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How Many Solar Panels Do I Need for 1000 kWh per Month. 4000 kwh solar system

How Many Solar Panels Do I Need for 1000 kWh per Month. 4000 kwh solar system

    Kilowatt Hours to Watts (kWh to W) Conversion Calculator

    Use our interactive calculator to easily convert kilowatt hours to watts (kWh to W).

    Kilowatt Hours to Watts Conversion Chart

    Here is a chart converting kilowatt hours to watts for a few common time periods. Note that one month is assumed to be 30 days long.

    Kilowatt HoursWatts for 1 dayWatts for 1 monthWatts for 1 year
    100 kWh 4,166.67 W 138.89 W 11.42 W
    200 kWh 8,333.33 W 277.78 W 22.83 W
    300 kWh 12,500 W 416.67 W 34.25 W
    400 kWh 16,666.67 W 555.56 W 45.66 W
    500 kWh 20,833.33 W 694.44 W 57.08 W
    600 kWh 25,000 W 833.33 W 68.49 W
    700 kWh 29,166.67 W 972.22 W 79.91 W
    800 kWh 33,333.33 W 1,111.11 W 91.32 W
    900 kWh 37,500 W 1,250 W 102.74 W
    1000 kWh 41,666.67 W 1,388.89 W 114.16 W
    1100 kWh 45,833.33 W 1,527.78 W 125.57 W
    1200 kWh 50,000 W 1,666.67 W 136.99 W
    1300 kWh 54,166.67 W 1,805.56 W 148.40 W
    1400 kWh 58,333.33 W 1,944.44 W 159.82 W
    1500 kWh 62,500 W 2,083.33 W 171.23 W
    2000 kWh 83,333.33 W 2,777.78 W 228.31 W
    3000 kWh 125,000 W 4,166.67 W 342.47 W
    4000 kWh 166,666.67 W 5,555.56 W 456.62 W
    5000 kWh 208,333.33 W 6,944.44 W 570.78 W

    How to Convert Kilowatt Hours to Watts (kWh to W)

    Before we go into how to convert kilowatt hours to watts, it is important to understand what these two units actually measure.

    Watts is a measurement of power, which you can think of simply as an instantaneous amount of electrical energy. Kilowatt hours is a measurement of this same electrical energy, but over a period of time (measured in hours).

    So in order to convert kilowatt hours to watts, you must know how many hours it took to generate (or use) the measured amount of kilowatt hours. To calculate watts from kilowatt hours, divide kilowatt hours by the number of hours and then multiply by 1,000.

    Formula: watts = (kilowatt hours ÷ hours) × 1,000

    Abbreviated: W = (kWh ÷ hrs) × 1,000


    Let’s look at an example many homeowners face when considering adding solar panels to their home.

    In this example, you know your monthly electrical energy usage in kilowatt hours over the course of a year. You want to know how many panels you would need on your roof to completely solar power your home. Let’s say the panels you are looking at purchasing are rated at 300W each.

    First, find the highest-usage month out of the year. Let’s assume it’s July, with a usage of 1,000 kWh.

    Let’s also assume that your roof gets full sun for an average of 7 hours each day during July. So the total number of hours your solar panels could generate electricity during the month is 7 × 31 = 217 hours.

    The total number of watts you would need is:

    (1,000 kWh ÷ 217 hrs) × 1,000 = 4,608.29 W

    Dividing this peak usage by the rating for each panel gives us the total number of panels you would need:

    4,608.29 W ÷ (300 W/panel) = 15.36 panels

    Based on this estimate, you’d need about 16 panels to completely solar power your home during your highest-usage month.

    Why Convert Kilowatt Hours to Watts?

    Converting kilowatt hours to watts is important for a few reasons, especially when considering solar for your home. First, knowing your monthly energy consumption in kilowatt hours over a typical year allows you to calculate the total number of solar panels you would need to power your home, as in the previous example.

    Second, you may find that your solar panel system can produce more electricity than you currently need or use. Converting those extra kilowatt hours to watts will give you an idea of other appliances or devices you could power, without having to add more panels to your home.

    Finally, converting kilowatt hours to watts gives you an idea of your average power consumption in watts over a certain period of time. This number can be helpful for reducing energy usage or designing a DIY solar power system.

    How to Convert Watts to Kilowatt Hours (W to kWh)

    You can also convert watts to kilowatt hours. To calculate kilowatt hours, multiply watts by hours then divide by 1,000.

    Formula: kilowatt hours = (watts × hours) ÷ 1,000

    Abbreviated: kWh = (W × hrs) ÷ 1,000


    In this example, let’s assume you want to add a freestanding water cooler to your home. You want to know how many kilowatt hours this appliance consumes over the course of one year, to see if your solar panels can handle the extra energy consumption.

    Look at the electrical specifications for your water cooler to find the amount of watts it uses. This is typically found on a sticker on the back of the appliance. In this case, we aren’t given the watts rating, but we do know that our water cooler is rated for 5.5 amps (A) at 120 volts (V).

    Simply multiply volts and amps together to find watts:

    120 volts × 5.5 amps = 660 watts

    Even though your water cooler is plugged in year-round, let’s assume it only uses this amount of electricity to actively cool your water for about 2 hours maximum per day. Over the course of one year, this is about 730 hours (365 days × 2 hours per day).

    So to find the total kilowatt hour consumption of your new appliance, simply convert watts to kilowatt hours:

    (660 W × 730 hrs) ÷ 1,000 = 481.8 kWh

    How to Convert Watt Hours to Watts (Wh to W)

    In small-scale solar and electrical systems, it’s sometimes easier to express energy consumption in terms of watt hours (Wh) rather than kilowatt hours.

    To convert watt hours to watts, divide watt hours by the number of hours.

    Formula: watts = watt hours ÷ hours

    Abbreviated: W = Wh ÷ hrs

    How Many Solar Panels Do I Need for 1000 kWh per Month

    Solar power is becoming more efficient and more affordable. Government initiatives, called net metering laws, now require many power companies to buy excess power produced by solar powered homes during sunlight hours by giving credit for power during off-hours when the use [1].

