In the event you ask ten photo voltaic professionals methods to orient a rooftop array within the Northern Hemisphere, most will reply the identical approach: face it south. And for a lot of tasks, that is still a stable default. A south-facing array usually squeezes probably the most vitality out of every panel.
However on many industrial roofs, and particularly on flat rooftops, the actual constraint isn’t the solar. It’s area.
When roof space is proscribed, the query turns into: What format allows you to set up probably the most space-efficient photo voltaic capability inside finances on the obtainable space? In these eventualities, an east–west (E–W) format can outperform a south-facing format. The South format could also be “higher positioned”, however the E-W permits the set up of extra panels in the identical space.
This text walks by when an E-W configuration is smart, utilizing an easy roof instance and 5 case research throughout the U.S.
A Fast Clarification: What We’re Evaluating
Earlier than the numbers, it helps to outline what “higher positioned” means:
- South-facing mounted tilt at optimum inclination typically maximizes vitality per panel.
- E-W at low mounted tilt typically maximizes energy per obtainable space.
The Two Situations the place East–West Shines
East–West isn’t a substitute for south-facing arrays in each scenario. The benefit tends to point out up when each situations apply:
- You might be engaged on a flat floor. This contains flat roofs (similar to malls, warehouses, workplace buildings, flats, and homes), flat canopies with area constraints, and probably floating PV platforms, similar to these on ponds or reservoirs.
- The lean angle is low: from 5° to 10.° Low-tilt arrays are generally used on flat roofs as a result of they will cut back wind uplift forces and reduce row-to-row shading.
Low tilt is frequent on flat roofs for sensible causes:
- It reduces the uplift load and helps handle wind-related structural necessities.
- It could actually cut back row-to-row shading constraints as a result of the array sits decrease.
- It could actually simplify roof loading methods when utilizing ballast techniques.
When these two situations are current, east-west layouts typically enable tighter packing, that means the next energy density. Additionally, on a space-limited roof, increased energy density can translate into stronger mission economics.
A Easy Roof Instance (4,290 sqf)
For instance this trade-off, take into account a flat floor measuring 4,290 sq. ft (sq ft) with the purpose of putting in as a lot photo voltaic capability as is sensible.
Choice A is a traditional design method that will use a south-facing ballast-mounted system. Utilizing 450-watt modules at a ten° tilt, this floor can accommodate 120 panels, leading to a 54 kW DC system.
Choice B is an E-W configuration utilizing the identical 450-watt modules. With an 8° tilt (the identical angle utilized by the identical producer for the South instance), the identical floor can match 152 panels, for a complete of 68.4 kW DC.
What Modified?
The roof didn’t get larger. The kind of module didn’t change. What modified is the format effectivity.
On this instance, the east–west configuration will increase put in capability from 54.0 kW to 68.4 kW, a 27% improve in capability on the identical footprint. That’s the core benefit: extra watts put in per sq. foot, which can generate extra vitality.
What Does that Imply for Power Manufacturing?
To know how this performs out, 5 case research had been evaluated utilizing NREL’s PVWatts device, assuming a 0.5% annual module degradation charge. The places had been chosen to signify a spread of U.S. climates:
- Orlando, Florida
- Bakersfield, California
- Malta, New York
- Seattle, Washington
- Lincoln, Nebraska
As anticipated, the east–west techniques produce extra vitality in each location, not as a result of they’re extra environment friendly per panel, however as a result of they’re bigger techniques on the identical roof. In fact, if you happen to can set up the identical quantity of PV modules going through south, you’re going to get increased vitality era than the E-W, however can you put in extra?
The extra vital query, nevertheless, is whether or not that further manufacturing justifies the associated fee.
Put in Price: Extra Capability Does Not All the time Imply Greater Price
Estimated put in prices had been calculated for every system, accounting for typical regional labor charges and site-specific structural necessities.
Structural prices range by location. Excessive-wind areas, similar to Orlando (design wind speeds as much as 137 mph), and heavy-snow areas, similar to Malta, New York which may attain as much as 76 kilos per sq. ft (psf), improve racking and ballast necessities. These elements have an effect on each layouts, although E-W techniques can generally distribute hundreds extra effectively.
