Battery back-up determining

benatwhodotnetbenatwhodotnet Registered Users Posts: 16
For the size of your daily usage I would look at the size of your daily usage. 10kW/hrs is massive for off-grid. Sounds like some people need to learn that switches have two positions, and one of them is "OFF".

Trying to supply that much power with solar is daunting ... and expensive. I agree with audredger; 15 panels won't do. You've got to get that 10kW into the bank in about 4 hours of good sun. That's 2500 Watts per hour, and with the usual panel de-rating that means roughly 3200 Watts of panel minimum - and that on a good day. :p

Hi, I'm new to this forum. I felt compelled to join because I'm here doing battery backup research. The kinds of quotes I'm getting definitely reflect the thinking and discussions that I see here. There is a completely different paradigm because of my starting up as a grid-tied urban desert dweller. My system is sized based on the contractor asking how much solar power I wanted -- my answer was "How much can I get?". You see the answer is based on pay-back of the original costs using HIGH ELECTRIC BILLS on a house with no upgrades since it was built in 1980. There's a pool, two conventional electric water heaters, two 10 S.E.E.R. package AC units, and a lot of older appliances... at least that's how I bought the place 2 years ago. Now with 23,760 Watts of PV grid-tied co-generation, increased shading and insulation, a hybrid electric water heater, a 2-hour limit timer on the conventional water heater, an upgraded 16 S.E.E.R. AC and a programmable t-stat on the 10 S.E.E.R. to reduce it to night-time use on the master bedroom, and a new pool pump motor -- my payback on this system (after taxes) is May 2014. It was commissioned in March 2012. You can see that this is very rapid payback and I have the numbers to back this up. But my point is that I don't need battery backup for 160kWh per day that I produce. I need enough to get through one night with one AC running. I can survive comfortably on 5kW peaks at night and my system generates more than I use even on rainy days in winter. The only time I need backup is when the grid fails because I have beaucoup surplus in our net metering account. But I asked for a quote from Blue Pacific Solar and they wanted to sell me 48 Full River DC400-6 6V 400AH L16-AGM batteries in 6 enclosures. My house is equipped with a "load controller" which can easily be activated to limit major appliances to below 7kW (measures total to throttle the appliances and AC back). So I discussed with Blue Pacific Solar that I wanted to handle grid failure by 1) disconnect from grid, 2) switch on load controller, 3) activate battery backup or generator. The problem is they assumed I need the power I generate on the roof. I make 50% more than I can use on the hottest day of the year.

So I'll be looking at reducing my loads too. No worries. How do I size my battery backup for 1 AC unit and a new efficient fridge overnight. I assume my Sunny Boy inverters (3 SB7000US) will carry me through the day with 2 Sunny Island 6048 control units.
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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery back-up determining

    Welcome to the forum.

    I've moved your inquiry to a new thread because it is bound to get interesting.

    Can I start out by saying most utilities wouldn't let you have more than 10kW of GT system? How you got 23k+ I don't know!

    So what you need to do is get out the Kill-A-Watt and measure those things which plug in and must be kept running in the event of an outage. For hard wired and/or 240 VAC items you'll need to do a little Ampere measuring and timing of typical runs to make a determination. Then it's all down to numbers.

    How often does the power go out, and for how long? Chances are adding the Sunny Islands and batteries may not be the cheapest option here.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Battery back-up determining
    How do I size my battery backup for 1 AC unit and a new efficient fridge overnight. I assume my Sunny Boy inverters (3 SB7000US) will carry me through the day with 2 Sunny Island 6048 control units.

