Each version has its own place where it can only make sense to do one or the other. For most people they do in fact have enough space to do a ground mount system. Lets take a look at the benefits of installing a ground mount if you have the ability to.
1. Roof Space requirements, for a lot of people there may not be enough due south roof space meaning that you may be using east and west roof space. This is not the end of the world, on a typical east/west roof section your solar system will typically loose aproximately 20% of year round production that you could have had if you were to face due south. That number changes based on the pitch of the roof. You can use PV watts website to play with the numbers and see exactly the losses. If you are on the ground we can orientate the array Due south and at the optimum tilt for your particular location.
2. Roof Maintenance... Eventually your roof will need to be re-shingled if you have a typical roof. If you have a solar system on your roof then this will need to be removed and reinstalled after the new shingles go on. This is not a big deal, but it does effect your overall investment. Typically your solar system will pay for itself and start reaping the rewards after year 12 on a cash system on a typical utility grid with no rebates. If you are replacing your roof at year 25 and need to pull your panels off, then your system has already paid for itself and any out of pocket expenses at this point is just less over all cash saved over life of the system. However if your system was on the ground, then you will not need to re-invest any cash to pulling the panels and re-installing them.
3. Aesthetics... We have installed a solar array as far away from the source as 600'. This did incur a slight additional cost, and based on your total system size may be less to zero additional cost. Point being that with a ground mount, if you have land then you are able to choose where it sets. Where as on your roof, you really are limited to which roof section you will be using and the best orientation may be the front of your home. For some, they dont want to look at their solar panels, for others they are proud of their investment and love to see it every time they pull in the driveway. (to each their own) I am personally on the side of things where I want to see it as I pull in the driveway.
4. Maintenance and Repair... If their is ever a large snow storm that rolls in and you want to get out their with a broom and brush off the snow on your ground mount solar system you can... On the roof you are limited. Note: leaving the snow till it finally melts off is completely fine, and based on your solar projections for the year this has already been accounted for, but if you would like to take the time to clear the snow off your solar array, you definitely have the option with a ground mount vs. a roof mount. If their is ever any issues that need to be addressed in the future with any components in the system you will definitely make it easier on your solar installtion company for this purpose of being on the ground vs. the roof. Not that it should matter, but its the truth.
5. Roof Mount has its place... obviously not every one has the option for a ground mount solar system, and a roof mount is 100% necessary. Your personal solar installation will have a good Return on investment no matter if you choose roof mount or ground mount. The biggest take away from this blog post should be: If you have the option to put it on the ground, then just do it.
Solar and Generator Division Coordinator