Pete Dignan, a homeowner going solar in Littleton, Colo. writes about his experience in the first of three installments in this guest column for SolarChargedDriving.Com. –>Link to Part I –>Link to Part 2 We’ve been thinking about solar for a couple of years, out of concern over climate change and a desire to “walk our talk” by taking meaningful action. But we knew we were going to need a new roof first. Our cedar shake shingles were starting to leak and we were finding more and more shingles in the yard after every big storm.
It wouldn’t make sense to put a new solar system on an old roof, only to have to carefully remove and re-install the solar system when the roof needed replacing. This spring (2010), we decided it was time. So we made a plan to have the roof installed in August, then to shoot for a solar installation before the first snow flakes.
Our initial thought was that we would pay for the system out of savings, or maybe dip into our home equity line if necessary. We did some preliminary investigation and found that our electric utility, Xcel Energy, was offering rebates of $2.45 per watt installed, and the federal tax credit was 30 percent of the post-Xcel rebate system cost.
Assessing annual home electric use We went online (again, to an Xcel website) and found 24 months of electricity usage data for our home, to get a good sense of our consumption. Two years ago, we used 12,190 kWh; we have a larger-than-average home, and we had old, inefficient appliances.
Unlike central inverters which have to down-shift the power produced by all the panels to match the production of the weakest, shadiest or dirtiest panel, micro-inverters deliver the maximum available power from eachand every panel, all the time. But they cost more, and some installers question their reliability based on the shorter history of usage.
This past year, after switching out all light bulbs to CFLs, adding attic insulation and updating some appliances, we dropped our usage to 10,814 kWh. So we used that figure as our target production number for our solar system. We hoped to replace 100 percent of our usage with clean solar energy if possible.
Next we contacted three providers of residential solar systems – two from Colorado (Namaste and Bella Energy) and one national (REC Solar). We requested quotes from all three. There was quite a bit of variety in their approaches. Two companies jumped right up on the roof to create a preliminary design; one used only satellite imagery for the same purpose.
One company had very long installation backlog – six months! The others estimated six to eight weeks and eight to ten weeks. I learned to ask about the workers who would do the installation – employees or subcontractors? One company emphasized that their job foreman would always be a master electrician.
You may already know that solar panels produce DC (direct current) power that has to be converted to AC (alternating current) for use in your home. This is done by a piece of equipment called the “inverter.”
Two of the companies we talked with proposed the traditional “central inverter” approach – one device, mounted someplace on or in the home, to which all the panels are connected. The advantages of central inverters: they are simple, proven to work by many installations, and relatively inexpensive.
Micro-inverters The alternative approach is a newer technology called micro-inverters, where a small inverter is installed on the underside of each solar panel.
The advantage of micro-inverters: Unlike central inverters which have to down-shift the power produced by all the panels to match the production of the weakest, shadiest or dirtiest panel, micro-inverters deliver the maximum available power from eachand every panel, all the time. But they cost more, and some installers question their reliability based on the shorter history of usage.
There is a third option – a so-called “energy module maximizer” product from a company called Tigo Energy, which uses both hardware and software to provide the benefits of micro-inverters coupled with a traditional central inverter.
As you might have guessed by now, all three options were represented in the proposals we received from the three companies. And they were by no means in agreement about which approach was preferable. Nor did they all propose the same size of system – only one thought they could deliver close to 100 percent of our electric consumption.