What Size Solar Generator Do I Need?

An EcoFlow Solar Generator / Power Station and extra battery power a home at night during an outage using energy from the sun stored in the batteries. 

Finding the Right Size Solar Generator

Like most ‘What Size?’ questions, the right size solar generator depends on the intended use. Some possible uses for a solar generator include:

A Solar Generator is a combination of solar panels and battery storage. Solar panels convert energy from the sun into electricity to charge storage batteries in the solar generator. The generator converts energy stored in the battery to electricity for appliances like a fan or refrigerator, or for charging batteries in electronics such as a cell phone.

In short, a solar generator is useful for anything that you could do with a generator, but it can be more versatile, especially where location is concerned. If the only place to put your power source is indoors, a solar generator can operate where a portable generator cannot, like inside an apartment on the fourth floor.

Even better, you don’t need to store volatile fuels or find somewhere to exchange a propane tank, or have it filled. In fact, you don’t have to buy fuel at all. Just hook up the solar panels and charge the battery. Most come with multiple charging options. Some even charge at electric vehicle stations. Add extra batteries to extend run time or keep the power on while you charge up.

Solar Generator / Power Station Calculator

Understand Power and Energy Storage

Sizing a solar generator or power station requires understanding power and energy and their relationship.

Voltage (volts) is a force that pushes electricity through a circuit. It takes very little force to light an LED, but a lot of force to start and run an air conditioner.

Current (amps) is how much electricity is moving through a circuit. It takes very little current to turn on a tiny LED, but a lot of current to start and run an air conditioner.

Power (watts) measures the work being done. Volts x Amps = Watts. To light an LED requires very little power, like from a pair of AAA batteries. Each AAA battery provides 1.5 volts. The LED draws .02 Amps. 1.5 Volts x .02 Amps = 0.03 Watts. That’s a tiny amount of power compared to a 3-ton central air conditioner, which might need 5000 watts to run (running watts) and 12000 watts to start (starting watts).

Energy (watt-hours) is a measure of power used over time, typically in hours. If you turn on a window fan, the power needed is 90 watts. Run the fan for an hour, and the energy used is:

Power x Hours = 90 Watts x 1 Hour = 90 watt-hours (Wh).

We all know that a cell phone with a larger battery will stay powered on longer than one with a smaller battery. The difference is how much energy each battery can store. The same is true of solar generators and power stations. The solar generator battery capacity is how much energy it can store, and the power rating is the amount of power it can put out at any given moment.

For example, a solar generator with a 1000 Wh battery and a 500-watt rating can power any device or combination of devices up to 500 watts. If the load (the devices connected to the solar generator) totals 500 watts, the solar generator has enough stored energy at full charge for two hours of use before it needs recharging.

If we reduce the load by half to 250 watts, the battery lasts twice as long. 1000 Wh / 250 Watts = 4 hours of run time. A 250-watt load that runs for 2 hours uses 2 hours x 250 watts = 500 watt-hours of energy.

Always look at the power rating in watts and the energy storage capacity in watt-hours.

Note: A kilowatt is 1000 watts. Watts / 1000 = kilowatts (kW) Kilowatts x Hours = Kilowatt-Hours (kWh)

What Size Solar Generator to Run Refrigerator and Freezer

This question gets asked often. During a power outage, the food in a refrigerator begins spoiling in four hours or less. That could mean hundreds of dollars worth of food headed for the trash can. A full chest freezer will make it about one day without power before thawing starts.

Required for 1 refrigerator and 1 chest freezer:

(example only. Check your appliances for energy use and power requirements.)

• 1600 Continuous Watts Output
• 3600 Starting Watts Output
• 2400 Watts Connected Solar
• 6kWh Storage Capacity

Refrigerators and freezers, if they are the similar in size, use similar amounts of power. But they only run when necessary, not all the time. That makes figuring out the required energy storage a little different.

When you bought your refrigerator or freezer, you probably remember a bright yellow energy usage tag. If you still have that tag, you already have a pretty good idea how much energy it requires. The manufacturer’s website will also have that information. For this example, we’re going to use the average daily energy use of a typical household refrigerator of around 2kWh. Energy use varies by age, model, size, and efficiency. Do your research.

For our typical refrigerator and freezer, we need 4kWh of energy every day.

The solar generator must provide enough power to start and run both appliances multiple times throughout the day. Our typical refrigerator and freezer each require 800 running watts and 1800 starting watts. We should ensure that if both start at the same time, there is enough power to start both—1600 running watts and 3600 starting watts. And we also want to ensure that after a cloudy day, the next morning we still have enough power to start and run our refrigerator and freezer.

