Saturday, March 14, 2009

Hooking into the power mains

I know that it's nice to aim to be completely self sufficient power wise, but I'd like to suggest some consideration for the benefits of not being completely disconnected from the city power. Every estimate I've heard concerning batteries and electrical storage is that they're terribly inefficient. See our discussion on this post.

Many clean electricity projects aim to look at net consumption of power from the mains. This means that they hook themselves up to the electrical mains like everyone else in the city but also have small-scale forms of energy production. Then when they need energy they use what's available from their own sources, and if they need it, from the mains, and if they have extra energy at any given time that energy goes back into the mains. The goal being to produce, overall, the same amount of energy as is consumed. The Solar Decathlon generally seems to work under this model.

Unfortunately, the almost permanent availability of energy in this scenario is more conducive to excessive use of electricity than having to use only what you've just created, but I think that's acceptable to most people who want the house to be usable and livable.


  1. I think this is definitely worth considering- it's a balance, right? If people have to be aware of where their energy comes from, then they are less likely to use it carelessly. Of course, convenience is something we've become accustomed to, and we don't want to scare away users because they are worried that they might have to deal with technicalities.

    I think that one way to deal with this would be to build the prototype and connect it to the grid, then test it to see if we can produce more energy than we consume. It's one of those things that may need to be tested onsite.

    I've also been playing with the Kill-a-watt you gave me, and I've got some questions. We'll meet and chat- most of my questions have to do with the relative meaning of the different measurements of power. I'll document, then we can do research on specific power sources.

  2. RE: Rachel's Electrical Education

    Here's a really good link describing the values that you will find important in measuring your input.

    Important one that I think will help you with interpreting your data from the Kill A Watt:

    W = V*A

    This means that the Watts(power) of a connection is the product of the Volts(forward bias) and Amps(current).

    My reading on this subject is not that great, but I know how to put this information to work. Perhaps Dan could help out with a good description/verification of the validity of the site?

  3. I also have a bunch of Forrest Mim's books on electrical wiring which contain useful formulas and information, with which we can interpret the results.

  4. Net metering and time based power usage costs (Smart Metering) is the next big thing to hit North America.

    Net metering is pretty simple, you sell power back to the grid, and therefor power the houses around you. You need to have some method of providing VERY clean power back, and in order to install you usually need to get certified from the hydro company. (A company called Xantrex makes these grid tie inverters)

    Smart metering passes the electricity market to the consumer. Unlike gas, electricity is VERY hard to store. Batteries are slow and inefficient, and contain lots of deadly components, and other methods don't store enough power. For this reason, power companies pay up to 10 times as much for power during peak hours as on off nighttime hours. This led to the famous "rolling blackouts" and factories shutting down at peak hours because the could make more by re-selling their allotted power usage.

    These together can be a HUGE push for solar energy, as you can produce power for people to run their air conditioners, or what have you, and then pull power from the grid at night. This ends up being hugely economical, not just in the small scale for a single dwelling, but it can change how the electricity infrastructure needs to be built to deal with peak power demand.