South-facing versus east-west, side by side
Why south-facing wins on total output
A true south-facing array at the optimal tilt for your latitude captures the most direct sunlight available across the year, which is why it remains the benchmark for maximum annual kWh. An east-west split typically produces 12 to 20% less energy per kW installed, since half the array always faces away from the sun's strongest midday position. Run both orientations for your own address in NLR's PVWatts calculator to see the exact output difference before you choose.
Why the lost output doesn't always mean lost savings
South-facing arrays generate a sharp peak around midday, often more than a household without a battery can use in real time, pushing the surplus to grid export at a lower credit rate. East-west arrays spread generation across more of the day, aligning better with morning and evening usage patterns common in most households. That shift in timing can raise the share of solar power used directly, sometimes closing much of the financial gap even though total kWh is lower. How much the timing is worth depends on your utility's export rules, which the DSIRE database entry for net metering lists for your state.
How roof shape changes the math
A roof with only one usable south-facing slope has a fixed ceiling on panel count. A roof with two usable slopes, one east and one west, can sometimes fit more total panels across both surfaces than a single face would allow. When that's the case, the extra panel count can offset some or all of the per-kW output disadvantage, since more total panels are converting sunlight even if each one is individually less efficient than a south-facing panel would be, a tradeoff the panel orientation output comparison tool quantifies directly for a given roof layout.
When to pick each layout
Choose south-facing when you have a good south-facing roof, plan to add battery storage, or want to maximize total annual kWh for a full-value net metering arrangement. Choose east-west when your best roof faces are east and west instead of south, your household uses more power in the morning and evening, or your utility pays less for exported power than what you save by using it directly. A battery narrows this gap considerably, since a well-sized battery lets a south-facing system store its midday surplus for evening use instead, a comparison the self consumption battery size calculator works through directly. If your roof pitch also differs from the optimal tilt for your latitude, the roof pitch adjustment calculator shows that separate factor.
What to do with this comparison next
Check your exact roof's compass direction with the roof azimuth orientation calculator if it isn't a clean east-west split, or confirm your usable panel count with the usable roof area calculator before finalizing either layout.