Solar/battery set up on a Handwashing trailer

squinkosquinko Registered Users Posts: 5 ✭✭
Hello, 
I am VERY new to solar and battery power. I have a 10 sink Handwashing trailer I use on Wildland Fires. Currently I use either a small generator to power the trailer or I plug into shore power. I want to add a battery system with solar panels to run my pump, LED lights and to power my tankless water heater.  It’s a propane water heater but still needs power. I’ve done some research but it’s like learning a foreign language to me. I’ve seen other systems on similar trailers as simple as a Harbor Freight solar panels hooked up to batteries and the batteries power the inverter.  Also seen pretty advanced stuff like on motor homes. 

My sinks are not used all the time. They mostly get used in the morning and evening. The pump will only run for 20-30 seconds then shut off. It may start up and shut down multiple times while people are coming and going. It’s an on demand style pump.  Same with the hot water heater. Any advice would be greatly appreciated on inverter size, battery type (Acid or lithium) and portable solar set up.  Below are the specs on my pump and water heater. This trailer sits all winter and is only used during the summer for about 2-4 weeks at a time. 

Thanks in advance for any advice. 

Bur Cam well pump
120 volt electrical connection
3/4 HP
115 VAC
60Hz
7.5 Amps (15 Apms when the pump starts)

Rinnai (RL75i) Propane tankless water heater
120 volt electrical connection 
Normal 76W
Standby 2W 
Anti frost 120W
Max current 4A



Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,803 ✭✭✭✭✭
    squinko said:
    Bur Cam well pump
    120 volt electrical connection
    3/4 HP
    115 VAC
    60Hz
    7.5 Amps (15 Apms when the pump starts)
    Unless you are pulling water out of the ground, this is 'silly over kill'. It says well pump, but sounds like you are just creating pressure for hand washing. I'd look for something more realistic. If you aren't needing shower like water pressure, and the water is just a few inches below delivery, look at a DC water pump.  I can't recall the exact pump I purchased for my friends hydroponic garden, but pretty sure it had a 1/4" inlet/outlet maybe 10mm (I think we used 3/8" hose and clamps) and it would fill a 5 gallon bucket with about a 3' lift in a 3-4 minutes. Actually ran it directly on an old solar panel 55 watt? from the 80's.



    I'll hunt around and see if I can find a link, it was a 12-24 volt so no have with the 17-18 volts the panel produced. I think 1amp. Pretty sure it was a reed pump (no surges like a Shurflo RV pump which uses a membrane)

    I'll hunt around, see if I can find some info, think I have the little pump in stuff in storage. Perhaps you want more than this? 10 wash stations at once? 7.5 amps at 120v = 900watts, That's before adding 10% inverter losses. 1 amp at 24 volts = 24 watts (at 12 volts it would either have lower flow or run at 2 amps)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • PhotowhitPhotowhit Solar Expert Posts: 5,803 ✭✭✭✭✭
    You will want to know what pressure is required for the water heater. 

    There are low flow propane heater that just need a 'C' cell for the piezo lighter.... Camping equipment.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.BB. Super Moderators, Administrators Posts: 32,593 admin
    As Photowhit says--You need to "conserve" energy usage for solar+battery systems. Solar power is not cheap.

    I would suggest looking at 12 or 24 VDC systems and an RV 5 gallon propane water heater rather than tankless heater... Some suggestions (just links for you to start your research).

    12 or 24 VDC Water pump... 20 up to 60 PSI (higher pressure, higher current draw):

    https://www.solar-electric.com/aquatec-550-series-m638-12-volt-booster-pumps.html ($85 each)

    I don't work for NAWS (just a volunteer here on the forum)... I did purchase the 120 VAC version of the pump, and so far (light use), it has worked well for my needs (garden watering from tanks).

    You are looking at probably 8-16 amps @ 12 VDC depending on pump/water volume/pressure. Your 120 VAC pump draws almost 10x more power vs this 12 VDC pump... And you need an AC inverter + battery bank that is capable of those Amps/Watts delivery. Much cheaper/easier to use the 12 or 24 VDC small "RV type" water pump instead with solar power.

