Building a Home Solar System

A home solar system is three decisions stacked on top of each other: what kind of system (grid-tied, hybrid, or off-grid), how big (panels sized to your usage and your roof), and whether to add a battery. Get the first one right and the rest follows. Get it wrong — usually by buying more panels or more battery than your rate rewards — and you spend thousands for kWh you'll never get paid for.

This guide walks the decisions in order, then shows how to model the whole thing on this site before you talk to an installer.

System types: pick this first

Everything downstream depends on which of these you're building.

System	What it is	Backup during outage?	Cost	Best for
Grid-tied	Panels + inverter, no battery. Exports surplus, pulls from grid at night.	No — dies the instant the grid goes down	Cheapest per kWh	Good net metering, stable grid, lowest cost per kWh
Hybrid	Panels + hybrid inverter + battery, still grid-connected	Yes — battery + islanding backs up loads	Middle	Most homeowners; poor export credit or outage-prone grid
Off-grid	No utility connection at all	N/A — you are the grid	Most expensive	Remote sites where a utility line is impractical

Grid-tied is the cheapest way to lower your bill and, counterintuitively, the one that leaves you dark in a blackout — a standard grid-tie inverter shuts down when the grid fails (anti-islanding, for lineworker safety) even in full sun. If that surprises you, you want hybrid.

Hybrid is the most popular new-build configuration. The battery gives you outage backup and lets you self-consume solar instead of exporting it for pennies — see Net Metering for why that gap matters.

Off-grid means every kWh you'll ever use has to come from your own panels and battery, sized for the worst week of winter, not the average. You oversize everything — array, battery, and often a backup generator. Only build this when running a utility line to the site costs more than the equipment.

Sizing panels to your usage

Solar is sized against your annual consumption, not your roof or your ambition. Start from your bill.

System kW ≈ annual kWh ÷ (peak sun hours/day × 365 × 0.8)

The 0.8 covers real-world losses (heat, wiring, inverter, dust, panel aging). Peak sun hours is the daily average of full-strength sun for your area — roughly 4 in the cloudy north, 5–6 in the sunny southwest.

Worked example: a home using 10,000 kWh/year at 5 peak sun hours:

10,000 ÷ (5 × 365 × 0.8) ≈ 6.8 kW

So about a 7 kW array to offset nearly all annual usage.

Don't blindly aim for 100% offset. How far to size depends on how your utility pays for exports:

• Full retail net metering — sizing to cover your full annual usage (even slightly over, to bank winter credits) is rational.
• Avoided-cost / low export credit (e.g. NEM 3.0) — every kWh you export past what you consume earns pennies. Size closer to what you actually use in real time, and let a battery soak up the rest.

The Net Metering guide covers the reconciliation and export-rate math in detail. The short version: oversizing only pays if something rewards the surplus.

Panels: watts, count, and placement

Panels are the cheap, modular part. The specs that matter:

• Wattage per panel — modern residential panels are 400–450 W. Higher-wattage panels mean fewer panels and less roof for the same kW.
• Count — panels = system kW × 1000 ÷ panel watts. A 7 kW array at 420 W is ~17 panels.
• Roof area — budget roughly 18–20 sq ft per panel. 17 panels ≈ 320 sq ft of unshaded roof.
• Orientation — south is best in the northern hemisphere. East/west split arrays produce a little less total but spread production across the morning and evening — which can be worth more under time-of-use export rates that pay more in the evening.
• Tilt — a tilt roughly equal to your latitude maximizes annual production. Most roofs aren't at the ideal angle; the penalty for being off is usually small (a few percent).
• Shading — the quiet killer. A single shaded panel in a string can drag down the whole string. Trees, chimneys, and neighboring roofs all count. If you have partial shading, that's an argument for microinverters or optimizers (below).

Inverters: string vs micro vs hybrid

The inverter converts panel DC into house/grid AC. Three architectures:

Type	How it works	Best when
String inverter	One central inverter, panels wired in series	Unshaded roof, simple layout, lowest cost
Microinverters	One tiny inverter per panel	Shading, multiple roof faces, per-panel monitoring
Hybrid inverter	String inverter with a built-in battery port	You're adding a battery now or later

DC/AC ratio. Arrays are deliberately overbuilt relative to the inverter — a ~1.2 DC/AC ratio is standard. A 7 kW inverter might carry 8.4 kW of panels. Panels rarely hit their nameplate (that requires perfect cold, clear, straight-on sun), so a modestly oversized array keeps the inverter working near full output for more of the day.

Why the inverter caps AC output. The inverter has a hard AC ceiling. On the brightest few hours of the best days, array DC can exceed it and the extra is clipped — thrown away. A little clipping is fine and expected; it's the price of keeping the inverter busy the rest of the time. Too much clipping means the inverter is undersized for the array. Size the inverter on the Inverter Sizing page rather than guessing.

