Some questions and answers on solar energy systems.
What is Wp?
Watts Peak. this is the Output at Standard Operating Conditions (STC)all manufacturers use STC which allows you to compare Price Output Size.
STC Isolation=lOOOW/m2 Temp=25c AirMass=1.5 spectrum.
All of which add up to almost perfect conditions, you will see Outputs approaching that at STC Due to manufacturing tolerance, many of the panels will give a higher Output than expected, as all panels are individually tested the rated wattage will be a minimum .
How do they work?
Light is converted directly into D.C. electricity this is a semiconductor process within the silicon cells where the light energy is transferred to electrons where it is available as electricity from this you will see that the output is dependant on the amount of light energy falling on the panel. Temperature has no effect but is negligible in comparison to a difference in light levels.
Why all the different voltages.
Panels are designed to charge a battery of 12 Volts this is the nominal battery voltage, during charging a higher voltage is required to force a charge into the battery. A panel or module will have a Voltage of about 2O Volts with no load this is the open circuit voltage (o/c V) measured with a meter. When the panel is connected to the battery a charging current will flow into the battery causing the panel voltage to drop to the battery voltage of 12 - 14 Volts
What power Can I expect ?
As this depends on the weather, siting of panels and many other variables exact figures are very difficult.
From experience in clear sunny weather an Output peak of about 8O- lOO% of Wp can be expected.
An average of about 5O% over the day can improved upon by moving the panel to track the sun, in fixed installations this of course will be difficult but provision should be made when designing the frame work to be able to change the angle to suit the seasons.
Panels should never be sited horizontal, allow a minimum of 10 degrees to allow an effective cleaning action by rain, if possible connection box or joints to be at the highest point to prevent the ingress of water.
As it is difficult to define light levels without expensive equipment a guide to when panels begin to charge the battery system is that dark & grey clouds remove the direct light that the panels require to give a useful output.
White clouds allow enough direct light to pass through. Overcast days even in winter will usually produce enough to overcome battery self discharge.
Do I need a charge controller?
Only if maximum current into battery exceeds 10% of battery capacity in Amp hours assuming battery is in use.
Why use a diode and fuse?
The diode acts as a one way valve when panel is able to supply power to the battery the diode lets it through.
When panel cannot supply power (at night or in bad weather) the diode prevents any battery discharge back through the panel. Fuses must be fitted to the larger sizes as a safety measure should a fault occur it will blow and isolate the battery from the wiring.
Can equipment be used directly from panels?
Yes panels will run equipment direct, these should be loads such as fans & pumps, not voltage sensitive such as TVs or radios. When using solar power to charge a battery, equipment can be connected and used at the same time as the
battery will stabilise the voltage.
Any maintenance required
Clean using a non abrasive cleaner. In the long term check the sealing especially in marine use and reseal as needed with a silicon sealant.