    Check out the stickies on inverter size and battery size calculations. Because of the way the SI and SB units interact, you would be able to use a separate AC-input battery charger to refill your batteries during the day from the extra power you are getting from PV and/or generator, so your battery bank does not need to be as large as the "standard" recommendation.
    1. Conventionally, we say to size your bank so that a typical night's usage will not take more than 20% of your batteries capacity. This allows for a couple of days without sun while still keeping above the 50% threshold at which battery life is reduced.
    2. But since you will have plenty of extra PV and will only be using the battery backup occasionally during the year, you could design to go down to or below 50% over 24 hours.
    Get a Kill-a-Watt (TM) meter and get actual numbers from the fridge (and if possible from the A/C) rather than just looking at nameplate ratings. For the A/C you may need to keep track of how many hours it actually is running per night and multiply by the nominal consumption.
    3. What you are looking at is really a super UPS rather than straight off-grid, so some of the guidelines in the sticky threads will not apply completely. See 2.
    SMA SB 3000, old BP panels.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Battery back-up determining
    How often does the power go out, and for how long? Chances are adding the Sunny Islands and batteries may not be the cheapest option here.

    But if he wants to be able to use the full output of his oversized PV during the day during outages, that may still be a good way to go. He should not get hooked in advance into one specific solution and then try to size it, though.
    SMA SB 3000, old BP panels.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining
    Welcome to the forum.

    I've moved your inquiry to a new thread because it is bound to get interesting.

    Can I start out by saying most utilities wouldn't let you have more than 10kW of GT system? How you got 23k+ I don't know!

    I had no idea about the 10kW limit on GT... but the previous owner of this foreclosed property may have done me a favor. He didn't fix the AC units when they ran all the time and he must have run the pool and a window AC unit non-stop most of the year. His AVERAGE BILL was $518 -- when I requested this info from APS before closing. Now I've been told by APS that they no longer provide such info at all, but I had this when I met with the contractor to talk about PV solutions in June 2011. I fixed the broken stuff and never had a bill over 470 the first year... with 2 water heaters, 2 big AC units, pool, and bad roof insulation. The hail damaged foam roof was replaced with 2 inches of new foam and super-white coating. The AC units were rebuilt (by me) with 1 new compressor, two outside condenser fan motors, one inside blower motor and of course all the run caps, start caps, contactors, etc. APS may have allowed the 24kW system because it matched the consumption history. However, we produce $500 per month and have usage below $330 average, maybe better now. I'm running a surplus since 1/1/2013 of over 8MWh. I received a check for $450 last year after the final meter reading. This was after only 9 months of co-generation (3/16/2012 commissioning to 12/18/2012 meter reading). The surplus was 6.8MWh. Most of that was carried into the fall from the sunnier months. I expect we'll see twice that surplus this year. My worst bill was for 3100 kWh in one month. I don't expect we'll ever hit that kind of consumption with the improvements I've made. My new fridge is rated for 55 dollars per year and replaced one that was probably 300 per year. The new stove is induction cooktop over convection oven. The dishwasher is new and super efficient (slow). One water heater is hybrid now -- a "signing" bonus from the solar contractor. I relocated it into the laundry room to assist cooling that area. The conventional electric water heater has a timer and runs no more than 1 hour in the morning and 1 hour in the evening since it serves only the master bathroom.

    I can see that I've taken a simplistic approach to battery backup. And you're right, it's about being able to use my power when the grid fails. We had one outage last summer for 6 hours on a very hot Saturday and my elderly neighbors had to go to a hotel. It was the first time I even realized that I would be off-line when the grid failed. I had to read up on the "anti-islanding" features of the Sunny Boys. I had studied my PV system extensively, but just didn't grasp that concept early on.

    The simple solution I grabbed onto, is that I have a load controller already installed that can limit usage or shed load to stay under 7kW peak. It has relays to disconnect either AC, either water heater, and the clothes dryer. I would prefer to switch out the pool pump instead of the hybrid water heater, but that circuit is in a different sub-panel and the current detection loops would not be able to read that part of the load anyway. If I can battery backup a peak of 7kW and a sustained load of 4kW for up to 6 hours of run time then I will have enough juice to see through a night-time power outage. With the SI 6048 units I would not need any battery backup to handle peaks during the daylight hours. My AC units draw 12-amps and 16-amps on single phase 240v. The higher 16 S.E.E.R. 3-ton will drop to under 8-amps when using the lower compressor speed (2 speeds). The 10 S.E.E.R. unit will always pull 16-amps, slightly higher when ambient temps are above 110F. This unit got the new compressor. With "free" electricity I cannot cost justify changing to a new more efficient unit for $3500 when I can replace a compressor (my labor) for $550 in parts. I'd rather divert funds to battery backup since the house can be cooled at night using only one AC unit. We could actually just shut off the conventional water heater and one AC at the breakers once the power failure is underway.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery back-up determining

    Just one thing. You said:
    With the SI 6048 units I would not need any battery backup to handle peaks during the daylight hours.

