Front End and User Experience: Customer acquisition costs in the U.S. for distributed solar is extremely high. Think of cleantech sales like the insurance industry 20 years ago. Most of the sales are human-to-human, and take a lot of time and legwork. We need to follow the path of the insurance industry, and start automating the initial quote and feasibility analysis. A consumer interested in solar or batteries or thermostats or whatever, should be able to get a savings quote instantly and buy the product online without having to talk to anyone. It's a complex problem (you have to combine energy pricing data inputs, easy user experience, complex data science, and dynamic pricing calculations), but the insurance industry has solved it, so we should, too. Whenever you go to Home Depot, you should be able to get a free energy audit with recommendations for what energy products would save you what. Software like this is how you scale energy efficiency and distributed energy resources.
Data Science and High Scalability: Intermittent power from solar and wind will become a huge chunk of the grid's power. What happens when the sun doesn't shine or the wind doesn't blow? How do we keep the lights on? Storage? Demand response? It's going to be an extremely complex operation that will require much more complex software to be able to optimize deploying storage and demand response. If you want to do software in machine learning and NP optimization, grid operations is a place that needs it yesterday.
IoT and Security: All of the new distributed energy resources (solar, storage, demand response, HVAC) are internet connected. The firmware and cloud software that run these resources are now a critical part of grid operations. If there's anything we've learned on HN, IoT software is complete shit when it comes to security. Beefing up the software security of all these resources is critical to keeping the lights on. That's all software and efficient protocols.
The next Google will be an energy company.
Edit: Shameless plug. If you're in the bay area and interested in getting involved in the cleantech software sector, check out the Powerhouse solar startup incubator (https://powerhouse.solar/) and my energy events calendar (https://bayareaenergyevents.com/). Just start showing up!