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.
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.
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.
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.
Angelinos typically struggle with cloudy “cold” days more than those accustomed to less sunny locales. So after the last few months of gloom it was no surprise to hear the National Weather Service announce that it was in fact a very abnormal year for Los Angeles.
Temperature data from around Southern California showed that the region experienced a “reverse” meteorological spring, meaning average monthly temperatures decreased instead of increasing. Average temps for downtown Los Angeles in March, April and May were 68.2 degrees, 65.8 degrees and 64.2 degrees, respectively, according to NWS. The normal averages between 1981 to 2010 were 60.6 degrees, 63.1 degrees and 65.8 degrees. Since recordkeeping began in 1877 only three documented “reverse” springs have ever occurred. But this is the first in nearly a century!
While many Angelinos may feel as if it is colder than usual, these past three months have actually been warmer and drier than normal across Southern California. The difference is we have been experiencing a cooling trend overall since the warmer than usual February. April and May actually felt more like LA’s “June gloom", typical only for June.
For those fretting over low output from your solar system…don’t worry! Your system is NOT malfunctioning. We’ve just experienced a less productive than normal spring. I’m sure the sunshine will return and your solar meter will continue to spin in the right direction before you know it. In the meantime, be thankful for any precipitation we get, and maybe even get out and enjoy the grey days that are neither too hot nor too cold!
UPDATE - Due to looming weather concerns, the Solar Impulse team decided to divert to Nagoya, Japan to await better weather. Disappointed but undaunted, pilot Andre Borschberg landed successfully in Nagoya this morning after flying for 44 hours and more than 2,000 miles, roughly one-third of the intended distance to Hawaii. Now the team will study the weather to determine the optimal time to resume their mission to fly around the world, powered only by the sun!
Solar Impulse 2 - the entirely solar-powered airplane that is attempting to fly around the world - just took off on the most audacious leg of its amazingly audacious mission: to fly non-stop from Nanjing China to Hawaii. This is a non-trivial flight in a conventional jetliner, one from which many passengers will disembark complaining of cramped quarters and a lack of sleep. But the pilot of SI2, Andre Borschberg, will need to stay awake (mostly) for six days in a cabin slightly smaller than Dr. Who’s TARDIS Police Box!
Updates from SI.TV
We have written about the Solar Impulse project before, with a mixture of awe and envy. This particular flight, however, is all awe. We are in awe of the raw human fortitude required to succeed at this attempt, and we are in awe of the courage that this pilot is displaying. Of course, he is far from alone in this undertaking, supported by a mission control center and an extensive ground support crew. But at the end of the day, he is in that cockpit alone, and the success of the flight will come down to his skill and determination.
Each day the plane greets the sunrise by a climb to altitude (flight level 280, or 28,000′), allowing the solar cells (17,000 of them) to fully recharge the plane’s batteries. During the night, the plane descends, flying on stored solar power. As morning comes around, the plane and pilot reach a critical moment - can they get to a point of energy production that will sustain them through another cycle? If they have encountered too many clouds, there will not be enough energy to sustain the mission and the pilot faces the very real possibility of ditching the plane in the middle of the Pacific Ocean! Wow!
Rest for the weary pilot comes in 20 minute breaks, ended by a gentle alarm if all is well, or a more insistent alert if something has gone awry. To maintain physical and mental health, the pilot practices both yoga and self-hypnosis, as well as a limited set of exercises that can be performed within the cabin’s confines.
You can learn more about the background of this mission, and even monitor how solar energy is powering the flight at the Solar Impulse website.
We will update this post as the flight progresses, and the video embedded here will provide live streaming of the flight so be sure to check back often during the week ahead.
Elon Musk is a visionary and a showman, but occasionally his enthusiasm for his vision gets way out ahead of reality. Nowhere was that disconnect more on display than this past week when he made his much talked about announcement of the Tesla Powerwall battery storage system. While we share the vision for the potential of battery systems (such as the one Enphase Energy is set to release later this year, albeit in a far more understated fashion), when 38,000 people go online to order a product that doesn’t yet exist, it is time to debunk some of the more exorbitant claims made by Musk.
