☀️ Stuff Every Solar Owner Should Know: Training Guide

From cell to array

A photovoltaic cell turns sunlight into direct current electricity. One cell typically produces only about 1 or 2 watts, which is too little for a home. That is why cells are wired together into larger units.

Cells are made of semiconductor material. Cells are wired into modules, also called panels. Panels are then combined into arrays to make a home solar system.

By the late 1970s, PV panels were providing electricity in remote off-grid locations where running power lines was too costly. Those systems still needed storage for nights and cloudy days.

State-of-the-art PV module efficiency is now approaching about 25 percent, so a panel turns about one quarter of the sunlight energy that hits it into electricity. Experimental cells have reached nearly 50 percent efficiency.

Direct current to alternating current

Solar cells produce direct current, which flows in one direction. Homes and the grid run on alternating current, so an inverter converts the DC to AC. Without this conversion, most home appliances could not use the power.

Modern inverters can both provide and absorb reactive power to help grids balance. That makes them one of the most important pieces of equipment in a solar energy system.

EIA classifies a PV system as small-scale if its capacity is under 1 MW, or 1,000 kW. Most small-scale PV systems are on buildings and are sometimes called rooftop PV systems.

Most PV systems in the United States are grid-connected. They stay tied to the utility so the grid can fill in when panels are not producing.

Power and energy

A kilowatt is 1,000 watts, and one megawatt is 1,000 kilowatts, or 1,000,000 watts. Solar arrays are often sized in kilowatts, such as a 7 kW system, to describe their power rate.

A kilowatt-hour is one kilowatt of power used for one hour. Power is the rate, and energy is that rate over time. Your electric bill charges you for kilowatt-hours.

A 40-watt light bulb used for five hours uses 0.2 kWh. That shows how power and time combine into an energy total.

Energy storage capacity is measured in kilowatt-hours or watt-hours because it is a total amount. Power capacity is measured in kilowatts or megawatts because it tells how fast energy can be delivered.

Where sunlight lands

Lower latitudes and arid climates generally receive the most sunlight, called insolation. Latitude, climate, and weather are the major factors. Dry regions with few cloudy days get more direct solar radiation.

The greatest amount of solar energy reaches the surface around solar noon. At that time the sun is highest, so its light passes through the least atmosphere.

Solar radiation data for PV is often given in kilowatt-hours per square meter. Instant sunlight strength can also be expressed in watts per square meter.

EIA's 2022 data shows yearly electricity purchases per residential customer vary widely. Hawaii had the lowest at 6,178 kWh, and Louisiana had the highest at 14,774 kWh. Hawaii's low purchased amount may miss power made by rooftop solar.

Seasons and shading

Earth's axis is tilted 23.5 degrees, which causes the seasons. DOE uses Denver near 40 degrees latitude as an example. Denver receives nearly three times more solar energy in June than in December.

The sun's path changes with the seasons, so shading in an area can change from summer to winter. Trees, chimneys, nearby buildings, and vents can all shade panels and cut output.

Thick clouds can reduce the direct beam of sunlight by 100 percent. Even on clear, dry days, the atmosphere can reduce direct beam sunlight by about 10 percent.

A solar professional can use software to estimate site shading. Checking shade at different times of year helps avoid placing panels in a spot that is sunny only part of the year.

Peak sun hours and clipping

A location with 3.5 peak sun hours receives sunlight equal to 1,000 watts per square meter for about 3.5 hours a day. Peak sun hours are not the same as hours of daylight.

To estimate system size, divide daily energy needs by peak sun hours. In a University of Arizona example, a home using 6,000 kWh a year with 6.5 peak sun hours needs about a 4.5 kW array.

When a PV array briefly produces more power than the inverter's AC rating, the output is clipped to the inverter's AC rating. Power above that limit is lost.

Inverter layouts

A microinverter is installed on every individual panel. Each panel works independently, so one shaded or dirty panel does not hold back all the others.

A string inverter connects a set of panels in series. If one panel on the string is shaded, the output of the whole string is reduced.

In large utility plants, many panels may be attached to a single central inverter. DOE still describes the string inverter setup as cost-effective despite its shading drawback.

Solar can charge a home battery directly over DC or after conversion to AC. The inverter setup decides which path is used.

Grid behavior

Traditional grid-following inverters need an outside signal from the electrical grid. If the grid goes down, they lose that signal and shut off. Grid-forming inverters can start up a grid that has gone down, called a black start.

Ride-through means an inverter stays connected during small grid disturbances. If the disturbance lasts long or is large, the inverter disconnects and shuts down.

Smart inverters add two-way communication with the utility. That helps the grid manage many rooftop systems at once more smoothly and can reduce outages.

A solar-plus-battery system will keep your home powered during an outage only if it is designed to run without the grid. Ask before you buy if backup is the goal.

Battery ratings

Battery energy capacity is measured in kilowatt-hours. Power capacity is measured in kilowatts and tells how fast the battery can release energy.

