VRICONIAN

Solar photovoltaic (PV) Generation

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Introduction

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Photovoltaic (PV in short) panels capture energy from sunlight which, in creating a voltage between two poles, can flow as an electrical current (DC), which can be used to power devices.

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Solar PV panels don't require to be in direct, or even bright, sunlight in order to provide power, which means that they can still work even in cloudy conditions, albeit at levels which are proportionate to the level of light available - for example, in dull conditions a panel may be generating 20% of it's nameplate (rated) capacity.

Cells, Panels & Arrays

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Although other technologies exist, the vast majority of solar PV panels are constructed from a number of individual crystalline silicon cells which are mounted behind a sheet of glass and electrically connected in both series & parallel in order to achieve a given power rating in prescribed test conditions.

The majority of panels which are currently available for domestic or commercial systems are rated to generate in a range between 200W and 330W, the difference being due to cell technology, conversion efficiencies, physical cell size and the number of cells being used to make a particular panel, the dimensions of which still tend to vary widely between manufacturers.     

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Small groups of PV panels can be electrically connected in series and/or parallel as necessary to form an array in order to provide appropriate higher voltages or DC current which can either be used in DC form, for example to charge off-grid batteries, or through using an  inverter to convert the current to AC, providing power to small electrical items.

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Batteries or Grid-Connectivity - or both?

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In order to provide sufficient power for high draw domestic appliances, such as a kettle or washing machine, a solar PV system would really need to be rated to generate somewhere around 4kW, which would require a system based on an array containing something along the lines of 16 x 250W panels, however, such a system could only be used on continuously sunny days with the panels in direct sunlight. To provide stable and continuous AC power to appliances, solar PV needs to work in conjunction with either a battery system (off-grid) or near-seamless integration with the national grid (on-grid), effectively using the battery or grid connection to balance supply to demand during the day as cloud conditions vary, as well as providing power when there's no sunlight available.

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Recent developments in battery & control technologies are starting to provide the option to integrate storage into both existing and new grid connected domestic-scale installations in order to increase the level of self-consumption and help smooth grid demand in peak conditions. The cost of domestic scale battery solutions for grid-connected systems currently (06/2017) makes little financial sense unless there are additional factors to be taken into consideration, for example, high availability requirements or exceptionally unreliable local grid supply. 

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Very large storage systems are also currently being used or trialled as grid balancing solutions, especially so in conjunction with intermittent generation sources such as solar PV farms which would include many individual arrays and thousands of individual panels.

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