While there was a comment saying this might be off-topic if the poster is using a machine translator and asking for clarification, the English text doesn't look like something that came out of a machine translator. So I will go ahead and answer.
まぁ、そんなものですかな？
"まぁ" has a feeling of hesitation, possible when something is thinking about something, and can be often translated as "well".
"もの" has multiple meanings, primarily to refer to a physical object, but sometimes referring to an abstract thing in a (for lack of a better term) "emotional" sense. "そんなもの" (often そんなもん") is an expression that fits more with the second definition, though the first also applies here too since the contexts talking about physical things. In both cases "something" often fits as a translation.
Using the above understanding to make a rough translation we get:
Well, something like that.
The "かな” in the phrase is often used when the speaker is wondering about something, often thinking out loud without giving a direct question to anyone.
However, given the context that we are in the middle of a sentence, especially after listing one possible option, this would probably be better:
(a new energy source)...or something like that.
Here the "well" is not directly translated, but implied by the "..."
To help add the feeling of the ”かな”, you could possibly throw the phrase "I guess" somewhere in the phrase (probably at the beginning).
