Can You Install Solar Panels on East and West Facing Roofs?
By Aniket Bhor on in How Solar Power Works
Ask any solar expert about solar panel orientation and they will tell you that North-facing arrays perform the best. This is true, for reasons we’ll go over shortly; but what if your house doesn’t have a North-facing roof? Also, are there benefits of East and/or West facing panels that could make an E-W layout more beneficial?
Let’s answer these questions one by one. But before that, a quick revision on the relation between directions and power output.
The Best Direction for Solar Panels
A solar panel generates the maximum possible power when it faces the sun directly. In other words, every ray of sunlight hitting the panel should hit it at a 90° angle for maximum output. Sunrays hitting panels at a different angle are more likely to bounce off instead of getting absorbed and converted into electricity.
And since we’re paying thousands of dollars for our solar power systems, we want them to produce the maximum possible power. However, the sun keeps moving through the sky (of course we know it’s the Earth that moves around the sun, but let’s keep it simple here), which means it is impossible to catch sunrays at 90° throughout the day.
In New Zealand, since we are situated in the southern hemisphere, sunrays strike us from the northern side for the most part of the day as well as the year. And while the angle might not always be 90° even for north-facing panels, it is as close to perpendicular as it can get. This is why the recommended direction for solar panel installation is facing North.
Here’s a simple drawing that shows the variation in the angle of sunrays throughout the seasons. Note that no matter the season, the sun always looks at us from the North.
Now let’s move on to the main question of East-West facing roofs.
Does it Make Sense to Install East/West Facing Solar Panels?
Needless to say, most homes in New Zealand are not designed with solar panels in mind. Therefore, there are plenty of houses where there is no North-facing roof. Thankfully, this is not much of a deal-breaker. Because although we said that North is the best, we never said that solar panels don’t work when facing other directions.
Solar panels convert particles of light into electricity, which is why theoretically they can work anywhere there’s light - even indoors (although it would be a terrible waste of money to install solar panels indoors). Naturally, panels can generate power if they are installed on a roof that faces directions other than North.
But let us get one thing out of the way - solar panels hate south-facing roofs in NZ, because they spend most of their time devoid of sunrays, producing little to no power. What remains is the East and West directions.
East and west-facing solar panels on a house (source: SMA)
Solar panels can definitely be installed facing East and/or West. While the maximum sunlight in a day comes from the northern side, E-W installations can actually have unique benefits that north-facing panels don’t. Let’s take a look at those.
Benefits of installing East or West facing solar panels
There are two ways to look at the power generated by a solar array. First is the total power generated throughout the day, and second is the hour-by-hour power generation values. As we already mentioned, north-facing panels generate the most power in any 24-hour cycle.
On the other hand, solar panels facing east and west receive more sunlight during the mornings and evenings. Here’s a graph that compares the power generation values of E-W vs south-facing panels throughout the day. Note that this study is done in England, where the south is the desired direction for panels, just as it is north in NZ. If we were to replicate the study in NZ, we would have similar graphs, with the purple line showing output from a north-facing array.
Based on the generation values, the south-facing (north-facing for NZ) graph has about 15% higher generation on average. However, as we said before, total daily generation isn’t the only important metric. E-W facing arrays can generate more power during mornings and evenings, which can be seen from the broader area covered by the blue graph. Let’s talk about what this signifies.
North-facing panels will generate much more power during mid-day when the sun is directly shining on the panels from the north. However, most homeowners need the least power during mi-day, when people go to work, and the lights and TVs are switched off.
East-west facing panels, on the other hand, generate more power in the mornings and afternoons, as seen in the graph. And in most cases, homeowners need more power during these hours - when their coffee machines, toasters, lights, TVs, etc. are running.
For north-facing panels, you would have to store all that energy in a battery bank to use during the evenings and mornings. Or you'll need to put timers on appliance (increased self-consumption) to start around this time.
If you rely on a battery to soak up the excess solar instead of shifting your energy load, while you’d have more energy, you would also need a larger battery bank to accommodate all that energy or shift the energy demand time. In the case of E-W panels, the greater power generated during mornings and evenings can be consumed instantaneously, and you’d need smaller battery storage.
What this means, is that east-west facing solar panels are not just a compromise, but can also be advantageous in a certain way.
