Hi,
Understand first that 4x42W ie at best about 160W at best, and only when the sun is shining directly on them and you use them optimally from an electrical point of view, is not going to power as much as you might be hoping.
I'd quite like to build a sun porch with them if I had the space, so they get good sun and I get nice shade. It's all the rage with architects these days I think.
Maybe you should think of a simple MPPT controller (to get the best out of your high-voltage panels) into a 12V battery bank and wire up some 12V LEDs to work by instead of your normal grid-powered lighting: that way you can use your solar power instead of grid when you have it (and save a few pennies) and it's not a disaster when you run out because you can just use your normal lights again.
In my home-office I work by either a 3W LED or a 9W LED or both when really pushing the boat out! It's been fine for a couple of years or so now. B^>
I understand that funds are a problem: maybe others here can advise how it might be possible to get a 'cheap' MPPT for ~160W.
If you are prepared to be a human controller then you can parallel up all the panels for maximum current and minimum voltage to waste as little as possible, and carefully connect/disconnect the solar manually directly to the batteries watching to avoid over/under charging the batteries. Obviously the voltages are high enough to be lethal so treat as if grid I guess. You might also want to run (say) a 24V system if you can get cheap batteries to get twice as much of the useful power out of the manual system, and still buy relatively cheap accessories such as lighting from an auto/truck store, but without an MPPT/step-down tracker you'll still be throwing most of it away.
Rgds
Damon