25. Google Sunroof Solar
Rooftop PV’s in theory vs. practice
As an architect, I have helped numerous clients with solar panel systems on their custom high-end homes. We team up with engineers and installers to optimize these systems for a particular location. With new construction, things get coordinated during design and carefully orchestrated during construction to work together seamlessly.
But what about your average remodel project? What if you are just curious about solar potential, but not sure if it is even worth pursuing as an idea? For me, Google Project Sunroof helped to shed some light on the situation.
Google Sunroof
Go to the Google Project Sunroof site, plug in your address, and voila — solar analysis customized to your home.
Now I know that we get 1,172 hours of usable sunlight per year, our house has 4,510 square feet suitable for solar panels, and that we could expect $4,000 in savings over 20 years.
Neat.
Refine the results.
The one toggle you can modify is your average monthly electric bill. Ours ranges anywhere from a couple of hundred to twice that. This toggle impacts the recommended solar installation size. Here were my results:
Further you can get more info on the payback and estimates of installation costs. Yikes.
Theory vs. Practice
Since I have the roof plan for our house, I was curious to compare what Google suggested with our actual plans. The Google PV array size estimate was pretty close, assuming I covered nearly every available surface of my roof — 3488 square feet needed and 3358 square feet of PV’s shown.
However, there is a problem.
Our roof geometry is complex.
I wasn’t surprised to see that the Google analysis said that only about 4,500 square feet of the total 6,035 square feet of roof area was suitable for PV’s. I was surprised, however, when I tried to layout actual panels. I could only get to 3,358 square feet of PV panels to fit. Where does Google think those extra thousand square feet of potential PV roof area should go?
This is the theory versus practice clash that so often occurs in a design project.
In some perfect or mathematical realm, there is enough area. Once you plug in real world constraints of actual panels and panel supports plus account for complexities like roof valleys, hips, ridges, and skylights, and not to even mention roof vents and other imperfections that typically dot a roof plan, the reality of available space get a lot more constrained very quickly.
Competitor’s Analysis
I was curious what other results I could find on-line.
Here are my Sunpower Solar Power Calculator results assuming the same $350 per month electric bills, shady site, and no electric vehicle. They didn’t allow me to see a result for 100% solar, so these are the results with 80% solar for our house.
Back of the napkin comparison:
Google Project SunRoof 100% solar was 191 PV’s (80% would be 152 PV’s)
SunPower Solar Power Calculator for 80% solar was 119 PV’s
That is a pretty big delta between the two estimates, but it works for me as a very fuzzy gut check for the overall size of a PV array that our house would need.
Solar Panel System Components
So what are these real world products I talked about? How big are they? What are they? Here are four main components of a solar panel system.
1 - Solar Panel
These are panels with photovoltaic cells that convert sunlight into energy. There are lots of options out there, here are some of the most common solar panels in the US:
A designer’s favorite is the Signature Black Residential Solar Panel. They come in many sizes, for example, the X21-335-BLK is 335 W with dimensions of 41.2” wide x 61.3” long x 1.8” thick.
2 - Solar Panel Support
The frame that holds the panels in place. Here are a few common manufacturers:
Invisimount: located along roof rafters, follows slope of roof
Flat Roof
flat, 5 degree tilt, 10 degree tilt options
can be mechanically fastened or ballasted
Pitched Roof
3 - Inverter
The machine the converts the Direct Current (DC) generated by the solar panels in to Alternating Current (AC) used in homes. It can ben installed inside or outside.
4 - Battery
Stores excess energy. Not a required part of the system.
Tools for Design
As an architect, I like to generally understand how a system works, but I would leave it to the professional PV array designer and electrician to figure out the system and all of the required pieces to make it work. Even with a fully designed PV system, there is still a lot for me, as an architect, to do; for example, coordinate any structural considerations, review building codes, design orientation and tilt, and establish the overall aesthetics of the PV system.
Early on in the house design process I like to use tools aimed at the homeowner to discuss PV array feasibility. I would like to dig a bit deeper into the details, but for now that is left to the pros.
Tool for the homeowner
For quick, easy estimates these tools seem to work pretty well:
Tools for the Pros
PV Watts Calculator - US site, requires detailed input
RETscreen - Canadian site, requires detailed input
Ladybug - Grasshopper plugin
So, how about this electrifying post? Would you do solar on your house? Based on this quick research I am pretty sure that a massive solar panel array won’t happen on our main house, barring some technological advances or pricing changes. My next step is to see if we could use some solar on our pool house, maybe to power the pump and heater?