What Is a Solar Array?

What a solar array means in plain terms

A solar panel is one flat, framed unit. An array is all of them together. If a crew puts 14 panels on your roof, you have 14 panels and one array.

The word comes from how the panels work as a team. Each panel makes a little direct current, or DC, which is power that flows one way, like a battery’s.

The array joins that power and sends it to the inverter. The inverter turns it into the alternating current, or AC, that your outlets use ¹.

Installers use four words with care: panel, string, array and system. Most mix-ups on a quote come from treating “array” and “system” as the same thing. The table below sorts them out.

Panel, string, array, system

How an array is wired

Panels can be joined in two basic ways. In series, the plus side of one panel connects to the minus side of the next. The voltage adds up, but the current stays the same.

A row joined this way is called a string. In parallel, several strings join side by side. The current adds up, but the voltage stays the same.

With a central string inverter, each string feeds one input on the inverter. A string carries one current, so the weakest panel sets the pace for the rest.

The DOE notes that output drops if any panel in the string is shaded or has a problem ³. That is why designers keep panels on the same string facing the same way under the same shade.

With microinverters or power optimizers, each panel is handled on its own. Shade or damage on one panel does not pull down the others ³. That lets an array spread across several roof faces. Our inverter types guide compares the options.

Where the array’s power goes

1. Sunlight → each panel in the array makes DC
2. Panels → strings (series) → combined array output
3. Array DC → inverter → AC for the home
4. AC → main electrical panel → your circuits, with any surplus sent to the grid

Types of arrays by where they mount

Fixed arrays versus tracking arrays

Almost every home array is fixed. The panels sit at one angle and never move. Rack mounting, on rails bolted to the roof or ground, is the most common method ².

A tracker is a motorized mount that turns the panels to follow the sun. It catches more light. But the DOE notes that trackers add upfront cost and maintenance ². You will mostly see them on large ground-mounted solar farms, not on houses.

Example: sizing an array with a published utility rule of thumb

Berkeley Electric Cooperative in South Carolina publishes a sizing rule for its members: annual kWh ÷ 1,800 gives the system size in kW ⁷. Here it is applied to a home using 10,800 kWh a year, with 435 W panels ¹³:

The 1,800 divisor is Berkeley’s figure for its territory, not a national constant. Sunnier or shadier sites change it. A proper design models your own roof. The system size calculator starts from your own usage, and the panel count tool turns kW into panels.

Where the word shows up on your paperwork

On a quote, “array size” or “system size (DC)” is the total panel wattage in kW. A separate “AC size” is the inverter rating. The two often differ, and the gap is called the DC-to-AC ratio.

On permit drawings, the roof plan shows each array as a block of panels on each roof face. The electrical diagram shows how many panels are in each string. On your monitoring app, you may see output for the whole array or for each panel.

Your utility also uses array size. Many net metering rules set their caps in kW, so the number on your application must match the drawings.

What a well-designed array gives you, and its limits

When an array is the wrong size or shape

An array that is too big for your usage can send surplus to the grid at a low credit rate, depending on your utility’s rules. An array that is too small leaves most of the bill in place. Both are design errors, not equipment faults.

An array spread over many small roof faces can work, but each extra face adds racking, wiring and labor. Sometimes a ground mount in an open yard is the better shape.

What drives the cost of an array

We do not quote dollar prices here. These are the things that move the price of the array part of a job. See cost per watt for current figures.

• Size in kW DC. More panels cost more in total, though the cost per watt often falls as size grows.
• Panel model. Higher-wattage panels mean fewer panels, fewer roof holes and less racking for the same kW.
• Mounting type. Ground mounts need posts and trenching; roofs need flashing and sometimes repairs first.
• Roof shape. Several faces mean more strings, more rails and more labor.
• Electronics. Microinverters or optimizers add parts at each panel but help with shade ³.
• Lifespan and warranty. DOE material for low-income programs says major parts typically carry 25-year warranties and the system should produce for at least 30 years ⁵. Check each warranty on your own contract.

How an installer designs and installs your array

A licensed installer and electrician do this work. You should not wire or mount panels yourself.

1. Collect 12 months of your electricity use from your bills.
2. Check the roof: age, structure, faces, tilt and shade. Replace an old roof first if needed (see roof before solar).
3. Model output for each roof face. NLR’s PVWatts calculator is a public tool for this ⁶.
4. Set the array size, panel count and string layout. Check the utility’s size cap.
5. Draw the permit set: roof plan, string diagram and structural notes. Submit to your building department.
6. Apply to the utility to connect. See solar interconnection.
7. Install racking and panels, then wire the strings to the inverter.
8. Pass the local inspection, then wait for the utility’s permission to operate.

