kWh Face Off! East-West Vs South
Every time a commercial flat roof PV system is designed a decision to build facing South or East-West must be made. While everyone knows European solar systems will perform best facing South with a decent sized pitch, there are a number of other factors at play that influence the most profitable solution for a commercial PV system owner.
Many analyses of East-West vs South facing PV systems for commercial projects still focus on year 1 costs (price per Wp) and estimated production. In the same way that we offer a kWh Guarantee that offers reduced risk and simplicity to installers and system owners, we believe the East-West vs South question is best considered looking at the returns on investment and the levelized cost of energy. After all, solar PV customers are not looking to solve a one-off component hardware problem priced in EUR/W, they are looking for a long term energy solution.
This long term energy solution needs to consider the total costs related to the yield of a system for its complete lifespan and of course the risk related to the solar production over the same lifespan. So what are the expected returns of a solar system?
Comparison.
Let’s look at an example where we compare both alternatives for a reasonably sized commercial project in the Netherlands. We cover some of the assumptions we have made in detail below.
Over the 15 year life of the Dutch SDE+ subsidy, the system owner can generate nearly 20% more profit with an East-West system at a slightly higher return on investment. While a south facing system in the Netherlands does produce nearly 7% more yield per Wp, this power is more costly given the current solar economics of 2018.
| Azimuth | Annual yield per kWp (kWh/kWp) | Annual yield per m² (kWh/m²) | Annual savings (€) | Cost of energy produced over 15yrs (€/kWh) | ProjectIRR * |
|---|---|---|---|---|---|
| East-West | 934 | 127 | 20,443 | 0.059 | 19.30% |
| South | 997 | 100 | 16,000 | 0.076 | 17.20% |
*IRR excludes any fiscal/tax benefits
Autarco’s insured kWh Guarantee lowers the risk profile of the project for the bank, helping system owners and investors unlock more debt at lower costs. As a result, the additional initial investment required for an East-West system should not be a barrier to completion.
The drivers behind this result and some of the key factors to consider are discussed below. Regardless of the choice, Autarco’s kWh Guarantee, insured by Lloyd’s of London, delivers peace of mind to both installers and end customers by providing a minimum production level that protects your investment.
Yield per wattpeak.
| Assumption: | Face Off result |
|---|---|
| Base Assumption: 10/12 degrees | Win for South. 7.3% more yield/Wp. |
| Factor: Greater module pitches | A 30 degree pitch south system will produce 13% more than a 10 degree pitch East-West system. |
As we all know, the yield per modules it at its best when the module is facing South. However, since the pitch of the solar panels in flat roof mounting systems is relatively low (10°-12°), the non optimal azimuth of East-West systems are more than compensated by other benefits.
Yield per m².
| Assumption: | Face Off result |
|---|---|
| Base Assumption: 10/12 degrees | Win for East-West. 22.5% more yield/m². |
| Factor: Spacing of South facing | Can reduce difference to around 8% if weight is not an issue. |
The yield per module might be a little less in East-West facing systems, the total number of installed modules outweighs this, leading to much better total yields per m² roof surface. This difference can be as much as 25%, so symmetrical systems are the way to go when roof surface is limited.
Impact of increasing pitch and reducing row spacing of South facing systems is offset by other issues such as shading and ballast requirements.
Yield distribution.
| Assumption: | Face Off result |
|---|---|
| Base Assumption: Low module pitch (10-15) | Marginal win for East-West |
| Factor: Greater module pitches | Makes East-West more competitive by increasing self consumption. |
Another supposed advantage of symmetrical systems that is widely published is the distribution of yield over the day. Where a South facing system has a clear peak around noon, with solar panels facing East and West the yield is more evenly spread out. This results in a more steady production of kWh and a better match to the actual energy usage. However, the most common flat roof structures use a pitch between 10-15 degrees, so this advantage is really quite negligible as shown below.
Because of the difference in azimuth, yield distribution differs over the course of a day.
Shade.
| Assumption: | Face Off result |
|---|---|
| Base Assumption: No Shade | Win for East-West |
| Factor: Morning or evening shade | Makes South more competitive. Morning or evening shade will result in greater shade losses for East-West facing modules |
When the modules are directly facing the sun they experience higher plane-of-array insolation – the amount of direct and indirect sunlight hitting the surface of the solar panel – which of course leads to higher yields. Since most shading occurs during sunrise and sunset, the general influence of shade is worse for symmetrical systems. Common rooftop obstacles such as air conditioning units and sky lights are easily capable of causing 5-10% shade losses for East-West systems if the PV array does not avoid appropriately and plan stringing accordingly.
The Autarco modelling software is designed to make exact shading calculations, making it possible to compare both alternatives on any given location.
With modules facing south, there is a small amount of self-shading from one row to the next.
