gonna be a lot of power cuts in near future when some power stations close down....
http://www.dailymail.co.uk/news/article-2213362/Britain-blackouts-70s-style-blackouts-withing-years-EU-rules-force-bills-warns-Ofgem.html
in my camper the same set up lasts me for a few days if wild camping in a remote place with no mains power,
depends on what you are running and you should always be conservative with energy,save power as much as you can .
no if you look around you can get it for that,prices have come down,i expect they could go back up again soon.
http://www.ebay.co.uk/itm/100W-Monocrystalline-12v-Solar-Panel-full-set-up-racing-pigeon-boat-caravan-/261145389699?pt=UK_Gadgets&hash=item3ccd7a6a83
truth is i ve moved this set up to my campervan,that shed was far too small lol,i could nt have any mates in as there was no room,and yes that pint pot was my faithful companion after the dog.
ah if your on an alotment still a 12 volt bulb and a decent 12v olt battery should be better just swap with another battery and charge up the other at home.
i ve had that one it's not worth bothering with. Just get one of the 12volt energy bulbs like a fluorescent they are very bright and get the biggest size solar panel you can afford with a decent 12 volt battery for a bit extra you ll have a much better set up and can run other stuff too.
this is my shed powered by solar