|
|
| ► | Home |
Vertically Mounted Photovoltaic Panels
By Bruce Barbour - June 2020As discussed on other pages on this site I have a domestic solar photo-voltaic (PV) system on my roof. Looking at the electricity production and consumption patterns from my site it was apparent that the production and consumption patterns often do not line up in the morning and in the afternoon. In the morning there would be a peak in consumption while I made breakfast and there would be another peak in the early evening when I made dinner. Annoyingly these peaks would usually occur before and after the photo-voltaic system was generating enough electricity to cover the consumption peaks. Sometimes this was not because the sun was below the horizon, it was just because the sun was too low in the sky to strike the PV panels sufficiently perpendicularly to generate electricity. The panels are attached to the roof directly and are therefore at an angle of 25 degrees to the horizontal. Any sun that would have hit the panels would most likely be reflected as the angle of incidence was too high*. This was the case even though I had both East and West facing panels as well as some North facing panels.
This made me think: It was not that there was no solar available in the early and late daylight times - it was just that the panels were not set up the receive the solar and convert it to electricity. What if some panels were placed vertically pointing towards the East and the West to catch the early and late rays. Would this assist in resolving the issue?
Conventionally panels are aligned to face North. This orientation maximizes the total solar electricity that the panels generate over the year. In domestic situations if there is not enough space on the North facing roof panels can also be placed on the East and West faces. These panel will not generate quite as much electricity over the year as the North facing panels but may be only a 10 to 20% degradation. Vertical panels are not usually considered because of the much higher degradation in energy production on all orientations. Vertical East and/or West facing installation seems counter intuitive, because an East or West facing panel will not generate as much power as a standard North facing panel at the optimal slope.
However total energy production is not the only consideration for panel orientation. The time of generation may also be important.
Firstly let’s look at amount of the decrease in generation of East and West facing vertical panels. Chart 1 included below is from the Your Home Technical Manual (4th edition - page 208). This chart is not on their current web site.
Chart 1
This is a chart for latitude 35 degrees South – Canberra and Adelaide. It would be different for other latitudes.
Looking at an East facing vertical panel the chart indicates that the panel should achieve about 55% of the maximum generation of a well oriented and sloped North facing panel. A West facing vertical panel would achieve a similar percentage of maximum. Why this may still be attractive is the time of day that the panel generates the power. It would be generating its maximum power much earlier in the morning than the North oriented panel. Chart 2 below is speculation on my part on what the generation curve of an East facing vertical panel might look like – hopefully it is about right – I have no way of testing. A West facing panel would be a mirror image of this – mirroring around solar noon – for simplicity taken as 12 o’clock on charts.
Chart 2 – East Facing Vertical Panel Generation - Speculation
What becomes really interesting is when the generation of East and West vertical panels is combined with standard North facing panels. In Chart 3 below the blue curve is the standard north facing generation curve. The green curve is the combined curve. This is a case of “flattening the curve”. PV electricity generation is spread more evenly over daylight hours.
Chart 3 – East West Facing Vertical Panel Generation Combined with North Panel Generation - Speculation
If it was thought that earlier generation was more important than middle of the day generation this could be achieved by increasing the proportion of East West Vertical panels compared to North panels.
The reason why I believe East West vertical panels have merit, despite the (possibly) increased cost per kWh generated is the time of generation. With the installation of a large amount of North facing panels there are going to be occasions when there is a lot of PV generated electricity in the system which is going to be of low value. The earlier and later production times of East West vertical panels mean that the power generated will likely be of higher value for the grid which may compensate for the increased installed costs of East West vertical panels.
While this arrangement could work with having two one sided standard panels back to back it would be better to use one panel that has generates electricity when the sun hits either side of the panel - the front and the back. These panels are called bifacial panels and basically consists of two side photo-voltaic cells sandwiched between two panes of glass.
