the major types of fossil fuels?

coal, natural gas, oil

What are the two phases of photosynthesis?

light dependent and light independent

Light Dependent reaction

converts light energy into chemical energy; produces ATP molecules to be used to fuel light-independent reaction H2O splitting to produce O2 and H+ and subsequently ATP/NADPH)

Light Independent Reactions (Calvin Cycle)

consumes CO2, uses ATP produced to make sugars, and regenerate ADP/NADP.

The electromagnetic light spectrum

Gamma Rays, X Rays, UV, Visible light, Infrared/Microvwaves, Radiowaves

Visible light (nm) is only a small part of the electromagnetic spectrum

Light Harvesting Materials

Pigment/dye, chromophore, auxochrome

Pigment

dye, a material that changes the color of reflected or transmitted light as a result of wavelength selective absorption

Chromophore

an atom or group whose presence is responsible for the color of a compound

auxochrome

the charged portion of the chromogen that allows it to act as a dye through ionic or covalent bonds between the chromogen and the cell.

Beer-Lambert Law

Used to relate the concentration of colored solutions to the amount of visible light they absorb.

bathochromic

shift to longer wavelength

hypsochromic

shift to a shorter wavelength

basic energy concept during photosynthesis

energy transfer: a pure physical process that only involves the excitation of molecules. Electron transfer: A pure chemical process

Z Scheme of photosynthesis

PSI and PSII: The Z refers to changes in redox potential of electrons. Note that PSII comes before PSI because they're named in terms of discovery, not sequence.

PSII

Functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm (The reaction-center chlorophyll a of PS II is called P680)

•Oxidized P680 (P680+) is the strongest biological oxidizing agent known. It has an estimated redox potential of ~1.3 V

•This makes it possible to oxidize water during oxygenic photosynthesis

PSI

is best at absorbing a wavelength of 700 nm

The reaction-center chlorophyll a of PS I is called P700

Conductors:

materials that allow electric charges to flow through them easily; no band gap

Semiconductors

elements that conduct an electric current under certain conditions; medium sized band gap

Insulators

materials that prevent electric charges from flowing through them easily; large band gap

band gap

an energy gap that exists between the valence band and conduction band of semiconductors and insulators

FRET energy transfer

The Forster Resonance Energy Transfer. The phenomenon that an excited donor transfers energy to an acceptor group through a non-radiative process. It is a special technique to gauge the distance between two chromophores. Fret only works when the separating distance between donor and acceptor is under 10 nm. FRET is distance-dependent and is a popular tool to measure dynamic activities of biological molecules within a nanoscale.

Dexter Energy Transfer

•sometimes called short-range, collisional or exchange energy transfer which is a process with electron exchange.

• similar to Förster energy transfer but differs greatly in length scale (<10 Å) and underlying mechanism.

•two molecules (intermolecular) or two parts of a molecule (intramolecular) bilaterally exchange their electrons.

•reaction rate constant of Dexter energy transfer exponentially decays as the distance between two parties increases.

•On account of the exponential relationship to the distance, the exchange mechanism typically occurs within 10 Å.

Silicon Photovoltaic efficiency limit

Silicon is transparent at wavelengths longer than 1.1 microns (1100nm) 23% of sunlight passes through with no effect. only 77% of the solar spectrum is absorbed by silicon, and of that 77% only 30% is used as electrical energy.

Dye-sensitized solar cells

When light strikes the solar cell, dye sensitizers on the surface of a TiO2 film excite and inject electrons into the conduction band of TiO2 film. The electrons diffuse all the way through the mesoporous film to the anode.

Theoretical capacity of Li

3860 mA h g−1

Theoretical capacity of Na

1165 mAh g−1

Theoretical Capacity of Zn

820 mAh/g

Theoretical Capacity of S

1675 mAh g−1

Redox flow battery

The power is defined by the size and design of the electrochemical cell. Energy depends on the size of the tank

Standards of good catalysts

Activity, stability, selectivity

Activity

describes the effective concentration of that substance in the reaction mixture

Stability

How long the catalyst can work

Selectivity

how selective the catalyst can facilitate the production of a certain product

Water Splitting

chloroplast splits water into hydrogen and oxygen (H is used in sugars and O2 is released)

Water Splitting Overpotential

Real water electrolyzers require higher voltages for the reaction to proceed. The part that exceeds 1.23 V is called overpotential or overvoltage, and represents any kind of loss and nonideality in the electrochemical process.

What is electrical energy measured with?

Kilowatt-hours

What is heat energy measured with?

British Thermal Units (BTU)

Joule

SI unit of energy

1 kilowatt-hour (kWh)

3.60 x 10^6 joules (J)

1 calorie of heat

the heat needed to raise 1 gram of wwater 1 degree centigrade

1 calorie

4.184 (J)

1 BTU

the amount of heat necessary to raise one pound of water by 1 degree F

1055 J

252 cal

1.055 kJ

What is an intermittent renewable?

Generation Capacity Resource with output that can vary as a function of its energy source

What is a fossil fuel?

a natural fuel such as coal or gas, formed in the geological past from the remains of living organisms.

What are fossil fuels made of?

hydrocarbons, and they contain carbon hydrogens such as methane

FRET and Dexter Comparison

The difference between Förster and Dexter mechanism include

•Dexter mechanism involves the overlap of wavefunctions so that electrons can occupy the other's molecular orbitals.

•The reaction rate constant of Dexter energy transfer sharply decreases while the distance between D and A increase and the distance is generally smaller than 10 angstroms.

•The Dexter mechanism can be applied to produce the triplet state of some molecules of interest.

•The special case of exchange-triplet-triplet annihilation-can "push" the electron to upper singlet states by exchanging the electrons of two triplet molecules.

Different types of batteries

Small scale batteries are concerned with energy density, while flow batteries are concerned with energy on a larger scale

Calculating Theoretical Capacity