Calculate Solar Panel kWp & KWh (KWh Vs. KWp + Meanings)

Solar power is certainly a great way to save on some electricity bills and move your home toward a greener, more sustainable future. That said, calculating your power needs and designing a solar system to match those needs can be confusing, and there are a handful of important factors to understand.

One of these is the KWp rating or kilowatts peak. This is the rate at which your solar system generates energy at peak performance, such as at midday on a sunny day.

But how do you calculate your solar system’s kWp?

It can be challenging to calculate your solar system’s kWp, as it’s difficult to predict the exact power output of your system due to factors like component efficiency, temperature, location, and weather.

There are some methods, though, and in this article, we’ll be covering the following:

  • The standard for determining kWp
  • Calculating the kWp of your system
  • Determining the kWp you need in your home
  • Examples of typical solar installations

Calculating the correct kWp of your solar system can be confusing, but we’re here to help! Read below for our in-depth guide on calculating your solar needs and output.

Calculator and calculations

What is kWp in a solar panel?

Put simply, kWp is the peak power capability of a solar panel or solar system. The manufacturer gives all solar panels a kWp rating, which indicates the amount of energy a panel can produce at its peak performance, such as in the afternoon of a clear, sunny day.

kWp, or kilowatt peak of your panel, is calculated with a standardized test that all solar panel manufacturers must adhere to, with standardized radiance, temperature, and size. These standards are as follows:

  • Solar radiation of 1,000-watts/m2
  • Ambient temperature of 25-degrees C
  • Clear skies

This standardization makes it possible to accurately compare solar panels and their performance when choosing which to purchase for your needs.

kWh vs. kWp

kWh, or kilowatt-hours, refers to an appliance’s energy in one hour. A kilowatt equals 1,000-watts, so if you use a 1,000-watt appliance for one hour, you’ll be consuming 1 kWh of energy.

If your solar system has a kWp of 1,000-watts, for example, your kWh to kWp ratio is 1:1. Of course, this is at peak performance, so the ratio is, in reality, a fair bit lower.

A 1 kWp system operating at peak performance would supply you with one kilowatt of power, but this depends on many factors like efficiency, temperature, and weather, so these two metrics are certainly important but somewhat unrelated.

See also: Do Solar Panels Produce Volts? (Calculations + Examples)

How do I calculate my solar panel output?

Calculating solar panel output is fairly simple but depends on your panels’ efficiency, location, and the amount of sunlight hitting the panels daily.

For example, people living in equatorial regions will have far more sunlight per day than those closer to the poles.

The first metric to check is your solar panel’s wattage rating. If you’re using a 300-watt panel, your panel will be kicking out 300-watts (maximum kWp) under perfect conditions, but again, likely a bit less on average due to temperature, weather, and placement.

A simple formula for calculating solar panel output is:

  • Average hours of sunlight x solar panel wattage x 75% (for dust, pollution, weather) = daily wattage output.

So, if you’re getting 6 hours of sunlight per day — on average — with a 300-watt panel, you’ll be getting 1,350 watt hours per day.

Solar panels on a tiled roof

See also: What Voltage My Solar Panel Produces (Calculations + Examples)

How many units does 1kw of solar panels produce?

Typically, one “unit” of solar energy equates to 1kWh, which is what a 1kw system is capable of producing in 1 hour under perfect conditions. This means you would again use a very simple formula, system capacity (1kw) x hours of sunlight.

  • Going back to our example above, 6 hours of sunlight multiplied by your system capacity (1kw) would give you roughly 6 units, or 6 kWh of energy per day.

See also: How Much Do Solar Panels Save? (Lifetime Savings)

How many kWh does a house use per day?

On average, the daily kWh consumption for an average home in the United States is just under 29 kWh hours. This accounts for using energy-heavy appliances like geysers and heating, which can be substantially reduced.

This energy usage also depends on the size of your home, the building materials of your home, and the number of residents. Also, people in colder climates naturally use significantly higher power to warm their homes.

See also: How Many kWh Does a Solar Panel Produce?

How do I calculate kWh?

Calculating the kWh usage of your home is simple: you take the total kWh on your electricity bill and divide it by the days the bill covers. Again, this may fluctuate during the year, but it’s a good ballpark figure.

You can calculate the amount of kWh your appliances use based on how long they are on. For example, if you use a 1kWh appliance for 3 hours, that appliance will use 3 kWh per day.

See also: How To Read Solar Panel Meter (Do This)

How do you calculate PV per kWh?

Now that you know how much kWh your home consumes, you’ll naturally need to calculate how many panels you’ll need to generate sufficient power.

Let’s assume your home uses 10 kWh per day. You’ll need at least 10kWh hours of solar panel output to match this, but most likely a lot more.

This is because no solar panel — or solar setup for that matter — is 100% efficient, plus, this kWh rating is under perfect conditions, which are not guaranteed.

  • If you use 10 kWh per day, you’ll need at least 12-15 kWh of solar power output to account for losses.

As an example, a 200-watt solar panel will produce roughly 200-watt hours per hour under perfect conditions, or 1,200-watt-hours (1.2 kWh) per six hours of sunlight.

You’ll need at least ten of these panels to cover your daily energy usage with solar power completely.

See also: Number of Solar Panels You Need (Energy – Sunlight – Consumption – Efficiency – Roof Space)

How many solar panels do I need for 50 kWh per day?

