4kWh per Day Solar System: How Many Panels and What Size You Need
Short answer
To make 4 kWh a day you need about 1.1 kW of solar panels at 4.5 peak sun hours and 80% system efficiency. That is three 430 W panels, six 200 W panels or twelve 100 W panels. Off grid, add about 2.2 kWh of battery to cover the night, or 4.4 to 8.9 kWh for one to two cloudy days, plus an MPPT controller and a 2,000 W inverter.
Four kilowatt-hours a day is a small, very livable energy budget. It covers a fridge, lights, a laptop, a fan, a water pump and some electric cooking, which is why it is a common target for cabins, tiny homes, RVs, workshops and sheds that sit far from a utility line.
This guide starts from that daily number and works outward: the array size, how many panels at each wattage, a sample load list that adds up to exactly 4 kWh, the battery you need for nights and cloudy spells, controller and inverter sizes at 12, 24 and 48 V, and the extra panels winter demands.
How big a solar system do you need for 4 kWh a day?
Divide your daily energy target by your peak sun hours, then by the system efficiency. This site plans with 80% efficiency, which accounts for heat, dust, wiring, charge controller and inverter losses, and 4.5 peak sun hours as a US middle value.
Example: 4 kWh ÷ 4.5 ÷ 0.80 = 1.11 kW, or about 1,100 W of panels
Sun hours change the answer more than anything else. A sunny desert site needs less than a 1 kW array, while a cloudy northern site needs well over 1.5 kW for the same 4 kWh.
| Peak sun hours | Array needed | 430 W panels | 200 W panels |
|---|---|---|---|
| 3.0 | 1.67 kW | 4 | 9 |
| 3.5 | 1.43 kW | 4 | 8 |
| 4.0 | 1.25 kW | 3 | 7 |
| 4.5 (US middle) | 1.11 kW | 3 | 6 |
| 5.0 | 1.00 kW | 3 | 5 |
| 5.5 | 0.91 kW | 3 | 5 |
| 6.0 | 0.83 kW | 2 | 5 |
Panel counts are rounded up, because a fraction of a panel does not exist. At 5.5 sun hours, two 430 W panels would make only 3.8 kWh, so the table keeps three. Check the figure for your exact address with the free NREL PVWatts calculator, which models local weather data.
A 1.1 kW array is close to the setup covered in our guide to the 1000 watt solar panel, which shows output city by city. The difference here is that the target is fixed at 4 kWh and the array grows or shrinks to hit it.
How many solar panels make 4 kWh a day?
Once you know you need about 1,110 W, divide by the panel rating and round up. Small panels suit RV roofs and 12 V systems, while full-size residential modules are cheaper per watt and better for ground mounts and cabin roofs.
| Panel rating | Panels needed | Array total | Output at 4.5 sun hours |
|---|---|---|---|
| 100 W | 12 | 1,200 W | 4.32 kWh |
| 200 W | 6 | 1,200 W | 4.32 kWh |
| 300 W | 4 | 1,200 W | 4.32 kWh |
| 400 W | 3 | 1,200 W | 4.32 kWh |
| 430 W | 3 | 1,290 W | 4.64 kWh |
| 550 W | 3 | 1,650 W | 5.94 kWh |
Two 550 W panels give 1,100 W and about 3.96 kWh a day, which is just short of the target. Three 430 W panels are the simplest fit: they leave about 0.6 kWh of daily headroom and cover roughly 66 square feet at 21% panel efficiency (1,290 W ÷ 210 W per square meter = 6.1 m²).
What does a 4 kWh day actually look like?
A daily budget is easier to judge once it is written as appliances and hours. Here is a sample day for a small off-grid cabin or tiny home with an efficient full-size fridge, a shallow well pump and a little electric cooking.
| Load | Power and use | Energy per day |
|---|---|---|
| Energy Star refrigerator | cycling, 24 hours | 1.20 kWh |
| Single induction burner | 1,400 W for 20 minutes | 0.47 kWh |
| Box or ceiling fan | 50 W for 8 hours | 0.40 kWh |
| LED lights, 8 bulbs | 9 W each for 5 hours | 0.36 kWh |
| Laptop | 60 W for 6 hours | 0.36 kWh |
| Microwave | 1,200 W draw for 15 minutes | 0.30 kWh |
| Water pump | 750 W for 20 minutes | 0.25 kWh |
| Wi-Fi router | 10 W for 24 hours | 0.24 kWh |
| TV | 60 W for 4 hours | 0.24 kWh |
| Electric kettle | 1,500 W for 6 minutes | 0.15 kWh |
| Two phones | about 15 Wh each | 0.03 kWh |
| Total | 4.00 kWh |
The fridge is the single biggest line, so its real rating matters. Our guide on how many watts a refrigerator uses shows typical new models at 1 to 2 kWh a day. Swap in your own appliances with the solar load calculator before you buy anything.
