Monthly Archives: July 2015

How Solar Works

This is a somewhat technical description of how solar panels work to power your house.  If you would rather just read about how I got solar panels for my house instead of how solar panels work, you should head over and read my Solar Energy Spill post.

Every good description about how solar works starts with the sun.  Since the idea is to take energy the sun is pouring out and to claim some of it as your own, it stands to reason that the sun is a good place to start.  First you must consider that the sun does not just follow the exact same line through the sky every day.  In fact, it doesn’t even follow the same line through the sky based on where on Earth you are watching it from.  Add to that the tidbit about how even from the same place (your house for example) the sun traces a different path depending on what time of year it is.  All this means that there is a little bit of math involved in making sure your solar panels are pointing the right way to capture as much sun as possible.

First, imagine the sun lives in a specific direction from the Earth.  (Which of course it does, so it shouldn’t be hard to imagine.)  Now add to that mental picture that the sun is more or less actually over the equator.  That means if you live in the northern hemisphere, the sun doesn’t actually travel directly over your head during the day.  Sure, it may seem that way, and expressions like “high noon” seem to back that up, but it actually travels through the sky to the south of your house.  This in turn means that you want to put solar panels on something that faces south.

So now we’ve established that the northern hemisphere means south facing panels, but how much south?  I mean the sun is definitely to the south, but it’s also definitely way up in the sky.  This means the angle you point your panels to the south matters.  Worse, there is a difference between “true south” and “magnetic south”.  Where I live, the angle of my roof works very well, but in other places it is better to put them on funny brackets that make them point at a better angle.  As it turns out there is a name for this angle.  It’s simply called your latitude.

If you think about this whole equator, sun up in the sky, hemisphere thing you can draw a couple of cool conclusions.  At the equator, your latitude is 0 degrees.  That means the sun travels almost directly over your house, which means you want your panels to point straight up.  Which makes the best possible roof angle perfectly flat (parallel to the ground).  A flat roof has an angle of 0 degrees.  Look at that, 0 degrees latitude, 0 degrees roof angle, 0 for both, so far this theory holds.  Now imagine the other extreme and pretend you live on the north pole.  For you, the sun is always extremely in the south since the sun is following a line all the way down by the equator.  In fact, it’s so far to the south that the best possible angle for your panels isn’t on your roof at all, but rather on your south facing walls.  These walls are 90 degrees toward the south, your latitude is 90 degrees too, so the theory still holds.

Finally we examine the most likely of cases.  Otherwise known as your case.  In general you aren’t very likely to be living directly on the equator (though certainly possible) and you really, really aren’t likely to be living on the north pole.  That means you live at a latitude of somewhere between 0 degrees and 90 degrees.  For me, I live at a latitude of roughly 41.4 degrees.  That means that if I had a perfectly south facing roof, the angle needed to point directly at the sun at its highest point in the sky would also be 41.4 degrees.  It doesn’t have to be perfect, but the closer you get the better your panels will do.

Here is a picture to demonstrate this concept.  It has little houses with solar panels on them at the places we talked about.  Notice that the house on the equator has the solar panel facing straight up, the north pole house has it facing sideways, and the house in the middle the solar panel lines up with the angle of the roof.

solar_angle

 

So now that we have a pretty solid grasp on how to capture the most possible sunlight, it’s time to turn that energy into something useful.  Solar panels produce direct current (DC) power.  Your house runs on alternating current (AC) power.  These two concepts of power are not compatible.  If you wanted to power something that uses batteries like a flashlight or a cell phone the solar panels are already correct.  If you want to power your refrigerator or a vacuum cleaner, you’re going to need to convert that DC power into AC power first.  Fortunately a device that can do that already exists.  It’s called an inverter.

There are little inverters available for use in your car or RV.  Those take the DC power from your car’s battery and turn it into AC for your RV’s microwave or your shaver.  Of course you’re probably going to need a much larger one to convert enough power to run your whole house.  Some houses use so much power that they need multiple inverters to handle the load.

