SolarUnplugged Direction

It’s been a while since my last post and I have been reflecting a lot on the direction of SolarUnplugged.  I originally set out to start a resource for the homeowner to learn the ins and outs of solar and be more informed.  I have spent too many years in solar as a professional and have seen too many undesirable things happen.  After a recent chat with a colleague of mine and the decline of incentives, it became clear that I need to re-engage in this pursuit and put more time in it as well.

With all the changes going on in the industry with tariffs and tax credits, it would s eem that solar is doomed.  Well, at least that is what most people would want us to think.  Sure, the incentives were great things.  They drove down the cost of solar and made it more affordable for everyone.  But those same incentives did something else- they brought more greed and bad practices as well.  I hate to say that, but it’s true.  The incentives drove a lot of companies to enter the arena who weren’t necessarily the best companies.  And then the market became quickly saturated and quality went out the window.

When the incentives came, people left the realm of energy conservation and went to the highest maximum array they could put on their house.  Please don’t get me wrong, it was a strategy that worked for the moment.  But in the long term, I am not here to teach that methodology.  My goal is to show you how to optimize your house and save as much energy and money as possible first.  Then, I can show you how to design your solar array to match your new needs.  Trust me when I say, there are ways to make all of this more affordable without the incentives.  It just takes a little bit more time.  But the result is you being more sustainable and freer. 

So why am I sharing all of this in a blog post, because I think the change is a good thing in the long run.  It will shake out a lot of unscrupulous companies and already has.  The change will also force the industry to re-employ best practices to be competitive once again.  Sometimes, incentives can cause some real negative side effects as well.

With all that said, my next blog posts are going to start really drilling down into proper system design and practices.  I plan on sharing the processes I use to develop and design the correct system size and types for my clients.  Issue like shading strategies, energy consumption/usage, site analysis and much more will be covered.  There are so many ways in which you can really optimize a system that just isn’t discussed anymore.  I also plan on speckling in some overall sustainability strategies as well. 

Bypass Diodes

Imagine you are driving down the highway.  All the sudden, all traffic comes to a stop.  There is an accident ahead.  Luckily, there is a secondary road you can take and keep moving forward.  Without this secondary pathway, you would be stuck on the highway.  Solar modules function in the same way as above.  If there is even a little bit of shade, the flow of electricity is blocked.  By adding bypass diodes, a solar module now has multiple pathways.  This allows for the electricity to flow even if there is a blockage.

Typical solar modules will have at least three bypass diodes.  These three diodes separate the solar module into three sections.  In other words, your solar module has three pathways for electrical production.  If one section of the module is shaded from the Sun, the other two sections will still produce electricity.  This does mean the module will be reduced to 2/3 of its normal production.  However, without the bypass diodes, the production would be zero.

The question now is how these sections are created.  If you look at your solar module, you will notice silver tabs at the bottom.  And typically, there will be three separate silver tabs.  This tells you how the module is divided into sections (See figure 1).  Because of the bypass diodes, each of these sections can function independently of the other two.

What does this mean for your solar array?  If you have a location for your solar array that has some shading issues, you can still optimize that array.  Let us look at two examples:

Figure 1

Example one:  You have morning shade that affects the Eastern edge of your array.

In this example, it would make sense to mount your modules in portrait.  This is just like when you print a piece of paper.  The longer side of the module faces North-South.  By mounting the solar module this way, we are allowing the bypass diode to do its work.  If the Eastern edge of the array is shaded, we may lose a few sections in our modules, but the remaining sections will still produce electricity. 

Example two:  You have morning shade that will cover the bottom edge of the array.

In this example, if we mounted our array in portrait like above, we would have zero production.  This is because we have blocked every bypass diode.  Mounting the modules in landscape would be a better idea.  By doing this, you will lose roughly 1/3 of your electrical production during the shade.  But the bypass diodes still work, and you get 2/3 production.

Remember, when it comes to off-grid arrays, our goal is maximum production.  This allows us to have a more reliable off-grid array.  And that reliability will also translate into a longer lasting system.

Deficit Cycling equals Dead Batteries

In the last article, we mentioned the term deficit cycling.  But what is deficit cycling?  And more important, how does it affect you and your solar array?

Deficit cycling refers to a situation where the consumption of the batteries stored energy exceeds the energy production of the solar module.  This will cause the batteries capacity to slowly drain down towards zero.  Once that happens, you have a dead battery on your hands.

Here is how it works.  When you first get your battery, it is boosted to full capacity.  Let’s say this battery capacity is 200Ah for this example.  At a 50% Depth of Discharge, your available battery capacity for use is 100Ah.  With that in mind, you go ahead and use 100Ah.  Now, lets assume your solar module can only replace 90Ah worth of energy in a day.  This leaves your battery at a 10% deficit for that day (based on Depth of Discharge only).  The next day, you use 100Ah of battery capacity.  Again, the solar module can only replace 90Ah.  At the end of the day, your battery is at a 20% deficit.  In two more cycles, your batteries will be at a full 40% deficit.  A few more beyond that and the battery will begin to drastically reduce in performance and reliability.

An easy way to think about deficit cycling is like your bank account.  If you withdraw more funds than you are putting in, eventually you will have a zero balance.  The problem with batteries is that a zero balance means you finished off the battery and will need a new one.