A visual explanation
What the heck is the difference between a Kilowatt (kW) and a Kilowatt-hour (kWh)?! When looking over your solar proposal, you're probably trying to understand that before making the plunge. This question is one that puzzles many people, so here's the scoop.
When you get your electric bill, of course most of us just look at the total cost. But do you ever look closely at the number of kWh’s you’ve used - and do you know what it means? If you know what a kWh is, it can help you understand:
A kilowatt-hour (kWh) is a measure of how much energy you’re using.
It doesn’t mean the number of kilowatts (KW’s) you’re using per hour. It is simply a unit of measurement that equals the amount of energy you would use if you kept a 1,000 watt appliance running for an hour:
So, if you switched on a 100 watt light bulb, it would take 10 hours to rack up 1 kWh of energy. Or a 2,000 watt appliance would use 1 kWh in just half an hour. While a 50 watt item could stay on for 20 hours before it used 1 kWh.
It’s hard to be precise, as similar appliances can have very different wattage's, but here are some examples of consuming 1 kWh:
kW stands for kilowatt. A kilowatt is simply 1,000 watts, which is a measure of power. So a 1,000 watt drill needs 1,000 watts (1 kW) of power to make it work, and uses 1 kWh of energy in an hour. That’s why, if you leave a TV or computer on standby, it is still using power and creating a kWh cost on your energy bill.
For the purpose of relating to solar energy: A 260 watt solar panel may generate 260 Watts (or 0.26kW) of power when the sun shines on it. No matter how long the sun shines, 260 Watts will be the power output from the panel (more or less - this is a complicated area, but for now we'll just say it's 260). When the sun goes down, the panel stops functioning and 0 Watts are produced.
However, if you want to know how much energy this same panel will produce, we need to consider a time factor - how many kWh's can the same panel deliver in, say, 1 month? To answer this, we need to know how many hours the panel is generating power for each day during the month. Let's estimate 5 hours per day, for 30 days.
This means the panel will deliver 260 (Watts) x 5 (hours) x 30 (days) = 39,000 Watt-hours in a month - we can divide this big number by 1,000 so it's easier to read. This makes it kWh’s. So, the panel makes about 39 kWh's of electrical energy per month.
If you pay your electric provider 13 cents per kWh, then that panel would generate 39 kWh’s x .13 = $5.07 worth of electricity for that month.