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Making batteries and arbitrage work, selling back at peak rates

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  • J.P.M.
    replied
    Originally posted by Ampster View Post
    Salesperson dishonest or just not complete?
    Ever hear of lying by omission ?

    Leave a comment:


  • Ampster
    replied
    Originally posted by Harok375 View Post



    Sounds like the sales guy was dishonest then, cuz I asked him a direct question - " can I charge my batteries using solar only and then dump the power onto the grid during peak rate times for $.35?" and he said yes.

    ...
    Salesperson dishonest or just not complete?

    Theoretically the answer is yes, but it is uneconomical and permission from the utility is not likely. There are many things about utility rates and rules that defy logic.
    As to your question it depends on the rates and whether you can use the tax credit economically.

    Leave a comment:


  • Harok375
    replied
    Originally posted by Ampster View Post

    Also to take the Federal Tax credit you have to charge your batteries from solar which means those kWhrs will not get credited at $0.35 per kWhr. The best you could due is offset loads at $0.35 per kWhr less inverter/charger inefficiency and wear and tear on your batteries. That is negative arbitrage.


    Sounds like the sales guy was dishonest then, cuz I asked him a direct question - " can I charge my batteries using solar only and then dump the power onto the grid during peak rate times for $.35?" and he said yes.

    To flesh out my thoughts a little, I was thinking that in order to fully utilize the battery capacity, I would charge using solar during the day ( which, I believe, PG&E would want anyways to avoid the duck curve thing ) and then dump onto the grid during peak usage times (which, I believe, PG&E would want anyways to avoid starting up peaker plants ). Granted, I'm aware of the wear and tear on batteries, but to me, that's the point of the exercise - it either makes financial sense or it doesn't. So all that would be factored in - cycle life, install cost, replacement cost, etc. So the plan would be - 1) charge batteries during the day 2) dump onto the grid during peak hours to get the best payback and full utilization of your investment 3) buy back from PG&E what you have 4) batteries will be at 20%-30% capacity overnight (which kinda eliminates FLA ? 5) charge batteries during the day, repeat......

    But from the way it sounds, which will be fine if the inverter is sophisticated enough, the better plan would be 1) charge during the day 2) set the inverter preference to use battery power rather than grid power during peak hours 3) excess power goes to the grid 4) buy what you gotta 5) batteries at 20-30% at night..

    Sound about right ?

    Of course, this assumes that batteries make sense financially. Which I think everyone here would agree, that it doesn't. If one wants to for other reasons - power outages, off grid living ( which I won't be doing ) etc, then that's another thing.

    So for us personally, power outages would be the only consideration. And I've been toying with the idea of using my rv generator - a Champion 3400 watt inverter generator - to power the house. Basically, during prolonged outages, the generator would be hooked to the batteries to continually charge them and the house would run as usual. A/C would run and draw down the battery, and when it kicks off the battery would recover - all the other loads aren't much, typically 600-800 watts/hour until the a/c kicks on when I look at the hour by hour breakdown on the PG&E website for our house. 3400 may not be enough, but we'll see, especially once you factor in that the solar panels would be charging at some unknown and variable rate also. Might not even need to start the generator until late afternoon? Who knows....

    Leave a comment:


  • khanh dam
    replied
    If only the natives in Hawaii would use the geothermal resources under their feet they would have reliable independent electricity. Geothermal plant was shut down last year, hopefully it will reopen on schedule in 2020. In other areas concentrated solar should be in use. HI. had ONE trial concentrated solar plant, from what I have googled it never produced electricity for the general public, weird. instead HI is using https://recsolar.com/all-case-studies/waianae-solar/
    huge PV plants, I thought Concentrated solar was more efficient? and one can store the extra energy in heat storage. of course much MUCH more expensive to get up and running and with a volcanoe potentially wiping it out easily, I guess that is why PV is more common.

    Leave a comment:


  • inetdog
    replied
    Originally posted by khanh dam View Post
    Because they want to live off grid or where grid tie power is not available. if you have GT, then batteries are typically not economically a good move.
    One notable exception is a location like Hawaii, with the following features:

    1. Very expensive grid power (all fuel must be imported to the islands). Ranging upward from $.50 per kWh.
    2. Large solar PV penetration (approaching 50% of grid capacity in some areas) which require POCO control of PV sellback to maintain grid stability. As one result new PV installs may not be allowed to sell back at all, and have to use batteries if they want to make use of excess PV generation during peak sun hours.

