Planning for an upgrade

Rybren
Rybren Solar Expert Posts: 351 ✭✭
I have an off-grid camp that I purchased in the spring of this year. It consists of 3 cabins (500 sq ft, 350 sq ft, and 150 sq ft). The previous owner had set up a small PV system to provide 12V lights to the two larger cabins. While not optimal, the solar system works well enough for the intended purpose but can't support much else. Both of the larger cabins have propane fridges and stoves.

My winter project is to come up with an upgrade plan to meet the needs of my BCW (Beautiful and Charming Wife)

The camp will only be used from April to early November (the road doesn't get plowed in the winter). For the next year or so, it will mainly be used on weekends; once I retire, we plan to spend a lot more time there.

First and foremost, my BCW wants running water (hot and cold), so I'll need a pump. I've been looking at the Shurflow AC diaphragm pumps - the run from the battery bank to the planned pump location is ~100 feet, so I think that the DC versions are a non-starter. I’m on the fence as to whether I should use a water tower or pressure tank for the system. There are certainly pros and cons to both, but having never used either, I’m open to suggestions. FWIW, the largest pressure tank that I can find locally has a max volume of 50 Gal (~30 G useable water)

Next is hot water: Solar water heating is an option, but in all likelihood the real choice will be between a propane powered on-demand system vs a traditional tank style. Again, having never used either in a camp setting, I’m open to recommendations. I suspect that the choice will be impacted by whether I go with a pressure tank over a water tower. Will a traditional tank work with the low pressure of a water tower?

Now for my loads:

I have 82W in 12V CFL and LED lights. Based on my usage over this season, a worst-case scenario is that I would use 164WH per day.

Other planned loads that I have measured with a Kill-a-Watt are:
Cell Phone – 10WH
Tablet – 10WH
Laptop – 50WH
Drill Charger – 150WH

Obviously, I wouldn’t need to run these loads on a daily basis (and for weekend use, I don’t need to run any of them) In addition, by only running them after the batteries are charged, I can minimise the draw on the bank.

Seeing as how I don’t have one yet, the Shurflow will have to be a guess. Max draw is supposed to be 0.9A, so with a guesstimated ~2hr per day use, I’ll use 220 WH/day for planning purposes.

So, total max potential use is 604WH/day. If my math is correct, that equates to roughly 50AH on a 12V system. In reality, because I won’t need to run all of the loads on a daily basis and by load shifting, the actual demand should be closer to 25-30 AH. I’ll stick with the 50AH to allow for growth.

Based on a 50AH demand and max 50% DOD, the battery bank should be 100AH. Add in a no-sun factor and I’m up to 200AH.

I figure that I’ll need about 400W of panels to meet the 10% charge rate:

200AH*14.5 volts charging*1/0.77 panel+controller derating*0.10 rate of charge = 377W panel

I do have a cheap 1400W continuous/ 1750W surge genny that can be used for extra loads.

Feedback would be greatly appreciated:

Am I on the right track? Is my math ok? What have I missed? What are your recommendations for water and water heating?

Thanks
Jerry
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Planning for an upgrade

    The water system is going to be dependent on what the situation is for water source and how much lift/flow/pressure is required. As far as putting it in a water tower goes, how much elevation do you have available? Water is heavy, and raising any significant amount up high enough (more height = more pump power needed) to have decent water pressure can become a problem. On the other hand you can connect as many pressure tanks together as you like. Draining for freeze situations need to be considered too.

    Now, long-term plans: do they include enough time spent there that electric refrigeration would be desired? That would be a major player. I'm looking at whether or not you might be needing a 24 Volt system instead. Adding on to the existing 12 Volt system is probably not a good idea in any case; having separate systems gives you the safety factor of redundancy.

    If there will be just two of you using hot water the tankless can save a lot of propane. If more than two and a lot of hot water is needed it's just the opposite. In either case consider the possibility of direct-thermal hot water if at all possible; just as hot and uses no fuel.

