UPS/inverter system

thehardway
thehardway Solar Expert Posts: 56 ✭✭✭✭
I'm new here so forgive me if this has been covered and if so please point me to the thread.

I am looking to install a PV array at the new home I am building.

I am located in Virginia. All heating loads for the house will met by an evacuated tube collector and cooling loads through a cold water ground loop leaving only circulating pumps, lighting, cooking, refrig/freezer and accessory loads. I am estimating my average continuous load at 1kw and peak load at 6.5kw with daily usage to be 26kw/hrs per day.

I have a 17kVA 120/240V ferro ressonant UPS system manufactured by BEST Corp. that is in good working order that I would like to use in the system.

I have a couple reasons for this, we are on an electric co-op here and at the end of the line, street power is unstable and undependable, I do not use much power during the daylight hours, I will likely generate more than we use during the day and would like to store it in the UPS batteries (there are 10, 12V lead acid batteries installed and I have additional battery racks available) for use in the evening/early morning. Excess power after my usage needs are met and the batteries are charged would be net metered. This should save me the cost of buying an invertor and give me clean/regulated street power thereby increasing appliance efficiency


Questions:

I am assuming that as long as the UPS does not see street power it will work in the inverter mode and supply conditioned AC power from the battery bank as well as giving me a readout of the charge level and the reminaing time available. The array would charge the batteries through its own charge controller and provide continuous charge throughout the day. Is there an automatic switching mechanism available for switching the street power on when I drop below a certain charge level?

Should the array be connected to its own charge controller? I assume there is no way to utilize the UPS systems on board charge controller for the PV array?

Are there any other potential pitfalls I should be aware of when doing this?


Any insight and objective criticism of this plan would be helpful.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: UPS/inverter system

    Welcome to the forum.
    thehardway wrote: »
    I'm new here so forgive me if this has been covered and if so please point me to the thread.

    I am looking to install a PV array at the new home I am building.

    I am located in Virginia. All heating loads for the house will met by an evacuated tube collector and cooling loads through a cold water ground loop leaving only circulating pumps, lighting, cooking, refrig/freezer and accessory loads. I am estimating my average continuous load at 1kw and peak load at 6.5kw with daily usage to be 26kw/hrs per day.

    You're going to need a huge and expensive array to meet those power needs. Rule #1 of off-grid: conserve. Start by eliminating any and all electrical heating devices. Get a Kill-A-Watt meter and measure what loads you can with it for some "real world" numbers. The more you can reduce your needs the better.
    I have a 17kVA 120/240V ferro ressonant UPS system manufactured by BEST Corp. that is in good working order that I would like to use in the system.

    I'm not familiar with that particular unit so my answers will be based on the assumption it is viable for the application.
    I have a couple reasons for this, we are on an electric co-op here and at the end of the line, street power is unstable and undependable, I do not use much power during the daylight hours, I will likely generate more than we use during the day and would like to store it in the UPS batteries (there are 10, 12V lead acid batteries installed and I have additional battery racks available) for use in the evening/early morning. Excess power after my usage needs are met and the batteries are charged would be net metered. This should save me the cost of buying an invertor and give me clean/regulated street power thereby increasing appliance efficiency.

    First problem: Your UPS unit if hooked to the grid will "see" grid power and use it to charge batteries. It is not designed to sell anything back to the grid.

    Questions:

    I am assuming that as long as the UPS does not see street power it will work in the inverter mode and supply conditioned AC power from the battery bank as well as giving me a readout of the charge level and the reminaing time available. The array would charge the batteries through its own charge controller and provide continuous charge throughout the day. Is there an automatic switching mechanism available for switching the street power on when I drop below a certain charge level?

    Yes; a proper battery-backed grid-tie inverter. Or a Voltage-controlled switch operating a heavy relay.
    Should the array be connected to its own charge controller? I assume there is no way to utilize the UPS systems on board charge controller for the PV array?

    Correct. Never seen an industrial UPS unit that has PV input. That doesn't mean there isn't one; it just isn't likely. Charge must be regulated.
    Are there any other potential pitfalls I should be aware of when doing this?

    Lots. Legal ones like "would this be allowed in your area?" and technical ones like "is it feasible to wire this up?" The devil is in the details. For instance your 26 kW hours per day on 120 Volts (I presume that's the DC side, based on 10 * 12) of batteries. That will require over 400 Amp hours of battery @ 50% DOD. How big are these batteries in Amp hour capacity?

    Any insight and objective criticism of this plan would be helpful.