    Let's not lose sight of the fact the Sunny Islands do have a minimum battery size too. What you mean is that AC coupling from the Sunny Boys during daylight should handle the big loads (daytime A/C) so you would only need the minimum battery size for the SI units. This should work. How well it will work depends on how much you really do need to run "overnight" (off from the batteries).

    IIRC the SI needs 600 Amp hours (each) so one such bank would give you about 12 kW hours AC max available, which is fairly substantial. How well would that work for you?
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining
    inetdog wrote: »
    But if he wants to be able to use the full output of his oversized PV during the day during outages, that may still be a good way to go. He should not get hooked in advance into one specific solution and then try to size it, though.

    You nailed it... I want the output of the PV system available during the day. I could even use a generator for minimal stuff to run at night. I have a 9hp Yanmar diesel rated 6500W with sustained 5200W (80%) using 3 gallons per 12 hours. I want to make whatever backup solution I get, capable of handling a long outage (days or weeks). Perhaps some of you have read the doomsday prepper columns predicting US power grids cannot recover from certain outages in a reasonable (24-48 hour) time frame. I don't plan to sink huge amounts into "prepping" but a long power outage might be too much for my generator -- it can barely run one of my air conditioners (startup load is high). So if I can use my daytime PV the need for generator power is only at night. Perhaps batteries are not the answer... only get SI 6048 units to run off-grid.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining
    Just one thing. You said:



    Let's not lose sight of the fact the Sunny Islands do have a minimum battery size too. What you mean is that AC coupling from the Sunny Boys during daylight should handle the big loads (daytime A/C) so you would only need the minimum battery size for the SI units. This should work. How well it will work depends on how much you really do need to run "overnight" (off from the batteries).

    IIRC the SI needs 600 Amp hours (each) so one such bank would give you about 12 kW hours AC max available, which is fairly substantial. How well would that work for you?

    You have read more of that 250 page manual than I have... (SI 6048 installation guide). I will definitely study up. The quote I received with 48 batteries in 6 cabinets also included a wiring diagram indicating that only 2 of the SB7000US could be controlled by the SI6048 units (2). But I found a diagram in the install guide where more than 2 SBs were controlled by 2 SIs. Since I have 3 SB7000US, the pair of SI6048 should do nicely to operate off grid. Perhaps minimum battery power is all I need. I'll definitely have to either use the load controller or isolate the critical loads to a new panel. At present, my co-generation goes through a mechanical meter and then a disconnect box before it hits the APS meter buss on a 125A breaker. My main panel isolates the PV backfeed from the main breaker and the buss bars below. For this reason, any off-grid solution will have to start with a shunt (DPDT) switch or contactors at the combiner panel. Placement of critical loads is not allowed into that panel because it would bypass metering of PV production under normal grid-tied operation. But a breaker could be added to the combiner panel for the purpose of backfeeding when operating off-grid. This combiner panel is very close to the main panel.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining

    Info on my system can be found at http://AZBen.blogspot.com and at http://www.sunnyportal.com/Templates/PublicPage.aspx?page=308a0674-ce3f-4e2f-b31b-e7577f7a4f74 which is the public page of my SunnyBoy portal.
  • solar_davesolar_dave Solar Expert Posts: 2,347 ✭✭✭✭
    Re: Battery back-up determining

    So how often does APS go down, mostly never here. With a PV system that size you should probably switch back to the standard tier tariff. You should be able to get down to system connection charges only for every month with EPR6 net-metering and get money/credit back. Taken as credit the following year you should be net zero outlay.

