Can You Power Your Whole Home With Solar Panels?
May 9, 20267 Common Solar Scams to Avoid (From a 15-Year Installer)
May 9, 2026The number of panels your home needs depends on three things: your annual electricity usage, your roof’s sun exposure, and the wattage of the panels being installed. Here’s the calculation.
Step 1 — Find Your Annual Usage
Pull 12 months of utility bills and add up your total kWh consumed. The average NJ home uses 10,000–12,000 kWh/year. If you have an EV, electric water heater, or pool, yours may be higher. PSE&G, JCP&L, and ACE all show monthly kWh on your bill or in your online account — add up all 12 months. Don’t estimate this number. The difference between 10,000 kWh and 14,000 kWh is 4 panels, which changes the cost of your system meaningfully.
Step 2 — Calculate System Size Needed
In New Jersey, each kW of solar produces approximately 1,100–1,200 kWh per year, depending on your location and roof orientation. Central and southern NJ — Marlboro, Hamilton, Toms River, Cherry Hill — tend to come in around 1,150–1,200. Northern NJ counties like Morris and Bergen are slightly lower, around 1,100–1,150. Divide your annual usage by your local production factor to get your target system size in kW.
Example: 12,000 kWh ÷ 1,150 = 10.4 kW needed.
Step 3 — Determine Panel Count
Modern premium panels — REC, QCell, Silfab — run 400–440 watts each. Divide your system size in watts by the panel wattage to get panel count. A 10,400W system with 440W panels is 23–24 panels. The same system with 400W panels is 26 panels. Higher-wattage panels mean fewer panels on your roof, which matters when roof space is the constraint.
Roof Space and NJ Setback Rules
Each panel covers roughly 18–20 square feet. 24 panels needs about 430–480 square feet of usable south-facing roof space. But “usable” isn’t the same as total area. NJ municipal code typically requires a 3-foot setback from all roof edges, a clear fire access path (usually a 3-foot aisle along one ridge line), and setbacks around vents, pipes, and chimneys. Your installer should account for all of this in the panel layout design — not just count total roof square footage and assume it’s usable.
Size for Future Usage — Don’t Get This Wrong
If you’re planning to add an EV, a heat pump, or an electric water heater in the next few years, size the system for your future load now. It is significantly cheaper to install extra panels in the original design than to come back and add them later.
Adding 4 panels in the original design typically adds $1,400–$1,800 to the project. Coming back to add those same 4 panels later means another permit, another interconnection application, possibly additional engineering, and a second mobilization — usually $3,500–$5,000 total. If an EV is on your horizon within 5 years, size for it now. Each EV adds roughly 3,000–4,500 kWh to your annual load depending on the vehicle and how many miles you drive. A heat pump replacing gas adds another 2,000–4,000 kWh.
What Shading Does to Your Panel Count
Shading changes the panel count calculation in two ways. First, it may eliminate parts of your roof from consideration — sections with more than 15% shading during peak hours usually aren’t worth using. Second, heavy shading argues for microinverters rather than a string system, which can affect how your roof is laid out.
The right shading analysis uses satellite irradiance data and horizon modeling to show you production from each potential array location by month. If your installer doesn’t show you this before proposing a panel count, ask for it. Jon uses Aurora Solar on every NJ project — the output is a month-by-month production model with shade loss percentages for each array section. That’s how you know whether the production estimate you’re being quoted is realistic for your specific roof.
Panel Degradation and Long-Term Sizing
Solar panels degrade slowly over time — about 0.5% per year for premium panels. A system producing 12,000 kWh in year 1 produces roughly 10,500 kWh in year 25. Some installers size a system to cover 100% of usage in year 1, which means it slightly over-covers early and slightly under-covers late in the panel life. Others size for the midpoint. Ask your installer which approach they’re using — both are legitimate, but you should understand the production forecast across the full 25 years, not just year 1.
The Professional Design Step
A good installer uses satellite imagery and shading analysis software to model your specific roof. The panel count from that model is more accurate than any rule of thumb. What you should receive in writing before you sign anything: panel placement on a roof diagram, production estimate in kWh by month, shading loss percentage, and a 25-year production forecast. If you’re getting a quote with a monthly savings number but no production model, you’re getting a sales estimate, not a professional design.
Should You Oversize Your System?
Some installers recommend sizing a system for 110–120% of your current usage to build in a buffer for future usage increases or panel degradation. The case for this is real — panels degrade slightly each year, and your usage may grow as you add an EV or heat pump. The case against it: NJ’s net metering compensates surplus annual generation at below-retail rates, so any production above your annual usage earns less per kWh than production you use in your home.
Jon’s approach: size the system for your actual annual usage, then add capacity specifically for any planned loads — an EV, a heat pump, a pool — that you expect to add in the next 3–5 years. Don’t oversize speculatively. Don’t undersize to hit a price point. Size it for what you’ll actually use, and you’ll maximize the value of every kWh your system produces.
What a Good System Design Document Looks Like
Before you sign with any NJ installer, you should have a design document that includes: a satellite image of your roof with each panel’s proposed placement shown, the system size in kW and total panel count, the production estimate in kWh by month for a full year, the shading loss percentage for each array section, the inverter type and model proposed, and a 25-year production forecast with degradation factored in. This is what a professional solar design looks like. It takes less than an hour to produce with current software.
If an installer is proposing a system without showing you this document, ask for it specifically. If they can’t produce it, they either don’t have the software or don’t have the experience to interpret it correctly. Both are disqualifying for a 25-year investment on your home.
The Panel Count Conversation to Have Before the Quote
Before any installer visits your home for a site assessment, do this: write down your annual kWh usage from 12 months of bills, and estimate how many kWh per year you’ll add if you get an EV or heat pump in the next 3 years. Share both numbers when the installer visits. This gives them the correct target to design around, rather than a rule of thumb or an assumption based on your square footage. A system designed around your actual and projected usage will be more accurately sized than one designed by someone guessing at your load.
A Quick Rule of Thumb — and Why to Check It
A quick sanity check for any NJ solar quote: take the quoted system size in kW, multiply by 1,150, and compare to your annual kWh usage. If the numbers are within 10% of each other, the system is sized correctly for your load. If the system is 20% or more above your annual usage, ask why — the installer may have good reasons (future EV, planned load additions) or they may be upselling capacity you don’t need. If the system is 15% or more below your usage, ask whether the design accounts for shading constraints or whether you’re being offered an undersized system to win on price. This calculation takes 30 seconds and tells you whether the proposed system is in the right ballpark before you dig into specs.
If you’re getting close to the conversation with a contractor and want a quick gut check on the numbers before anyone visits: PSE&G and JCP&L let you download 12-month interval data through their portals. Download it, add up your annual kWh, divide by 1,150, and you’ll know your system size within 5% before a salesperson sets foot in your house. That 30-minute prep step changes the entire quality of the conversation.
Find Out What Solar Saves You in Your Home
Every home is different — roof angle, usage, utility rate, and local incentives all affect your numbers. Enter your monthly electric bill below for a free savings estimate. Jon reviews every submission personally and follows up within 2 hours.
Find Out Exactly How Many Panels Your NJ Home Needs
Jon calculates panel count based on your actual usage, roof layout, and sun exposure — not a rough formula. The estimate includes NJ SREC income projections and your net metering credit forecast by season. Book a free call or use the Solar Savings Estimator.
