I'm surprised no one has asked this, but why don't you just go and work for a startup (or small company)? You mention that you are well positioned for a role where you have many different responsibilities.
Another option is that you can start your own (you mention this too). It doesn't have to be solo. From the experience you describe, it seems like you could partner with a technical cofounder and really compliment their skills. There's a lot to gain from experience like that and it can open the door to a lot of opportunities in the future that you don't know about right now.
You haven't made a mistake. You can provide a lot of value to an organization. You just have to find the right opportunity where you can do so.
We are going to need more than just those 3 solutions they mentioned. One of them is demand side management systems, as you mention. These behind the meter (BTM) solutions are going to vary a lot in the scope they address.
You mention using EVs. This will happen in the future, but it is still a ways a way for a few reasons. The primary reasons are because EV adoption is still rather low (adoption is increasing fast and penetration varies by region), and because there is often little monetary incentive, largely because tariffs (electricity rates utilities charge) are not sophisticated. For more sophisticated (and effective) rates to incentivize actions like what you mention, we are going to need more intelligent systems in front of the meter (the transmission and distribution systems that utilities control), and those are often enabled by smart meters (AMI).
For demand side management, think beyond physical batteries. Think virtual. Buildings can act as virtual batteries as they can vary consumption (which is largely enabled by thermal inertia). A lot can be said about energy right now, so I'm not trying to be long-winded...
Also, we're on it! At yize nrg[1], we are lowering HVAC energy costs for large buildings using intelligent agents. We save money by lowering consumption and by doing so at advantageous times, like when prices are higher (based on LMP or tariff). This is demand side management, and we can also offer demand response services back to the utility.
[1]: http://www.yizenrg.com
Another option is that you can start your own (you mention this too). It doesn't have to be solo. From the experience you describe, it seems like you could partner with a technical cofounder and really compliment their skills. There's a lot to gain from experience like that and it can open the door to a lot of opportunities in the future that you don't know about right now.
You haven't made a mistake. You can provide a lot of value to an organization. You just have to find the right opportunity where you can do so.