Solar energy is one of the most booming technologies and results shows that the number will increase in the coming years. For today’s word it’s a game changer in terms of cost reduction. Studies shows that around 11.22 million people switched from electric to solar bulbs in the year of 2018. Now the question is how many solar panels we should install on our roof. Why kilowatts are used to describe the power off your solar system? To get around the answer one must perceive the idea of how many kilowatts does a solar panel produce?

First of all we need to understand the IS units like watt (W), kilowatt (KW), megawatt (MW), gigawatt and terawatt to understand a basic solar energy source which comes in term of kilowatt.

## What is watt and watt-hour?

Watt is the rate of power used by an electrical device with in a moment of time. For example if you turn on a 20 watt bulb you are consuming 2000 watt energy over that moment in time. The flow of energy will increase with the rise in the number of watts flowing through that product. Hence the energy flows through a simple light bulb will be 50 watt but an energy flow through 100 w bulb will be twice.

Now if you keep on consuming that amount of energy for an hour it is said that the energy is used for “watt-hour “. The term (Wh) means the rate of consumption of energy in a specific span of time. It actually defines the speed of energy used with respect to a length of time.

Let’s say when a 1500 watt dishwasher turned on for an hour the consumption of energy with respect to an hour will be watt-hour. The total watt hour consumption will be 90000 (Wh) of a 1500 watt electric dishwasher.

Watt = joule p/s

Watt-hour = watts* hours

## What is kilowatt and how much is kilowatt

1 kilowatt contains one thousand watt power. Kilowatt hour is thousand times greater than watt. Watt is the unit of power used per second whereas kilowatt is the measurement of rate of power used per second. The watt is equal to 1 joule per second whereas the kilowatt is equal to thousand joule per second. Kilowatt measures the speed of energy per second.

1 kilowatt = 1000 watt

1 kilowatt = 1000 joule p/s

There are thousand watts in a kilowatt. Kilowatt is used for the appliances consuming greater energy. It is mainly use to avoid greater numbers. As you must have heard very few products fall in term of watts.

Let’s take an example of 10 solar panels with the energy flow of 1500 watt each will have energy flow of 15000 watt (10*1500W=15000W). To avoid the zero it’s simple to say 15kW (15000W/1000)

### What is kilowatt hour and the difference between kilowatt (KW) and kilowatt hour (KWh)?

Kilowatt and kilowatt hour are interrelated. Kilowatt measures the power while kilowatt hour is used to measure energy. Kilowatt hour (KWh) measures 1000 watt electricity consumed per hour. In simple words one kilowatt consumption per second for continuous one hour is stated as KWh. Electricity bills shows electricity consumed in the form of KWh. All the appliances contains greater energy are measured in kilowatt hour. Household and commercial consumption of energy usually measured in kilowatt.

For instance if a 50 watt bulb turned on for 20 hours it uses 1 kilowatt hour

Here

KWh = watt *hours/1000

KWh= 50*20/1000

KWh = 1

## A table shows the difference between the KW and KWh

Sources | KW | KWh |

measurement | It measures the rate of power consumed per second | It measures the energy consumed per hour |

time | Per second | Per hour |

formula | 1000 watt | Watt into hrs./1000 |

Used for | Small electric devices | energy sources like electricity meters, residential solar panels |

## What are megawatts and gigawatts

Megawatts are used to gauge a power plant’s output or the total electricity needed by a city. 1,000 kilowatts or 1,000,000 watts make up a megawatt (MW). For instance, a typical coal plant has a capacity of roughly 600 MW.

The capacity of massive power facilities or multiple plants is measured in gigawatts. 1,000 megawatts, or 1 billion watts, make up a gigawatt (GW). The capacity of all electricity-generating facilities in the United States was around 1,100 GW in 2012 [2].

### How many kilowatts are there in a megawatt and gigawatts?

One megawatt consist of thousand kilowatts. It is used to state the energy produced by a power plant for an entire city. Megawatts are generally used to produce power for a city or a plant.

### Number of megawatts in gigawatts

One gigawatt contains thousand megawatts. It is use for the output of multi power plants or a huge plant capable of providing electricity for many cities.

### Watts to Megawatts

Watts, KW, MW and GW can be converted easily as below

watts | kW |

1000 W | 1 kW |

10000W | 10 KW |

100000 W | 100 kW |

There are one thousand kilowatts in one megawatt

kW | MW |

1000 kW | 1 MW |

10000 kW | 10 MW |

100000 kW | 100000MW |

One gigawatt consist of one thousand megawatts

MW | GW |

1000 MW | 1 GW |

10000 MW | 10 GW |

100000 MW | 100000 GW |

Similarly we divide gigawatts with 1000 to get megawatts and megawatts with 1000 to get kilowatts.

## Use of solar panel systems to reduce cost

Now the point to ponder is the capacity of a solar panel to produce the energy. Mainly there are four factors which effect the amount of electricity produced by a solar panel. The main factors are size of the panels, direction of the panels and the roof as well, area of the roof and weather conditions where it’s installed. The increase in demand of solar panels can be seen with the fact that in USA the demand for solar panels reached at its highest point of 114,678 million kilowatt hours in the form of photovoltaic and thermal power. Results shows that the increase in trends of solar energy use can be seen especially after 2011 initially started from the net output of two terawatt hour or below.