    Can you supplement or possibly supplant your fossil-fuel powered electricity use with solar-generated power? And how much solar power do you actually need to power your house?

    Obviously, there can be a significant range depending upon the size of your home, your family, your energy consumption habits and whether you are in Alaska and using a lot of power to heat your home or in Florida and using a lot of power to cool your home or whether you live in a more temperate climate.

    You can check your electric bill to find your usage. Adding a cushion for those times when your solar panel might not be operating at peak performance, and because it’s easier to do the math, let’s examine how many solar panels you will need to power 1,000 kWh per month.

    How many kWh does a solar panel produce per month?

    First, it is important to note that not all solar panels are created equally.

    Presently, the range of efficiency, that is, how much of the sun’s energy hitting the solar cell is converted into electricity averages 18 percent, but can vary depending on the quality of the solar panel. A premium panel, manufactured with more expensive materials will cost more and be more efficient. You can have a look at our updated list of the best solar panels currently available in the United States.

    A solar panel operating at 20 percent efficiency produces around 265 watts of power per hour [3].

    Manufacturers are required to label the panels with the number of kilowatts they can power per hour during ideal conditions, i.e. direct sunlight on a cloudless and sunny day. This number is called a Standard Test Condition rating (STC) and will be for example 265 if the panel produces 265 watts of power.

    So, how much energy does a solar panel produce per day?

    If for example, the solar panel has a rating of 250 watts of power, and the panel received a full hour of direct sunlight, and no other factors diminished the power, then you would get 250 watt-hours of electricity.

    On average, one such panel would produce one kilowatt hour per day and 30 kWh per month.

    How many kWh per month can you expect to generate from sunshine in your area?

    Many solar power company websites provide calculators for the average annual solar panel output per day in kWh for areas across the United States.

    Combining all of the sunshine that falls on the solar panel over a 24-hour period, the average roof in the United States gets about four hours of “full” or “usable” sun a day.

    Again, this number will vary depending whether you live in a cloudless desert or in foggy mountains.

    As an example, there is a map that shows a solar energy potential in each state of the USA. But goes on to caution that this estimate is based on a south facing array and that you must consider the tilt of your roof, citing that a solar array facing west rather than south can cause a nearly 11 percent output reduction.

    But let’s get back to the example so that we can have a starting point for considering the size of your domestic solar system.

    If you have one 250-watt panel receiving four hours of sun, then you will get 1,000 watts or one kWh per day from that panel. If you have four panels, you will get 4 kWh per day.

    If you have 33 panels, assuming a 30-day month, you will get 1,000 kWh per month.

    Or will you? What can affect solar panel output efficiency?

    The Standard Test Condition rating is based on ideal conditions converting the sun’s energy into power. But the solar system itself is not 100 percent efficient in converting the energy into power.

    • A solar system requires an inverter to convert the Direct Current power the photovoltaic cells receive from the sun to Alternating Current power used in our homes. Power is lost as it goes through the inverter, which can be a single inverter per system, or a single inverter per solar panel. It is estimated that about three percent of electricity is lost passing through the inverter.
    • Different materials used to manufacture the cells can resist the flow of electricity as can resistance passing through the cables.
    • Inevitably, solar panels will pick up grime and dirt from the atmosphere, blocking full sunshine.
    • Temperature can effectively create power losses as well. While it seems that a hot, sunny local would be ideal, the fact is that the STC is based on a temperature of 25 degrees Celsius (77 degrees Fahrenheit). The flow of electrons across the photovoltaic cells is not as efficient at higher temperatures. All in all, solar companies estimate a de-rating factor of around 20 percent.

    Be aware that system sizes are calculated inversely in the United Kingdom and the United States.

    Thus, a typical 1 kWh system in the UK is estimated to produce 850 kWh unit per year, a 2 kWh would create around 1,700 kWh units per year and a 5 kWh system is estimated to create 4,500 kWh [5].

    Accordingly, if you are talking with a solar installation company about purchasing a system, then chances are they are already including the 20 percent de-rating factor in their estimate.

    But it is best to do your own preliminary calculations and then talk with them about their energy system offering so that you can be certain the system you purchase provides your anticipated needs.

    So how many solar panels do you really need to get 1000 kWh per month?

    If your goal is to produce 1,000 kWh per month, then truly you must produce 1,250 kWh per month to allow for loss in output efficiency.

    Remember, if you are receiving an average of four hours of usable sunshine per day and your solar panel is rated at 250 watts of power, then you will need forty panels to reliably generate 1,000 kWh per month.

    An average residential solar panel size today is about five and a half feet by three feet.

    But the number of panels and consequent space needed can vary depending upon whether you select lower-efficiency economy panels or high-efficiency premium panels.

    Consider this table when trying to figure out how many solar panels you can put on your roof:

    So go out and take a look at your roof and consider the sunlight falling on it. Think about the size and placement of solar panels. Do a cost analysis of the savings you will experience from creating your own clean, renewable energy.

    Read our article about available solar power incentives and rebates that might make financing your savings attractive now.

    kW, kWh and kilowatt/hour : What do they stand for?

    One of the most common sources of confusion I encounter when talking to non-electrical people about solar power is related to the terms kW and kWh. What do they stand for? What do they mean? And what’s the difference between the two? Watch the video, or read below to find out…

    many, solar, panels, need, 1000, month

    Folks who are really confused also throw the term “ kilowatt/hour” into the mix. I’ll deal with that doozy in this footnote 1.

    Starting with the absolute basics

    Please excuse this post if you think I am explaining the bleeding obvious! But I think it is vital to write a post that describes these key units of electricity in a way that requires zero prior knowledge of anything electricity-related.

    So here is my humble attempt to answer the question:

    What is the difference between a kW and kWh?

    Let’s start with what each letter stands for.

    k stands for kilo. Which means “one thousand”.