    You might want to look at replacing one of the AC units with a dual speed which would soften you start-up loads and allow the generator to get it on the move for your backup needs. I have a Trane 3-ton that does that and it starts up then runs at ~2500 watts first, if the cooling demand is not met then it escalates to ~5000 watts. Another option would be to replace the 10 seer AC unit with a high efficiency mini-split (multiple ceiling cassettes?), they definitely are a much softer start.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Battery back-up determining
    that only 2 of the SB7000US could be controlled by the SI6048 units (2). But I found a diagram in the install guide where more than 2 SBs were controlled by 2 SIs. Since I have 3 SB7000US, the pair of SI6048 should do nicely to operate off grid. Perhaps minimum battery power is all I need.

    The SB to SI limit is based on the power output of the SB(s) and the AC power input of the SI, not the number of devices. AFAIK the limit is 2W of SB for every W of SI, so 21kW of PV should work fine with 2 x SI6048.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining

    Solar Dave,

    You're perfectly describing my current situation. I am on the flat rate EPR6 and I am getting paid at the end of the year. I started out looking only at how to hook up my generator, or a UPS setup, for short duration power failures. We had one failure of 6 hours since my PV system was commissioned.

    However, I would be very sad if I found myself sitting in a hot house in August with my generator overheated or out of fuel on day 10 of a major grid failure. Just thinking about TEOTWAWKI from time to time. I have a friend at work who is the consummate prepper and chides me for being grid tied only.
  • solar_davesolar_dave Solar Expert Posts: 2,347 ✭✭✭✭
    Re: Battery back-up determining

    Yes a 10 day outage would be bad in August. hmmm quick vacation out of town (Flagstaff or Southern Colorado) is in my books for just such a situation. I have a pair of Chevy Volts to use in the event of a short outage, a day or so would not be a problem to keep the food storage and basic lights and such working. I am looking at a small Honda as well maybe a EU3000i which would start my mini-split no problems.

    If it gets that bad that I would need to run off grid "forever" here, I would probably disassemble what I have and move, cause the water situation is really unsolvable for the water pumping, for delivery and treatment without grid power. Just from a prepper aspect.

    For short duration stuff a Generator is the best solution, bang for the buck. You will invest more money and time into a seldom used hybrid system. The maintenance headaches alone of the batteries would put me off.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining

    The generator is looking more attractive than batteries for making it through the night. The SI units would allow me to run through the hot summer days if there's an extended outage, but how much is it worth to be that "prepared". And there's the minimum battery requirement for SI that puts me into the battery maintenance world - way of life.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery back-up determining
    Welcome to the forum.

    I've moved your inquiry to a new thread because it is bound to get interesting.

    Can I start out by saying most utilities wouldn't let you have more than 10kW of GT system? How you got 23k+ I don't know!

    So what you need to do is get out the Kill-A-Watt and measure those things which plug in and must be kept running in the event of an outage. For hard wired and/or 240 VAC items you'll need to do a little Ampere measuring and timing of typical runs to make a determination. Then it's all down to numbers.

    How often does the power go out, and for how long? Chances are adding the Sunny Islands and batteries may not be the cheapest option here.

    SRP's limit for Net-Metering is 100KW. Don't know APS (Glendale is APS territory). Glendale is not permit-free. Mesa is permit-free if it is grid-tie or bi-modal (They let SRP do the inspections).

    AZ is one of the more secure states for power reliability and generation capacity. Outages are currently very uncommon.

    Powering an 3+ ton air conditioner off-grid will be a challenge unless you got the dough. Swamp coolers are your friend and will save electricity more than solar itself will except during the monsoon season, but are far better than nothing even in the monsoon.

    Your battery bank can service load shifting - get some money's worth isntead of your batteries rotting on float. Load shifting also allows you to use lower cost flooded batteries without issues as it will provide cycle exercise for them even if you only do it once a week.