Other Options
If you do not have a north-facing, shade-free roof area, and you are not convinced with the east-west orientation, you still have a few other options.
Firstly, if you have a flat roof, you can choose to install the panels flat. This makes for a simpler, cheaper installation and even saves space. When installing flat, there’s really no such thing as orientation, as they will not face any particular direction except straight upwards.
Secondly, if you have sufficient space around your house, you can choose to install the panels on the ground, in which case, there are no restrictions on the orientation. Ground-mounted panels are also easier to maintain, and can be installed with tracking mechanisms.
Speaking of tracking mechanisms, you can make the panels always face the sun directly if you keep turning them throughout the day and/or throughout the year. Tracking mechanisms change the angle of the panels based on the sun’s trajectory. Naturally, solar arrays with trackers generate unbeatable amounts of power, surpassing any single orientation.
However, this comes at a cost of hundreds or thousands of dollars. And in pretty much every scenario, that money is better spent buying a few extra panels than spending on complicated trackers.
Homeowners who have a limited north-facing roof can also split their arrays. For example, suppose you need a 5 kW array, which needs 400 sq. ft. roof space, but you have just 200 sq. ft. of north-facing roof area. In such a case, you can also opt for a combination of north and E-W orientation, as seen in the following image.
Combination of north and east-facing panels (credit: Charlie Wilde/Pixabay)
The Rising Popularity of East-West Facing Solar Panels
Remember those videos with clickbaity titles like ‘You’ve been peeling oranges wrong your whole life’? Something similar happened with solar panels. A few years ago, a slew of new articles populated the internet, with titles like ‘We have been installing solar panels wrong our whole life’.
In truth, we weren’t necessarily doing ‘incorrect’ installations, just as our orange-peeling wasn’t so criticisable. But the articles did have some point. They claimed that east-west facing modules provided more electricity at times of high demand than south (or north) facing modules. In other words, the articles stressed on the quality of energy profile than simply the quantity of energy generated in a day.
The authors of these articles were inspired by studies that corroborated this fact, such as the 2013 study by Texas’ Pecan Street Research Institute, or the 2014 study by UK’s Loughborough University. But these studies didn’t just influence blogs. The California Energy Commission recently announced a bonus of up to $500 for new installations that point west. Similarly, the Columbia Water & Light utility also offered a 25% higher rebate for west-facing panels.
While we don’t expect to see a similar ‘awakening’ here in New Zealand regarding E-W orientation, we can rest assured that not having a north-facing roof is no bane.
Utility-Scale and Commercial Projects
In 2016, shortly after the sensational headlines about conventional solar installations being ‘wrong’, French company Cestas installed a 300 MW solar power plant with panels facing east-west. The result was a power generation that was 15% lower than traditional, south-facing arrays. However, strings of E-W facing panels can be installed much closer to each other, and the plant generated about three times more power per square meter than a south-facing orientation.
East-west orientation of the Cestas plant, allowing closely mounted panels (source: Clemessy)
This meant that while the net generation was lower, the company saved on the fixed costs, resulting in a higher levelized cost of electricity (LCOE). The lesson from this story is that in places where land is expensive, E-W facing panels might make more sense through the saved initial costs. Moreover, if the plant is located in an area with time-of-use pricing, more power during mornings and evenings (peak times) may also mean higher revenue.
Conclusion
Until solar panels become dirt cheap, we will be fretting over things like performance, efficiency, and subsequently orientation. And when it comes to orientation, conventional wisdom states that for New Zealand, north is the best direction. Most solar installers in the country still offer north-facing systems as their default options.
But homeowners who don’t have a north-facing roof don’t need to be discouraged. As trends change, east-west orientation is now suddenly the next big thing. E-W facing solar panels may generate less energy than north-facing ones, but they generate energy when you need it most, making them a popular orientation.
For aesthetic reasons, Kiwis with a north-facing house may even choose to install E-W to avoid installing panels on the front-facing roof. Utility-scale plants, on the other hand, can save huge amounts of land and thus initial costs by going east-west. As solar panels get cheaper, it might not be surprising if the east-west orientation becomes the default choice.
Ultimately, to answer our original question of whether you can install solar panels on east and west-facing roofs - it is a big ‘Yes’!