Choice A (left): South-facing ballast system, tilt angle 10,° 120x450W PV modules. Choice B (proper): E-W going through ballast system, tilt angle 8,° 152x450W PV modules. © Baker Makarem
{The electrical} scope, typically the supply of unexpected challenges throughout development, was assumed to be comparable for each instances.
A Useful Metric: Price per Put in kW peak ($/ kWp)
This metric helps reply: How a lot photo voltaic capability do you get for every greenback invested?
Throughout these 5 instances, the east–west configuration averages about 16% decrease value per put in kilowatt than the south-facing format, with some places exhibiting variations as little as 23%.
For instance, with a $20k finances in Seattle, a south-facing format would enable for as much as 11.69 kWp of put in capability, producing about 11,228 kWh within the first 12 months.
With the identical finances utilizing an east–west configuration, you may set up as much as 13.69 kWp of PV, with an estimated annual manufacturing of 12,074 kWh.
Payback and ROI: The place the Comparability Turns into Actual
Payback Interval. Payback refers to how lengthy it takes for the system’s financial savings (from electrical energy generated) to get better the preliminary funding.
The evaluation for town of Orlando assumes an electrical energy worth of $0.11 per kWh and a 6% annual improve in electrical energy charges. The east–west system reaches payback prior to the south-facing system, reflecting its increased manufacturing and decrease value per kilowatt.
Payback time in years, Orlando, FL. © Baker Makarem
A shorter payback additionally leaves extra monetary margin over the system’s life to cowl capital bills, similar to inverter replacements.
Return on Funding (ROI). That is one other metric to think about, which measures internet financial savings vs. funding. Throughout the 5 eventualities, the ROI ranged between 130% to 252%. These values can range relying on bills through the 20-year estimated lifespan of the system.
The message is constant: in these examples, east–west layouts ship stronger ROI as a result of they set up extra capability per roof space and usually accomplish that at a decrease value per kilowatt, with increased vitality manufacturing, in comparison with what might be put in going through south.
A Few Essential Concerns
These workouts had been deliberately simplified to concentrate on format trade-offs. A number of real-world elements can change outcomes:
- Financial savings had been calculated with out rebates or incentives. Which is, in some side, a greater perspective, for the reason that Federal Photo voltaic Funding Tax Credit score (ITC) is not obtainable.
- For industrial tasks, depreciation remedy can shorten payback durations and improve ROI.
- Operations and upkeep prices weren’t modelled intimately. Whereas these techniques will incur upkeep bills over a 20-year lifespan, the general profitability stays robust.
- It is usually value noting that east–west arrays typically produce a broader day by day era profile, with extra output within the morning and late afternoon. In markets with time-of-use pricing and demand fees, this flatter manufacturing curve can add further worth.
Takeaways
East–west photo voltaic configurations will not be a substitute for south-facing techniques, however they are often extra worthwhile in the fitting eventualities.
They have an inclination to carry out finest when:
- The floor is flat (frequent in industrial buildings)
- The design makes use of low tilt angles (5° to 10°)
- Roof space is the first concern
These situations are frequent in industrial buildings, warehouses, and more and more in floating PV techniques. As floating photo voltaic continues to develop, east–west layouts might play an vital position in maximizing vitality output per obtainable floor.
Generally, the most effective photo voltaic design isn’t about chasing the right angle, however about profiting from the area you may have.
In regards to the Authors
Baker Makarem is a Mechanical Engineer and NABCEP-certified ESIP, PVIP, and PVSI. He’s the founding father of Bakertech, an organization specialised within the photovoltaic (PV) and vitality storage techniques (ESS) trade. He has been within the renewable vitality subject since 2017.
Carla Monzer beforehand labored as a advertising and marketing guide in a world market analysis agency offering client, trade, and market intelligence. She is at present a PhD pupil in Advertising and marketing on the College of South Florida. Her analysis pursuits concentrate on sustainability, with explicit consideration to renewable vitality and its interplay with client conduct.
