What Are the Key Factors to Consider Before Purchasing Solar Panels
Before purchasing solar panels, key factors include your home's sun exposure (4+ peak hours daily), roof condition and angle, current electricity bill, and available incentives like the 26% federal tax credit.
Assess Your Energy Needs
The average U.S. household uses about 10,400 kilowatt-hours (kWh) of electricity per year, but this number can swing wildly. A 2,000 sq. ft. home in Texas with central A/C might use 16,000 kWh annually, while a similarly sized, well-insulated home in Oregon might only use 7,500 kWh. Your personal baseline is the foundation for every other calculation, from system size to cost and payback period. The goal is to right-size a system that covers a significant portion, but not necessarily 100%, of your unique usage pattern, ensuring you get the best financial return.
You might use 900 kWh in a mild May but over 1,400 kWh in a hot August. Solar production also peaks in summer, which helps, but you need to know the scale of your demand. For a concrete example, if your annual usage is 11,500 kWh, a common initial solar proposal might be for a 7.5-kilowatt (kW) system. This is because, depending on your location, 1 kW of solar panels can produce between 1,200 and 1,600 kWh per year. In a sunnier state like Arizona, that 7.5 kW system might produce 12,000 kWh annually, covering 104% of your need. In Michigan, the same system might produce 9,750 kWh, covering 85%.
Adding a pool pump or a hot tub can increase daily use by 5-10 kWh. If you anticipate these, it's smarter to oversize your system now by 15-20% than to face costly additions later.
Your Annual Electricity Use | Recommended System Size (Est.) | Estimated Annual Solar Production | Rough Coverage |
8,000 kWh | 5.7 kW | 7,980 kWh | ~100% |
11,000 kWh | 7.9 kW | 11,060 kWh | ~100% |
14,000 kWh | 10.0 kW | 14,000 kWh | ~100% |
17,000 kWh | 12.1 kW | 16,940 kWh | ~100% |
A system sized to meet 80-90% of your annual need often delivers the fastest return on investment, because pushing to 100% might require adding marginally less efficient panels in a suboptimal roof location.
Check Roof Condition
Installing panels on a failing structure is the single most common and costly oversight, often leading to expenses of 5,000 to 15,000 for a premature roof replacement just to access and reinstall the solar array. In the United States, the average asphalt shingle roof has a functional lifespan of 20 to 25 years, while solar panels typically carry a 25-year performance warranty. This timeline misalignment is critical. If your roof is already 15 years old, its remaining 10-year lifespan directly conflicts with your panel's 25-year guarantee, risking a disruptive and expensive mid-system-life repair. A professional assessment is not a suggestion; it is a financial imperative to protect an asset costing 15,000 to 30,000 or more.
For the most common material, 3-tab asphalt shingles, you must plan for replacement if they are beyond their 15-year mark. Higher-quality architectural shingles may last 25-30 years. The material also dictates installation methods and costs; standing-seam metal roofs are excellent for solar, often allowing attachment without penetration, while tile roofs require specialized hardware that can increase installation labor time by 20-30%.
For every 30 degrees of deviation from true south, you can expect a 10-15% reduction in annual energy production. The ideal tilt angle often matches your geographic latitude, but most residential roofs have a fixed pitch between 18 and 34 degrees. A steeper pitch can slightly increase winter production but may require more expensive racking. Shading is a silent killer of output. Even 10% shading of an array can reduce total system production by 30% or more, due to how panels are wired in series.
A typical solar system adds 2.5 to 4 pounds per square foot of dead weight. Your roof's framing must handle this plus the local building code's live load (like snow, which can be 30+ pounds per square foot in northern regions). A structural engineer or qualified installer will check the spacing and size of your roof rafters; 2x6 rafters spaced 24 inches on center are common, but may need reinforcement for heavy snow zones.
Compare Solar Panel Types
Monocrystalline silicon panels are the most efficient, commonly converting over 20% of sunlight into electricity, but they cost about 10-20% more than polycrystalline options. Polycrystalline panels, with their distinctive blue hue and slightly lower efficiency range of 16-18%, offer a lower upfront cost per panel. Thin-film panels are the least efficient at 13-18% but can perform better in high heat and on non-standard surfaces.
A premium monocrystalline panel with 22% efficiency will generate more power in the same physical space than a 17% efficient polycrystalline panel. This is critical if your roof area is limited or partially shaded. For example, to install a 7.5 kW system, you might need only 20 of the high-efficiency panels (at 375 watts each) but could require 28 lower-efficiency panels (at 270 watts each), significantly altering the layout and mounting hardware needed.
Most panels lose between 0.3% and 0.5% of their peak power for every 1°C (1.8°F) increase above the standard test temperature of 25°C (77°F). In a hot climate where roof temperatures routinely hit 65°C (149°F), a panel with a coefficient of -0.3%/°C will perform about 2-3% better on a scorching summer day than one with a -0.5%/°C rating, directly affecting your seasonal energy yield.
Most quality panels are guaranteed to lose no more than 0.5% to 0.7% of their output per year. Over a 25-year period, this means a panel is typically warranted to produce at least 85% to 92% of its original nameplate power. The product warranty (often 12-15 years against defects) and the separate performance warranty (25-30 years) are non-negotiable checkpoints.
