Save and Conserve

I've neglected to post details of the last few solar energy courses because, as the class has progressed, we have not been introduced to new topics as much as we have drilled down deeper into the world of details and calculations around system sizing, wire sizing, balance of system components. All of which I've touched on in previous posts.

While producing electricity from solar cells is fairly simple, the devil is in the details. System efficiency is obviously critical to the long-term success (and ROI) of any residential solar system. To that end, quite a bit of time and thought needs to go into the size of system components (especially inverters), the amperage of conductors, voltage drop in a conductor over distance and batteries (on a battery backup system).

In Class 9 we did cover some new ground. We discussed bypass diodes, which are integrated into solar panels and activate when the panel becomes shaded. The idea is that the shaded portion of the circuit is not flowing current, so the diode bypasses that section of the circuit to maintain current flow through the panel and array. Pretty neat.

We also reviewed trigonometry. SOH CAH TOA mean anything to you? Well, it comes in quite handy when you need to figure out how to space out rows of tilted panels so the row in front doesn't shade the row in back. Commonly used for flat roof systems where the rack mount tilts the panel up to the sun at some angle.

If nothing else comes of my solar energy course, at least I can say I was reminded how to figure out the length of the sides of a right triangle. Awesome ...

Last class happens tonight and then comes the NABCEP test on Saturday. Wish me luck ... think I'm gonna need it

Notes from previous classes:

Class 1
Class 2
Week 2
Class 5

Posted by tom c. at 5:29 PM | Permalink | Comments (4)

Last weekend, my solar PV class toured 3 area homes that have active solar systems installed. Although it was about 10 degrees and snowing, the tour was really interesting. Our first stop was to a home in Troy, NY that uses a combination of active and passive solar energy.

Originally I planned to post some photos, but I found a video the owners posted. It's way more fun to watch solar junkies than read about them:

Posted by tom c. at 5:27 PM | Permalink | Comments (0)

Class five focused on solar PV system components. We discussed charge controllers, mounting options, inverters, combiners and batteries.

Although the solar modules (or panels) are the most expensive and most visible piece of any solar system, they would be worthless without the various components they connect with and feed power to.

Charge controllers regulate the amount of energy distributed to batteries so that the batteries do not overcharge, which is critical to the long term health and operability of the batteries. There are, of course, various types of charge controllers available:

• Pulse with Modulation (PWM) controllers are the most simplistic controllers available. They are switch-based and send power to charge the battery when the switch closes the circuit.
• Diversion controllers are smarter than PWM. When the battery is charged, these controllers have the ability to send the power to another place.
• 3 Stage controllers are even better - they can switch into 3 modes. In bulk mode, the controller will send all available current to the battery (like PWM0. In absorption mode, the voltage being delivered remains constant while the current is decreased. In float mode, the battery can be trickle charged.
• Maximum Power Point Tracking controllers are the best option and what most people use today on battery-tied systems. These controllers track the module IR curve and send the right amount of voltage to the battery. These controllers make it easier to match a high voltage array with a lower voltage bank of batteries (which is typical).

After controllers, we discussed the different module mounting options. This boils down to roof mount, ground mount and pole mount. There are various pros and cons for each type of mount. For example, roof mount typically looks better, but the panels can get very hot in the summer time up there. Heat creates resistance in the circuit, so the hotter panels get, the fewer volts they produce. The ground mount will not be as hot, but it is more susceptible to damage or theft. A pole mount can offer easy access for repairs or maintenance, but it can also be an eye sore. Like most things in this world, there is no best single best option. The site and personal preference will play into the equation.

We wrapped up with info on inverters, combiners and batteries. My take-away from this (pretty boring) class was that the devil is in the details. You can see from the notes above that there are a lot of different options available, at different power points and at different price points. As a solar installer, if you don't nail down the system components and deliver the customer a solid quote, you won't be in business for too long. Obvious, yet a good dose of reality.

Posted by tom c. at 12:52 PM | Permalink | Comments (0)

Previous entries detailing week 1 available at these links: Class 1 | Class 2

Week 2 was all about digging deep as we rolled up our sleeves and began to get our hands dirty, applying our rudimentary understanding of basic electricity and learned more about how solar PV actually produces power.

We wired up some small solar panels in series and parallel circuits. Solar systems consist of solar modules wired together in an array. Depending on how the modules are connected to each other (whether in series, parallel or a combination of the 2), total array voltage and current will shift. When wired together in a series circuit, the voltage of each module adds together while the amps (current) remain unchanged. So if you have 2 17 volt, 3 amp modules wired in series, together they produce 34 volts at 3 amps. Parallel circuits work the other way; volts remain unchanged while amps are additive. Using our example, the same 2 modules wired in parallel will produce 17 volts at 6 amps.

Sidebar: Mike, one of the instructors, had asked the class to bring in their most recent electric bill at the end of class 2. At the tail end of class 3, we each read out the number of kilowatt hours (kWh) used in the most recent ~30 day period. My GF and I live in a 2 bedroom apartment that is probably 850 square feet. Our most recent bill told us we used about 160 kWh. I was stunned as I listened to the usage stats from my classmates. 900 kWh ... 1,100 kWh ... the "winner" used about 1,400 kWh! That last guy is spending roughly $375 per month. Way to go! Now, admittedly, we walk around in the dark a little bit and we don't have a dishwasher - but that's a pretty big spread. Most of the other classmates own homes, so they have a much bigger AC load to power, but I was amazed to say the least. It actually makes me feel a bit better about our energy predicament - conservation and reduced use can obivously make a huge impact on the amount of electricity we consume in this country. If price continues to rise, expect people to start switching to CFL bulbs and turning the TV off when the room is empty.

We conducted a mock shading analysis. The "perfect" solar site is a rarity - trees and weird roof features or dormers cast shade, especially in winter when the sun is lower on the horizon. If one section of the array is shaded, it effectively reduces output of the entire array to near zero. Essentially, shade shuts down the electric circuit - and electrons stop flowing. No electrons, no power. The solar installer must know how much shade the panels will take at each daylight hour throughout the year. If you don't calculate the percentage loss in power resulting from shading, you end up with an undersized system and an unhappy home owner.

We delved into solar cell fundamentals. Most people know that cells are (for the most part) made from silicon, which is one of the most abundant elements on earth. Most people know that solar cells convert sunlight into electricity. But how that process actually works is a mystery to most, including myself prior to Tuesday night. The link above contains more details than I could ever hope to include here, but suffice it to say that most solar cells are "doped" in order to create a permanent electrical field. When sunlight hits the cell, it liberates electrons and those electrons are attracted to the positive side of the electrical field. The cell is wired with conductors and - as the freed electrons build pressure - they flow to the wire and ultimately power the load the circuit is connected to.

As you might imagine, there were a lot of questions about this process and the class bogged down quite a bit on this subject. Eventually, we began to discuss maximum power points, voltage open circuit amount and short circuit amounts (measured in amps). It's critical to know the boundaries of any circuit, in order to properly size inverters and wires.

Next up is a solar tour of homes on Saturday morning, which should be pretty neat. I'll be sure to take some photos.

Posted by tom c. at 1:27 PM | Permalink

Notes from class 2 of Introduction to Solar Energy Systems. With introductions and other requisite class 1 dealings behind us, the class last Thursday (1/18) switched the course into a new gear and we covered ground focused on solar energy fundamentals and basic electricity.

Solar Fundamentals
When you start to think about solar energy, you have to think about units of measure, because you are ultimately trying to figure out how much power a system has the potential to produce. The class discussed radiant energy, irradiance and irradiation. Irradiance basically refers to the measure of the rate of solar radiation falling on an area. Measured in watts per square meter, this is - for lack of a better phrase - intensity of the sun. Irradiation is subtly different from irradiance, in that it measures the amount of solar energy impacting an area over time. This is measured in kilowatt hours per square meter.

There are, of course, different types of solar radiation. These include direct, diffused (through clouds, for example) and reflected (off water or snow). Further, there are a variety of factors that affect solar radiation, including the angle of incident, cloud cover, snow, rain, fog, air pollution, reflective materials and more.

When you begin to consider the amount of power a solar system will produce, you have to calculate the number of peak sun hours available in a day at a given location at a given time of the year. Because of earth's orbit, the sun is not always located at the same altitude year round. In summer, the sun is much higher above the horizon - around 70 degrees above horizon. In the winter, however, the sun is only around 30 degrees above horizon. The difference in altitude angle is important because a lower sun will often create more potential shading at the solar site. In addition, the height of the sun is important in order to properly pitch the solar panels and increase irradiance.

The instructors use a handy device called a solar pathfinder to analyze the sun's position and path at a site. The pathfinder helps to identify potential shading spots on the roof throughout the year.

We also discussed magnetic declination, which is somewhat confusing to a navigational newbie like myself. In short, the "true north" pole is not the same as the magnetic north pole (which a compass will point to). In order to properly align solar panels (they should ideally face due south), the solar installer must identify true south prior to using the solar pathfinder or reading charts. In Albany, true south is 14 degrees west of compass south.

Basic Electricity
I know next to nothing about electricity, so I was listening with rapt attention to this part of class 2. We discussed power, voltage, amps, current, resistance and Ohm's law.

I'll spare the gory details here, because I'm not 100% sure I would be telling the truth. For more info, just head to Wikipedia.

We also discussed parallel versus series circuits. We did some wiring of small solar panels to test changes in volts and amps. All in all, it was a good intro to basic electricity.

Notes on Class 1 available here

Posted by tom c. at 11:45 AM | Permalink

Last night, I attended the first class of the solar energy course I am taking at Hudson Valley Community College. I plan to chronicle progress of the 6 week course here at Save and Conserve.

The course instructors are the two principals who own Renewable Power Systems, an Albany-area PV design and installation company. There are about a dozen people taking the course and many of them are currently working as contractors/electricians.

Having run Renewable Power Systems for over 3 years, it goes without saying that the owners know their stuff; it looks like I'll learn a tremendous amount about how to size, design and install a residential solar energy system.

Some interesting notes from class 1 last night:

• Beginning in 2011 in California, home builders will be required by law to offer solar power as an option to buyers of new homes in developments of 50 homes or more.
• The most attractive thing about solar energy is that it fixes the future cost of electricity production.
• Most of the silicon supply is in the US, but most silicon-based solar panels ship overseas (especially to Germany and Japan, which both heavily subsidize solar).
• The average size of a residential solar system in California is 2 - 3kw compared to 4 - 6kw in New York. This is due mainly to the number of peak sunlight hours available per day.
• In New York, the legislature has provided virtually zero incentive for businesses to install commercial solar energy systems. New York only allows Net Metering (or feeding unused electricity on site back into the grid) for solar systems that are 10kw or less in size. This is insanity and, as another class member asked last night, makes you wonder if the utilities and associated lobbyists have undermined commercial solar in NY state.

Posted by tom c. at 2:35 PM | Permalink