What to do with unused energy?

soleilsoleil Posts: 45Solar Expert
One thing I didn't anticipate when I was installing solar on my RV, is what I would do with the energy generating potential when I wasn't using the RV. The setup works great when camping, but within a day or two of coming back, the batteries are fully charged and the potential of the solar panels is being wasted. One heck of a trickle charger. I wish I could think of something practical to do with that energy. Any ideas?

Comments

  • CariboocootCariboocoot Posts: 17,615Banned
    Re: What to do with unused energy?

    The bane of off-grid systems: "surplus" energy.
    In fixed location applications the popular thing (other than load shifting) is heating water. With a parked RV, you have to take into consideration the mechanics of hooking up the charge system to something else. You could drain power off the RV to run some particular circuit in the house, thus reducing your electric bill. Just be sure it is fully isolated from grid with a transfer switch and that the RV system has enough power to handle whatever load is applied (including maintaining good insolation) without draining the batteries too much.
  • techntrektechntrek Posts: 1,357Solar Expert ✭✭✭
    Re: What to do with unused energy?

    I was going to recommend the same thing, with one additional point. Make sure whatever circuit you choose is a base load so you get the most out of the system. A fridge, freezer, cordless phone, clocks, TV that you watch every night. Whatever total load it will handle. Usually the base loads of a house are in the range of 300-500 watt-hour 24/7, and most of that is fridges, clocks and wall-warts. Another advantage to putting your fridge and/or freezer on it is you don't have to worry about them during an outage.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • dgsloandgsloan Posts: 22Registered Users
    Re: What to do with unused energy?

    I have hooked up my RV so that after charging the batteries it dumps the load (wind type charger) into a GTI - that way when I am plugged into the house it feeds the power back into the grid. Unfortunately there are no "approved" GTI's for this purpose that run 12v in and 120v out, so you have to make sure that you have a proper GFI and overheating protection. An inverter (12 to 120v) is an option but you have to find a constant load to look after this senario. Yard lights to drain the battery is an option - I use a 50w LED to run eight hours when I am not connected to the grid, which allows me to store my RV in a farm yard and light up a couple of acres of land.
  • soleilsoleil Posts: 45Solar Expert
    Re: What to do with unused energy?

    Thanks for the ideas. dgsloan, your lighting idea might be easiest and not require use of my inverter. My RV is parked so it's back is near my garage, where I have a couple lights on at night. As you suggested, I could use the RV's light instead of the garage house light. I would just need to figure out how to get the RV light to be switched with a dusk to dawn sensor. Do they have those for 12V, or would I have to make something myself?

    Would the additional wear on my batteries be significant rather than just let them sit and float all the time? I don't want to ruin my not cheap batteries just to save a few dollars on electricity.
  • BB.BB. Posts: 24,676Super Moderators admin
    Re: What to do with unused energy?

    NAWS has 12 volt timer and even a 12 volt motion control sensor (which I prefer for security lights anyways).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bmetbmet Posts: 630Solar Expert
    Re: What to do with unused energy?

    The spec sheet doesn't say what the illumination is for that product, only that the 'lamp' is supplied with the product. I wonder if it could be used with those DC lights that NAWS also carries?

    Right now I have a low wattage AC lamp for an exterior light, but if I could use all DC products that would be nicer.
    BB. wrote: »
    NAWS has 12 volt timer and even a 12 volt motion control sensor (which I prefer for security lights anyways).

    -Bill
  • BB.BB. Posts: 24,676Super Moderators admin
    Re: What to do with unused energy?

    Inductive DC circuits can be hard on electronic and mechanical relay contacts. But you can "fix that" with a clamping or snubbing diode between the device + and - power lines.

    I have not used their products--so you have more detailed questions, I am sure NAWS would be more than happy to address them.

    Do you have a couple of devices you are interested in connecting together (i.e., controller and lamp assembly) we can look at the specs. on?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • soleilsoleil Posts: 45Solar Expert
    Re: What to do with unused energy?

    Thanks Bill. That looks like a nice 12V timer that NAWS is selling. When you were stating that "inductive DC circuits can be hard on electronic and mechanical relay contacts", were you referring to the timer or the security light?
  • BB.BB. Posts: 24,676Super Moderators admin
    Re: What to do with unused energy?

    Really, inductive DC loads and "affect" any switch type.

    Inductors store "energy" as moving current (typically in coils, inductors, motor windings, transformers, etc.).

    When a switch (transistor, relay, etc.) "turns off" the current flow--the "inductor" wants to keep the current flowing.

    For the ignition coil in a car--this is the old points in the distributor that when combined with a high voltage transformer causes the spark for the plug.

    The most irritating thing I ever do--take a regular Ohm Meter and measure the resistance on a good sized AC transformer. Just removing the Meter Lead from the transformer can generate a couple hundreds volts from inductive kick back--enough to give me a shock. (the capacitor across the points was to protect the points against arcing in normal operation).

    Anyway, a snubbing diode (or capacitor) can reduce the inductive kick back that can damage electronic switched or DC relay contacts.

    If you do not have inductive loads (just an LED or filament lamp for example), then the snubbing function is not needed. And in many cases, the controller should be designed to "withstand" or "manage" such inductive kickback anyway (with its own internal snubbing diode or other solution).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Posts: 741Solar Expert ✭✭
    Re: What to do with unused energy?

