Solar Panel kWh Calculator: kWh Production Per Day, Month, Year

How much energy can solar panels generate? Everybody who’s looking to buy solar panels should know how to calculate solar panel output. Not because it’s fairly simple – and we’ll show you how to do it yourself with the help of our simple calculator – but because you need to know how to calculate solar panels output to estimate how many kWh per day can a solar panel produce.

To calculate solar panel output per day (in kWh), we need to check only 3 factors:

  1. Solar panel’s maximum power rating. That’s the wattage; we have 100W, 200W, 300W solar panels, and so on.
  2. How much solar energy do you get in your area? That is determined by average peak solar hours. South California and Spain, for example, get 6 peak solar hours worth of solar energy. The UK and North USA get about 3-4 hours. Below we include solar maps so you can determine how many peak solar hours you get in your area.
  3. Solar system losses. All the electric connections in a solar panel system incur a loss. We differentiate between inverter losses, DC cables losses, AC cable losses, temperature losses, and so on. The most efficient systems have a 20%. In our solar panel output calculations, we’ll use 25% system loss; this is a more realistic number for an average solar panel system.

Here is the formula of how we compute solar panel output:

Solar Output  = Wattage × Peak Sun Hours × 0.75

Based on this solar panel output equation, we will explain how you can calculate how many kWh per day your solar panel will generate. We will also calculate how many kWh per year do solar panels generate and how much does that save you on electricity.

Example: 300W solar panels in San Francisco, California, get an average of 5.4 peak sun hours per day. That means it will produce 0.3kW × 5.4h/day × 0.75 = 1.215 kWh per day. That’s about 444 kWh per year. With California’s electricity costs being around $0.21 per kWh, you’re saving about $93,24/year on electricity costs.

To help you make these calculations for your area and panels, we have designed a Solar Output calculator. You just input the wattage, peak solar hours, and you get what is the estimated output of your solar panel like this:

how-to-calculate-solar-panel-output-with-solar calculator
Example of how Solar Output Calculator works: 300W solar panel with 5 peak sun hours will generate 1.13 kWh per day. You can find and use this dynamic calculator further on.

On top of that, you will find a solved example – for 100W solar panel output – to illustrate how the Solar Output Calculator works. We have also calculated outputs of 5oW to 15,000W (15 kW) solar panels and gathered them in a neat table found at the end of the article.

Before we check out the calculator, solved examples, and the table, let’s have a look at all 3 key factors that help us to accurately estimate the solar panel output:

1. Power Rating (Wattage Of Solar Panels; 100W, 300W, etc)

The first factor in calculating solar panel output is the power rating. There are mainly 3 different classes of solar panels:

  1. Small solar panels: 5oW and 100W panels.
  2. Standard solar panels: 200W, 250W, 300W, 350W, 500W panels. There are a lot of in-between power ratings like 265W, for example.
  3. Big solar panel system: 1kW, 4kW, 5kW, 10kW system. These include several solar panels connected together in a system (2 – 50 solar panels).

Now, we need to understand what these ‘maximum power ratings’ actually mean. These are the solar panel outputs at ideal conditions. These ideal solar conditions are known as STC or Standard Test Conditions. These wattages are measured at 1,000W/m2, 25°C (77°F), and air density of 1.5 kg/m3.

All the energy efficiency of solar panels (15% to 25%), type of solar panels (monocrystalline, polycrystalline), tilt angles, and so on are already factored into the wattage.

Example: In theory and in ideal conditions, 300W produces 300W of electrical output or 0.3 kWh of electrical energy per hour. In practice, however, 300W solar panel produces, on average (24-hour cycle), 46.9W output and 0.0469 kWh per hour.

Why don’t 300W panels produce 300W all the time?

Here because of the other two factors, we need to account for when calculating solar panel output:

2. Number Of Peak Sun Hours (4-6 Hours)

If the sun would be shinning at STC test conditions 24 hours per day, 300W panels would produce 300W output all the time (minus the system 25% losses).

However, we all know that the sun doesn’t shine during the night (0% solar rated output), it’s a bit shy in the mornings and evenings (about 20% solar rated output) but it does shine brightly during the day (up to 150% solar rated output).

Now, calculating exactly how much solar energy hits our solar panels is a mindboggling task. That’s why we use a factor called ‘Peak Sun Hours’. Here is a definition by PVEducation, ‘Peak sun hours refers to the solar insolation which a particular location would receive if the sun were shining at its maximum value for a certain number of hours’.

