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Solar panels produce direct current (DC). The home grid runs on alternating current (AC). An inverter converts DC to AC at 95–98% efficiency. System sizes can be quoted in either; we use kW DC throughout.
Total kWh a system delivers in a year. system_kW × peak_sun × 365 × performance_ratio.
The wholesale value a utility ascribes to a customer-generated kWh delivered to the grid. Typically 4–10 ¢/kWh vs. retail of 15–35 ¢/kWh. Used as export credit under net-billing tariffs.
Compass direction a roof faces, in degrees from true south (180° in the Northern Hemisphere). Due south is optimal; east/west ≈ 88%; north 60–70%.
Behind-the-meter battery (5–20 kWh, typically LFP or NMC chemistry) that stores surplus solar for later use. Quintessential under TOU rates and net-billing regimes.
Actual annual output ÷ nameplate × 8,760 hours. US residential solar: 15–22%. Utility-scale tracking arrays in the Southwest exceed 30%.
The 30% non-refundable federal tax credit for residential solar installed 2022–2032. See our guide.
Standard pricing unit for residential solar. Industry midpoint: $2.90/W DC pre-incentive. Quotes well above $3.30 or below $2.20 warrant scrutiny.
Bill component based on the highest 15-minute load during the period. Rare residentially today; Salt River Project (AZ) is the notable exception. Solar offsets demand charges poorly without storage.
Reduction of solar output from nameplate due to real-world factors: temperature, soiling, wiring loss, inverter conversion, mismatch. Rolled into the performance ratio.
Database of State Incentives for Renewables & Efficiency, operated by NC State University. The authoritative source for state, utility, and federal renewable-energy incentive programs. CC BY-SA 4.0.
U.S. Energy Information Administration. Federal agency producing US electricity-rate, consumption, and generation statistics.
A regulatory provision under which existing solar customers remain on the NEM tariff in effect at the time of their interconnection, typically for 10–20 years.
P.L. 117-169 (2022). Established the current 30% federal residential solar credit through 2032, extended the commercial ITC, and added domestic-manufacturing incentives.
The process by which a residential solar system is approved by the utility for grid connection. Time from application to Permission to Operate: 4 weeks (TX, FL) to 6+ months (parts of CA).
Device that converts panel DC to grid-compatible AC. Three topologies: string inverter (cheaper), microinverter (better shading performance), DC optimizer + string inverter (hybrid).
Standard unit of electricity consumption: one kW of power for one hour. Your bill is denominated in kWh. Typical US home: ~900 kWh/month.
DC kW = sum of panel nameplate output at standard test conditions. AC kW = maximum inverter output to the grid. AC is usually 80–95% of DC.
A solar panel. Modern residential modules are 350–450 W nameplate, made of 60–66 monocrystalline silicon cells.
Successor to net metering: exports paid at avoided-cost / wholesale rates while imports billed at retail. California NEM 3.0 (April 2023) is the largest US example.
Tariff structure crediting solar exports at full retail rate, offsetting later imports 1-for-1. Increasingly replaced by net billing — see our guide.
National Renewable Energy Laboratory, operated under U.S. Department of Energy contract. Source of NSRDB peak-sun-hour data and the PVWatts modeling tool.
Years required for cumulative bill savings to equal the net upfront cost of a solar installation. We compute via linear interpolation within the crossing year.
Daily average hours during which solar irradiance averages 1,000 W/m². State averages: 3.0 (Alaska) to 6.5 (Arizona).
Unitless factor (0–1) representing real-world delivery vs. theoretical nameplate. Industry default: 0.80.
Formal utility approval allowing a newly installed solar system to begin delivering energy. Until PTO, the system must remain off.
Financing arrangement: third party owns the system; homeowner pays for the electricity produced, typically below utility rates. Third party claims §25D. Generally inferior to cash or solar loan.
NREL's free site-specific solar production calculator. Accepts roof azimuth and tilt directly — the standard tool for sanity-checking installer projections.
On-site visit by an installer to measure roof, document shading, evaluate electrical service, assess structural adequacy. A serious quote depends on a real site assessment.
Solar Renewable Energy Credit. Tradeable certificate for 1 MWh of solar generation. Active markets in NJ, MA, PA, DC, MD, IL. Prices range $10–$400.
Lab conditions for panel nameplate ratings: 1,000 W/m² irradiance, 25 °C cell temp, AM 1.5 spectrum. Real rooftops rarely match.
Single inverter handling all panels in a series string. Cheaper than microinverters but underperforms when any panel is shaded.
Rate structure where each successive block of monthly consumption is billed at a higher per-kWh rate. Common in CA, AZ, and the Northeast. Favourable for solar because it offsets the top tier first.
Rate structure where electricity price varies by hour of day, typically with peak prices late afternoon/evening. Default residential rate for new CA IOU customers.
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