    W stands for Watt, which is a measure of power.

    h stands for hour, which is obviously a measure of time.

    kilowatts: kW

    So kW means kilowatt, which is 1000 Watts. It is a measure of power. Notice that, if you like to keep anal electrical engineers like me happy, the correct way to write it is always with a small k and a capital W. Peak power defines a solar system’s size. e.g. a 3 kW system can produce 3 kW of power at solar noon (when the sun is at its strongest) on a perfect solar day:

    A 3 kW solar system can produce 3 kW of power at around midday on a perfectly sunny day.

    kilowatt-hour: kWh

    kWh stands for kilowatt-hour. A kWh is a measure of energy (not power). If your solar panels (for example) continuously output 1 kW of power for a whole 60 minutes, you will have produced 1 kWh of energy. The amount of electricity you use (or generate) is defined in kWhs. e.g. “My solar system produced 4 kWh of electricity today!”

    So at the highest level: kW measures power, and kWh measures energy.

    Why is the difference between Energy and Power important?

    It is very common for people to mistakenly interchange the terms energy and power as if there is no difference. Most people do it all the time without noticing. It drives electrical geeks like me up the wall, especially when I read it in national newspapers and books!

    For example: If someone is talking about their electricity usage and says:

    “I used 8 kW yesterday”

    They probably really mean that they used 8 units of electrical energy yesterday, In which case they should have said

    “I used 8 kWh yesterday”

    Yeah, yeah I know what you are thinking: Who cares?

    Well, it is actually quite important if you are buying a solar system.

    If a buyer has studied their energy consumption and carelessly says they need a solar power system to produce 12 kW, they might end up being quoted a 12 kW solar power system, which will cost about 10,000 at today’s and produce about 48 kWh per day.

    If what they actually meant was that they need one to cover an energy usage of 12 kWh per day, they really need a 3 kW solar system that costs about 3,500 at the time of writing!

    So please don’t confuse kW and kWh. If you do, you may end up with a solar system that is completely the wrong size!

    How do kW and kWh relate to batteries?

    When buying batteries, you need to think about both the power of the battery and the energy storage capacity of the battery you are looking at.

    The battery’s energy storage capacity is measured in kWh—for example, the ‘Powerwall 2’ stores 13.5 kWh of energy.

    Its power is 5 kW, so it can charge or discharge at that rate. At full power, then, it can fully discharge in under 3 hours.

    The more energy (kWh) a battery has, the more you can store and the longer it will last, the more power it has the faster you can get that energy in or out of the battery,

    In other words, the more power it has, the more appliances you can power with it and the more energy it has, the longer you can power those appliances.

    For normal household use, you want enough energy to get you through the night and at least 5 kW of power for speedy charging.

    Top tip for filtering out the worst solar and battery salesmen: Ask them to explain the difference between a kW and kWh. If they get this wrong how on earth are they gonna understand your requirements? A lot of cold calling door knockers will fail this test in my experience.

    The technical bit for those that are interested:

    Energy: Energy is measured in Joules. Energy is the capacity of something to do work.

    Power: Power is the rate at which energy is used. Power is measured in Watts.

    1 Watt is a rate of energy usage of 1 Joule every second, or 1 Joule per second (J/s).


    • A kilowatt/hour is a nonsensical unit in most contexts. If you find yourself using this unit, double-check what you really mean, which is probably kilowatt-hour. Kilowatt/hour means kilowatts per hour. Kilowatt is a measure of power (units: Joules per second ), so you are really saying joules per second per second, or joules per second squared. Which would be a measure of how quickly power is increasing. An acceleration of power if you like. There are very few circumstances where that is a relevant measure. Especially when talking about solar or batteries. Lots of people get kilowatts/hour confused with kWh. Please don’t let it be you. 99% of the time, you’ll mean kWh. ↩


    I’m a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of My last real job was working for the CSIRO in their renewable energy division.

    Комментарии и мнения владельцев

    I don’t care how simplistic it sounds, your article has been a revelation. AT LAST I understand what it is all about. Thanks a heap, much appreciated. Peter L

    Hi Finn I am looking at a floor tile for using under ‘click floor’. The specification includes an RT rating of 0.07 m2 K/W. Does this mean it has some insulation properties ?? High / OK / Low. I see plenty of U Value and R Value and would like to know where RT sits with the others. Thanks Ian ( Shropshire)

    Hi Ian, Ronald here. RT rating presumably stands for R Total and is similar to R except it is supposed to take into account its actual R value when installed normally. A rating of 0.07 for RT is very low. Pretty much anything should have a value higher than that so it’s probably worth checking if it’s correct. The manufacture should be able to help. This page from the US has typical R values for flooring: And this page from Australia recommends polyester floor insulation: I’m not an expert on floor insulation so I can’t really say what’s best.

    Pete, “ if ya got this now. In being able to understanding it all, well done to ya ! Now, please ask or tell us about PF of it all, eh ? “ Power factor

    Hi Finn. Good site mate…I am ready to start a new job with Goforsolar in Port Melbourne. Haven’t seen any reviews on them on here yet…Do you know much about them and there quality please. Cheers Mick

    It sounds like it would be better to have a system that is not connected to the grid. After reading your info, very enlightening BTW, it sounds like the authorities and retailers are making it harder for people to reduce their reliance on fossil fuel produced electricity. Sounds like retailers are complaining to government authorities that they are not making enough profit.

    In actual fact, I think that makes it even more necessary to increase PV generation and feed it to the grid. The retrogressive Australian government is busy supporting the fossil fuel industry, which means we reduce fossil fuel consumption in Australia despite the government.

    Awesome website. Thank you so much for the lay persons explanations. Starting to get an understanding of this stuff.

    Hey Finn I also think your delivery was perfectly acceptable and in no way offensive but can see why Jock “mighta” been annoyed but the facts WERE provided in a humorous way and I thank you for that. After all it was my English teacher at school many years ago told me “English as she’s wrote ain’t as she’s spoke”

    Im still confused Finn….im off grid and my regulator, PL60, tells me how much solar energy I have harvested in Amp/Hours….so how do I convert this to kWH?

    To convert Ah (Ampere-hours) to kW hours, simply multiply by the voltage (because Power = Voltage x Current) and divide by 1000 (because it is kilo Watt hours). For example: If a 12V battery has given you 100Ah, then: 12V x 100 = 1,200 Watt hours 1,200 divided by 1000 = 1.2kWh

    I’ve seen some inverters here (Zambia) either rated using kVa or kW. Are these terms interchangeable?

