I need help with the math!

I am not going to tell you how many you need but maybe I can help you to understand the math involved.
25,000 watthours divided by the number of equivalent hours of full rated output from a PV (photovoltaic) module.
In other words all of the power produced over the period of a day divided by a PV modules full rated wattage.
You can find that at this site.
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/
Select; Average, Annual, and Flat Plate Tilted South at Latitude. Find your area on the map and that is what you would divided by.

I am just going to pick a number out of the "hat."
4 hours of equivalent full rated output per sunny day.
25,000 / 4 = 6,250 watt PV array and at $4.00 per watt not installed equals $25,000.
You say your paying $60. a month now for grid power?
$25,000 / $60 = 34 years of electric bills.
Of course PV can be modular, which means you do not have to install it all at one time. You could have a PV array installed with provisions of adding more to it as time goes by. It sounds as though you are thinking about a "grid interactive" system. No batteries. You could search in your area for qualified supplier/installers and maybe get a quote. Who knows you might get lucky and find one that does it all for you "turn key," including any government handouts oh!, I mean tax incentives, to help you purchase a system




On a personal note, I had greater expectations from the RE (renewable energies) industry. More so from the PV industry. It would seem, to my mind anyway that, all that has happend is, RE has jump into bed with the politician's and other energy producers, all three holding their hands out wanting more and more tax payers money. I will give them this much, RE has convinced the politician's and energy producers to use saving the planet as a selling point.
In the words of Jethro Tull, "he who made little kittens, also put snakes in the grass."

Because of my arrogance, I may have made a mistake.
You said 25 kWh's. I assumed that to be; per day, averaged over a month.
25 kWh's x $0.09 national average = $2.25 per day x 30 days = $67.50 per month.
Is this correct?
$2.25 per day doesn't look like a lot does it?

One of the arguments I have read form RE enthusiasts about this is that, this isn't the whole cost, that there is money being paid to maintain the established electric power grid as a whole that is not reflected on that monthly bill. They say that money comes from the American taxpayers in the form of subsidies and other items as doled out by the U.S. government. The catch phrase is, "if your on grid, your paying for your power and light out of more than one pocket."
http://www.homepower.com/home/
 Well... I could say the same thing about RE. I also read about billions of tax dollars going to the RE industry, as a whole, for R&D and to promote the use of RE. Then there is the government incentives to end users to buy RE. There is even a certain amount of, what can only be called "gripping" in those articles because the coal, oil and, nuclear fired electric energy providers get more tax dollars than the RE industries get.
http://www.renewableenergyworld.com/rea/home
Please don't get wrong, I am not against RE, its just that I have lived off grid for 30 years. Only in the last 10 years have I had any electricity here at home, and that all comes from PV. The first 20 years was with no electricity what so ever. So I hope you can see, I have a some what unique perspective. I don't need, either one of these energy pushers. For that matter, I believe the one reason for the world wide human population explosion that started around the 1900's is because of the increased use of fossil fuels and electricity.
http://www-popexpo.ined.fr/english.html
I can see this in the time lines that history provides.
The discoveries of these energies happen at an earlier time but the wide spread utilization of them by the masses becomes established just prior to the 1930's.
But think about this. For well over 7,000 years mankind did not need all of these energies we take for granted today. We are a living testimony to this fact. It has only taken a little more than 100 years, and we have gotten to the point where we believe that we cannot live without these energies. From the beginnings of mankind up to the 1900's, (how many thousands of years?) world population is estimated to have reached 2 billion people. From the 1900's to present day that number has reached 6.5 billion. 4.5 billion more in just 108 years. I don't know about you, but to me, that fact is frightening.
Pity about Earth.