For most garages, the kit’s name tells you very little. Which kit will actually run your lights, door opener, tools or EV charger, and which one will leave you short?
This article shows you how to size a kit from your own loads, how to check your roof and local rules, and which kits to look at.
The short answer for most garages
For most garages, the kit’s name tells you little. What decides the fit is your total daily energy use, in watt-hours (Wh). Add up what each device draws and how long it runs.
An EV charger changes the picture. A Level 2 charger, the faster type used at home, draws about 6.6 kW. A 400 W kit cannot run it alone at the same moment, and air conditioning is the same story.
If outages matter to you, compare battery backup with a generator before you choose. To see what a kit includes and how it is installed, read how plug-and-play solar kits work.
Add up what the garage will run each day
Start with each appliance. Multiply its power in watts by its hours of use per day to get watt-hours (Wh). Add the results for every device. A 100 W light running 5 hours uses 500 Wh.
Turn that total into panel power. Divide the daily Wh by your peak sun hours, meaning the full-strength sun hours at your location, then divide by 0.8 to allow for losses.
With 1,500 Wh and 4 peak sun hours, you need 469 W of panels. Peak sun hours change with location and season, so use a local figure, not a general one.
If that total is more than a small kit can store, compare portable power stations and fixed solar batteries first.
Panels, battery and inverter do different jobs
Panels set how fast energy comes in
Panel wattage sets how fast energy comes in. Rated watts show nominal output, but real production depends on location, season and system design. If the garage needs backup power, portable solar kits for home outages may be simpler.
For a first estimate, divide daily energy use in watt-hours by peak sun hours, the hours of full-strength sun per day, then divide by 0.8. That gives the panel wattage you need.
The battery sets how long loads can run
Battery capacity, in kWh, is the energy it can store. Divide it by your average load in kW to get the theoretical runtime. A 10 kWh battery feeding a 2 kW average load runs 5 hours.
For an evening, add the watt-hours of each load over the hours you run it. Pick a battery that holds that total, with a margin, because real runtime is shorter than the theory.
The inverter sets how much can run at once
The inverter’s rating, in watts, must cover all loads running at the same time. Lights, a door opener and a compressor add up when they run together.
Motors draw much more power at startup than while running. Check the startup demand in the appliance’s manual, and make the inverter cover that peak. The battery must supply that power too, not just the average load.
Can the garage roof take the panels?
Before you choose an array, check that the garage roof can carry the weight of the whole system.
Then check the local snow and wind load rules, because they depend on your address.
Permit rules depend on your local authority and your project, so call the building office before you buy. Ask which snow and wind loads apply at your address and whether a permit is needed.
Also check the snow and wind ratings printed for the panels. If you are new to standalone power, this beginner’s guide to off-grid solar power walks through the basics.
Off-grid, grid-tied or backup: which setup fits
Off-grid kits for standalone loads
An off-grid kit suits a detached garage only if it is sized for the loads it will feed. List the lights, door opener and tools first, then check the battery and panels against that list.
Renogy’s kit lists its components and cables, but it does not say it is approved for a building’s wiring. Read safety standards and fire risks of plug-and-play solar panels before using extension cords or power strips.
Grid-tied systems for loads alongside the utility
A grid-tied system needs utility approval before any installation. Start with an interconnection request. It lists the system size, the panel and inverter locations, and the inverter specs.
Then the utility reviews it, you install, and a local inspector checks the work. Approval takes time: in the states studied in 2020, legal deadlines before installation ran from 10 to 40 business days. Your utility’s timeline may differ.
Backup power for outages
A grid-tied system shuts down during a power cut, for safety reasons. Its inverter stops feeding power into the lines, so the panels cannot run your garage even when the sun is shining.
For lights and tools to keep running during an outage, you need a battery. Only storage keeps the loads powered, so size it for the loads you want to keep.
What an EV charger does to the numbers
An EV charger changes the numbers completely. A level 2 home charger draws about 7,200 W on average, far more than a 400 W kit can supply. One hour of charging needs about 7.2 kWh, before charging losses.
Settle the charging source before you size anything. Solar only means charging happens only while the panels produce power, which is slow. Utility-backed means the grid supplies that energy.
Solar plus battery means the battery must hold the 7.2 kWh per charging hour when the grid is not used, so check the battery bank sizing guide before buying.
The two Renogy kits to compare
Renogy has two 400 W kits, and both start at $1,899.99. The 3.6 kWh version is aimed at a workshop or shed. It has four 100 W panels and can come with one of two battery types.
Before you choose, check the battery capacity and battery type of the version you order.
The 2.4 kWh and 3.6 kWh versions store different amounts, so the shared starting price tells you nothing about how long your loads will run.
Compare the kWh figure with the energy your garage uses each day. For a full sizing example, read Solar panel kits for detached garages: a complete setup.
Start with your own loads, not the kit’s name. List each device with its power and daily hours, then add up the watt-hours. That total decides whether a kit fits.
Check the roof and the local snow and wind rules, then compare the battery’s kWh with your daily total. Next, call your building office and ask whether a permit is needed.
Frequently Asked Questions
What size solar battery do I need to run an air conditioner?
Add up the energy the air conditioner uses over your planned hours, in kWh (kilowatt-hours, the unit of stored energy), and pick a battery that holds that total.
The inverter must cover its startup power and running power, since compressors draw more at startup.
Can I plug a solar kit into my garage outlet?
No. The Renogy kit is wired through a charge controller and a battery, and nothing in its description says it can run from a garage outlet. Check the wiring and the manual before you plug anything into a socket.
Do I need a permit to install solar panels on a garage roof?
There is no single answer, because the permit requirement depends on your local rules and on your project. The same panels can need a permit in one town and not in the next, since the local authority sets the rules.
How long will a 12V battery last with a 3000W inverter?
You can’t get a runtime from the 12V and 3000W figures alone. The inverter rating is only the maximum load it can handle.
What counts is how much energy the battery can actually deliver and the real watts your devices draw.