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Can I face solar panels North, East and West?

Solar Panel Design East West North

It’s a solar panel design question I pose to almost every electrician and solar salesman I interview: “Can we install solar panels without optimisers on three different orientations?” Nine out of ten times, their answer is wrong.

To explain the answer, I’ll go back to the basics with the power formula. Next, I’ll explain how we design solar panel systems both in series and in parallel, and how this affects voltage and current. Then I’ll show how, with a standard string inverter, we can install solar panels in more than two orientations. Finally, we’ll consider some things we should avoid when paralleling east and west, and more efficient options that are available in these situations.

 

 

Lesson #1: Power = volts × current.

Watts, volts, amps, power, current. You may be familiar with all these terms but might be uncertain about how they relate to one another. I’m going to explain these terms with the water pipe analogy. (The way I explain it is simplified – it’s not a perfect analogy.)

  • Current is similar to the size of the waterpipe. The bigger the pipe, the more water can flow.  We measure current in Amps (I).
  • Volts is like the water pressure on the street or the pressure behind the water pipe. In Australia, that “pressure” for electricity is 240 volts (V).
  • Power (P) is the result of the two. A fire hose has a lot of power because it’s a big hose flowing at high pressure. We measure power in Watts (W).

There are three ways we can write the formula; all mean the same thing.

The Power Formula

You can use this basic formula with household appliances.

A 2400W kettle plugs into a 240v powerpoint. How much current does it draw?
2400W = 240v × 10A

Or use it for solar design:

A single solar panel is operating voltage is 30V and 8amps. How much power is it producing?
240W = 30V × 8A

 

Lesson #2: Voltage is added in series

Solar Panel Design Series string

When we design a solar panel system on a roof, we generally connect them in”strings”. A string is a group of panels (usually between 5 and 13 panels) “daisy chained” together – or more correctly connected in series.

In this diagram, we have seven solar panels strung together in series. One panel (with reasonable sunshine) produces 8amps and 30 volts. As mentioned earlier, that one solar panel will produce: 30V x 8A =240W.

When we combine the seven solar panels, we have 210v but still only 8amps.
210v x 8a = 1680 W.

Note that the voltage is added in series, the current remains the same.

 

Lesson #3: Current is added in parallel

Solar Panel Design parallel

 

When we parallel two of these strings, instead of adding the parallel voltages together, we add the current together, and end up with 210 Volts and 16 amps,

210v x 16a = 3360W

 

This time the current is added in parallel, the voltage remains the same.

 

Lesson # 4: Solar panel design on a simple roof

solar panel design

Now let’s design the parallel string of 7 solar panels and the single string of 7 panels on the roof. To make the job simple, we’ll first choose a big house with a solar-friendly roof.

Most string inverters have two separate inputs called Maximum Power Point Trackers or MPPT’s.  As the sun’s intensity and angle on the solar panel changes during the day, the MPPT continually “Tracks” and adjusts the voltage and current to find the “Point” where it can achieve the “Maximum Power”.

Notice how each string of solar panels is facing the same orientation. We have one string of eight panels facing North, and two strings of eight panels parallelled into the other tracker facing east.

But let’s get back to reality. Not every roof is so solar panel design friendly. Let’s look at what happens if your roof is more limited for space.

 

 

Lesson # 5: A series string of solar panels must face the same direction

This one is straight out of the Australian Standards.

PV modules that are electrically in the same string shall be all in the same orientation within ±5 (azimuth and tilt angle).
ASNZ 5033 clause 2.1.6

Poor Solar Panel Design

There is a good reason for this. Current flowing through a string of solar panels is limited to the weakest panel just like water flowing in a hose is limited by a kink in a hose.

This example shows a series string of six panels, three panels facing east and three facing west. In the morning, the eastern panels would be dragged down by the west. Then in the afternoon the western panels would be dragged down by the east.

(As a side note, we could not parallel these panels, as a string of 3 will only run at around 90 volts, which is too low for most inverters. In this case, we would need to use optimisers).

 

Lesson 6:  The Myth, Parallel strings must face the same direction

Solar Panel Design in 3 orientations

Here’s where many solar electricians and solar salespeople get unstuck with a solar design. They know that all panels in a string must face the same direction, but then they assume all the panels connected to one MPPT must face the same direction.

If we apply the knowledge we have so far; it seems to make sense. We face series panels in different orientations because the panels that run at a lower current will act like a kink in the hose.

The idea then is that we also cannot design parallel panels to face different orientations, because the panels that run at a lower voltage will drag down the panels that run at a higher voltage.

But, it turns out, working within inverter input current limitations, we can!

 

Solar panel design East-West on 1 MPPT

You may know enough about you household electricity to know that runs at 240volts. This figure is relatively constant, in fact by regulation it can be should sit between 220 volts and 253 volts. So when you are using more power at home, it is not because the voltage is changing – it is the current that is changing.