    Hi Finn, I am buying a 3 bedroom house in the country and it has gas cooktop gas hws,electric oven and all the rest lights fridge etc.(2 people) My question is Is it worth installing a solar power system to go help keep the power bill down? We will be on the pension very shortly.Your Комментарии и мнения владельцев would be much appreciated. regars Steve

    Hi Steven, Solar may be worth it, especially as you will be home in the day. But… your priority should be to first invest in energy efficiency, and get your electricity usage down. The cheapest kWh is one you don’t use! The priorities should be: 1) Heating/Cooling – Insulate, insulate, insulate. Shade north facing Windows in summer. Draught proof any gaps. Then go for 7 efficient Heater/Aircon units. 2) Hot Water – if you have electric hot water, consider solar hot water or a heat pump 3) If your fridges are old – consider upgrading, new ones use 5x less energy 4) LED lights throughout: 5) Solar! Hope That Helps, Finn

    My name is Tim Forcey. You can shorten that and call me Tim if you want, and you probably won’t get in any trouble whatsoever (unless there are other “Tims” around). But never ever shorten kilowatt-hours to kilowatts!

    Finn I am lost, I really am. Here is the deal I use 30kwh per day on a single phase house which is our current house. We are building a new house which will be 3 phase. ( Most of the house is single phase but i will be spreading circuit loads across all 3. there will be 50 some odd different circuits spread across 3. The only thing I have that is 3 phase is a 30 kw/cooling capacity not electrical capacity air con unit ) I am hooking up a daisy chained Tesla power wall system ( the 7kw versions. ). I wanna stay on the grid ( so hybrid ). I live in melbourne. I dont wont to pay a single bill. I refuse to be told from solar sales people as the ones i have dealt with honestly have no idea what they even sell let alone the tesla system. What on earth do I need? I.e How many watts or kilowatts must I produce from the panels? What size inverter do i need? ( the biggest I can find tesla ready is the fronius Symo 5.0-3-S Hybrid 5kw. I would like to use this brand of inverter as they are tesla ready and have had over 60 years experience in battery charging ) Will i need more than 1 inverter? How many tesla batteries do I need, Can the tesla batteries be daisy chained? Any help dude would be great. Im just lost.

    Hi Robert, How many panels depends on when you use the energy: You can daisy chain the Teslas and use a single inverter, they’ll just throttle the power output so as not to exceed the inverter rating, but you’ll get double the energy storage. I’d get one battery to start with and see how you go. 5kW of panels and a Powerwall are being installed for about 18k right now.

    Im in Canada and we are years behind you in Austrailia in solar tecknowledgy, aiways a interesting read. Thx

    G’day Finn and team, 12 years ago when we built our house I had it connected to 3 phase supply, I no longer have a need for the 3 phase, should I have it changed to single phase, is there any advantage o disadvantage? I also have two separate solar systems. A 1.5 kW about 6 yeas old and a 5 kW about 3 yeas old, they are separately connected to two of the three phases. On average my system exports twice the amount of power that I import, yet I still get a power bill although most of it is the ridiculous supply charge, or connection fee as some call it. I also have a 6kW petrol generator that is connected to my power board via a mains/ emergency switch. because of the high number of blackouts we get. I’d like to go off grid. Am I right in thinking that with the generator as backup I don’t really need to calculate battery storage for the occasional 3 o 4 day low solar period, and could allow for say only two days battery supply. Thanks for the great work, Bob

    Hi Bob, I don’t see any advantage in taking 2 phases off your house. I’d leave all three. And yes – a generator lets you have much fewer batteries – if you find you are using your generator too much – then you can add more batteries later. Hope That Helps, Finn

    many, solar, panels, need, 1000, month

    The use of kWh as energy unit is as clumsy as saying the length of a trip is 100 km/h day. The proper energy unit in the international system is the Joule (J) and 1 kWh is 3.6 MJ. Alas energy companies are unable to speak properly of energy.

    I agree kWh is so premetric But whats in a name? Actually quite a lot of history. Joules in Australian lingo should not be confused with other words like jewels or Jules’ diamond engagement ring. joule (J) The amount of work or energy exerted when a force of one newton causes a displacement of one meter. or joules) = force (newtons) x distance (meters), where a joule is the unit of work. And isnt it also amazing that a Joule is also equal to a watt second so that 1 kWh is 3.6 MJ. Why the CAPITALS? W is capitalized in recognition of the 18th Century inventer James Watt who produced a much improved steam engine that helped British industry lead the world during the industrial revolution. J also capitalized as it also honours an English physicist named James Prescott Joule who pioneered the understanding of the relationship between work and heat. The world owes a lot to Mr Watt and Mr Joule IMHO. Feel free to Google “Joule” and “Watt”.

    Yes. Talking about “kWh” is much more intuitive to nearly everyone than multiples of “3.6MJ”, EXCEPT that it is buggered up more than 50% of the time, even by people in the industry (both with electric vehicles, and stationary PV systems in my experience).

    Hi, a usage of 8kWh per day as you say can be done with a 2kW solar system. Do you multiply 2kW x 4 ( meaning 4hr of sun per day? ) please clarify this. Thank you. Regards Lothar

    yes – you get about 4 ‘sun hours’ per day averaged over the year in Australia – a bit more up north – a bit less in Melbourne and Tassie. So 4 kWh owe kW installed.

    I am setting up of the grid as there is no mains where i am so what kva invertor would i need when i on two oanels one 12vokt battery to run a small house that only using piwer for a five start rated frigde a TV and led lights threw out and a water pump ? The system i have has a gen back up of 2800kva max and the solar can be added to as miney permits. So the wuestion is is my daily usage is up to 16kwh what kva do I need ?

