My head is spinning!

Goose
Goose Registered Users Posts: 2
I am purchasing property in Cibola County, NM...a little over 7000' elevation where I'll be located. I'll be moving a portable cabin onto the property, and finishing the inside to meet my needs. . . that includes all the wiring. The cabin is about 450 sq. ft., will be heated with a wood stove, well drilled (would like to have solar pump), considering septic vs composting toilet. I can do electric up there as it runs to the property line, however, I very much want to do a solar system...including a roof solar water heater. Appliances will include a propane stove/oven, a compact, or smallish refrigerator (would love a Sundanzer, but that will have to come later), an energy efficient - water saver portable/compact washing machine, LED lights (if I'm understanding my research properly, they're the best to use with solar), a laptop (occasional use), a 19" LED flat panel (an hour or two per day...news junkie), a fan or two (during warmer months)...maybe an energy efficient ceiling fan...haven't decided on that for sure, and various small appliances. Most wouldn't be used at the same time...of course...although there would be times when two would be running at same time.

I don't understand the wiring requirements, nor can I figure out how to determine what size panels/inverter/charge controller/batteries/etc I'll be needing. I'll have an electrician do the wiring...he/she will know what needs doing for that. However, I don't know if you can help me figure out the sizing of my system, or if I need to hire someone to do it for me. Help!

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: My head is spinning!

    Welcome to the forum.

    Your basic problem is that you don't have a consumption number to work with. Listing equipment you want to power isn't of much use, as any two of the same type of device can have quite different power requirements. Without knowing how many Watt hours and total Wattage you need to power you can only guess at system components. Then you have to wonder what the consequences will be if you put in a system that does not meet you power demand (it is not easy to scale up).

    If you have grid power available at the property, price its install. In almost every case it will be cheaper than off-grid power, and it does not have limits for consumption beyond your ability to pay the monthly bill.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: My head is spinning!

    On your list your well is likely the heaviest load on a daily basis, maybe the fridge. Might look at the "Energy use and conservation" section of the forum to get an idea of what things use, please not the section on "how bad a small fridge is...". Usually a pump would be a special pump for use with solar.

    If your determined for what ever reason, energy independence, don't like power lines, ex-wife works for the electric company... you might pick up a Kill-a-watt meter, so you can see what the energy use is of some of the items you'd like to power.

    DON'T put in solar if you think your going to save money!!! If the power company is close and there is little up front cost, likely it's cheaper per Kwh to hook into the grid. That's from someone who is very likely as efficient as possible and 'off grid'!
    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: 33,431 admin
    Re: My head is spinning!

    Check your monthly charges too... There are a few folks here that did a lot of conserving and some solar, and found that the $40 per month (in some places approaching $90-$100 per month minimum charge (and not too expensive $$$/kWH charges)--For seasonal cabins, it made more sense to go off grid pay for batteries+panels+a small genset and fuel for winter/bad weather weekends.

    To give your self some ideas...

    1 kWH (1,000 WH) per day--Lights, small computer, radio, cabin water from stream/shallow well.
    3.3 kWH per day--Add an Energy Star Refrigerator + well pump + washing machine (close to "normal" modern home life)
    10 kWH per day--Central heat, several refrigerators/freezers, kids with computers+TV+Video games+...
    33 kWH per day--Add some electric heat (or heat pump heat) and A/C in well insulated home (plus family+kids, etc).
    100 kWH per day--Texas or Florida full A/C in hot/humid summers

    Around 33 kHW per day is the "average" north American home energy usage.

    If you had to start with something, I would plan on 3.3+ kWH per day. Usually it is the Refrigerator + Well Pump (and irrigation) that pushes up power usage (besides any appliances that run 24x7 such as central heat, computer servers, etc.).

    I don't live off grid--But from what I have read, if you can do septic and want a "normal home" life--Not a bad way to go if legal for your area.

    If you want a composting toilet--There are ones with heaters in them to evaporate "water"--Those heaters are pretty costly even for grid power. If you can "deal" with separate wet and not-so-wet separation, a composting toilet may work. We have some threads that discuss the pros-an cons (simple outhouse and pit--If legal in your area--Can be an easy way to go).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: My head is spinning!

    To give an example of a 3.3 kWH per day system design for Albuquerque New Mexico (using PV Watts) with a fixed array tilted to latitude.

    First, size the battery bank... Assume 2 days of no sun (1-3 days recommended) and 50% maximum discharge (for longer battery life) is a good balanced system on a 24 volt battery bank:
    • 3,300 WH per day * 1/0.85 inverter efficiency * 2 days * 1/0.50 maximum discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank

    That would be approximately 3 parallel strings of 4 * 6 volt @ 225 AH golf cart batteries each or 24 volts @ 675 A battery bank

    A battery bank needs between 5% to 13% rate of charge (20 hour battery capacity):
    • 675 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,271 watt minimum array
    • 675 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,542 watt nominal array
    • 675 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,305 watt "cost effective maximum" array

    For a deeply cycled system that is more than a weekend/seasonal cabin, I would suggest the 10-13% sized array.