Panel Type | Typical Efficiency Range | Avg. Cost per Watt (Installed) | Key Performance & Application Notes |
Monocrystalline | 20% - 23%+ | 2.90 - 3.30 | Highest efficiency, best for limited space. Better high-temperature performance (coefficient ~ -0.3%/°C). Dominates residential market (80% share). |
Polycrystalline | 16% - 18% | 2.60 - 2.90 | Lower cost option. Requires ~15-20% more roof area for same output as mono. Slightly higher temp sensitivity (coefficient ~ -0.4%/°C). |
Thin-Film (e.g., Cadmium Telluride) | 13% - 18% | Varies Widely | Lowest efficiency; requires most space. Best high-heat performance (coefficient ~ -0.2%/°C). Often used for large commercial roofs. Lightweight, flexible options exist. |
Your final decision should weigh these factors against your personal constraints. Use this checklist to guide your vendor discussions:
l Calculate your available, unshaded roof area in square feet. Divide by the physical size of sample panels (approx. 18-22 sq. ft. each) to see how many can fit.
l Ask for the panel's nameplate power rating (in watts), its efficiency percentage, and its temperature coefficient.
l Request a projected first-year and 25th-year energy output (in kWh) for each panel option, modeled for your specific address.
l Get the total gross system price and the final net price after incentives for each option.
l Compare the 25-year performance warranty minimum output guarantee (e.g., 92% in year 1, 85% in year 25).
Calculate Costs and Savings
The national average installed cost for residential solar is between 2.80 to 3.50 per watt, before incentives. This means a typical 7.5-kilowatt (kW) system has a gross price range of 21,000 to 26,250. Your final cost and savings are a dynamic equation with at least five variables: your local installed price per watt, the 30% federal Investment Tax Credit (ITC), any state or utility rebates, your current electricity rate, and how quickly that rate increases over time.
The panel hardware itself typically accounts for only about 25% of the total expense. The rest covers the "balance of system": the inverters (which can be string inverters at 1,000 - 2,000 for the system or microinverters at 200 - 300 per panel), racking and mounting hardware, labor for installation, permitting fees (which can range from 200 to 800 depending on locality), and the profit margin for the installer.
Now, calculate your annual savings. This is your system's annual production (e.g., 10,500 kWh) multiplied by your current electricity rate (e.g., 0.18/kWh). That equals 1,890 in Year 1. This is where the critical factor of annual utility rate inflation comes in. Historically, U.S. electricity prices rise at an average of 3-4% per year. Your solar savings are locked in at a fixed cost (your loan payment or upfront investment), while the alternative (grid power) gets more expensive. After 10 years, with a 3.5% annual increase, your effective savings per kWh produced grows from 0.18 to over 0.25. This compounding effect dramatically improves your long-term return. Your payback period is your net system cost divided by your first-year savings. For a 16,000 net cost and 1,890 Year 1 savings, the simple payback is about 8.5 years.
A key mechanism for savings is net metering. Under a typical 1:1 net metering policy, for every 1 kWh of excess solar energy you send to the grid, you receive a credit for 1 kWh to use later.
Understand Installation Steps
On average, the physical installation on your roof only takes 1 to 3 full days for a standard residential system, but the administrative and inspection work before and after can span 6 to 10 weeks. A key data point: a 2023 survey of installers found that approximately 65% of project delays are caused by utility interconnection review and local permitting, not the installation itself.
Your installation will follow a predictable sequence of distinct phases, each with its own responsible parties and typical duration.
l Phase 1: Consultation, Design, and Contract (Duration: 1-2 weeks). The installer uses satellite imagery and your energy data to create a site plan and system design.
l Phase 2: Permitting and Utility Approval (Duration: 3-10 weeks). This is the most variable period. Your installer submits engineering plans for building/electrical permits and an interconnection application to your utility.
l Phase 3: Physical Installation (Duration: 1-3 days). The crew delivers equipment, mounts racking, installs panels, and sets up the inverter and electrical gear.
l Phase 4: Inspections and Permission to Operate (Duration: 2-4 weeks). Local inspectors and your utility must approve the work before you can flip the switch.
This includes a roof load analysis to ensure your rafters (typically spaced 16 or 24 inches on center) can handle the added 2.5 to 4 pounds per square foot of weight. They design the electrical stringing, specifying the exact number of panels per series circuit and the gauge (thickness) of the wiring, usually 10 AWG or 12 AWG for residential DC circuits. This plan is submitted for permits. The local building department review can take anywhere from 2 to 6 weeks, while the utility's interconnection agreement review often takes 3 to 8 weeks.
A crew of 4 to 6 installers will typically arrive with all equipment. On Day 1, they install the racking system, anchoring it to your roof rafters with lag bolts. They then run conduit and the main system wiring. On Day 2 or 3, they place and secure the panels—a crew can install 15 to 25 panels in a single day. Simultaneously, the electrician installs the inverter (either a central string inverter or multiple microinverters behind each panel) and integrates it with your main electrical panel. A critical task is installing a new, dedicated 240-volt circuit breaker in your main panel for the solar. If your main panel is old or full, this may require a sub-panel or a full main panel upgrade, costing an additional 2,000 to 4,000 and adding 1 to 2 weeks to the schedule.