[Elecraft] Re: Solar Panels (Douglas Todd

[G3VVT at aol.com]

From: "charles allison" charles at atcweb.com who wrote:

"These are needed because the open circuit
voltage could be 20 VDC  for a 12.6 volt panel without the regulator."
 
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This is not really correct as this open circuit voltage will fall to the  
normal charging voltage for the battery(s) depending on their charge state as  
soon as these are connected, with or without a charge regulator.
 
Otherwise the reply to the original question is excellent.
 
Charge regulators are definitely needed when the capacity of the solar  
panel(s) exceed the current drain of the equipment connected and the  battery 
charging current requirement. The result of failing to have charge  regulation 
under these circumstances is that permanent damage to the battery(s)  can occur 
and also possible damage to the equipment connected due to excess  voltage.
 
Using 5 to 15W solar panels the average amateur would probably never need a  
charge regulator as the panel could struggle to provide anything more than  
replenish the power used in running the equipment. However, the charge regulator 
 could be looked on as an insurance policy to protect the batteries and the  
connected equipment, so if affordable will not be lost.
 
With solar charge regulators what is needed is a type that will  
automatically restore charging when the battery voltage starts to fall  sufficiently, 
though with some hysterisis to prevent the charge regulator going  into 
oscillation.
 
I worked on solar powered communication equipment in the Middle East from  
1981 for over 20 years and a problem was that some types of solar charge  
regulator after disconnecting the solar charge would not come back on charge  again 
until the next day after a night time reset. Not a desirable situation for  a 
24/7 system.
 
There was certainly some junk marketed commercially in the early  days!
 
A lot of our early systems had the compact (3ft x 1ft) USA made Arco 55W  12V 
panels (Exxon) which I rated very highly for dependability. The only things  
that seemed to slow them down were bullets or rocks directed at them, though  
even then they often carried out working to a degree. These are now marketed 
by  the Siemens after Exxon apparently pulled out of the business. Sadly a lot 
of  these early systems were let down by shortcomings of the solar charge 
regulators  apart from the simple shunt regulator type which bypassed excess 
charge  voltage as heat. These however could contribute to problems in site  
cooling.
 
The latter systems worked on before retirement were 15kW 200 panel solar  
arrays to run microwave sites. These used the larger 75W 12V BP solar panels  
which also seem to work well. They were configured into 12 banks of 48V by  
paralleling them in series banks of 4 to provide the nominal comms -48V supply.  
Everything was on a much larger scale in these systems as with a 7500Ah battery  
plant it need to be. The regulation was done by switching banks of panels 
with  large switching contactors to regulate the charge voltage when the float 
charge  period was reached. It was not uncommon to see up to 140A at 54V or 
higher  during the early morning boost charge phase when all 12 banks of the 200 
solar  panels were on line.
 
A point to note with solar panels is that most seem to be rated at 25C  
temperature. The available current falls with increased panel temperature above  
this, as will be seen in the hotter desert regions of the USA. Conversely in  
winter time on cool clear days the available current can rise substantially from 
 the nominal rating. This means that solar power can be a reality in more  
temperate regions due to lower solar panel surface temperatures.
 
All a thing of the past after returning to the UK in 2002 on mandatory  
retirement at 60. No work in UK comms for "wrinklies", so a change of direction  to 
working at the local Walmart store checkout area. At least it provides  food 
for the kitchen table and funds for new radio equipment.
 
Regards,
Bob, G3VVT