Archive for November 2013
I think it’s time we talk about solar energy.
We now have 337 homeowners living in solar all-electric urban infill townhomes in 8 coastal California cities. They’re enjoying having no monthly natural gas bills, and depending on usage, little or no electric bills. The reason I want to talk about solar energy because even though it’s easy to understand that monthly utility costs are lower for everyone in these townhomes, many people do not understand what is actually going on and how this is all happening. I thought I’d use the Blog to take the education to the next level.
In the world of energy, understanding kW (kilowatts) of installed capacity is different from kWh (kilowatt hours) of production.
Power is the rate at which energy is consumed or generated.
The Watt is the unit of power used in the residential electricity world. A 1000 watt device consumes 1000 watts of power (not energy) while it is operating. Likewise a 1000 watt (1kW) solar system generates 1000 watts (1kW) of power (not energy) while operating at premium efficiency and capacity.
A kilowatt is equal to 1000 watts. The kilowatt is the most commonly used unit to describe the power rating of residential solar arrays and residential consumption.
Energy is the amount of power consumed, or generated, multiplied by the amount of “time” it is operating. A 1000 watt device turned on for 1 hour would consume 1kWh of energy. Likewise a 1000 watt (1kW) solar system operating at premium efficiency and capacity would produce 1 kWh of energy. Therefore a 1kW solar system that runs for 6 hours at capacity produces 6kWh of energy.
During a typical month, a homeowner will run all kinds of “devices” that require power. When you multiply the amount of power they require by the amount of time they’re operating, you’ll end up with a monthly number for the amount of energy the home used in terms of kWh’s. Ten 100 watt bulbs on for 10 hours will be 1kWh. At the end of the month the power company will send you a bill for the amount of kWh’s used times the amount per kWh they charge. That’s your electric bill. Most companies now “tier” their pricing but that subject is for another Blog. Assume they charge 22 cents per kWh and assume you used 350kWh in your 1500 sq ft townhome and your bill would be $77 for that month. Simple math.
Now let’s say you’re a City Ventures Greenkey homeowner and you have one of our standard 2.1kW solar system installed on your roof. During the day that system generates power. If you assume a 6.5 hour day of sun and an efficiency rate of 85% (also a subject for another Blog), then you have produced about 350 kWh’s of energy during the month. If you’re not home during the day that power goes into the grid and the power company sells it to power other devices in other locations. They “pay” you for that energy your system generated by crediting the amount of kWh’s generated, against the amount of kWh you use during the month and charge you an electric bill for the “net” amount. Because you live in an all-electric townhome, you use about 15% more electricity power than the townhome in the example above. Your townhome uses about 400 kWh instead of the 350kWh the non all-electric townhome consumes. The generated solar energy is 350kWh and the consumed amount is 400kWh, which leaves a “net” amount consumed of 50kWh. At 22 cents per kWh, your electric bill would be $11. Same size home. Same basic energy consumption rate. But a massive reduction in utility costs…. because remember the Greenkey home has no gas bill either.
A true net zero energy home would be one that generates the same amount it consumes therefore requiring nothing “net” from the grid. That is true sustainability and something Mother Earth loves to hear. The ultimate City Ventures goal is to get to net zero energy in 100% of what we build and we’re well on our way to achieving it.
Until next time