WSW panel orientation.

littleharbor2

 So down here in Northern Baja there's thousands of off grid PV systems and new ones being installed all the time.
There's a Alternative energy operation down here that is installing new systems with SW to WSW orientations. When asked by a curious neighbor about this was told that "I have been doing this for 40 years now and I know what I'm doing" Apparently, after a friend of his said, he's basing this odd orientation on some reports the theory that, After I read said reports, GRID TIED systems benefit the grid by producing peak power in the afternoon when demand is highest. The only other reason I could think of to choose this westerly orientation would be if you have a persistent Marine Layer problem, which we don't have on the Sea of Cortez side of the peninsula.. We're not talking "Virtual Tracking" here. Just a single array
Off Grid PV systems store power in your battery bank which gets drawn on when the sun goes away, overnight and in the early am hours. Wouldn't it make sense, in this scenario that you would want to begin charging your battery bank sooner, rather than later in the day? How can you EVER take advantage of opportunity loading when you're still charging into the afternoon?
Just thought I'd throw this out there and get the thoughts of others on this subject.

BB.

For battery based systems... I would suggest that you need to harvest as much energy as possible... And need to look at other issues too, such as weather (afternoon marine layer, morning fog, and ambient temperatures--High Temperatures -> lower Vmp-array -> lower energy harvest P=V*I).

One "retired poster" here that designed MPPT controllers--Lives in Florida (Solar Guppy) and decade ago was talking with folks building out utility sized solar arrays. And in Florida, he told them that SW facing arrays (for GT afternoon peak) would harvest a lesser amount of energy vs SE facing because of higher afternoon temperature and the tendency for afternoon clouds and thunder showers.

HOWEVER, solar panels are much cheaper these days (at least for now). And, especially, Lead Acid Batteries need "time on charge". Depending on rate of charge and depth of discharge... Possibly 3 hours "bulk" and 2-6 hours on "absorb".

Tracking arrays are great for time on charge. Panel always pointing at sun vs panel pointing south and sun morning/evening times with cosine losses (i.e., Cos 45 degrees = 0.707 = 71% harvest of sun on panel).

The alternative is to use "virtual tracking array". Half the panels facing south east, and the other half facing south west. Do lose a bit of overall efficiency--But get more time on charge.

For example:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Mexicali south facing array
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.54	5.15	6.14	6.47	6.64	6.57
Jul	Aug	Sep	Oct	Nov	Dec
6.18	6.06	5.99	5.64	4.93	4.43

Mexicali south west panels
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.31	4.89	5.83	6.15	6.31	6.24
Jul	Aug	Sep	Oct	Nov	Dec
5.87	5.76	5.69	5.36	4.68	4.21

Mexicali facing south east
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.31	4.89	5.83	6.15	6.31	6.24
Jul	Aug	Sep	Oct	Nov	Dec
5.87	5.76	5.69	5.36	4.68	4.21

The above link--Not sure I "trust" it as being accurate for weather/other conditions... But it is is a start (5% loss of harvest in winter with SE/SW array)

The next tool is PV Watts for Mexicali, 32 degree from Horizontal tilt (I think PV Watts is more accurate by including local conditions/weather/etc.:
https://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation South facing ( kWh / m2 / day )
January	5.87
February	6.37
March	7.19
April	7.66
May	7.57
June	7.39
July	6.97
August	7.19
September	7.26
October	7.15
November	6.18
December	5.56
Annual	6.86

Month	Solar Radiation South East Facing ( kWh / m2 / day )
January	5.13
February	5.72
March	6.76
April	7.44
May	7.66
June	7.61
July	7.20
August	7.16
September	6.89
October	6.47
November	5.46
December	4.83
Annual	6.53

Month	Solar Radiation South West Facing ( kWh / m2 / day )
January	5.11
February	5.67
March	6.68
April	7.51
May	7.60
June	7.58
July	6.97
August	7.03
September	6.81
October	6.50
November	5.37
December	4.77
Annual	6.47

A bit more than 6% loss of harvest using South vs South West facing array.

PV Watts also has a CVS hour by hour download so you can see the amount of harvest throughout the day (365 days a year).

So--At least for Mexicali, the SW facing array is "costing" him ~6% of the potential annual harvest. And appears to be costing almost an "hour of sun" per day in December.

For deep cycle Lead Acid batteries which "like" 10-13% rate of charge (for longer battery life), Having a SW array and day/afternoon loads would tend to reduce "peak/average" charging current to the battery bank... I would guess that this is not "great" for best battery life and optimum harvest (especially in winter).

The SW/SE array does pick up more December sun than a pure SW array. But overall a South Array is going to be the best average harvest--At a cost of "time on charge".