    You'll probably get lots here. :D I'm sure some of the "grid tie" folks will have something to add, as well as some of the other "off-gridders".
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: UPS/inverter system

    Cooling loads by recirculating ground water? Doubt you have water cold enough in Virginia to do it. A company tried to sell me this system but upon close inspection it is not easy to use - generally not practical.

    Evacuated tube collectors for heating - you will need a very, very large roof covered with collectors plus hot water storage. Doable but not small or cheap.

    Russ
  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: UPS/inverter system

    Coot,

    Problem: I'm not living in the house yet so I can't measure loads. I am calculating based on average grid tie consumption otherwise I would follow your advice on the Kill-a-watt. Real world load will probably be much less than stated. The only heating loads I will have are stove (induction cooktop), oven (convection) clothes dryer and backup for hot water. Perhaps someone can give me what their real world loads are for a 1300sq.ft 1 1/2 story superinsulated ICF/SIP home with three occupants, in slab radiant cooling/heating, reflective roof, and optimized glazing/solar orientation.

    Let me be clear, I am not going to try to build a PV array to meet my peak loads as I will be grid tied and have battery.

    I fully expect I will be using a substantial amount of grid power in the winter but have a surplus in the summer.

    I was figuring a 4.5- 5KW array. Is this realistic?

    I am planning to switch grid power off to the UPS unit unless batteries are low and array is not providing charge, however, your point is well made. Inverter to Net meter circuit from invertor will need to bypass UPS input voltage sensor once batteries are charged. Connecting the invertor output to the Meter connection could be tricky.

    Local inspector is very reasonable. He rocognizes that this is not an ordinary home and would never be sold as such. All electrical supply equipment will be external to the house itself housed in a mechanical building. As such I am not concerned with UL or insurability issues.

    The battery bank is a string of 10 C&D Technologies UPS12-300MR VRLA battteries with a capacity of 78 amp/H 300W each. 13.5-13-8 VDC float.
  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: UPS/inverter system
    russ wrote: »
    Cooling loads by recirculating ground water? Doubt you have water cold enough in Virginia to do it.


    Russ

    Russ,
    Due to thermal mass in the ICF walls I have almost no diurnal temp swing. With super insulated SIP roof and ample summer shading, interior temps remain in the 70-80 degree range throuout the day with no cooling during the hottest months. I have 37 tons of gravel in an insulated bed with water loop under the slab. I intend to circulate 65 degree water through the conrete slab. Any colder water in the slab would cause sweating of the floors and be generally uncomfortable. Additionally valance cooling units will supplement this upstairs and serve to dehumidfy. My well puts out water in the 50-56 degree temp range year round.

    I agree ground water cooling would not be practical for house of average constuction.

    I have already done the load calcs on the evac. tubes. I only need 90-95 degree water for the slab. 2 racks of 10 tubes ea. will meet all my hot water needs and my heating needs and I will have additional storage capacity for excess. This is not very large or expensive considering it will all be free energy and I am able to eliminate ductwork, compressors, blowers, refrigerants, and it will work for 25+ years with no efficiency loss.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: UPS/inverter system

    A requirement that all utilities have for inverters connected to the grid is that it do anti-islanding, that is, in the event of a grid outage it must immediately disconnect itself from the grid, and it must be UL listed with that capability. I apologize if I'm telling you what you already know, but I'm not familiar with how those UPS units work.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: UPS/inverter system

    I think you are missing a key point regarding grid-tie and selling back to the utility. Your UPS unit is not designed to do this. It has no method of synchronizing its output to the grid signal and has no anti-islanding function to prevent accidental energizing of the grid in the event of a power failure. In short, it can not function as a GT inverter and it will not be legal to connect it as one. These is quite a problem as it affects a key (and sensible) portion of your plan.

    What you really want here is one or two Xantrex XW6048 hybrid grid-tie inverters. Regrettably they're about $3,000 each. That's a lot of money. You would still need a battery bank, solar panels, and charge controller(s).

    You can get some prospective numbers for your array size by using the PVWatts program http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/ (I think that's the old link?). Input the data for your area & proposed system and it will give you a pretty good idea of what you can expect for a given array size - including financial value. In terms of your over-all daily needs estimate, a 5 kW array looks like less than half your requirements. Your 78 Amp hours of battery would only provide roughly 4.6 kW hours power.

    This is often the problem when you try to adapt some existing technology; it doesn't actually fit the needs and ends up being more difficult and/or expensive to get it to work than if you swallow the bitter pill and buy the right equipment to begin with.

