The (Gory) Solar Details - AKA Solar Power 101

Several people contacted me with requests for details and more information about our solar power installation, so I asked Dennis to write a series with the nitty-gritty.  Here is his first installment of installment:

How do you move from being entirely ignorant in an area, to being able to design and implement infrastructure that will support your daily life?  There is no short answer, but people take up the challenge when they move from a small city with municipally provided electricity and water to living off-grid where you have to be the utility company.

We are building off-grid in remote Southern Belize and have no access to municipally provided electric services.  The availability of electricity will be highly dependent on a solar power system, so big errors cannot be tolerated.  While we do have a small diesel generator on site, and batteries that were charged by it, this was not truly optimal since it is noisy, messy (nothing like diesel soot to make you feel like you need to be steam cleaned), and expensive to maintain and operate.  We were spending about US $500 a month to generate electricity, as well as paying for very costly generator repairs.  Rewinding a generator stator and rotor can set you back well over US$1000 here in Belize.  But the biggest issues from my perspective are that early on in the process you do not even know what you need to know to be successful, and you do not really know where to even find that information, if you even knew what it was! It is enough to make your head spin (click here for music).

In 2010, while still living in the US, I started looking at what it would take to get a solar installation in place at the vacation cabana we had already built in Belize.   I was immediately overwhelmed by the magnitude of the task, especially the details that are needed to make a system work properly.  In the USA, there would be no problem having a solar installer do all of this for you.  In Belize, especially 5 years ago, there might have been a dozen potential installers in the entire country and perhaps only 3 of those had meaningful credentials or experience.

Neither Wilma nor I have any background in the fields of renewable/solar energy; our expertise lies in the realms of biological and clinical sciences.  But we read, and ask questions of people who have these systems, do calculations, change and refine plans, and then talk to the experts who install solar systems.  If you can remember the simple math you learned probably by the 5^th grade, are willing to read, be puzzled, feel foolish/stupid on occasion, but persist, it can be done.  Oh, yes I almost forgot.  You do need to remember a little trigonometry to calculate angles for orienting the roof on which solar panels are attached (uhoh!).  But let’s start at the beginning.

Where Do You Place the Solar Panels? The very first step is to determine how to site your solar panels. We had decided that we were going to mount them on the roof to minimize the potential for them walking away in the middle of the night, which has happened for some ground-mounted panels in Belize, and also to minimize shading of the solar cells that deteriorates the solar efficiency of the panels.

There is a fair amount of academic research on how to situate solar panels for optimal performance, and to how to ascertain what degradation might occur with various panel orientations.  Here is one paper I found online early on and though the reading was a bit “thick”, with perseverance I did get some useful information from it:

Mondol, J.D., Yohanis, Y.G., and Norton, B. The impact of array inclination and orientation on the performance of a grid-connected photovoltaic system. Renewable Energy  vol 32 (2007) pp 118–140.  You can obtain a copy online from Science Direct.

In the Northern Hemisphere, optimum solar collection is obtained by orienting the solar panels facing “True South”, or at an “azimuth of 180 degrees”.  Even the language is a bit obscure to those not in this field.  In 2006, the builder of our vacation cabana had oriented the roof ridgeline such that it was about 25 to 30 degrees off of optimum.  Not only was it facing the wrong direction, it was also not structurally sound enough to support the weigh of the panels in their frames plus personnel on the roof for installation and maintenance.  Since we had planned to build an addition to the vacation cabana for visiting friends and family, we decided to design the addition with roof orientation and structural integrity specifically for solar installation. Using a compass, we laid out the plan so that the roof ridgeline ran East/West giving us a roof surface for installing the panels was oriented to True South.  I don’t believe building a new house is included normally in one’s solar budget calculations, but that s the route we chose to go.

The Truth about True South.   True South refers to the location of the geographic South Pole, which is not the same as Magnetic South. True South will be where the sun is the highest in the sky during the day and you want to optimize the orientation of the solar panels for this. 

I know what you are thinking!  He said he used a compass to establish True South, is he clueless?  Well maybe so, but not about this - keep reading.  The compass established where Magnetic South is.  But True South will be off the Magnetic South heading, sometimes quite a bit, depending on where you are on earth. Click here for a longer online article for determining “magnetic declination”, the angle difference between Magnetic North and True North and using a compass to assess the angle difference between these, and consequently between Magnetic and True South, which is what you really want to know.

There can be a fairly large angular difference between True and Magnetic South in some parts of the World, which can undermine your solar efficiency.  Luckily for us, in Monkey River Village, Belize, True South is not even a full degree off of Magnetic South.  In fact, just 3 miles to the east of us, there is no difference between True South and Magnetic South.  So we could (and did!) just use a compass to find Magnetic South and used that without having to go through any complex calculations.  How did I know?  I looked it up online at this site.  In San Jose, California; Livermore, Colorado; and Asheville, North Carolina (the locations where where Wilma’s siblings reside), the respective Magnetic declinations are +13° 37', +8° 41', and -6° 31', pretty large differences.  Other examples are London (-0° 49'), Seville (-1° 37'), Kuala Lumpur (-0° 1'), Hawaii (+9° 28').  Now you know. 

But if the difference is small (i.e. Kuala Lumpur and Belize), then don’t sweat the small stuff when there is plenty of big stuff to sweat!  But how do you know when starting out what IS the small stuff?  And how quickly does the small stuff add up to become something big?  Hmmm?

From the website listed above.  Check out your location by clicking here.

Then it is necessary to decide on tilt, or inclination, of the solar panels relative to the horizon.  A rule of thumb is to tilt the panels by the degree of the latitude and adding 15-16 degrees for winter and subtracting 15-16 degrees for summer. This takes into account the height of the sun in the sky:  lower in winter and higher in summer.  This improves collection of solar energy and reduces loss of sunlight from reflection off the glass of the solar panel. This was incorporated into the roof design for the addition.  Since we are at roughly 16 degrees North Latitude, it would mean a tilt from 0 degrees in the summer to 32 degrees in the winter.  We decided to maintain the tilt at 16 degrees latitude where we are and added 16 degrees to maximize collection of the winter sun when the day length is shorter.  Therefore, we have the roof set at 32 degrees and the panels are firmly fixed in an aluminum rack attached directly to the roof.  We decide not to incorporate any means of changing the angle for summer vs. winter sun in order to keep as low a profile as possible.  We think keeping the panels nearly flush with the roof may be a big deal during a hurricane or tropical storm.  As an aside, Category 4 Hurricane Iris made landfall at Monkey River Village in 2001, utterly destroying the village and the two establishments in Englishtown. 

At 32 degrees the tilt of the panels is well optimized for the Winter Solstice!  BTW, this is where you need to recall that trig in order to calculate the height of the roof with a known span (from ridgeline to exterior wall) in order to get the desired 32-degree angle. 

For a brief moment I wished that I had paid a bit more attention in the boring trig classes 50+ years ago.  But then I come back to my senses.  After all, there are kingfishers, pelicans, orioles and hummingbirds to watch, orchids in bloom, and the occasional manatee and iguana to view!  I know - I'll let Wilma figure it out.

There - that looks about right.

At this point, we had enough information to design our addition and commence building.  The construction started in mid-year 2013 and the cabana was ready for solar installation in May 2015; 2 years including time off during the extensive rainy seasons.  Two years during which to learn how to calculate how much electricity we will need, how to size the battery bank, and how many solar panels we will need; two years during which to separate the small stuff from the big stuff.  That’s what will be up next in this series.

Oh, there will be a quiz next week.