A battery rated at 5 kW and 10 kWh can run 5 kW of loads for about two hours. The kW rating describes how much power it can release at once.

Depth of discharge is the percentage of capacity used when a battery is discharged. Draining a battery to 65 percent of its capacity means 35 percent was used, so the depth of discharge is 35 percent.

Usable capacity is what a battery offers once practical limits apply. A 10 kWh battery operating at a 90 percent depth of discharge has 9 kWh of usable capacity.

Most US utility-scale battery systems use lithium-ion chemistry. EIA says its high cycle efficiency and fast response suit grid support.

A battery cycle is each time it is discharged and then recharged. A battery that stores solar every day runs roughly 365 cycles a year.

Ways to own and pay

The average US home buys about 900 kWh of electricity per month, but your own yearly kWh total is the best guide for sizing solar.

To compare quotes, divide the total price by the system's watts. This gives a cost per watt that puts different bid sizes on the same scale.

With a solar lease, the leasing company owns the system and is generally responsible for maintenance. When a lease ends, the company must remove the system and return the roof to its original condition.

In a solar power purchase agreement, a third party owns and maintains the panels. You agree to buy the power the system generates.

A solar co-op is a group that pools buying power for rooftop solar. Co-ops are free to join and have no binding commitments.

Even with rooftop solar, you will usually still pay the utility's fixed charges. Solar cuts how many kilowatt-hours you buy, but most homes still buy some power.

Federal tax credit timing

As of October 2026, you cannot claim the federal residential solar credit for a system installed in 2026. The IRS says the credit is not available for property placed in service after December 31, 2025.

Before it ended, the credit equaled 30 percent of qualified costs for new clean energy property installed from 2022 through 2025. It applied to solar electric panels and, since 2023, to battery storage.

A home battery had to have at least 3 kWh of capacity to qualify for the federal credit starting in 2023. It also had to be installed on a home in the United States.

If your tax liability was too low to use the whole 2025 credit, you could carry the unused part forward to 2026. Only expenditures through 2025 count for the credit.

State, utility, and local incentives are separate from the federal credit and may still exist.

Utility billing and scams

A federal consumer advisory calls claims that the federal government pays for your solar power a scam. Claims that panels are free are major red flags.

Be careful about signing documents on the seller's computer or tablet. Get the contract and disclosures in a form you can keep. If you do not get a paper copy of your contract, that is probably a scam.

The right to cancel a solar transaction lasts at least three days from signing. Ask how to use that right and whether early termination fees apply.

With PACE solar financing, the loan is usually repaid through extra amounts on your property tax bill. Missing payments can lead to default and even foreclosure, and the property tax lien takes priority over your mortgage.

California's net billing tariff applies to rooftop solar customers who apply to connect on or after April 15, 2023. It succeeded NEM 2.0, and exports earn credits based on their value to the grid instead of the full retail rate. The same decision let new rooftop systems be sized to cover up to 150 percent of a customer's electricity use.

California's 2022 solar tariff aims to encourage solar exports during the late afternoon and early evening, especially in summer. Batteries let owners store daytime solar for those hours.

State HOA rules

In Florida, an HOA may choose where solar collectors go on the roof, but it must allow them to face due south or within 45 degrees east or west of due south. The law also protects clotheslines.

In Texas, a property owners' association generally may not ban solar energy devices. It may restrict a roof-mounted device that extends higher than or beyond the roofline, among other listed conditions.

A 2025 Texas law clarified that solar roof tiles count as solar energy devices under that rule. This gives tile systems the same protection as traditional panels.

Vetting the company

Confirm that the installer is licensed, bonded, and insured for residential solar in your area. A license, a bond, and insurance protect you if the work is bad or someone is hurt.

Ask whether the company will use subcontractors, and verify the subcontractors' credentials. You want the people on your roof to be properly qualified.

Ask for references from previous clients. Past customers can tell you if the crew was neat, on time, and responsive after the install.

Use DOE's rule of thumb that an installer should have been in business at least three years. A few years of track record means the company has finished jobs and still stands behind them.

NABCEP certification is the solar industry standard for installers. DOE points homeowners to it as a credential to look for.

Ask the installer to put roof repairs and vent relocation in the proposal. Writing these items into the contract avoids surprise bills later.

Permits and process

Your installer usually obtains local permits and arranges inspections using information from you. Your local government sets the permit and inspection rules.

Once permits are done, the physical PV installation generally takes only a few days. The longer waits come from design, permits, and utility approval.

Ask what warranty coverage applies if a component has a problem. A good installer should explain this before you sign.

Most experienced installers will come look at your home before giving a price proposal. An in-person look helps them see the roof, shade, and electrical panel.

Falls, electricity, and generator safety

OSHA requires fall protection at six feet in the construction industry. Solar installers facing falls of 6 feet or more need guardrails, safety nets, or personal fall arrest systems.

