Now sit down for a second kiddies, and let Uncle Pfitzy teach you a couple of things about electricity.
Power is not equal to energy when we're talking grid thingees. And I still have to keep reminding myself of the difference in casual conversation.
ENERGY is the capacity of something - it usually refers to the capacity of batteries in this case, and is measured in MWh or Megawatt Hours.
So when someone says "She's a 300MWh setup mate" they're referring (laconically) to how much storage the thing has at maximum.
POWER is the rate at which energy can be delivered.
When the same someone says "She's a 20MW setup mate" they're referring to how much power can be delivered at a given moment.
Use the water tank analogy: energy is the tank, power is the pipe.
To put
that into perspective: my house at any one time might draw between 200 Watts (or 0.2kW - when only the fridge is on at night) up to 12kW when the wife decides to go menal with the air con, the oven, the fucking microwave, blender, etc.
Every 1000W = 1 kilowatt so if that is per hour that's 1kWh of energy consumed. Geddit?
If you want to understand your usage a bit better, dig out your bills, look at each of the rates you pay, and the number of kWh assigned to those rates. Careful: you might learn something.
I know from looking at all my charts and bullshit (
http://unleashthepowerwall.com/statistics/) that I consume about 17kWh per day, or an average of 0.7kWh per hour. From looking at my old bills it was higher than that - in the range of 21 per day.
Now to the balls of the argument - let's say we're talking about:
- 300MWh battery
- 20MW output
- Houses drawing 1kW on average across the day - or 24kWh per day
If the shit hit the fan and the coal fired piece of ancient dog shit up the road died, how many houses could run off this facility, and for how long?
Welp, we have 20MW - or 20,000,000 Watts - of output to feed houses drawing 1kW - or 1,000 Watts - at a time. That's 2,000,000 / 1,000 = 20,000 houses.
And for how long can we do that?
We're running at capacity of 20MW and we have 300MWh of battery storage at full.
300 / 20 = 15 hours. So that is a fair bit of juice in the tank.
The problem of course is that the grid comes under pressure (peak) during times of excess usage, like the shitty hot days we had back in Feb. At that point, my house is importing about 5kW to power the air con and related family bullshit that I'm not already running off my solar. Bump assumption 3 up to 5kW per residence.
Suddenly we only have capacity to run about 4,000 houses, but still for 15 hours.
As you can see, a 20MW power output is fairly shit. you're not going to do much with a pipe that big when your tank is massive. Its almost a stranded asset at that point. With 300MWh of energy, 15 hours is your best-case scenario (which is also your worst-case because people be losing their shit on hot days).
Far better to get the energy and power to have a ratio well under double-digits. In this case, if we could deliver 100MW off a 300MWh facility, we can service 5 times as many houses, even though the energy will only sustain us for 3 hours.
Mostly, that's what you need to meet a peak demand, so everything there should be good.
And if half of those houses have a solar setup of their own, and only need a couple of kW here and there, you can spread your reach a lot further.