The Basics of Solar Radiation

Sunlight is the Earth’s most important natural resource. It gives us light & heat, it indirectly provides us food (by supporting plants and subsequently herbivorous animals) and in our not so distance future it will support a large portion of our energy demand. So if sunlight is just so important, what exactly is it?

Sunlight starts as hydrogen atoms in the sun. These hydrogen atoms are fused into helium due to the intense pressure caused by the sun’s gravity. The energy released from this fusion is known as solar radiation. The solar radiation travels through space until it reaches earth. At this point, its intensity is significantly lower than it was near the sun as its intensity is inversely proportional to the square of the distance traveled. Then, Earth’s atmosphere filters the solar radiation and so only about 40% of the solar radiation that arrives at Earth, makes it to the surface.

Of course, the remaining intensity of the solar radiation varies significantly according to the location on earth, altitude, season, time of day and weather.

Solar Radiation Map of the USA. Picture Courtesy of NREL.

So now that we have solar radiation, what is it?

This is not a simple answer, but generally, solar radiation is the transfer of energy particles in the form of a wave. There are many types of waves, but solar radiation is composed of mainly ultraviolet, visible and infrared waves. Each type of wave has a different amount of energy, but of the total energy from the sun 53% is from IR, 44% is from visible and 3% is from UV.

Efficiently exploiting the energy from this solar radiation is key to any solar product.

Thanks to our newest team member, Yasir Diab for helping with this post.

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The Chemistry of Solar Part I: Propylene Glycol

Propylene Glycol is used in a lot of solar thermal applications. But why? Simply put it’s because of its heat transfer properties. So what does that mean?

Well, let’s take water as a baseline. Water freezes at 32˚F (0˚C) and boils at 212˚F (100˚C). Using only water can be problematic as most solar systems are located outdoors. If a system is outdoors during a cold day and with no sun to heat system, the fluids inside the system could freeze. Of course if the water freezes, the system would no longer operate, but additionally, as the ice expands it could break the system causing leaks or other damage.

Since these systems are designed to produce heat, one might also wonder what happens when the water gets too hot. At a certain temperature the water will boil and create steam. For a closed system, this can become dangerous as steam can significantly increase the pressure in the system. Most closed systems are designed for this and can take extremely high temperatures before becoming a hazard.

So what happens if we use propylene glycol instead of water? Well, the freezing and boiling points of the system change significantly. With a 60% solution of propylene glycol to water, the freezing point drops to -55˚F and the boiling point increase to 225˚F. This makes solar applications possible in cold locations.

One negative about propylene glycol is that adding it will decrease the specific heat of the fluid. The specific heat is a measure of the fluid’s ability to store heat. In other words, water does a better job of storing heat and keeping your system warm for an extended period of time. But, depending on the application this may or may not be desirable.

Propylene glycol is a very safe chemical that poses no health hazards, is not reactive and takes extremely high temperatures to catch on fire. You can find it in pharmaceuticals, food coloring, sanitizers and many other commonly used products.

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The Good, The Bad & The Ugly of Solar Standardization

Standardization of solar equipment has been a hot topic in recent months in the solar community.

The difficulty with standardizing parts is that solar is not a mature industry. In fact, solar technology is  changing so rapidly that the speed of technology is outpacing installations (at least in R&D, not necessarily in adoption). Like the computer revolution, as soon as you’ve purchased the latest state-of-the-art solar product another superior technology is introduced.  As you can imagine, it would be quite challenging to write industry standards when in 6 months time that part might be obsolete.

There are good, bad & ugly parts of solar standardization.

The Good

  1. Consumers will know what they are getting
  2. Mass production is easier so parts will become cheaper
  3. Design requirements are clear

The Bad

  1. Discourages creativity
  2. Inhibits customization of parts
  3. Standards may not meet customer’s needs

The Ugly

  1. Expenses in verifying parts meet the required standards
  2. Increased quality assurance oversight
  3. Bureaucracy in creating and changing standards

Read more about solar standardization in a recent article on CSP today.

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Golf Ball-Sized Hail Quality Solar

This post is about the quality and certification of solar products.

I’ve had the opportunity to work in the highly regulated and quality-controlled world of the aerospace industry. In this industry, the FAA keeps close tabs on everything that goes into an airplane (rightfully so as there are huge liabilities as a failed part caused a plane to crash!). The regulation helps to ensure the quality of the airplanes parts.

Now, when I say regulation, what I’m referring to is a vast network of strict requirements for each product. Each product must adhere precisely to these specifications before it is allowed to be put in an airplane. This includes things like size, workmanship, material, performance… and the list goes on and on.

