What happened

Pity Plug Power (PLUG 4.78%) investors. They're getting diluted -- again.

Last night after close of trading, the fuel cells-for-forklifts company announced that it will sell anywhere from 40 million to 46 million newly issued shares of stock in a secondary public offering. No offer price was stated, but investors are getting a chance to suggest a price today: $3.40 per share.

And as of 10:30 a.m. EST, Plug Power shares are trading down 10.8% from where they closed yesterday.

Glowing red stock arrow trending downward.

Image source: Getty Images.

So what

This is par for the course for Plug, which hasn't earned a full-year profit -- ever -- in its lifetime as a public company. Despite sales that have risen rapidly in recent quarters, Plug Power has been more dependent upon selling shares than on selling fuel cells to keep its business afloat. Indeed, over the past decade, Plug's share count has grown more than 18 times in size, from 12.9 million shares at the end of 2009 to 245.8 million shares at the end of last quarter.

Now what

And now Plug's share count is growing again. Yesterday's share sale announcement means that once accomplished, this floatation of new shares will grow the share count by approximately 16%. Thus, while the offering will raise additional cash to sustain Plug's operations, it will shrink the ownership stake of existing shareholders by about 16% as well.

If Plug Power shareholders are upset by this today, can you really blame them?