In other words, peak sun hours are ‘the average daily solar insolation in units of kWh/m2 per day’. Basically, it refers to how much energy from the sun we get.

Obviously, California will get more sunlight than New York or the UK. The number of average peak sun hours depends on two main factors:

  • Location. Closer to the equator you are, the more pean sun hours you’ll get.
  • Season. You get more sunlight in the summer than in the winter.peak sun hours month by month in los angeles california

We use maps with yearly average peak sun hours to adequately estimate how much sunlight will our solar panels get. As you correctly figured out, the amount of sunlight (ie. number of peak sun hours) will affect solar panel output quite a bit.

Here is a solar map of the USA that shows how many peak sun hours you’re expected to get state-by-state:

us peak sun hours average state by state
Average yearly peak sun hours for the USA. Source: National Renewable Energy Laboratory (NREL), US Department of Energy.

Example: South California gets about 6 peak sun hours per day and New York gets only about 4 peak sun hours per day. That means that solar panels in California will have a 50% higher yearly output than solar panels in New York.

We made a quick calculation for small 100W panels with the Solar Output Calculator.

A single small 1ooW solar panel in California will generate an estimated electrical output of 164,25 kWh per year. On the East coast, the same solar panel on the roof in New York will generate an estimated electrical output of 109,50 kWh per year. That’s quite a difference.

Before you use the Solar Output Calculator below, you have to try to nail down the peak sun hours in your area as precisely as possible.

3. Solar Panel System Losses (20% – 30%)

Every electric system experiences losses. Solar panels are no exception.

Being able to capture 100% of generated solar panel output would be perfect. However, realistically, every solar panel system will incur 20% losses if you’re lucky (have a superbly efficient system). Some older and more complex systems can have up to 30% losses.

In 2021, it’s generally considered that an average solar panel system has about 25% losses.

These losses occur when the electricity generated by the solar panels is passed through batteries, inverter, DC and AC cables. Here is the most simple diagram that illustrates which ‘barriers’ electricity generated by solar panels has to pass to become available for end consumer:

solar panels losses for calculating how much electricity do solar panels generate
This process incurs on average about 25% of output losses. Example: If the theoretical output is 100W, the practical output will be closer to 75W.

These losses need to be accounted for when calculating the realistic solar panel output. The 0.75 factor in the solar output equation accounts for the losses.

Solar Output(kWh/Day) = PowerRating \times PeakSunHours \times 0.75

Broadly speaking, here is how much losses are incurred when electricity passes through the following electric circuit elements:

  • Inverter losses. Anywhere between 5% and 10%. Inverter is the main source of electric output loss.
  • DC cable losses. Anywhere between 1% and 3%.
  • AC cable losses. Anywhere between 1% and 3%.
  • Temperature losses. At 25°C (77°F) solar panel temperatures are minimal. When the temperature rises in the summer, heated solar panels can lose up to 20% of electric output.
  • Environmental losses. Shadings, snow, dust, weak radiation, and so on can all contribute to the decreased realistic output of solar panels.

With all these 3 factors accounted for, we can proceed to the main calculator:

Solar Output Calculator

Here you can simply input what size solar panel you have (100W, 200W, 300W, and so on) and how many peak sun hours you get (average is about 5 hours). You get an estimate of how many kWh per day such a solar panel will generate:

Here is how this solar output works:

Let’s say you have a 300-watt solar panel and live in an area with 5.50 peak sun hours per day. How many kWh does this solar panel produce in a day, a month, and a year? Just slide the 1st slider to ‘300’, and the 2nd slider to ‘5.50’, and we get the result:

In a 5.50 peak sun hour area, a 300-watt solar panel will produce 1.24 kWh per day, 37.13 kWh per month, and 451.69 kWh per year.

Example: What Is The Output Of a 100-Watt Solar Panel?

Let’s look at a small 100-watt solar panel. How do we calculate the electrical output of such a solar panel?

Well, we know that it has a rated power of 100W. Let’s also presume that we live in a very sunny area that gets 6 peak sun hours worth of sunlight per day (annual average).

Here’s how we can use the solar output equation to manually calculate the output:

Solar Output(kWh/Day) = 100W × 6h × 0.75 = 0.45 kWh/Day

In short, a 100-watt solar panel can output 0.45 kWh per day if we install it in a very sunny area. Let’s confirm that with the Solar Output Calculator:

output-of-100-watt-solar-panel-per-day confirmation

We see that we can confirm the same result with the calculator.

