Advice on small off grid system for mountain cabin

Hi i am new member of the forum, and is looking for some advice or tips from the forum members, regarding a small off grid system for a mountain cabin in southern Norway.

Until now the cabin have had no electricity at all, but i am planning to install a 12 volt system primarily for lighting(LED) purposes, and charging/powering small consumer electronic devices like mobile phone etc.

I have estimated the worst case requirement for LED lights to approx. 20 Ah pr day. The cabin is typically used one week at a time and total about 6 weeks per year, spread across different seasons. However rarely in the darkest winter months (November -> February).

So far i have the considered the following main components.

Panels: 2x100W
Charge controller: 15A MPPT MorningStar
Battery: 3x100Ah AGM (Vision or Excide)
Inverter: 275W Studer 12/230V with standby option (0,3 watt standby)
Battery monitor: Trimetric 2025-A incl Shunt
Generator: Honda Eu20i
Battery charger: CTEC MXS25 - 25 amp.

Does this sound like a reasonable setup?

Thanks in advance
Anders

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Advice on small off grid system for mountain cabin

    Welcome to the forum Anders.

    Your power demands, whereas not specific, don't appear to be very high. As such I don't see why you'd want or need three 100 Amp hour batteries. They certainly will not recharge properly from your proposed 200 Watts of panel.

    100 Amp hours of 12 Volt battery discharged 25% will yield approximately 300 Watt hours.

    If you can connect some of your charging directly to the batteries that will save you some inverter power and conversion loss.

    200 Watts of panel on a PWM charge controller will give you enough current for about that 100 Amp hours of battery.

    If you're going to have the generator available that will be a great insurance as you can use it to recharge whenever the batteries get low, regardless of sun.

    But I think you may want to work out a more precise power usage plan before you buy anything.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    Look into LED lights that run on 12v direct from the battery, lots of hits on Ebay and other similar sellers from 1 watt up to 10 watts.
    I used MR 16 bayonet types. Also look at IKEA they have lots of low voltage lighting.

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
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    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
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  • mike95490mike95490 Solar Expert Posts: 8,757 ✭✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    Just remember to switch off the 12V led's when solar charging, voltages can hit 15v or more when running an EQ cycle, which the bulbs won't like
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    Starting out with 3 batterys in parallel is a mistake. Also consider your possible upgrade path. Using 12v pretty much stops you in your tracks. I would go 24V, get a cheap 24v-12v converter, and run the LEDs off that direct. Itll be nice and regulated. Plus allows you to add to pv up to 1 or 2 kW should you go there. 2x 110Ah batterys in series gives you 110Ah at 24v or about 500-1000Wh/day usable. Your led loads of 250Wh, plus all the other "little' things, that add up, laptop, cell chargers etc. Overall less wire losses, less wire.

    Downside to this plan is that low wattage 24V inverters are less common. But Victron, powermaster and others do make them. Do you even need an inverter? Ive never met an electonic toy that cant be run off a 24v battery with a dcdc converter. Use the gen for the powertools etc.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • AndersEAndersE Registered Users Posts: 4
    Re: Advice on small off grid system for mountain cabin

    Hi all

    Thank you for tips and comments, and sorry for my late reply.

    The reason why i ended up with the 3x100Ah battery bank, was in order to run on batteries for a few days in periods without og with less sun, without discharging the to deep.

    I must admit that I have not been aware of the panel watts to battery bank ratio that you refer to. I thought that this was less important since the cabin typically only will be used for one week at a time and would have good time in between to get the batteries fully charged. Also, if I look at complete DIY kits from the main cabin suppliers in Norway, they typically have very large battery banks compared the the amount on watt from the PV panel included.

    I see this rule mentioned in a lot of posts here, but have not found a detailed explanation of why and what will happen to the batteries, in the long run, if the peak charge current is to low.

    Regarding running the LED directly of the battery bank, I also had not considered the over voltage issue when charging. It seem to be a good idea to run the PV system in 24 volt, and then convert to a stable 12 DC with a Victron DC-DC converter or similar.
    BTW: will a change to 24 volt increase the requirent for PV panels further to get the same charge current at 24 volt, or is it only related to the amount of Ah in the bank ?