    As for how much power you're likely to use ... Our cabin is about the same size as your house. We use propane for cooking & hot water, wood for heat. There is an electric refrigerator, microwave, computer/satellite set-up, electric water & septic pump. It eats up 2.4 kW hours per day with careful management. There's room for improvement. There's no AC, which you'd probably want. In general I suspect that if you rework your design ideas you should be able to cut your planned usage in half, possibly to one quarter (6 kW hours per day) and still live reasonably well. I can't say for sure because I've never lived in Virginia so I don't know what the availabilities and precise power usage might be. But someone around here can probably get you closer to what you need.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: UPS/inverter system

    I guess you are in a location that needs Air Conditioning?

    Anyway... Assuming 26 kWH per day and you can choose ~0.77 derating for a Grid Tied Installation or ~0.52 system derating for an Off-Grid (battery/inverter) application.

    Using PV Watts website, fixed array, using program defaults (except as above) and 1,000 watts of panelos as a nice round number (1 kW in program), and assuming you are in the mountains near Lynchburg VA, first 0.77 GT derating, second as 0.52 off grid derating::
    "Station Identification"
    "City:","Lynchburg"
    "State:","Virginia"
    "Lat (deg N):", 37.33
    "Long (deg W):", 79.20
    "Elev (m): ", 279
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 0.8 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 37.3"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.0 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.84, 93, 7.44
    2, 4.73, 101, 8.08
    3, 5.57, 128, 10.24
    4, 5.69, 124, 9.92
    5, 5.69, 123, 9.84
    6, 5.87, 120, 9.60
    7, 5.87, 124, 9.92
    8, 5.67, 120, 9.60
    9, 5.39, 113, 9.04
    10, 4.99, 113, 9.04
    11, 4.15, 93, 7.44
    12, 3.56, 84, 6.72
    "Year", 5.09, 1336, 106.88
    and Off Grid:
    "Station Identification"
    "City:","Lynchburg"
    "State:","Virginia"
    "Lat (deg N):", 37.33
    "Long (deg W):", 79.20
    "Elev (m): ", 279
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 37.3"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.0 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.84, 62, 4.96
    2, 4.73, 67, 5.36
    3, 5.57, 85, 6.80
    4, 5.69, 82, 6.56
    5, 5.69, 81, 6.48
    6, 5.87, 79, 6.32
    7, 5.87, 82, 6.56
    8, 5.67, 79, 6.32
    9, 5.39, 75, 6.00
    10, 4.99, 75, 6.00
    11, 4.15, 61, 4.88
    12, 3.56, 56, 4.48
    "Year", 5.09, 882, 70.56
    Less assume you want to design the system to run from the array for 9 months of the year... The lowest production 9th month is February at ~4.73 hours of sun per day.

    26 kWH per day:
    • Feb GT: 26 kWH per day * 28 days per Feb * 1/101 kWH per month per 1kW of panels = 7.2 kWatt Array
    • Feb Off Grid : 26 kWH per day * 28 days per Feb * 1/67 kWH per month per 1kW of panels =10.9 kWatt Array
    For a pure Grid Tied system, you are looking at around $6k-$8k per kW of solar array installed:
    • $6,000 per kW Array * 7.2kW panels = $43,200 installed
    For an off-grid/hybrid system, perhaps around $10k to $20k per 1 kW of array:
    • $15,000 * 10.9 kW panels = $163,500 installed
    The above numbers are just to set your expectations--I am not in the solar business and the numbers are just rough estimates. Does not include possible tax credits and other local rebates.

    In general, solar PV power is very expensive and going with an off-grid implementation works out to be ~10x as expensive per kWH (charge controllers, batteries, replacement batteries every X years, new charge controllers, inverters every ~10 years, repairs, etc.).

    Assuming you use an average of 26kW per day 365 days a year for a $163,500 system and $10 per watt maintenance over 20 years:
    • ($163,500 + $109,000 maintenance) / (20 years * 365 days * 26 kWH per day) = $1.44 per kWHr
    That is vs the ~$0.08-$0.10 per kWH you may pay today. And does not include fuel/power you have to purchase to make up for deficits during the 3 months of winter.

    Anyway, my assumptions are probably way out of wack vs your real needs (assuming high electric power is only needed during summer).

    I would reconsider the Evacuated Tube Solar Collectors... they tend to be very expensive and fragile (I am not sure how long they will hold up over time and possible mineral build up over heat exchanger point at water/antifreeze contact point). And not really great in areas with snow (they are insulated so well, they do not melt snow off during the winter). Regular flat plate insulated glass/box collectors may be more practical unless you are after very hot water (160F or higher?) for some reason.

