That's a terrible essay; it's full of useless generalities, grammatical errors, unsupported claims, and at least one patently wrong statement.
Here are a few ways to improve it:
1. Use humble terms to describe coming events - I'm assuming you can't see into the future so using terms like "...is going to.." and "..it will take..." is pretentious at best. Better to use terms like: may, could, perhaps, it's possible that, etc.
2. Support your claims - It's perfectly OK to suggest nanotechnology may lead to "x" but you should really cite some sources for such predictions. I don't expect you to go digging through science journals, but citing an article in Popular Science magazine or from the BBC's website would greatly increase the worth of anything you write. It will also give you more information to discuss in your paper.
3. Avoid using terms you don't understand - It may tempting to use phrases like "margin of error" but it's best to avoid them if you don't understand how to use them correctly. For instance, you can't have a "margin of error less than zero"; that just doesn't make sense.
4. Don't switch "moods" twice within a sentence - Read the last sentence of your essay aloud. You'll notice it doesn't flow correctly. Instead it makes abrupt changes in style and tone that will just leave any reader frustrated and perhaps even confused. It's OK to discuss positive and negative traits of subject in a single sentence, just don't switch from A to B, then back to A again.
The biggest problem is that your essay lacks substance. You haphazardly spewed out three thoughts in the initial paragraph and just kept regurgitating those thoughts in the following paragraphs. You didn't really add any details to support your claims. The only way to remedy this is by doing more research. Learn how "nanomachines" can/are constructed, how they work, and what functions they perform. I'm sure the reader would love to know how such devices can lead to more efficient solar panels or how they can deliver medicine. If you're going to discuss the costs of the technology, get some real numbers. Exact figures aren't necessary, but "ball-park" estimates are useful. How will the cost of a nanomachine-built solar panel compare to the cost of a conventional panel?
Given that there are so many interesting questions to explore, I'm sure you can write a better, more interesting essay than this.