Here are the three biggest whoppers that Musk made during his Powerwall presentation (video below).
Musk touted the “peace of mind” that would come from having the Powerwall, and said, “if there’s a cut in the utilities you’re always gonna have power, particularly if you’re in a place that’s very cold, now you don’t have to worry about being out of power if there’s an ice storm.” (See video at 8:35.)
The Powerwall unit that Musk was talking about that was designed for “daily cycling” was a 7 kWh unit that is priced at $3,000. The average home in the Run on Sun service area uses 25 kWh/day. So a single Powerwall unit provides roughly one quarter of the energy demand of an average home. If your desire for “peace of mind” means running your home for a full day in normal fashion, you will need to purchase 4 Powerwall units (assuming you have the wall space to mount them) and that will cost you $12,000.
Of course, many outages last longer than a day. The longer you want to stay powered, the more units you will need.
Musk insisted that Powerwall has been designed to work with solar systems, “right out of the box." (See video at 8:25.)
Except… that the Powerwall is designed to fit between existing solar panels and the DC-AC inverter(s) in the system (i.e., on the DC side of the system). But here’s the thing - the vast majority of inverters are what are known as “grid-tied,” which means if the grid goes down, the inverter shuts off, and stays off until the grid comes back. If the Powerwall is on the DC side, there is no way for it to “mimic” the grid (which, of course, is on the AC side), and so the inverter will shut off. While the inverter could certainly be replaced with a hybrid inverter (that can work both independently and tied to the grid) such a replacement is a pricey undertaking and certainly not a plug-and-play installation.
But Musk, like the true showman that he is, saved his biggest Whopper for the end…
Warming to his subject, Musk really brought down the house with his most outrageous claim of all:
You could actually go, if you want, completely off-grid. You can take your solar panels, charge the battery packs and that’s all you use. So it gives you safety, security, and it gives you a complete and affordable solution. And the cost of this is $3,500." [Gasps and applause from audience.] (Video at 8:55.)
No. No you cannot.
Let’s unpack his statement. There’s two major claims here, neither of which is true. The first is that you could go completely off-grid, and the second is that it would cost you $3,500. So let’s start with the easy one to disprove, indeed, we already did above: this won’t cost $3,500. The Powerwall provides 7 kWh of storage. The average house uses 25 kWh/day. If the battery has to run your house for just one day, you would need 4 Powerwall units at a cost of $12,000. (The 7 kWh unit is the one designed for daily cycling - what you need to go off-grid, and it costs $3,000 - if you could actually purchase one, which you can’t.)
So that’s easy to debunk. But what about the second, more fundamental question. Can I use this Powerwall system to go off-grid without changing my middle-class, suburban lifestyle? For most folks the answer is simply, no. Here’s why. When you go off-grid you need to be able to meet all of your energy needs all the time without assistance from your local utility. To do that, you need a battery system large enough to last you during the longest typical shortfall of available energy (i.e., how many stormy/cloudy days in a row will you see), plus a solar array large enough to charge that battery on sunny days while meeting the household needs. Turns out, that is quite a lot of both.
Folks who design off-grid systems (very few of which are found in areas like Pasadena), typically design for three (or more) days of self-sufficiency (or autonomy, as they put it). For our typical, 25 kWh/day home, that would require storage of a minimum of 75 kWh. But according to Tesla, you can only stack a maximum of nine Powerwall units, which limits you to 63 kWh. Sometime around noon on that third day without sun, your house will shut down. Oh, and that much storage will cost you $27,000.
