Lauren HollandBy Lauren Holland

Updated November 2026

A solar power backup system for home keeps essential circuits running when the grid goes down. In this guide you will learn how to list the devices you need to power, convert their wattage into daily watt-hours, size a battery and solar input that covers your outage length, and avoid the mistakes that leave people short on power at 2 a.m. The method works for a small portable station running a fridge and a few lights, or a larger system meant to carry a sump pump and a CPAP machine through a multi-day storm.

Step 1: Decide What the System Must Power

Start with the loads, not the equipment. A solar power backup system for home is only as good as the list of devices it has to carry, so make that list before you look at a single product. Focus on what you truly need during an outage: refrigeration, medical equipment, water, communication and basic lighting. Heating, cooling and cooking loads are often the biggest, so treat them as separate decisions.

Shopping for one? See our guide: Top 5 EcoFlow Power Stations with Solar Panel Options for Home Backup (2026).

Essential loads to list first

  • Refrigerator or freezer: Typical household units use roughly 100 to 800 watt-hours per day, depending on age, size and efficiency rating. Check the yellow EnergyGuide label or the manufacturer’s kWh/year figure and divide by 365.
  • CPAP machine: Many run between 30 and 60 watts during use, with a humidifier adding more. Confirm the rated draw on the device label and estimate hours of use per night.
  • Sump pump: A 1/3 HP pump may draw around 600 to 1,000 watts while running, but the startup surge can be several times higher. Run time is intermittent, so the daily total is often modest.
  • Router, modem and phone charging: Usually 20 to 60 watts combined for the network gear, plus a few watts per charger.
  • LED lighting: Often 5 to 15 watts per fixture.

Non-essential loads to leave off

Electric water heaters, clothes dryers, central air conditioners and electric ranges can each consume more energy in an hour than a small system stores in a full day. Unless your system is sized for whole-home backup, plan around them rather than trying to force them into a battery designed for a fridge and lights.

Step 2: Convert Wattage Into Daily Watt-Hours

Watts measure how fast power is used. Watt-hours measure how much total energy is used over time, and that is the number battery capacity is rated in. The formula is simple: watts × hours of use per day = watt-hours per day.

Device Typical Running Watts Estimated Hours per Day Daily Watt-Hours
Refrigerator (efficient, 24 hr cycling) About 60 average 24 About 1,440 Wh (use label kWh/year for accuracy)
CPAP with humidifier About 50 8 About 400 Wh
1/3 HP sump pump About 800 while running 1 (intermittent) About 800 Wh
Wi-Fi router and modem About 20 24 About 480 Wh
LED lights (5 fixtures at 10 W) 50 total 5 About 250 Wh

These figures are illustrative. Your fridge in particular may use far less or more than the average shown, so measure or read the label before committing to a number.

Step 3: Size the Battery for Your Outage Length

Add your daily watt-hours together, then multiply by the number of days you want to cover. Most homeowners plan for one to three days. Next, add a buffer of about 20 percent, because batteries cannot be drained to zero without shortening their life, and inverters lose some energy converting stored DC power to household AC.

A worked example

  1. Daily load from the table above (ignoring the sump pump for the moment): 1,440 + 400 + 480 + 250 = 2,570 Wh per day.
  2. Add the sump pump’s intermittent load, roughly 800 Wh per day, for a total of about 3,370 Wh per day.
  3. Cover two days: 3,370 × 2 = 6,740 Wh.
  4. Add a 20 percent buffer: 6,740 × 1.2 ≈ 8,088 Wh.

That example points toward a battery in the 8 kWh range, which is typically a whole-home or large-format system rather than a single portable station. If your list is shorter, the required capacity drops quickly. A fridge, CPAP and router over one night needs only about 2,000 Wh of usable storage.

Step 4: Plan the Solar Input

Batteries store energy but do not create it. Solar panels recharge the battery during daylight, and the question is whether they can replace what you use each day. A rough rule is to divide daily watt-hours by your location’s peak sun hours, then divide again by the system efficiency (commonly around 0.75 to 0.85 once losses are counted).

Using the 3,370 Wh per day example and assuming 4 peak sun hours, you would need about 3,370 ÷ 4 ÷ 0.8 ≈ 1,055 watts of panels to recharge fully in one sunny day. Cloudy weather reduces output significantly, so many people choose more panel capacity than the minimum or accept that the battery will recover over several sunny days. Peak sun hours vary by region and season, so check local solar resource data before finalizing.

