1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How can I be energy independent?

  1. May 5, 2014 #1
    I am thinking about acquiring some battery storage units for single residential house. What is the cheapest and efficient battery for homes and where can I buy it? Would it be bloom energy, fuel cell or solar panel( transparent)?

    What are some creative solutions? One idea was next to a river and turn a small hydroelectric while the other is the classic solar rooftop?

    Thank you my brothers.
  2. jcsd
  3. May 5, 2014 #2
    How much energy are you looking to use?

    If you are doing this for "environmentalist" reasons you will probably make less impact on the environment by connecting to the grid.

    If you are doing this for "survivalist" reasons then you should need little to no electrical energy.
  4. May 5, 2014 #3
    Disappointed :(
  5. May 5, 2014 #4


    User Avatar

    Staff: Mentor

    Um....we can help you do something useful if you explain exactly what you are trying to do. How much electricity do you currently use, for example?
  6. May 5, 2014 #5
    Not exactly sure what number but the average household city uses.
  7. May 5, 2014 #6
    Thats quite a lot. I doubt you will be happy with the requirements...

    To consider it, first look up the average household energy usage. Here a key thing to know is the difference between a kilowatt (kW) and a kilowatt-hour (kWh). A kW is a "rate" of energy usage and a kWh is an "amount" of energy.

    Then lookup how many kW's a solar panel can produce. Of course this will not work at night, or in clouds, etc. Multiply the kW's the solar panal can produce by the couple of hours a day it will work to get kWh. You can then lookup battery's charge capability. Note these are usually listed in "amp hours" and you need to convert that to kWh by multiplying the amp hours by the voltage and dividing by a thousand. This is not all though. Because batteries are DC and your devices probably need AC. So you need some kind of converter to convert the DC from batteries to AC. To me, this all seems like a very expensive and fruitless task.

    A different option might just be to run multiple gas generators. I did a quick google search, the average house uses 900 kWh per month. With 730 hours in a month that is an average of 1.23kWh per hour or a rate of 1.23kW. This is average though, you probably want much more than this for peak usage. A home dryer for example uses many kWs. I just googled gas generator at walmart and its $5000 for one that produces less than 1kW. I googled how much gas they use and got roughly a gallon an hour. So you are looking at 24 gallons of gas per day and you wont even have enough energy to run one clothes dryer. I found this on a forum which seems to be more efficent than my quick googling, but still does not seem like a good idea if you have access to a grid,
    There is a reason we have a grid. Its better for the masses by making electricity affordable and better for the environment via the economics of scale. If you want to help the environment, best to try to minimize your electrical use. If you want to get a solar panel, it may or may not pay for itself. But trying to store energy via batteries is not going to work out well. Running a generator is equally prohibitive both with respect to cost and the environment. If you want a survivalist lifestyle you should give up on the idea of having an average house with of energy use.
  8. May 6, 2014 #7
    Life is hard. Can nikola tesla concept of wireless electricity help the environment or will it destroy the magnetic field of the earth and allow uv rays killing humanity ?
  9. May 6, 2014 #8
    Neither really... Its an overblown concept that is often embraced by crackpots. We already use/harness wireless energy in a variety of fashions (solar cells, radio transmissions, electric toothbrush). The energy involved is very low. That's why we need to plug our radios in, because the energy they collect from the incoming radio wave is not even enough to power the speakers - its needs to be amplified using batteries or a plug into the wall.
  10. May 6, 2014 #9
    What about the so call fuel cell, one individual claims he can you hydrogen to power a car? Is he a crackpot too, or is the concept of using hydrogen is lot feasible? Thanks for your response.
  11. May 6, 2014 #10


    User Avatar
    Science Advisor
    Homework Helper

    There is nothing crackpot about the basic idea of hydrogen fuel cells. They are already in use in "static" applications like combined heat and power systems, and also for space exploration.

    On the other hand there is a huge amount of crackpottery on the web about "cars powered only by water".

    First you have to make the hydrogen. There is a lot of hydrogen already being made for use in the chemical industry, but most of it is made from methane in natural gas and the process produces as much carbon dioxide as using LNG directly as a fuel. So there's nothing very "green" about that. On the other hand, if you are running an industrial plant that already uses a lot of hydrogen, you might as well use a small percentage of what you generate on-site for something else.

