How many peak sun hours do I get?

3–6 per day in most of the US depending on location and season.

What depth of discharge should I use?

80–90% for lithium; 50% for lead-acid to protect its life.

What system losses should I assume?

15–25% for temperature, wiring, inverter and soiling.

How much does 1 kW of solar produce in the US?

About 1,200–1,700 kWh a year depending on location.

What is the payback period?

It depends on usage, rates and incentives — compare estimated production with your bill.

Almost always — plus utility interconnection approval.

Solar: size your system

Number of solar panels, battery bank size and DC wire voltage drop.

Calculators

Solar panel calculator
System kW and panels from usage and sun hours.
Battery bank calculator
kWh, amp-hours and battery modules for backup.
Solar wire voltage drop calculator
DC voltage drop and minimum wire size.

How do you size a grid-tied solar system?

Start from annual usage (bills), divide by local peak sun hours corrected for system losses to get kW, then panel wattage gives module count and roof space. PVWatts or PVGIS estimate production by location, orientation and tilt.

With full net metering size near annual usage; without it, near daytime usage.

Do I need batteries?

Not for grid-tied systems, but they store daytime solar for night and add backup. Size them by overnight usage, days of autonomy, depth of discharge and efficiency.

Off-grid systems need them, ideally with a backup generator.

What about DC wiring?

DC runs — especially at low voltage and between battery and inverter — carry high current: generous sizes and short runs cut losses. Use PV-rated wire and proper overcurrent protection on each string.

Follow NEC Article 690 and get the system permitted and inspected.

Prices & Guides

FAQs

How many peak sun hours do I get?: 3–6 per day in most of the US depending on location and season.
What depth of discharge should I use?: 80–90% for lithium; 50% for lead-acid to protect its life.
What system losses should I assume?: 15–25% for temperature, wiring, inverter and soiling.
How much does 1 kW of solar produce in the US?: About 1,200–1,700 kWh a year depending on location.
What is the payback period?: It depends on usage, rates and incentives — compare estimated production with your bill.
Do I need a permit?: Almost always — plus utility interconnection approval.

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