How big a battery do you need for 4 kWh a day?
Panels only produce during the day. Off grid, the battery has to carry everything that runs between sunset and sunrise, plus any days when clouds cut production. Size it in three steps.
Step 1: cover the night
In the sample day above, the loads that run after dark are 14 hours of fridge cycling (0.70 kWh), the lights (0.36), the TV (0.24), the router overnight (0.14), two hours of laptop (0.12), the fan (0.40) and phone charging (0.03). That adds up to about 2.0 kWh.
Example: 2.0 kWh ÷ 0.90 = 2.2 kWh of lithium battery for one night
Step 2: add days of autonomy
One night is the bare minimum. A cloudy day can cut solar output to a small fraction of normal, so most off-grid designers plan one to two days of autonomy. The table uses 90% usable capacity for lithium iron phosphate (LiFePO4) and nominal battery voltages.
| Coverage | Usable energy | Battery size | Ah at 12 V | Ah at 24 V | Ah at 48 V |
|---|---|---|---|---|---|
| One night | 2.0 kWh | 2.2 kWh | 185 Ah | 93 Ah | 46 Ah |
| One full day | 4.0 kWh | 4.4 kWh | 370 Ah | 185 Ah | 93 Ah |
| Two full days | 8.0 kWh | 8.9 kWh | 741 Ah | 370 Ah | 185 Ah |
A single 48 V, 100 Ah LiFePO4 battery covers one full day. For two days, a 10 kWh battery gives about 9 kWh usable, which is just over the 8.9 kWh target. Lead-acid batteries should only be drained to about 50%, so they need roughly 1.8 times the capacity shown here. The battery calculator runs the same math for your own loads and chemistry.
Step 3: make sure the panels can refill it
This is the step most small systems miss. Three 430 W panels make about 4.64 kWh on an average day, so only about 0.64 kWh is left over after the 4 kWh load. Refilling a drained 8 kWh battery at that rate takes 12 to 13 sunny days.
If you buy two days of storage, buy more panels too. Five 430 W panels (2,150 W) make about 7.7 kWh at 4.5 sun hours, leaving roughly 3.7 kWh of surplus, enough to refill two days of storage in a little over two sunny days.
How many panels do you need for 4 kWh a day in winter?
Average sun hours hide a big seasonal swing. In much of the northern US, December sun hours can drop to roughly 2 to 3, so an array sized for the yearly average falls well short when days are shortest. Use your worst month if the system must run year round.
Example: 4 ÷ 2.5 ÷ 0.80 = 2.0 kW, or five 430 W panels
| Winter sun hours | Array needed | 430 W panels | Daily output |
|---|---|---|---|
| 3.0 | 1.67 kW | 4 (1,720 W) | 4.13 kWh |
| 2.5 | 2.00 kW | 5 (2,150 W) | 4.30 kWh |
| 2.0 | 2.50 kW | 6 (2,580 W) | 4.13 kWh |
Notice that the five-panel array is the same one that refills a two-day battery quickly. For a full-time cabin in the north, about 2 kW of panels is a more honest size than 1.1 kW. Tilting the panels steeper in winter, roughly latitude plus 15 degrees, also helps them catch the low sun and shed snow. For a part-time summer cabin, the smaller 1.1 kW array is enough.
Another option is to cut winter loads: skip the fan, and cook on propane instead of induction. Those two changes alone save about 0.87 kWh a day in the sample list.
What charge controller and inverter do you need at 12, 24 or 48 V?
Charge controller
The MPPT charge controller sits between the panels and the battery. Its current rating is the array watts divided by battery voltage, plus 25% headroom.
| Battery voltage | 1,290 W array | Suggested size | 2,150 W array | Suggested size |
|---|---|---|---|---|
| 12 V | 134 A | two 70 A units | 224 A | not practical |
| 24 V | 67 A | 70 A or 80 A | 112 A | two 60 A units |
| 48 V | 34 A | 40 A | 56 A | 60 A |
Also check voltage. Three full-size panels in series can approach the 150 V input limit common on small MPPT controllers on a cold morning, because panel voltage rises as temperature drops. The charge controller calculator checks both amps and cold-weather volts.
