If you've got the connection to the grid then you'd have to be in a situation where you can store and use the electricity for less than you can sell it to the grid and then buy back later. Given you're generating at peak time (daylight) that just doesn't happen. Add in the costs for the battery, the losses and the maintenance and it quickly makes a significant loss. The only time this form of "electrical arbitage" makes money is with the hydro plant in Wales that gets re-filled at night. You'd be doing it in reverse with solar.
If you're using battery storage for light duty work (as i have already said), then the additional cost of a couple of batteries and an inverter is not that great when you consider the costs of a full-scale PV installation on your roof.If you intend to go completely 'off-grid' with your domestic power arrangements then obviously the additional cost of storage will be eywateringly expensive.
The idea is that you run said light duty items off inverter power supplied from the battery storage all the time and the surplus energy goes into the grid -this is not difficult to do with a charge regulator. Considering the lifespan of a decent set of batteries is approximately the same as the PV panels themselves, the additional cost of the batteries and inverter over the 20-25 year lifespan of the panels becomes less daunting than first appears. Add wind into the equation and you're covered for most eventualities (except for still, cloudy weather which we ofc do get from time to time). The electricity you store is never sold to, or bought back from, the grid; it's only your surplus that is sold to the grid just like with a purely grid-tied system.
I'm not quite sure what you mean by losses here... If you are referring to losses of power in the system as it generates, stores and then inverts the power from DC to AC then tbh losses are a fact of life for any form of power generation -whether it's a 3Kw PV installation on your roof or a multi-megawatt steam turbine generator at the local gas fired power station, losses and inefficiencies are inherent and unavoidable.
As far as maintenance is concerned, if you know what your'e doing, liquid-cell batteries are pretty low-maintenance tbf whereas dry and gel-cell batteries are maintenance-free (trouble with the latter examples is that if you damage them by running them flat, you have no hope of doing any sort of restorative work on them as they are sealed units). Even if you don't know what you are doing with liquid-cell battery maintenance, a short course in the subject ought to bring you up to speed. As far as the rest of the electrical equipment is concerned, maintenance for that would have to be done by whoever you were going to get in to maintain it in the first place -unless ofc you were qualified or capable of doing the job yourself.
If you are referring to a financial loss then, to be frank, renewables don't come cheap and if you are going to make the most of this significant financial outlay, then having the means to store power at home as well as pumping it into the grid makes sense. After all, assuming this upscaling goes apace and a significant proportion of our energy comes from renewables, what would be done if the renewables were generating a surplus? Yes, you can short wind turbines so they don't turn in the wind but, to be flippant a second, you can't attenuate the sun. If you are generating a surplus and it cannot be made use of, then it ought to be stored up.
I suppose what i'm trying to say is that if you are going into this purely as a means of making money and not securing a reliable source of electrical power, then you are going into it with a pretty blinkered viewpoint. They way things cost at the moment, if you can afford a PV installation to your home, then it makes sense to have some form of domestic storage as well -especially when you factor in the predicted outages that may occur over the next couple of decades as the fossil fuel supply sputters and falters due to demand outstripping supply.
E2A: Just realised after looking around on one of those sites you linked above that i am describing a grid fallback system...