Right-size your solar.
Buy factory-direct.

Frequently asked questions

What does UL certified mean for solar panels?+

UL certification (specifically UL 61730) means the product has been independently tested by Underwriters Laboratories — an OSHA-accredited NRTL — and verified to meet North American safety standards. Tests include mechanical load, hail impact, thermal cycling, humidity freeze, wet leakage, dielectric withstand, and fire class rating. ETL listing (Intertek) is fully equivalent. Most US utilities and AHJs require UL 61730 listing for grid-connected solar. All panels on SolarDirect carry current UL 61730 or ETL-to-UL 61730 listings.

What is the difference between UL 1703 and UL 61730?+

UL 1703 was the original US solar panel safety standard (1980s). UL 61730 replaced it in 2019, harmonizing with IEC 61730 international requirements. Key changes: more rigorous fire testing with Class A/B/C ratings, stronger requirements for systems up to 1,500V, and more stringent humidity-freeze cycling. Panels with UL 1703 remain accepted by most AHJs. All new SolarDirect panels carry the current UL 61730 standard.

How do I size the solar system for my home?+

Four steps: (1) Calculate daily kWh — check your electric bill monthly kWh ÷ 30. (2) Find your peak sun hours — varies by location (Phoenix 6.5, Seattle 3.7, NYC 4.1 hrs). Our Wizard has data for 50 US cities. (3) Size your array: daily kWh ÷ peak sun hours ÷ 0.83 efficiency factor = kW needed. (4) Size battery: kWh needed × backup days ÷ 0.9 DoD for LiFePO4. The Wizard automates all of this.

What is the difference between MPPT and PWM charge controllers?+

MPPT controllers include a DC-DC converter to let panels operate at their true maximum power voltage, then step down to battery voltage — extracting 15–40% more energy than PWM in real conditions. PWM connects panels directly to the battery at battery voltage, wasting power when panel voltage exceeds battery voltage. Choose MPPT for systems over 300W, cold climates, or when panel Vmp differs significantly from battery voltage. Choose PWM only for very small systems under 200W with matched panel/battery voltage.

Why is LiFePO4 better than lead-acid for solar storage?+

LiFePO4 outperforms lead-acid in every metric for solar storage: (1) Cycle life: 3,000–6,000 cycles vs. 300–500 for AGM. (2) Usable capacity: 90% DoD vs. 50% max for lead-acid — a 100Ah LiFePO4 gives 90Ah usable; a 100Ah AGM gives only 50Ah. (3) Round-trip efficiency: 95–98% vs. 80–85%. (4) Weight: 50–60% lighter. (5) Safety: LiFePO4 chemistry is thermally stable — no thermal runaway risk. Upfront cost is 2–3× higher but lifetime cost per kWh is 2–3× lower. All SolarDirect batteries are ETL listed to UL 1973.

Do I need a permit to install solar panels?+

In most US jurisdictions, yes — both a building permit and electrical permit for grid-tied systems. Off-grid systems often require only an electrical permit. Grid-tied systems also need a utility interconnection application before net metering is enabled. Our certified installers handle all permitting. If DIY, check with your local building department. Permit fees typically range $100–$500.