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101 renewable - site assessment and survey tools

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Last Updated
1st of October, 2018

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Assessment Survey

Implementing and integrating PV Solar systems on a roof, poll or any other available structure must be carried through a set of procedures in order to determine if that site is suitable for a PV power plant power.

The first step for a well-dimensioned system is a proper site assessment. In performing a site assessment we have to consider microclimate variables in order to evaluate the system layout and the amount of energy we will be able to harvest. Shading analyze is the most important data acquisition procedure for our project. Typically, designers strive for placing systems in a wide-open, shade-free place, oriented in the time window from 9 a.m. to 3 p.m. towards the geographical south (for the case we are located in the northern hemisphere). Things are becoming more complicated when different obstructive elements are part of the layout. To do a shading site analyze we offer a couple of solutions where shadings and solar irradiance is mapped for a year long using software, GPS, and digital cameras. Besides shading assessment, power load estimates it is next to be performed in order to find out if the critical load can be covered by our PV power plant. In conclusion, our site assessment will be conducted based on shading analyze, wind factor measuring, critical load estimate, site layout and dimensional elevation (angle, pitch and distance measurement). Additional we will take in consideration in our design an array of indirect factors from recorded maps and climatic statistics with regard to that specific geographical microclimate. The indirect factors are those who debate the optimal values adjusting them towards the real working condition.

To determine maximum energy output for a PV power generation system, we should proceed with exact calculations. The energy output it is influenced by different factors and local climatic conditions; solar irradiation which is  different with each season, local cloudiness or fogginess, an average gradient of temperature and so on.

Shading losses of photovoltaic systems can not be avoided, but at least portion of them can be minimized.  To minimize shading at the string level, PV modules should be always mounted horizontally and never vertically. The reason is quite simple: each crystalline module usually includes two bypass diodes which are active if shading occurs. When modules are mounted horizontally the module still operates with some amount of power (50% or less) if the bottom row is shaded, because only one bypass diode is active. But if modules are mounted vertically and if the lower row is partially or completely shaded  both bypass diodes are active and the amount of power output  is close to zero.

In situations where shading can not be avoided the use of polycrystalline (amorphous), modules should be considered. Polycrystalline modules are far less sensitive on partial shading, comparing to Monocrystalline modules. Even in the case of partial shading, they produce a significant amount of power.

shaddingmppt.gif

Using shading analyzer tools it will allow us to estimate the amount of energy generated at a different period of times during a year time interval. Same tools will allow us to foresee modifications  in energy  production based on presumptive interference with different external factors: adjacent  building extensions, demolitions , tree growing etc.

What are the effects of shading over the solar panels and what will be the PV panels output all it depends on of different external factors:
>_ The degree of shading.
>_ Spatial distribution of the solar panels.
>_A number of panels influenced by shading (during the daylight sun revolution).
>_ Bypass diodes at the cell or/and string level.
>_ Power maximizer at PV panel level.
>_ Type of the interconnection between PV panels.
>_ Type of Inverter used.

Once the shading occurs the I-V characteristic curve of that array or string will start to shift and that will alter the M.P.P.T. range of values (M.P.P.T hysteresis) which will follow the sun- shaded area of the solar array. That translates into a reduction of the inverter power output.


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