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Part VII: Solar ElectricityChapter 11. Grid-Tied and Off-Grid PV

Portable and Vehicle PV

Small panels for a camper, a shed, or a trailer, kept separate from whole-house wiring.

Difficulty
Beginner
Cost
$100–600
published

A portable panel is a charger for a battery you can point at the sun and take with you. It runs lights, phones, a small fan, and maybe a fridge if you did the watt-hours honestly. It does not run a space heater, and it does not connect to a house. The moment a wire can reach the service panel, you have left this page and you are on the wiring page, whether the panel folds or not.

A hundred-watt panel in 4.5 hours of full sun, with a derate of about 0.75 for heat, angle, and the controller, yields 100 times 4.5 times 0.75, or about 340 watt-hours. That is a careful day's phone and lighting budget, or a small efficient fridge only if the fridge's own watt-hours fit inside it. A cloudy day is less. A panel lying flat in a tree is less again. The bill-sizing guide uses the same derate idea on a house scale.

Difficulty

Level
Beginner
Time
An afternoon to set up a kit, and a habit of aiming it
Skills
Keeping house wiring out of the hobby

Cost estimate

$100–600

A small folding panel and a simple controller sit near the low end if you already have a battery. A larger panel, a proper controller, and a lithium pack with a management system use the whole range and can pass it. The inverter is optional and is where people buy more watts than the panel can feed.

PieceWhat it is for
Panel around 100 to 200 wattsA few hundred watt-hours on a good day
Charge controllerSo the battery is not boiled
Battery you can carry or that is built into the vehicleThe night
Small inverter, if you truly need alternating currentA loss you should avoid when 12-volt loads exist

Materials

ItemQtyNotes
A panel you can aim and tie down1Wind takes an unsecured panel. A vehicle roof mount has to be a mount, not a suction cup at highway speed.
A charge controller sized to the panel1Match the battery chemistry in the settings. A panel clamped to battery posts is not a controller.
A battery with a management system if it is lithium1See the battery page for fractions and fuses. A car starting battery is a poor deep-cycle bank.
Fusing at the battery1Close to the positive post, at the rating the wiring can stand. Portable does not mean unfused.

What the watts can actually do

List the loads the way the battery page does. A phone charger at 10 watts for two hours is 20 watt-hours. A 40-watt light for five hours is 200. A fridge that averages 40 watts around the clock is nearly 1,000 watt-hours, which is three good days of a 100-watt panel and an argument for a bigger panel or a different fridge. Do that multiplication before you buy a 2,000-watt inverter. The inverter can only turn the battery's energy into alternating current.

Aim the panel. A flat panel at noon in summer is fine. A flat panel in winter, or a panel facing a wall, makes much less. Shade on part of a small panel matters even more than shade on a large array, because you had no extra modules. Wipe the dust. A controller with a readable voltage is how you know the battery is full and you should stop expecting more.

Heat inside a closed vehicle cooks batteries and controllers. Lithium has a charging temperature limit. Do not leave a pack on the dash in July. Put it where it can shed heat, and do not charge it below freezing unless it says so.

Portable power stays portableA folding panel, a charge controller, a battery, and a small inverter. A house service panel is drawn apart from them with a break.PanelControllerBatteryLoadsHouse panel: no100 W runs a lamp and a phone, but no space heater.
Panel, controller, battery, and small loads. The house service panel is a separate drawing with a broken link.

Vehicles

A vehicle already has an alternator trying to charge the same battery the sun wants. Those two chargers need a design, not two sets of clamps. A solar controller set for the battery chemistry, and a DC-DC charger if you are charging a house battery from the alternator, are the usual pair. Clamping a panel to a car battery while the engine is running, with no controller, is how you boil a battery or confuse both regulators.

Roof mounts on a camper have to survive highway wind and a low bridge. Follow a mount made for the vehicle. Seal the holes the way the vehicle maker allows, or you have bought a leak in the roof and a rust path. A panel that can fly off can land in the next lane. Take it inside or pin it down before you move.

Do not run a cord from the camper into a house outlet, in either direction, to "share." That is the same backfeed the wiring page forbids. Shore power, if the camper has it, is a listed inlet and a transfer method, not a jumper cable of extension cords.

  1. Add the watt-hours before you pick the panel

    Use 100 watts times your sun hours times about 0.75 as a first yield. If the loads do not fit, cut loads or add panel. Do not add inverter.

  2. Put a controller and a fuse in the path

    Chemistry settings match the battery. Fuse near the positive post. No bare clamps.

  3. Aim it, shade-check it, and keep it cool

    Perpendicular to the sun beats flat. Partial shade costs a small array more than a large one. Batteries do not live on the dash.

  4. Tie it down before the wind or the road does

    Use real mounting hardware. Unplug and stow a folding panel before you drive.

  5. Leave the house panel out of it

    Portable power stays on its own battery. A building with utility power needs a permit and an electrician, even if the panel folds up.

Further reading

These links go to outside sources. This book cites them by link and does not copy their words or pictures.

General education, not a permit or a stamped design. Follow the safety note in the guide, read the safety disclaimer, and hire a licensed trade when the work requires one.