    You can also look at using a pressure tank--Both for short usage at higher volumes, and to reduce the "pump pulses" if an issue:

    https://www.amazon.com/rv-water-pressure-tank/s?k=rv+water+pressure+tank

    And for water heater... Simple RV water heater tank:

    https://www.amazon.com/s?k=rv+water+heater&sprefix=rv+water+heater (wow--Those are more expensive than I thought)

    Or, if you do want tankless--There are Tankless water heaters for "camping" use:

    https://www.amazon.com/EZ-101-Tankless-Water-Heater/dp/B09N9VH37B/ref=sr_1_56?keywords=tankless+rv+water+heater&qid=1652318081

    Asuming that water may be hard to get... A tanked water heater will probably "waste" less waver vs a Tankless heater that needs to heat up and the users need to adjust water temperature.

    For lighting, if needed, there are 12/24 VDC LED lighting. There are LED units that will work on either 12 or 24 VDC battery banks:

    https://www.amazon.com/s?k=12+24+vdc+led+lights&i=tools&crid=33BDCJEWRJLTI&sprefix=12+24+vdc+led+light

    If you needed 120 VAC for a few things (small loads, laptop/cell phone chargers/etc.)--A smallish 300 Watt 12 VDC (or other) AC inverter can be nice. Here is a popular reliable 300 Watt AC inverter that runs from 12 VDC bus. Also has automatic standby mode (cuts power usage if no AC loads) and remote on/off switch:

    https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?manufacturer=79

    To run some quick solar power calculations. Say you have a 3 GPM water pump @ 60 PSI and 3.2 gpm @ 16.3 amps @ 12 VDC. And 100 gallons of water storage. And want to run that in one day (refill for next day, or use 100 GPD and much larger water tanks):

    https://www.solar-electric.com/lib/wind-sun/Aquatect_ds55xx-xx01-b636.pdf
    • 100 GPD / 3.2 GPM = 31.25 minutes or ~ 1/2 hour of pumping per day
    • 1/2 hour per day * 16.3 Amps = 8.15 AH per day @ 12 volts
    • 8.15 AH per day * 12 volts = 97.8 WH per day
    Generally, suggest 2 days of electrical energy storage and 50% max discharge (suggested for Lead Acid batteries):
    • 8.15 AH per day * 2 days * 1/0.50 max planned discharge = 58.6 AH suggested minimum @ 12 volt battery bank
    There are lots of options here... Just a first pass guess at water/pump usage... And what other loads you may want (LED lighting, charging laptops, cell phones, etc.)...

    For example, using a pair of 6 volt @ 200 AH flooded cell "Golf Cart" batteries are a nice "starter bank". That would give you a much larger bank for very reasonable costs.

    Now sizing the solar array... There are two calculations. One based on your daily usage and location (hours of sun per day). The second is based on recommended rate of charge for Lead Acid battery banks.

    Based on daily power usage and location--You did not say where your wash station is located... Pick a random spot:

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Chandler Arizona
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 72° angle from vertical:
    (Optimal summer settings)

    JanFebMarAprMayJun
    4.29
     
    5.04
     
    6.22
     
    7.23
     
    7.58
     
    7.45
     
    JulAugSepOctNovDec
    6.75
     
    6.28
     
    6.29
     
    5.56
     
    4.69
     
    4.09
     

    Let's say you can be out into October at 5.56 hours of sun per day (long term average):
    • 97.8 Watt*Hours per day * 1/0.61 DC solar power system efficiency * 1/5.56 hours of sun per day = 159 Watt solar array (October "break even")
    I would suggest a 2x larger solar panel/array to allow for a week of cloudy weather or some very smoky days:
    • 2 * 159  Watt array = 318 Watt array with 50% "fudge factor"
    And there is sizing the array based on the size of the battery bank... 5% minimum. 10%-13% typical "optimum":
    • 58.6 AH battery * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 55 Watt array minimum
    • 58.6 AH battery * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 110 Watt array nominal
    • 58.6 AH battery * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 143 Watt array "typical" cost effective maximum
    Or if you used a 200 AH @ 12 volt battery bank (2x 6 volt golf cart batteries).
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 188 Watt array minimum
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 377 Watt array nominal
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 490 Watt array "typical" cost effective maximum
    Obviously lots more to discuss. Once you size the system for your needs--Then need to pick hardware.

    Lithium Ion (LiFePO4 type) are very nice. Can be expensive. Li Ion generally should have a BMS (battery management system) of some sort to ensure batteries are charged/discharged correctly. Li Ion are great in warm to hot weather. Do not work well in sub freezing conditions (Li Ion batteries generally need to be >~40F to cycle). Lead Acid are pretty nice for sub freezing conditions.