As we’ve already discussed, solar panels are subject to efficiency issues, weather, sun hours, and location, so it’s almost impossible to give an exact answer. However, there are some rough calculations we can do to get a fairly accurate answer.

Let’s assume you’re using 200-watt panels, with around 4-hours of sun per day(just to be safe), you’ll be getting roughly 800-watt hours (0.8 kWh) per day, per panel. This would mean you’ll need around 62, 200-watt panels to generate 50 kWh per day.

See also: Solar Panel Cost Per Sq Foot (1000 to 3000 sq. ft)

How much power does 5kW solar produce?

On average, a 5kW solar system will produce around 20kWh per day, depending on your location and sunlight hours per day. You may find the system producing more in summer months, 25-30kWh, and less in winter, 15-20kWh.

See also: How to reduce solar panel VOC (Important!)

Is 1 kW enough to run a house?

Considering the average household in the United States uses roughly 29kWh per day, and 1kW of solar will give you 4-5kW of power with 5 hours of sunlight, this will not be enough for most homes.

That said, it can help lower your dependence on mains power and save you money on electricity bills.

It also helps to look at your energy requirements and usage and see where you can save on power. For example, using a solar geyser to heat water, a gas fridge, and a stove and heating your home with a fireplace or gas heater will save a ton of power overall.

I have a 1kW solar system in my home that provides me more power than I need since I save on energy usage by using gas appliances and a solar geyser. This is enough to run lights, computers, a TV, and other small appliances.

See also: How Do I Know How Much Electricity My Solar Panels Are Generating? Your Ultimate Guide

How much is a 30 kWh solar system?

For a 30 kWh solar system, the cost depends on several factors:

  • The quality of the components you purchase
  • Your location
  • Installation

You can save quite a bit of money if you install the system yourself, but this is certainly tricky. Installation costs will vary widely depending on who does the installation for you, but for a system this large you can expect to pay around $10,000 for installation.

In general, solar panels cost around two or three dollars per watt. Taking into consideration the quality of components you choose, installation, and your location, you can expect to pay anywhere from $60,000 to $80,000 for a 30 kWh solar setup.

See also: How Many Solar Panels Do I Need for 1000 KWH Per Month? A Comprehensive Guide

How many solar panels do I need for 2000 kWh per month?

2000 kWh per month equates to roughly 66 kWh per day. Again, let’s go with 200-watt panels (as these are some of the most common), with around 4-hours of sun per day(just to be safe), you’ll again be getting roughly 800-watt hours (0.8 kWh) per day, per panel.

In order to produce 66 kWh per day of power, you’d need 82, 200-watt solar panels.

Solar Panel Cost Over Time

See also: How Many Solar Panels for 900 kWh Per Month? Your Detailed Guide to Optimal Solar Energy Usage

How much should I pay for a 6kW solar system?

As mentioned earlier, the average cost per watt for solar setups is $2-$3 in the US. This costs roughly $12,000, but you’ll also need to consider installation, bringing the cost up to roughly $14,000-$15,000.

1 kWp solar panel size

If you wanted to run a solar system with a panel output of 1 kWP, you’d need 1 kilowatt of power. 1 kilowatt would be the peak capability of your panels on a day with full sun, which is 1,000-watts. Solar panels usually come in 200-350 watt units, although some higher power panels are available too.

For 1 kWp, you’d need five 200-watt panels, four 250-watt panels, or three 350-watt panels. Remember, this is your solar array’s peak performance rating, so your panels will only achieve this kind of output for a few hours a day if it is clear and sunny.

How to calculate solar panel efficiency

Most solar panels have an efficiency rating of between 10% and 23%, which the manufacturer usually indicates.

Efficiency also depends on the type of panel you’re using (monocrystalline vs. polycrystalline), where your panel is facing, and much heat it is generating (solar panels should never be laid flat on a roof, as they lose efficiency exponentially when they overheat.)

The efficiency rating of a solar panel refers to its ability to convert sunlight into usable energy.

So, if a panel has an efficiency rating of 15%, it can harness 15% of the photons that hit it. Due to real-world weather conditions and placement, a solar panel rarely produces its full wattage output rating.

To calculate the efficiency of your panel, you’ll need to look up the amount of sunlight that hits the earth in your particular area. Multiply this amount by the surface area of your panel, divide the maximum kWp of your panel by this number, and then multiply it by 100% to get an accurate efficiency rating.

Let’s say 1,000-watts per square meter of sunlight is hitting your area, and if you have a 1 square meter panel, you’ll end up with 1,000-watts exactly. If you have a 200 kWp panel, the efficiency will be roughly 20% (negating any other environmental factors, of course.)


The first step in designing a solar setup for your home is to calculate how many kWh or kWp you’ll need. Check your electricity bill for your monthly use, and divide that number by 30 to calculate your daily needs.

Of course, you can always reduce your electricity usage or use solar power to augment your mains power and reduce your electricity bills.

Once you’ve calculated your power requirements, you can design a solar system that can provide you with all or even just a portion of your power needs.

Hopefully, we’ve helped you with all the calculations you need so you can get started going off-grid, today!

Photo of author
Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

SolVoltaics is an affiliate and an Amazon Associate, we earn from qualifying purchases - at no extra cost to you.