Our Five Minute Guide
The solar cell turns light photons into electrons by what is called the “photovoltaic” effect.
The rays of photons in sunlight strike the surface of a silicon semiconductor material setting off free electrons from the materials atoms.
The electricity produced is DC direct current at voltages in multiples of 12v, typically 36v.
The electricity can be stored in batteries or converted directly into 220v AC by inverting and transforming the voltage.
Intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meter.
By the time it reaches the earth surface it is less than 1,000 kw. Factor in the clouds and ambient temperature, considering a UK installation, this is reduced to around 700 watts.
PV solar panels are only 10% to 20% efficient (depending on the type) so that reduces the available power to 150 – 200 watts
This is all per M2.
Shade, dirt and snow will severely reduce or eliminate solar radiation reaching the panel.
Solar PV are typically placed at a fixed angle, directly facing south in UK.
They work at maximum efficiency when the sun’s rays are directly tangential with the panel surface so most of the days in the year they are not working at their maximum efficiency. Sun tracking devises are available to increase the effectiveness of the system but these are expensive.
Considering the UK installations, the intensity of the sun is not the same in all regions, for example Cornwall has an average of 3.16 kWh/m2/day, whereas Norfolk has an average 2.74 kWh/m2/day
Quality of installation plays a big part in the efficiency of the system. Hidden short-cuts like cable sizing, panel to panel shading, inverter efficiency and off-south positioning will reduce the capacity of the system.
Solar power can be used directly from DC for lighting with no complication with feed-in tariffs and no need for an inverter. The downside is new lighting cables have to be installed.
An inverter is needed for AC and restrictions are imposed as this is fed into the grid.
The weak link is the inverter, replacement costs and guarantees should be an inherent part of the price negotiation.
When valuating tenders for a PV installation, consider;
· All-inclusive maintenance, especially the inverter. Include cleaning in maintenance.
· Monitor the output regularly
· Life cycle costing.
· Positioning and the total M2 area covered
Types of PV panel
· Monocrystalline Silicon Solar Cells
· Polycrystalline Silicon Solar Cells
· Thin-Film Solar Cells (TFSC)
The below table is a very brief comparison;
