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Understanding kWh, Watts, kW, and Volts
When exploring solar power, you’ll often come across technical terms like kilowatt-hours (kWh), watts, kilowatts (kW), and volts. These terms are key to understanding how solar energy works and what system best fits your needs. In this guide, we’ll break down these basic units, explaining what each one means and why they matter when choosing and managing your solar power system. With a clear grasp of these concepts, you’ll be better equipped to make informed decisions on your solar journey.
Key Takeaways:
Basic Electrical Terms: Volts, amps, and watts are essential for solar power. Volts measure electrical pressure, amps measure the flow of electricity, and watts (volts x amps) represent the power a device uses.
Power vs. Energy: Power is the rate of electricity use (measured in watts or kilowatts). In contrast, energy is the total electricity used over time (measured in watt-hours or kilowatt-hours). This distinction is critical when evaluating energy consumption and solar savings.
Difference Between kW and kWh in Solar Systems: The size of a solar system is given in kilowatts (kW), which indicates its potential power output under ideal conditions. However, the energy savings and production are measured in kilowatt-hours (kWh) based on real-world sunlight exposure.
Location Impacts Solar Efficiency: Solar system output varies by location due to differences in sunlight exposure. As a result, two identical systems may produce different energy outputs depending on their geographic installation location.
The Basics of Power – Volts, Amps and Watts
To understand electricity and power, it may be easier to think of electricity as water running through a hose. In this pretend comparison:
What Is a Volt?
Volts would be the pressure of the hose (e.g. if you were to squeeze a bag full of water, the water would shoot out with force). Volts are the standard measure of electromotive (i.e., electrical movement) force.
In Australia, our power supply is set at 240 Volts (it varies up and down a little from this, but that’s another story).
What is an Amp?
Amps (amperes) would be the volume/amount of water flowing through the pipe. It’s the amount of electricity you have in your wire.
To assist with this, a high-drawing appliance such as a heater or air conditioner would draw (use) more Amps than a low-drawing appliance (such as a computer or TV screen), even though the voltage is the same.
What is a Watt?
Watts is a combination of Amps and Volts. It’s calculated by Amps x Volts.
A Watt is the standard measurement of power that we generally use in day-to-day terms.
How to Convert Watts to Amps – the Power Formula
Here’s how to calculate Watts from Amps and Volts:
Power (Watts) = Volts x Amps
Therefore, an appliance that uses 2 Amps on a 240V power supply will use 480 watts.
kW Meaning - Converting kW to W
A kiloWatt (kW) is simply that – 1,000 Watts. We use kilowatts for the same reason we use kilometres – a Watt is generally too small to be usable, just as measuring the distance from Sydney to Melbourne in metres would be impractical.
What Is the Difference Between Power and Energy?
So, this is the bit that is worth knowing.
Power is the amount of electricity (in this case) used at a particular time.
Energy is the amount of power that is used over a period of time.
To use the water hose analogy above, Power is the amount of water coming out of the hose (whether it is flowing quickly or slowly). Energy is the amount of water to have flowed out of the hose in a period, say one hour.
Power is measured in Watts or kilowatts (the speed at which the water leaves the hose).
Energy is measured in watts/hours or kilowatt hours (the amount of water in the bucket).
What Is a kiloWatt hour (kWh)? – Convert kW to kWh
A kilowatt-hour (kWh) is 1,000 Watts of Power used over an hour.
A kilowatt hour could, therefore, be used by:
An appliance using 1kW for 1 hour; or
An appliance using 10kW for 6 minutes; or
An appliance using 100W (0.1kW) for 10 hours.
Why Is This Important?
This is important to understand because when we buy electricity from our supplier, we are (at least for residential customers) buying Energy, not Power.
In other words, on our bills, we are charged for kiloWatt hours – not for kilowatts.
Therefore, when we install a solar system, we want to reduce the Energy Usage, not necessarily the Power Usage.
How are the Terms kW and kWh Used When Buying Solar?
When we talk about the size of a solar system, we generally talk in kiloWatts (e.g. a 5kW or a 10kW system).
When we talk about how much a solar system will save you in energy usage and dollars, we talk in kilowatt hours.
Why are Solar Systems Sold by kiloWatts, Not kiloWatt Hours?
When a solar system is described as a 10kW solar system, it doesn’t refer to the amount of power it will produce.
Instead, this refers to the Peak Output of the panels in a test (or laboratory) environment.
The reason for this is twofold:
Every rooftop is different, and every location worldwide (i.e. Sydney versus Oslo) gets a different level of sunlight.
Solar panels are manufactured to different quality levels, using various technologies, and their performance may vary wildly from one panel to another over time.
When solar panels are manufactured, they are tested as they leave the production line. This test is done at 25 degrees Celsius, with 1,000 watts of Solar Irradiance per square metre and an air mass of 1.5 (known as AM1.5, but we won’t try to explain that here).
Notably, the kW rating of a solar system only refers to the potential output of the panel; the actual production of the system will usually be lower once the power has been converted to AC power and run through cables, etc.
It is also worthwhile noting that it will rarely, if ever, be 25 degrees on your rooftop with 1,000 W/m2 and an air mass of 1.5.
As mentioned above, the quality of the panel will mean the output after a few years could be dramatically different.
However, using this Standard Test Condition lets us know that at least when new, 1kW of panels should output 1kW in the same conditions under which they were tested. Whether or not this is 1kW is not essential, rather that, similar output panels should all output approximately the same, and everyone uses the exact measurement.