    In the end, if you where going off grid--It would be nice to plan on a home that uses ~3.3 kWH per day (100 kWH per month) as a reasonable size/capital cost system.

    For my home (just south of San Francisco CA), old in moderate climate with 2 adults and 2 kids around 200-300 kWH per month or 10kW per day (central heat, washer/drier, all heat from natural gas) is certainly possible. Natural gas bill is around $20 to $60 per month (summer/winter, no solar thermal panels).

    It really does get back to conservation and knowing your loads. Since you have grid power--Just install your normal grid powered system and monitor your power usage/needs. Get a "cheap" backup generator plus alternative fuel (natural gas, propane, etc.) for emergency power (if needed).

    A UPS/Power Conditioner is another loss of efficiency (80%?) and frankly, only a few of your devices probably need clean/battery backed power. A few computers (go low power--a single computer on 24x7 takes more power than most folks use their for their microwave ovens). You can go with a standard fail over type system for TV's, washer/driers/lights, etc.

    If your local utility allows Net Metered power (Grid Tied) and you want the ability to run your whole home off grid, take a look at the Xantrex/Schneider XW Hybrid Inverter... It does fit well in the Grid/Off-Grid/Generator backup type home. And use a small (or several small) UPS's at point of power usage (computer, server) to ride through the XW power fail over...

    All the above is in my humble opinion. Power usage is a highly personal subject. I am not trying to tell you that my power usage is greener/better than your plans. Just some suggestions at how to look at the whole issue and how to assign "cost" to Grid and Off-Grid power. The conservation/usage decisions are much different at $0.10 vs $1.44 per kWH for electricity:
    • Grid Power: $0.10/kWH * 26kW per day * 30 days per month = $78.00 per month
    • Off-Grid Power: $1.44/kWH * 26kW per day * 30 days per month = $1,123.20 per month
    -Bill

    PS: Try to define your power needs and what your local power company will allow first... Designing the System first can be pretty frustrating.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: UPS/inverter system

    This is good info. I am about 40mi. south of Lynchburg so those figures should be pretty close. I am definitely going to size it as a GT system.

    The UPS definitely provides a UL listed anti-islanding device. UPS systems would not support computer equipment very long at all if they were leaking power back into the grid at the same time.
    It also comes with a large and expensive manual maintence bypass switch. These are typically Make-before-break type although make-after-break are also common. I could use this when I want to switch between grid and solar, doing something with a large load (running the clothes dryer or welder) and change it back when I wanted to go back to battery.

    I guess I need to start by doing a schematic drawing of the system.

    Since I would not run the UPS itself on PV power, just merely pirate the DC/AC invertor there should not be an efficiency loss. The 80% loss would only be when running in grid power mode with online UPS battery/PV backup.


    I might be best off to leave the Net metering part out of the equation right now just for the sake of cost and simplicity.

    From what I am hearing I need to limit my daily kW/h to 12/14 peak rather than the estimated 26 if i am going to live with this system configured as a GT at my location in Feb.?

    None of this is going on the roof. I have 10ac. of land to play with so space is not an issue. The evacuated tubes are more efficient at producing heat in the winter and on cloudy days. If one tube breaks it can easily be replaced and does not interrupt anything in the system. Cost per BTU is not that much different from flate plate collectors these days. Flate plates suffer from heat dissapation in cold ambient temps, and have the same issues with mineral buildup at heat exchange unit as they are no different in that part of the system.

    I already have a bunch of surplus tubes I am going to build heat pipes and manifold for. I can clean snow off of the collector with it at ground level and we sledom get much snow anyway. Round tubes offer less wind resistance and debris falls through rather than laying on them (leaves and pine needles). I may be able to use their higher water temos in the future to run an adsorption chiller should I not have enough cold water capacity in the summer.

    This is not to say anything bad about flat plates, they have their place as well.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: UPS/inverter system

    I think you need to read up on the functioning of the UPS unit you're planning to use. Generally, these things work one of two ways:

    1). Feed incoming AC to loads until power is dropped, then switch loads to battery (charged by grid when available) and inverter.

    2). Convert incoming AC to DC to maintain battery level, all outgoing AC supplied by inverter running off batteries.

    They do not have anti-islanding functions because they are not design to ever feed AC back to the grid.
    If you look at the manual for a battery backed-up GT inverter you will see quite a lot of programming variables; most importantly the "sell" Voltage. When the batteries reach that point, the inverter starts back-feeding the grid with any surplus AC Watts it can produce. I do not see how any standard UPS unit is going to perform this function as they're just not built to do so. Looks like grid tie is out of the plan if you use the UPS unit.