Solar Output Table For 50W To 15 kW Solar Panels / System

Here we presume that our solar panels get 5 peak sun hours per day (annual average). We have calculated the solar panel outputs and summarized them in this table:

Solar Power Rating (In Watts) Solar Output (in kWh/day)
50 Watts 0.19 kWh/Day
75 Watts 0.28 kWh/Day
100 Watts 0.38 kWh/Day
125 Watts 0.47 kWh/Day
150 Watts 0.56 kWh/Day
175 Watts 0.66 kWh/Day
200 Watts 0.75 kWh/Day
250 Watts 0.94 kWh/Day
300 Watts 1.13 kWh/Day
350 Watts 1.31 kWh/Day
400 Watts 1.50 kWh/Day
450 Watts 1.69 kWh/Day
500 Watts 1.88 kWh/Day
1 kW (1,000 Watts) 3.75 kWh/Day
2 kW 7.50 kWh/Day
3 kW 11.25 kWh/Day
4 kW 15.00 kWh/Day
5 kW 18.75 kWh/Day
6 kW 22.50 kWh/Day
7 kW 26.25 kWh/Day
8 kW 30.00 kWh/Day
9 kW 33.75 kWh/Day
10 kW 37.50 kWh/Day
11 kW 41.25 kWh/Day
12 kW 45.00 kWh/Day
13 kW 48.75 kWh/Day
14 kW 52.50 kWh/Day
15 kW 56.25 kWh/Day

You can see an interesting result here. To produce more than 1 kWh per day, you would require a 300W solar panel. To produce more than 10 kWh per day, you would need at least a 3 kW solar system.

Hopefully, the topic of how to calculate solar output is clearer now. If you have any questions, you can pose them in the comments below. We’ll try to help you would as best we can.

24 thoughts on “Solar Panel kWh Calculator: kWh Production Per Day, Month, Year”

  1. I have today in St.Petersburg FL March 20th 2023 recorded 23.5kWh from 3900W solar array, power from 20 – 190W panels placed in two rows with solar tracking E-W and fixed to 33 degrees N-S. I believe the number will increase as the days gets longer, but we will see.

    • Hi there, the acute power output is rather difficult to calculate; it depends primarily on solar irradiance. For example, if solar irradiance is 1,000 W/m2, a 5kW system will produce about 5kW (since 5kW was measured at STC test conditions and they use 1,000 W/m2 irradiance). You get that 1,000 W/m2 on a sunny day during 11 AM and 1 PM.

      The best way to understand the power output of a solar system (wattage) is to install a measuring device. You will see how the wattage increases from 8 AM to 12 AM due to increase in solar irradiation. Hope this helps a bit.

  2. Thanks I live in city so I have 4 – 100W Rich Solar Panels but there in side the window glass is what I see is making me loose 50 % of what I could be making , usually on my meter for 2 panels in series behind glass I’m making .4-.8 of a W & I have another set the same way inside I’m in Boston

      • I want to help my son with a science experiment and actually measure how much power a mini solar panel produces in a day. What equipment do I need and how do I take actual measurements instead of estimating with calculations? Thank you

        • Hi Dusty, cool experiment with your son. The first idea would be to just get a 100W solar panel kit and a multimeter. Example: You can get a Renogy 100W 12V with 30A charge controller and a simple AstroAI multimeter. You can measure a bunch of stuff with that, it’s a good learning experience. Hope this helps.

  3. I have 44(230 watt) panels and live in SW Arizona. When it comes to our whole system, do I actually figure out our total as
    .23k x 6 x .75 = 1.035 x 44 = 45.54 kwh per day?

  4. i have been approved for 42 @ 440 Wt solar pannels for my roof
    now i have change to ground mounted solar tracking system
    I live in gloucester county NJ
    how many KW will i produce in a year

    • Hi Karl, if we check the average yearly peak hours per day in New Jersey here, we see that NJ gets about 4.21 hours per day. Now, the 42 440W panels have a total 18,480W capacity.
      Here is the kWh/day calculation, accounting for 25% losses in the system: 18,480W * 4.21h * 0.75 = 58,350 Wh/day or 58.35 kWh/day.
      To get a yearly production, let’s just multiply that number by 365 days.
      We get 21,298 kWh/year. So that’s over 20 thousand kWh every year.

