It is, and has been for quite some time, in some countries.
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It's only effective/efficient if the home's foundation is configured so that the roof is North/South configured. The panels would go on the south most side only. Furthermore, you'd need to clear any close trees to ensure maximal sunlight. Otherwise, there's inadequate return on the investment of panels from a financial perspective. Furthermore, you'd be killing trees... murderer.
In the US, the sun is over the southern sky. Think of the Analemma on a globe. Here's a picture of it as observed in the Northern hemisphere:
http://upload.wikimedia.org/wikipedi...in_the_sky.jpg
I couldn't find out where the picture was taken from... so here's the Analemma from the Royal observatory in Greenwich, England, latitude 51.48 degrees north. For a point of reference, Gillette Stadium in MA is at 42 degrees north.
http://upload.wikimedia.org/wikipedi...emma_Earth.png
I think the justification for Southern-side solar panels is a bit self-explanatory. But as far as east/west configured rooflines go, you're guaranteed that all not panels will be gathering solar energy throughout the entire day (Source: the sun rises in the east, sets in the west, and angles). Therefore you're lowering your effective rate of return on investment of the cash for solar energy derived. Additionally, the angle of the roof in a north-south orientation may not be proper to maximize the benefits!
Lets take a look into the total cost of actually deploying solar panels on your house. But before we do that, lets take a step back for a second because I'm not sure you fully understand how the power grid works.
The power grid has a very consistent voltage and frequency. Too much energy can cause shortages at the consumer level (thus why you have circuit breakers, which break the ties prior to overloading the electronics). Too little energy causes brown/blackouts (racist). Lets also keep in mind... the US runs on alternating current!
You have two options... you can either store energy for yourself (greedy bastard), or put energy back into the grid and make it more of a pain for the power plants to regulate the voltage and frequency of the power grid. Fortunately, Batteries store energy via direct current... Which is great because solar panels generate electricity in DC!
This kinda sucks though, because the entire US runs on AC. So regardless of whether we want to use batteries or not and store our own damn energy, we need to convert it to AC prior to using it anywhere in the house, or throwing it back to the masses in the power grid. So, we get to invest in some additional Inverter hardware that'll convert DC to AC. You know... more money to dish out.
http://static.ddmcdn.com/gif/solar-cells-5a.jpg
In the end, it's not just attaching a solar panel to a house = profit... there's a lot more workings that make it less economically viable if you don't have proper orientation or roof pitch. And while I guess you could attach mountings to your solar panels to orient them to the south on an east-west roof, you've effectively just created a patch of perpetual shade, which increases the likelihood of moss growth and roof decay, while also increasing exposure of the sensitive electronic wires and other things to the elements. There's a reason that every google image search of solar panels on houses are solar panels flush with the roofline.
Some types of Moss are ok.
http://www.comedy.co.uk/images/libra...crowd_moss.jpg
But nobody likes roof cancer moss.