    Another suggestion: wire your "critical" loads to the UPS, and your "heavy" loads to the grid. Nothing says you can't break up the breaker box! You could use a charge controller like the Outback or a Voltage-controlled switch to activate a circuit to feed grid Voltage to the UPS when the batteries get too low and there's no solar available. Not quite grid-tie, but it would automatically keep your grid usage to a minimum.
  • arkieoscar
    arkieoscar Solar Expert Posts: 101 ✭✭
    Re: UPS/inverter system

    R.E. Your cooling system idea. I had a client try just that in the late 80's and he had major sweating problems in the summer here in N. Arkansas. Had to abandon the system. See if you can find how many days that the dew point is above 65 or 70 degrees.
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: UPS/inverter system

    thehardway, it sounds like you'll be doing about what I plan on doing. I have a 6 kw UPS, and this is how I plan on making it work with the grid. As in one-or-the-other, no grid-tie. First, plan on running your big loads utility-only - stove, etc. Pick your core loads, such as a fridge and small appliances and run them through the UPS. Your solar charge controller will charge your batteries during the day. Get a timer that will remove your UPS from the utility for X number of hours during the day, extending into the evening. How many hours will depend on how much solar you have and therefore how many amps you are putting into your batteries each day. Once the timer brings the utility connection back online the built-in AC charger will top off the batteries and also supply your loads directly.

    Things to look into. Usually UPSs come with sealed lead-acid batteries. You should convert to flooded lead-acid batteries for better performance. Also, the UPS you have will have a very very large amp draw just for itself, so make sure you factor that as one of your loads. Especially one with a ferrous core transformer like yours (and mine). Finally, often these UPSs require a utility (or genset) input before they will start up, you can't just start them up from your battery bank if the utility goes down. For all of these reasons you may want to seriously consider buying a non-transformer based inverter. I consider mine to be on the edge of too-big and too-amp-hungry for off-grid use and would definitely consider yours to be.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    Re: UPS/inverter system
    thehardway wrote: »

    The UPS definitely provides a UL listed anti-islanding device. UPS systems would not support computer equipment very long at all if they were leaking power back into the grid at the same time.

    That's because it's NOT a grid-tied inverter. The grid side is an INPUT ONLY!!

    It is not capable of pushing power to the grid and you can not legally make it into a grid-tied inverter, all you can do is use it as an UPS with solar charged batteries.

    Also I don't think you are taking battery charge efficiency into account. Your plan to run off batteries every day means that this will be an important consideration. Lead-Acid batteries are at best 75% efficient at storing energy.
    To do what you want to do you will need an array that is at least 30% larger than a typical grid-tied setup for the same average energy use.
    All of those extra panels will probably cost as much or more than simply buying a proper grid-tied inverter.

    Plus I'm gathering that you plan to use the original UPS batteries. These are typically NOT designed from frequent deep cycling and will like wear out within a year or two, assuming they aren't partially worn out already.

    If you really want to use the UPS, then simply buy a grid-tied inverter and then put the UPS between the inverter and your house.
    If the grid goes down, then the GT inverter will shut down and the UPS will take over. When the grid comes back up the GT inverter will kick in, the UPS wiil start recharging the batteries, the bulk of this energy will hopefully come from the GT inverter (unless it's dark out)

    You'll be able to get by with a smaller array, you won't need a battery charge controller, and THIS setup will be able to sell excess power back to the grid
  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: UPS/inverter system

    I made a few mistakes here. I thought the term Grid Tied referred to the house, not the array. It all makes more sense to me now.

    What I meant to say was that the house will be tied to the grid. The array may remain off-grid and just charge the UPS batteries for now. That should simplify it and negate the need for the GTI.

    I mis-stated the size of my UPS. It is a 10kVa UPS Specs are:

    AC input:
    39A @ 240V

    AC output: 41A @ 240V, 82A @120V

    DC input: 120V at 71A

    10kVa .75 leading PF


    I was thinking of a different unit when I said 17kVa


    Battery specs are still the same, 10 @ 12v ea.



    Cooling system: Many have tried radiant floor cooling unsuccessfully. What makes me think I can succeed where others have failed? I have a much tighter envelope, much better insulated than most and with a lot of thermal mass. I have less than a 10 degree F diurnal temp swing inside the envelope, even without heating/cooling. This allows me to work with a much smaller DeltaT and better control of relative humidity and indoor heat gain.