    I'm sure others will have some ideas too.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Hi,

    Water would be drawn from the lake - I plan on putting the pump as close to the shore as possible to minimise the suction run. If I went with a tower configuration, I suspect that base of the tank would only be about 15' high and 30' from the pump. It wouldn't provide much pressure.

    We'd likely have 4 people at the camp more than just two.

    While electric refrig would be nice, with two propane units on hand already, I'm not planning on it.

    I don't plan on connecting to the existing 12V system - amorphous panels and marine/rv 75AH battery.

    Thanks
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Planning for an upgrade
    Rybren wrote: »
    I have an off-grid camp that I purchased in the spring of this year. It consists of 3 cabins (500 sq ft, 350 sq ft, and 150 sq ft). The previous owner had set up a small PV system to provide 12V lights to the two larger cabins.
    First and foremost, my BCW wants running water (hot and cold), so I'll need a pump. I've been looking at the Shurflow AC diaphragm pumps - the run from the battery bank to the planned pump location is ~100 feet, so I think that the DC versions are a non-starter. I’m on the fence as to whether I should use a water tower or pressure tank for the system. There are certainly pros and cons to both, but having never used either, I’m open to suggestions. FWIW, the largest pressure tank that I can find locally has a max volume of 50 Gal (~30 G useable water)

    Next is hot water: Solar water heating is an option, but in all likelihood the real choice will be between a propane powered on-demand system vs a traditional tank style. Again, having never used either in a camp setting, I’m open to recommendations. I suspect that the choice will be impacted by whether I go with a pressure tank over a water tower. Will a traditional tank work with the low pressure of a water tower?


    Seeing as how I don’t have one yet, the Shurflow will have to be a guess. Max draw is supposed to be 0.9A, so with a guesstimated ~2hr per day use, I’ll use 220 WH/day for planning purposes.


    Feedback would be greatly appreciated:

    Am I on the right track? Is my math ok? What have I missed? What are your recommendations for water and water heating?

    Thanks
    Jerry

    Hi Jerry,

    The conventional tank and the on-demand tankless will both operate with the same overall pressure range, with a few exceptions. Here are some things to consider that you might not have thought of:
    1. The conventional tank does not need any pressure at all to work correctly, as long as the water level does not go down exposing the area heated by the propane. The available pressure, the resistance of the piping, and the design of the faucet or shower will determine the flow rate you get.
    2. The tankless will require a minimum flow rate in order to regulate the hot water temperature out. If you go lower than that flow rate you will get only cold water or alternating too hot and too cold. So the tank or tower pressure would have to be able to supply that minimum flow rate to your uses. Some tankless use electronic controls and so will need to have power when you use them.
    3. The tower will provide pressure through the night without having to run the pump, so you could pump only when the panels are producing, to minimize the strain on your batteries.
    4. If you do not use a tower, you might want to get a small DC pump to be connected to the existing PV system for emergency use if the new system goes down.
    5. You can count the contents of the tank heater as a backup water source, provided you turn off the burner. The tankless will not give you that redundancy.
    6. Do you need/want to have water available for fire fighting? If so, then the elevated tank will give you a more secure system and a higher volume when you need it. (Although at a lower pressure, so look at the hoses and nozzles with that in mind.) A separate gasoline-engined or generator-driven fire pump pulling directly from the lake might be the cheapest way to handle that.
    SMA SB 3000, old BP panels.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Thank you for the thoughts. I had considered a gas-powered pump for filling the tower and for fire-fighting - the cottager next to me does just that. In the end, I more or less decided that I didn't want to deal with the gas pump - for now.

    The more I think of it, the more I'm leaning toward a traditional tank-type water heater. As for pressure tank v tower, I'm still not sure; the tank would be a cheaper solution. Heavy duty 50G food-grade tanks are $20 at the local wine making store. A few tied together would give me a good capacity for not a lot of money.

    Does anyone have an opinion on my numbers for battery bank and panel sizing?

