RENEWABLE ENERGY | Key Considerations for an Off-grid Solar Energy System

Joe Lade of earthRight builds a solar panel pole mount on the ground prior to hoisting it to a pole and attaching the panels. Photo: Ron Young

Joe Lade of earthRight builds a solar panel pole mount on the ground prior to hoisting it to a pole and attaching the panels. Photo: Ron Young

By Ron Young –

Yogi Berra said it best, “If you don’t know where you are going you will wind up somewhere else.”

If you are considering a solar energy system for your off grid home, ranch, or seasonal residence here are a few pointers to help you through the decision making process.

 

Solar Availability

To determine what the solar availability is at your location there are a few things to consider. First of all you need a good south-facing view of the sun through the hours of 11 a.m. – 3 p.m. at a very minimum. Solar radiation is roughly three times stronger through the middle part of the day than it is the rest of the day.

The ideal orientation of solar panels is true south not magnetic south. True south is the geographic location of the South Pole and is about 17 degrees east of magnetic south in the Cariboo.

Some types of panels such as solar hot water heating panels are less sensitive to precise orientation due to larger surface area, but where possible you should try to be as accurate as possible to get the most from your investment. If you go to www.solareagle.com you can click on a link to get a free online estimate of the solar potential of your site. We also do site visits and use tools such as our Solar Pathfinder that are helpful with particularly difficult sites involving buildings, hills, and trees. It can give us a precise estimate of your solar potential year round.

earthRight uses a Solar Pathfinder to map the solar horizon at a site. This device gives an accurate representation of what obstacles are in the path of the sun on an hour by hour basis each season of the year. The reflections in the dome are plotted to a computer program that calculates the potential energy available. Photo: Ron Young

earthRight uses a Solar Pathfinder to map the solar horizon at a site. This device gives an accurate representation of what obstacles are in the path of the sun on an hour by hour basis each season of the year. The reflections in the dome are plotted to a computer program that calculates the potential energy available. Photo: Ron Young

Types of Solar Panel Mounting

There are basically three types of common solar panel mounting systems: roof, ground, and pole. Each has its pros and cons.

Roof Mounts

If you have a south-facing roof and are considering a roof mount you will want to make sure the roof has the structural integrity to withstand the added weight of the solar panels and racking as well as any added stress that can be introduced by wind. Wind is usually a minimal consideration if you are mounting the panels flat, but if you are considering an elevated mount then wind is a big consideration.

The type and age of the roof is probably the biggest deciding factor. If you have composite shingles that need to be replaced eventually, then factor in the added cost of removing the solar panels when the roof needs re-shingling. A metal roof presents fewer complications.

Ground Mounts

Ground mounts are often the least expensive method when all is said and done but they need to be in a safe location away from vehicles, livestock, wildlife, and humans and be sufficiently elevated to be clear of any winter snow pack. Although easy to clean and adjust they are also more vulnerable to theft and vandalism. Most ground mounts can be adjusted seasonally for best performance.

Pole Mounts

While pole mounts are the most expensive option they are also the most versatile.

A pole mount can easily be adjusted to optimize energy production from winter to summer. I adjust my solar panels twice a year, once in the spring and once in the fall, which involves loosening a few bolts and rotating the entire array (assembly) so it has the most perpendicular angle to the sun.

If you have a seasonal residence you can leave your PV (solar) panels hooked up to the batteries through the winter off-season to keep them charged. You will want to put your panels as vertical as possible in the winter to allow for snow shedding because once PV panels are covered with snow they pretty much stop working until the snow melts or falls off. If the PV stops working then the batteries slowly self discharge and can easily freeze.

Another advantage of a pole mount is the ability to place the pole where it is most aesthetically pleasing, doesn’t block your view, and is in the most appropriate location for sun. You may not want to cut the trees down around your dream cottage just to accommodate solar panels but if you can mount them on a pole in a more appropriate nearby location that is a desirable outcome.

Pole mounts need to be mounted on steel poles that are set into concrete in the ground sufficiently deep enough, based on soil type, to withstand high winds.

 

Length of Wire Run

The length of wire (conductor) from the solar panels to the charge controller, typically called the home-run wire, used to be of greater importance a few years ago when solar panels were low voltage and the charge controllers were either 12, 24, or 48v.

A conductor has to be sufficiently large enough to minimize voltage drop and home-run wire in lower voltage systems will get quite large and expensive with greater length. Nowadays most modern solar panels are higher voltage and can be strung together in series for up to 250 volts keeping the home-run wire manageably small and inexpensive. However, there are still limitations; once you get over about 60 meters, wire costs start becoming a significant percentage of system cost.

 

Charge Controller

A charge controller is the device that monitors and controls the incoming current from the solar panels and sends that regulated current to charge the batteries. Controllers come in a lot of different sizes and types and you will want to make your selection carefully based on both present and anticipated future needs.

Simple installations with one or two low voltage panels will often use what is called a pulse width modulated (PWM) controller. These controllers are reasonably efficient and inexpensive. However in a medium size system of two or more panels, if you want to realize the many benefits of modern technology you should consider the more expensive maximum power point tracking (MPPT) controller.

MPPT controllers allow you to string (connect) up to six panels together in series. When you string panels together you increase the total voltage but also increase he system efficiency. MPPT controllers can take a high voltage of up to 250 volts down to your battery voltage of 12, 24, or 48 volts automatically. As previously mentioned, this configuration allows you to keep the home-run conductor small and keep the cost down while getting the added benefit of being able to locate your PV array in the most convenient location.

A further benefit of MPPT controllers is that they incorporate technology that uses more of the available solar energy than their earlier PWM counterparts. You will see increases as high as 30% more power from identical solar arrays and over time that easily pays for the added cost of the MPPT controller.

Controllers are rated in amps and the rating determines how many panels you can connect. You can buy a controller just the right size for the number of panels you have but if you think you might want to add to the array at a later date then it’s wise to oversize the controller.

It is also possible to connect more than one controller to a single set of batteries allowing even more scalability over time. Advanced controllers like the Midnite Solar Classic series have the ability to ‘talk’ to each other and co-ordinate their charging programs. The Midnite controllers can also be updated online with the latest software upgrade, which is always free.

I’ve come to the end of the allotted space for this article and still haven’t covered some major components such as batteries and inverters so they will have wait for an upcoming column. As Yogi used to say, “You give 100 percent in the first half of the game and if that isn’t enough, in the second half you give what’s left.”

 

Ron Young is a renewable energy professional who designs and sells solar, wind, and micro-hydro systems. He operates the earthRight store in Williams Lake, BC and can be reached at info@solareagle.com.         

Copyright Ron Young 2016

 

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