I have not had anything to do with these panels in the past - they are not standard for domestic installations. I anticipate that the panels would be more expensive than standard one sided panels however they should not be double the price. (If they were you could just use two one sided panels back to back.) And in theory the panel when used in the vertical East West facing configuration should generate 110% of a standard one sided North facing panel on the ideal slope (at least for latitude 35 and assuming similar panel efficiency).
While initially I thought about vertically mounted East West panels for domestic situation on reflection there are issues with it. I thought that some vertical bifacial panels could be placed along a North South running ridgeline of a domestic house. But the main issue with this is the not insignificant additional wind loading it would put on the roof structure of a domestic house – the roof and support structure would have to be designed to allow it. And also there is also the potential for additional shading of the neighbouring properties in many situations - which may not be desirable. It could work domestically for a country property. If the block of land was big enough then the panels could be mounted vertically close to the ground. It would be advantageous in spreading the generation over a longer period of the day and may enable the use of a smaller battery bank or better effectiveness of the batteries. However I think the real potential is for commercial installations - solar farms - to flatten the generation curve across the day - to generate electricity from PV both earlier and later than standard PV installations.
There are further benefits of vertical East West panel installation for commercial solar farms:
- Installation would be simple – panels slid down between two vertical columns which would be installed on the true North axis. Might install 4 to 6 panels high – panels laid on long side.
- The lines of mounted panels are going to have to be
significantly wider spaced compared to normal solar farms so
they don’t block each other’s solar access to low to the horizon
solar. The land on which they would be installed would need to
be flat. While this might seem a disadvantage it is not really.
The land around the line of installed panels will remain largely
usable for grazing purposes and maybe some types of crops as
well – so cheap land use arrangements could be negotiated with
farmers. However it does require a different mindset to
traditional solar PV farms. The solar farms would probably be
geographically bigger than standard solar farms.
Another option may be for the panels to be mounted solely along a farm's north south (+/- 15 degrees) running fence lines and therefore effectively take up no farmland. Again it would be much more spread out than a traditional solar farm.
- Inverter size would be less than for a similar sized North oriented panel - as the vertical East West facing panels would never get to the highest power output even though the total energy output over the day should be similar. This is a further cost saving.
- Because to the time of generation it would not require (much of) an upgrade of electrical transmission lines if installed in the same general area as - or in combination with - other traditional solar farms - unless of course a huge amount is installed or the current North facing farms are already excessively exceeding existing transmission capacity in the area and the existing farm's output is capped by regulation.
I think this arrangement should be more widespread as the solar PV generated electricity in the middle of the day becomes more saturated. The logic of the arrangement is compelling. What is needed is firstly a bit of simple testing to confirm assumptions followed by a pilot plant to show proof of concept and then other developers may jump on board. I don't know much about ARENA but I would think this may be the type of project they could be interested in.
* * * * *
Notes:
Here is one example of a bifacial panel:
https://www.solarpowerworldonline.com/2018/04/what-are-bifacial-solar-modules/.
There are other sites as well.
After I finished writing this article I did a Google search and
found that other people have also proposed the arrangement of
double sided East West facing vertical panels - https://www.solarquotes.com.au/blog/bifacial-panels-solar-farms/.
However installation in this configuration is still not very wide
spread.
I did find one site in Germany doing this - https://www.next2sun.de/en/homepage/.
The photos on the website show the panels closer together than
ideal – but this may be because of the smaller property sizes in
Germany and the availability of suitable sites. They are also
located on rolling hills. Both these factors would impact on the
amount of electricity generated and therefore the economics of the
arrangements. In Australia there should be less restriction to
spreading the panels further apart and also the availability of
suitable flat land. I couldn't find anything in Australia - but it
may be out there.
* Overcoming the angle of incidence.
Just another thought thrown out there - if the issue is with angle
of incidence of the sun's rays hitting the glass at too shallow an
angle and reflecting, could this perhaps be partially addressed by
having the glass of East and West facing panels grooved
horizontally in a fine saw tooth pattern. Like a Fresnel lens.
Perhaps it might improve the performance or spread the production
time of low angle East and West facing panels? Perhaps vertical
grooving might do the same for North facing panels.
