General knowledge question .

To gain more early morning power to an existing flat roof {on brackets] north facing system [all on 1 mppt] one could erect another array of bi-facials on second mppt facing east . With winter in mind and using bi-facials what angle would be best? My brain tells me steeper equals more power early morning but dropping quicker. Flatter equals less early on with longer duration as the sun moves to the north .However that could also allow setting sun to to have a chance to add power if they were steeper . Would mounting frame shadows nullify any gains in the afternoon .Not sure if modern day panels have good optimizers l suppose a white roof would be a bonus .This system is in PE latitude 34*. Original existing north array would not shade potential new east array fortunately. .

4 hours ago, Rory Kilpatrick said:

My brain tells me steeper equals more power early morning but dropping quicker. Flatter equals less early on with longer duration as the sun moves to the north .However that could also allow setting sun to to have a chance to add power if they were steeper.

Your thinking regarding slope angles is correct - for your location, with panels facing due north, the year round optimum angle would be about 34 degrees, winter optimum production would be around 49 degrees, and for summer optimum production it would be around 19 degrees. Facing the panels due east would, as you noted, result in a higher early morning yield if the angle of the panels were steeper, and a better late morning yield if they were flatter. The problem, as I see it, would be the actual solar intensity (or lack thereof) in the early morning.

As an example, would the solar intensity between 07:00 and 08:00 (predicted to be 306W/m2 in Bloemfontein for Sunday 1 February...) at an ideal angle for that time (keep in mind that the figure shown above is for north facing panels, and thus not correct for your application - only shown as an example), result in more kWh yield than (say) 537W/m2 between 08:00 and 09:00 - see my predicted yield obtained from https://en.tutiempo.net/ below (this is just one of many online sites that one can use for this kind of data - here is another): https://solar.meteosource.com/

I suggest you obtain similar data for your location, and then calculate the hourly yields using the various panel slopes that you want to consider.

Put the bi-facial panels at 90 degrees to the horizontal, facing east and west.

12 hours ago, HennieL said:

The problem, as I see it, would be the actual solar intensity (or lack thereof) in the early morning.

I've given this some more thought, and there is another potential problem with east facing PV panels in PE - Fog and sea mist, and moisture rising into the air.

I'm not all that familiar with PE, but do have some family there that we visit every year, and I recall a lot of early morning mist moving inland from the ocean. This will obviously have an effect on your early morning solar harvest - also, I suspect that the moist air rising from the ocean might still decrease your PV harvest even if there is no visible mist/fog in the early mornings, as the sunlight must travel through a substantially thicker layer of (moist) air whilst the sun is low on the horizon. In my opinion, you will harvest more kWh throughout the year if you keep the panels at an optimum angle for late-morning capture, and not at a steeper angle to try and squeeze out the most from the early morning sunrise.

I stay in PE. And is located on the Baakens river in the western suburbs. Fog and mist doesn't appear that often on this side of town, but when it does it dissipates before 10am, and will appear again around 4pm.

I have a mixture of 9 mono (545W ea) and 9 bi-facial (550W ea) panels spread across 3 MMPT's ( 3 banks of 6 ea: MPPT1 = 6 x 550W bi-facials, MPPT2 = 3 x 550W bi-facials + 3 x 545W mono, MPPT3 = 6 x 545 W mono). All of them face north and angled at about 35 degrees from the horizontal. Roof is flat and painted white to get the maximum reflection for the bi-facials.

I've noticed that production is good all day from all 3 banks, but on very hot days bank 3 performs better. However, on overcast and rainy days, the bi-facials perform slightly better. Production on the bi-facials starts about 30 minutes earlier and ends about 30 minutes later in the day). Banks 2 and 3 does cast shadows over the banks behind it in winter, but the bi-facials are halfcells so they still perform in those situations, and I will be moving the panels on bank 1 (6 x bi-facials) slightly higher soon to get more sun on them when winter comes. I was considering moving the one bank to face east and another to face west, but the prevailing winds in PE blow from the west and I don't want to risk them being damaged or blown off by the odd gale force winds in the area. I also have the option of adjusting each banks angle, but over the past 18 months, I've hardly used any Eskom power as all 4 batteries are fully charged when the sun sets in winter. In summer, the batteries are full around 9:30, before geysers, pool pumps, etc starts. The whole house is wired to the essential output and batteries charge rate is set to 0.1C.

Hope this helps in your decision making.