    Michael, the answer yo your question is a long one. It is not as simple as giving you a number. I highly recommend this book which answers your question comprehensively: Hope That Helps, Finn

    Hi Mr:- Finn Peacock, My daily usage is 2kwh, i have 3 phase system, only air conditioner is in 3 phases, pool and others are in balanced 3 phase, i have an off peak meter with heat pump, cooking on gas converted, ready to install in 2 weeks, solar of 5kw with 7.5kw 3 phase inverter, best in market, how much i will save in quarterly payments, no one in home, from 9am to 4pm, pool in auto timer in morning, before 11am and after 4pm, that cause pump run out of water, burnt the seals of motor, happen when i am not there, so auto timer i cancelled and i start by myself, after come home at 4pm, no battery requested for solar system, so what is your advice to save money, washing done at the same time, when i am back, due, to unbalance load stoppage, and drain plug blocked,in sink, and wet my carpet, please advice me sir, dishwasher, i disconnected, drier none in home, fridge is 4 yrs old, with 5 star, no old tvs, 56inch, led, use 1hr/per day, whole home is compact fluorescent lamps(CFL), how far i go sir, ready to retire, please advice, me thanks.

    Hello Leslie, Ronald here. If you have gotten your electricity use down to 2 kilowatt-hours a day then you have already done very well. I can’t think of anything at the moment to further reduce your electricity use. But if you are going to retire soon then you are likely to be home during the day which should let use more solar electricity and even less grid electricity.

    I need air conditioner to run in nights, not in the morning, when i am along, please, advice me, sir.

    You could install a battery system to store solar energy during the day to use at night, but at the moment they are too expensive to pay for themselves for normal households. There are air conditioners that can use solar electricity during the day to make ice to cool a house at night, but they don’t make financial sense either. I am afraid there is not anything I can really think of to help you, apart from suggesting you use solar power in the afternoon to cool the house down so you won’t have to use quite so much grid electricity to cool it at night.

    If you mean what will happen to solar electricity you don’t use, it will be sent into the grid and you will receive a small feed-in tariff for it. In most states it is usually only about 6 cents a kilowatt-hour. While this isn’t a lot, it will still help to reduce your electricity bills.

    Hi you don’t say what size your pool is. but most common pumps for domestic pools are around 0.75kw and generally are recommended to run 4 to 6 hours a day. To make best use of solar power you should set timer to run in late morning and again in early afternoon. It is unfortunate you damaged the pump by running out of water. but don’t explain how this could happen. I’ve never had this experience in 12 years. you could fit o loss of pressure switch that would stop the pump if it ever happened again

    We find there is very little direct sunlight in our part of Tasmania. Does Cloud cover still produce power in solar panels? Should more panels be purchased to compensate for lack of direct sunlight?

    Hello John, I’m afraid Cloud cover really reduces the output of solar panels and so Tasmania is the worst place in Australia for solar power. Light Cloud may result in panels producing about 30% as much as under clear skies while heavy Cloud can reduce it to 10% or less. Installing extra panels can make up for the lack of sunshine. You can have panels that total to 133% of your inverter capacity and still receive Small-scale Technology Certificates (STCs) for them that reduce the cost of rooftop solar. I wrote about this here: Getting a larger inverter and installing a much larger solar system overall is an option, but note that the larger your rooftop solar system, the less electricity you will use yourself and the more will be sent into the grid for a low feed-in tariff and this will increase its payback time. So from a purely dollars and cents perspective it doesn’t make sense to make your rooftop solar system too large. But if you are doing it for environmental reasons, then go for it. But note that, unlike in South Australia, if you want a solar inverter larger than 5 kilowatts in Tasmania, it unfortunately complicates matters.

    Hi Finn – just perusing your great website and beginners guide to solar – full of excellent pertinent information. Has got me thinking – is it feasible to install a small 3kW system and not connect it through your fusebox/metering system? For example, install a hybrid system, but run new wiring from the inverter to say new power points in the laundry and bathroom and use the washing machine/dryer etc during the day. Lights might be the only thing needed in these areas overnight and could run off the grid. Perhaps different coloured power points could indicate solar. Similarly, new individual wiring could be run to free-standing wall heating units to warm the house during the day via solar to limit heating expenses. Is something like this legal and feasible? I own an old turn-of-the-century house that is hard to heat in winter, especially the upstairs bedrooms – maybe this is all I need? Cheers Daryl

    Hello Daryl, Ronald here. What you suggest is possible, and provided it is never connected to the grid it is legal. But economically speaking it doesn’t make a lot of sense, as you would have to pay extra to get a hybrid inverter installed and you wouldn’t be able to send surplus solar electricity into the grid for a feed-in tariff. In addition, because the output of solar panels varies a lot during the due to the position of the sun and because of clouds, you would need batteries to have a reliable off-grid supply of electricity and they are still too expensive to pay for themselves. So if you are able, it makes much more economic sense to install a grid connected solar system.

    Hi Finn I have a tesla 14k system and would not have purchased it if I had known about the evergen 17 k unit in time. I was wondering though if I could still purchase the evergen unit and create extra storage from my 5.2 k solar? I also have solar hot water which I started with but there doesn’t seem to be a need anymore with the battery being fully charged up each day by noon?

    Hello Ray. Extra storage capacity will only be of use if you regularly use more than the 13 kilowatt-hours you can get out of the Powerwall 2 at night. But if you did want the extra storage, the Evergen Equinox is DC coupled, so while you could technically get it, this would involve scrapping your current inverter. Assuming your Powerwall 2 is AC coupled, it should continue to work, although I don’t know if you would have problems balancing their use. One might end up doing most of the work. Economically it won’t pay for itself for an on-grid installation.

    Jack, I’ll give you two definitions and you can decide which one is most likely to be correct: (1) An anal engineer specializes in building artificial sphincters. (2) It is a term from Freudian Psychology that is short for “anal retentive” and, “is used to describe a person who pays such attention to detail that it becomes an obsession and may be an annoyance to others.”

    ….er…. Can you give us some more detailed information about that?…. I thought an “anal electrical engineer” was a strangely wired electrician….?

