West facing solar panels are no good...or that is what we were told!

Designing a Roof Mounted Solar Harvesting System"

Getting our fundamentals correct will result in the best or optimum solar panel harvesting system.

We have 4 orientations that we can use for solar panels.  Unless under extreme conditions, I would never use north facing panels.  You will get some energy harvested from north facing panels, especially in the summer months but it is far from ideal.

A microfit solar panel harvesting system injects a limitation of 10 kW inverters into all design considerations.  There is a limit of what the electrical lines feeding your house can carry.  For a 200 A system that is around 16-17 kW or so peak or maximum power output.  The lines are under ground which keeps them cool which is a good thing.

Anything that limits the amount of solar energy hitting your roof, like fog, clouds, shade from trees, poor roof angle, etc, hurts you. We have a 22.5 deg roof which we can not change.  It is great from April to September and poor at other times of the year.  That said, it is optimum when we have the longest days and most sun energy to harvest.  One feedback comment recommended 30 deg was ideal and that seems to me to be good or correct.  A 45 degree slope will help with snow melting off in the winter.

My Golden rule is this:  Grab or harvest all the sun's energy when ever you can.

Maximize your output first from your south facing panels followed by east and then west facing panels.  OPA should strongly encourage harvesting from the east and west because of the electrical peaks that need to be met at this time of day.  They do not do that.

If you are new to solar, South facing panels give you your best ROI or return on investment.  East and West facing panels are great from sunrise to sunset respectively, and help significantly to harvest more energy when it is need the most before your south facing panels get going.  You need a combination of all 3 to maximize energy production.  Of course, solar trackers would be the best but that is not a roof mounted system.


We were initially told that west facing panels do not work well.  That simply is not true at all.  We need west facing panels to produce power for the 6 and 7 pm peak demand.  In the summer, west facing panels start producing over 100 W as early as 10:30 AM  and of course continue until sunset. East facing panels stop producing around 5 pm.  South facing panels also have reduced output after 6 pm.  Choosing solar panels that produce the best off axis harvesting is also an important decision.  See my reviews of some solar panels, especially the newest generation of poly panels.

I noticed in Windsor area that in the fall, we get early morning fog and dew on our panels.  This makes having some west facing panels important to have as you lose the effect of your east facing panels on many days.  We are seeing excellent results in August, September and hopefully the other fall months as well.  I will admit that the fall of 2014 was very poor.  2015 is looking for +20% for September over 2014.  It all depends on how much cloud cover we get.  The sun light is always there.

The sunlight has to travel further though the clouds in the fall/winter/spring because of the lower angle of the sunlight due to the tilt of the earth on it's axis.  Add the shorter days for that time of year and production will diminish.  On over cast days, all of your panels work about the same, including any north facing panels.  I am against north facing panels for obvious reasons.

With the microfit limitation on inverter output, you want to reach maximum inverter output as fast or as early as you an and to maintain that output for as long as you can.  SolarEdge is outstanding for this as you can mix east, south, west facing panels with no penalty.  The smart inverters simply turn off some panels when maximum power levels are reached and the bus voltage is increased at this time to help lower the current flow and hence reduce the power line losses.  The inverters themselves do not seem to get hot ever.  The microfit program should never have been limited to 10 kW but rather 50 kW and individual limitation based on the maximum allowable current flow back to the transformer.  For our house that would be 15 kW but we can only dream of that.  Never add more inverters to your system.  We put our two 5000 W inverters on the north side of our house to keep them cooler in the summer and to reduce exposure to rain and snow.  They are also beside the electrical meters with easy disconnect if needed.  When shut down, bus voltage drops to 1 V dc per panel and NOT 600 V by some manufacturers.

In conclusion, choosing the right inverters from the start like SolarEdge will give you the opportunity to produce the maximum power from your system.  Remember this, at 39 cents per kW, if you harvest only 1 kW hr more  per day, you will get $3000 over the twenty year contract.


Beware of contractors.  We have had no problems with Flexible Solar.