No moving parts, everything is solid state, and if one has an on-grid system, there are no batteries to have to keep watered or replaced.
Out on the bleeding edge, you can already build electrical storage that is maintenance-free, and does not require grid connection. I built a pilot installation for my radio trailer - I'm a ham operator - where the storage is entirely ultracap based. I've got enough out there to provide about as much power as two 110 AH car batteries, which is more than enough to run the three LED lights in the trailer and my 265 watt consume / 100 watt output (on transmit only, it's about 10 watts consumption on receive) radio. I mostly listen, so that's an excellent consumption to supply ratio.
One of the thing that many people don't appreciate about standard solar panels is that they produce energy on cloudy days, albeit a reduced amount; my system never, ever goes down, because there is sufficient capacity to keep it up as compared to the amount of use it gets.
In the future, I expect the cost of ultracaps to come down considerably, and if that happens, the whole battery issue will go right out the window. Ultracaps have very long lifetimes, just as solar panels do. They're not nearly as toxic, either.
For now, I freely admit up front that the cost to do this was not something that is practical for a large installation, such as that which would be required to run a home with a typical 10 KW electrical service. You'd need a lot of panels and a lot of ultracaps (ultracaps are presently at about 10%-20% of energy storage as compared to a comparable size / weight bank of batteries.) However, that 10 KW service is almost always that large to deal with surge demands, rather than constant demand, and that means that you'd need fewer panels overall. The ultracaps are actually far better at delivering surge power than either the grid or batteries, so that cost is only about what you use on average, not peak usage. The converter (ultracaps have a very different discharge curve than batteries do, and require dedicated electronics to produce a steady output comparable to batteries), however, still has to handle the peaks.