Now back to solar panels. When the inverter first turns on in the morning, each solar panel operates at about 30 volts and 0.1 of an amp. As the sun comes up in increases to 2amps, then 3amps and until it reaches it’s maximum of around eight amps at full sun. The voltage, however, remains about the same: around 30 Volts.

Below is Fronius monitoring data of an east-west system we installed last year. Because we did not need to parallel this job, we have the voltage data of the east and west array running on separate MPPTs.

 

Fronius East West ArrayFronius East West Voltage meaurements

 

 

 

 

 

 

 

The Blue line shows the power increased during the morning. For simplicity, I haven’t displayed current it in this image, but it follows the blue power curve. While the two DC voltages don’t perfectly match, they remain similar – usually within 5 percent of 350 volts. If this solar panel design was with two strings to only one MPPT, then the MPT would adjust the voltage to the point that would allow the most power to be produced out of the two strings.

Note, there was a point in the morning when the purple line drops off. This is the western panels that were producing very little power. If both the east and west panels were on 1 MPPT, the voltage would have remained high, and losses on the western array would still have been minimal.

 

How much efficiency is lost?

In 2012, a case study by Fronius showed how installing east-west panels on 1 MPPT caused losses of less than 1 percent compared to using two inverters / 2MPPTs. This case study is admittedly outdated as the inverters that were used were less efficient than inverters available today. The actual amount of  efficiency loss will depend on several factors:

  • Orientations only 90 degrees apart will cause less voltage variance and less loss.
  • Solar panel design on flatter roofs will cause less loss.
  • Installing one array in the shade will cause significantly more losses on the other array and should be avoided.
  • The inverter’s optimal power and voltage efficiency curves.

However, in the right situation, splitting panels east and west on 1 MPPT can be a cost-effective way of installing a larger system on your roof.

 

Complicated and shaded roofs

If your roof line dictates it, or if increased cost is not a concern, Module Level Power Electronics may be a better option. MPLE allows every panel to run independently of each other, regardless of orientation or shade. Here are the options available:

Just as a ballpark, a 6.6kW optimised solution can cost you about $1000 more than a standard Fronius non-optimised system.
If you are in South East Queensland, we’d be happy to advise on a solar panel design that would best suit your home.

 

Conclusion

When designing solar, (without optimisation) installing a series string of panels in two different orientations will cause significant power loss. For this reason, AS5033 does not allow it. However, running two parallel strings of panels in different orientations will only affect the voltage slightly, so power loss will often be minimal. As a result, a solar panel design on 3 different orientations with a dual MPPT inverter will cause minimal power loss. We take factors such as shading, pitch, and inverter efficiency curves into account, and in some situation, we recommend using optimisers.

For further reading on basic solar design, read my post:  What’s the best direction to face solar panels.

Leave a Reply

10 Comments on "Solar Panel Design : North-East-West"

10 Comments on Solar Panel Design : North-East-West

Mark C said : administrator Report 2 weeks ago

Hi Julie, no we don't, but you have one of the better companies in Australia near you. NRG Solar in Richmond has a great reputation amongst their peers in the industry.

Julie said : Guest Report 2 weeks ago

Hello Mark, Do you have an installation service in Adelaide. Thanks

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Mark C said : administrator Report 2 months ago

Hi Julie. depending on where you are, I wouldn't focus on self-consumption, I'd focus on production. Read this blog. https://mcelectrical.com.au/blog/whats-best-direction-face-solar-panels/. The reasons installers don't do it is more because they don't understand it. When they understand it, it usually makes their life easier, as they have more roof space to work with. 180 degrees of separation isn't a problem, but couple that with 35 degrees and a short string of 6, and it isn't ideal, but it should be ok. The better option would be to install Tigo optimisers on the 12 panels, but that increases cost, and probably won't increase production by much. In short, maybe just keep it 6&6 paralleled east & west unless you can instal all 12 panels east or west.

Jules Baker said : Guest Report 2 months ago

Very interesting and clear article thank you very much . I'm installing a 6.6 kW system of 24 panels with 12 North 6 East and 6 West with the aim of producing power during maximum length of daylight hours to facilitate self consumption . I don't want to go to optimisers or micro inverters due to cost so must parallel two strings into one MPPT of a 2 MPPT 5 kW inverter My roofs are at nearly 35 degrees inclination so I am wondering whether an east-west split into the one MPPT would be inefficient as there is no direct sunlight on the opposing roof paralleled into the aame MPPT for a considerable period of the day . I therefore wonder whether the voltages will be equal ? Is this the reason why your article says that it is better for the parallel strings to relate to arrays only 90° separated ? If this is the case maybe I should split my north into two arrays of 6 and have North 1 and East paralleling into one MPPT and north2 and west into the other? Finally installers seem reluctant to parallel strings into the one MPPT. Is this because they are incurring some hidden extra cost apart from a few metres of extra cabling ? Like maybe additional isolators for each string... ?

