Solar Panel Installation and Repair for West Covina

MPPT versus PWM and why the controller decides the yield

A charge controller stands between the array and the battery bank because panels produce at a voltage the batteries cannot take directly. A PWM controller does that job by switching the connection on and off rapidly, which effectively pulls the panel down to battery voltage. It is cheap, it is reliable, and it throws away a meaningful share of what the panel could have produced whenever panel voltage sits well above battery voltage.

An MPPT controller converts instead of switching. It finds the voltage and current combination where the panel produces the most power at that instant, then converts that down to whatever the battery needs while preserving the energy. On a cold bright morning, when panel voltage is highest and battery voltage is lowest, the difference between the two controller types is substantial. Over a full day it is the difference between reaching full charge and stopping short.

MPPT also unlocks higher array voltage, which is where the practical advantage lives. Wiring panels in series raises voltage and lowers current for the same power, and lower current means smaller cable for the same loss over a long run from the roof to a controller in a bay. On a forty foot coach that is not a small saving.

Controllers have limits that get exceeded surprisingly often. Maximum input voltage is the one that kills them, because panel voltage rises as temperature falls, and an array sized at its warm rating can exceed the controller ceiling on a cold morning at elevation. We size arrays against cold weather open circuit voltage rather than against the sticker on the back of the panel.

Shading, string mismatch and where the output actually goes

Solar panels in series behave like a chain. The string carries the current of its weakest member, so shading one panel drags the whole string down with it. That is why a system can lose most of its output to a single shadow from an air conditioner shroud, a vent, an antenna or the roof ladder crossing one panel for an hour.

RV roofs are the worst possible environment for this because they are crowded. Every coach has an air conditioner, at least two vents, an antenna and usually a satellite dome, all of them casting long shadows in the morning and afternoon. Panel placement is a shadow study, not just a fitting exercise, and we lay out an array around the obstacles rather than fitting panels wherever there is bare membrane.

Wiring topology is the other lever. Parallel wiring makes each panel independent, so a shaded panel drops only its own contribution. The cost is much higher current for the same power, requiring larger cable. Series parallel splits the difference. Some installations justify separate controllers per string or per panel so shading on one does not touch the others, and on a heavily obstructed roof that is often the right answer.

Mismatch also comes from mixing panels. Adding two new panels of a different model to an existing string almost always underperforms, because the string runs at the lowest common denominator. If an array is being expanded, we either match the existing panels or wire the new ones on their own string with their own controller input.

• A shadow on one panel in series pulls the entire string down
• Air conditioner shrouds and vents cast long shadows morning and afternoon
• Parallel wiring isolates shading at the cost of much larger cable
• Mixing panel models in one string wastes the better panels
• Panel voltage rises as temperature falls, which is what kills controllers

Roof penetrations, brackets and sealing that lasts

A solar install is a roofing job with an electrical job attached, and the roofing half is where the expensive failures come from. Every bracket foot and every cable entry gland is a hole through the membrane and into the decking. Done correctly, each one is bedded in butyl, mechanically fastened into structure rather than into thin decking alone, and capped with the correct self leveling lap sealant for that membrane chemistry.

Done the way we usually find it, brackets are screwed straight down with a bead of hardware store silicone on top. Silicone does not bond to EPDM. It skins over, looks fine for a season, then peels away in a sheet and leaves an open screw hole feeding water into luan decking. By the time a ceiling stain appears the decking has been wet for a year, and now the customer has a roof repair on top of a solar repair.

Fastener location matters as much as sealant. Thin luan decking has almost no screw holding power on its own, and a bracket anchored only into decking works loose under highway vibration and thermal cycling. We locate structure, anchor into it, and use backing where the layout demands a foot away from a truss. On fiberglass roofs we also watch for stress cracks radiating from any hole drilled without a backing plate.

Adhesive mounted panels avoid penetrations entirely on some builds, which suits van conversions well. That decision depends on membrane type, panel weight and how the roof gets walked. We make the call per vehicle rather than applying one method everywhere, and if the roof is already compromised we deal with the roof before adding an array to it.

Combiner boxes, fusing and breaker sizing

Once there is more than one string on a roof, the strings meet somewhere. A combiner box is a sealed enclosure where each string lands on its own fuse or breaker before the combined output heads down to the controller. It exists so a fault in one string cannot back feed through the others, and so a technician can isolate one string without disconnecting the array.

Fusing on the array side gets sized from panel short circuit current with the required safety margin, not from the operating current, because a panel in full sun can deliver its short circuit current indefinitely without anything tripping. Undersized string fusing opens on the brightest days of the year, which owners report as the system quitting in the afternoon.

Between the controller and the battery there needs to be protection sized for the controller output, and it needs to sit close to the battery rather than close to the controller. The purpose of that device is protecting the cable from the battery, which is the source capable of delivering enormous fault current. This is one of the most common omissions we find on used coaches with owner installed solar.

A disconnect on both sides of the controller is standard practice and worth insisting on. Controllers must be connected to the battery before the array and disconnected in the opposite order, and without disconnects that sequence is impossible to follow safely. Every conductor gets labeled so the next person to open the bay is not guessing which pair goes where.

Sizing a system for how the coach is actually used

The right array size comes from measured consumption rather than from a number an owner heard somewhere. We start with what the coach actually uses in a day: the refrigerator on DC, lighting, the water pump, fans, device charging, the furnace blower on cold nights, and whatever runs through the inverter. A coach that boondocks with a residential refrigerator and a coach that dry camps two nights a month need completely different systems.

Battery capacity and array size have to grow together. A large array on a small bank spends the afternoon producing power nothing can absorb. A large bank on a small array never recovers between trips. Usable capacity differs by chemistry too, since lead should not be pulled below half while lithium delivers most of its rating, so an equivalent lithium bank is roughly half the nameplate.

Roof space is the real constraint on most RVs, and after subtracting the air conditioners, vents, antenna and ladder there is usually less usable area than owners expect. That is why we lay out the array on paper against a photographed roof before quoting anything, and why the honest answer sometimes is that the roof will not hold what the use case requires.

All of this work happens in shop at Yorba Linda, about 22 miles and 30 to 45 minutes from most West Covina addresses. We do not offer mobile service, and solar in particular needs a covered bay with sealant cure time and controlled conditions on the roof. Call (949) 799-3387 with your year, make and floorplan to get on the schedule.