How to Know What Size Solar Generator You Need

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Off grid solar systems and solar powered RVs often have generators installed. A generator can be used to run power hungry appliances, serve as backup/charging for solar panels or an emergency power in case the solar system won’t run. This is a guide on how to find the right solar generator size for your needs.

A solar generator should be double the size of the inverter running watt capacity. If you have a 3000 watt inverter you should get a 6000 watt solar generator, so there is enough power to run appliances and charge the battery at the same time.

Solar Generator Size Guide for Home/RV Backup Power

Majority of solar generators produce 1000-5000W per hour. The average hourly watt consumption in American homes is 1250W, so these should be enough. This guide will show you how to find out your requirements so you’ll be able to buy the right generator. This information covers residential homes and RVs.

A home backup generator is designed for emergency in case of a long power outage. The system is often used to run only essential appliances. What counts as “essential” varies from person to person. You might include indoor lights, phone, laptop, refrigerator, microwave and a radio. Some may add running the TV for a few hours, an air conditioner or a heater.

Regardless how much the total watts is, you have to follow the double the inverter capacity rule. So if the appliances total 4000 watts, you can get a 5000W unit like the Giandel Heavy Duty Power Inverter and pair it with an 8000W or 10000W generator.

List all the appliances and devices you intend to use during a power outage. The following is a general guide to watts and voltage. Check the power consumption on your device’s label.

DeviceRunning WattsStarting Watts
Lights (5 lights at 6W each)450450
Desktop Computer720720
Window AC12002160
Electric Fan8002000
Coffee Maker15001500

To calculate a device’s average daily watts:

  1. Check the device’s watts per hour on the label or manufacturer website.
  2. Multiply watts per hour by the number of hours you’ll use the device daily.
  3. For starting/peak watt surge, go with the highest number to be safe.
  4. Combine the average daily watts of all the devices you want to use. That’s the minimum power output needed from your generator.

The total is usually a third of what you regularly use at home. For RVs, even fewer devices are used. Many RVers opt for camping utilities as they consume less power than regular appliances. Just like in the table, list all the RV devices you’ll use with the generator and total the watts.

Watts, Voltage and Amperage Explained

  • Watts is the power consumed by a device. 1000 watts is 1 kilowatt.
  • Voltage rating: devices that run on DC (direct current) have a 24 or 12 VDC rating. Devices that run on AC (alternating current) is 110-120V or 220-240V 60Hz in the US. In other parts of the world it is 220-240 50Hz.
  • If wattage isn’t listed on the device label, multiply volts x amperage to find its watt equivalent.
  • Amperage (amp): is used to determine the electric current an appliance needs to initialize (surge) and operate continuously.

Adjusting Power Consumption Calculations

The average daily watt consumption is an effective guide but only for devices that consume a fixed amount like laptops, TVs, radios, mobile devices and light fixtures. For these and similar devices, if its rating is 50 watts per hour, that’s how much it is going to consume.

But this calculation is not applicable to devices with variable power consumption. Blenders, hair dryers, air some AC units and refrigerators. Your microwave may have an 800W rating, but in reality you’ll only be using it for a few minutes a day. So its power consumption will be lower. The same rule applies for blenders, coffee makers, vacuum and other devices.

To compensate for this, use only 20% of a variable power device’s maximum watt usage. To get its average daily watts, multiply wattage consumption x 24 hours x 20%.

How Much Solar Generator Battery Capacity Do I Need?

Battery capacity is measured in amp hours (ah) or watt hours (wh, which is similar to watts). if the capacity is in ah, multiply ah x 110V (or whatever your appliance’s voltage is). To find out what battery capacity you need:

  1. Add the total average daily watts for the devices you’ll use. The result is your total wattage needs,
  2. Jot down how many days you’ll be using the generator.
  3. Multiply your total wattage needs by the number of days you will use the generator.

The result is the power output you need from a solar generator. Note that this total is only for running your device list. You have to increase the generator power (doubling is recommended) so it can charge while running your devices.

Can I Charge a Generator with Solar Panels?

Yes, you can charge a solar generator with solar panels. And you should because it allows you to use the generator continuously. Well, almost.

Home and RV generators are usually set up this way. The generator is fully charged and when the need arises, it is used until power runs out. Without solar panels, you won’t be able to use the generator until it is charged.

But generators offer support for solar panel trickle charging. That is, you can charge the generator as it’s being used. It sounds great, but often the charge isn’t fast enough to cope with device demand. But even if the charge cannot keep up with the demand, you will know how long it takes to recharge the generator.

The time it takes depends on the solar panel power output, efficiency and how good – or bad – the weather is. If your system production surpasses your generator’s trickle charge, you’ve got ample solar panels.

Battery Charging Time for Trickle Charge Solar Generators

Follow these steps to get a general idea of the battery charge time. You should check your generator’s manual and your solar panels’ for information about this.

  1. Add up the total power output (in watts) of all your solar panels.
  2. Check your generator’s trickle charge rate, also in watt hour.
  3. The battery recharge time is the lower number between the solar panel total power output and the generator’s trickle charge rate.
  • If the charge time is under 8 hours, your solar panel can charge the generator as it runs. You have nonstop supply as long as the panel can draw power from the sun.
  • if charge time is more than 8 hours, the solar panel cannot provide enough power to keep the battery charged. The demand outstrips the power being supplied and will run out at some time.

Features to Look For in a Solar Generator

Battery capacity and inverter rating are just two features to consider. There are many more you have to account for.

  • Solar panel connectivity: some solar generators require solar panels to be directly linked to the system. Others allow the panels to be installed at some distance.
  • Strong casing: look for generators with steel casing to protect from damage from pets or children.
  • Scaling: look for generators with link capabilities so you can combine several into system. This is useful if you see yourself using more solar power in the future.
  • Ports: 110120 AC and 12/24 DC are the most important. USB ports also come in handy for charging mobile devices.
  • Display readout: keeps track of available power, current, and notifies you of any problems.
  • Peak power: this figure needs to be greater than your daily power needs.

So far we have been talking about powerful solar generators for home or heavy duty RV use. But what if you just need one for a few days of camping or outdoor adventures?

Solar Generator Size Guide for Outdoors & Camping

in another post we mentioned how the term portable is loosely applied to solar generators. 35 lb. power stations are called portable and in a sense they are. But for outdoor and camping, you only need smaller, handheld power stations.

These solar generators are usually in the 150W-350W range, though more powerful options are available. They don’t have the power to match large power stations, but these are not meant to run appliances in emergency situations.

These power stations are for hunting, camping, hiking, weekend RV trips and the like. They’re small enough to carry and put in a backpack. You can recharge them on a wall outlet or with solar panels. Usually the panels are purchased separately, but you can connect them to the generator easily.

For a few days of camping, a fully charged 240W-350W power station should last. It’s enough for a laptop, mobile phone, mini cooler and other small devices. You’re not going to carry a lot of electronic devices when camping so one will be sufficient.


Buying a solar generator doesn’t have to be complicated. To summarize, a home/RV generator should be double that of the inverter continuous watt capacity. For outdoor camping, a 240W-350W portable power station is enough. With this knowledge you can buy with confidence.