    During the summer, RV's can get like an oven inside. Look at running a fan or two to keep the temps down.
  • soleilsoleil Posts: 45Solar Expert
    Re: What to do with unused energy?

    That's a good idea too, Ken. Thanks.
  • dgsloandgsloan Posts: 22Registered Users
    Re: What to do with unused energy?

    The LED light has an amp limiting controller at 12v or 120v to prevent overloading the LED. The 120v units are the least expensive and I have mine plugged into a cheap 80w inverter as there is little loss in efficiency. Best to purchase the whole unit with LED heat sink. The 50w unit I have will drain approximately 35 amps from your battery in 8 hours (hopefully you have a 100 ah battery or better) 50 percent drain is about the limit on Lead Acid. The solar panels have to make up this difference on a daily basis = Two 80 w panels minimum. The suggestion of a fan is good because if the sun is out and hot then some EXTRA power can be drawn to cool the trailer. I use a Comair Rotron Model CLE2T2 as they are very quiet and energy efficient (50w) and fit in a standard RV vent and run on a cheap 80 w inverter.
  • dak664dak664 Posts: 13Registered Users
    Re: What to do with unused energy?

    Enphase microinverters ought to be a good match for your panels, e.g. http://enphase.com/wp-uploads/enphase.com/2011/03/Enphase_M190_Datasheet.pdf. Since you already have the panels the inverters might even pay for themselves in ten years. They would require a 240 volt connector to your house; I expect you could leave the DC side connected all the time and unplug one or both to adjust how much power is available for other loads.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: What to do with unused energy?
    dak664 wrote: »
    Enphase microinverters ought to be a good match for your panels, e.g. http://enphase.com/wp-uploads/enphase.com/2011/03/Enphase_M190_Datasheet.pdf. Since you already have the panels the inverters might even pay for themselves in ten years. They would require a 240 volt connector to your house; I expect you could leave the DC side connected all the time and unplug one or both to adjust how much power is available for other loads.

    This isn't actually relevant, as the panels are installed on an RV. He's looking to make use of the available power while the RV is parked at home (not in use). You cannot just buy some Enhase inverters, attach the panels' to the input, and back feed the grid. All GT installs must meet regulations and be permitted.

    Advocating "guerrilla install" GT systems is frowned on here as they are illegal and often unsafe.
  • dak664dak664 Posts: 13Registered Users
    Re: What to do with unused energy?

    I admit I am not a close follower of NEC code, but are you saying there is currently no legal way to use microinverters on RVs to backfeed a plug-in grid connection?

    As far as I can tell the existing RV plug-in (with all intervening plugs) can be used for backfeeding, as long as they are locking connector(s) and "a tool" is required for disconnect. Enphase is arguing against these restrictions for the next code iteration http://enphase.com/wp-uploads/enphase.com/2011/03/Enphase_White_Paper_AC_Connectors.pdf

    No doubt there will be some clarification of the issue when plug-in cars become common, and hackerillas start tapping the revenue from their load-shifting capability.
  • BB.BB. Posts: 24,676Super Moderators admin
    Re: What to do with unused energy?
    1. You need building inspector approval--There is no way you can parallel energy sources via standard plugs that do not add current to a branch circuit that is safe (or legal). You have a 15 amp branch circuit, plug in upwards of 15 amps of GT Inverters. Now that 15 amp branch circuit has 30 amps available in a short circuit.
    2. Typically Utilities are required to inspect/check for insurance/grant approval. Since there cannot be a UL/NRTL approved "plug in" GT inverter, they can never grant approval.
    3. Solar panels need to be safely attached to the roof (structural).
    4. Solar panels/GT Inverters need to be safely wired into the home/business in such a way that home wiring does not get over heated (correct sized panels/wiring) and that proper material/equipment is used (UL/NRTL approved materials).
    5. Utilities are replacing meters with ones that either do not turn backwards (you cannot get paid for your power) or even turn forward no matter which way the power flows (you actually will get charged for generating energy to the grid).
    6. Utilities are keeping track of who is generating power. In California, the utility only has to allow 1% of power to be generated by "small generators". My guess is by 10% worth of small generators, the grid will become unstable and new technologies (central control of GT inverters) would be required.
    7. As more people install GT systems--they can actually exceed the local grid's ability to handle the increase in current (flowing the "wrong" direction). Quebec is now preventing new installs for (last I read) not very clearly defined reasons (local grid capacity?).
    8. Most net metered setups do not make economic sense for the utility--Buying power back at retail and selling it again at retail just does not make sense. In California, about 1/2 the cost of power is generation, and the rest is cost of distribution, billing, repairs, running a company, etc.
    Is that to say that you placing a small 200 watt unapproved GT inverter+panel in your RV is going to blow up your corner of the world.... Not really.

    At this point, I do not see people actively time shifting power using the electric cars. It does not make economic sense because the cost of wearing out the batteries usually exceeds the savings from shifting power (at least at my TOU billing levels).

    Some countries have already made battery connected GT inverter systems illegal already (I guess, so they cannot buy cheap power at night and sell it during the day).

    Is it safe--No idea. Too many variables.

    Panel Fire Question

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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