Solar and software are a great mix.

But it's a work in progress.

For the past year, I've written about companies that have turned to the internet and satellite imagery to concoct estimates for solar jobs and link installers with potential customers. Installation still accounts for 30 percent or more of a solar system. Conducting a solar estimate on line can cut the overall cost of a solar system by 5 percent to 15 percent, according to Sungevity president Danny Kennedy, the first company in this market.

It also smooths out the kinks in the sales cycles. "There are tens of thousands of jobs that are lost in the pipeline," said Jack Hidary, founder of rival Global Solar Center.

But which one of these work best? This will be the big challenge for the solar industry. For the past 20 years, the solar industry has focused on a grand physics problem: how to increase the efficiency of solar cells. Software, however, is all about psychology. Do people understand it and enjoy it or not?

I tested three: Sungevity, Global Solar and RoofRay. Sungevity and Global Solar are close, but Sungevity was easier to use and actually got me closer to buying a system.

RoofRay left me confused. It's the sort of software program that consumers have to adapt to, which can be annoying to someone being asked to shell out $20,000.

Here is the closer comparison.

1. Initial interface

Sungevity and Global Solar are pretty similar in this regard. Both companies ask you to provide some basic information (name and address) and up pops a satellite image of the street you live on, including your home. (Sungevity also has a video narrated by someone who looks like the Bionic Woman but it's not all that helpful.) Global Solar also includes a large yellow arrow you can move around to make sure it points at your home. It's a great touch. Sungevity doesn't have the arrow, but the satellite image was better. You can see an example of Sungevity's interface below:

Global Solar gave me a straight overhead shot of the street: I could only pick out my house because I know the difference between the look of my roof (aluminum) versus my two neighbors. Sungevity's shot comes at an angle so I could see the front of the house too for easy identification. (Sungevity uses Microsoft's aerial data throughout. Global uses Google for the site, but Microsoft to determine the final quote.)

RoofRay pulled up the less-helpful overhead Google shot of my street and then told me to "drag the map and zoom in/out until you're above the property." Or, in other words, find it on my own. It then asked me to click on each corner of the roof to outline where a solar system might go. Unfortunately, I mis-aimed quite a bit, and eliminating mistakes requires a secret incantation: sometimes the markers disappeared with a second click. Sometimes not. The final tracing of my roof resembled a pentagram consisting of overlapping triangles.

I was then asked to determine – on my own – the orientation of the house toward the sun and the pitch of my roof. "Guesstimate your pitch using the slider. Mid 20 degrees in typical," it said. Global Solar also has a roof pitch tool, but it just gives you three options: high, medium and flat, with a helpful drawing.

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Tags: bp, carbon abatement, cost, energy saved, global solar, installation, internet, roofray, solar, sungevity