A few miles from the beach, the weather changes, and so does the solar math. Inland homes get more sun, run more air conditioning and face more fire weather, and a system designed for the coast won’t fit them.
Key takeaways
- Inland San Diego County is much hotter in summer. In August 2023, average highs were about 77°F at San Diego’s airport, about 90°F in Escondido and about 92°F in Ramona, according to the National Weather Service.
- Inland roofs also get more sun. In the federal PVWatts model, a south-facing system in Escondido produces about 6 percent more per year than the same system near downtown San Diego, with the biggest gains in May and June.
- Heat trims panel output, typically about 0.26 to 0.40 percent for every degree Celsius above 25°C (77°F) for modern panels, so panel choice and airflow matter more inland.
- Bigger air conditioning loads land in SDG&E’s 4 to 9 p.m. peak, so inland homes get more value from west-facing panels and a battery.
- Backcountry areas around Ramona, Alpine and Jamul face more fire weather and power shutoffs, which makes backup power part of the design.
Frequently asked questions
Does solar produce more inland than on the coast in San Diego?
Usually, yes. In the federal PVWatts model, a 1 kW south-facing system produces about 1,700 kWh a year in Escondido versus about 1,600 kWh near downtown San Diego. Inland areas tend to clear the marine layer sooner, which shows up most in May and June.
Do solar panels lose efficiency in the heat?
Yes, a little. Modern panels typically lose about 0.26 to 0.40 percent of output per degree Celsius above 25°C, and a panel on a hot roof runs well above the air temperature. Inland homes still come out ahead on annual production, but panels with a low temperature coefficient are worth a look.
What is SDG&E’s Inland climate zone?
SDG&E divides its territory into Coastal, Inland, Mountain and Desert baseline zones. The baseline allowance, the amount of electricity SDG&E treats as a basic need, is a little higher in the Inland zone in summer: 10.4 kWh per day versus 9.0 on the coast under SDG&E’s Schedule DR.
How big should a solar system be for a hot inland home?
Size it to a full year of your actual usage, not a rule of thumb. Inland homes often use far more electricity in summer for air conditioning, and much of that falls in SDG&E’s 4 to 9 p.m. peak, which is why many inland designs add west-facing panels or a battery.
Do I need a battery in Ramona or East County?
It depends on your goals, but inland homes have two extra reasons to consider one: evening air conditioning during the most expensive hours, and power shutoffs during fire weather, which hit backcountry communities more often than the coast.
San Diego County has two climates, and anyone who drives from Carlsbad to Escondido in August knows it. The coast stays mild under the marine layer. Inland North County and East County bake. That difference shows up in your electric bill, and it should show up in your solar design.
Here’s what changes when your home is in Escondido, San Marcos, Vista, Ramona, El Cajon, La Mesa, Spring Valley or anywhere else east of the coastal strip.
Inland summers run hotter
The National Weather Service’s monthly climate summary for August 2023 shows the gap: the average high was about 77°F at San Diego’s airport, about 90°F in Escondido and about 92°F in Ramona. El Cajon and the East County valleys run hot for the same reason. They’re far enough from the ocean that sea breezes don’t cool them down.
More heat means more air conditioning, and air conditioning is usually the biggest summer load in an inland home. We break down how much of that solar can cover in how much of your summer AC can solar offset?
Inland roofs get more sun
The good news is that the same distance from the coast that brings the heat also brings more sunshine. Coastal neighborhoods spend many late-spring and early-summer mornings under May Gray and June Gloom. Inland, that cloud deck usually burns off sooner.
You can see it in the federal PVWatts calculator. For a 1 kW south-facing system with standard assumptions, PVWatts estimates:
| Location | May | June | Annual |
|---|---|---|---|
| Downtown San Diego | 143 kWh | 147 kWh | about 1,600 kWh |
| Escondido | 163 kWh | 161 kWh | about 1,700 kWh |
That’s about 6 percent more energy per year from the same panels, already accounting for the heat.
Heat costs a little output
Solar panels are rated at 25°C (77°F), and they get slightly less efficient as they warm up. The measure is the temperature coefficient: modern panels typically lose about 0.26 to 0.40 percent of output for every degree Celsius above 25°C. A panel on a dark roof on an inland August afternoon can run 30°C or more above that rating, which can mean roughly 10 percent less output in the hottest hours.
You can’t change the weather, but you can design around it:
- Choose panels with a low temperature coefficient. Many premium panels are rated around 0.26 to 0.30 percent per degree.
- Leave airflow under the array. Standard racking keeps panels off the roof surface so they shed heat.
- Don’t oversize to compensate for heat. The production estimate already accounts for it, so size to your usage.
The bill is shaped by the evening
SDG&E’s most expensive hours are 4 to 9 p.m., every day of the year. On a hot inland afternoon, that’s exactly when the house is hottest and the air conditioner works hardest. Under the Solar Billing Plan, solar you export at midday earns far less than the power you buy back in the evening, so the inland design question is how to cover those hours.
Two tools do most of the work:
- West-facing panels shift production later into the afternoon. We explain the tradeoff in why west-facing solar beats south in San Diego.
- A battery stores midday solar and runs the house through the evening peak.
Your baseline zone
SDG&E divides its territory into four baseline climate zones: Coastal, Inland, Mountain and Desert. Your zone sets your baseline allowance, the amount of electricity SDG&E treats as a basic need. Under SDG&E’s Schedule DR, the summer baseline is 10.4 kWh per day in the Inland zone versus 9.0 on the coast. Most inland homes blow well past either number on a hot day, so the zone matters less than the air conditioner. Higher-elevation areas can fall in a different zone, and SDG&E’s baseline tools show which applies to your address.
Fire weather and power shutoffs
The backcountry around Ramona, Alpine and Jamul sits close to wildland, and SDG&E is more likely to shut off power there during Santa Ana wind events. If you live east of the I-15, it’s worth checking your address against the state’s fire-threat map, which we walk through in do you live in an SDG&E High Fire Threat District?
Grid-tied solar shuts off during an outage, so backup takes a battery. For larger inland homes with pools, well pumps or medical equipment, it’s worth deciding up front which circuits need to stay on.
A few city notes
- Escondido and San Marcos. Hot summers, plenty of sun, and many homes with pools and big air conditioning loads. Strong candidates for west-facing panels and a battery.
- Vista. Sits between the coast and the inland valleys, so summer temperatures fall in between. Production estimates should use your actual address, not a coastal or inland average.
- Ramona. Higher elevation, hot summers, cold nights and larger lots. Ground-mount solar is sometimes an option, and backup deserves extra attention.
- El Cajon, La Mesa and Spring Valley. East County valley heat makes the evening peak the main design challenge.
Design for where you live
An inland home isn’t a coastal home with a bigger air conditioner. It has more sun, more heat, a later peak and, in some areas, more shutoff risk. Stellar Solar designs around all four, using your address and a full year of your usage. 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. Call 866.787.6527 for a free evaluation, or get your free quote here.
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