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One thing everyone asks right away is how much does it cost?
The answer is less than you think. There are many incentives available that offset the cost.
For our system the net cost after incentives is $8576.
After estimating the energy savings of both systems over 5 years our cost should be around $2,179
See my Presentation for a more detailed explanation of these benefits.

Cheaper than you think
 Electric Hot Water
 System Cost Installed
 $31,600  $10,570  $42,170
 Maryland Grant Program
 ($5,560)  ($2,500)  ($8,060)   
 Local Property Tax Credit
 ($5,000)  ($1,500)  ($6,500)
 Federal Tax Credit
 ($9,480)  ($3,171)  ($12,651)
 Net Cost After Incentives
 $11,560  $3,400  $14,960
 Savings Over 5 Years
 SREC Revenue
 ($6,384)    ($6,384)
 Energy Cost Offset
 ($5,196)     ($1,200)  ($6,396)
 NET Cost after 5 Years
 $2,199  $2,179

I should also mention that the company I used (grosolar) has a 12-month "same as cash" option.
That way we did not have to come up with $42k up front. It gives us some time to get the grant and tax money.

NOTE: Your mileage may vary. Hell MY mileage may vary. It will take a few months of monitoring to see for sure.
Here is my "back of the napkin" Calculation of the payback period.

  • Electric.
    • 433 kWhr per month. Cost per kWhr from Pepco = $0.20. --> $1040 per year.
    • NET Cost of electric system = $5176.
    • Payback in years is $5176/$1040 = 5 Years.
  • Water
    • My avg summer gas usage is about 20 Therms. Each Therm costs $2.
    • Assume 80% of Gas usage is summer is for Hot water. = 16 Therms or $32 per month for Hot Water.
    • Assume 75% of Hot Water will come from Solar. = $24/month or $288 per year.
    • Payback in years is $3400/$288 = 12 Years.
    • This will be more difficult to verify since I also installed a new Furnace about the same time. 
    • The good news is the Water system tracks the kBTU is generates each month so I should be able to deduce the savings in Therms.
    • 1 Therm = 100,000 BTU = 100 kBTU. So each kBTU generated by the solar system should be equal to 1/100 Therm. 
    • So Each kBTU from Solar saves me 2 cents. Stay Tuned.