Off Grid Solar Kit: How to Size and Specify One From Your Loads

Last updated: 2026-11-04

A cabin owner opens a product page for an off grid solar kit, sees "2 kW" in the title, and cannot tell whether it will run a fridge through three cloudy days. The headline wattage often describes the panels only; the battery, inverter and cabling decide what the kit actually delivers at night. This guide shows how to size each part from your own loads, how voltage changes the hardware, and what to send when a project needs a specified system instead of a catalog kit.

What an off grid solar kit should include

An off grid solar kit should include panels, a charge controller, a battery bank, an inverter, cabling with fuses, and mounting hardware, and only an all-DC system can leave out the inverter. An off grid solar kit is a bundle of those parts sized to power loads with no utility connection.

The panels collect energy and the charge controller regulates it into the battery. The battery stores energy for night and low-sun days, and the inverter converts battery DC into the AC that household appliances use.

Check whether the kit includes the following items: the DC fuses and breakers between battery and inverter, the battery cables sized for the current, the grounding conductors, and the roof or ground mounting. Compare two kits on this list as well as on wattage.

For a worked cabin build, the step-by-step off grid DIY sizing guide follows the same sequence used below, and the off grid cabin solar page shows how these parts are grouped for that use.

Size the kit from your loads

Sizing an off grid solar kit starts with a daily watt-hour total built from each load: watts multiplied by hours of use per day. Every later number, from panel watts to battery capacity, is derived from that one total.

The worksheet below uses assumed appliances for a small cabin. The wattages and hours are example inputs, not measurements; replace them with the nameplate watts and real hours for your site. A refrigerator needs its duty cycle, because the compressor runs only part of the day.

Load	Watts	Hours per day	Watt-hours per day
LED lights (5 x 8 W)	40	5	200
Refrigerator (45 W while running, 40% duty over 24 h)	45	9.6	432
Laptop	60	4	240
Router and phone charging	10	24	240
Water pump	100	0.5	50
Total	255	n/a	1,162

The total is 200 + 432 + 240 + 240 + 50 = 1,162 Wh per day. The 255 W figure is the sum of all running loads if every one were on at the same moment, which sets the inverter size later.

The off grid living panel guide covers how to collect these loads for a full household, including daily load classes and why heat loads usually break the budget.

Panel, battery and inverter sizing

Panel, battery and inverter sizing each follow one formula, and each needs an assumption you must state: peak sun hours, days of autonomy, and system losses. The numbers below are a worked example, not a recommendation for your site.

Assumptions for the example: 4 peak sun hours per day (peak sun hours are kWh per square metre per day of sunlight), 90% inverter efficiency, 75% overall efficiency from panel to battery, a 24 V battery bank, 2 days of autonomy, and 80% usable battery depth. Look up the peak sun hours for your own location and worst month before you fix the array size.

1. Battery-side energy per day = 1,162 Wh / 0.90 = 1,291 Wh. Also add the inverter's idle draw from its datasheet. An assumed 15 W idle over 24 h adds 360 Wh, or about 31 percent of this load. The steps below show the figures before idle draw; with it, this example needs 1,651 Wh a day, about 550 W of panels and 4,128 Wh of battery, or about 172 Ah at 24 V.
2. Panel watts = 1,291 Wh / (4 sun hours x 0.75) = 430 W of panel rating.
3. Battery capacity = 1,291 Wh x 2 days / 0.80 usable = 3,228 Wh, which is 3,228 / 24 V = about 135 Ah at 24 V.
4. Inverter size = 255 W running load x 1.25 headroom = 319 W, so this example assumes a 500 W inverter. A compressor start can draw several times its running watts, so check the surge rating against the refrigerator nameplate.

Four 110 W panels or two 215 W panels would cover the 430 W requirement, with the panel count set by the size you can mount.

Even before idle draw, this array only matches the daily load, so add margin to recover after cloudy days. Check usable depth on the battery datasheet, because it varies by chemistry. Panels, battery and inverter all scale linearly with the load total, so doubling the loads doubles each answer.

For inverter choices beyond the size, the pure sine wave inverter guide explains waveform, continuous rating and overload duration, and the off grid energy storage buyer's guide covers matching usable capacity to the load schedule and checking compatibility with the charging equipment.

