Although, the use of کاشت may be irregular in Urdu in context of energy, but it is an equivalent expression as "harvest" and gives more information about the process of collecting and using ambient energy.

The answer is based on the Wikipedia explanation as follows:
(http://en.wikipedia.org/wiki/Energy_harvesting)
Energy harvesting/scavenging, is when external energy is captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks.
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The same page also refers to "external energy" as "ambient energy", i.e. energy present around us in the environment such as solar, thermal, wind etc.
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The definition also mentions that this energy is used for smaller wireless electronics. Unless this is present in the context, it may have to be included in translation. E.g:

چھوٹے لاسلکی/ریڈیائی برقی آلات کے لیے ماحولیاتی توانائی کا استعمال (کی کاشت)۔

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Note added at 16 hrs (2011-07-17 17:18:23 GMT)
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Another suggestion based on fahmed's suggestion below:
ماحولیاتی توانائی کا حصول، ذخیرہ اور استعمال
Or the detailed version:
چھوٹے لاسلکی برقی آلات کیلئے ماحولیاتی توانائی کے حصول اور ذخیرہ کرنے کا طریقہ