Solar Array
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Solar array

 

The output of a solar array depends on the type of panels used, the amount of sunshine, temperature, orientation and atmospheric conditions. As a guide, a 1kW [1000W] solar array installed in an unobstructed sunny position in Cairns will produce an average daily output as follows:

· polycrystalline solar array 4.0kWh/day
· monocrystalline solar array 4.2kWh/day
· amorphous solar array 4.9kWh/day

Not all the electricity produced by the array is available to the grid, as there are small cabling losses and also losses in the inverter. The figures quoted include an allowance of 10% to cover these losses.
An array is sized according to the amount of electricity required, subject to constraints such as budget and available roof space. There may also be some technical and administrative constraints applicable and these are mentioned below.

The array comprises a number of interconnected and usually identical solar panels. The panels typically have a nameplate rating of between 64W and 160W and have a nominal voltage of either 12V or 24V. The operating voltage of each panel is determined by the inverter, which continuously adjusts the voltage of the array so as to yield maximum output.
The peak power voltage depends on the intensity of the sunlight and also on temperature. For a nominal 12V panel it typically lies between 15V and 17V, for a nominal 24V panel the values are 30V to 34V.

The solar panels are connected together in series to form one or more strings. The voltage of each string is the sum of its individual panel voltages. The number of panels in each string is chosen so that the peak power voltage of the entire string suits the inverter. This value is usually between 85V and 180V.
Some solar panels designated specifically for grid-connect applications have much higher peak power voltages, being about 70V. They offer an advantage of requiring fewer panels per string, but in other respects have similar properties to nominal 12V or 24V panels

Mounting and Orientation


The solar array needs to be securely installed, able to withstand wind and other loads and as far as possible face the sun. The three methods described here are roof frames, solar roof tiles and ground frames.
The most common method is to mount the solar panels on frames attached to the roof of a building. If the roof faces north, the panels can lie almost flat on the roof. In fact, the panels are raised a few centimetres off the roof to allow ventilation and not obstruct the flow of water.

A more common method is to provide the frame with legs so that the array is mounted at an angle to the roof. This is particularly effective on a gently sloping south facing roof as it allows winter sun to be reflected off the roof onto the panels in addition to direct radiation. As far as possible north or south facing roofs are chosen, this being consistent with the design principle of aligning dwellings so that the long side of the building runs east-west.

Solar tiles allow the array to become part of the roof, being fixed directly to battens in place of conventional tiles. Monocrystalline 75W and 85W solar tiles are commercially available for this purpose.
Ground mounted frames are used where the roof is too steep, shaded or otherwise unsuitable. Ground mounted arrays have the disadvantage of being more expensive than roof frames and taking up garden space. Any ground frame needs to be certified by a qualified engineer.

Usually solar arrays are mounted in a fixed position and are not adjusted to allow for the daily or seasonal movement of the sun. This is especially so for roof mounted arrays. Nevertheless tracking systems are available, however this topic lies outside the scope of these notes.

For grid connected solar systems, the array is oriented so as to maximise the expected average yearly output. For Cairns and the Tablelands the optimum orientation is facing north, tilted at an angle of between 14 deg. and 17 deg. from horizontal. This is different from arrays for stand- alone systems where the tilt is about 30 deg. in order to improve winter performance.

Electrical Installation


A solar array is a generator of electricity that can produce a potentially lethal voltage and which cannot be readily switched off. The electrical protection and fire safety issues involved have motivated the development of a comprehensive Australian standard for solar arrays. A draft of this document is currently being circulated within the industry and stakeholder organizations for comment. It is likely to be promulgated as a standard in 2004.
Whilst at this stage the cost of compliance is not clear, for grid-connected arrays it is likely to be significant.

Shading


Shading of solar panels, for example that from tree branches, accumulated dust on panel surfaces or ash deposited from bushfires will reduce output. For amorphous panels the reduction in output is in proportion to the amount of shading. However for monocrystalline and polycrystalline the reduction is much greater.
Solar panels should be cleaned periodically with a damp cloth. This is especially so after bushfires or after lengthy periods without rain.

 

 

Solar System mounted on rooftop
with Solar array frames


Solar Batteries

Solar panels gather solar energy
and it is stored in a deep cycle solar battery bank

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



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Planetary Power - Renewable Energy Solutions
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