Now how does this relate to the solar industry? Compared to aerospace, the solar industry is still in its infancy. But, there are still a ton of independent regulators ensuring the quality of solar products, namely SRCC (Solar Rating & Certification Corporation). A comprehensive list of certifying agencies can be seen here:

So, what do these certification mean? Some certifications like ISO attempt to assure that your manufacturing processes do not give room for production errors. Others agencies ensure the safety and usefulness of the product.

Let’s take a solar panel mounting system on the roof of a house.

Without knowing much about the product, we could still venture a guess at some of the requirements. The mounting system has to:

  1. Be resistant to severe weather
  2. Attach to a roof and prevent the solar panels from slipping
  3. Be the correct size to hold the solar panel, while being unobtrusive to sunlight
  4. Have durability to last the length of a solar panel warranty (>20 years)

In order to be certified by the particular agency, the mounting system manufacturer may have to perform tests on their product to prove they pass the requirements.  For instance if a manufacturer wishes to prove its mounting system is “resistant to severe weather”, it may have to pass the following environmental tests (these are not actual requirements; they are just an educated guess as to what a mounting system manufacturer might have to prove):

  1. Hot and Cold Temperature Cycling
  2. Severe Rain and Wind Tests
  3. Golf-Ball Sized Hail
  4. Lightning Strikes

If you don’t think Golf-Ball Sized Hail should be a test, take a look at this video (fast-forward to 1:30).

The bottom line is that these tests are necessary, but can be very expensive (another cost delivered down to the consumer). How does one reduce these testing costs? I’ll save this for another post in the near future.

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Can’t Put Lipstick on a Pig

Pigs are considered some of natures ugliest and dirtiest animals (although I’d have to go with the Komondor instead). No matter the shape, size or vantage point of the pig, it’s difficult to make it look appealing. You can even try lipstick… but when it comes down to it a pig… is a pig.

The same is true among solar products as they are large, heavy and frankly…just plain ugly. In fact, this is a huge issue for the average consumer. No one wants an eye-soar on top of their roof. The New York Times recently covered this topic.

Developers have tried to design products to blend in with the roof and appear unnoticeable, but that is not solving the real problem… they are ugly to begin with. How about making solar look cool by itself… like taking a cassette player and replacing it with an iPod. People would actually would want that new edition to their house or small business because it looks stylish.. oh and by the way, it also saves you a ton on your electricity bill.

Elegant Focus participated in a startup incubator at MIT this past spring as part of Venture Well East funded by NCIIA and Microsoft. At this incubator I was fortunate to meet Sam Cothran, CEO of SolarIvy, who is trying to make solar design into an art.

Sam has developed a solar product that makes solar cells look like ivy. The “SolarIvy” uses highly efficient Konarka solar cells and can be attached to the side of a building. Sure, it doesn’t produce as much output as other systems, but it looks cool. Cool enough to be featured in New York’s famous Museum of Modern Art (MoMA).

Anyways, for solar to become cheaper it needs to hit the mass market and that transition would happen much faster if the products were aesthetically pleasing.

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Solar is still an educational sell

Despite the prevalence of solar technology, and its growing importance worldwide, the general public has surprising little knowledge of the solar industry. Photovoltaics? Concentrated Solar Power?  You’d be hard pressed to find even well-educated folks that could define these terms well, if they weren’t an engineer or in the solar industry (now of course this is not true for everyone, my point here is just that for its growing importance the general public has a lack of knowledge about solar systems and products).

So who cares? Why does this matter?

1. It is much tougher to sell when the customer doesn’t know what he or she wants.
2. A large amount of customer service turns into on-site troubleshooting instead of a customer self-fix.
3. You spend more time educating than selling! Significant resources are wasted educating the customer, instead of building the product.

Solar installers and manufacturers have to pay for these overhead costs, and they pass those costs down to the consumer! If the mass public had a better understanding of solar, the cost of implementing it would be much cheaper.

So how will the general public ever get this information? Basic information about solar technology seems within reach, but selecting the proper solar product and system is not something most people can do, at least.. right now. But, we’ve got a few ideas brewing at Elegant-Focus to fix that.

If the cost of solar is going to come down, its got to reach the mass market without needing individual engineering for every household!

To learn more about the basics of solar energy, I recommend the following sources:
1. NREL Solar Energy Section (National Renewable Energy Lab)
2. DOE – Solar Section (Department of Energy)

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Welcome to the Blog

On a suggestion from two people whose opinion I respect, I’ve decided to start a blog. This blog will be about everything and anything related to the topic of affordable solar. I will use my background as an engineer, personal research and experience with the new startup company to base most of my material. I hope to incite meaningful conversation and look forward to your feedback and comments.

Thanks again for visiting the blog.

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