Not being an expert in physics there are a few base concepts you should take under account before asking this question.
a) What gravity really is - you need to ask this question before you can really move forward and start asking other questions (like questions you asked). And what the gravity really is? Well, this is what nowadays physics is trying to find out - we do not yet know. This is connected a bit with an attempt to come up with "theory of everything" - a supreme set of laws that connect everythig with everything else (i.e. electromagnetism with gravity) - such theory does not exist (yet?) and therefore phenomenons like gravity, or light for that matter, are not yet bound by definite set of theorems (of course we all heard about black holes that can lock light within event horizon).
b) What energy is - again a concept of energy is present in physics and I'm sure you was learning about it in your primary school physics course; in short energy is a way to represent a potential to do work - right? In such way we already know what kind of energy can you harness gravity to store a potential to do work for you - i.e. you can bring huge mass somewhere high enough so you can drop it, when object hits the ground you can transform that original work you have done into different kinds of energy - i.e. energy of impact (maybe to destroy an object, or to have another object lifted?) or heat (which is actually energy loss);
I can imagine when you say "energy" you really think "electricity" and as such I have not heard people being able to use a space attribute which (according to my current knowledge) gravity is to transform potential energy you can store with it to electricity.
So - is your question possible to answer? In my humble opinion, with current state of knowledge, not to your satisfaction.
a) What gravity really is - you need to ask this question before you can really move forward and start asking other questions (like questions you asked). And what the gravity really is? Well, this is what nowadays physics is trying to find out - we do not yet know. This is connected a bit with an attempt to come up with "theory of everything" - a supreme set of laws that connect everythig with everything else (i.e. electromagnetism with gravity) - such theory does not exist (yet?) and therefore phenomenons like gravity, or light for that matter, are not yet bound by definite set of theorems (of course we all heard about black holes that can lock light within event horizon).
b) What energy is - again a concept of energy is present in physics and I'm sure you was learning about it in your primary school physics course; in short energy is a way to represent a potential to do work - right? In such way we already know what kind of energy can you harness gravity to store a potential to do work for you - i.e. you can bring huge mass somewhere high enough so you can drop it, when object hits the ground you can transform that original work you have done into different kinds of energy - i.e. energy of impact (maybe to destroy an object, or to have another object lifted?) or heat (which is actually energy loss); I can imagine when you say "energy" you really think "electricity" and as such I have not heard people being able to use a space attribute which (according to my current knowledge) gravity is to transform potential energy you can store with it to electricity.
So - is your question possible to answer? In my humble opinion, with current state of knowledge, not to your satisfaction.