I’ve had a lot of people asking me the following questions:

- How big of a generator do I need?
- How many watts does my generator need to be?
- How many solar panels do I need?
- How many watts does the wind turbine need to put out to power my home?

So I made this calculator for all of you people going green and wanting to generate your own green power. You can use this calculator to calculate how many watts you need to generate to power your home. Keep in mind that this will calculate the amount of watts you need to generate for a grid tie system or an off grid system with a battery bank. If you are not using either one of these systems then you will just need a generator that can generate the same amount of watts or greater watts than your peak wattage pull at any given instance.

Please note that if your electric company supports grid tie systems and you create less power than you use, you will be charged for only the electric you used of the electric company’s. If you generate more electricity than you use the extra electricity goes to the electric company and they pay you for your unused power.

### Watts Generator Calculator Usage

To use this calculator you will need to know 3 things for the formula to work, your yearly kWh usage, the inverter’s efficiency rating, and the amount of hours per day you will be generating electricity.

**Yearly kWh Usage**: You can find your yearly kWh usage by looking at your electric bill. Your electric bill will either have last 12 months kWh usage listed or each month’s kWh usage listed individually. If your electric bill lists yearly kWh usage enter that number. If your electric bill lists the last 12 months individually, add all 12 month’s kWh usage together and enter the number. If neither is listed you can call your electric company and ask the power company for your kWh usage.

**Inverter’s Efficiency Rating**: This will be listed in the inverter’s specifications sheet. You can even look this information up online on the manufacturer’s website or even on other websites that sell the inverter. I think the average inverter efficiency is around 96%. Remember do not enter the % symbol in the box below, just the number itself.

**Hours Generating Electricity**: This will be the average number of hours per day your generator, wind turbine, or solar panels will be generating electricity each day. If you are using a wind generator I’m sure you can look up the average wind speeds for different hours of the day for your geographical area on the internet. For those of you using solar panels to generate your electricity you will want to enter the number of hours each day you have direct sunlight. You can look up solar insolation map on the internet and find a map of your area. Remember to look up the solar insolation maps for each month and take an average. Add all the months together then divide the sum by 12 to get the average hours of sunlight for the year.

Please enter only numbers in the boxes below, do not enter any symbols. Thanks.

I hope this wattage calculator has helped you figure out what size generator, wind turbine, or solar panels you need to get for your green electricity! If you’re not sure which alternative electricity system you want to use, you can check out Solar Power vs. Wind Power Pros and Cons.

November 12th, 2012 at 8:56 PM

I want to build a 2500 watts battery bank. And charge with a 12V permanent magnet alternator and inverter how do I calculate the alternator battery bank and inverte. Thanks

January 22nd, 2013 at 9:38 PM

Fernando

It depends on how much power you plan on using. What are you going to power with this? How long?

June 28th, 2015 at 2:17 PM

On your calculator, if i am doing wind generator and my average wind speed is 6 mph is that what i put or is there more math needed to figure how many hours per day the turbine will be generating electricity. you explain the solar panels well but left out an example about wind turbines.

August 29th, 2015 at 11:30 AM

I use 6 kWh per day during spring, summer and fall months (SW Ontario), but 50 kWh per day during December, January and February.

Would I have to have a solar system that produced 50 kWh or would power stored in batteries during the summer last long enough to get me thru the winter?

August 31st, 2015 at 10:15 PM

Grace,

I would imagine you’d need a little of both, little more storage batteries, and more solar panels. That’s a large jump, but you could average it out and see how much storage and panels you’d need. Depends on what’s more cost effective. This is not actual numbers, but you could spend $1,000 more on batteries to store enough to get you through the winter, or spend $600 on a few more panels. All just depends on your budget. Do you have space for more batteries, or more space for more solar panels. Most likely you will want more panels to generate more electricity.

January 16th, 2018 at 9:42 AM

I purchased a 8 kw system from Enphase..my daily av. usage is 70 kwh. My average production is less than 40 kwh.. Have I been had? 28 panels 180 degrees 45 degree angle. Location SE VA. Production last month 650 kwh. Was told it would meet my needs based on my utility companies invoices. please respond with my thanks.

February 22nd, 2018 at 11:15 PM

Wendell Raby,

You should have been able to plug in your numbers into this calculator at the bottom of the page and it tell you, but I noticed there was an update with php, which broke my code, so I fixed it. You can try different numbers if you like. If you use 70kwh a day on average that’s. 70 kWh x 365.25 days = 25,567.5 kWh/yr consumed. So we plug that into the above calculator, I’ll use 25600 just to round up. I’m not sure what the efficiency of your inverter is, so I’ll use 96. I’m also not sure how many hours of good sunlight you have for your panels, but I’ll use 8 hours a day. Which gives us 9126 watts generator, or rounding up and converting to kW, you need to generate around 9.2kW not 8kW and you may even need sightly more if you have a less efficient power inverter, or less hours of good sunlight for your panels. If you look in the comments here somewhere, I gave a person a link to a website that had each areas solar data on a map/chart. So you can find out if you’re only getting 5 hours of full good sunlight, and then maybe 3 hours of 40% good sunlight, which means you won’t generate the full output of the panels during those hours. I hope this helps.