    Hi, My latest electricity bill suggests I am using around 60 kWh per day. Can you please give me an idea of what size system would be the best? Thanks

    Hello Emma This is a difficult question to answer. I generally recommend people install as much as they reasonably can: I recommend this because for most people the largest system they can easily fit on their roof will pay for itself. But it will depend on your personal preferences and budget. If your home has single phase power then the largest system you can easily install is a 5 kilowatt inverter with around 6.5 kilowatts of panels. In most Australian cities this will generate an average of around 25 kilowatt-hours a day. Or, if you have the roof space, you can pay extra for a system that export limits and this will enable you to install more panels and with your large electricity consumption you may find this worthwhile. If you have 3 phase power then the limit is more likely to be the size of your roof, so you could either follow my suggestion of installing as much solar as will easily fit or an easy option would be to just install a 5 kilowatt inverter with around 6.5 kilowatts of panels which will help lower your electricity bills but will produce around half or less of your daily electricity consumption.

    Hi! How can this be solved to come up its consumption per day in Peso for example. 0.90kWh/24h given that 4.8218 pesos/kWh How much is the consumption in a day?

    That would be 0.9 multiplied by 24 which gives a total of 21.6 kilowatt-hours. You then multiply that by 4.8218 pesos to get 104.15 pesos.

    This is so really really helpful, thank you so much. I was getting all confused on trying to figure out what exactly I need.

    My electric bill says I used 1000 kwh for this month. 1000kwh / 30 equals 33kwh per day (presume 30day month) 33kwh per day / 24 = 1.389 kw used in an hour so, the basic question is, if 1.389 kw is average, with peaks and valleys, what size system would I need.

    For most people I suggest they get as large a solar system as they can conveniently fit on their roof. This is because rooftop solar can provide an excellent return even if households only use a small portion of the electricity it generates. The largest system most homes can install without complications is around 6.5 kilowatts. How much that will generate depends on where you are but generally speaking it will produce an average of about 25 kilowatt-hours a day. If your home has 3 phase power then it is easier to install a larger system and the limiting factor may be how many panels you can easily fit on your roof. If your budget is tight you can install a smaller system. Small systems can potentially pay for themselves very rapidly, especially if there are usually people at home during the day using the solar electricity generated, but it is possible you will end up regretting not having the additional savings a larger system could have resulted in. Here is an article I wrote on why larger systems usually make sense:

    Thank you so much for this info, though you are now communicating with a well intentioned technophobe. So we wacked on 16 panels and two inverters a couple of years ago. (Both inverters have had to be replaced? Bad bunch they said…side topic). Do we invest in solar hot water then onto a battery system or will the battery system make solar hot water sort of retrograde?

    Hello Andrew, Ronald here. At the moment a battery system won’t save you money but hopefully they’ll continue to fall in price. A solar hot water system can same you money but it may be more cost effective to increase your solar PV capacity and use the extra generation to heat water instead. If you choose that route, rather than expand your current system it may be easier to add an new system on a free section of your roof or possibly replace your old system with a larger new one.

    Thanks for that. The reason I am responding now is that the situation has changed (and to give some previously not disclosed info). I have a teenage daughter who, 90% of the time, doesn’t suffer from autism cause she thoroughly enjoys it! We had a 16 hour blackout this week and I can assure you that became part of the 10% and none of us wish to suffer breakdowns like that again. So my wife insists we get a battery soon. Call it a lifestyle choice rather than economic. So say 12 grand for an installed Tesla Powerwall 2 (just to chuck a figure out there). Over 10 years it doesn’t seem too bad an insurance policy. But it will be cheaper than 1200 bucks a year won’t it? We will decrease that cost with use of the battery every night and not using mains power right? We are big power users, so will a battery simply use itself up each night, then turn off and we use mains power and so on every 24 hour cycle? We understand that if, no make that when, the next blackout occurs we will have to conserve to make a battery last.

    Hello Andrew I’m afraid Tesla has raised the price of their Powerwall 2 and the middle of their estimated installed price is now 15,275. I don’t know where you are, but if you are paying 27 cents for grid electricity while receiving a 10 cent solar feed-in tariff and have a high overnight electricity consumption and a large solar system and use an average of 0.8 cycles per day then over 10 years you would save around 6,650 on your electricity bills over 10 years, depending on how efficient it turns out to be and how rapidly its capacity deteriorates. This would leave you 8,625 in the hole after 10 years. But since backup is very important to you, if you used only have its usable capacity and left the rest for backup you’d only save around 3,325 over 10 years leaving you about 11,950 behind. In your situation a generator may be a much lower cost option. You could invest in one that’s wired into your home or you could follow the cheaper route of getting a portable generator and making do with extension cords to power loads.

    I live in Hawaii, my landlord has a Toshiba 20000 btu,204 watts how much will it cost him using on a 5hr day?

    BTUs? Are you still using them in America? Not even the B’s use BTUs any more. Well, as one BTU is 1055 joules that’s a 21 megajoule air conditioner. An air conditioner should cool at least 4.5 times the amount of electrical energy it uses so you are looking at an air conditioner that draws around 1.3 kilowatt-hours. If it ran continuously for 5 hours it would consume about 6.5 kilowatt-hours. But it’s unlikely to do run continuously unless it’s a heatwave, so you might need to ask someone who knows about air conditioning in Hawaii to get an accurate estimate.

    Hi sir, I’m trying to go solar for my home in the Philippines, I found an online calculator that says I need a 36.32 kWh battery to supply the 454 kWh/Month consumption I currently have. I found a 150 AH battery for P7,500 (AUD 192.47), will that be enough? I’m confused.

    Hope you and your family got through the recent hurricane unharmed, Gilbert. The estimate of 36.32 kilowatt-hours is about right for an American or Australian household going off grid with lead-acid batteries. You may need a very different amount depending on your electricity consumption and budget. If a 150 AH battery is the usual 12 volts then it will only hold 1.8 kilowatt-hours. I think it would probably be best to talk to people in your area who are installing solar and batteries. I’m not in a good position to be able to help you.

    Curious. trying to learn and improve. Electric bill shows 8kwh on days not home… Is that average or do I need to make some changes? 1350 sq ft home gas water heater and furnace. Thank you !!

    Hello Betsey If your home is using 8 kilowatt-hours a day when you are not there that is way above normal. Unless you have a large pool filter or something operating it’s very unusual. A refrigerator might use one kilowatt-hour a day, although it can be higher in summer. You can install monitoring to see exactly where your power is going: But just experimenting by turning things off may show you what is using the energy. If you find the electricity consumption is by something you can’t or don’t want to reduce then you would be very likely to benefit from solar. Note I am assuming you are in Australia.

