How To Calculate How Much Power You Need From a Solar Generator?

How To Calculate How Much Power You Need From a Solar Generator

Solar-powered generators enable us to live an eco-friendly life without adjusting or limiting our power needs. 

A solar generator provides clean energy with its quiet operation without any hazardous gases/fumes. 

You don’t need to place your solar generator several feet away from the house to prevent noise & air pollution, unlike fuel-powered generators. 

The portable and USB charging provision of solar generators allows you to take it camping, hiking or boating as well. 

An all-in-one solar generator includes the batteries, inverter, charge controller, etc., covered in a rugged water-resistant cover along with the lightweight solar photovoltaic (PV) cells.   

 A solar generator has plenty of room to charge your cell phones, cameras, drones, and other gear when you’re out on a picnic.  

If you want to power heavy AC devices, coffee makers, etc. daily you may want to know precisely how to calculate how much power you need from a solar generator.

What size solar generator do I need for my requirement?

The advancements in the solar generator industry have been phenomenal in the last few years. Solar generators have been dominating the renewable energy industry due to their mobility and adaptability.

The improvements in capacity and expandability made the usage of solar generators much more convenient. 

Solar generators are a great option for charging portable devices like smartphones or if you want to run a big item such as the coffee maker from time to time. 

  • You may as well power up a water pump, hairdryer, tv, light, fan, etc.
  • You can run kitchen items such as the microwave, and fridge. 
  • And essential devices such as the fridge. 

However, you may still need to properly size your solar generator unit for a balanced system of design. 

Only a few solar generator units can power several appliances simultaneously. 

After buying a solar generator, you will be disappointed only to find out that the unit can’t operate an air-conditioner or any other appliance of your choice. 

If you want to power the boiler, electric furnaces, etc. during an emergency, a portable solar generator may not suffice it as they consume a lot of energy. 

The solar backup generators comprise several batteries to charge up the above-mentioned devices comfortably.  

Since the solar generators can only run electronic devices for a specific no. of hours/day, you must know what you want to power with your solar backup generator. 

What appliances can run on solar power generator?

Let’s say, the power rating of a refrigerator is 1000 kwh/year. 

The running watts/hour gives a proper idea of whether a solar generator can operate it or not. 

Running watts/hour

= 1000 x 1000 Watt-hour/year

= 1000000 / (365 x 24) Watt-hour/day

= 114 Watt-hour/day

You can thus precisely calculate how much power you need from a solar generator.

How do I calculate how much solar power I need from a solar generator?

So here goes a simple guide to calculating your solar power needs.

A simple guide on how to calculate how much power you need from a solar generator:

The very first step in calculating the power you need from a solar generator is to know how much energy (watts/day) you want to use regularly. 

Calculate the power requirements/day (in watts) by totalling the multiplication of running watts and running hours for all your appliances. 

Energy demand chart: 

AppliancesRunning WattsRunning hours/dayRunning watts x Running hours/day
1. Refrigerator100 (Surge watts660)242,400
2. Rice cooker200 (Surge watts 500)0.1 (10 minutes)20
3. Light bulb7510750
Total = 3,170 Watt-hours / day
  • Power consumption of electronic appliances such as freezers, coffee makers, etc., varies with how and when they are operated. 

Surge wattage is a device’s peak power for a few seconds to start the motor. 

The power rating of a refrigerator maybe 660 watts/hour for example. 

But it is the highest power consumption (when the door is open). 


  • the highest power consumption occurs for 6 minutes (6 / 60 = 0.10 hours) in an hour and 
  • the rest of the hour (54 minutes i.e., 54/60=0.9 hours), it consumes maybe 100 watts only. 

So, the running watts for a refrigerator in an hour

= 660 x 0.1 + 100 x 0.9 Watts 

=156 Watts, which is 25% of the rated power (660)

So, take 20-25 % of the rated power (the highest power that it consumes) for the required energy demand/hour for such an electronic appliance.

How to calculate number of solar panels required? 

