I'll be impressed if you can collect energy using solar panels and turn that into coal.
But I was thinking about something kind of like a battery.
We already have a technology that can capture and store solar energy; It's called 'trees'. Coal is trees that have held the stored energy for some time.
There are lots of battery technologies out there; None are even CLOSE to being able to provide sufficient storage, at a low enough cost, to make large-scale wind and solar power viable, with the possible exception of pumped-storage hydropower - and there simply are not enough suitable sites for pumped-storage to be significantly increased much beyond the existing capacity.
If you want reliable, carbon neutral, and reasonably priced electricity on a suitable scale for a developed nation, the only good option is nuclear power - and nuclear power is hands-down the best way of making large scale electricity ever devised, by pretty much every single measure you can imagine other than popularity and public perception.
It's cleaner than coal, it's many thousands of times less dangerous than coal; it's more reliable than coal (has a higher capacity factor); It produces many orders of magnitude less toxic waste than coal; It's competitive with coal on price (despite needless and crippling regulatory compliance costs that coal plants don't have to match); It uses fuel that is more abundant than coal; It uses fuel that's far safer to mine than coal; the plants have a longer useful service life, with less or similar maintenance and running costs than coal plants. But despite all this, people are (needlessly) terrified of it.
Meanwhile people tolerate continued use of coal for power on a massive scale; and they just love solar power (unreliable, low capacity factor, massive toxic waste production in manufacturing of panels, short serviceable life, no recycling ability for decommissioned panels) and windmills (unreliable, low capacity factor, massive toxic waste production in manufacturing of magnets for generators, short serviceable life, unsightly, kills birds); Both of these also require either gas power as backup, or massively expensive and polluting storage facilities in addition to the already polluting manufacturing of the generators themselves, or large numbers of new hydroelectic pumped-storage dams to be built flooding huge areas of land, generating greenhouse gasses, and putting millions of lives at needless risk. (see
Banqiao Dam for an example.
If 60-100 deaths from Chernobyl make you think twice, then 116 children and 28 adults at
Aberfan (coal), the 191 dead at
Chongqing in 2003 (gas), and the 171,000 dead and 11 million homeless at Banqiao (hydro) should turn your hair gray - because the thing these accidents have in common (other than a larger death toll than Chernobyl) is that A) Unlike Chernobyl, they are far from being the only examples of fatal accidents for these technologies; B) Unlike Chernobyl, they are not particularly well known; and C) Unlike Chernobyl, nobody even suggests for a second that we should restrict, close down, or even more closely regulate, these deadly industries as a result of their many fatal accidents.
Suggest building a gas power plant, and nobody says 'But what about
Accra?' (7 dead; 132 injured). Suggest building a hydro plant, and nobody says 'But what about
Sayano–Shushenskaya Dam?' (75 dead). Suggest building a coal power plant, and nobody mentions the
eight to ten deaths each year in coal mines in
the USA alone, or the estimated
9 million people per annum killed by air pollution. But hint at keeping a perfectly good nuclear power plant open until the end of its design life, and people say 'But what about Fukushima?' (Death toll zero, 2 minor injuries, second worst accident in the history of the industry).
People are really not very smart. Particularly when doing risk-benefit analysis.