    I forgot to ask in my previous post this question… If I install solar panels, and I can’t afford both these plus a solar hit e water system is there any reason why myself and others simply switch our electric hot water system from off-peak to only run during daylight and heat our water tanks using solar energy and thus save the 2 to 3 thousand dollars it costs to have a separate system? Surely, there’s a simple method to change the heating hours without the energy companies gouging their clients with extra fees etc… And I sure hope this wasn’t too dumb a question…

    Hello I recently got solar panels installed I was supposed to get 12 panels installed but only got 6. 335kw the contractor said that the 6 they installed produces the same as the 12 I was supposed to get. Because they are bigger panels. It’s a 2.0 solar system that I was gonna get but with the 6 I’m now at a 2.1kw LG panels with individual inverters and a electrical panel upgrade. what’s the average cost for this system?

    Hello Miguel This seems very odd. No one has made 170 watt panels for a long time so 6 panels will not do the work of 12. I’d suggest checking your quote to make sure you have received what was agreed. If uncertain about what you should have received you can send a copy of the quote to may email: [email protected] It sound like you have LG panels with microinverters. This is high quality hardware so a 2.01 kilowatt system, which is what you’ll have with 6 panels of 335 watts, can be quite expensive. I would expect the maximum reasonable price to be perhaps 4,000.

    I have a simple doubt. For example, if a solar panel produces energy of 4kwh per day does it means that it is producing the 4kw of power every hour. If it is so it will generate 94 kWh of energy for the whole day. Or else the second case is, it is producing 4kWh of energy in the whole day which means 0.166 kWh of energy every hour. What exactly is the case? Please do answer.

    Hi The rule of thumb for north facing solar on Australian roofs is it will generate an average of 4 kilowatt-hours per day per kilowatt of panels. The amount of power produced per kilowatt of panels will vary through the day as the sun moves through the sky and due to clouds. Unless there are exceptionally good conditions the power output will never be more than 1 kilowatt. Even in the middle of a sunny day it will normally be less than this due to various factors.

    Thanks for this information. I have a 1.5kW system that has been producing about 10kW/h per quarter in south east QLD over the past 2 years. Working on 7 hours of sunlight per day this equates to 1.7kW/h per day (0.24 per operating hour). The system was installed when the Govt was offering the rebates a few years ago. Is this system working to capacity or should it be producing more that this?

    Hi Uwe A 1.5 kilowatt north facing solar system in Brisbane that isn’t shaded should produce an average of around 4.1 kilowatt-hours a day when new. Because it’s an older system it’s unlikely to produce as much, but if we assume it is operating at 90% of its original capacity it should still be producing a average of around 3.7 kilowatt-hours a day. If it is only producing around 1.7 kilowatt-hours a day it is definitely under performing. UPDATE: I’ll jest check where you are getting your figures from, Uwe. If they are from your solar inverter you can be certain your system is under performing if it’s not heavily shaded. If the figures are from how much your electricity bill says you are exporting for a solar feed-in tariff, then your solar system could be fine and the low amount is because your home is directly consuming most of the solar energy produced.

    Hello Steve Helpful article, generally. But a slight criticism. You talk about salesmen and consistency etc. However, after talking in your first couple of sections about firstly power, then secondly about energy. NEXT HOWEVER, YOU REVERSE THE ORDER, and refer to energy then power. Most people would get a bit confused by this, and made me think twice. Thus, your own criticisms of sales people etc, esp in this generally dodgy industry, can be applied to yourself and your company. How can we trust you if you’re not Consistent. PS I’m not in the industry. Ken

    “I used 8KW yesterday” Actually both does and does not imply a time factor. “Yesterday” implies a day or a 24 hour period. So, they could have literally meant 8KW for the whole day or 333Wh/h At the same time, it does not imply a known time component and that they did consume a total of 8KW between some unknown period of time less than 24h. Maybe it was all within an hour? Then your assumption is correct. Maybe it was 4 hours? Although the accepted nomenclature does not accurately reflect it, KWh is a rate. It should be KWph,or KW/h like Mph or m/s

    many, solar, panels, need, 1000, month

    kWh is not a rate. kW (= kJ/s) is a rate. A kWh is a more intuitive unit for electricity consumption or production use than multiples of 3,600,000J. Now, for a bit of a brain-teaser, see if you can explain what you mean by “KW/h” (let’s ignore the capital “K”). :-O

    I am consuming around 10kWh on average per day. I have a 9kW shower used twice daily for a total of 30 minutes. I am planning a 3kW array and to use cheaper overnight energy to charge my battery. To get a free shower do I need a 9kW battery and hybrid inverter? My cooker is rated at 2.1kW, would it be cost effective not aim for a free shower and go for a 3kW battery/inverter. Meaning I could get free cooking. Also is it worth getting a larger system and use it for heating? Thank you for your help in advance.

    Hi Steve, Ronald here. If you have a 9 kilowatt electric instant hot water heater then a small solar system won’t do much to reduce its energy use. If you shower during the day a small solar system will help a little, but its still likely to draw a lot of power from the grid, especially in winter when hot water use is high and solar output is lower. While I don’t know your exact situation, my general advice would be to install a larger solar system (perhaps 6.6 kilowatts) and instead of getting a battery get an electric hot water system with a small heating element and a storage tank and and have it on a timer so it switches on during the day. This will be entirely powered by solar on most days and will store energy as hot water at a much lower cost than a battery. Because home batteries are still quite expensive they won’t pay for themselves for a home with below average electricity consumption like yours, so they are only worth getting if you don’t mind them not paying for themselves. While a larger solar system will produce more energy than your home uses, it will minimize the amount of grid electricity you use during the day and you’ll get a solar feed-in tariff for the surplus energy it sends into grid. Also, if you get a larger solar system you’ll be prepared if you decide to get a battery in the future or an electric car.

