Thoughts on Solar

So, you are considering a solar power system for your home or business… and why not, given the myriad of social, environmental and economic benefits! But how do you know if your roof is a good candidate? This is one of the top questions to consider carefully before investing in solar. 

1. Do I have enough space?

The size of your solar system is dependent on your usage needs and the amount you want to offset. However, it is not uncommon to find homes and businesses which are “footprint-constrained” - meaning their system size is limited by the space available.

A few things to keep in mind as you look at your roof and ponder how big is big enough… First, while there are many different solar panels they are typically the same size. Run on Sun uses LG panels which are about 65 x 40 inches and can be placed in either a portrait or landscape layout. Panel energy ratings vary, 285-315 watt panels are currently available from LG. For an average home (5 kW) that means you would need around 16-18 panels to offset the bulk of your electricity.

Another limitation is that fire code requires three feet of clear space from all ridges. If you have an irregular shaped roof with many valleys and peaks it may make the layout very challenging. Given that the panels are rectangular and racking is mounted parallel to the roof, rectangular spaces are ideal. However, the 3-foot rule does not apply to uninhabited spaces such as garages and carports making them good options if your home lacks the perfect solar roof. 

2. What if my roof is shaded?

Shading from trees, tall buildings, chimneys, or even parapets on flat roofs can significantly degrade the energy output from solar panels. Sometimes all that needs to be done is a generous trimming of that tree that’s gotten a little out of control over the years. Other times it means you really won’t get your money’s worth out of a solar system. But, if the shade elements are few and only during a short time each day, your roof may still be a viable candidate.

If this is the case be sure to talk to your solar contractor about inverters. We have written a great deal about the advantages of “microinverters” in handling shaded roofs, particularly those made by Enphase Energy.  “String inverters” on the other hand would be a bad choice as the entire system would degrade when any single panel is shaded. 

3. Should I re-roof my house before adding a solar system?

This may be the most important and frequently overlooked question to consider when researching if solar is right for you. Part of what makes solar a great investment is the 25+ year lifetime of the system. But if you have to re-roof during that time there are added costs to remove and re-install the system. If you are planning to re-roof during the lifetime of your solar array be sure you select components, such as the racking system, from companies that…A. will still be around 15-25 years later, and B. will be able to provide compatible replacement parts when pieces are lost during removal and re-installation. Avoid newer companies testing out “state-of-the-art” racking systems and cheap companies banking on the solar boom alone.

For this reason we always ask owners the age of their roof. In southern California, a roof over ten years old should get a makeover before installing solar. If you are unsure of the condition, it is a good idea to have a professional roofer take a look and give you an expert opinion. Sometimes solar contractors can offer this as part of their free assessment. (Run on Sun works with a very reliable roofer who is happy to take a look at any roof in question!) If the roof still has some life left in it but not enough to outlast the solar system you could re-roof only the area where the solar array will cover and plan to do the rest later. An added benefit is that the solar panels will actually protect your roof from the elements, helping it to last longer.

Unfortunately, you will likely be able to find someone willing to put solar on your roof even if it isn’t a good candidate. But if they aren’t discussing the above issues with you, then red flags should be flying! To ensure you get the best investment possible, do your research, take a good long look at your roof, and discuss all of your concerns with your solar contractor. 

There is a vigorous debate among solar installers about the relative merits of microinverters, such as those made by Enphase Energy, versus those of string inverters, such as those made by SMA. We can’t claim that we have resolved that debate once and for all, but our experience this past week reaffirms our confidence in the microinverter choice.

Almost exactly a year ago we did a residential installation at a seriously shaded site.  We explained in detail to the homeowners about the reduced yield that any solar power system would provide given just how much shading they had, but they were still eager to press forward.  The shading mandated that we use microinverters, and they were excited to see how their system would perform using the Enlighten monitoring system.

In addition to the shading, there was another limitation - a 150 Amp service meant that we couldn’t install as big a system as they needed.  However, they were about to embark on a six-month renovation of the home and as part of that they were going to upgrade the service.  We decided to build the first half of the system right away and include the additional infrastructure that would be needed for the later addition - down to the standoffs on the roof.

Here’s how the install looked a year ago:

As you can see from the photo, there really is substantial shading present - and you can also see our Unirac standoffs waiting for Phase II.  Sitting on top of those Enphase M215’s are LG 250 Watt solar modules - our preferred product at that time.

Fast-forward to this past week.  We are still using M215’s but LG has moved up the curve and the new modules for the second phase of this project are 280 Watts each.  The homeowner wanted the higher power modules incorporated into the existing system, and they wanted them installed not on the open bottom row, but wherever they would be able to get the greatest amount of sun to maximize their return on investment.

The first great advantage of having microinverters on this project then was the ability to combine significantly different power modules into the same array.  But the second goal - placing the new modules in the ideal locations - was one that we could only solve with confidence thanks to the Enphase Enlighten data.  Indeed, all we had to do was go to the monitoring page for this site and request the display of lifetime energy.  Here’s how that looked:

Now isn’t that interesting?  There is a huge difference going from the NW corner down to the SE.  Overall, taking the top row along with the three west-most modules from the second row seemed like our best plan.

Here is how the expanded array looked after we completed the install:

Pretty easy to see where the new panels were installed - they are the bright shiny ones!  (The break in the bottom row is to avoid the utility service mast.)

Here is how the new system performed yesterday (after the old panels were cleaned!):

Our higher power modules are installed in the optimal locations, thanks to the ability to mix and match modules in the array, combined with the ability to know at the module level where are our best performing slots in the array.

Trying doing that with a string inverter!