With or without a battery

This is the decision that most changes your total cost. A battery roughly doubles a system's price, so add one for a reason:

Reasons to add a battery

• Outage backup — the top reason. Grid-tie solar alone gives you nothing in a blackout; a hybrid system with a battery keeps critical loads running.
• Low export credit (NEM 3.0 and similar) — when exports earn pennies but evening imports cost 40–50¢, storing your midday solar to use at night is worth far more than exporting it. See Net Metering.
• Off-grid — non-negotiable; the battery is your night and your cloudy days.

Reasons to skip it

• Grid-tied with good net metering is the cheapest cost per kWh, full stop. If your utility credits exports near retail and your grid is reliable, the grid is already acting as a free, infinitely large "battery." Adding physical storage there is mostly buying outage insurance, not bill savings.

If you do add one, size it deliberately — Sizing a Home Battery walks the kWh-vs-kW math for backup, self-consumption, and peak shaving.

Economics: what it actually costs

Rough numbers to frame the decision (they vary widely by location and installer):

• Gross cost — installed residential solar runs roughly $2.50–$3.50 per watt before incentives. A 7 kW system is ~$17K–$25K gross. Add a battery and you're often at $10K–$15K more.
• Federal tax credit (ITC) — currently a 30% federal tax credit on the total system cost, batteries included. A $22K system nets ~$6,600 back. This is a credit against tax owed, not a rebate — confirm you can use it.
• Labor vs DIY — labor, permitting, and overhead are often half the installed price. DIY (or owner-assisted) installs cut that substantially, but you take on the permitting, interconnection, and roof work yourself, and some utilities require licensed-installer sign-off.
• Payback years — payback ≈ net cost ÷ annual bill savings. Grid-tied with decent net metering commonly lands in the 6–10 year range; adding a battery usually lengthens payback because the battery earns less per dollar than the panels do.

The Solar Savings page runs these numbers against your real location and rate — use it before trusting any installer's spreadsheet.

Permitting & interconnection

Not glamorous, but real steps you can't skip:

• Building/electrical permit from your local jurisdiction, usually before install.
• Interconnection agreement with your utility — the contract that lets you legally push power onto the grid and get credited for it. Approval can take weeks.
• Inspection — both the local authority and the utility typically inspect before granting permission to operate (PTO). You are not allowed to switch the system on until PTO lands.

Budget weeks, not days, for this paperwork. It's the most common reason a finished install sits dark.

What to avoid

• Oversizing beyond your net-metering benefit. Panels past what your rate rewards produce kWh you give away for pennies. Size to what you use plus what your export tariff actually pays for.
• Ignoring shading. A little afternoon shade on a string array can gut production. Assess shade honestly, and use microinverters/optimizers if you can't avoid it.
• Undersizing the inverter. Too small and you clip away your best-hour production every sunny day. Model the DC/AC ratio instead of guessing.
• Assuming a battery pays for itself. Under good net metering it usually doesn't — it buys backup and resilience. Justify it on those terms, not on bill savings alone.
• Skipping the interconnection paperwork. No signed agreement and PTO means you legally can't turn the system on — and unpermitted work can void insurance and block a future home sale.

How to model it on PowerUsage

Design the whole system on the site before you commit a dollar:

1. Solar Savings — the main tool. Two ways to use it:
   • Enter a number of panels to model a specific array, or enter a target annual kWh and it tells you how many panels you need to hit it.
   • Set panel watts, orientation, tilt, sunny-days %, inverter cost, labor, tax-credit %, and an optional battery kWh.
   • It outputs your system kW, install cost, payback years, and annual savings, using your location's sun hours and rate automatically.
2. Inverter Sizing — size the inverter for your array and check the DC/AC ratio so you don't clip away production or overpay for capacity.
3. Battery Runtime — if you're going hybrid, size and compare storage here for backup duration and self-consumption.
4. Electricity Rates — look up your area's rate so the savings math reflects what you actually pay. Browse the Catalog for solar panels to plug real wattages into the model.

Work them in that order: rate first, then array in Solar Savings, then inverter, then battery if you need one.

The bottom line

Pick your system type first — grid-tied if your net metering is good and you can live with no outage backup, hybrid if you want backup or your export credit is poor, off-grid only when a utility line isn't practical. Size the array to your annual usage and no further than your rate rewards. Size the inverter for a ~1.2 DC/AC ratio. Add a battery for backup or poor export credit — not on the assumption it pays for itself. Then model the whole thing on Solar Savings with your real location and rate before you sign anything.