Photovoltaic or PV panels utilise photovoltaic effect, i.e. generates electricity from sun radiation. The sunlight is an electromagnetic wave with multiple wavelength (IR,1500nm to UV,200 nm), what can release electrons (by absorption) in the silicone crystal. The electricity if a flow of free electrons in the crystal.

The efficiency of the solar cell is the capability to release electrons: the generated energy power over the energy of exposed sunlight.

The production method of monocrystalline solar cell is to grow the silicon into bar (ignot) then sliced into wafers, so one-cell is made of single crystal silicon.In general, monocrystalline silicon has higher efficiency, since the electrons has larger space to movefreely (generate electricity)in the single-crystal structure.

Monocrystalline panels have black hue.

Case of polycrystalline solar cell, the manufacturers combine (melt) silicon crystals to create fragmentedsilicone crystal structure. Because of fragmented crystal structure, the electrons have less free space to move, thus the polycrystalline cell has lower efficiency.

Melting of existing silicone crystals requiresless energy than create single-crystal structure, thus the manufacturing price of polycrystalline solar cell is lower than monocrystalline.

Polycrystalline solar cells have blue hue.

In general, monocrystalline PV cell has a higher efficiency than polycrystalline PV cell, but the later can be less expensive.

MonocrystallinePV module has advantage in case of space constrained PV installation, such as commercial and residential rooftop installations.

Polycrystalline PV module could have financial advantage if financial issues has priority over available space for installation.

PERC is an emerging technology against standard solar cell manufacturing technology. The PERC stands for Passivated Emitter and Rear Cell or Passivated Emitter and Rear Contact, i.e. achieves higher energy conversion efficiency by adding additional layer to the back of the cell. The additive passivation layer reflects the unabsorbed sunlight back to the silicon layer to release electron.

The advantage of the PERC technology:

1. reduced electron recombination, what is blocks the free flow of electrons.
2. increased ability to capture sunlight, by a reflective back layer
3. reflection of specific wavelength of sunray, what normally causes heat (absorption of energy without electron release) in the silicone crystal

Current efficiency of competing, but not yet commercialized PV cell technologies in 2020Q1:

• Crystalline Silicone cells,Single crystal (non-concentrator version, by ISFH): 26.1%,
• Single junction gallium arsenide cells (single crystal version, by LG): 27.8%
• Multijunction cells, Three-junction cells(non-concentrator version, by Sharp-IMM): 37.9%
• Thin films, CIGS (Copper Indium Gallium Selenide)cells (non-concentrator version, by SolarFrontier): 23.4%

Please note, that commercializes, high volume product may have lowerefficiency.

Crystalline Si cells-based PV modules represents the mainstream (90%) of PV installations, but other technologies have specific market share as well. The above-mentioned technologies are use different materials to convert sunlight into electrical energy, with different efficiency around 10-20%. Beside the efficiency, other properties can play important factor in case of PV installations, such as installation cost in USD/Wp (currency over peak power), and space constrains, Wp/m2 (installed peak power over installation area or surface).

Thin film CdTe (Cadmium Telluride) technology has the smallest energy need or CO2 footprint. Monocrystalline Si cells has the highest efficiency, but the most expensive technology available on the market. The advantage of thinfilm technology is the structural flexibility, it can deployonto variety of surfaces. The major application area of thin film technology is building photovoltaic, where PV modules are an integral part of the building structure, such as glazing or any other non-flat surface.

One key specification of PV solar module is the generated peak power in Watts. The peak power can be achieved under certain operational and environmental conditions, what are standardised in order to create comparable technical specification of PV panels.

The standardised operating conditions (called STC, Standard Test Conditions) are:1000 W/m², very bright sunny day, with clear sky; PV cell temperature is 25°C, moderate PV module temperature; and AM 1.5, what is a simplified model of the atmosphere (global energy distribution versus sunray wavelength).

