How to Determine Home Solar Potential – by Matt McPherson – 7-17-2013

There are many factors that determine if a home has good solar potential or not. As an energy consultant for HelioPower Solar in Thousand Palms, CA part of my job is to look at the different variables that create this potential and determine if solar is a good fit for a homeowner. Many solar companies look past solar potential and promise the world without taking into consideration the factors that affect solar panels from making the maximum power possible. Many of these companies have started in the past few years and are just jumping on the solar bandwagon. This is bad for the solar industry because homeowners with poor solar potential will not be happy in the long run. They are basically being conned into buying a solar system that is not going to work to its maximum potential.  If installed incorrectly the solar systems will under-produce and the customer will be left buying more power from the utility company than they anticipated.

The first factor to consider when determining solar potential is irradiance factor. That is how much sun- light actually hits the area where you plan to put the solar panels. The amount of sunlight is a measurable quantity. In the industry we call this ‘insolation’. By using tools such as a Solmetric SunEye, solar professionals are able to take a picture of the southern sky and see exactly where the path of the sun will be each day of the year. Thus we are able to capture what effect objects (such as trees and chimneys) will have on the solar irradiance of particular area.  A solar panel with 100% solar irradiance is going to make more power than a solar panel that is shaded for half of the year from a large tree. When determining if a home or area has good solar potential solar professionals will always look for trees or other objects that might shade the solar panel. Shade and solar do not mix therefore the more shaded the solar panel is, the less power it will produce over its lifetime. In order to determine if your home has good solar potential you should take a quick look around and see if you have any large trees or obstructions shading your roof.

The second factor to look at when determining a home’s solar potential is to determine if you have enough roof or ground space available. Depending on the size of the home solar panel system needed this will determine how much ground or roof space you need.  In a ground mount situation you want a large open area with slight slope facing south if possible. Solar panels facing south will always make more solar power than a panel facing another azimuth such as east or west.  Ideally you want to stay off of a north facing roof as the sun will never be shining directly on a north facing panel (unless you live in the Southern Hemisphere). When looking at a roof to install solar it is important to determine the roof type. There are many different roof types in residential solar from flat roofs to concrete or clay tile roofs. The architecture of a roof greatly influences the ability to install solar. Ideally you want one large roof that is all facing the same direction at the same pitch. This allows home solar panels to work optimally and produce power at the same voltage and provide the maximum amount of power to the house.  It is important to determine what type of roof you have before going solar as the roof work needed to install the solar panels will change depending on what type of roof your home has.  A home with a flat roof will be installed with tilt kits which allow the panels to be tilted at 5, 10 or 15 degrees. The higher the tilt angle the higher the solar output will be in the winter months when the sun is lower in the sky. Not all roofs are built the same and many roofs do not face directly south. If your roof is cut up into smaller sections, it is now possible to use micro inverters or DC optimizers in order to make solar work. Micro inverters and DC optimizers allow each panel to work individually thereby maximizing overall yield. This is very helpful when you cannot fit all the panels on the same roof pitch. So for example if you have a string inverter you must have a certain number of panels all facing the same direction and the same azimuth. This is not the case if you are using a micro inverter or DC optimizing inverter. This is why it is important to always have a professional energy consultant determine your solar potential.

The third and most important factor in determining if your home is a good candidate for solar is to look at your current annual electrical utility bill.  If you have a very efficient home and do not use much power than solar might not be for you. But because home solar panel pricing has dropped down since the inception of the California Solar Initiative program and it is now possible to pay less for power that is generated from your solar panels then you do from your current utility company. This is called grid parity and has only been possible in the past couple of years. Typically I use a benchmark of $150 per month. So if your bill is over $150 per month it is going to save you money if you go solar today. You will pay less for the power produced from the solar panels starting day one. Which means you will only save more money over time as utility rates continue to rise.  One of the primary reasons homeowners go solar is to hedge their bets against utility rate increases in the future. If you make the majority of your power from solar panels you are immune to rate increases in the upper tiers because you do not buy power in those tiers.

If you are interested in learning more about the solar potential for your home and if you are a good solar candidate please contact me at [email protected] for more information.