    Functionally, the cold water will not pass directly into the floor, it will first pass through a valence coil. Air is cooled there and any extra moisture is condensed on the coil and carried away via a drain pipe. The cooled and dry air then falls to the floor via natural convection and the warm air rises to the coil. No power required. The dry cool air falling to the floor will not condense as it is above dewpoint and the water in the floor slab has been tempered. As long as air is less than 3 degrees above floor surface temp at 90% relative humidity, no condensation will form.

    This is pretty extreme. Unlikely that one would experience 90% RH at 70F and if so you better have your sauna checked out for malfunction.

    More likely scenario, at 50% RH I can lower floor surface temp to 56F before getting any condensation. Tempered water would never get this cold nor would you want the floor that cold.

    I am going to draw out the PV/UPS system and rethink it all tonight. Then I will post what I came up with and let you pick it apart again.

    There are lot's of interesting ideas and approaches that might work for my purpose mentioned.

    Is it true that to equal the output of the 240V/ 40A DC/AC inverter in the UPS, I would have to have something the likes of a Sunnyboy 10000TL US to a tune of $4500.00? Any cheaper alternatives?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: UPS/inverter system
    thehardway wrote: »
    I mis-stated the size of my UPS. It is a 10kVa UPS Specs are:

    AC input:
    39A @ 240V

    AC output: 41A @ 240V, 82A @120V

    DC input: 120V at 71A

    10kVa .75 leading PF

    Is it just me, or do those numbers not add up? :confused:
  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    Re: UPS/inverter system
    thehardway wrote: »
    What I meant to say was that the house will be tied to the grid. The array may remain off-grid and just charge the UPS batteries for now. That should simplify it and negate the need for the GTI.

    Is it true that to equal the output of the 240V/ 40A DC/AC inverter in the UPS, I would have to have something the likes of a Sunnyboy 10000TL US to a tune of $4500.00? Any cheaper alternatives?

    If you connect the array directly to your batteries you will need charge controllers (and probably need to disable the charger in your UPS).
    Have you looked at the price of charge controllers? The cost for enough charge controllers to handle your array will be pretty close to the cost of a GT inverter.

    You still have the 75% battery loss, which means you'll need a 30-35% larger array.

    Once again it's probably cheaper to go with a GT inverter.

    Do you NEED a 10kw inverter? How much energy do you use per day on average? Add up a years worth of kwh from your electric bill and then divide by 365.

    You only need a GT inverter large enough to handle an array large enough to produce the same AVERAGE energy as you use.
    For the average US home this is only around 5-7 kw.
  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: UPS/inverter system
    Is it just me, or do those numbers not add up? :confused:

    Seems strange doesn't it. How can you get more out than you put in? I took it straight off the plate on the unit.

    Is there a way on this board to post pics or diagrams?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: UPS/inverter system
    thehardway wrote: »
    Seems strange doesn't it. How can you get more out than you put in? I took it straight off the plate on the unit.

    Is there a way on this board to post pics or diagrams?

    Yes; when you post, scroll down past the text box. There you'll find "Additional Options" which includes "Attach Files".
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: UPS/inverter system

    Peter V - he'll need a PV array that is 100% larger than his projected load to account for battery, wire and inverter inefficiencies. He will need a charge controller to deal with the PV output but he does not need to disable the UPS's charger. As I mentioned in my post above, he can use both (even at the same time if necessary) by using the PV during the day and then the grid to power the AC charger overnight.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • keyturbocars
    keyturbocars Solar Expert Posts: 375 ✭✭
    Re: UPS/inverter system

    Just a related note on using a UPS.

    I've got an APC Matrix 5000 which is rated for around 5000VA and 3750W at typical power factor. It actually works quite well for occasional emergency backup power. It can be cold started with no grid power. However, as with most UPS units, there is very little surge capacity above the rated output. And, the idle power consumption is quite high. On mine, it draws around 125W just sitting there waiting for a load! Under higher loads (50% and above), then the efficiency goes into the 90's, so it's actually not bad. I've calculated efficiency using a DC clamp on ammeter to determine power draw on the DC sidem and the Kill-A-Watt meter to determine loads on the AC side.

    At 700W load, efficiency was 83.9%.
    At 825W load, efficiency was 86.3%.
    At 1495W load, efficiency was 88.8%
    At 2705W load, efficiency was 91.5%.

    That last reading was around 50% of the APC Matrix's capacity, since I was using resistive loads with PF = 1.0. At higher loads, the high idle consumption becomes less of an issue on these UPS units.

    I'd suspect your UPS unit is similar in the limited surge capacity and the high idle power consumption. I'd check to verify your idle power consumption to see if it's even worthwhile to use in your system.

