Technology Explained

Panel types, briefly

The differences matter less than the marketing suggests, but they are worth being able to name.

Monocrystalline

Cut from a single silicon crystal. Highest efficiency per square foot, so the usual choice where roof space is the constraint. Handles light shading somewhat better than the alternatives.

Polycrystalline

Cast from multiple crystals. Slightly less efficient per square foot, historically cheaper. Fine where space is not tight.

Thin film

Deposited layers rather than wafers. Light and flexible, lower efficiency per square foot. Mostly seen on large commercial flat roofs and specialist applications, not typical homes.

Bifacial

Collects light on the back face as well, from whatever reflects off the surface underneath. Genuinely useful on a white commercial roof or a ground mount over pale gravel; close to pointless flush against dark shingle.

Where the conversion happens

Panels in a string share a circuit, and a string inverter reads the whole string at once. That is efficient and cheap when the array is uniform and unshaded — and it is the weakness when it is not, because a panel under a chimney shadow can pull down the panels wired with it.

Microinverters convert at each panel; power optimizers condition each panel and pass DC to a central inverter. Both cost more and both mean one underperforming panel stays one underperforming panel. On a complex roof with several faces, dormers, or a stubborn tree, that difference is the whole design.

Inverters are sized to the array, and their warranties are shorter than the panels'. One question worth asking early: can this inverter charge a battery later? Choosing a hybrid inverter up front is usually far cheaper than replacing a perfectly good one in five years.

Orientation and shade — in this region

The sun rises in the east, sets in the west, and sits to the south of us all year. A south-facing surface presents the most area to it, so it produces the most. Roughly speaking, in the mid-Atlantic, east or west faces give up something like a fifth of that production and a north face gives up something closer to two fifths — before tilt legs, which can prop panels off an unhelpful surface to meet the sun at a better angle. Treat those as orders of magnitude, not numbers to repeat: the real figure comes out of a site-specific design.

Small differences in pitch and tilt change the outcome far less than people expect. Direction matters more than pitch, and shade matters more than either.

Shade is the one genuine disqualifier, and only shade across peak sun hours. Dense tree cover or a neighbouring building over the middle of the day is hard to design around. A branch that clips the array at 7am mostly is not.

Roofs, ground mounts, and carports

A roof mount is the cheapest option with the least equipment. Attachments bolt to the rafters, or clamp directly to the seams of a standing-seam metal roof with no penetration at all; flashing and sealing at each penetration is ordinary roofing work, and workmanship warranties normally cover leaks. The array's weight is modest — typically under five pounds per square foot.

A ground mount costs more but can be aimed properly, which is why it wins on a shaded roof with clear land beside it. A carport or canopy does the same and shelters what is parked underneath, which is the whole idea behind covering parking lots.

Roof age is the constraint that catches people out. Putting an array on a roof with a few years left in it means paying to remove and reinstall it when the roof is replaced. Where the roof needs doing anyway, doing both at once is the sensible order.

Batteries, and the thing nobody tells you about outages

A grid-tied system without storage shuts down when the grid goes down. This is deliberate and required: if it kept exporting, it would energise lines that utility crews are working on. It surprises — and annoys — a lot of new owners during their first storm, so it is worth knowing before rather than after.

A battery, with the right inverter and a separate sub-panel for critical loads, is what keeps selected circuits alive. It adds real cost, and its value depends on how often your power actually fails and what you need running when it does.

Storage prices have been the fastest-moving part of this equipment list. Keeping the option open — a hybrid inverter now, a battery later — is generally the cheaper bet than committing either way today.

Warranties and what actually wears out

Panels are typically warranted to still produce around 80% of their rated output at 25 years, and degrade slowly and predictably — on the order of half a percent a year. Panels made decades ago are still generating.

Inverters and batteries have shorter lives and shorter warranties; assume the inverter is a component you will deal with once in the system's life. Workmanship cover from the installer, usually around ten years, is a separate thing from the manufacturer's cover on the hardware, and the difference is worth reading on any proposal.

Maintenance is close to nothing. Rain removes most dust and pollen. Snow that will not slide, tall grass around a ground mount, and bird mess are the realistic list.