Solar power supply for load requiring high starting current

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing shows a solar power source 10 according to the present invention connected to a domestic hot water system 12.
Hot water system 12 is of conventional design having a solar collector 14 and a storage tank 16.
Cold water is circulated from the bottom of storage tank 16 through inflow pipe 18 to collector 14 and hot water is returned through outflow pipe 20 to the top of storage tank 16.
This circulation is produced by a pump 22 connected to a drive motor 24.
It will be understood that while a domestic hot water system 12 is shown, the solar power source 10 of the present invention could be used to produce energy for any system having a load which requires a high initial current.
Motor 24 is preferrably a D.
C.
motor which can be operated directly by current from a photovoltaic panel 26.
As is conventional with all D.
C.
motors, the current required to initially start the motor is substantially greater than the current required to keep the motor running.
This is due to the fact that the voltage across the motor terminals is a function of the input voltage minus the voltage produced by the motor back e.
m.
f.
When the motor is idle, there is no back e.
m.
f.
generated and the voltage seen by the motor is relatively high, thus a relatively large amount of current is drawn.
Once the motor begins running, the back e.
m.
f.
increases and the amount of current required is reduced.
Photovoltaic array 22 comprises a plurality of photovoltaic cells connected in series.
Each cell can be a silicon-type photovoltaic cell such as an Arco M-81.
Silicon photovoltaic cells have an open circuit voltage of approximately 0.
8 volts and an optimum operating voltage of 0.
42 volts.
As is well known, the operating voltage of a photovoltaic cell is a function of the current produced by the cell.
Such cells have a high internal resistance and the voltage increases from a minimum to the optimum level as the amount of insolation, and, therefore, the amount of current produced increases