What about the solar array side of the equation? Let’s start by asking how big an array can you fit on an average house? House sizes have trended bigger in the past couple of decades, so more recently built houses are an overstatement of the average house out there. Still, to have a starting point (and to give Musk the benefit of the doubt), let’s assume that our average house is 2,400 square feet (a fair estimate based on US Census data), and that it is optimally designed to maximize solar production: a near perfect square with a true south face, pitched at latitude (34° here in Pasadena), with no shading. Of course, we still have to give the Fire Marshall the desired setoffs so that gets us to 1,115 square feet of roof space (math available upon request), enough for 62 LG 305 solar modules, but because we need to use a hybrid inverter with fixed string sizes, we will drop that down to 60 solar modules. That yields an 18.3 kW system which at $3.50/Watt would cost a cool $64,000 - and be bigger than our biggest ever residential installation.
So the Sixty-four Thousand Dollar question becomes: How well will that do on meeting our needs? Per the CSI calculator, this maximal system will produce roughly 29,000 kWh in Year 1, or an average daily output of 79.5 kWh. (Less in the winter, of course, when you are most likely to see those cloudy days.) After providing for my daily needs of 25 kWh, I have 54.5 kWh to spare, not quite enough to fully charge my batteries (which require 63 kWh). A scenario where I have two cloudy days, followed by one partly sunny day, followed by two more cloudy days could easily leave you in the lurch. And for this you paid a total of $91,000! If you live somewhere with poorer weather than what we find in the Run on Sun service area (i.e., pretty much the entire rest of the country!) your performance will be even more dismal.
The sad part of this whole thing is that battery storage combined with solar is going to be huge, but not for the reasons Musk alluded to in his speech. The future of utility rates is the shift to time-of-use rate structures - a fact already well and painfully known by our clients in SCE territory, and soon to be seen by everyone. Time-of-use rates, where utility customers pay more for energy during the peak part of the day, are the only way to match utility costs with customer charges. (It is the head of the Duck in the famous Duck Curve below.)
That “overgeneration” that drives down demand at noon is presently fed back to the grid, where the grid operator has to modify the power mix to accommodate it - in essence, it is wasted. (Although presently, net metering customers get full retail credit for it - something, that in all likelihood, will soon go away.)
But add storage to the mix, and you shift that overgeneration from the middle of the day, to the evening peak hours, benefiting the time-of-use customer as well as the utility. It is the way to bring about a peaceful end to the utility-solar wars, and it is the true benefit of storage to solar customers - without oversizing either your solar array or your storage system.
So let’s all get excited over solar with storage, but for the right, and much more cost-effective reasons - and not the nonsensical hype being spewed by that super showman, Elon Musk.
We don’t often announce our latest projects, but one this week really stands out, and that is our upcoming project for Chandler School here in Pasadena. (Indeed, it is just down the street from where I once lived!) The 44.8 kW system will be installed this summer, in time for the 2015-16 school year.
Chandler is a special place that puts great emphasis on challenging its students. As they note in their Mission Statement:
Chandler students gain a love of learning, a means of thinking independently and an ability to work collaboratively. A Chandler education seeks to develop good character, self-reliance and a commitment to community in students as a foundation for academic and personal success.
It will come as no surprise to readers of this blog that we at Run on Sun have a soft spot for non-profits, and we take great pride in working with schools and churches to expand their mission while making the world a greener, cleaner place. We understand the process involved, with its many twists and turns, and we have found that our collaborative, information-intensive brand of “selling” solar meshes well with the non-profit world.
In the case of Chandler School, the process actually moved quite quickly - spurred on, at least in part, by the rebate step down announced by Pasadena Water and Power for May 1. Once the decision was made, the design team at Run on Sun was able to move quickly and get the rebate application completed and filed in time to meet the deadline.
As noted by John Finch, Chandler’s Head of School:
As an independent school in Pasadena we have a public purpose to make our environment cleaner by reducing our dependency on fossil fuels and limiting our carbon footprint.
If we want our students to be stewards of the environment in the future, schools need to be examples of best practices. The installation of solar panels on our gym roof is a best practice. I am looking forward to the learning opportunities that the project will give to our students.
We are excited to be working with this renowned Pasadena institution, and we look forward to providing the Chandler community with a wonderful asset that will both save money, and enhance the educational experience of its 450 students.