I recently saw a different article on that study. It will be interesting to see if other studies can reproduce the same results. With only 2% difference it makes little sense to go through the hassle and expense of reorientation on existing systems.
The best part of this revelation is the reduction in peak demand. It was well known that facing west has this effect but the net 2% overall gain is the surprising part. Its also great to know that if you have a roof that faces anywhere from S to W its a good fit for PV without complicating the mounting hardware.
"If you want to save the environment, build a city worth living in." - Wendell Berry
We don't set our panels according to some chart in some book somewhere. Instead we observed the sun and set the panels accordingly. The vast majority of our best sun comes before noon, and even so, by 10 am the clouds often move in. Thus four panels are set for that pre-10 sun, the rest for post-10 sun. Living below the Tropic of Cancer, our sun crosses the zenith overhead, so we change the rank angle twice a year to accommodate that. Our panels are on a ground rack so that it is easy to work with them.
There's no need to use a chart if you just use common sense, as far as I'm concerned. If we went by the charts, we wouldn't be producing the amount of power that we do.
It's never too late to start! I retired to homestead on the slopes of Mauna Loa, an active volcano. I relate snippets of my endeavor on my blog : www.kaufarmer.blogspot.com
* It depends.
* Observe through all 4 seasons before implementing any major system.
Depending upon your climate, you may be energy dollars ahead if you place the panels facing EAST, and plant huge shade trees on the west side. There are too many variables for somebody living elsewhere to say which direction your panels should face.
Off grid vs. grid-tied makes a difference as well. With a proper storage system, it makes little difference at which time of day you collect the power.
If you have predominantly sunny mornings, followed by cloudy afternoons, the advice of that study could be sending you off in the wrong direction. By observing the patterns for all 4 seasons, you can best determine the proper orientation for your site. Long, sunny summers are a no-brainer, but what direction gives you the best advantage for the leaner months of winter, when you will be spending more time indoors?
The results of this study make perfect sense to me (of course, as always, it depends). It's clear the study considered grid-tied homes, and a solar array facing southwest (northern hemisphere) makes sense in that setting based on the discussion (i.e. to increase production during the latter half of days when electricity consumption rates are highest). For the off grid setting, I had considered using two independent arrays that feed a common battery. One array is facing southeast and the other southwest. The goal is to flatten the production profile, especially during summer days, and use air conditioning as an opportunity load. The goal is to operate a/c as long as possible while reducing or eliminating battery discharge for this purpose while also increasing efficiency by lessening battery losses. This would be particularly effective with a modest home that has excellent thermal mass. This approach could also allow for using a smaller battery system in the off grid setting and/or reducing battery depth of discharge which can increase battery life in most settings.
The link to that study doesn't appear to work anymore.
We have several arrays facing due east, due south and due west. This is a photo of two of our 1.5 kW arrays that face east and south, as an example, that I am able to get in one snapshot:
We tilt our two south facing arrays up to 75° for winter time. However the east/west arrays remain fixed at roof pitch (22.5°) on the house. In the summer the east/west arrays far out-produce the south because the sun comes up in the northeast and sets in the northwest, and at solar noon is 8° north of directly overhead. That fact is why the pine trees to the east of the south facing array in the photo does not affect the output of the array at all. Whether the pine tree is there or not, the sun angle is such that the south facing arrays don't get any direct sunlight until about 9:00AM.
In the winter the south facing outproduces the east/west on sunny days, simply because the sun rises in the southeast, makes a short trek across the southern sky reaching 36° elevation, and sets in the southwest. The east/west outproduces the south on cloudy days any time due to being aimed at the brightest part of the sky. In winter time we will see usually 3x the output from the east/west on a cloudy day that we get from the south facing arrays.
We run the two east/west arrays on a single XW-MPPT60-150 @ 92.4 Vmp input and it works fine.
the planks from the company that installed mine on a near flat roof put the array in facing north 10 degrees! they could face south if they had brackets that were long enough but they havnt got them. the best they can do is flat - FLAT. id prefer more angle towards south if they could but they refuse saying - 'the brackets holding them up need to be certified parts' hmmmm or you just get some strong metal drill a few holes - whack a bit of paint on - fit it. that's too hard for some companies...
Terry Brown wrote:or you just get some strong metal drill a few holes - whack a bit of paint on - fit it. that's too hard for some companies...
While that might work for you, for a certified installer it won't. The mount has to meet snow load, wind load and grounding/bonding requirements to meet NEC. Depending on your latitude, flat oriented solar panels can work quite well.
Panel orientation depends a lot on latitude as far as which direction to aim them. For our off-grid home at 48° N latitude the east/west arrangement works the best for about 9 months of the year (roughly). The south facing does work better on sunny days in the winter. We have gone with more east-facing installed capacity than west because for off-grid where we are trying to catch batteries up and need a morning "boost" after the night time hours, the east facing makes more sense. Our batteries are usually floating by mid-afternoon on a summer day so west facing installed capacity is wasted.
Our high-voltage array (370 volts) is oriented perfectly flat for the summer months and is tilted up to the winter angle in mid-October. Our low-voltage arrays (92 volts) are fixed except for the south facing, which cannot be oriented flat because of the roof slope it's mounted on. I have found this flat and east/west orientation is by far the best most of the time.
On things like this:
'the brackets holding them up need to be certified parts' hmmmm or you just get some strong metal drill a few holes - whack a bit of paint on - fit it
You have to remember that the grounding and bonding on solar panels is pretty important for your safety, especially when dealing with higher voltage arrays on MPPT controllers. If just get some strong metal and drill a few holes and whack some paint on the chances of galvanic corrosion between your aluminum panel frames and the mount is pretty good. That is why certified installers use all stainless steel and anodized aluminum hardware and rails, and WEEB bonding clips to insure a good corrosion-free bond to the mount. Solar panels are quite dangerous if they are not grounded properly - especially when dealing with arrays at 100 volts or more. High voltage DC power is way more dangerous than AC, and the last thing you need is somebody getting laid out deader than a rock because they touched a solar array that was not grounded properly and they became the path to ground. There are two distinct and separate grounding systems on a solar array and they MUST be installed properly for your safety.