Beside the sun radiation intensity, the PV cell temperature affects the peak power: if the cell temperature rises, then the energy conversion efficiency reduces.The value of this degradation is around -0.35 %/°C, if the cell temperature is 45°C (+20°C than SOT) then the nominal efficiency 20.0% 25°C drops to 13%@45°C!

If the generated electrical energy is originated from renewable energy system, such as PV, and the generation power (AC side at grid connection point)is between 50 kW and 500 kW (0.5MW), then it is promoted through feed in tariff. The eligibility period and the maximum amount of eligible electricity are determined for each eligible electricity producer by the Hungarian Energy and Public Utility Regulatory Authority (HEA).

Please note, there is multiple translation of the same RES support scheme: the “KÁT” system often translated as “feed in tariff” (to represent the support scheme) or “Obligatory Off-take” what is a mirror translation of the Hungarian expression, “Kötelező Átvételi Tarifa”.

The KÁT system is a RES support scheme of the Hungarian Government. KÁT stand for Obligatory Off-take, what is a part of National Renewable Energy Action Plan.

The regulations for the feed-in tariff set out in Decree No. 389/2007 apply to renewable energy installations already approved eligible for the feed-in tariff before 31 December 2016.The feed-in tariffs are fixed and adjusted every year with the consumer price index or inflation minus one percentage point, depending on the application date.

Installations up to 0.5 MW are either eligible for the feed-in tariff or the green premium (market premium). The green premium (like METÁR support scheme) is obligatory for plants with a capacity of 0.5-1 MW.

Hungarian Parliament accepted new renewable support scheme in 2016 Q2, called “METAR”, “MEgújuló TÁmogatási Rendszer”,”REnewable Support Scheme”. The new support scheme is effective from 1^st of January 2017.The key feature is that the energy generated from renewable source, in kWh unit, receive the aid as a paid premium over the market reference price.

Renewable energy power stations can be classified into the following three categories:

1. under 0.5 MWp and demonstration plants can remain under the KÁT support scheme,
2. power plants, over 1 MWp, can register for premium support scheme, with a tender procedure. The annual quantities to be supported will be announced regularly (by HEA) and it is likely that the quantities will be distributed by technologies (eg. wind, photovoltaic).
3. between 0.5 MWp and 1 MWp renewable energy utilisation power plants, are not obligated to participate to tender procedure, they are able to receive administrative premium over the market price.

PV installations can be classified into different application area:

1. Off-grid systems to provide electricity, where grid connection is not available (due to cost or otherphysicallimitations). For example: remote rural areas, mountain areas, remote islands, cultural heritage site, where any construction is prohibited. The primary use of electricity to maintain or improve quality of life to supply household appliances; provide support for agricultural or local industrial activity, such as irrigation.
2. On grid system, residential area, where the primary objective is to lower energy usage from grid. Local energy storage feature can be added in order to improve electricity supply stability. The PV system can be 100 to 400V AC or 12-48 V DC, in the range of 1 kW to 50 kWp DC (peak power on the DC side). The PV system is connected to the residential level of the grid, wat is 240V AC, one phase or 400 V (0.4kV) 3 phase system. Different technical requirements may be applied, set to the local utility company.
3. On grid commercial and industrial installation, where the primary aim is to support the electrical energy consumption of the given commercial building or manufacturing facility. The connection level to the grid is 3 phase, 0.4 kV, in the order of 50 kW to 10 MWp DC side. The physical installation can be done on the roof or separated land area.

On grid system for utility level, where the primary aim to generate electricity to sell to other consumers on the grid. The PV modules are organised (connected in series) to 1000V or 1500V groups (called string) and connected to inverters (DC to AC converters) to generate AC power at 3 phase 0.4kV level. Transformers can be used to convert 0.4kV AC level to higher, MV of HV level (MV: medium voltage level, less than 35 kV; HV: high voltage level, above 35 kV).