Consumer Reports, which six months ago was skeptical about the viability of Tesla's Solar Roof product, has once again "done the math" using newly announced pricing estimations.

Tesla Solar Roof - Available To Order Now, Installed In The US This Summer (Textured Glass shown/available now)

Tesla Solar Roof - Available To Order Now, Installed In The US This Summer (Textured Glass shown/available now)

According to CR, it's not easy to weigh value of the offer, as company’s online calculator "relies upon some important assumptions and predictions that delve deep into the economy of residential solar power in the U.S."

In its first analysis, CR said that costs need to be below $24.50 per square foot to match costs of conventional roofs (including the cost of Powerwall batteries, but excluding solar incentives or rebates). A 3,000-square-foot Solar Roof would then cost $73,500.

Tesla announced an estimated cost at $21.85 per square foot, which would be $65,550 for the same example house.

After using Tesla calculator for example homes in New York, Texas and California and a 30 years period, CR found out that in some cases Tesla offers a good savings opportunity, although in other cases, it doesn't look so good.  (Check out CR's breakdown for those regional examples here)

However, even if one's first calculations seem tempting, CR advises to answer some questions before placing deposit.

"How will you cover the hefty upfront costs? If you finance the project, obviously it will cost more due to interest. Even with today’s historically low rates, that would add significantly to the cost over 30 years. Alternatively, if you pay the total cost at the time of installation, you’re likely pulling money from savings or investments that could potentially be earning value. “You need to look at that as an investment, relative to other investments,” says Sarkisian.

Also available now - Tesla Solar Roof in Smooth Glass

Also available now - Tesla Solar Roof in Smooth Glass

How long do you plan to own your home? Because Solar Roofs front-load the cost of electricity, the amount you stand to save or lose hinges heavily on how long you stay in your home. A typical owner of a single-family home will stay put for 13 years, according to the National Association of Homebuilders.

Using the example of our staffer’s home in New York, after paying $45,400 for the solar roof and Powerwall, he would save about $16,935 in electricity after 13 years. Even with that savings and $12,500 in federal tax credits, he’d still come out behind by $15,965 if he moved at this point. Some of that loss could be offset by potentially increased resale value, but it’s impossible to predict how much a Solar Roof will add to the value of a house.

How much sun does your house get? Got a lot of tall trees? A tall building next door? That can make a huge difference for the value of any solar array. You can plug in your address at Google’s Project Sunroof to see whether your roof is a good candidate for solar — whether from Tesla or some other manufacturer.

How old is your existing roof? Obviously, it doesn’t make a lot of sense to tear up a new conventional roof to replace it with a Solar Roof. But if it’s not new, you’ll want to factor the age of your current shingles or tiles into your decision, because if you’re going to need a new roof anyway, you may prefer to apply the cost toward a roof that also generates electricity.

Our staffer got two quotes for a traditional asphalt shingle roof with a 30-year warranty, and both came in around $6,800. When you deduct that from the price of a Solar Roof, it increases the savings over 30 years to $20,700 from $13,900.

How effective will these tiles be? It’s important to emphasize that most of these numbers are Tesla’s own estimates and that Consumer Reports has not tested Solar Roof and cannot verify its energy efficiency claims."

Tesla's solar calculator can be found here.

Check out the full report at Consumer Reports (via Teslarati)