    Leave a comment:


  • nwdiver
    replied
    You have to 'value stack' to justify the cost of batteries. They're generally not going to be worth the cost simply due to arbitrage or backup or ease of maintenance vs a generator or the peace of mind that you don't need to hunt for fuel if there's an extended outage. But you add all of it together and they start to make sense.

    Personally I got a small-ish 20kWh bank of cheap lead-acid batteries because if there's a civil emergency I want to be able to use my solar array. A generator is cheaper but you could end up like this;

    Screen Shot 2019-08-16 at 8.22.39 PM.png

    Leave a comment:


  • khanh dam
    replied
    Originally posted by Harok375 View Post

    This being the case, why would anyone get batteries?
    Because they want to live off grid or where grid tie power is not available. if you have GT, then batteries are typically not economically a good move.

    Leave a comment:


  • Ampster
    replied
    Originally posted by Harok375 View Post
    ...........
    PG&E will control if and when your battery power is dumped onto the grid?
    Also to take the Federal Tax credit you have to charge your batteries from solar which means those kWhrs will not get credited at $0.35 per kWhr. The best you could due is offset loads at $0.35 per kWhr less inverter/charger inefficiency and wear and tear on your batteries. That is negative arbitrage.

    Leave a comment:


  • Harok375
    replied
    Originally posted by J.P.M. View Post
    Before you go further, do some homework. You seem to be under a lot of perhaps mistaken assumptions. Start with POCO rules as they may impact those assumptions about buy/sell/net metering arrangements and know that things are likely to change in the future.
    Ahhhhhh.

    PG&E will control if and when your battery power is dumped onto the grid?

    Leave a comment:


  • Harok375
    replied
    Originally posted by J.P.M. View Post
    Before you go further, do some homework. You seem to be under a lot of perhaps mistaken assumptions. Start with POCO rules as they may impact those assumptions about buy/sell/net metering arrangements and know that things are likely to change in the future.
    Well, we'd be put on net metering 2.0 , which is time of use rates.

    What am i missing

    Leave a comment:


  • Harok375
    replied
    Originally posted by SunEagle View Post

    Batteries are not always a "waste of money" but for most people it will cost more to generate a kWh from a battery system then to purchase it from your POCO. So it seems to be a financial mistake to make.

    Places like Hawaii seem to muddy the waters when it comes to batteries since their POCO's are charging a lot more then other POCO's.
    Agreed on it not necessarily being a waste to some

    1- they might want to use it as an emergency supply - I looked into this, and for us, not an option, since the likely outage event will be a rolling blackout during the hottest part of the day. A/C use would drain all but the largest battery system, plus you've got inverter sizing to handle inrush amps, etc. Not worth it for us.

    2- may be a tinkerer and don't care

    3- etc.

    From my VERY basic analysis, it looks like about $20/kWh storage for every expected year of life is about the break even point

    Leave a comment:


  • J.P.M.
    replied
    Before you go further, do some homework. You seem to be under a lot of perhaps mistaken assumptions. Start with POCO rules as they may impact those assumptions about buy/sell/net metering arrangements and know that things are likely to change in the future.

    Leave a comment:


  • SunEagle
    replied
    Originally posted by Harok375 View Post

    Well, that's the point of the post.

    Am I correct that including batteries is a waste of money, since that's the best case scenario?
    Batteries are not always a "waste of money" but for most people it will cost more to generate a kWh from a battery system then to purchase it from your POCO. So it seems to be a financial mistake to make.

    Places like Hawaii seem to muddy the waters when it comes to batteries since their POCO's are charging a lot more then other POCO's.

    Leave a comment:


  • Harok375
    replied
    Originally posted by Mike90250 View Post
    > So, best case would be to daily produce 35kWh at $.12, then sell it at $.38, 5 days per week.

    This statement makes no sense - can you clarify it ?

    if you are NOT going to use batteries for backup, you cannot make $ wearing them out with daily sell-back cycles. replacement batteries will eat all your sales $
    Well, that's the point of the post.

    Am I correct that including batteries is a waste of money, since that's the best case scenario?

    Leave a comment:


  • Mike90250
    replied
    > So, best case would be to daily produce 35kWh at $.12, then sell it at $.38, 5 days per week.

    This statement makes no sense - can you clarify it ?

    if you are NOT going to use batteries for backup, you cannot make $ wearing them out with daily sell-back cycles. replacement batteries will eat all your sales $

    Leave a comment:

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