The Lowdown on Standalone P.V. Solar Systems

by Geoff PPC Solar 08/08/2013

 

Standalone photovoltaic (P.V.) systems are very common.  Until the last decade, when Grid-Tie Systems have become very popular, Stand-Alone was the predominant type of photovoltaic system.  There are two principle system designs:  P.V. Direct & Storage Battery… more

P.V. Direct

P.V. Direct Systems are systems without connection to the grid or to storage batteries.  These systems consist of one or more solar module, a disconnect, over-current protection, and electrical devices.

A common example of this is a solar water pumping system:   a solar module powers a pump, the pump pumps water into a cistern, and then a float switch disconnects the panel from the pump when the cistern is full.  A system like this could be as simple or complex as you wanted it to be.  You could have your float switch divert the water being pumped to an irrigation system and simultaneously turn it on, rather than just disconnecting power when the cistern is full.

Another example of a P.V. Direct System:  a solar module powers greenhouse fans when the sun rises and turns off fans when the sun goes down.  Because greenhouses get hot during the day and solar panels produce power during the day this works out perfectly.  Of course this can get more complicated too.  You could interrupt the circuit with a thermostat so that the fans only turn on when the greenhouse reaches a certain temperature during daylight hours.  This would keep the fans from operating on mornings when it was cool out (a distinct possibility at high altitudes and desert regions).  You could also use a timer to interrupt the circuit to coordinate the fans operation with other equipment such as Co2 enrichment equipment.

Storage Battery

Storage Battery systems are systems with no connection to the grid that utilize storage batteries to store power during the day when the solar modules are producing electricity.  This stored power is then used at night when the solar modules are not producing.  This is what most people think of when they hear the term “off-grid solar”.

Residential properties are the most common example of this.  A person may have solar modules mounted on their home or in their yard.  These panels send Direct Current power to a charge controller, the charge controller steps down the voltage and steps up the amperage, the power then goes to a DC bus and then to storage batteries.  From the storage batteries the inverter turns the DC power into alternating current (which is the type of power that most household devices use).  Of course these systems have proper grounding and over-current protection.

A common example of a commercial Storage Battery System application is a remote radio transmitting site.  This system would be very similar to the system above except that it may have a much larger solar array, battery bank, and may use several charge controllers.  Some remote transmitting systems do not need an inverter, as most radio equipment can be run off of direct current.  This application was one of the first ways that solar modules were used.  Bell labs used solar this way in the 1950’s, although back then solar cells were only 6 % efficient.

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