How online estimates are created
Most online estimates come from software that uses satellite imagery, local weather data, and an assumed electricity bill to estimate system size and yearly production. That’s enough to produce a preliminary cost per watt and a rough monthly outlook, but it can miss roof condition, exact shading patterns, small obstructions, and panel orientation changes. Think of an estimate as a directional figure — useful for comparison, but unlikely to be the final contract price.
Why a real quote often differs
A site visit can reveal things an estimate can’t see. Common reasons quotes change include: roof repairs or reinforcement needed, actual shading from nearby trees, required electrical upgrades, differences in panel or inverter choices, permit and inspection fees, and the addition or removal of a battery. Timing and supply availability can also affect price. Since pricing depends on your location, roof, utility usage, financing, and installer quality, expect some variance between an online estimate and a signed proposal.
What to verify before signing anything
When you get a formal quote, check these items line by line: system size in kilowatts and the estimated annual production, specific panel and inverter models (or at least the brand and efficiency range), who installs and their credentials, what’s included in written warranties and who backs them, details on permits and whether those fees are included, what happens with unforeseen roof or electrical work, and the process for change orders. If the quote includes financing or a lease, get clear, written terms. Also ask about monitoring and how production will be measured and reported. It’s reasonable to request references and to compare offers from national firms like Sunrun, Tesla Energy Solar, and Palmetto Solar alongside local installers.
How to compare multiple quotes
Compare apples to apples: match system size and expected annual production rather than just the price per watt. Check that quotes use similar panel and inverter classes, list the same warranty coverage, and include the same fees for permits and interconnection. Note payment timing, any escalation clauses, and who is responsible for roof repairs and local approvals. Look at installer experience, local reviews, and whether the company will provide a site-specific performance estimate rather than a generic number.