Now we have power from the sun conveniently converted into that juice your house needs.  What happens if you make too much power?  What happens at night when you aren’t making any power at all?  These situations are typically covered by your electric company in the form of a device called a net meter.  It’s just like the meter everyone else has except it can go backwards too.  Normal meters “count” the power as your house uses it.  Modern power meters don’t typically have an actual spinning wheel anymore but they liked the concept so much they imitated it digitally in the display.  If you use a small amount of power the wheel spins forward slowly and if you use a lot it spins quickly.  A net meter does the same job, except if you are actually producing more power than you are using, the extra makes the meter spin backwards.

Extra power is essentially sold to the electric company and provides you with a “bank” of kilowatt-hours (kWh).  Lets assume you have no extra power in your bank and walk through a hypothetical sunny day.  The sun is not up all the time so you will use some power before the sun comes up.  Let’s say you use 5 kWh during that time.  Now your meter shows that you’ve used 5 kWh from the electrical grid (which i will just call “the grid” going forward).  This is the same way it works if you don’t have solar.  Then the sun comes up and with a properly sized solar system, you start making power faster than you are using it.  This powers your house completely and the extra is sold to the electric company.  By the time the sun is setting and your solar panels are turning off, you will have built up some extra power in your bank.  Let’s say that during the day you made 30 kWh and used 10 kWh more throughout the day.  That means you gave 20 kWh back to the grid.  Now because your meter can go backwards it now shows -15 kWh.  That means you can use 15 kWh throughout the night for free.  How cool is that?

Here is a picture that shows the typical layout of all of the parts of a solar system in your house.

solar_power_layout

So that’s the basics of how solar panels work.  In general, the more power you make and the less power you use the bigger your bank will be with the electric company.  That doesn’t mean you should put as many panels as possible on your house.  Panels are expensive and the more of them you have the longer it will take to recover their cost with the power savings they provide.  Your target should be to cover 100% of your power needs in a typical year.  More than that tends to be a waste of money on panels and less than that tends to mean you haven’t completely eliminated your electric bill.  Don’t worry though, your solar company will walk you through all of that.

 

Solar Energy Spill

There is an expression out there that goes something like “When there is a solar energy spill, it’s just called a nice day.”  This is in obvious contrast to oil spills (killing wild life and making a general mess of things) or nuclear melt downs (killing everything and poisoning entire areas for centuries).  At this point I suspect I may be a bit biased, but no matter how you look at it a nice day beats ruining things every time.

This is the story of how and why I got solar panels on my house.  It’s been something I’d considered for years and years and never did anything about.  Let’s face the truth here, it’s a lot of work, a lot of research and a lot of money.  I’m all for saving the environment where I can, but solar panels are super expensive and a bit over the top for even the most tree-hugging of folks.

A few years back, my dad got solar panels on his house.  He explained the process and the costs to me and I started thinking about it all over again.  And I didn’t go through with it again.  Even with all of the potential government rebates and potential savings on my electric bill, I was still scared to consider the expensive modification to my house that is solar panels.  After the following years of my dad enjoying his panels and his lower electric bills, I had enough evidence that they were something to seriously consider.

That started the official research phase for getting solar panels.  I started researching everything I could find.  First I looked at government rebates.  The federal government had a great plan where I would get 30% of the cost of the system back as a tax credit.  (Not to be confused with a tax deduction.)  This was a good start because it essentially means that I would pay 30% less thanks to that program.  Then I started looking into whether or not Connecticut would help out too.  As it turns out, they will, but in a vastly less impressive way than my dad enjoyed in New York.  (He got a system that was 40% bigger than mine and I paid twice as much as him.  Most of that difference was the size of the state rebate programs.)

Once I figured out how much I could save, the next part was to figure out how much it would cost.  This started me down the road of researching three separate solar companies.  I chose a local guy, the company my dad went with, and SolarCity.  This spawned a lot of research into how solar stuff works.  It would obviously be tricky to understand the various offerings of each solar company if I didn’t understand what they were offering in the first place.  As it turns out, there was a lot I already understood about solar, but there are a lot of ways to do each individual part, and the differences between those ways were what I didn’t fully understand.  To read up on what makes up a solar system and how it all works together, head over to my How Solar Works post.  It’s a bit too long to include here.