You must follow a few steps to precisely calculate how much solar power you require from a solar generator. 

It necessitates you to consider a few variables as well. For instance

  • The efficiency of your solar panel 
  • Positioning of the solar panel generator
  • Recharging time 

Watt-hours / day of a solar generator unit depends on the efficacy of the solar cell and the hours of sunlight it gets. 

Let’s say,

  • A solar generator unit comprises four 300-watt solar panels.

But a 300-watt solar generator can generate 300 watts only during the standard testing conditions unless the ideal conditions are met.   

  • The sunlight hour (average) of a particular geographical location be 6 hours

But peak sunlight hours can be much less than the average sunlight hours (around 3-4 hours). Only during this hour, 1000 watts of sunlight per square meter hits the solar cells.

  • And the solar generator battery will go out of capacity if the recharging time of the battery is longer than the average sunlight hours. 

If any device is being used while recharging or the solar generator unit has a PWM charge controller, then it’ll take few more hours to fully recharge the battery. 

An MPPT (maximum power point tracking) charge controller recharges the solar generator unit more efficiently than the PWM (pulse width modulation) charge controllers.  

Considering the above variables, the output (watt-hours / day) of a solar generator unit maybe 60-70% of the theoretical value. 

Solar generator output 

= wattage of solar cells x Sunlight hour (average) x 60%

= 4 x 300 x 6 x 60 /100

= 4,320 watt-hours / day

= 4.320 kwh / day

How to calculate solar panel battery and inverter requirements for my solar generator?

  • During the winter or rainy season, you may get insufficient solar energy. 

If you want a solar generator as a backup in your home, you need to figure out how much should be the capacity of the solar generator battery. 

Accounting for the inconsistency of solar energy, you may want to store 2x the energy demand in your rechargeable batteries.

Total Watt-hours / day from the energy demand chart = 3,170

3,170 (Watt-hours / day) x 2 = 6,340 Watt-hours 

So, you need to store 6,340 watt-hours (6.34 kwh) 

  • to supply electricity on demand or 
  • for emergency preparedness. 

Solar generator batteries are rated at ampere-hours (AH), and most run at 12 Volts. 

Then, the watt-hours for four 125 AH batteries will be

= 4 x 125 AH x 12 V 

= 6000 WH

= 6 kwh

Then again, you should not overcharge the battery as it deteriorates the quality of a solar generator battery. 

Find a solar generator unit that enables the interruption with its regulator (charge controller) when the battery is overcharged.

  • In an emergency scenario during a power outage, it is not feasible often to keep powering devices such as the freezer or fridge.

To run the appliances, a solar generator inverter converts the Direct Current (DC) from the battery to Alternative Current (AC). 

The inverter rating indicates the highest wattage it can withdraw i.e., it suggests whether the solar generator unit can run an electronic appliance or not.


If it necessitates you to live off-grid suddenly due to an overwhelming power outage, it’ll cause a huge setback in the powered-up lives.  

Since the fuel-powered generators emit fumes and cause huge sound pollution, they are unsuitable for indoor uses. The solar generators on the contrary, effectively and silently power up phones, laptops, and other essential devices causing no concern of refueling.  

You don’t have to worry about the recharging options as well. There are many solar generator units that you can charge with a conventional wall outlet (home AC) or car adapter (12 volts) along with the traditional solar cells. 

You have to be a bit cautious only for calculating the power need for your solar generator so you can stay powered up and be protected in crucial moments. In this article, we’ve tried to explain exactly how to calculate how much power you need from a solar generator. The list of things to do to get to the formula is as follows. 

Summary: Solar power calculation formula

  • Go through the power ratings and convert to running watts/hour 
  • Estimate the wattage of the electronic appliances/day
  • Take into account the recharging time, weather conditions, and other variables

To figure out the watt-hours of solar power generator to meet your needs, multiply the running watts/hour of your electronic appliances by the running hours/day and add them up. 


Solar generator output 

= wattage of solar cells x Sunlight hour (average) x (60-80) %


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