Understanding Solar Production
Two numbers cause most of the confusion in solar quotes: kilowatts (kW) and kilowatt-hours (kWh). They sound similar, but they measure very different things.
Last updated 2026-08-19
kW (kilowatt)
A measure of power at an instant — how big your system is. A 10 kW system can produce up to 10 kW at any given moment under ideal conditions.
kWh (kilowatt-hour)
A measure of energy over time — how much electricity is actually produced or used. Your electric bill is measured in kWh.
System size
The total wattage of all panels, usually shown in kW (e.g. 10 kW).
Annual production
The modeled estimate of how many kWh the system will generate over a year.
Consumption
How many kWh your home uses in a year — found on your electric bill.
Solar offset
Your estimated production divided by your consumption, shown as a percentage.
A simple example
A homeowner uses 10,000 kWh of electricity a year. If a solar design is estimated to produce roughly 10,000 kWh annually, that represents about a 100% estimated annual energy offset.
Key distinction
What affects production
- Roof direction (south, west, east, north)
- Roof pitch (steepness)
- Shade from trees, chimneys, or nearby buildings
- Panel orientation and tilt
- Equipment — panel efficiency and inverter type
- System size (total kW)
- Temperature (panels are less efficient when very hot)
- Weather and clouds
- Season (longer, sunnier days in summer)
- Snow cover in winter
- System availability (downtime reduces annual output)
Why production changes throughout the year
Days are longer and the sun is higher in summer, so a system can produce two to three times more in July than in December. Snow can briefly shut production down entirely. Your monitoring app will show a predictable curve across the year — that's normal, not a sign something is broken.
Why two solar quotes can show different production
This trips up a lot of homeowners. Two contractors can propose systems with similar system sizes but very different modeled production numbers — because production is an estimate built on assumptions.
When you compare quotes, compare these together:
- System size (kW)
- Panel count
- Panel wattage (each)
- Annual kWh estimate
- Shading assumptions used in the model
- Orientation and tilt used
- Equipment (panels and inverters)
- Modeling assumptions/derate factors
A practical tip
Next step
Already have a solar proposal?
Send it to Charles for help understanding the design and production estimate.
About Charles Brogden
Charles Brogden works directly with homeowners through AllSeason Solar & Roofing, helping customers understand solar system design, equipment, roofing considerations and available solar options.
Serving homeowners throughout New Jersey and Pennsylvania.