    There are now a bunch of DC meters for measuring Amps/Amp*Hours and such. You could build the system in your shop and run some tests to see how much energy you really use:

    https://www.amazon.com/dc-power-meter/s?k=dc+power+meter

    I will stop here... Your thoughts/requirements/questions/corrections to my guesses.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • squinkosquinko Registered Users Posts: 5 ✭✭
    Wow that’s a lot info. Thank you. The equipment I have is what I am using. I will not be changing it for different pumps and water heaters. I am currently on a fire in New Mexico and use a generator to power the trailer. Trying to get a battery/solar set up with the equipment I have so I don’t have to use the generator all day long.  Going to try and order some stuff and install it at the fire.  Location wise my trailer can be anywhere in the country depending on the need but it’s primarily in Arizona and New Mexico. 

    I was told not to get a big inverter that has a large maintenance draw on it because it will be stealing some of the charge while it’s just sitting. That is the confusing part for me. Not sure if I need a 1000 watt inverter or something less or more. I fell like I am learning a new language:) 

    I’m looking at getting this battery or something similar. Really want a sealed battery. 

    https://www.renogy.com/deep-cycle-agm-battery-12-volt-200ah/?gclid=CjwKCAjwve2TBhByEiwAaktM1BnyIykmP6q4_PN8fRqkI7-GhZOhdd8eKIVPpKF4j0ki1ZFXSMz9VxoCi3IQAvD_BwE

    Thanks for all the help. This is a very interesting topic.  

    Any more suggestions will be greatly appreciated.  


  • BB.BB. Super Moderators, Administrators Posts: 32,593 admin
    edited May 13 #6
    Can you tell us what genset you have (Watts, inverter-generator or plain genset) and how much fuel per day you burn?

    Plain old gensets (non-inverter type) can supply high surge current because of alternator momentum, and the can "droop" the output voltage while starting the pump/surge load. An Inverter-Generator will generally turn off the AC output if the surge/run ratings are exceeded.

    I am going to take a quick stab at what a solar power system would be for your present equipment.

    @mike95490 posts a nice chart of what typical induction motor well pumps draw for start/run current:

    https://forum.solar-electric.com/discussion/comment/421114#Comment_421114



    Even a 1/2 HP @ 115 VAC draws ~55 amps at starting...
    • 55 amps * 115 VAC = 6,325 Watts (really VA) starting surge for a second or so
    • A good quality AC inverter will surge 2x rated load, so minimum suggested inverter is 1/2*6,325W=3,163 Watt minimum rated
    You should use a minimum of 24 volt or even move to 48 VDC battery bank. Using 48 VDC, you are looking at needed around 320 AH @ 48 volt battery bank. (using the rule of thumb of 100 AH per every 1 kWatt of AC inverter capacity minimum).

    Or, with 12 volt @ 200 AH batteries, 4x series * 2 parallel strings for a 48 volt @ 400 AH battery bank -- Or 8x batteries total.

    Guessing you are using this pump (possibly with pressure tank?). This is a shallow well jet pump (jet pumps tend to be inexpensive but inefficient too).

    http://www.burcam.com/files/Web/Infos/Anglais/506227P.pdf

    Upwards of 850 GPH (14 GPM) with low lift. Seems like overkill for sinks.

    Now... assuming an 18 hour day, a guess at your loads. 30 seconds per cycle (15 amps @ 115 VAC). Pump may run for 60 minutes per day total (i.e., ~120 x 30 second cycles?).

    Guess the water heater does not use the anti frost heater (warmer weather for fires?). 2 Watts standby, 76 Watt running. Runs ~60 minutes per day?).

    Estimated energy use per day:
    • 1 hour * 15 amps * 115 VAC for pump = 1,725 Watt*Hour per day for pump
    • 18 hours per day * 2 Watts anti frost = 36 WH per day for standby heater
    • 1 hour * 76 Watts = 76 WH per day for running water heater
    • 18 hour per day * 20 Watt inverter "Tare losses" = 360 WH per day inverter losses
    • Total = 2,197 Watt*Hours per day (pure guesses)
    Using our standard 2 days of storage and 50% planned max discharge, the "minimum" (guess) battery bank would be:
    • 2,197 WH per day * 1/0.85 AC inverter operational losses * 2 days storage * 1/0.50 max planned discharge * 1/48 volt battery bank = 215 AH @ 48 volt battery bank (or 4 series * 1 parallel 12 volt @ 200 AH set of 4x batteries).
    As you can see here, your actual daily energy uses are relatively small compared to the high surge energy requirement to support the (mostly) high starting/running power of the water pump and running a (minimum) of 3,200 Watt AC inverter.