    A Generator will allow you to get away with significantly undersizing your battery bank on a bi-modal system, but there are limits: fuel shortages? Good luck. Storing gasoline can be impractical as it stores for 3-6 months without stabilizer and 6-12 months with (and Diesel generators cost more).
  • solar_davesolar_dave Solar Expert Posts: 2,347 ✭✭✭✭
    Re: Battery back-up determining
    The generator is looking more attractive than batteries for making it through the night. The SI units would allow me to run through the hot summer days if there's an extended outage, but how much is it worth to be that "prepared". And there's the minimum battery requirement for SI that puts me into the battery maintenance world - way of life.

    Got nat gas? One of these starts to look pretty good when you starting figuring all the battery headaches and equipment costs.
    http://www.northerntool.com/shop/tools/product_200448671_200448671
  • VicVic Solar Expert Posts: 2,977 ✭✭✭✭
    Re: Battery back-up determining
    solar_dave wrote: »
    Got nat gas? One of these starts to look pretty good when you starting figuring all the battery headaches and equipment costs.
    http://www.northerntool.com/shop/tools/product_200448671_200448671

    Hi Dave,

    Not to argue too much, but this genset is air-cooled, and in the AZ H E A T, I wonder about the longevity of such a unit.

    Kohler CAN make good gensets. Did read the reviews on the Northern site, one of the two reviewers is not so happy with this particular generator.

    I DO have a Kohler water-cooled genset that runs on LP, and it has been fine, although, who can afford to put very many hours on an LP genset?
    OPINIONS, FWIW Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery back-up determining
    The generator is looking more attractive than batteries for making it through the night. The SI units would allow me to run through the hot summer days if there's an extended outage, but how much is it worth to be that "prepared". And there's the minimum battery requirement for SI that puts me into the battery maintenance world - way of life.

    The off-grid part of my system is 'generator assisted'. I have 3 circuit breakers that I would leave on in a long-term off-grid situation though (generator fuel unaffordable or not available) - they have the fridge, chest freezer, 2 port-a-cool swamp coolers, solar hot water pumps, and an extra outlet to plug in a small 600W microwave and gadget chargers. 4 more circuits are 'genererator-assisted off-grid' as the battery bank is not big enough to power these through a long night without power. The 8th circuit is an unintended move due to the house being wired with 14/3 and 12/3 with two circuits sharing neutrals. This circuit and any circuits moved for the expansion (double the panels & inverters, no additional batteries) are 'short-term sun-out daytime outage' only (such as a California power crisis rolling blackouts).

    Bi-modal systems will destroy any ROI a solar system might have, if it has any to begin with (There is none without the government subsidies; PV prices are dropping, elecrical prices are stagnant, battery prices are rising).

    For ROI, this is the order:
    **Good ROI**
    Shade screens on the windows
    Swamp coolers
    Seal duct work and attic spaces
    **Average ROI**
    Blow-in Insulate the attic
    Solar hot water (properly sized, flate-plate or flexible, non-drainback)
    Solar pool heating
    **Very Low ROI**
    Solar space heating
    Solar Hot Water (Evacuated Tube Glycol or Oversized Drainback)
    Grid-tie PV
    Dual-pane Low-E Air-filled windows
    **Negative ROI**
    Solar thermal air conditioning
    Dual-pane Low-E Argon-filled windows
    Insulate the walls
    **Very negative ROI**
    AC-coupled Bi-Modal PV
    Triple-pane Low-E Krypton-filled windows
    DC-coupled Bi-Modal (lots more electrical work & materials) or off-grid PV (big battery bank)
  • solar_davesolar_dave Solar Expert Posts: 2,347 ✭✭✭✭
    Re: Battery back-up determining
    Vic wrote: »
    Hi Dave,

    Not to argue too much, but this genset is air-cooled, and in the AZ H E A T, I wonder about the longevity of such a unit.

    Kohler CAN make good gensets. Did read the reviews on the Northern site, one of the two reviewers is not so happy with this particular generator.

