Proposed System - 1000W - Advice Needed!

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  • treeforttreefort Registered Users Posts: 12
    Re: Proposed System - 1000W - Advice Needed!

    I would need 1647 watts of panels if I was to use a 1kWhr/day fridge. Twice the panels required if I use a 360Whr/day 12V Sundanzer.

    I thought I had taken the 12V voltage drop over distance problem into account by running 14AWG to all the 11W max LED lights, and odd cigarette lighter adapter(2A total max). That was at the time where I didn't realize the total amount of feet in a voltage drop calculator is there and back. So, at 2A, I can go 21'. That's going to be short for a few runs. So, maybe I will run AC to the lights and deal with the 10% loss from the inverter. I still think I should probably run DC for the Sundanzer, the water pump(the AC one is over twice the cost), and a cigarette lighter hub for charging phones. Why would the voltage drop to 10V? I monitor remote solar powered oil and gas well sites(low power systems..maybe 400W) all with AGM batteries, and if they dropped to 10V the LVD would drop them out or devices would brown out, gas wells would shut in, operators would be crying..
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: Proposed System - 1000W - Advice Needed!
    treefort wrote: »
    I would need 1647 watts of panels if I was to use a 1kWhr/day fridge. Twice the panels required if I use a 360Whr/day 12V Sundanzer.

    Again, it depends on your needs.... The 1kWH per day AC upright refrigerator is ~16 cuft refrigerator+freezer.

    The Sundanzer at 360 WH perday is only ~8 cuft chest refrigerator @~$1,200 or so (I guess--US pricing).

    You could, in theory get a ~8 cuft chest freezer from Homedepot/etc. for ~$350-$380 (again--US pricing)... And spend another $800 on solar panels + battery bank (plus larger AC inverter if you do not have one already) and come out about the same (you would need a refrigerator range thermal switch of some sort too).

    The AC chest freezer as a refrigerator is probably only going to use around 250-400 WH per day to (depending on ambient temperatures)...

    Yes, the AC Chest Freezer conversion is going to take some testing/modifications to make sure it meets your needs.... But it can be competitive.
    I thought I had taken the 12V voltage drop over distance problem into account by running 14AWG to all the 11W max LED lights, and odd cigarette lighter adapter(2A total max). That was at the time where I didn't realize the total amount of feet in a voltage drop calculator is there and back.

    Some calculators use one way length and others use round trip length--You have to check.
    So, at 2A, I can go 21'. That's going to be short for a few runs. So, maybe I will run AC to the lights and deal with the 10% loss from the inverter.

    Again, check the prices for 12 vdc vs 120 vac lighting... It can be all over the map--Some folks here have used 12 volt tracking LED bulbs and have been very happy. I suggest you get one of each 12 vdc (and even 120 vac) lights and test them in your application. Sometimes it is difficult to tell if they will work well for you by just reading the specifications.
    I still think I should probably run DC for the Sundanzer, the water pump(the AC one is over twice the cost),

    DC pumps can be a nice/cost effective solution. When you pick one, check around for reviews and make sure they will have the life you expect. Pumps do use a lot of power--So you have to make sure they you can get 12 VDC power to them with reasonable wire gauge.
    and a cigarette lighter hub for charging phones. Why would the voltage drop to 10V?

    In general, a good low voltage assumption for a 12 volt system would be 11.5 volts minimum battery voltage and 0.5 volt wiring drop at rated current. Leaves another 0.5 volt drop for 2x surge current.
    I monitor remote solar powered oil and gas well sites(low power systems..maybe 400W) all with AGM batteries, and if they dropped to 10V the LVD would drop them out or devices would brown out, gas wells would shut in, operators would be crying..

    Sounds interesting (hey--I am an engineer, I am always curious about how things work :roll:).