    Jerry
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Planning for an upgrade

    Another option with a non-pressurized storage (on the ground) is to add a separate small pump just to provide pressure to the house.
    Water weighs roughly 8 lbs. per gallon; something you need to be well aware of if constructing any structure to hold it up in the air.

    Your math based on the numbers provided is correct (600 Watt hours per day on 12 Volts being roughly 50 Amp hours and necessitating at least 100 Amp hours of battery).
    Did you include the inverter draw in that? Your loads are all quite small it seems, so something like the Morningstar 300 Watt would work. It has very low consumption, especially in stand-by mode.
  • Volvo Farmer
    Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Planning for an upgrade

    I'm thinking with three separate cabins, you'll want to consolidate all the DC stuff in one place and run AC to the outlying buildings? People here will tell you that the first rule off off grid living is that demands grow over time. I don't know if you have a tight budget or not, but my instinct would be to buy a decent sized sinewave inverter, maybe 2.5KW or more, and a decent amount of panels, maybe double your current estimation. At $1.25 a watt, the difference between 400 watts and 800 is only $500. Maybe keep the battery bank small, batteries are a consumable and you'll likely murder the first set anyway.

    Plenty of folks are living happily with small systems, but I have seen time and time again where people size a system to meet their loads and then need to buy new inverters and more panels as their loads increase. I know you say you don't need an electric refrigerator, but if you really calculate how much propane two refrigerators use over an eight month season, you might be shocked as to how much extra you could spend on a larger solar system over a period of four or five years, rather than write an endless string of checks to the propane delivery company. $500 energy star electric refrigerators are remarkably efficient nowadays, and way bigger than their propane counterparts.

    We used one of those AC shurflo diaphragm pumps for years here. They work great but seem to have a 3-4 year lifespan in household use. Ours provided enough pressure for an on demand LP water heater. Tank heaters are simpler though.

    BCWs can never get too much electricity. If money is tight, do what you gotta do, but a little toast in the morning or a few minutes of microwave cooking can be a precious gift that a 300W inverter ain't gonna handle.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade
    Another option with a non-pressurized storage (on the ground) is to add a separate small pump just to provide pressure to the house.

    This is an interesting idea. I take it that it could be rigged via a switch of some sort to only turn on when the taps are opened?
    Water weighs roughly 8 lbs. per gallon; something you need to be well aware of if constructing any structure to hold it up in the air.

    Yup, I'm an aquarium guy and have worked on stands for 500G tanks.
    Did you include the inverter draw in that?

    Nope, I missed it.
    At $1.25 a watt, the difference between 400 watts and 800 is only $500.

    Best I can find up here is $2.35/W for new panels. There is a local guy selling 3 year old used grid-tie 210W panels for $1.05/W. I'm waiting to get the exact specs from him to see if they might work for my application.
    I know you say you don't need an electric refrigerator, but if you really calculate how much propane two refrigerators use over an eight month season, you might be shocked as to how much extra you could spend on a larger solar system over a period of four or five years, rather than write an endless string of checks to the propane delivery company.

    We do turn off the propane supply when we're not at the camp, so it's not all that bad. I must admit that part of me wants an electric fridge or freezer conversion that can be left running all season so that we don't have to haul as much back and forth.
    demands grow over time

    I do think that my planned system is actually oversized for my current needs, but I really don't know if I've left enough room for expansion.

    Thanks to everyone for your thoughts.

    Jerry
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Planning for an upgrade
    Rybren wrote: »
    The more I think of it, the more I'm leaning toward a traditional tank-type water heater.

    Jerry
    One more thing to consider for the future is that solar thermal water heating (if you are at all interested in it) works far better with a tank type water heater than with an on-demand heater. Even if you put in a lower temp storage tank just for the solar thermal input, running already warmed or heated water into an on-demand tankless just does not work well. The control systems and minimum flow rate are not designed for high temp input water.