By connecting a solar array, we can rely on the array to charge the batteries every day. We need at least 4kWh of energy per day, and we get up to 6 hours of usable sunlight per day. 1kW of connected solar will charge the solar generator batteries while the two appliances turn on and off throughout the day.

1kW of solar is about 33% more than actually required, but it compensates for cloudy days.

6kWh of storage is about 50% more than required which gives us a good reserve for those days when energy production does not fully meet the requirement.

A solar generator with 6kWh of battery storage and 1000 watts of connected solar panels fits this application with room to spare.

What Size Solar Generator Will Run a House

In the United States, the average household electrical energy consumption is approximately 30 kilowatt-hours per day. Daily use can vary from day to day and by the season, especially in hot or cold climates.

What size solar generator do I need for my home? Check with your utility company. They should have an annual and seasonal or monthly energy use for your home. Select the months when energy use is highest and make your decisions based on those months.

If we’re planning to run our house entirely on solar, perhaps in an off-grid scenario, our solar generator must supply 30kWh of energy every day. In the middle of the country, we can count on 6hours of usable direct sunlight every day. 30KWh / 6 hours = 5kW of solar energy. But not all days are sunny; we have system losses, and cloudy days lower energy production. 7000 watts of solar panels will provide enough energy to power our home for more than a full day.

Related: 4 Ways to Keep the Power On

The right size solar generator to run a house includes the solar array and battery storage, plus a charger/ inverter. On-grid homes require an automatic transfer switch or relay to disconnect the grid during power outage.

Solar Array:

• 6-7kW for reliable energy production on cloudy days.
• 7-8kW for strong performance, shorter winter days, and future energy growth.

Battery Storage:

• 25-35 kWh storage: 1 day of storage + a small buffer.
• 30-40kWh storage: 1-1.5 days of autonomous power. Good reliability, especially off grid.
• 60-60kWh storage: 2 days of autonomous operation off grid including days of heavy clouds.

In the northern tier of the USA, we’re going to have power for our air conditioner in the summer and heat pump in the winter.

42kWh is far more than most energy-efficient homes need for average daily use. A 36kWh system is more practical and provides plenty of power.

Did you know: A CPAP machines uses 30-60 watts per hour, or up to 480 watt-hours per night. Your solar generator keeps your machine going for restful sleep during blackouts, outages, camping, or remote nights away from home.

What Size Solar Generator Do I Need for Camping

Solar generators are great for camping. Small models are easy to transport and with a portable solar panel, can provide lights and a few other amenities. Image by truthseeker08.

It depends entirely on what you want to power with your solar generator. Most people like a few small lights, perhaps a light string to hang around the fire ring or picnic table. A fan is good in the summer when it’s hot.

For the most common uses like charging electronics, LED lights or light strings, and small fans for inside the tent, you don’t need a lot of power.

Any solar generator that offers at least 500 watt-hours of storage will keep your fan running all night and any lights as needed. When the sun comes up, hook up the portable, foldable solar panel to recharge. It’s a simple, practical, and easy to pack solution that won’t take up a lot of space. Even better, you won’t need a campsite with a shore power outlet to make it happen.

What Size Solar Generator Do I Need for My RV

One factor that limits RV solar generator size is available space for the solar panels. If you’re planning on a rooftop solar array, the items already on your roof (air conditioners, etc) will limit how much of the space is available for solar. Maximizing your solar capability might mean a mix of 100-watt, 200-watt, and 400-watt panels. For a typical van or Class C motor home, truck camper or trailer, installations could range from 800 watts to 2000 watts. Larger RVs may have room for more space.

Depending on the setup, adding portable solar panels to supplement the rooftop panels might be possible at some locations if the solar generator has more than one solar input.

Solar generators usually charge from almost anything that can provide power. Small generators, shore power outlets, automotive outlets, EV charging stations, and more. Some allow combination charging for faster charge times.

Air conditioners use the most power and will quickly drain all but the most powerful systems, and those take up a lot of space. Air conditioner use usually requires generator backup and charging.

Larger RVs have more roof space, but may rely on supplemental portable panels and generator backup.

Choose the Right Solar Generator

Whether you’re planning to power your off-grid home with solar, preparing for weekend of camping or extended RV travel, or backing up your home power needs, it’s not hard to determine what you need.

Figure out your energy use and peak loads, how long you plan to rely on the solar generator for power, and plug the numbers into the calculator. Err on the high side and it’s hard to go wrong. Try to get by with as little as possible and you might end up with less than you need.