    To supply the daily power needs via solar panels:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Albuquerque New Mexico
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 70° angle from vertical:
    (Optimal summer settings)

    JanFebMarAprMayJun
    4.29
     
    4.86
     
    6.00
     
    6.76
     
    7.02
     
    6.90
     
    JulAugSepOctNovDec
    6.24
     
    5.84
     
    5.79
     
    5.38
     
    4.51
     
    4.07
     
    Assuming October end of "fire season".
    • 2,197 WH per day * 1/0.52 off grid AC system eff * 1/5.38 October "break even" = 785 Watts of solar panels (Oct break even)
    Since you have a generator already--Perhaps just use that when bad weather/smokey conditions limit solar harvest.

    Then charging the battery bank. Assuming 48 volts @ 400 AH battery bank:
    • 400 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,506 Watt array minimum
    • 400 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 3,113 Watt array nominal
    • 400 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,917 Watt array "Typical" cost effective maximum
    Because of the high surge/run current/AC inverter size, you need an "over sized" battery bank to support those surge/run currents. Which pushes up the minimum suggested solar panel array charging power.

    Being in the sunny south west, you have lots of sun, don't need power during the winter (except to float charge the battery bank), so the overall daily energy usage (my guess) is relatively small (don't need a large array for Watt*Hours/Amp*Hour loads).

    There are members here with lots more water pump + solar sizing than I... The above is just a guess on my part for a minimum/reliable system based on my guesses.

    And note that a larger array for "charging current requirements of 5-10%+), means that your daily available energy (WH) available goes up too... I.e., a 2x larger solar array means 2x more water pumping and heating "time" too with the suggested "large" battery bank and large array.

    Cost wise--Using solar for a couple summer months of the year is "expensive"... The hardware sits for ~8 months of the year unused (energy available from solar panels is not harvested so lost). Depending on your genset usage (fuel, how long between genset replacement/overhaul, etc.)--Solar may not be very cost effective.

    In any case--The water pump is your "biggest villain" here. If you are running a 3,500 Watt standard genset because of the pump--You are burning a lot of fuel X hours per day.

    Just based on some quick research/numbers I found...
    • Generic standard 3,500 Watt genset runs around 0.39 GPH with 50% or less loading
    • Honda inverter-generator eu2,200 1,800 Watt genst runs around 0.117 GPH with 25% or less loading

    If you can find a water pump (1/4 HP or less) that meets your needs and will run on a smaller inverter-genset, the fuel savings (and noise reduction) could be:
    • 0.117 GPH small inverter-generator / 0.39 GPH (3,500 watt) standard genset = 0.3 reduction in fuel usage (basically 1/3rd the fuel usage)
    Or say 8 hours per day (4 hours morning, 4 hours evening):
    • 0.117 GPH small inverter-generator (+low power water pump) * 8 hours = 0.936 gallons per day
    • 4 weeks usage * 7 days per week * 0.936 GPD = 26 gallons per month
    • 26 gallons of fuel * $6 per gallon = $156 per month
    • 0.39 GPH (3,500 watt) standard genset (with jet pump) * 8 hours = 3.12 gallons per day
    • 4 weeks usage * 7 days per week * 3.12 GPD = 87 gallons per month
    • 87 * gallons of fuel * $6 per gallon = $522 per month
    Standard genset are just "fuel hogs" at less than 50% loading (i.e., Champion 3,500 Watt uses ~ 4.7 gallons for 12 hours). A Honda inverter-generator uses much less at 25% loading (around 0.95 gallons for 8 hours of runtime).

    And you can easily convert to an external fuel tank for some of the Honda euXXXX family changing the vented fuel cap to a plumped "fuel draw" cap/tank system (or even make your own conversion--Some other gensets may be convertable, or require an additional fuel pump addtion):

    https://www.amazon.com/s?k=honda+eu2200i+fuel+extender&sprefix=honda+eu2200i+fuel

    An RV type water pump (AC or DC) + smallish pressure tank--It will dramatically reduce the energy usage of your trailer system. And you can always put two (or more) smaller RV pumps in parallel with check valves if you need more water flow.