    I DO have a Kohler water-cooled genset that runs on LP, and it has been fine, although, who can afford to put very many hours on an LP genset?
    OPINIONS, FWIW Vic

    I am no genset expert, It was just a shot in the dark for the money. The point I was trying to make was a generator for the rare occasional outage looks much better in the light of having to buy and maintain and off grid/hybrid setup.
  • VicVic Solar Expert Posts: 2,977 ✭✭✭✭
    Re: Battery back-up determining

    OK Dave,

    You are correct. Stand-by generators are great for occasional gird outages, which are often short in duration. And as you said, the alternative of a hybrid system only for those occasions seems unattractive, unless the grid is quite unreliable.

    Perhaps got derailed by the 'ben's' reference to a major grid failure for ten days in August, and for that NG may be fine, but was thinking that a HD water-cooled genset would be better than air-cooled.

    Rainy day here, just sitting inside nit-picking on Forums. Keep cool, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • westbranchwestbranch Solar Expert Posts: 5,175 ✭✭✭✭
    Re: Battery back-up determining

    It sounds like he will need a cross between a Teleco backup AGM and a lift truck FLA... or maybe a NiCd as the use is few and far between but then he needs full power fro a day or 3 or more. NiCd's sit well with float charge and do have the capability to go well below 50% DoD...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining
    Vic wrote: »
    Hi Dave,

    Not to argue too much, but this genset is air-cooled, and in the AZ H E A T, I wonder about the longevity of such a unit.

    My smallish Yanmar diesel 6500W max (5200W continuous) ran a fireworks booth for my church youth pastor. He was raising money for a missionary trip and enlisted all the young missionaries to man the booth day and night since the inventory was in a tent. Once the fire marshall shut them down for using a gasoline genset, they called me and used my diesel in peak June heat in a Phoenix parking lot for over 100 hours non-stop to operate multiple swamp coolers, a 24-foot camping trailer AC, and lots of floodlights. There was no problem with the air cooled diesel. It recently was at Country Thunder, a desert country music festival, for a week running two campers with AC and refrigerators and microwaves.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining

    My daughter came over at 6:00 AM yesterday and we washed panels for a couple of hours. This is the report from last night.

    Attachment not found.

    The revenue figure is based on high German utility rates, not real APS rates.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery back-up determining
    My daughter came over at 6:00 AM yesterday and we washed panels for a couple of hours. This is the report from last night.

    Attachment not found.

    The revenue figure is based on high German utility rates, not real APS rates.

    Your average daily production per panel is comparable to mine. I have 27 240W panels. Running about 39.5 KWh per day at the charge controllers on sunny days over 110. Production is a little bit over 40KWh when temperatures are around 105. Friday is going to be a whopping 118, saturday 117.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining

    Very interested to read your ROI list by category. With this in mind, you decided to go bi-modal with batteries and generator, is that because you believe there is a high probability of a more than 48-hour grid outage?
    The off-grid part of my system is 'generator assisted'. I have 3 circuit breakers that I would leave on in a long-term off-grid situation though (generator fuel unaffordable or not available) - they have the fridge, chest freezer, 2 port-a-cool swamp coolers, solar hot water pumps, and an extra outlet to plug in a small 600W microwave and gadget chargers. 4 more circuits are 'genererator-assisted off-grid' as the battery bank is not big enough to power these through a long night without power. The 8th circuit is an unintended move due to the house being wired with 14/3 and 12/3 with two circuits sharing neutrals. This circuit and any circuits moved for the expansion (double the panels & inverters, no additional batteries) are 'short-term sun-out daytime outage' only (such as a California power crisis rolling blackouts).

    Bi-modal systems will destroy any ROI a solar system might have, if it has any to begin with (There is none without the government subsidies; PV prices are dropping, elecrical prices are stagnant, battery prices are rising).

