Two identical systems on identical roofs can produce identical power and still save very different amounts. The difference is when the household uses energy. Running dishwashers, laundry, and EV charging during daylight hours means consuming your own production instead of buying evening grid power at retail rates.

Most savings projections assume utility rates rise around three to four percent a year, which has held across recent decades. Every rate increase widens the gap between what the grid charges and what your panels cost you, so year-ten savings usually look better than year-one savings.

Modern panels lose roughly half a percent of output per year, which means a system still produces close to ninety percent of its original power after two decades. Honest savings models bake this in, so degradation should never arrive as a surprise on your bill.

Most underperforming systems fail quietly — a tripped breaker, a faulty optimizer, new shade from a growing tree. A quick monthly glance at your monitoring app catches these early. The households that check occasionally keep their real savings closest to the projection.