    The AC version of this pump will supply upwards of 60 PSI at 2.5 GPM and 4 GPM at 20 PSI. For less than $110 per pump (1.6 amps * 115 VAC = 184 Watts running).

    https://www.solar-electric.com/aquatec-550-series-m528-115-volt-booster-pump.html
    https://www.solar-electric.com/lib/wind-sun/Aquatect_ds55xx-xx01-b526.pdf

    Remember too--Batteries have a limited life if used, or even just sitting around (around 5-7 years life for good quality AGM batteries typical). For a genset--I "pickle mine" between uses (run out of fuel, drain tank, fuel lines, carburetor, use fuel preservative, put a teaspoon of oil down spark plug hole, pull start cord to close intake/exhaust valves)--And the genset is ready to fuel and run 1+ year the next time I need it (I just use for power failures at my home in California--Which are rare other than the last major wildfires we had--So far).

    I obviously am only guessing at your needs and usage. Your needs/knowledge need to be met by any system design... In general, with off grid solar (and genset power)--It is almost always less expensive overall to conserve your energy usage (i.e., low power and more expensive efficient appliances, devices) vs running a larger solar/genset to power the "inefficient loads".

    I like to "model" the problems and "different" solutions (solar vs genset; large loads vs small/efficient loads). And figure out what is "most cost effective" for 'your' needs.

    Again lots of guesses on my part... Your thoughts/needs/corrections/etc.?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • squinkosquinko Registered Users Posts: 5 ✭✭
    edited May 13 #7
    Well I guess I will change out the pump.  I can get some on demand RV pumps then set up the solar battery power. Now to find some time between fires.  

    Thank you for all the info!!!  Amazing!  I’m sure I will have more questions down the road.
  • BB.BB. Super Moderators, Administrators Posts: 32,593 admin
    You are very welcome.

    One option is to plumb the "new small RV pump" in parallel with your existing pump. And just use a valves or check valves--That way you always have a backup.

    Another question is the use of a pressure tank (accumulator) to supply short term water usage if all the taps are open at once (10 sinks * 2.5 gpm = 25 gpm "demand" for something like 10 seconds? Anyway, remember that pressure tanks are rated for air+water capacity, but actual useful water capacity is much less--A 20 gallon tank may have 5-6 gallons of "40-60 PSI" water storage...

    Anyway. please feel free to ask questions. The first time, there are lots of hardware dependencies (solar panels, PWM/MPPT charge controller, Battery bank 12/24/etc. at XXX AH, etc.).

    Highly suggest that you do (probably several) paper design(s) and figure out the proper mix of hardware, rough costs, and ensure that the solution meets your needs.

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • squinkosquinko Registered Users Posts: 5 ✭✭
    I ordered three of these pumps below. Pretty sure two will run the system and the third is a spare. I may get a small pressure tank if I need to.  I plan to get a 100 watt solar system to charge the batteries.  These pumps are what the other Handwashing trailers are using and they work great. Most guys have 4 panels that equal 100 watts and works well.  My question now is how big of a battery or batteries should I get? I would like to have sealed AGM type battery. Lithium would be great but that’s way out of my budget range. The info for my water heater is in the first comment on this thread. I do have 4 small LED light strips and I charge a phone. That’s about all the power I use. Still not sure how big of an inverter I should get. Love to hear some recommendation.  

    The info you guys have been giving has really helped. I pass it on to the other guys looking also.  Much appreciated!!!




  • BB.BB. Super Moderators, Administrators Posts: 32,593 admin
    Those pumps should be fine and last many years--As long as the water is "clean" (no sand/etc.) and they don't freeze (set up lines with slope to drain, possible compressed air purge at end of season).

    Regarding sizing battery bank for pumps... How many gallons per day do you pump? Are you limited (for example) to 100 gallon tank full per day? Do you have a 500 Gallon tank truck/trailer for more water or what?

    3 gpm and 7.5 amps @ 12 volts.... The reality (Amazon)--You need to look at the spec sheets:

    https://www.amazon.com/shurflo-4008-101-e65-revolution-water-pump/dp/b002xm5g70#:~:text=Product Documentation (PDF)

    Say average of 30 PSI -> 1.5 GPM and 5 amps @ 12 volts...