Solar panels use for homes are capable of generating 1000W to 5000W energy. On average the family of 4 to 5 members tend to install a system with 3kW to 5KW of energy. A 4000W system is capable of generating 3400KWh energy p/y generally. It is enough to make the needs of a small family with basic needs.

Here we can conclude that the amount of energy produced

- 5947 hours of dryer machine
- 10244 hours of the refrigerator
- 1990 hours of dishwasher
- 1655 hours of microwave

Generally 14 panels are installed to cover the need of 4kw system where as for a small household use 1kw system is considered as enough. 3000kw energy is being consumed by an average 3bhk family in the UK reported by energy saving trust(EST).

These days’ solar panels are coming with the meters. Meters are installed to check the usage of electricity. Many companies are giving a special feature with the panels. The apps are generated to track the performance and they are the easiest way to check the energy levels being generated and consumed.

Rating of solar panel is done according to the solar panel current that they produce in a standard condition of environment. Units of watts (W) are used to present the theoretical amount of power that is produced by a panel. In an ideal sunlight condition wattage calculation is performed by multiplying x amps into volts.

## How many kilowatts per solar panel

Power produced by most of the latest solar panels in the market ranges from 250 and 400 watts. Penal output will be quoted by the seller along with the name and other details of the panel. Output capacity or wattage is mostly between “245W”, “300W. However, there are many factors that can affect the overall output of the panel that may range from geography of the area to shading, hours of sunlight and orientation. Placement of solar panels matters a lot so while installing a system it is important to look into these factors along with the output. Usually more than enough electricity is produced by a 30 panel system. It will match the annual needs of a normal household and sometimes generates more than the required amount of energy. There are many sites that allow you to compare different brands of energy and the wattage per panel they expect to produce.

Mostly higher power rating solar panels are preferred as compared to the lower power rating but another thing that matters here is the price of the solar panel that is determined as $/W or dollars per watt. So the total wattage of solar panel is a significant factor that determines the total cost of a solar system.

Calculation of solar panel output can be done easily by knowing the number of direct sunlight hours. For instance in California if peak sunlight hours are 5 then a premium solar panel generate of 290 watts will produce as following:

5 sunlight hours x 290 watts= 1,450.

Solar panel efficiency is also determined by the number of solar cells. Solar panel can be divided into two groups based in their sizes; one is 72 cell solar panel and the other one is 60 cell solar panel. 72-cell solar panels are large in size because in them an extra row of cell present and their average output is also higher ranging from 350 to 400 watts. On the other hand, average output of cell solar panels ranges from 270 to 300 watts. The size of this solar panel is around 5.4 feet in height and 3.25 feet in width. Large solar panels are used in bigger building such as industries and smaller ones are preferable for normal households.

### Why are solar panel systems sold in kilowatts?

In most of the cases output of the electricity is determined in kilowatt hours or kWh. Most of the solar panels that are present in the market will produce 250 to 400 in one day. The capacity of a solar system used in a household ranges from 1kWh to 4kWh. It means during a year time period 3,000 kWh of electricity will be produced by this system taking into consideration the peak sunlight hours in the area. This calculation makes sellers introduce their systems in kilowatts.

### How many kilowatts of solar should you install on your roof?

Why a residential or small commercial solar panels are installed in kilowatts? Kilowatt is the measurement use to measure the production of a solar energy. This measurement can assess whether the amount of energy produced is enough to run a house or a business. On average the electricity produced by the panels for a home is 250 -400 watts. Per annum production of an installed panel is 750 – 850 kilowatt hour (KWh) if it’s 1 (kW). The consumption depends on the size of the households. The larger the household the more a consumption will be. On average the annual consumption of energy of an American household is around 10000 kWh. The consumption of energy differs for everyone according to their needs and habits. Usually solar panels are tested at 25 degrees Celsius with the exemption of winds or any other obstacles. Keeping in mind the highest amount of energy that can be used by a household it’s generally tested above the highest end of consumption.

Take an example of dishwasher, it can use 6000 W power. To calculate the energy used per month by a dishwasher if it works daily. Here is the calculation

(6000/1000) kW = 6 KW p/h

6kWh* no. of days (30) = 180 KWh

180 KWh* rate ($ 0.15) = $ 27 p/m

$ 27* no. of months p/y (12) = $ 324 p/y

$ 324 p/y can make a huge difference in your annual budget. This moves us to invest in other energy sources like solar panels. For the understanding of total cost reduced by solar panels we need to understand the concept of W, KW, KWh, MW and GW.

Now the question is how much energy will your system produce per day?

A simple formula is used to calculate the daily watt-hours a solar panel is capable to produce

Formula is

(Power in watts/1000)*average hours of direct sunlight = daily kilowatt-hours

Kilowatt *average hours of direct sunlight = daily KWhs

For instance if our solar system produces 500 watt of energy per day for 6 hours daily than total produced energy will be 3kWh or 300 watts calculated as

(500%1000)* 6= 3KWh

P (W) = 3%1000

P (W) = 3000 watt

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#### Kateryna Ryzha

Kateryna is an experienced writer with a focus in solar energy. She is a specialist in several topics related to energy efficiency, technical applications, renewable energy, and more as a consequence of her extensive reading.