    Edward
  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    Re: UPS/inverter system
    techntrek wrote: »
    Things to look into. Usually UPSs come with sealed lead-acid batteries. You should convert to flooded lead-acid batteries for better performance. Also, the UPS you have will have a very very large amp draw just for itself, so make sure you factor that as one of your loads. Especially one with a ferrous core transformer like yours (and mine). Finally, often these UPSs require a utility (or genset) input before they will start up, you can't just start them up from your battery bank if the utility goes down. For all of these reasons you may want to seriously consider buying a non-transformer based inverter. I consider mine to be on the edge of too-big and too-amp-hungry for off-grid use and would definitely consider yours to be.

    I have an 18KW Best FE UPS. It will start with no grid from batteries. But these things are BIG power hogs. Mine draws a little over 1KW idling.

    I think all the FE UPS will have this issue. Finding a 120 volt charge controller is an issue also.
  • keyturbocars
    keyturbocars Solar Expert Posts: 375 ✭✭
    Re: UPS/inverter system
    Jburgess wrote: »
    I have an 18KW Best FE UPS. It will start with no grid from batteries. But these things are BIG power hogs. Mine draws a little over 1KW idling.

    I think all the FE UPS will have this issue. Finding a 120 volt charge controller is an issue also.

    The new Midnite Classic 250KS can handle 120V battery banks.

    http://www.midnitesolar.com/productPhoto.php?product_ID=259&productCatName=Charge%20Controllers&productCat_ID=21

    However, if those FE UPS's draw over 1kW at idle, then that might be a show stopper for serious long term use.

    Edward
  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    Re: UPS/inverter system
    The new Midnite Classic 250KS can handle 120V battery banks.

    http://www.midnitesolar.com/productPhoto.php?product_ID=259&productCatName=Charge%20Controllers&productCat_ID=21

    However, if those FE UPS's draw over 1kW at idle, then that might be a show stopper for serious long term use.

    Edward

    Unfortunately I need a charger that has 600V max PV to match my arrays. Thanks for the link anyways.
  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: UPS/inverter system

    I'll have to check and see what the consumption at idle is. Still thinking on the layout. Too many ideas spinning in my head at this point.

    Based on the feedback here, at this point I am thinking about using the UPS like an emergency backup generator. . I could manually turn it on if I lose street power, hence no idle load. The battery bank could be shared between it and the solar array or just used as an auxillary bank. I could put just specific loads on it, like the well pump and the circulator pumps, this would keep me in heat and water during a power outage if used with discretion.


    Part of the equation is this. I have been approved for a state rebate program of up to 30% of installed cost up to 10KW. I also have been approved for solar thermal up to 5KW. I have 180 days to complete install starting last Mon. I have 3 installers lined up to do site survey's and proposals over the next week.

    Probably best to leave the UPS out of the equation for sake of time and simplicity. Should I install the full 10KW of PV panels in this deal or just what I need? Probably 4-5K as mentioned earlier?
  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    Re: UPS/inverter system
    techntrek wrote: »
    Peter V - he'll need a PV array that is 100% larger than his projected load to account for battery, wire and inverter inefficiencies. He will need a charge controller to deal with the PV output but he does not need to disable the UPS's charger. As I mentioned in my post above, he can use both (even at the same time if necessary) by using the PV during the day and then the grid to power the AC charger overnight.

    The problem is how to prevent the UPS from using the built in charger when the grid is UP and he wants to run off batteries.
  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    Re: UPS/inverter system
    thehardway wrote: »
    Probably best to leave the UPS out of the equation for sake of time and simplicity. Should I install the full 10KW of PV panels in this deal or just what I need? Probably 4-5K as mentioned earlier?

    What would be the point of installing way more than you need? It's unlikely you'll make any money on this, in fact you'll probably pay through the nose with no chance of recouping your expenses (for the surplus capacity)

    Assuming your only rebates are the 30% state and 30% federal, it's important to note that they don't stack.

    I.e you don't get 60% off. The federal rebate is only for 30% of what you're left paying after all other rebates. So your total rebate will be about 50%

    Assuming you can get a bid for approx $5 a watt, and your system will last 20 years with no extra costs (hey, it could happen)...