Step 5: Check Inverter Capacity and Surge Ratings

The inverter converts battery DC power into the AC your appliances need. Its continuous rating must exceed the sum of loads running at the same time, and its surge rating must handle motor startup spikes. A sump pump, a refrigerator compressor and a microwave all surge when they start. If the sum of your simultaneous running loads is 2,000 watts, a 1,500-watt inverter will trip, even if the battery is full.

Step 6: Connect Safely

Whether you use a portable station with a transfer switch or a permanently installed system with an interlock, follow the manufacturer’s manual and local electrical code. Never backfeed a household circuit through a standard wall outlet, because that can energize utility lines and injure line workers. Permanent connections should be installed by a licensed electrician. For guidance on safe connection methods for portable units, see Home Backup With a Solar Generator: What It Can Power and How to Connect Safely.

Common Mistakes and Tips

  • Ignoring startup surge. Size the inverter for the peak, not the average.
  • Using nameplate watts instead of real usage. Nameplate numbers are often maximums. Measure with a plug-in watt meter where possible.
  • Forgetting battery reserve. Draining a lithium battery to zero repeatedly shortens its life. Plan for usable capacity, not total rated capacity.
  • Overlooking cloudy-day performance. Solar recharge drops sharply in overcast weather, so consider extra panels or a generator as backup.
  • Skipping a dry run. Test the system with your actual loads before a storm arrives.
  • Assuming a bigger system is always better. Oversizing raises the upfront investment without necessarily improving outage coverage.

If you are comparing whole-home and portable approaches, the guide Portable Solar Generator vs Home Battery System outlines the tradeoffs. For a practical sizing walkthrough tailored to outages, Home Backup Power Systems: A Step-by-Step Guide to Sizing for Outages (2026) goes deeper on the math.

  • Plug-in watt meter: Measures real draw for each appliance so your watt-hour math is based on data rather than label estimates. View on Amazon
  • EcoFlow Delta 2 portable power station: A portable option for smaller loads like a fridge, router and lights, and a useful reference point when sizing. View on Amazon
  • Jackery Explorer 1000 v2: Another portable station that many owners use for CPAP and lighting during short outages. View on Amazon

FAQ

How many watt-hours do I need for a fridge during an outage?

Check the EnergyGuide label for annual kWh and divide by 365 to get daily watt-hours. Many modern refrigerators fall roughly between 400 and 1,500 Wh per day, but your unit’s label is the best source.

Can a solar power backup system run my whole house?

Yes, if it is sized and installed as a whole-home system with adequate battery storage, inverter capacity and panels. Large loads such as electric heat or central air conditioning require significantly more capacity than most portable units provide.

How long will a home battery last during an outage?

Divide usable battery watt-hours by your average daily load in watt-hours, then multiply by 24 to estimate hours. Actual runtime varies with weather, temperature and load timing.

Do I need a generator as well as solar?

Many households keep a generator for extended cloudy periods or heavy loads. Solar handles routine outages well, while a generator provides a fallback when batteries run low.

Will solar panels work during a power outage?

Grid-tied solar panels typically shut down during outages for safety unless the system includes a battery and backup-capable inverter or transfer switch. Confirm this capability with your installer before buying.

How much solar do I need to recharge a battery each day?

Divide your daily watt-hours by local peak sun hours and by a system efficiency near 0.8. The result is the approximate panel wattage required for a full daily recharge under typical conditions.

Is lithium or lead-acid better for home backup?

Lithium iron phosphate batteries are common in modern home systems because they offer longer cycle life and deeper usable discharge. Lead-acid is heavier and often used in lower-cost designs, with shorter service life.

Should I consult a professional for installation?

Yes. Permanent connections to a home electrical panel should be handled by a licensed electrician familiar with local code and utility interconnection rules.

Conclusion

A solar power backup system for home works best when it is sized from your actual loads, not from marketing numbers. List essential devices, convert their use into daily watt-hours, add a buffer, and match the inverter and solar input to your conditions. Test the setup before you need it, and consult a licensed electrician for any permanent installation.

Ready to choose one?

Lauren Holland

About Lauren Holland

Lauren Holland is part of our editorial team and reviews and edits our solar generators for home backup & emergencies guides, checking product details against manufacturer specifications and owner feedback.