However, if folks are using Li Ion battery bank--The minimum rate of charge is not a requirement for longer battery life. And Li Ion tend to be much more efficient than FLA. And they do not need Absorb (between zero and 1 hour I have read in specs). So time on sun is not really an issue.

For Li Ion banks, facing south gives you the most harvest. SE the next best. And SW the worst...

That is the modeling--In "real life", I would suggest that when "everything" is taken into account, anything less than 10% reduction (or increase) in harvest is going to be very difficult to even measure without laboratory grade instruments and a test bench setup--Not just the numbers from an Off Grid Home. (i.e., 5-6% "less harvest--Probably will not see that on Battery/System Monitor vs all the other variations in energy usage, weather, temperature, etc.).

-Bill

littleharbor2

BB. said:

For battery based systems... I would suggest that you need to harvest as much energy as possible... And need to look at other issues too, such as weather (afternoon marine layer, morning fog, and ambient temperatures--High Temperatures -> lower Vmp-array -> lower energy harvest P=V*I).

One "retired poster" here that designed MPPT controllers--Lives in Florida (Solar Guppy) and decade ago was talking with folks building out utility sized solar arrays. And in Florida, he told them that SW facing arrays (for GT afternoon peak) would harvest a lesser amount of energy vs SE facing because of higher afternoon temperature and the tendency for afternoon clouds and thunder showers.

HOWEVER, solar panels are much cheaper these days (at least for now). And, especially, Lead Acid Batteries need "time on charge". Depending on rate of charge and depth of discharge... Possibly 3 hours "bulk" and 2-6 hours on "absorb".

Tracking arrays are great for time on charge. Panel always pointing at sun vs panel pointing south and sun morning/evening times with cosine losses (i.e., Cos 45 degrees = 0.707 = 71% harvest of sun on panel).

The alternative is to use "virtual tracking array". Half the panels facing south east, and the other half facing south west. Do lose a bit of overall efficiency--But get more time on charge.

For example:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Mexicali south facing array
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.54	5.15	6.14	6.47	6.64	6.57
Jul	Aug	Sep	Oct	Nov	Dec
6.18	6.06	5.99	5.64	4.93	4.43

Mexicali south west panels
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.31	4.89	5.83	6.15	6.31	6.24
Jul	Aug	Sep	Oct	Nov	Dec
5.87	5.76	5.69	5.36	4.68	4.21

Mexicali facing south east
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.31	4.89	5.83	6.15	6.31	6.24
Jul	Aug	Sep	Oct	Nov	Dec
5.87	5.76	5.69	5.36	4.68	4.21

The above link--Not sure I "trust" it as being accurate for weather/other conditions... But it is is a start (5% loss of harvest in winter with SE/SW array)

The next tool is PV Watts for Mexicali, 32 degree from Horizontal tilt (I think PV Watts is more accurate by including local conditions/weather/etc.:
https://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation South facing ( kWh / m2 / day )
January	5.87
February	6.37
March	7.19
April	7.66
May	7.57
June	7.39
July	6.97
August	7.19
September	7.26
October	7.15
November	6.18
December	5.56
Annual	6.86

Month	Solar Radiation South East Facing ( kWh / m2 / day )
January	5.13
February	5.72
March	6.76
April	7.44
May	7.66
June	7.61
July	7.20
August	7.16
September	6.89
October	6.47
November	5.46
December	4.83
Annual	6.53

Month	Solar Radiation South West Facing ( kWh / m2 / day )
January	5.11
February	5.67
March	6.68
April	7.51
May	7.60
June	7.58
July	6.97
August	7.03
September	6.81
October	6.50
November	5.37
December	4.77
Annual	6.47

A bit more than 6% loss of harvest using South vs South West facing array.

PV Watts also has a CVS hour by hour download so you can see the amount of harvest throughout the day (365 days a year).

So--At least for Mexicali, the SW facing array is "costing" him ~6% of the potential annual harvest. And appears to be costing almost an "hour of sun" per day in December.

For deep cycle Lead Acid batteries which "like" 10-13% rate of charge (for longer battery life), Having a SW array and day/afternoon loads would tend to reduce "peak/average" charging current to the battery bank... I would guess that this is not "great" for best battery life and optimum harvest (especially in winter).

The SW/SE array does pick up more December sun than a pure SW array. But overall a South Array is going to be the best average harvest--At a cost of "time on charge".

However, if folks are using Li Ion battery bank--The minimum rate of charge is not a requirement for longer battery life. And Li Ion tend to be much more efficient than FLA. And they do not need Absorb (between zero and 1 hour I have read in specs). So time on sun is not really an issue.

For Li Ion banks, facing south gives you the most harvest. SE the next best. And SW the worst...

That is the modeling--In "real life", I would suggest that when "everything" is taken into account, anything less than 10% reduction (or increase) in harvest is going to be very difficult to even measure without laboratory grade instruments and a test bench setup--Not just the numbers from an Off Grid Home. (i.e., 5-6% "less harvest--Probably will not see that on Battery/System Monitor vs all the other variations in energy usage, weather, temperature, etc.).