    For ROI, this is the order:
    **Good ROI**
    Shade screens on the windows
    Swamp coolers
    Seal duct work and attic spaces
    **Average ROI**
    Blow-in Insulate the attic
    Solar hot water (properly sized, flate-plate or flexible, non-drainback)
    Solar pool heating
    **Very Low ROI**
    Solar space heating
    Solar Hot Water (Evacuated Tube Glycol or Oversized Drainback)
    Grid-tie PV
    Dual-pane Low-E Air-filled windows
    **Negative ROI**
    Solar thermal air conditioning
    Dual-pane Low-E Argon-filled windows
    Insulate the walls
    **Very negative ROI**
    AC-coupled Bi-Modal PV
    Triple-pane Low-E Krypton-filled windows
    DC-coupled Bi-Modal (lots more electrical work & materials) or off-grid PV (big battery bank)

    Jesus loves (you and me)... yes He does.
  • BB.BB. Super Moderators, Administrators Posts: 29,813 admin
    Re: Battery back-up determining

    Some of this is a "it depends".

    I installed double pane low-e vinyl windows in two homes I have lived in. The first was a 1 story small rancher with stucco walls. The windows made a huge difference--especially in the west facing bedrooms. Home already had blown in ceiling insulation and we choose specifically not to redo the walls with insulation (no insulation presently in walls, slab on grade floor). Very happy with the results.

    Home really only "gets hot" from running appliances/people that heat the place up (and opening windows on hot days for ventilation).

    The second home was built in the late 1930's and had only blown-in insulation in the second floor attics. House was very hot in summers and very cold in winters. Dusty inside.

    Stripped walls and installed fiberglass batts, double pane vinyl low-e windows, insulated/operating skylights. Home is much cooler in summer (and quieter from outside noises). And does not cost very much to heat in winter (~$40 a month for ~3-4 months of winter for natural gas).

    The second home just hand redwood shiplap siding which had no thermal mass and was not very air tight (as in none). Home is now very air tight and we have to open windows for air circulation. Also put in a 95% effficent central heat system--Old one was flooded by water in pit. And would probably have used 80% efficient (less money up front, use to by a few dollars a month more in natural gas) but exhaust stack was too long to chimney (replacement 80% heater was constantly dripping water/condensate and did not comply with code).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_davesolar_dave Solar Expert Posts: 2,347 ✭✭✭✭
    Re: Battery back-up determining

    I would also say "it depends"

    Solar PV payback depends lots on the situation. Here my payback was right at 3 years with the tax and utility supports. I consider that a great ROI.

    One I think that was missed is improved efficiency AC units. In support of Solar PV it is pretty essential. The conservation of vs the generation of power. Again the tax man and the utility helped make that a smart move.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery back-up determining

    No more daytime rolling blackouts possibly going into the night. California blackouts were only 2-3 hours at a time. That is short compared to other prior incidents. 3rd world countries (which USA is headed in that direction - 3rd world banana republic) have rolling blackouts from 4 to 12 hours at a time, most of that in the afternoon peak hours (rural areas the most, city commerce centers the least). Texas was 4-8 hours when they had theirs (wasn't statewide like CA though). AZ will probably the last to have grid issues though unless Obama progresses in his plans to tax and regulate all the coal plants into the ground or forces AZ to assist CA.

    My ROI list does not factor in hyperinflation, which hits food and energy hardest. But people don't want to hear about that stuff and hyperinflation could be more than 10 years away (battery/inverter replacement time) - one never knows, only know that the dollar is being printed like its going out of style, and the markets are full of immature money junkies addicted to easy credit and money like it was heroin.

    If my system survives into the tribulation it could very well be used by tribulation believers. Tribulation will be probably SHTF. Hopefully the rapture really is pre-trib. Also, hyperinflation could very well render power bills completely unaffordable, if the government decides to let the inflation run its course instead of draconian and incompetent regulations and price controls. If the government does enact draconian measures, shortages will abound, as well as other problems from people gaming the system.
    Very interested to read your ROI list by category. With this in mind, you decided to go bi-modal with batteries and generator, is that because you believe there is a high probability of a more than 48-hour grid outage?



    Jesus loves (you and me)... yes he does.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery back-up determining
    solar_dave wrote: »
    I would also say "it depends"

    Solar PV payback depends lots on the situation. Here my payback was right at 3 years with the tax and utility supports. I consider that a great ROI.

    One I think that was missed is improved efficiency AC units. In support of Solar PV it is pretty essential. The conservation of vs the generation of power. Again the tax man and the utility helped make that a smart move.

