The Solar array collects the energy from the sun and converts it to electricity.
While the cost of the modules used to be the major portion of an "Off Grid" Solar Power System, with the module prices so low now, the other components now account for the majority of the costs.
Generally, the modules are either roof or ground mounted.
Ground mounted arrays have the following advantages
- Installation is generally easier and safer (safety regulations are making roof mounted installations quite expensive)
- Snow is easily cleared off the modules
- There is no extra roof engineering required. (roof mounted installations are getting to be much more the subject of structural requirements)
- Typical "Off Grid" size arrays are much easier to place on the ground rather than the limited space on a roof.
- The combiner box can be in a readily accessible place. In our climate, a combiner on the roof may not be accessible for half of the year which can be a real problem, especially with the high tech combiner boxes coming out that may need service or resetting of circuit breakers and disconnects.
Type of Ground Mounting
When choosing the type of ground mount, consider that the array is going to be there for 40 + years. The array should have a support system that will not move with the shifting ground and frost heaving. The best system uses screw piles which go below the frost level. Avoid really long runs that are tied together unless the whole array can expand and contract with the changing temperatures. Also avoid systems that are just placed on top of the ground or barely below ground, as they will move over time and cause damage to the array. While it is tempting from an initial cost perspective to cheap out, it will be more expensive in the long run when the array is damaged and needs to be repaired and done properly. It may also be worthwhile to consider our container mounted systems as any movement of the ground will not affect the array as there is no relative movement between the modules.
The bottom edge of the array should be high enough off the ground so that snow will not build up on the bottom of the solar modules. This distance will vary with the installed location. Typically 2 to 3 feet is a good elevation. This also applies to tilted roof mounted systems.
This is the proper type of screw anchor to use. The "screw" at the bottom is below the frost line, which then anchors it properly and provides a good supporting base. Standard pipe just put into the ground or embedded in concrete is subject to being moved by the ground, so should not be used for these applications.
One of the trends in the industry and by consumers as well for that matter is trying to reduce the cost to an absolute minimum. While keeping costs down is good, this has led to the use of support systems that can easily lead to failure and the associated high costs of replacement with a proper system. A recent article indicated that the majority of Solar related claims were related to mounting system failures. Remember as well, that even a well-engineered system can fail, if even once in its lifetime, the design parameters are exceeded. Also, fatigue and corrosion play a large factor because of the long lifespan of the system. Many mounting systems that are engineered are actually quite flimsy and the fine print needs to be read. Most are only designed for a mounting angle of 60 degrees or less. This is not appropriate for "Off Grid" systems at our latitude. We need to be mounting the solar panels at 65 to 70 degrees to maximize the winter production. When we have enough solar power in the winter, the summer is not problem, even if the summer angle is not ideal. The following diagram shows the angles with blue being 65 degrees and grey being 70 degrees.
The question frequently comes up on whether to use a solar tracker. Off Grid systems at our latitude generally are better off having a fixed, larger system. First of all, a dual axis tracker only provides an extra 15% of energy in December, which is what we size a system for. A tracker is expensive and a mechanical device, so subject to problems. It is much better to invest the money in a larger fixed array. For the same amount of money, the amount of energy that a larger fixed array produces is much more than an array on a tracker. Also, for the size of array that is typically required for Off Grid homes, it would take more than one tracker. They would need to be spaced apart enough to prevent shading of adjacent modules.
What is the best angle to have the Solar Array at for an Off Grid system?
To answer this question, we need to consider the following:
- When do we need most of the power?
- When do we need the least amount of power?
In an Off Grid situation, normally, we use the most power from November to January, so that is what we would base the angle on. The second item to look at is not to have the angle so steep, so as to lose too much in the summer, so let's look at an output comparison at various angles.
So as we look at this comparison, we can eliminate the 2 extremes right away, the 60 degree curve is too little when we need it, and the 80 Degree is too little in the summer. So then, which of the remaining do we choose? There is very little difference in the winter between the 70 and 75 degree curves, but the summer suffers quite a bit with the 75 degree mounting, so let's eliminate the 75 degree mounting as an option. That leaves us with the 65 and 70 degree options. The 70 degree option would give us a bit more in the winter and likely enough in the summer, so somewhere in between 65 and 70 would give the best results. Traditionally, latitude plus 15 degrees has been the standard. So, since this was a calculation for Calgary, it would be 51 degrees plus 15 which would call for a 66 degree mounting angle, which would appear to be about right in looking at the chart.
Grid interactive arrays would yield the best output at about 3 degrees less than latitude. Keep in mind though that in the winter they will likely be covered with snow, so pragmatically, overall better results may be achieved with a lower mounting angle. Also, aesthetics and regulations will normally play a much larger role in deciding the angle than gaining optimum output with a grid interactive system.