Maintenance work falls under general industry rules, where protection is required at four feet. Panels covering a roof can push workers close to skylights and roof hatches.

Workers should never climb ladders while carrying solar panels. Panels are big, catch the wind, and keep hands off the rails, so crews should use hoists or conveyors.

Near skylights, employers must guard them or have workers use personal fall protection. A skylight is not built to hold a person.

Stay at least 10 feet from overhead power lines, and cover panels during installation or service. Overhead lines carry extremely high voltage, and sunlit panels keep making electricity even with a breaker off.

During backup generator use, keep the generator outdoors more than 20 feet from windows, doors, and vents. Use a battery-powered or battery backup carbon monoxide detector, because CO is invisible and odorless.

Credentials and codes

NABCEP's Energy Storage Installation Professional credential focuses on battery energy storage systems. It covers design, installation, and commissioning decisions for energy storage.

PV Associates need 12 continuing education units, or CEUs, to renew their Associate credential. They can earn all 12 at NABCEP's annual CE Conference.

NABCEP's PV Associate exam reference list includes NFPA 70, the National Electrical Code, and OSHA's construction safety rules, 29 CFR Part 1926. It also cites a textbook called Photovoltaic Systems by James P. Dunlop.

NABCEP also offers an Operations and Maintenance Associate Technician Credential and a Veterans Pathway for veterans applying for the PV Associate exam.

Lifespan and end of life

A PV system can produce energy equal to what was used to build it within about 1 to 4 years. Most PV systems operate for 30 years or more, so the energy payback is much shorter than the panel lifespan.

NREL's review of published studies found typical PV output loss of about 0.5 percent per year, with a mean of 0.8 percent. A panel typically keeps most of its output for decades.

A performance warranty guarantees that power output declines slowly over the years. It often ends near 80 percent of the original rating after 25 years.

Expect an inverter to need replacement at least once during a 25-year PV array's life. Panels have no moving parts, but inverters work hard converting DC to AC and wear out sooner. Inverter warranties of 10 years are now common, and 20-year extended plans are gaining ground.

Recycling a solar panel generally costs more than landfill disposal. DOE says that cost gap limits how many panels get recycled today. Several states have enacted laws that encourage solar panel recycling.

Some discarded solar panels may count as hazardous waste under EPA rules. Lead or cadmium can leach out and fail a toxicity test, even within the same model and manufacturer. Some types of PV cells contain heavy metals that need special handling when retired.

Cleaning and weather

NREL recommends plain demineralized water and a mild detergent for cleaning PV modules. Avoid high-pressure water, solvents, abrasives, and harsh detergents.

Uneven dirt like bird droppings can cause localized hot spots. A covered part of a panel can heat up instead of making power, so reduce uneven soiling.

If snow is never cleared from solar panels, NREL says about 3 percent of yearly production is lost on average. Snow is rarely removed because it is not cost effective and clearing can damage panels and wiring.

In very snowy places like Truckee, California, snow losses can reach about 15 percent. Snow tends to slide off arrays tilted more than about 30 degrees.

Microinverters or horizontal strings lose less output when snow only partly covers an array. That layout choice can reduce snow-related losses.

Inverter, monitoring, and electrical safety

Inverter failure is one of the most frequent causes of lost PV performance. Watch your monitoring data for a sudden drop to catch a failed inverter fast.

NREL says microinverter or power optimizer communications are making automated remote monitoring more feasible on small residential systems. Basic monitoring can be as simple as checking the inverter's total generation once per year.

Rapid shutdown rules first appeared in the 2014 National Electrical Code to protect firefighters and emergency responders. The original rule required controlled PV conductors to drop to 30 volts or less within 10 seconds of shutdown. Rapid shutdown can come from microinverters, AC modules, or DC optimizers with built-in shutdown.

When a string inverter shuts down after losing grid power, the panel strings connected to that inverter stay energized in daylight. The inverter stops sending AC power, so the AC side goes dead, but sunlit panels still produce DC voltage.

An arc fault is more persistent in DC wiring than in AC wiring. AC current drops to zero many times each second, which helps an arc go out, but DC never does, so loose DC connections are a fire concern.

Electricians working on live DC circuits need arc-rated clothing, insulation gloves, and a face shield. When power optimizers shut down, each one outputs only about 1 volt, which de-energizes the string wiring more safely.

Battery cycles and capacity

A battery cycle is each time it is discharged and then recharged. A battery that stores solar every day runs roughly 365 cycles a year.

Battery longevity depends mainly on depth of discharge, cycle count, time at each charge level, and temperature. The relationship between depth of discharge and battery life is non-linear.

A 10 kWh battery operating at a 90 percent depth of discharge has 9 kWh usable capacity. Spec sheets list both nominal and usable numbers for this reason.

Some battery products list long warranties. Enphase's IQ Battery 5P page lists a 15-year limited warranty up to 6,000 cycles.

Most US utility-scale battery systems use lithium-ion chemistry. Its high cycle efficiency and fast response suit grid support.