Looking after an array

A fixed roof array has no moving parts. DOE guidance says no routine maintenance should be needed. Rain usually keeps panels clean enough, and dust from a dry spell has little effect.

Your main job is to watch the monitoring app. If output falls well below the same month last year, call the installer. After heavy snow on a low-pitch roof, DOE says you may use a long-handled snow rake from the ground. Do not climb onto the roof. Our panel cleaning guide covers when washing helps.

Sources: [5]

Warning signs: when to call a pro

Call your installer, not a handyman, for any of these. The array carries DC power whenever the sun is up.

• One string or panel reads zero or far lower than its neighbors in the app.
• Total output drops sharply on clear days with no new shade.
• Cracked glass, burn marks or a panel lifting off its rails.
• Loose or hanging wires under the array, or chewed wires from animals.
• A roof leak or water stain below the array (see roof leak after solar).
• Hail damage after a storm. DOE says panels are built to resist hail of at least 1 inch but very large hail can break them ⁵.

Safety

Rules that shape an array

Three sets of rules decide how big an array can be and how it is built. Your local building department enforces the building and electrical codes it has adopted. Your utility sets interconnection rules and size caps in its tariff. Your state sets net metering law.

In South Carolina, the state has the 2021 building codes in force, and the 2024 International Residential Code is scheduled for local use from 1 January 2027 ¹². South Carolina also splits solar work by license.

A registered Solar Panel Installer may install panels, but the wiring must be done by a licensed residential electrician, a residential builder or a mechanical contractor with the electrical classification ¹¹.

Size caps are set by each utility or state law. The next section lists verified caps for South Carolina, Georgia and Virginia. Elsewhere, check your utility’s net metering or interconnection tariff.

Array size limits in SC, GA and VA

Solar array compared with related terms

Common misconceptions about solar arrays

Myth A bigger array always saves more money.

Reality Past your own usage, extra output may earn only a low export credit, and utility caps may stop you anyway.

Myth The array size is the same as the inverter size.

Reality Array size is in kW DC. Inverter size is in kW AC. They are often different on purpose.

Myth All panels must face south.

Reality South is best over a year ², but east and west faces still produce, and panel-level electronics help mixed layouts.

Myth Arrays need regular cleaning.

Reality DOE guidance says rain usually keeps panels clean enough ⁵.

When the array details matter to you

Use these rules when you read a quote:

• If two quotes list the same kW DC, compare panel model, string layout and which roof faces they use.
• If part of your roof gets shade, ask whether the design uses microinverters or optimizers.
• If your roof will need replacing within the warranty period, replace it first.
• If the array is larger than your utility’s cap, ask the installer to show the cap in writing.
• Next step: run the system size calculator, then check quotes with the proposal analyzer.

Related terms

Solar Panel

A solar panel, called a solar module in the industry, is a weatherproof assembly of photovoltaic cells wired together behind glass in a frame, which turns sunlight into direct-current electricity.

Solar System

A home solar system is the full set of equipment that turns sunlight into electricity your house can use: solar panels, an inverter, mounting hardware, wiring and safety disconnects, and the utility meter, sometimes with a battery.

Solar System Sizing

Solar system sizing is the process of choosing how many kilowatts (kW) of solar panels a property needs, by dividing the electricity it uses in a year by what one kW of panels produces there.

String Inverter

A string inverter is a single wall-mounted inverter that converts the DC output of one or more strings of series-wired solar panels into AC for the home.

Microinverter

A microinverter is a small inverter mounted behind a single solar panel that converts that panel’s DC output to grid-ready AC on the roof, so each panel works independently of the others.

Solar Mounting System

A solar mounting system, also called racking, is the set of attachments, rails, clamps and bonding hardware that secures solar panels to a roof or the ground and holds them at a fixed angle against wind and snow.

Solar Shading

Solar shading is any shadow that blocks sunlight from part or all of a solar array, from trees, chimneys, vents, nearby buildings or other panels, reducing the electricity the system produces.

DC-to-AC Ratio

The DC-to-AC ratio, also called the inverter loading ratio (ILR), is a solar array’s total panel rating in DC watts divided by the inverter’s AC output rating.

Also referenced from: Photovoltaic, Solar Panel, Solar Combiner Box, Solar Mounting System, Ballasted Solar Mount, Roof Penetration