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.

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Calculators courtesy of Chuck Wright at Chuck Wright Consulting, LLC     Visit him at  http://cwc-das.com