When planning a home renewable energy project you need to work out what it is you want to achieve first. Do you want to produce a certain proportion of your electricity needs or are you aiming for 100% electricity production to effectively take you "off grid"? Perhaps you even want to go as far as producing more than 100% of your own needs so you can sell the excess back to the energy companies via the grid. To be able to do any of these things you need to know how much you use.
You can guesstimate or find some stock values to use if you're not too bothered or you can try and get a more accurate figure for your energy usage. When I say accurate we don't need to win any awards here, a rough figure is fine, we don't need to go into efficiencies of appliances and measure exactly what voltage you're receiving in your house (it's usually not exactly the "standard" value for your country). In this article I'm going to show you two ways to get an accurate enough maximum usage figure for all your appliances.
You can go out and buy an energy meter which works by unplugging your appliance from the wall, plugging the meter in then re-plugging the appliance into the meter. Some are more sophisticated than others, we want one that will give you an instant power consumption reading in Watts (W). Most will also give energy consumption in Joules (J) as well and various other readings. We want a kilo-Watt figure (kW). Some meters will also give a kilo Watt hour (kWh) figure but you don't really want to spend an hour for each appliance to achieve this and we don't really need it. Simply go round your house and measure all your appliances noting down each one on a piece of paper as you go. At the end add them all up and that's the maximum amount of power you will need but remember that many appliances use different amounts of power in different states. A TV, for example will use much more power when it's on than when it's in stand-by mode. A computer uses more power when it's booting than when it's just sitting doing nothing on the desktop, it will use more whilst playing a game than when word processing. Some appliances are "hard wired", often electric cookers and water heaters are like this so you can't use the meter and will have to use the calculation method which I will detail next.
There are many complications you can bring to this method including VA vs. W but I'm going to gloss over all the complexities and make this very simple to do. There are power factors for efficiency and the different power states mentioned above but we'll not concern ourselves with those here. On the back of any appliance there should be a sticker or plate that tells you what voltage it operates at -- V -- and how much current it draws -- I -- measured in Volts and Amps respectively. The formula you need is P = I V. Power = Current x Voltage. As mentioned above "standard" voltages vary from country to country and even within countries depending on the quality and age of your local transformer and the quality and age of cable from the local transformer to your house. Then there's your house's wiring. Don't worry about this though, just use the "standard" value for your country.
In the USA the standard mains Voltage is commonly known to be 110V (although it's supposed to be 120V). My information for Canada has both 120V and 240V so I'm afraid I can't help you there, you'll need to find out for your self. In parts of continental Europe it was 220V and the UK 240V but has now officially been harmonised at 230V although it will be some years until this happens in practice in all areas. Australia it is commonly known to be 240V and New Zealand 230V. As an aside most appliances from anywhere within Europe, Australia and New Zealand will work anywhere else within these areas as they'll work from 200V to 250V, you'll just need a socket adapter. Many modern appliances with a switch mode power supply will work with 110V too without the need to move a switch like you used to see on the back of old computers for 110V or 240V operation but obviously before taking your 110V appliance to Europe, for example, check it first!
An example: In the USA you have a computer monitor that states 110V 1.3A. Grab your calculator and simple multiply 110 by 1.3 to get 143W, write that down on your piece of paper and move onto the next. The same monitor in the UK states 240V 0.6A giving 144W, the same power consumption (allowing for calculation rounding) as in the US because it's the same piece of equipment but using a higher Voltage, it will draw proportionally less current. Ignoring "power factors" this will give you a good maximum power consumption figure for your appliance, most appliances will use less in normal operation.
Once you have all your appliances calculated or measured you can add them all up to get a total house maximum power consumption and simply use that (realistically though everything will not be on all the time so a proportion of that figure would be better to use but that's really a judgment call on your part based on your own usage habits) or you can get a little clever about it and sit down to work out which appliances are on for how long and at what times of day on average and calculate your peak usage in kilo Watt hours (kWh) which will be far more accurate if done properly but far more complex to do.
As you can see it's simple enough to do although a little time consuming. It is necessary though if you have a home electricity generation goal in mind, you need to know what you're "shooting for". One last thing, always remember your electrical safety!
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