  5. Thank you, I am currently doing a course on solar energy and the lecturer always has the most confusing ways of explaining everything. Please can you teach it instead!

  6. We have a 24’X20’ garage with metal roof in central Florida, what do I need to purchase to get max output from panels installed on that roof, I can also duplicate that by adding solar to our small house. What will I expect to pay for maximum efficiency on a dollar for dollar return?
    Thank you

    • Hi there, well, you get the max output if you cover max square footage with solar panels (max efficiency ones, obviously). Let’s take this 24×20 garage: theoretically, this is 480 sq ft of solar panels. You will need a bit of roof clearance (solar panels can’t go all the way to the end of the roof), so you could count of about 75% (general figure) of this roof; that would be 360 sq ft available for solar panels.

      Now, what size solar system can you install on 360 sq ft of available roof area? We did a bit of math on solar panel output per sq ft here; on average, you can install 17.25 W of solar panels per sq ft.

      That means the 360 sq ft of solar panels can constitute a 6,210 W system. Let’s round this up to a 6 kW solar system.

      Checking the peak sun hours for Florida here, you can see that annual average peak sun hours in Florida come to 6.16 h/day.

      That means that a 6 kW solar system in Florida can generate (on average) 27.72 kWh per day, 831.60 kWh per month, and 9,979.20 kWh per year.

      All in all, the garage roof has a potential to generate about 10,000 kWh per year. Hope this gives us a bit of insight in what you can do. To get the prices, you can contact local installers to see how the numbers look like.

  7. My 2 x 200 watt solar panels are producing less than half the yield expected using your calculations as well as others I have found. The panels were installed by my RV dealer, then I switched their pwm controller to a Victron SmartSolar 30 amp MPPT connecting to a single Renogy 400 amp lithium. In NW Arkansas parked in an unshaded spot during 5 sunny days during the end of February I recorded daily yields of 690, 470, 560, 610, & 850 Wh.
    Could the panels be wired incorrectly? There is only 2 PV wires (+ & -) coming into the battery compartment from the roof.
    Thanks in advance!

    • Hi Gary, alright, let’s do some math: You have 400 watt combined solar panels. If we apply 25% losses in the system, you should be expecting to get 300 Wh per peak sun hour. According to this state-by-state peak sun hour averages, Arkansas gets an average of about 3.88 peak sun hours per day in the winter. So, the expected daily electricity producting for you 2 x 200 watt solar panels is 1164 Wh/day (a good 1 kWh per day).

      You have correctly figured out you are getting only half of that, even on sunny Arkansas days. Something seems to be wrong with the system, yes; wiring, battery, charge controllers? The 30 amp MPPT is the correct choice, 400 Ah battery on 12V (this is the Renogy battery) has a 4800 Wh capacity.

      One way to explain the less-than-expected electricity production is a full battery. Another would be some wiring issue. It’s really hard to tell without seeing the wiring but it might a good idea to get a hands-on electrician or solar panel installer to recheck the wiring and see what’s amiss. Hope this helps.

    • Hi Wendy, let’s do some estimations: 1 liter of diesel in a generator will generate about 0.3 kWh of electricity. So, with 130,000 liters of diesel, we are talking 39,000 kWh of electricity.

      Now, let’s say you have a single 300W panels, live in area with 5 peak sun hours (12-month average). This panel should produce about 1.125 kWh/day (accounting for 25% lossess); that’s 410 kWh/year from a single 300W panel.If you have to match solar generation with 300W panels with 130,000 l of diesel annually, you have to install 95 or so 300W solar panels. Hope this helps.

  8. Since Solar is an intermittent power generation, functioning on the average 17% -22%, this renewable electricity has to be backed by base load, mostly “dirty”
    energy that has to be available 24/7 to balance the solar power generation, in order not to damage transformers, how do we actually come up with the real cost per kWh for the solar generation?
    The transmission of electricity has to be balanced even during the peak hours,
    so even during the production of solar generation, we have to run the “dirty” generation as well. Am I right?

    • Hi Paul, this is a good point. We can calculate the cost to generate solar power quite easily. Calculating the overall electricity costs from various sources (including “dirty” energy) is somewhat complex, depends on a lots of factors. In many cases, we have to run “dirty” generation even during peak sun hours, yes.


Leave a Comment