    In general, the (very rough) minimum voltage for a 12 volt lead acid (and AGM) battery would be around 11.5 volts under load (warmer batteries, ~-0.03 volts per degree C rise on 12 volt battery). If you cycle a lead acid battery dead (~10.5 volts or below at 77F/25C), then the batteries will usually not recover (in my limited experience, especially if the battery is over ~1 year old).

    Some batteries (like industrial traction/fork lift) can take deeper cycling... But there are other issues with them.

    I try to suggest design guidelines that will work over time and temperature... Not just with new, fully charged batteries.

    But these are just starting point suggestions--If you have other needs, or more experience than I (very easy, I am not a battery guy)--Then use your fudge factors instead.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Proposed System - 1000W - Advice Needed!
    zoneblue wrote: »
    The place to start is your expected load Wh/d. You do have to draw a line in the sand somewhere, and demand is where it starts. Demand dictates PV, PV dictates battery. Bill probably said all this already :)

    Did Bill ever really say that? I seem to remember him writing something more like: Load dictates Battery, Battery dictates PV. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Proposed System - 1000W - Advice Needed!

    Guys weve debated the ac v dc thing ad nausium here. OP if youre interested in further discussion on that topic i suggest you look in the archives. There are pros and cons to each and theres no right answer, very much depends on your setup. In general, if your place is "cabin" sized, using DC is going to be more possible for many of the reasons youve listed. If you do DC, forget 14 gauge, look around for some cheap surplus cable, obviously doenst need flash 1000V rated insulation, but you looking for pounds of copper. For my DC runs i use a a mixture of 6awg, and 6mm2, and im on 24v. All of that cable cost less then $1.50 per meter new... just a matter of looking around.

    For the fridge, yes, complicated. The one big upside to using a DC fridge is that you can turn the inverter off for much of the day. Most inverters use an fair chunk of power just doing nothing. The 300W inverter recomended here is not so bad, but, then it wont run a fridge so thats kinda academic. This inverter tare load is mostly an issue for mid range systems. On bigger systems, the tare disappears into a haze of other background loads, less of an issue. Again "cabin", DC has benefits, full size house, not really. In the latter case you get your 6kW XW or whatever and forget about the 30W odd its sucking 24/7. BTW dont be seduced by low "standby" draw figures. The standby feature is next to useless, as it only takes one thing that you need to leave on 24/7, wifi router, trickle charger, whatever and your inverter will never get to use its fancy standy feature. The exception there is some inverters will actually power some tiny loads in standby, eg clocks on dvd players or so.

    LEDs. Yes a sudden rush to market in AC leds recently has brought the price down. My main comment about LED is color. Predominantly there are two colors warm and cool, of which neither is very nice. Combinations of both i find creates a nice balance. For just a few bucks you can make your own which is fun.

    For your loads. In general the presence of an electric fridge, is one of the notable features that trips a system from small to medium. The 0.5-1kWh draw does kinda trip you into systems that tend to have 1.5+kWp PV. Not so say it cant be done on less, with clever optimisations. But a fridge is a relentless load. If you dont wont to end up spending a lot of time fussing with generators in bad weather, having more PV is desireable, lets face it its cheap now right. This is one area where AGM shines, high PV to battery ratios. I know a guy with a 10kW array and a battery bank no bigger than mine. Even the worst weather he's fine. Conversely i once did a design for a motorhome with a danfoss compressor fridge on just 320Wp. The fridge was turned off at night with a relay.

    So your load budget 530Wh/d. First i always include a contingency, say 20%, for things you forgot! Did you actually measure the laptop, the adapter might be rated at 60W, but it probably wont draw that. Maybe its a huge one? Lights, unless you like living in the dark, LEDs dont make that much light, at least not 5W ones. My 20W ones, yes, but then we have at least two of those, sometimes three or four. So maybe you need a bit more lighting allowance there. Is that really it, no cell phone chargers, cordless tool chargers, soldering irons or other tools? Gees what kind of techy are you ;) Then if theres a Mrs OP, then man youre into a whole nother league mate.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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