01 / ENERGY FOUNDATIONS
Solar energy,
without the magic.
A panel is not a tiny battery or a miracle box. It is a device that turns part of the sunlight arriving on it into electrical power. Start with that, and the estimates get much easier to read.
THE TWO WORDS THAT MATTER
Power is a rate. Energy is an amount.
Power describes how quickly electricity is being produced or used. It is measured in watts (W) or kilowatts (kW). Energy is power accumulated over time, commonly measured in watt-hours (Wh) or kilowatt-hours (kWh). A 1,000-watt appliance running for one hour uses 1 kWh. If it runs for ten minutes, it uses about 0.17 kWh.
This distinction explains why a panel's nameplate rating and its daily output are different numbers. A panel marked 400 W can produce 400 W only under specified test conditions, not all day. Sun angle, clouds, heat, shade, inverter behavior, and wiring losses all shift the real output.
energy (kWh) = average power (kW) × time (hours)A FIRST ESTIMATE
Use peak-sun-hours carefully.
“Peak sun hours” are a convenient way to express the day's sunlight as an equivalent number of hours at a standard strong irradiance. Four peak-sun-hours does not mean the Sun was overhead for four clock hours; it means the day's total solar energy is roughly equivalent to four hours at the reference level.
A rough daily estimate is installed array power multiplied by local peak-sun-hours, then multiplied by a performance factor to allow for losses. For example, a 4 kW array, 4 peak-sun-hours, and an illustrative 0.8 performance factor gives about 12.8 kWh for that day. The factor is not universal: equipment, temperature, orientation, shading, and system design change it.
Try it: Change the array size or sunlight assumption in the Solar Energy Lab. Treat the result as a planning estimate, not a promise or a quote.
THE SYSTEM AROUND THE PANEL
Panels are one part of a chain.
Photovoltaic cells produce direct-current (DC) electricity. An inverter converts that electricity into alternating current (AC) for ordinary household circuits or a grid connection. Mounting hardware holds the modules in place, while conductors, disconnects, protective equipment, and monitoring complete the installation.
Some systems add a battery and a device that can safely isolate selected circuits during an outage. A standard grid-connected inverter generally shuts down when the utility grid is down, even if the Sun is shining: this protects workers repairing the network. Backup requires equipment specifically designed and approved for that mode.
READ THE WHOLE PICTURE
Annual energy is not the same as independence.
A rooftop system can produce as much energy over a year as a home consumes and still import power at night or during a cloudy week. Timing matters. So do local export rules, retail electricity prices, connection fees, and seasonal variation. A bill credit for exported energy may be worth less than the price paid for imported energy.
To compare designs, ask for the assumed annual production, monthly seasonal profile, estimated losses, equipment warranties, and the exact export tariff used in the financial model. Read the roof-readiness checklist before comparing quotes, and the battery guide before treating storage as an automatic upgrade.