Principles of Solar Power Electrical Power Generation notes

Includes:
- Multi-Junction Solar Cells (MJSC)
- Intermediate Band Solar Cells (IBSC)
- Photochemical
- Thermophotovoltics

Single cell (~1 cm $^2$ )
Solar cell → Module → Panel → Array
Several cells with edge length 10 to 21 cm are combined in a solar module, many made up of 33-36 cells
Multiple modules form a panel

Monocrystalline cells
- Largest in the market.
- Expensive to make.
- Efficiency in the range of 26.1%.
Polycrystalline cells
- Cheaper.
- Efficiency is about 22.3%.
Amorphous cells
- Thin film, ~0.3 mm thick sheets of silicon.
- Cheap to make.
- Efficiency ~22.9%.
Mesoscopic solar cells
- Recently made an impact in commercial markets.
Perovskite solar cells
- Currently, the fastest-advancing solar technology (efficiency 25% to 28%).
- Threatening to challenge both DSC, thin film, and polycrystalline silicon ones.
Materials used in photovoltaic devices:
- Silicon
- Gallium arsenide
- Metal chalcogenides
- Organometallics

MJSCs are tandem solar cells with multiple p–n junctions made of different semiconductor materials (not made from silicon).
Each material's p-n junction will produce electric current in response to different wavelengths of light.
Allowing the absorbance of a broader range of wavelengths, which improves the cell's sunlight to electrical energy conversion efficiency.
Also known as III-V semiconducting devices

Offers:
- High reliability
- High power-to-mass ratio
- Excellent radiation hardness
- Small temperature coefficients
- Possibility to operate at high voltage and low current
Despite higher production costs compared to silicon solar cells, III-V MJSCs are integrated into flat-plate modules for space applications.
Higher price-to-performance ratio have limited their use to special roles, notably in aerospace where their high power-to-weight ratio is desirable.
The determining measure for cost in space is (£/kg) rather than (£/ Wp) as in terrestrial application.

Have become the state-of-the-art photovoltaic power generator for satellites and space vehicles.
This exciting and promising technology is emerging in concentrated Photovoltaics (CPV).
Widely used in:
- Space applications
- Terrestrial concentrators
- Niche markets such as power-by-light (laser power converters) or thermophotovoltaics.
High concentration multi-junction solar cells achieve an efficiency of up to 47.1% today.
Today, III–V devices find terrestrial applications only under high concentration.
III–V on silicon may be an attractive path to reduce cost and eventually penetrate this high-performance technology into conventional applications of flat-plate photovoltaics.

Consists of the so-called intermediate band (IB) material sandwiched between two ordinary n- and p-type semiconductors; this acts as selective contacts to the CB and VB
In an IB material, sub-bandgap energy photons are absorbed through transitions from the VB to the IB and from the IB to the CB, which together add up to the current of conventional photons absorbed through the VB–CB transition.
The operation of the intermediate band solar cell (IBSC) relies on the electrical and optical properties of the intermediate band (IB) materials.
An electron–hole pair can be generated in this material by two mechanisms:
- Absorption of one photon in a conventional VB→CB transition (labelled (3)).
- Absorption of two sub-bandgap photons through the IB-mediated transitions labelled (1) and (2).

Multi-junction solar cells MJSC
- Conventional PV cells have a max theoretical efficiency of 33.16%.
- Theoretically, an infinite MJSCs would have a limiting efficiency of 86.8% (under highly concentrated sunlight).
- Currently, lab examples of MJC have demonstrated performance over 46% under concentrated sunlight.
- Efficiency of best lab examples of traditional crystalline silicon PV cells is between 20% - 25%.
- Commercial examples are widely available at 30% under one-sun illumination and improve to around 40% under concentrated sunlight.
- Improved efficiency is gained at the cost of increased complexity and manufacturing price.
Intermediate band solar cells IBSC
- Maximum efficiency of 77.2%.
- Less than that of an MJSCs with infinite junctions.
- In MJSCs, electrons are captured exactly after being excited to a higher energy state, while in an IB device, the electrons still need another energy transition to reach the conduction band and be collected.
- Full development IBSC is not trivial.
- It is expected that once fully mastered, IBSC should be able to operate in tandem in concentrators with very high efficiencies or as thin cells at low cost with efficiencies above the present ones.

Spectral concentrators
Semiconductor nanostructures
Optical coupling structures
Plasmonic structures
Photoelectrochemical
- Dye-Sensitized Cells
Artificial photosynthetic systems use molecular light absorbers to convert sunlight into useful chemical fuels such as hydrogen, methanol, or ammonia.
Organic solar cell
- Utilizes organic electronics for light absorption and charge transport to produce electricity from sunlight by the photovoltaic effect.
Thermophotovoltaics
- An innovative system is able to convert the radiant heat of combustion into electrical energy. This conversion is realized by using photovoltaic cells.
- Do not require direct sunlight to generate electricity and instead can harvest heat from their surroundings in the form of infrared radiation.
- Predicted to be more than twice as efficient as conventional solar cells

Efficiency is constantly improving over the years (this is an indication of the research, not commercial, cell efficiency!).