Why Is the Yield or Benefit of a Solar System Measured in kW hours, Not kiloWatts?
As we discussed above, 10kW of solar panels can have different levels of output based on where they are located.
A 10kW solar system in the Northern Territory, operating at total capacity on a sunny day, will output a much higher power level than an identical system operating in Hobart.
When we buy electricity, we buy it in kilowatt-hours, so measuring the benefit of solar power in kilowatt-hours makes sense.
In Australia, for residential customers, we generally estimate a solar system's yield (or energy production) using guidelines published by the Clean Energy Council.
In Sydney, for every 1kW of panels installed facing north without shade, the CEC estimates it will produce 3.9kWh of energy per day on average across the year. In Melbourne, the same panels are expected to produce 3.6kWh per day; in Brisbane, they are expected to produce 4.2kWh.
These numbers vary based on the system's quality, shade and other site-specific issues. In reality, most of our system generally outperforms these numbers in the right conditions.
So, What Does All This Mean?
All this really means is that a solar system is designed to reduce the amount of money you pay for your energy, not necessarily run any given appliance at a particular time.
In other words, it is about having the most water in the bucket at the end of the day rather than how fast the water pours out in the middle of the day.
Therefore, good quality panels, advanced technology inverters, sound design and installation are usually much more important than just the kilowatts the panels may have produced at the factory.
To further your understanding of solar power, it's our free resource for everything you need to know about investing in it. This resource will answer your questions about solar power and its potential benefits for you and your home.
FAQ
Frequently Asked Questions about Installing Solar Power
There are great government rebates/incentives still in place for eligible households. Basically, the larger the panel array, the more STCs your solar system generates as it is based on the expected output of the system over time.
When you buy a solar system, the purchase price is normally reduced by the value of the STCs created by your system. You simply fill out a form on the day of installation to confirm that the system has been installed, and that’s it. There is no additional paperwork that you need to do.
Small-scale Technology Certificates (STCs)
Small-scale Technology Certificates (STC’s) – previously known as Renewable Energy Certificates or RECS – are created when a Renewable Energy System such as a Solar PV system is installed.
The number of STC’s depends on the predicted amount of energy generated and hence the larger the system the greater the rebate. In essence, one STC is created for every megawatt-hour of production capacity of the system.
This is further multiplied by the number of years the system is likely to generate energy (for home solar systems, this is usually 15 years, although the life of the solar panels themselves is considerably more than that).
This incentive program is being phased out until 2030, so each year the number of certificates your system is eligible for reduces.
STC Price
The system for trading and pricing STCs for small systems is managed by the Small-scale Renewable Energy Scheme (SRES).
STCs are bought by Liable Parties (usually electricity retailers) and must be surrendered at the end of each quarter. As the number of STCs that are required to be surrendered is a fixed amount each year, but the number of STCs created is variable, the price paid for STCs also varies and is determined by supply and demand.
The Federal Government legislated in 2010 a fixed price for STCs by implementing a Clearing House system where STCs can be bought and sold for $40. However, there is no requirement for Liable Parties to purchase from the Clearing House, so they are likely to only do so if there is a shortage of STCs or the market price exceeds $40. There is currently a surplus of STCs in the market which means the market price of STC’s below $40
The Feed In Tariff is only something you need to worry about if you don’t have battery storage.
The price your chosen energy retailer pays for any excess electricity generated from your solar panels is recorded as a credit on your power bill.
In NSW, solar power is fed into your home as it is generated and your household will use it first before you draw power from the grid.
This means that for every kWh of solar power used in the home you are directly saving money you’d spend on your power bill. This reduction in your power bill is the main financial benefit of solar power.
Everything else will be bought up at an agreed rate by your electricity retailer.
At the moment, most feed-in tariffs are between 5 and 10 cents per kWh, with many being about 7 cents. They bounce up and down a lot, for example in previous years they have been up over 20 cents per kWh. Typically, they are always at least 5 cents per kWh.
Once you sign up for a 1KOMMA5° Installation, we immediately submit your grid application to the relevant energy distributor. For systems up to 5kWs, this is a formality. For larger systems it can take a few days or more. Once we receive approval, your installation will be managed by our installation coordinator, who will welcome you to 1KOMMA5° and book an installation date for you. This is generally booked within around two weeks and installation dates are available Monday to Friday, weather permitting.
We endeavour to have your system installed within 2-4 weeks unless you request us to hold for whatever reason. Due to our strict safety policy, we do not install solar systems when it rains. In the event of inclement weather, we will rebook your installation as soon as possible. We always work with your requests as we strongly recommend that someone be home on the day of installation.
Green Loans can be an affordable way to pay for your solar power system and is only available for approved products. As a Clean Energy Council Accredited installer, all our systems qualify.
Green Loans can be used to finance 1KOMMA5° systems from $1,000 to $30,000 over a 2-7 year term. Once you have received a referral from 1KOMMA5°, online approval usually occurs within 1-2 business days. Green Loans have a competitive fixed interest rate that is as low as 7.99% p.a.* | Comparison rate 9.21% p.a.^ Establishment fee of $299 added to the loan amount. $2.70 per week account keeping fee included in repayments.
To be eligible to apply you must:
Be over 18 years old and an Australian resident or citizen
Own or be purchasing a home
Be employed, self-employed, a self-funded retiree; or is receiving the Government Age Pension
Have an Australian driver’s license or Passport
Provide two most recent payslips or 90 days of bank statements
There are a number of good, competitive Green Loan providers – ask us about the options available.
More Helpful Articles:
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