    100 GPD / 1.5 GPM = 66.7 minutes -> 1.1 hours per day pumping
    1.1 hours per day * 5 amps = 5.5 AH

    Say 3 days of battery storage and 50% max planned discharge (for longer battery life):
    • 5.5 AH per day (per 100 gallons) * 3 days storage * 1/0.5 max planned discharge = 33 AH @ 12 volt battery bank / 100 GPD pumping @ 30 PSI
    So, a 12 volt @ 100 AH battery would be fine (and lots more capacity for poor weather/more water pumping/etc.).

    Based on location and daily pumping estimate (above):
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Albuquerque New Mexico
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 70° angle from vertical:
    (Optimal summer settings)

    JanFebMarAprMayJun
    4.29
     
    4.86
     
    6.00
     
    6.76
     
    7.02
     
    6.90
     
    JulAugSepOctNovDec
    6.24
     
    5.84
     
    5.79
     
    5.38
     
    4.51
     
    4.07
     

    • 5.5 amp*hours * 12 volts = 66 WH per day
    • 66 WH per day * 1/0.61 DC solar system eff * 1/5.38 hours of sun per day (October) = 20 Watt panel/array
    So, a 100 Watt panel (based on sun, 100 GPD pumping, etc.) is great... Note that the more solar panels you have, the longer your batteries will probably last, and less (or no) genset usage during a stretch of poor sun/under partial shading (solar electric panels do not harvest energy under partial/any shading).

    Lets say you say with the 12 volt @ 100 AH AGM battery bank, charging at 5%, 10%, or 13% (suggest 10%+ for full time off grid):
    • 100 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 94 Watt array minimum
    • 100 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 188 Watt array nominal
    • 100 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 245 Watt array "Typical" maximum cost effective
    Notice--I have not discussed the water heater usage... In next post.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,593 admin
    The tankless water heater you have/reference has some issues for "off grid" usage... I see there are many options/variations in this water heater--So you will need to confirm that the information below is correct for your unit.

    https://www.rinnai.us/residential/product-detail/rl75ip (product website)

    Water flow wise, it does "light" at pretty low flow rates for a tankless water heater (many heaters need 2-4 GPM or so for minimum flow):

    https://media.rinnai.us/salsify_asset/s-22bec185-aa7e-4db7-9364-1b1d6c9bc19b/RL75i (VC2528FFUD-US) SP.pdf

    Minimum activation flow of 0.4 GPM... Good (depends on actual sink faucets used for actual flow rate).

    2 Watts standby and 77 Watts running is not bad The Max Draw of 4 amps @ 120 VAC (4a*120VAC=480Watts)--That is for a few seconds (lighting) or freeze protection or something else...

    There is a spec for "battery backup" of the tankless heater... 

    https://media.rinnai.us/salsify_asset/s-0eb20889-56fe-4f49-8042-a4bb3177b6b6/TB-130 Battery Backup for Tankless Water Heaters and Home Heating Products.pdf

    It appears that Hugo is no longer available (?) and the other two brand/models have been replaced by other models (2019 PDF document).

    Looking around for the Hugo specs:
    https://www.supplyhouse.com/Hugo-Power-Supply-SUPS350A-Tankless-Battery-Backup
    Features:
    • ETL certified
    • 5 hours of continuous operation
    • Portable or permanent mount
    • Indoor/Outdoor installation
    • IP54 grade for all-weather protection
    • 35Ah AGM non-spill battery
    • Chirp alarm
    • LED indicator for easy troubleshooting
    • Flow sensor switch to prolong battery life
    • Maintenance free operation
    • Anti-Frost assist
    • Auto activate within 8ms upon power outage
    • Auto reset when main power becomes available
    • Auto switchover between main power and inverter mode
    • Built-in fuse to prevent board burnout and to protect downstream appliances
    • Solar capable
    • SMART technology to ensure constant clean power
    • PURE SINE WAVE Technology
    • Output: 500 VA I 350 W
    This unit should run a Rinnai 75x for at least 5-6+ hours on a 35 AH AGM battery...

    Back to how many hours per day do you run the Rinnai per day (xx hours standby; y hours running)?

    Computer backup power supplies are typically rated for two values... Watts (rate of power usage) and Watt*Hours (total amount of power usage per day...). For example, above 500 VA and 350 Watts. I saw the other UPS systems were rated around 750 VA and 450 Watts...

    For off grid AC inverters, typically, they are rated for VA=Watts... I.e., a 750 VA AC inverter will be rated for 750 Watts also (and 2x surge for a few seconds to a few minutes--depending on brand/model).