Inverter
The inverter is sized to the loads that run at the same moment, not to the panels. In the sample day, the worst case is the induction burner (1,400 W) running while the fridge, lights, laptop and router are on, about 1,700 W in total. A 2,000 W pure sine wave inverter covers that and leaves room for the fridge compressor’s startup surge.
| Battery voltage | DC current at 2,000 W (90% inverter efficiency) | Verdict |
|---|---|---|
| 12 V | 185 A | Works, but needs very heavy cable |
| 24 V | 93 A | Good for most cabins and vans |
| 48 V | 46 A | Best for tiny homes and fixed cabins |
At this size, 24 V is the practical floor for a fixed building, and 48 V keeps cables thin and lets a single controller handle a winter-sized array. Stay at 12 V only if an RV’s existing system and appliances already run on it.
What can a 4 kWh a day system not run?
Four kilowatt-hours disappears quickly once heat is involved. A 1,500 W space heater running for three hours uses 4.5 kWh, more than the whole daily budget. A rooftop RV air conditioner or a window unit running through a hot afternoon can do the same.
- Electric water heaters: a 4,500 W element running for one hour uses 4.5 kWh. Use propane or a solar thermal heater instead.
- Electric clothes dryers and full ranges: both draw several kilowatts for long periods.
- Air conditioning all day: possible only for short runs, or with a much bigger array and battery.
- Well pumps that run for hours: fine for household water, not for irrigation.
For comparison, an average US home uses close to 30 kWh a day, so a 4 kWh system is roughly one-seventh of a typical house. If your plans grow past it, the off-grid solar calculator sizes panels, battery and inverter together for a larger daily load.
Is 4 kWh a day right for your RV, cabin, tiny home or shed?
RVs and vans: roof space is the limit. Six 200 W panels need about the same area as three large panels, but they fit around vents and hatches. Flat-mounted RV panels produce less than tilted ones, especially in winter, so many RVers plan 4 kWh as a summer figure and carry a generator for gray weeks.
Weekend cabins: a 1.1 kW array with a one-day battery is a good fit, since the battery has the whole week to refill while you are away.
Full-time tiny homes: plan the winter-sized 2 kW array, a 48 V battery of 5 to 10 kWh, and propane for heat and hot water.
Sheds and workshops: power tools draw high watts for short bursts, so the inverter matters more than the battery. A 2,000 to 3,000 W inverter with a 2 to 5 kWh battery suits most hobby shops.
How much does a 4 kWh a day solar system cost?
These are typical US ranges in late 2026 for a DIY off-grid build with a 1.1 to 1.3 kW array and about 5 kWh of lithium storage:
- Panels: about $450 to $1,400, with small RV panels at the high end.
- LiFePO4 battery, about 5 kWh: about $1,000 to $2,500.
- MPPT charge controller: about $150 to $500.
- 2,000 W pure sine inverter or inverter-charger: about $300 to $1,200.
- Wire, fuses, breakers and mounts: about $300 to $800.
That puts a complete system at roughly $2,200 to $6,400, with the battery as the biggest swing factor. A winter-sized 2 kW array with two days of storage costs more. The 30% federal residential clean energy credit ended for homeowner-owned systems installed after December 31, 2025, so do not count on it.
Frequently asked questions
How many solar panels do I need to make 4 kWh a day?
About three 400 to 430 W panels, six 200 W panels or twelve 100 W panels at 4.5 peak sun hours. That is roughly 1.1 to 1.3 kW of panels at 80% system efficiency. Sunny desert sites can get by with less, and cloudy or northern sites need four or more large panels.
What size battery do I need for a 4 kWh solar system?
For overnight use only, about 2.2 kWh of lithium battery covers a typical 2 kWh night. For one full day of autonomy, plan about 4.4 kWh, and for two days about 8.9 kWh. Lead-acid batteries need roughly 1.8 times those figures because only half their capacity should be used.
Is 4 kWh a day enough to live off grid?
Yes, for a small, efficient household that heats water and space with propane or wood. It covers a fridge, lights, a laptop, a fan, a water pump and some electric cooking. It is not enough for electric heating, an electric water heater or all-day air conditioning.
Should a 4 kWh system be 12 V, 24 V or 48 V?
Use 24 V or 48 V for a cabin or tiny home. A 2,000 W inverter draws about 185 A at 12 V but only 46 A at 48 V, so higher voltage means thinner cable and a smaller controller. Keep 12 V only for RVs and vans already built around it.
How many panels make 4 kWh a day in winter?
With 2.5 winter sun hours you need about 2 kW, or five 430 W panels. With only 2 sun hours, plan about 2.5 kW, or six panels. Steeper tilt helps, and moving cooking and heating to propane lowers the winter target.
