Tiny Home Solar Systems: Sizing, Panels and Mounting

Solar is the heart of most off-grid tiny homes, and it is also the part where small decisions about roof space, shade and wiring decide whether you have power in January. This guide explains how to size an array, what the main equipment choices mean, and how to avoid the mistakes that waste panels.

How much solar do you actually need?

Your array has to replace the energy you use each day, plus losses, in the weakest sunlight you will live with. Start with your daily watt-hours from the energy audit in our power overview. Divide by the peak sun hours for your location in the worst season, then divide by roughly 0.7 to 0.8 for wiring, heat and controller losses.

As an illustration only: a home using 1,500 Wh a day, in a place and month that gets about 3 peak sun hours, needs about 1,500 / 3 / 0.75, or around 670 watts of panels. In summer, with 6 peak sun hours, the same array makes far more than needed. That gap is normal, and it is why winter sets the size.

A peak sun hour is one hour of sunlight at a standard strength, not simply an hour of daylight. You can look up typical values for your area with the free PVWatts calculator from the National Renewable Energy Laboratory. Use the lowest month you will actually be living there.

Types of panels

Most residential and RV panels today are made from crystalline silicon cells. Monocrystalline panels are common and efficient, which matters when roof space is limited. Polycrystalline panels have largely been replaced in new products. Flexible panels are light and can follow a curved roof, but they usually run hotter, cost more per watt and tend to have shorter lifespans than rigid glass-and-aluminum panels, so many builders reserve them for places where weight or shape rules out a rigid panel.

Check the rated watts, the open-circuit voltage and the short-circuit current on the label. You will need those numbers to match the panels to a charge controller. Buy panels with a clear warranty from a seller who will still be around.

PWM or MPPT charge controllers

The charge controller protects the batteries and decides how the panels' output is delivered. There are two main types.

• PWM controllers are simple and inexpensive. They work best when the panel voltage closely matches the battery voltage, typically in small 12-volt systems.
• MPPT controllers convert extra panel voltage into extra charging current, which is useful with larger arrays, higher system voltages, long wire runs and cold weather. They cost more but usually harvest noticeably more energy from the same panels.

For anything beyond a very small system, an MPPT controller is usually the better choice. Make sure its maximum input voltage and current exceed your array's values with margin, remembering that panel voltage rises in cold weather.

Series and parallel wiring

Wiring panels in series adds their voltages while the current stays the same. Wiring them in parallel adds their currents while the voltage stays the same. Series strings allow thinner wire and suit MPPT controllers; parallel arrangements tolerate shading on one panel better. Many arrays use a combination.

The key limit is that the string voltage, including the cold-weather rise, must stay under the controller's maximum input. A controller that sees too much voltage can be destroyed, so check the numbers before you connect anything. If the math feels uncertain, ask the controller's manufacturer or a qualified installer.

Where to put the panels

Roof mounting uses your existing footprint and keeps panels out of the way, but a tiny home's roof is small and may be shaded by trees or tilted the wrong way. Ground mounting lets you aim panels at the sun and move them away from shade, and it makes snow clearing easy, at the cost of cable runs and some security concerns. For a home on wheels, a roof array has to survive highway wind, so use mounting hardware designed for that, and weigh the added roof weight against your trailer's limits (our guide to weight and balance explains why).

In the northern hemisphere, panels generally face south. For fixed panels, a tilt close to your latitude is a common starting point, with steeper angles favoring winter output. Even a small amount of shade on part of a panel can reduce its output noticeably, so study the roof and surrounding trees at different times of day before you commit.

Wiring, fusing and keeping it safe

• Use wire rated for outdoor and sunlight exposure for runs from the panels, and use proper connectors rather than twisted joints.
• Place a disconnect or breaker between the array and the controller, and a fuse or breaker between the controller and the battery.
• Size wire for the current it will carry and the length of the run to limit voltage loss.
• Ground the system as local code and the equipment manuals require.
• Keep cabling off sharp edges and seal roof penetrations carefully so they do not leak.

Solar wiring involves high direct-current voltages that do not behave like household current. If you are not experienced, have a licensed electrician check the design. Rules and permit requirements vary, so check with your local authority.

Maintenance and expected performance

Panels need very little care. Rinse off heavy dust or bird droppings, clear snow when you can safely do it, and check the mounting and wiring once or twice a year. Output declines slowly over the years, and the manufacturer's warranty will describe the expected rate. If the energy you harvest falls suddenly, suspect shade, a failed connection or a controller fault before you blame the panels.

A simple battery monitor and a watt meter turn guesswork into data. After a few weeks, you will know your real daily use and your real daily harvest in each kind of weather, and you can adjust the system with confidence.

Common mistakes

• Sizing for an average month instead of the worst one.
• Ignoring shade on part of the roof.
• Choosing a controller whose voltage limit is too close to the panels' cold-weather voltage.
• Using wire that is too thin for the run.
• Skipping fuses and disconnects.
• Adding too much roof weight to a trailer without checking ratings.

Gear worth a look

Keep reading in this cluster

• Pillar: Off-Grid Tiny Home Power: The Complete Beginner's Guide
• Tiny Home Batteries and Inverters: Types, Sizing and Safety
• Composting Toilets for Tiny Homes: How They Work and What to Expect
• Off-Grid Tiny Home Water Systems: Sources, Storage, Pumps and Filtration
• Heating and Cooling a Tiny Home Off the Grid