How Much of Your Summer AC Can Solar Offset?

How Much Solar It Takes to Cover Your Summer AC

What your AC actually costs in a San Diego summer

A typical central AC compressor for a San Diego home draws somewhere between 3 and 5 kilowatts while it’s running. On a hot inland day it might run four to eight hours — and not always in one stretch, since it cycles on and off to hold your setpoint. Add it up and you’re looking at roughly 15 to 35 kWh of cooling in a single day, with the higher end common in places like El Cajon, Santee, Escondido, and the inland valleys where summer afternoons are genuinely hot.

That’s the part that stings under SDG&E’s rates. On the TOU-DR1 plan, summer on-peak power (4–9 p.m., June through September) runs about 69.65¢/kWh in 2026. Off-peak is around 46¢ and super off-peak about 38¢. So the same hour of cooling can cost you very different amounts depending on when the compressor runs — and unfortunately, late afternoon and early evening, right in that expensive 4–9 p.m. window, is exactly when homes are hottest and AC works hardest.

A quick worked example

Say your AC adds 25 kWh on a hot day, and about a third of that runs during the 4–9 p.m. peak. That’s roughly 8 kWh at ~70¢ (about $5.60) and 17 kWh across cheaper hours at, say, an average of 50¢ (about $8.50) — around $14 in cooling in a single day, or well over $400 across a hot month just for air conditioning. For a lot of San Diego homes, cooling is the single biggest reason the summer bill balloons, and it’s concentrated in exactly the hours SDG&E charges the most.

How much of that solar can offset

Here’s the good news: cooling season and solar season are the same season. Your panels produce the most in exactly the long, bright months your AC runs hardest. During the day, a properly sized system can run your AC directly on solar and send the excess to the grid.

For most San Diego homes, a well-designed system can offset the large majority of daytime cooling — often effectively all of it while the sun is up. The part solar doesn’t automatically cover is the 4–9 p.m. peak, when the sun is dropping but the house is still hot. That’s the gap a battery fills: you bank cheap midday solar and discharge it through the expensive evening window instead of buying 70-cent power.

So the honest answer is: solar can offset most of your summer AC, and solar plus a battery can offset nearly all of it, including the pricey evening hours.

Why the battery matters more under today’s rules

Under SDG&E’s current Net Billing structure, the surplus solar you export midday is credited at a relatively low rate, while the power you buy back at 6 p.m. is charged at that steep peak price. That spread is exactly what a battery captures. Instead of “selling low and buying high,” you store your own midday production and spend it during the peak — so a battery doesn’t just add backup, it directly protects the most expensive kilowatt-hours of your cooling load.

How many panels it takes

A modern residential panel is roughly 400 watts. As a rough planning number, each panel produces on the order of 1.5–2 kWh on a good San Diego summer day.

If your AC is adding, say, 20 kWh on a hot day, covering that load alone takes something like 10–14 panels’ worth of production on top of whatever the rest of your house uses. That’s why the sizing conversation matters: a system built only for your annual average usage can come up short in July and August, when cooling spikes your demand well above the yearly mean.

The fix is to size for the summer peak, not the average. When we design a system, we look at your actual highest-usage months and your afternoon load shape, so the array is big enough to carry the hot season instead of leaving you buying expensive top-up power exactly when rates are highest.

What changes the panel count for your home

• Your climate zone. A coastal home in Encinitas or Point Loma barely runs AC; an inland home in Ramona or Poway may run it for hours. Same house size, very different cooling load.
• Home efficiency. Insulation, windows, ductwork, and shade all change how hard the AC works — and therefore how many panels it takes to offset.
• AC type and age. An older single-stage unit draws more than a modern variable-speed or heat-pump system for the same comfort.
• Roof space and orientation. How many panels physically fit, and how they’re aimed, affects both the count and how much of the peak they can cover (a west lean helps into the evening).

The mistakes that leave AC savings on the table

• Sizing to the annual average. It looks efficient on paper but underperforms in the months you care about most.
• Ignoring the 4–9 p.m. window. Solar alone tapers in the evening. If beating the summer peak matters to you, plan for a battery.
• Forgetting future load. If an EV, a pool, or a heat pump is in your future, size for where you’re headed, not just where you are — adding panels later is more expensive than building the headroom in now.
• Chasing the cheapest quote. An undersized system is the most common way homeowners end up disappointed with “solar that didn’t lower my bill much.” It usually wasn’t solar’s fault — it was the sizing.

A few quick questions homeowners ask

Can solar run my AC by itself during the day? Yes — a correctly sized array can power your AC directly while the sun is up, sending any extra to the grid.

What about at night or during the 4–9 p.m. peak? That’s where a battery comes in. Panels can’t produce after sunset, so storage is what carries your cooling through the expensive evening hours.

Will one hot summer month wipe out my savings? Not if the system is sized for your summer peak. That’s the whole point of designing around your hot-season usage rather than a flat annual number.

The bottom line

In San Diego, solar and summer line up beautifully — the sun is strongest when your AC needs it most. A system sized to your actual hot-season usage can offset most of your cooling costs on its own, and adding a battery closes the gap on the expensive 4–9 p.m. evening hours. The key is designing around your summer peak and your afternoon load, not a flat yearly number.

Want to know exactly how many panels it would take to cover your AC on your roof? Stellar Solar has been San Diego’s trusted solar installer since 1998 — A+ rated with the BBB and a repeat winner of San Diego’s Best Solar in the Union-Tribune Readers Poll. Get a free, no-pressure system estimate built around your real summer usage at your free quote here or call 866.787.6527.

from Stellar Solar https://ift.tt/5GrX7R2