    Also, if you expect to have a lot of excess panel power later in the day, once the batteries are out of Bulk into Absorb or Float, using electric water heating elements as an opportunity load works very neatly. You do not get a lot of heat, but at least you do not completely waste the panel potential at those times.
    SMA SB 3000, old BP panels.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Both good to know and consider.

    Thanks.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    The fellow with the used grid-tie panels got back to me with the spec sheet (He upgraded to larger panels). Could I use them to power a 12V battery bank and if so, are there any special considerations that I should be aware of?

    Max Power (Pmax), (Wp) 210
    Max Power Voltage (Vmp) 29.1
    Max Power Current (Imp) 7.2
    Open Circuit Voltage (Voc) 37.0
    Short Circuit Current (Lsc) 7.7
    Max System Voltage (VDC) 600

    Thanks
  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Planning for an upgrade

    yes, but you must use an MPPT charge controller or you will only use roughly half of the panels charging ability.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Planning for an upgrade

    I keep getting this feeling of déjà vu: just answered the same question from someone else with nearly identical panel specs. And another very similar yesterday! :D

    Dill said it: they'll work, but use an MPPT controller or lose a lot of power.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Dill & Coot,

    Thanks for the answer and Coot... sorry

    It looks like I might be able to get them for less than $1.00/W, so I'm thinking of picking up four of them - even though my current plan only calls for ~400W of panel.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Planning for an upgrade

    No need to be sorry, Rybren; just my way of pointing out that it's the same stuff that confuses everyone. Or at least inspires them to ask questions. :D
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Thanks.

    What would be the best way to wire four of these panels together and what would be a good MPPT controller for the budget minded off-gridder?

    Jerry
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Planning for an upgrade
    Rybren wrote: »
    Thanks.

    What would be the best way to wire four of these panels together and what would be a good MPPT controller for the budget minded off-gridder?

    Jerry

    Jerry, "budget-minded" and "MPPT" don't really go together. :p

    What you have there is 4 * 210 Watts or 840 Watts. On a 12 Volt system you could expect the current output through an MPPT controller to be approximately 54 Amps max. This means you need at least a 60 Amp controller.

    MidNite Classic 150 Lite: $510
    Morningstar TriStar MPPT 60: $500
    Outback FM60: $515
    Xantrex XW MPPT 60: $480

    Of these, the MidNite is the best controller (no meter). The Outback is the best value (includes meter). I'd probably pick the Xantrex (meter) over the Morningstar (no meter). (My opinions only.)
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Planning for an upgrade

    How about a brand new in the box Outback FM60 with 5 yr warranty? $400

    Brought to you by the fine people at Northern Arizona, Wind and Sun...

    ... and the person who stuck it behind some other stuff a couple years ago...
    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.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Coot,

    I was afraid of that answer :( - even though it was what I was expecting.

    I've got my dunce hat on (again) and need a bit more help. If Imp = 7.2 A, how does the controller output a max of 54A? This certainly smacks of overkill for a 200AH, 12V system. I guess charging would be pretty quick.

    Photowhit: Sounds like a good deal - I'll have to see if I can complete the deal on the panels first; hopefully the unit will still be available
  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Planning for an upgrade

    that's 7.2a at 29 volts per panel. Once the MPPT controller converts 7.2a x 4 panels = 28.8a at 29 volts into a voltage for charging 12V batteries, you will get the 54 amps charging that Cariboocoot mentioned.
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Thanks Dill.

    Guess I have to do some more reading to fully understand the process.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Planning for an upgrade
    Rybren wrote: »
    If Imp = 7.2 A, how does the controller output a max of 54A?

    Try thinking in terms of power (watts = amps x volts). You have 840 watts of panel. If your batteries are at 14 volts while charging, 840 watts ÷ 14 volts = 60 amps. Of course your controller cannot be 100% efficient so you will get a bit less than 60 amps.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade
    vtmaps wrote: »
    Try thinking in terms of power (watts = amps x volts). You have 840 watts of panel. If your batteries are at 14 volts while charging, 840 watts ÷ 14 volts = 60 amps. Of course your controller cannot be 100% efficient so you will get a bit less than 60 amps.