    Grid-tie systems were computed at a 15 year payback through a lease program in 2010. I was going to get a 4.6KW grid-tie 15 year lease for $6,000 prepaid (20 235W Kyocera). That shattered when SRP ran out of rebate money (much more generous than 2012) and SolarCity rewrote the lease agreement (had to opt-in to accept). I ain't bothering with the leases again.
  • solar_davesolar_dave Solar Expert Posts: 2,347 ✭✭✭✭
    Re: Battery back-up determining
    Grid-tie systems were computed at a 15 year payback through a lease program in 2010. I was going to get a 4.6KW grid-tie 15 year lease for $6,000 prepaid (20 235W Kyocera). That shattered when SRP ran out of rebate money (much more generous than 2012) and SolarCity rewrote the lease agreement (had to opt-in to accept). I ain't bothering with the leases again.


    Yeah I looked at leases in 2010 as well, and then did the calculations for the 30% tax credit and the APS $3 a watt rebates. The lease just didn't fly. I have something quite a bit less than $20K out of pocket in to my 12.5 KW system. The big issue then was I had to front the complete cost out of pocket @ roughly $6 a watt. It was a sizable chunk of change. Home equity line of credit came into play for a few months while I sorted out the pay off, but I did have my cash portion plus some in hand at the time so that kept the borrowing under control.

    So far I am pretty satisfied with the results, but I do wish I had bumped the size to like 15 KW. That would have been better with charging 2 Chevy Volts. Still looking for a few more ways to conserve to make up the difference but the bills are pretty acceptable already so anything is hard to justify financially.
  • benatwhodotnetbenatwhodotnet Registered Users Posts: 16
    Re: Battery back-up determining

    About ROI. I have to believe that size matters and that there's some economy of scale in my system. I met with a contractor who did not offer any finance options. However, APS (utility) requires in the contract that the PV system must be warranted to function for 20 years by someone other than the homeowner. Therefore, the contractor offers only a pre-paid lease option with 20 year guarantee of the system function/performance. I asked if the inverters would be covered for 20 years since SMA offered to extend warranty to 20 years for $1500 each (SB7000US). The contractor says they cover that. My system is installed as a pre-paid lease. My CPA says I get a credit for the lease because the IRS asks "what did you pay toward the installation of a qualified solar..." and that the contractor is also equally entitled to double dip this same question. This means my final price is impacted once by the contractor's tax incentive and again by my own. Since the contractor priced the install at 94 cents per watt to me, and APS gave $1.45 per watt ($35K), then my ROI is about 24-26 months with elimination of a $335 equalized bill and 500-1000 in cash for surplus kWh at year end. I got $450 after only 9 months of operation in 2012. I'm at the end of 15 months of operation now and the unrecovered balance is down to $3500. A little over 10 months of electricity and we'll be in the black, better if we get paid for the surplus. I'm going into summer with 8MWh in the net metering bank.

    All that said, here's the fly in the ointment. My contractor is out of business, revoked on the ROC site here in AZ. I need to file papers to claim the cost of warranty or expected repairs. I am thinking of getting the SMA extended warranty and asking for reimbursement from the ROC bond. Also I have a broken glass on one panel and should be able to get a contractor out to replace it, and bill the ROC bond too. Looking into this ASAP as time is of the essence.
    solar_dave wrote: »
    Yeah I looked at leases in 2010 as well, and then did the calculations for the 30% tax credit and the APS $3 a watt rebates. The lease just didn't fly. I have something quite a bit less than $20K out of pocket in to my 12.5 KW system. The big issue then was I had to front the complete cost out of pocket @ roughly $6 a watt. It was a sizable chunk of change. Home equity line of credit came into play for a few months while I sorted out the pay off, but I did have my cash portion plus some in hand at the time so that kept the borrowing under control.

    So far I am pretty satisfied with the results, but I do wish I had bumped the size to like 15 KW. That would have been better with charging 2 Chevy Volts. Still looking for a few more ways to conserve to make up the difference but the bills are pretty acceptable already so anything is hard to justify financially.
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