Mounting costs and ballast.
| Assumption: | Face Off result |
|---|---|
| Base Assumption: 10m roof height. | Clear win for East-West |
| Factor: Roof height or increase module pitch. | The higher roofs and greater pitches strengthen the East-West advantage. |
With a symmetrical (East-West) system, you make the most efficient use of the mounting system. Since there is hardly any space between the modules, there is no redundant mounting to be installed. Due to its nature of back to back modules, a symmetrical system is less influenced by wind loads. They form a closed system within itself, without the need to provide wind deflectors like South facing modules would need. You can save up to 15% on the costs for mounting when using a East-West facing system.
Apart from using less material per installed module, it saves on the need for ballast as well. This saves costs and labor, but more important, it lowers the total weight of a system, especially for roofs above 10 metres height. This can play an important role in the decision, mostly for industrial buildings where load bearing capacity of existing structures can be limited.
AC connection and other fixed costs.
Projects that have high fixed costs regardless of total system size also favour East-West systems. These could include things like;
- Grid connections
- Crane fees / scaffolding
Conclusion.
We hope you found this analysis interesting and useful. We are committed to making solar simpler and less risky for installers and owners of commercial PV systems. If you have any questions about how to choose the best solution for your project, please contact us.
Sunny February
At Autarco, we continuously monitor solar irradiation levels for locations where our PV systems are installed. By doing so, we are able to analyze whether the yields of these systems are as expected and all components work as they should. The collected data leads to interesting results when comparing one year with another or looking for differences between various locations around the globe.
It’s not uncommon that a months irradiation levels may change from year to year by up to 20%. This is one more reason an intelligent monitoring system that tracks your systems actual performance against actual weather conditions is so important.
See how Autarco can offer you this here.
Last winter was quite dark...
For example in the Netherlands, irradiance levels last December and January have been lower than the long term average. On top of that, snowfall led to small decreases in yield, mostly for flat-roof systems. However, since average yields in these winter months account for only a small part of the yearly total, the impact of an incidental snow cover is minimal. The Royal Dutch Meteorological Institute (KNMI) measured that the number of sun hours in December and January were both far below average, this had a big influence on irradiation levels in this period, as we saw in our satellite data as well. The winter months were truly dark this year!
... but February made up for it!
Fortunately, February 2018 showed an entirely different image. Sun hours are far above average values, even so that it is the second highest number since the KNMI start monitoring these data back in 1909. On our satellite data we see this resulting in irradiation levels that are indeed above average, up to 30%, depending on the location within the Netherlands. Together with the low temperatures and the days lengthening again, this boosts the overall performance of PV systems, resulting in good yields for this time of the year.
Clean2Antarctica
Zero-waste expedition to the South pole.
Autarco is powering the Solar Voyager vehicle in the cleanest expedition ever, Clean2Antarctica. Dutch explorer Edwin ter Velde is planning to complete the worlds first ever energy neutral and zero-waste expidition to the South Pole.
Read more about his mission here www.clean2antarctica.com
The last unspoiled continent.
The South Pole is located on the Antarctic. This is the last untouched continent of the world. The Antarctic is not owned by anyone. Luckily the Antarctic Convention is in place. Military missions should not be carried out, no raw materials should be mined and nobody should leave waste behind. How swell is that! That is what the whole world needs. And that is possible, if we collaborate genuinely. We, at Autarco, want to be part of this journey, to help our next generation.
Why is there the need to go to the Antarctic, the cleanest continent in the world? With this clean expedition, it will draw attention to the Antarctic Convention, which is to be extended in 2048 so that’ the thermostat of the world’ is preserved for future generations.
A clean earth and a climate that ensures that the earth is and remains more live-able for the next generations to come. That is why it is necessary to deal with mother nature more sensibly. Nature is cyclical and change is the only constant. And needs to STOP! We need to stop burning raw materials as once they disappear, they never come back as a raw material, never ever again.
A vehicle made from waste.
The Clean2Autartica team wants to drive up and down 2300km to the South Pole with a 100% Autarco solar-powered vehicle, autonomously without outside help. The car is built from waste material like plastic in co-creation, with individuals, government, business and youngsters who use their ideas and creativity to shape the future! It will prove that it is possible to build a car with combined knowledge, purely on solar energy and through clean technology. This first solar expedition team is therefore determined to be the cleanest expedition ever! No waste, no emission! You have to follow your dreams, dare to simply do it. We, Autarco, strongly believe in this philosophy and therefore support this expedition wholeheartedly.
Autarco named in top 3 innovative businesses
Anne-Marie Rakhorst is a successful entrepreneur and a much sought-after speaker on sustainability. In the program Booming Brabant she pronounces her personal top 3 of most innovative Brabant companies, including Autarco because of the ‘real demand-driven solution they offer’.
The importance of the kWh guarantee
Roel van den Berg, our CEO, explains his vision on the solar market and why a guaranteed output of PV systems is so important for installers and owners. This interview was broadcast on a special on sustainable energy on Dutch television.