    How much will you make selling power to the grid?
    Around here you make about 4 cents per kwh, some places make 15 cents per kwh.
    If you make 4 cent per kwh, after rebates it will take you over 40 years to break even on the surplus capacity, if you make 15 cents it will only take you 12-15 years. Neither of these are a good ROI.
  • thehardway
    thehardway Solar Expert Posts: 56 ✭✭✭✭
    Re: UPS/inverter system

    My local net meter payback is $0.08 which isn't too bad. It appears I can get it installed as a simple grid tie for about $5.00 per Kw. Supposedly there are some SREC aggregators/brokerage companies that are front ending the cost of systems in exchange for a multi-year exclusive on SREC's. If anyone has dealt with the SREC portion I would be interested in insight. Is it best to auction them or use an aggreagator/broker

    Although my load may be small right now I will probably add to the house, build a garage/shop and get a plug in hybrid at some time. I will be commuting 80 mi. round trip each day.

    Is it best to add capacity on rebate funds now and begin generating revenue or to wait and add it as needed with falling PV cell prices?

    Some of these questions are probably best asked in a different category on the forum so I will post there on the whole SREC and payback issue.

    I think I decided last night that I will go ahead and install the solar system as a standard grid tie, and install the UPS just like a backup generator. If I install it with approved handle tied breakers and operate them manually during power outage, or put it on a Listed ATS, these would both prevent backfeed into the grid. I won't connect the batteries to the array at this time. Once I get moved in and know better what my loads are I can adopt a plan for battery storage.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: UPS/inverter system

    We'd better point out here that an array configured for a standard grid-tie inverter will not necessarily be able to be connected to a battery bank. Straight grid-tie inverters run arrays with hundreds of Volts (except microinverters, which is another scenario but also won't work with batteries) whereas most battery banks are < 50 Volts. Your UPS unit is 120 (I think) but that's still less than half what the GTI will take. Therefor wiring the system up so that the same array can run the GTI and charge the 120 Volt battery bank directly becomes a bit of a problem.
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: UPS/inverter system
    Peter_V wrote: »
    The problem is how to prevent the UPS from using the built in charger when the grid is UP and he wants to run off batteries.

    The solution is easy and is why I suggested using a timer on the utility input to the UPS. Simulate a power outage for X hours per day which will force the UPS to run only from the battery (being fed by PV). There are 240 volt water heater timers that could be used for this.

    Let's say his array can support 6 hours of his average load during the summer, 5 during spring/fall, and 4 during the winter (factoring in the higher efficiency of setting the timer for daylight hours so less is lost to battery inefficiencies). Set the timer for those lengths changing it every season. If he doubles his PV in a few years, re-figure the numbers and then maybe he can be off-grid 10 hours in the summer, 8 spring/fall, and 6 in the winter (the numbers probably won't double since he'll be relying on batteries more at the fringes of daylight).

    When the timer brings the utility back online the batteries may get a small top-off, the process won't be and doesn't need to be 100% accurate. If there is a long-term real outage he just has to reduce his daily loads to match his actual PV input or rely on the genset for a few hours in the evening.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • keyturbocars
    keyturbocars Solar Expert Posts: 375 ✭✭
    Re: UPS/inverter system

    I ran across this the other day and it made me think of this thread. I'll cut and paste part of the article below. This is an old article that APC put out advertising their Matrix UPS line (now discontinued). So, obviously this is biased since it's advertising. However, it brings up the question of how efficient are these Ferroresonant UPS units. Low efficiency combined with very high idle loads (1kW was mentioned for one unit) does not sound like a good combination for RE use. Below is part of the article cut and paste...

    Matrix-UPS vs. Ferro resonant UPS
    The Ferro resonant UPS (or FerrUPS) is not only limited in its manageability but also very inflexible when changing platforms. Matrix-UPS supports multiple loads in parallel. When multiple loads are powered on at different times, the FerrUPS risks dropping the load, while the Matrix-UPS will maintain stability. Efficiency with FerrUPS: At full load, the FerrUPS runs at 80% efficiency, compared to the 93% efficiency at full load for the Matrix-UPS. Fully loading a FerrUPS is dangerous due to the fact that Ferro resonant UPSs cannot handle a high inrush current. The FerrUPS must be de rated up to 50% to account for inrush current. As the load is reduced, the FerrUPS efficiency drops much faster than the Matrix-UPS. At 60% load, a Ferro resonant based UPS can have an efficiency as low as 65 to 70%, compared to a 90% efficiency at 60% load for the Matrix-UPS.

    Just food for thought.

    Edward
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: UPS/inverter system

    Mostly marketing BS. I ran all 120 volt circuits in my house through my UPS for over 2 years and never had it drop out, including running things like a vacuum cleaner which put it into overload briefly during the startup surge. Mine also has a higher efficiency under full load, going by memory I think it is 87%.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is