    Then there is the amount of sun you receive, on average... Again using PV Watts for Albuquerque New Mexico, fixed array, tilted 35 degrees from horizontal (you might think of tilting to 90 degree and raising off ground if you have deep snow in your area and use the place in winter):
    Month    Solar Radiation (kWh/m 2/day)
    1      5.33     
    2      6.06     
    3      6.44     
    4      7.16     
    5      7.40     
    6      7.10     
    7      7.13     
    8      7.02     
    9      6.71     
    10      6.55     
    11      5.73     
    12      5.14     
    Year      6.48      
    

    You have lots of good sun there--I typically "toss" the bottom three months and assume a generator--In your case--You can use 5 hours of sun per day for "year round" solar pretty easily (except for streaks of poor weather--Generators are made for that):
    3,300 WH per day * 1/0.52 end to end efficiency * 1/5 hours of sun per day = 1,269 Watt Array "break even" on average.

    So, the suggested array would be from 1,269 watts to 3,305 Watts, with 2,542 watt array being a nice sized array to battery bank ratio (charge bank pretty quickly after a few days of clouds/heavy power usage).

    A 2,542 Watt Array would produce, at 5 hours of sun per day (minimum average):
    • 2,542 Watts * 0.52 system efficiency * 5 hours of sun = 6,609 Watt*Hours = 6.6 kWH per day.

    If a lot of your loads are during the day--Then you can stay with the "3.3 kWH" rated battery bank and larger array... If you think you will not use that much power, you might consider falling back to the 1,271 watt array:
    • 1,271 Watt * 0.52 sys derating * 5 hours = 3,305 WH = 3.3 kWH per day

    A bit on the small side for a 9+ month cabin/home... But for a weekend cabin, it might be worth trying the minimum array first and see if it works well for you--You could always add more panels / charge controllers later.

    Note I carried out all of the digits on the calculations so you can check my math and see where the numbers are used (and to avoid too much round off error with multiple calculations). In Solar if you are withing 10% of predicted numbers--You are doing really well... Between variability in weather (year to year) and accuracy of measurements, 10% is "dead on" accurate.

    Power usage is a highly personal set of choices--You tell us what you need, it is not us telling you what to use. :D

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Goose
    Goose Registered Users Posts: 2
    Re: My head is spinning!

    Thanks for all the information, I really appreciate it. I do have numbers...watts...for everything but the fridge and laptop. I've not purchased those as of yet, and have been looking at several different makes/models. One of my issues is...for example...I have a stereo. How do I factor the watts used when it's only occasionally used? Same with several other electrical appliances...like a coffee grinder that states 140 watts...might be used for 10 minutes a couple times a month...a food processor that only gets used when I'm canning...450 watts...for maybe an hour a week all total. Do I even need to be concerned with these types of add ons since they're occasional/seasonal? I'm still trying to understand some aspects of this.

    I'll be moving onto the property in the spring, and will initially have the electricity connected into property/cabin. I will be living there full-time. However, it's my goal to be off grid by the end of the first year, and to be completely solar. The compost toilet is non-electric...so is not an issue. I suppose it's going to be easiest to see what my actual use is once I'm living in the cabin, and base solar needs on that information.

    Thanks again.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: My head is spinning!
    Goose wrote: »
    I suppose it's going to be easiest to see what my actual use is once I'm living in the cabin, and base solar needs on that information.

    You hit the nail on the head! And just wait until you realize how much more expensive it is to produce that power off-grid. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: My head is spinning!

    More or less, a pure off grid system can cost effectively store electricity for 1-3 days of use (we use 2 as good number) and 50% maximum discharge--Basically, the battery bank is ~4x your average daily load.

    For higher power usages a couple times a month... You either have to treat them like you uses them every day or two--Or use a genset to power them the couple days a month you use them.

    You do have some "room" to play with the numbers a bit... If you have a smaller battery bank and a larger solar array, and you can pick to run the "high power loads" during the middle of a sunny day--You can power the loads (more or less) with the solar array carrying most of the load.

    If you want to run the loads on any day, in any weather, daytime or night time, you will then have to pretend those loads are pretty much daily loads (form battery bank)... Or, again choose to run the generator during those periods.

    Note that not all loads are "equal"... A 140 watt loads 10 for 10 minutes is almost nothing:
    • 140 watts * 1/6th of an hour = 23 Watt hours

    A microwave oven -- 1,500 watts running 10 minutes a day:
    • 1,500 watts / 6th of an hour = 250 Watt*Hours

    A 30 watt laptop running 10 hours per day:
    • 30 watts * 10 hours = 300 WH per day

    A 200 Watt desktop server running 24 hours per day with networking + laser printer + monitor + etc.:
    • 200 watts * 24 hours = 4,800 WH per day = 4.8 kWH per day

    Once you have a decent sized battery bank--They can usually supply short term loads pretty easily.

    It is the loads that run 10-24 hours per day that, many times, are what drive up the size of the solar array and battery bank--And the costs of the system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: My head is spinning!

    You do need to 'factor in' those added energy users, or only run them as opportunity loads, once you batteries are charged during the day.

    Things like refrigerators run on thermostat so the load can't be calculated by the 'wattage' specs. If you want to spend extra money (3-10 times as much) and be "off grid" then one of the things you have to consider is that the system must be many times larger than needed to supply your energy on sunny days.

    Composting toilets are a topic unto them selves. Non-electric tend to not compost as well as electric/heated ones. They also work on thermostat and to me, aren't the energy hogs someone here has suggested. The waste will heat somewhat by it's self as composting, but I've yet to set mine up and use it. I planned on running the heater (300watt from my faulty memory) as an opportunity load when the batteries were charged during the winter, feeling the summer it should be able to maintain it's heat.
    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.