    Solar system size: Calculate yours

    It is now better to buy bigger due to the lower cost of solar panels, higher feed-in tariffs and the fast payback on additional kilowatts. If you can afford the upfront cost and have the roof space, we recommend selecting a system size of no less than 5kW; indeed, the new sweet spot of a 6,6kW system with a 5kW inverter is a good option.

    The price of a 5kW system varies according to your location but expect to pay between 5,000 – 8,000 for a good, reliable unit and a quality installation.

    Is the system cost or roof space an issue?

    If you are not able to stomach the higher upfront cost, or you do not have the roof space, then you should size a system according to your electricity usage, in particular during daylight hours. Let’s delve into the calculations.

    Solar system size calculator

    Household Details

    Postcode This tells us know how many sunlight hours hit your existing solar array throughout the year.

    Daily electricity Enter the amount of your household daily electricity usage in kWh. If you are unsure how much this is, you can find it on your last electricity bill.

    How much electricity is used between 8am – 6pm each day?

    This is an important component of the storage calculation. This tells us how much of your electricity is directly powered from your solar panels, and how much excess solar energy is available to charge your solar battery. The lower the % of electricity use during daylight hours, the greater the reliance on battery stored power.

    Can you afford to pay more than 6,000?

    It is possible to finance your solar storage solution. If you wish to take out a solar loan for your battery purchase and pay nothing upfront, select either the add to mortgage or the solar loan button.

    Do you have over 25m2 of roof space for solar panels?

    It is possible to finance your solar storage solution. If you wish to take out a solar loan for your battery purchase and pay nothing upfront, select either the add to mortgage or the solar loan button.

    Battery storage

    Do you want a solar battery now or within 3 years?

    It is possible to finance your solar storage solution. If you wish to take out a solar loan for your battery purchase and pay nothing upfront, select either the add to mortgage or the solar loan button.

    How many solar panels do I need?

    The number of solar panels that you need depends on the system size that you select. However, you can have a different number of panels for the same size system. A 6.6 kW solar system can be made up of 16 x 410 W panels, or 18 x 365 W panels, it all depends on the efficiency of the solar panels you select. The higher the efficiency, the less solar panels you will need.

    Physical size of solar panels

    A 5 kW solar system may produce enough energy to power your home, but you may not have enough roof space for a system of that size. Solar panels for households typically come in the standard dimensions of 1.70m x 1.00m, that’s around 1.7m2 for every panel installed. However, the wattage output (W) of the panels will likely vary between 360W and 415W for a more efficient module.

    As a guide, you’ll need 14 x 360W panels, or 12 x 415W panels for a 5kW system, the modules will require anywhere between 20.4 – 23.8m2 of roof space.

    Why we recommend a larger system

    We recommend selecting a larger system size than what you may necessarily need; so long as you can afford the upfront cost and have the roof space. Our primary reasons for this are:

    • Higher feed-in tariffs
    • Lower cost of larger systems
    • Faster payback: cost vs value of additional kWs
    • Future planning for storage or greater use

    Higher feed-in tariffs

    Higher feed-in tariffs have made the solar payback and savings equation more appealing. Where once it was desirable to select a system size that met your daily needs, now you can select a larger system and be better rewarded financially for the excess power that you export back to the grid.

    Economies of scale of buying bigger

    The key cost difference between a smaller system and a larger one is in the labour time it takes to install the unit. It does not take a solar installation team much longer to install a 5kW system than it does a 3kW system. You will need a larger inverter and more panels, but the additional cost of these added components is relatively cheaper.

    Cost vs value of additional kWs

    If we look at the cost of different sized solar panels, it’s clear that the larger the system, the cheaper the price per kilowatt (kW). We can explain this by comparing solar panel in Sydney for 3kW and 5kW solar systems:

    The price you will pay per kilowatt:

    Fast payback on additional kWs

    The cost of increasing the size of the system to 5kW is only 657 per kW. If we assume that you receive a feed-in tariff of 11.1c for every kWh you export back to the grid, it will only take 4 years to pay back the extra 2kW; this is assuming that all of the additional solar power output is exported back to the grid. If you self-consume the power, it will pay back much faster. You can expect the panels to continue generating solar power for another 20 years.

    System size if you cannot afford a larger unit

    If you cannot afford, or do not want to buy a 5 or 6.6kW solar system, then you need to calculate the amount of electricity you consume during daylight hours and work back to find the right system size.

    System size based on daylight electricity use

    The average Australian household consumes 18kWh of electricity each day. If we use a house in Adelaide as an example, you would need a 5kW solar system to generate this amount of power. However, if the household only consumes 40% of its electricity during daylight hours, there is no point in installing such a large system. In this instance, a system that generates on average 7.2kW (40% x 18 kW) of electricity per day would be sufficient. Therefore, a 3kW system is likely to deliver the most affordable solution.

    Consider lower winter output

    Due to a shortage of sunshine hours in the winter months, the solar panel output is significantly less. Ideally, you want a solar power system to generate enough electricity to power your heating needs in the depths of winter. We look at the effect of winter generation on your system size decision using the example for a Melbourne property below:

    The output of a 5kW system:

    In this example, a 5kW system will produce enough electricity in winter to power the daylight usage of 7.2kWh. A smaller system would not be able to generate enough electricity to power the household’s daylight energy use in the winter months, and this is another reason why selecting a bigger system size is the best way to go.

    Considering adding a battery?

    If you are planning on installing a panel and battery system, the system size equation can change. Your solar panels need to generate enough to directly power your appliances during the day and charge your battery. If you can afford a 6.6kW system and have the roof space, then you may not need to buy more solar panels to charge your battery. The size increase depends on how much battery storage you believe you need and, your solar expectations during winter months. Consider the example for a Brisbane property below:

    A 6.6kW solar system in Brisbane would generate, on average, nearly 28kWh per day. Enough in theory to power the household’s electricity day and night, in this instance, 25kWh.

    The output of a 6.6kW system in Brisbane:

    The winter output of the 6.6Kw system of 18.9kWh nearly generates enough to power the total daily electricity use, which includes charging the battery then drawing on that power at night. However, if the winter electricity demand was higher and more like the daily average of 25kWh, then the household should consider a system size of 8.5kW or more.

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