With prices for oil and gas plummeting, solar will not be as competitive and the demand for solar engineering specialists may plummet. Home solar cells are basically a commodity product, Chinese plants are putting these out at the same rate as flat screen TVs, not much room for fancy engineering in the US.
A degree in ME or EE is always in demand, for projects big and small.
Batteries for home use, hot water flow style heaters for heating pools or hot water or providing heating, passive solar … it’s all been around for a while, but becomes more popular as prices drop and energy prices rise.
The exciting work was really in the large scale plants that used technology like this, but the massive scandal slowed government investment in these technologies (but R&D is not a national priority now anyway).
http://www.solarreserve.com/en/technology/molten-salt-energy-storage
https://en.wikipedia.org/wiki/Solar_power_plants_in_the_Mojave_Desert
It’s the internet, start with google and wikipedia and move to more specific sites of interest. The odds of someone spending a lot of time to write “unreliable” technical info is pretty low, but some data is out of date, like the price of energy or current job markets.
You can also look for some good courses or papers on the financial aspects of solar and other renewable energy. Germany has been investing heavily in renewable energy to replace their nuclear plants … they may be at the forefront of the industry, but it’s easy to find interesting things to read.