12V, 24V or 48V

System size decides voltage, because higher voltage cuts the current for the same power. Current is power divided by voltage, so the same 1,000 W inverter load draws about 83 A at 12 V and 21 A at 48 V before inverter losses, or about 93 A and 23 A at 90% efficiency. Size cable and fuses from the inverter maker's input current.

Small kits usually stay at 12 V and higher-power systems move to 24 V or 48 V, with cable length and component availability setting the boundary.

Lower current means thinner cable, smaller fuses and less resistive loss in the wiring. Resistive loss rises with the square of the current, so halving the current cuts the heat in the same cable to a quarter. The table shows the currents for this article's examples.

System voltage	Current at 1,000 W inverter load, before losses	Charge current from a 430 W array
12 V	83.3 A	35.8 A
24 V	41.7 A	17.9 A
48 V	20.8 A	9.0 A

The battery must be built at the chosen voltage. The 3,228 Wh bank in the example is 269 Ah at 12 V, 135 Ah at 24 V and 67 Ah at 48 V, so the same energy needs fewer parallel strings at higher voltage.

Ready kit or specified system

A ready kit fits a small, fixed load list such as lighting, a router and device charging, while a specified system fits a project where loads, autonomy, voltage or mounting need to be set per site. The deciding test is whether a catalog kit's panel watts, battery watt-hours and inverter rating all meet your own worksheet totals.

Compare a retail kit to your worksheet in three numbers: panel watts against your required panel watts, battery watt-hours against your autonomy requirement, and inverter continuous rating against your running load. If any one falls short, the kit will not do the job however large the headline wattage.

A project system is the better route when you need several identical sites, a specific voltage, unusual mounting, or a battery and inverter pairing chosen for compatibility. Complete off grid systems that are not listed are not held as stock items; a project system is quoted to a specification and supply is confirmed at the quote.

The on-grid, off-grid and hybrid comparison helps if you are still deciding whether a utility connection should stay in the design. For a remote site, the remote solar power system page describes the project route.

What to send for a quote

A quote for an off grid solar system needs six inputs: loads, location, days of autonomy, system voltage, mounting type and quantity. These are the same inputs used in the worksheet above, so completing the worksheet is most of the work.

• Loads: each appliance with its watts, hours per day and whether it has a motor or compressor start.
• Location: the nearest town or coordinates, which sets peak sun hours, temperature range and snow or wind exposure.
• Autonomy: how many days the battery must carry the loads with no sun.
• Voltage: your preferred 12, 24 or 48 V, or "advise" if the loads decide it.
• Mounting: roof, ground or pole, plus the roof material if relevant.
• Quantity: one site or a repeat order, and the target market for the destination country.

The more of these you fill in, the fewer rounds of questions come back. If a load is uncertain, send the nameplate photo and the expected hours rather than a guess.

FAQ

Can you install your own off grid solar system?

Yes, a small low-voltage system can be self-installed where local rules allow. Wiring battery banks and inverters carries fire and shock risk, and some regions require a licensed electrician or an inspection for the AC side. Check local requirements before you buy, and use the sizing steps above to confirm the parts match.

How many solar panels do I need to go off the grid?

The number of panels equals required panel watts divided by the watts of one panel. In the worked example, 430 W of array before inverter idle draw is four panels of 110 W or two panels of 215 W. Your own count depends on your daily watt-hours and the peak sun hours at the site, so no single number fits every home.

How much solar do you need to be off-grid?

Daily watt-hours divided by inverter efficiency, then by the product of peak sun hours and the loss factor, gives the answer. A 1,162 Wh daily load through a 90% efficient inverter, at 4 peak sun hours and 75% efficiency, needs about 430 W before inverter idle draw. A larger household load scales that figure in direct proportion.

How do I ground solar panels off-grid?

Ground solar panels by bonding the panel frames and the mounting rails together and connecting them to a grounding electrode through a conductor sized by your local electrical code. The rules differ by country and by system voltage. Have the grounding scheme confirmed by a qualified electrician or the local code before energizing.

Can I go completely off-grid with solar?

Yes, a system sized for your loads, your worst-month sun and enough days of autonomy can run with no utility connection. Long stretches of low sun are the weak point, and a backup source covers those weeks. Each extra day of autonomy adds one more day of battery energy to the sizing formula.

Next step

Once the worksheet gives you daily watt-hours, panel watts, battery capacity and voltage, a specified system can be quoted against those figures. Prepare your power, size, quantity and target market, then Send your requirements.