-Bill

According to the numbers here there doesn't appear to be that much loss, but a loss all the same. My biggest  concern is the delay in getting fully charged till later in the day. I'm sure a hourly breakdown from morning to afternoon would show substantial differences. I for one like knowing I'm into absorb well before midday and using all that free power to run things like the vaccum, crock pot, power tools and others

Solar Guppy

As BB well described, there isn't a single orientation that works for everyone. If your in a sub , or fully tropical climate, you really need to understand how the local weather effects the overall harvest, assuming array size and cost is a dominant concern.

When I had SE and SW facing arrays, panels were 4-5 dollars a watt, my current system cost 25 cents a watt for the PV, so I just put as many panels that would physically fit on the roof and overall make more energy than the home will ever consume and can fully charge the BYD battery AND support the home loads at the same time.

These days the biggest cost is storage and regulatory compliance, while this does not apply to Baja, in the US we now have UL9540 to deal with which means one can't have any random pairing of inverters / batteries for systems above 24V. 

littleharbor2

Solar Guppy said:

As BB well described, there isn't a single orientation that works for everyone. If your in a sub , or fully tropical climate, you really need to understand how the local weather effects the overall harvest, assuming array size and cost is a dominant concern.

When I had SE and SW facing arrays, panels were 4-5 dollars a watt, my current system cost 25 cents a watt for the PV, so I just put as many panels that would physically fit on the roof and overall make more energy than the home will ever consume and can fully charge the BYD battery AND support the home loads at the same time.

These days the biggest cost is storage and regulatory compliance, while this does not apply to Baja, in the US we now have UL9540 to deal with which means one can't have any random pairing of inverters / batteries for systems above 24V. 

Well, for the local conditions I wouldn't expect a single array facing WSW  which delays getting morning after, battery charging to be a sensible or very efficient design. It sure looks odd alongside neighbors arrays which all have southern orientation.

Marc Kurth

Not identical, but the concept applies. I have a customer who designs remote PV systems for cell/comm towers in remote far Northern climates with heavy snowfall. At the risk of oversimplifying, he has had good success by using the "virtual tracking" approach in both planes. With PV being so darned inexpensive, it just makes sense to do this as required for local conditions, including incidental shading.

littleharbor2

Marc Kurth said:

Not identical, but the concept applies. I have a customer who designs remote PV systems for cell/comm towers in remote far Northern climates with heavy snowfall. At the risk of oversimplifying, he has had good success by using the "virtual tracking" approach in both planes. With PV being so darned inexpensive, it just makes sense to do this as required for local conditions, including incidental shading.

Not  identical at all, We have no weather issues to speak of locally. We do have night and day as usual and the need to recharge after sunrise Which is why this singular westerly orientation makes no sense

NANOcontrol

I have some due east facing panels and that is the best money I ever spent. I even paid my neighbor to cut down a tree to make it possible!  Solar panels are so cheap now that many are stuck in the past thinking about maximum production with south facing panels. I want to use power when it is created and not throw money down the toilet with batteries. For that are grid tied, south panels are more of a nuisance to the utilities.  With the coming of time of use meters, noon time power won't be worth a damn.   I have a summer home that runs on PV with just a car battery.  By noon my water heater is up to temperature, done two loads of laundry, have a cold refrigerator and done two loads of laundry.  The laundry even has its own water tank and all cycles are done with hot water. And at the end of the day the battery has to have a full charge to keep me alive at night.  Energy management by scheduling is the future. Big batteries are a crutch. 

littleharbor2

NANOcontrol said:

I have some due east facing panels and that is the best money I ever spent. I even paid my neighbor to cut down a tree to make it possible!  Solar panels are so cheap now that many are stuck in the past thinking about maximum production with south facing panels. I want to use power when it is created and not throw money down the toilet with batteries. For that are grid tied, south panels are more of a nuisance to the utilities.  With the coming of time of use meters, noon time power won't be worth a damn.   I have a summer home that runs on PV with just a car battery.  By noon my water heater is up to temperature, done two loads of laundry, have a cold refrigerator and done two loads of laundry.  The laundry even has its own water tank and all cycles are done with hot water. And at the end of the day the battery has to have a full charge to keep me alive at night.  Energy management by scheduling is the future. Big batteries are a crutch. 

I believe you have missed the point here.

NANOcontrol

No, maximum solar production is an outdated idea.

bnes`

My area has morning fog, often for months.
My grid tied West facing panels produce identical power on foggy morning days (about .9 kWH).
On all day sun days, the south panels produce more (1.8 kwH on average).

The south panels get the noon sun the best, but miss out on the evening sunlight.a