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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2. System Size and Cost

The remarkable news is that the estimates were all extremely close and easy to understand. Global Solar quoted a 3 kilowatt system, with all incentives included, at $11,100 while Sungevity's 2.8 kilowatt system came to $10,999. RoofRay said a 3 kilowatt would cost $11,658. Global gave three estimates – for a 5-kilowatt, 3-kilowatt, and 2-kilowatt system. Sungevity gave five, ranging from 7 kilowatts to 1.4 kilowatts. The key part is that both offered bids on small systems, which will take up a bigger part of the market. (Both Sungevity and Global have employees massage the quotes – RoofRay's is automated.)

Sungevity, though, eked out a lead in how the information was presented. Sungevity provided the total cost of a system – $42,551 for a 5.6 kilowatt system consisting of 32 panels from BP – and then methodically subtracted the subsidies. Rebates, which can be eliminated at the cost of sale, were subtracted first. Tax credits were taken out separately and it's important-installers can't take out the credits at the point of sale so homeowners shouldn't calculate it when estimating how much they need to fork out. It also separated the federal and state credits from my San Francisco local credit.

There is also an option to look at the cost figures for all five solar systems in a single chart. For cheapskates like myself, it eases the process of cost comparison.

Global Solar states the upfront costs, but subtracts the upfront costs in one lump sum, so it is hard to say what is saved where. Global solar also does not list the brand of the solar panel. Global actually does not do the installations itself: these are performed through their network of dealers. Sungevity does its own installations right now for the most part. While brand isn't completely crucial in solar, knowing I might get BP versus a generic Chinese panel is comforting information.

Another style point for Sungevity: It provides a simulation of what the solar system on your roof might look like. Call me simple-minded, but it does slightly tweak you toward buying. It is almost real.

RoofRay was somewhat confusing. It told me that I could get 1581.44 watts of peak power with a 153 square foot system orientated at 180 degrees. That's 10.28 watts of DC per square foot! It took a few clicks to find a page with a regular solar quote and then it came only with one: a quote for a 5083 watt system. I had to adjust to 3 kilowatts on my own. Have you ever filled out forms during open enrollment season? Same feeling

3. Energy Savings

Again, close between Sungevity and Global Solar. Both provide easy-to-understand information on energy saved, monthly reductions in utility bills and environmental benefits. Global Solar deserves an edge here for being a bit more realistic. Global Solar said that my 5-kilowatt system would be the equivalent of planting 783 trees or eliminating 150,840 car miles. Sungevity said its 5.6 system would be like planting 1,847 trees or eliminating 515,840 car miles. In this case, smaller might be better. Global also gives estimates for solar thermal water, another plus.

RoofRay gave me – immediately – a month-to-month breakdown of my power savings. My bill would drop to $3 in December and hit $91 in June. It also provided a breakdown on excessive use rates, cumulative cash flow charts that extended forward 25 years, a customizable calculator for energy inflation, and an estimate of output degradation in year 2024 (it's 10 percent).

But it took two clicks and a little guesswork to get to the table I really wanted: How much will it cost and how many years it takes to break even?

"Numbers not penciling out? Tweak 'em here," the site told me.

4. Closing the Deal

Here is where Sungevity really opened its lead. The email quote came with the name and direct phone number of a sales consultant. I called. She explained how the company came up with the estimate and how the different credits work. She also provided information about how the rates in California might change. It was not a high-pressure sales pitch, but really inched me toward buying. (Disclosure: I don't have solar yet because our electricity bill is $40 a month. It would take 14 to 17 years to pay off. We're investing in insulation.)

Because it doesn't install systems itself, Global could only refer me to others. Does it mean I wouldn't use them? No, but a little momentum clearly gets lost.

RoofRay asked me to resubmit some of the earlier information to get a free estimate.