If I use approx 1200 kws/month....would I need approx 6000 watts of solar panels to cover half of that?....

Let's consider some basics here. The monthly usage is an energy expressed in kiloWatt-hours (kWh). The panels are rated in power at a standard solar insolation, and this insolation level is roughly a peak solar power expected with the suns rays coming directly onto the panel at right angles on a clear day. The typical AC power peaks around this DC power rating, but is usually less due to angle of incidence as the sun tracks across the sky, and due to clouds. The relationship between energy and power is: power x time = energy.

Now to get an understanding, let us consider an example. I have a 3.15 kW DC rated solar system, and I live in a very sunny location with annual average solar insolation for panels tilted up at an angle equal to the latitude of 5.9 kWh/m^2 /day. Look at http://www.nrel.gov/gis/images/map_pv_national_lo-res.jpg to estimate the solar insolation at your location. My system generates about 5800 kWh per year, or about 480 kWh per month. So the same size system (3.15 kW) at your location should be very roughly 5800 kWh/year x solar insolation at your location / 5.9 kWh/m^2 /day. The power and energy scale with system size, so if you need more energy, just scale the system up. You could get a more accurate esimate of energy including monthly variations in power by using PVWatts, which you can download for free at http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/.

Thanks Lee!

Although...

at 1200kwh/month (14.4Mwh/year) average, there may be low-hanging fruit on the efficiency-front that would bring the size of the array necessary to support your use down by quite a bit. 14.4Mwh/year is well over the national average for a household of 4, but if both your space heating & hot water is done with electricity 14.4Mwh/year wouldn't be considered high. The unsubsidized installed price of PV has come down a lot over the past 5 years, but even at $5K/kw-pk there's usually better payback elsewhere. In places where the net-metering and/or direct subisidies are favorable, PV has become surprisingly cheap though. (IIRC this was the case for Lee.)

In most of the US a 6KW array cover more than half of an annual load of 14.4Mwh. (Even at my house in central MA if I cut down all of the neighbors' trees a 6kw array would deliver ~7.5Mwh/year. But with my site shading factors it would be ~4.7Mwh- less than half what Lee would yield for the same array.) But unless yours is a large house with favorable roof pitches, odds are that an array big enough to handle the bulk of the annual load would not fit on the house.

Yes, there are many caveats that need to be considered with a solar PV array. What I gave you is just a rough starting point. If the area that you put the array is shaded, then output will be much less. If the orientation is less than ideal, then performance will be degraded.

One bright spot (get it?) is that the interface for using PVWatts Version 2 has dramatically improved, and I would now recommend that version over Version 1. Version 2 has always been superior in that it has solar insolation data for any zip code in the U.S., while Version 1 just has major cities. Version 2 was harder to make work in the past, but now it is simple. Just go to
http://www.nrel.gov/rredc/pvwatts/grid.html, and hit the "PVWatts Version 2 calculator." In my last post, I mentioned downloading PVWatts, but you actually do not download it, but rather use it as a free, on-line calculator. Simple! A caveat about PVWatts is that it seems to significantly underpredict energy from PV panels, in my case by 23.3% over a year. I thought that I just had excellent panels, but the same underprediction also seems to be the case for two other PV systems in this town that I am also monitoring. Alternatively, maybe we had a high solar insolation year last year, and it is contiinuing high this year. Climate change?

PVWatts will account for orientation at any orentation. I also have a little data on the effects of orientation for my system computed in PVWatts V2 at http://www.residentialenergylaboratory.com/rel_energy_use_pv.html. If the roof angle is far from ideal, another option is to ground-mount the array. Ground-mounting also provides the option of using a steel pier buried into a concrete base, and using a tracking system. In this area, people that live in urban areas use roof-mounted panels, while people on larger lots, about 1 acre or larger, often use ground-mounted arrays with steel piers and 2-axis tracking. The output from these tracking PV systems is significantly greater than fixed arrays. PVWatts V 2 predicts the following for a 3.15 kW array: fixed, 4774 kWh/yr; 1-axis tracking, 6369 kWh; 2-axis tracking, 6854 kWh. The results that I have for 3 different fixed-array PV systems suggests that actual output might be 20% or so higher than these values. I do not know if the extra cost of 1-axis or 2-axis tracking makes economic sense in that I have not priced the tracking systems.

I have costs and payback for the modifications that I used on my standard production house to achieve net-zero source energy, including the PV system, at http://www.residentialenergylaboratory.com/costs.html. Of course, these are applicable only to my location, my situation, the mods were to a new house, etc., and include the actual price paid including federal and utility subsidies.

"...bright spot (get it?) ..."

:-)

In Germany there's a utility company doing great things with wind energy & micro-scale cogeneration called LichtBlick (translation==Bright Spot) too.

https://www.lichtblick.de/h/schwarmstrom_288.php