    --vtMaps

    Thanks vtMaps.

    I haven't had a chance to reread the stuff on MPPT v PWM controllers, but from what I can recall, using a PWM (not that I plan on doing it) on these panels would only output a max of about 28A?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Planning for an upgrade
    Rybren wrote: »
    Thanks vtMaps.

    I haven't had a chance to reread the stuff on MPPT v PWM controllers, but from what I can recall, using a PWM (not that I plan on doing it) on these panels would only output a max of about 28A?

    The PWM type controller can not down-convert the higher Voltage into more charging Amps; only an MPPT type can do that.
    As a result, any panels connected via PWM pass only the panel current; the Voltage will be "whatever".

    Looks something like this:

    For MPPT; 840 Watts @ 77% typical efficiency / 12 Volts (minimum) = 53.9 peak Amps.
    For PWM; four 210 Watt panels, each with Imp of 7.2 = (4 * 7.2) 28.8 peak Amps.

    The PWM's Amps will be max at 'whatever' Voltage, so at the same 12 Volt minimum your 840 Watts of panels is pulled down to 345.6 Watts of power. At 14.4 Volts Absorb charge it would be 414 Watts. Both well below the 77% efficiency available through the MPPT controller.

    Once a panel reaches its maximum current, that's it. It doesn't care if it's producing Imp @ 1 Volt or at Vmp. If the system holds the Voltage below Vmp, that power difference is lost. That is why 'true 12 Volt' panels have a Vmp around 17-18 Volts. Some power is lost to wiring, but the remaining 'Voltage overhead' is above the charging Voltage yet close enough to avoid any large losses.

    Does that help?
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Yes, it does help - a lot!

    You guys are great!
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade
    Another option with a non-pressurized storage (on the ground) is to add a separate small pump just to provide pressure to the house.

    Coot,

    How would you implement something like this? I assume that there would be some form of auto-switch that would turn the boost/pressure pump on when there is demand for water or would you need to manually turn the pump on prior to turning on the taps?

    Thx

    Jerry
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Planning for an upgrade
    Rybren wrote: »
    Coot,

    How would you implement something like this? I assume that there would be some form of auto-switch that would turn the boost/pressure pump on when there is demand for water or would you need to manually turn the pump on prior to turning on the taps?

    Thx

    Jerry

    RV's use this sort of system.
    There are several small pumps with built-in pressure switches which could work. One example: http://www.solar-electric.com/2088-594-154.html
    Exactly which one would best suit your needs depends on several factors, including how much water weight will be behind the pump and preferred Voltage.
    There are also constant pressure pumps which vary their power according to need but stay running all the time. This is due to the fact some people experience and dislike 'surging' of the pressure on small pumps turning on/off with the water demands. Adding a small pressure tank can help mitigate this as well.

    Several ways to go here. I'm sure Tony/Icarus is the best versed in these small pump systems around here. :D
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    Thanks.

    The linked pump is the one that I was thinking of using to draw water from the lake. I had never considered it's ability to provide pressure delivery to the cabins. Looks like it would work.

    Cheers
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Planning for an upgrade

    For any pump, make sure the suction (lift+length) distance is as short as possible. Screens are probably needed, but filters add resistance and can cause more pumping problems (vacuum leaks, cavitation in pump, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    Re: Planning for an upgrade

    My current plan is to site the pump about 5' from the water line and about 2.5' above it. That's about as close as I can get without risking a soaking from the waves.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Planning for an upgrade
    Rybren wrote: »
    My current plan is to site the pump about 5' from the water line and about 2.5' above it. That's about as close as I can get without risking a soaking from the waves.

    The distance from the inlet is not nearly as important as the height above water level (except in terms of the volume of water needed to achieve priming of the pump).
    SMA SB 3000, old BP panels.