    Companies like Honda and Toyota have made concept cars powered by fuel cells, but it will probably be decades before they start rolling off the production lines (and it might never happen).
  12. May 6, 2014 #11
    So much for hydrogen fuel cell idea. We might as well go to war for oil or go plutonium in nuclear energy. What about one idea about using thorium in nuclear energy instead of uranium?
    This is one last hope for humanity. Otherwise let us pray :)
  13. May 6, 2014 #12
    A mixed bag is probably best. A little oil, a little natural gas and coal. Some nuclear and of course some alternative fuels where they are viable. I think (not my original thought of course) that women's rights will play a big role in reigning in humanity's increasing population and consumption. Where women have rights women have birth control and families become smaller and more educated.

    Otherwise, its somewhat inevitable that extinctions will happen, habitat will be lost and climate will change. Coping with that is just as, if not more, important than trying to prevent it.
  14. May 7, 2014 #13

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Glad you feel that way.

    There's no painless way i know of to be energy independent at individual level, which i think is what you're asking.

    Falling water powering an alternator would be my first choice. Keep your turbine or waterwheel free of debris and it should last decades.
    Golf cart batteries and an inverter, around 1kw, to run a small refrigerator and efficient(LED or CFL) lights and radios. You'll have to replace the batteries every six years or so.
    Solar flat plate collectors to heat water - dont even think about heating water from 10% efficient solar electric cells.

    If you're going to live in the woods off grid, i'd suggest a steam boiler and gather wood for fuel.
    That'll let you charge batteries and it'll keep you occupied tinkering with the engine(remember "African Queen"?). There ar plenty of interesting youtubes...


    If you're urban, solar water heating is my choice to reduce electric bill. You can't beat electric company's rates for running a fridge and entertainment systems, though.
    If somebody would come up with a residential solar booster for airconditioning he'd make a fortune in the sun belt.
  15. May 7, 2014 #14
    Interesting, the last response should give the audience new ideas. Aside from that,

    The idea of transparent solar cells inner greenhouse farming will this help the farmers from migrating the old way to new way, urban farming.

    Just a random question if anyone will respond.
  16. May 8, 2014 #15
    Energy independence

    Assuming you are planning to run a normal household in a temperate climate with electric cooking and heatpump heating/cooling/hot water you would probably budget on 25-30kW.hr per day. If you make a high efficiency house, heavy insulation south (sun) facing double glazing and large thermal mass, efficient lighting LED or CFL and efficient appliance you can get that down to 7kW.hr per day or less.

    Some people get down to about 3kW.hr per day. Even in winter a solar power system will generate about 2-3kW hrs. per day/kW installed. However you need storage at night and on rainy/cloudy days.

    I would suggest that you should have both battery and thermal storage. So you have a a highly insulated hot water tank of 150 to 200 gallons and battery storage. If you are in a cold climate you can have a wood heater with auxiliary water heater built in, because your heat pump hot water system won't work very well below -2-3C. Depending on where you are you can use direct solar water heating but often these days solar power and a high efficiency heat pump hot water system is more cost effective. In some cases you could replace some or all of the solar with wind but most small wind systems are very ineffective unless you have a lot of wind and/or a very high mast which brings cost and planning issues

    If you have a thermally efficient house with auxiliary wood heating etc. you probably need about 10-15kW.hrs of battery storage and 4kW solar. In Australia that would cost about A$25-30,000 (US$20-25,000) plus all the other energy saving measures. If you have a standard house you probably need 8kW solar and up to 30kWhrs of battery storage. Ideally you don't want to discharge the batteries more than about 40-50% in normal operation. The cheapest battery systems are Gel or deep discharge lead acid. However they will only last 5-6 years maybe 10 if you don't cycle them too deeply. Lithium based systems are now becoming available but they are more expensive but last 2-3 times as long so the lifetime cost is lower as long as you can afford the upfront cost.

    A small gasoline or diesel generator could be installed as extra backup. If it is only to run about 100-300 hours per year you may be able to get by with a camping style 2-3kW generator rather than a heavy duty system primary supply system. You can then reduce your battery pack by about 1/3rd and more than pay for the low cost generator with the savings in the battery pack, but then you have fuel costs and noise.
  17. May 8, 2014 #16
    Maybe golf cart batteries
  18. May 8, 2014 #17
    Any batteries that are designed for long life, deep discharge. They have to be well ventilated and cannot be allowed to get too cold or particularly too hot.
    In the extremely unlikely event that you are drawing full power for an extended period on a hot day there is a small risk of fire, but while the risk is very small if there is a fire it can be very hard to extinguish. The fire risk however is smaller than that from a faulty oil or wood heater and in most cases the batteries can be housed outside the main structure
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook