Driving your home appliances with hybrid power

This system of hybridizing your home’s electric appliances is an interesting take on solar energy. It focuses on seamlessly switching appliances from the grid to stored solar energy as frequently as possible. There’s a promo video after the break that explains the setup, but here’s the gist of it.

Follow along on the pictograph above. We start on the left with solar panel. This feeds to a charger that tops off a 12V battery. When that battery is full, the charger feeds to the inverter which converts the 12V DC to 110V AC power. This is fed to a pass-through which is in between the appliance (in this a case a lamp) and the wall outlet. The pass-through will switch between mains power coming from the outlet, and the 110 coming from the inverter. The homeowner won’t know, or care, which power source is being used. But sunny months should result in lower energy bills. The real question is how long it takes to cover the cost of the system in saved electricity.

Comments

  1. scott says:

    If you really want to save energy, you just use a 12VDC lamp run directly from the battery and ditch the inverter… you waste quite a bit in conversion on most devices.

    • n0lkk says:

      The solar net wiki is interesting, and worthy of being featured in a Hackaday post. True if one is planning to build an off grid home from scratch, DC only lighting circuits should be a part of that plan. There are so many variables and many have plan within the constraints of an electrical code, codes that are sensible for the most part. The nation electric code in the US anyway, although some jurisdictions add BS requirements. In the event ceiling fans are going to be installed, on can expect some overhead lighting to be operated off the inverter. An inspector isn’t going to allow 12 V and 120 V coductors in the same fixture , but YMMV.

      • adcurtin says:

        “An inspector isn’t going to allow 12 V and 120 V coductors in the same fixture , but YMMV.”

        I’m curious about this. Some old homes have low voltage switching, which is 24v. If it was planned in advance, they probably have all the relays in a central box somewhere. If not, however, they often put the relay in the fixture with the light, which would result in both 24v and 120v in the same fixture. Why would it be any different with 12v?

    • zokier says:

      Wouldn’t 12VDC system have quite high transmission losses? eg 10 meters of 2x14AWG cable would have 160mΩ resistance, so driving a 60W load over it would cause 4W loss over the cable. Same 60W load over 48V system would cause 0.25W loss, and 110V -> 50mW loss.

      And 60W is quite modest load, losses would be even greater with larger loads

      Of course, I’m not a electrician or EE, so maybe I’m horribly wrong about this, but afaik the reason for 110V is to avoid transmission losses.

      • n0lkk says:

        12 volts will require larger conductors to have comparable loss to 110 volts in the same circuit. I suppose the extra cost could make using a inverter feasible, but compensating for losses in the inverter costs money too. I have yet to make myself grid capable, but I’m finding planning for that is lot ,ore involved that setting out to wire a building to run off the grid.

    • EccentricElectron says:

      12V direct works fine for low current items, but the currents soon become unsustainable for larger items. There’s also the problem of sourcing switch gear rated for those currents suitable for use in the home – you can’t use normal AC rated switches.
      I live off grid, and in the end I decided it just wasn’t worth the hassle and standardised on 240V – initially with CFL lighting, and now with LED (which are 5 times more efficient than CFL for the equivalent light output – my batteries love me for it). The inverter is 97% efficient, and the convenience of being able to use normal wiring, switches and appliances outweighs the 3% loss.
      Having said that, I did make a couple of exceptions to the 12V rule – I run water pumps and have a car cigar lighters for running phone chargers etc. direct off batteries to do away with wall-wart/transformer inefficiencies. And because I live in a remote location, I have a ship-to-shore radio for emergencies that is powered direct from a standby, solar powered battery bank to guarantee availability.
      No hacks here, but it is reliable :-)

    • n0lkk says:

      @adcurtin that’s why a I appended YMMV :) The low voltage switching I’m familiar with to keep the line voltage and low switching voltage separated. While this is a relay I’m not familiar with but it shows how separation can be accomplished http://www.galesburgelectric.com/GE-RR7P-20A-SPST-Low-Voltage-Relay.html The relay body and low voltage conductors remain outside the fixture. but the portion that switches the line voltage is inside the fixture or electrical box serving the fixture.

  2. SeeMikePlay says:

    “Try building one for yourself.” You know… just pick up a $50 car battery, a $40 inverter, a $400 solar panel and $30 in components, and you can charge a 60 watt lightbulb which would have cost $10 a year to power on grid power.

    This is not economically or environmentally feasible. It’s just fun. The manufacturing of the solar panels alone would have a higher impact on the environment than running a 60W light bulb ever would.

    • EccentricElectron says:

      Do it, but don’t use a car battery – they are not designed for this kind deep cycle use, they are designed for cranking (high current discharge, short duration) and you will be throwing you cash away. Pick up a mobility scooter, golf cart or “leisure battery” instead.

      • Sarang says:

        His point still stands

      • EccentricElectron says:

        @Sarang except his sums are wrong. $400 panel = 235Wp. Depending where on the planet you are, that’s going to generate upwards of 500kWh a year. The rest depends on how much you pay for grid electricity, and whether or not you consider this to be more environmentally friendly. Of course a REAL hacker makes his own panels, he doesn’t buy off the shelf, in which case the real capital cost of the panel is more like $100 + your time, and the payback period is much improved.

      • ar0cketman says:

        You are correct that car batteries do not handle deep cycle discharge well before dropping chunks of the plate into the bottom of the cell. However, car batteries can still be the low-buck winner. Due to overwhelming market penetration, used batteries can be obtained for a song, sometimes you can be paid to haul them away. Sure, you’ve got to crack the built up sulfide layer and they will always be weak, but on a amp-hour/dollar metric, they can’t be beat.

        New car batteries generally have a nice pro-rated warranty; if you deep cycle them too many times, just pay a small cash fee to get brand new batteries. Repeat as needed.

  3. Mike bradley says:

    I am curious, what about a small UPS, because it houses most everything, and there is no output interruption on switch over, so use a relay to cut mains, and the solar cell or any other alt form of power to charge the battery

    • The DON says:

      I agree …..

      I have a concern about his setup though, that being regarding the phase of the supplied power. A light bulb wont care a jot, but some other devices are more sensitive to that sort of thing.

    • adricm says:

      Ive done that before, the trick is finding a dumb enough ups to let you do it. alot of ups’s wont let you switch to battery until they dont see AC, and lots of ups’s wont power up if the power is out.

      i ran one without a battery in my car for a while, to run small chargers and appliances off of, trick was to find a small 12v based ups.

      later i did try to convert another one to be solar charged, it worked, but ran into problems with it powering off rather than switching back to AC when batteries were low. with this systems external control box it could be done…

  4. n0lkk says:

    1; yes probably not “green”. 2; initial cost means that few will duplicate the project. 3; This may kill most LA batteries in short order. 4; while I know 120 V converters don’t actually have a neutral, the neutral conductor wiring convention should follow from both power sources to the load. 5; my eyes are bit foggy today and I can’t tell if this will fail in a manner that will NOT connect the inverter output to the utility. Finally I hope this comment is seen as being too critical of some that engaged in DIY and posted his project to the world to review and consider.

  5. rallen says:

    The cheap, low-tech, way of powering a light is to go get a couple $2 LED landscape lights and put them in the window to charge. When it gets dark, you have light!

    Honestly, this is a simplified model of conventional hybrid electric installations today. It’s actually pretty accurate. Scale everything up, and put the isolation switch in the power panel (as required by code), and you’ve created a modern off-grid home.

    Nice!

  6. echodelta says:

    Imitations of whale oil lamps are not the way to the energy future. 12 volt is the earths truly universal standard, use it in it’s direct context. I have a Pioneer car stereo that is the heart of my system, it gets FM 2 horizons away. Another 110v model is for the local public station. When all else fails (besides ham gear)I would like this to work and the internal amplifier power get routed to the speakers that normally are on the ‘big amp’. Next would be led lighting in hall bath kitchen things that are mostly on at night. All good for low voltage solar. Bulky battery tech is still good for this. If you want to go lithium , put them on a electric bike. Green means getting it done with the best of what fits the situation.

  7. Dr. James says:

    Mains voltages created from inverters should be reserved for those devices which cannot be converted to 12V and are low enough power consumers to make them practical to power up for occasional use with 120V or 240V. One such device might be a microwave oven. Even if you have a large battery bank backed by a large array of PV panels, it would not be wise to heat water with electricity from battery powered inverters, especially when solar water heaters do the job quite nicely and far more cheaply.

    From someone who has lived off the grid for 15 years, it is necessary to pick and choose amongst the available technology in order to maximize efficiency. For example, it’s not wise to use an inverter to power mains lighting circuits, even if it were true that general use inverter/chargers could be 97% efficient (they are not). Instead, all task lighting should be converted to 12V LED fixtures while keeping area lighting down to a minimum. Convert your own fixtures (see Instructables) to 12V, or buy them on the marketplace. Take a look at the lamps offered by Alpenglow.com for examples of very efficient off grid LED lighting.

    My 400 Watt PV array with MPPT, 600 Ahr battery bank, and 1KW inverter/charger provides all the electricity needed for two people in a small house, including computer use, small appliances, water pumps, and occasional ham radio usage. During longer periods of heavy clouds, a propane fueled backup genset takes care of the batteries. Which is another point — make sure you normally have enough sunlight available to make solar power feasible. If you do have enough sunlight, great! Draft your energy budget, create a plan, and go for it.

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