The first differences I started to notice between the installers was their overall responsiveness to my questions and how they dealt with me on the phone.  I suppose that’s not exactly a part of how various solar systems differ, but let’s face the truth here these are people I am going to have to deal with a lot.  If your installer can’t provide you with accurate answers or doesn’t understand your questions you may want to look elsewhere.  Even if you only deal with your solar installer for the amount of time involved in actually getting the system installed, it’ll still be a rather long time.  Best case you have a reasonably long warranty period and the company you deal with continues to exist for the whole time, so you should definitely trust them and enjoy dealing with them.

After installers I started asking about the panels themselves.  You may simply assume that any roof covered in pretty bluish black solar panels has the same basic thing up there but in reality not all panels are created equal.  They have different efficiency ratings (how much of the sun they can capture and turn into electricity, typically expressed as a percentage like 12% or 18%), different degrade rates (all panels get less awesome over time, the slower they do so the better, also typically expressed as a percentage but more like 1.0%/year).  Beyond that they have factoids about which country they were made in, how many watts they can put out, and how they can be mounted to your house.  All of these things should be carefully considered too.

With loads of answers from solar installers that clearly had no idea what they were talking about when I was asking the harder questions, I moved on to the different arrangements of inverters.  After all, solar power for your house wouldn’t be of much use if your house can’t use that power.  The three major arrangements I discovered for inverters were single inverter, micro-inverters, and single inverter with micro-controllers.

Almost no one uses straight up single inverter any more because they are a disaster with things like shadows and dirt.  Panels are typically wired in series and the whole group of panels in a “string” only operates at the level of the lowest producing panel.  For example, let’s say you have 12 panels in a string and they are producing 250 watts each (3000 watts total).  If a shadow from your chimney covers one panel and drops its output to 100 watts, all 11 remaining panels also drop to 100 watts (1200 watts total).  That’s a huge loss considering the shadow is only over one panel.

Realizing this is a horrible arrangement, the solar industry came up with the idea of micro-inverters.  Instead of one large inverter running your 12 panels in the example above, now you have a small inverter for every single panel (12 inverters total).  Now that same shadow comes along and your one panel drops to 100 watts just like before.  This time the other 11 panels continue to operate at 250 watts because they aren’t being dragged down by the under performing panel in the shadow.  This means your 3000 watt system drops to a rather comfortable 2850 watts.  This is obviously vastly superior performance to a single inverter system.

They realized that having one inverter for every panel meant that maintenance has the potential to be a bit of a pain, and that wiring all of your panels that way meant a bit more work to install as well.  That is not to say that micro-inverters were a bad idea.  They do keep a lot more of your panels working when one of them is having trouble, and that is really the goal.  Then there was another idea.  With a single inverter and small controllers for each panel a similar result can be achieved as with micro-inverters, but with the maintenance and installation complexity reduced back down to where it was before.  The output of this arrangement with the same example as before would be the same 2850 watts as the micro-inverters produced.  Overall, this is a win in my book.

Recently the added complexity of battery units attached to solar systems became something to consider.  It is not however worth it in my opinion for several reasons.  You don’t need it, it would have pretty limited uses, it’s expensive, and there are cheaper options.

You don’t need it because your extra solar power typically goes to the power company through your net meter in the form of a kilowatt-hour (kWh) bank.  That means you are essentially using the electric company as a free battery, so why buy a battery that isn’t free?

Next, if you have a battery you can theoretically continue to use your solar panels even during a power failure.  (Which is not the case in a normal system because you don’t want your solar panels electrocuting people working on power lines that they think have no power in them.)  So in this case, the battery becomes a sort of generator for your house during power failures and would theoretically allow you to continue to use your solar panels in the case of a power failure.

The problem with this battery as a generator scenario is that a battery that can power your house for 12 to 24 hours (obviously depending on use) will run you about $7000.  A gas generator that will do the same job for as long as you have fuel available will run you about $800.  Sure you may have less maintenance on a battery and you may not have fuel handy when you need it for a gas generator, but how often do you really lose power?  How many poorly maintained generators can you buy before you’ve covered the cost of a single battery?

So with all of these tidbits considered and researched it was time to get solar for myself.  This story continues with the actual story of my own installation with SolarCity in the post From Zero to Solar (post is coming soon, not quite ready yet).