## PV Cell Basics for HobbyistsPhotovoltaic (PV) cells convert sunlight directly into electricity. They are a convenient source of power for certain hobby projects. Effective use of PV cells requires proper matching of cells to the electrical load. Here is a calculator that will help you estimate the electrical current and voltage that can be supplied by various PV cell configurations. The first part of the spreadsheet deals with characteristics of an individual cell, allowing you to relate the size of the cell to the amount of power it can deliver. Use the "?" buttons to get more information on individual items. Any of the values in the following table can be changed. Everything
is recalculated when you hit the "tab" key or click outside of the box
you changed.
PV cells are sometimes used alone, but more often connected together
to give more capacity. Connecting cells in series (positive of one to
negative of the next) gives higher voltage. Connecting them in parallel
(positive to positive, negative to negative) increases the current capacity.
Filling in the "series" or "parallel" boxes below will allow you to see the
results of connecting multiple cells in series and/or parallel.
Remember that PV cells are not like batteries. Once their current capacity is exceeded, their output voltage drops rapidly (they act as "constant current" sources). If you draw less than this current, the cell supplies a relatively constant voltage. But, there is only one operational point at which the cell is operating at maximum efficiency. This is the boundary between the constant current and constant voltage regions, and is known as the "maximum power point" (MPP). In practical terms, if your cells cannot supply enough current, your project may cease to work. If you size it to supply too much current, your cells will operate inefficiently. An excellent solution to this problem is often to use the PV cell to charge a battery. I have made considerable effort to present correct information. |