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Mark C said : administrator Report 4 months ago

Hi Aiden, seems you have missed just one button. Above, the Channels the is "Devices". Click on the Devices and then select the Inverter. (If you have a smart meter or multiple inverters you can also check them).

Aidan said : Guest Report 4 months ago

Hi Mark, great blog. Just wondering if you can help me find the graph you show with the two separate mppt voltages against total power? This seems to be in the Fronius inverter homepage, however under my “chanells” tab I get no information. We have a Fronius 5.0-1 running 11 and 14 CSun 270’s split west and north respectively. It would be great to have some measure of how each string is performing individually.

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Neil Smith said : Guest Report 4 months ago

Hi Mark, thanks for your reply. Yes, I understand the IV curve business. But I'm still a bit wary of paralleling strings of panels (e.g. 2, or 3, strings of six nominally 24 volt panels, so the Voc should be about 6x30 = 180V). You talk about "fault conditions" possibly causing reverse current in one string - I presume you mean a worse "fault" than just an east-facing string having very poor sun while the west-facing one is brightly lit. What if, say, the connection to the MPPT input went open circuit? Would the east string then cop reverse current? Should it have a fuse to protect against this? If not, what sort of "fault conditions" do you have in mind? I'd like some reassurance, since paralleling unequally-insolated strings is exactly what I'd like to do!

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Cameron Quin said : Guest Report 4 months ago

Hi Mark, great article mate. Nice to see a lot of work put into an explanation piece for the whole industry.

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Mark C said : administrator Report 4 months ago

Hi Neil, In normal operation, current flows towards a load, which is the inverter connected to the grid. The voltage will equalise to the voltage that the MPPT of the inverter dictates. ... ... ... ... The "IV curve" is a whole other topic that I began to write about in this blog, but it seemed to complicate it unnecessarily. ..... ...... ..... However, in the case of fault conditions, you can get reverse module current where current from 1 string can flow backwards through the other string. Panels can handle a certain amount of reverse module current. Most panels can handle 15 amps. IF a panel can handle 15 amps, and we paralleled 3 strings of panels (at 9 amps each), then under fault conditions, the current of 2 strings could flow reverse through the other string and damage that string of panels (18 amps). So, in this situation, we would have to use a fuse smaller than 15 amps in the positive and negative of each string to protect the damage. This is called "string protection" It is usually only needed in commercial size jobs. Bit of a tangent sorry ;)

Neil Smith said : Guest Report 4 months ago

It would have been worth mentioning that when two strings are paralleled, the string which alone would have (slightly) higher voltage can't drive current in reverse direction through the other string. Like a good battery charging a bad battery. Is it because solar panels are fundamentally solid-state diodes? Or because they all actually have auxiliary diodes installed in series? Explanation of this point would be good.

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Neil Smith
Guest

It would have been worth mentioning that when two strings are paralleled, the string which alone would have (slightly) higher voltage can’t drive current in reverse direction through the other string. Like a good battery charging a bad battery. Is it because solar panels are fundamentally solid-state diodes? Or because they all actually have auxiliary diodes installed in series? Explanation of this point would be good.

Cameron Quin
Guest

Hi Mark, great article mate. Nice to see a lot of work put into an explanation piece for the whole industry.

Neil Smith
Guest
Hi Mark, thanks for your reply. Yes, I understand the IV curve business. But I’m still a bit wary of paralleling strings of panels (e.g. 2, or 3, strings of six nominally 24 volt panels, so the Voc should be about 6×30 = 180V). You talk about “fault conditions” possibly causing reverse current in one string – I presume you mean a worse “fault” than just an east-facing string having very poor sun while the west-facing one is brightly lit. What if, say, the connection to the MPPT input went open circuit? Would the east string then cop reverse current?… Read more »
Aidan
Guest

Hi Mark, great blog. Just wondering if you can help me find the graph you show with the two separate mppt voltages against total power? This seems to be in the Fronius inverter homepage, however under my “chanells” tab I get no information. We have a Fronius 5.0-1 running 11 and 14 CSun 270’s split west and north respectively. It would be great to have some measure of how each string is performing individually.

Jules Baker
Guest
Very interesting and clear article thank you very much . I’m installing a 6.6 kW system of 24 panels with 12 North 6 East and 6 West with the aim of producing power during maximum length of daylight hours to facilitate self consumption . I don’t want to go to optimisers or micro inverters due to cost so must parallel two strings into one MPPT of a 2 MPPT 5 kW inverter My roofs are at nearly 35 degrees inclination so I am wondering whether an east-west split into the one MPPT would be inefficient as there is no direct… Read more »
Julie
Guest

Hello Mark, Do you have an installation service in Adelaide. Thanks

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