    If you have a running heater on your wash station now--You can get a Kill-a-Watt type power meter and measure Watts/VA/Watt*Hours per day--That would be a big help to properly design your solar power system:

    https://www.amazon.com/kill-a-watt-meter/s?k=kill-a-watt+meter

    These are also handy for use around your house--Figure out how much your computer/printer/entertainment center/etc. costs you in electrical power per day/month...

    Quick Definitions:
    • Volts -- 12 VDC, 120 VAC, etc...
    • Amps -- Current flow
    • VA (or V*A) -- Volt Amps. AC current is "complicated". More or less, VA is what you design the wiring, transformers, and AC inverter for (worst case current flow)
    • Watts -- A rate of power usage. VA is always greater than, or equal to Watts. Watts=VA*PF where PF is "power factor" or how "efficiently" the load uses the AC current. PF=1 is most efficient... 0.5 to 0.7 PF is typical for motors and many electronic systems.
    • Watt*Hours -- Power*Time or "amount" of energy usage. I.e., 100 Watt light * 2 hours = 200 Watt*Hours of energy usage
    We really need some accurate "numbers" (typically Watts standby, Watts running, hours of standby per day, hours of running per day) to figure out battery bank and solar system side.

    If we assume "worst case"--Heater running for whole time, and 35 AH @ 12 volt battery for UPS backup...
    • 35 AH * 12 volts = 420 WH of battery energy (from 100% to 0%)
    • 420 WH * 0.85 typical AC inverter eff = 357 Watt*Hours "available to water heater"
    • 357 Watt*hours / 5 hours runtime (worst case) = 71.4 Watt average load
    So--Your 76 Watts of "running" load seems about correct.

    But we have two numbers... 2 Watts of "standby" (very little power draw) and 76 Watts running (pump takes 5.5 amps * 12 volts = 66 Watts running)... So the heater does draw a bit more power than one water pump when "running hot water"... And "hours per day" that the heater runs is going to be significant energy usage (i.e, 1 hour, 2 hours, or what per day running. Do you turn off AC inverter "at night" or let run 24 hours per day, etc.)...

    Here is an example of a "nice" 700 Watt AC inverter:

    https://www.solar-electric.com/cotek-sp-700-112-700-watt-12-volt-pure-sine-wave-inverter.html

    Should be large enough for the Rinnai. But we also need to look at the "tare losses" (power usage of the inverter being "on" but no AC loads--I.e., inverter "wasted energy"):

    https://www.solar-electric.com/lib/wind-sun/SP700 SPEC_A3.pdf


    To power that 2 Watt standby Rinnai load, the inverter will draw 1.5 amps:
    • 1.5 amps * 12 volts = 18 Watts
    That is a significant load in and of itself... For example, if you just left the inverter (heating system) on for 12 hours per day:
    • 18 Watts * 12 hours per day = 216 Watt hours
    Or possibly more energy than your water pump and water heater will draw themselves when doing "work"...

    Looking around, might find an AC inverter that draws closer to 6 Watts--But the larger the AC inverter, the higher the Tare Losses...

    And why I was suggesting either a smallish "tanked" RV water heater (no or very little DC draw) or a "camping" tankless water heater (no power draw). There are also other tankless water heaters that use (for example) 2xD batteries for ignition--But many tankless heaters do not regulate temperature or even "light" at low water flow rates.

    Anyway--Something more to read and think about in the evenings before lights out.

    Be safe,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • squinkosquinko Registered Users Posts: 5 ✭✭
    I have a 525 gallon potable water tank. That would last me at least 5-7 days normally. I have access to water whenever I need it.  I am usually busy in the morning and evening (brushing teeth, washing hands and face). Currently I am stationed at the briefing area so I probably get 25-30 people using the sink in the morning and only a few at night.  If I am in the crew camping area that number would increase to maybe 50 people morning and night. Only 5-6 sinks are running at a time off and on. Very rare all 10 sinks are going at once.  During the day it does not get used much at all.  The system stays on all day 0530-2200 in the event someone needs it. 
  • BB.BB. Super Moderators, Administrators Posts: 32,593 admin
    There are other options for controlling the AC inverter for the water heater... Some AC inverters have a remote 12 VDC on/off control input... You could use a simple twist timer (twist for 1 hour/15 minutes/6 hours of "on time"--Whatever makes sense for your needs) to save inverter Tare energy...

    https://www.amazon.com/Intermatic-Twist-Timer/s?k=Intermatic+Twist+Timer

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.