    The resaon i added the 275W studer inverter was to make life a bit easier when working with different kinds of chargers/power supllies etc. However i agree that most standard electronic equipment should be capable of running of 12 or 24 v DC.

    Once again thanks for your very valuable inputs.

    Anders
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    If batteries are too slow getting recharged, they will be seriously / permanently damaged and their life can be drastically shortened.
    Thus the mentioned ratio between PV watts and battery capacity, to get the batteries back to full charge before damage occurs.
    Plan on not discharging your battery pack any lower than the 80% fully charged state for best battery life, and plan on never ever discharging below the 50% mark.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    Its really common to see older systems (or system designers still thinking the old way) with high batt to pv. Its a result of the price structure that used to exist. Now that pv is the cheap part, and batterys the pricy part, its much easier to get it right.

    The way ive heard it explained is that the C10 charge rate bubbles the electrolyte enough to prevent the acid statifying into dense and less dense layers. Which in turn leads to sulphation and early battery death.

    But other than that, adequatre pv makes it much more likely that the battery will live out happy days in its comfort zone of higher states of charges. Low pv OTOH often leads to batterys repeatedly and for length periods taken below 50%. And thats an even quicker route to sulphation.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
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  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Advice on small off grid system for mountain cabin
    AndersE wrote: »
    ... was in order to run on batteries for a few days in periods without og with less sun, without discharging the to deep.

    Batteries are expensive, compared to other parts of the system. And if you have too much of them, they're difficult to charge. There are better means to keep the power running during long periods of cloudy days, such as a small generator.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Advice on small off grid system for mountain cabin

    Actually the C/10 rate is recommended because it usually allows you to recharge the batteries in one day before you run out of sun.

    The more time batteries spend at a lower SOC the faster they sulphate and thus the shorter their lifespan. If you use the old "recharge over a few days" method they will spend more time at lower SOC and will have a shorter life. With PV being quite cheap now in relation to batteries (the inverse of how it was just a few years ago) recharging as quickly as possible immediately after use is the best plan for longevity.

    If there is a severe imbalance between the amount of PV and the battery capacity they may never recharge at all, as the self-discharge rate (which increases with time) can exceed the charge rate.

    You'd be surprised by the number of system that "worked for years" despite chronic deficit charging just because the battery capacity was so large in relation to the actual power used. Then they just drop dead one day when that capacity falls below the sustainable amount.

    And if sunlight is often in short supply even more panel is desirable.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Advice on small off grid system for mountain cabin

    I would rethink the DC lighting option if you're already going to buy an inverter. Much simpler to do everything over AC and the small loss of efficiency in using the inverter is cheaply made up by adding more panels. Saves a lot on wiring and on a 24v-12v DC-DC converter.

    And if you're getting an inverter and a charger to be used with the gen, then you could consider getting 1 inverter/charger integrated unit. This makes life with the generator more pleasant because it has an automatic transfer switch built in, so you won't have any interruption to power when switching from inverter to gen and back again. Unfortunately the smallest unit I can find is an 800W one from Victron: http://www.victronenergy.com/inverters-chargers/multiplus-12v-24v-48v-800va-3kva/

    I realise that what I'm suggesting is perhaps a bit too much for your needs, but if you compare the price of this type of system with the 300W studer + DC-DC converter it may come quite close.

    For panels, you could find that the more commonly used bigger panels (200W - 300W) can be cheaper than the 100W panels.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    Well stephen and i disagree on this matter :) For very small systems it makes even more sense to use DC loads where you can. The fact is, low voltage dc lighting is now well and truly here to stay. Why design and build new systems with ac lighting wiring and lighting fixtures, it just makes no sense.

    For a small system every drop of power counts. To convert from dc to ac and back to dc, probably kills 50% of the energy, a situation at odds with the adage that RE implores load/demand side conservation.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Advice on small off grid system for mountain cabin
    zoneblue wrote: »
    Well stephen and i disagree on this matter :) For very small systems it makes even more sense to use DC loads where you can. The fact is, low voltage dc lighting is now well and truly here to stay. Why design and build new systems with ac lighting wiring and lighting fixtures, it just makes no sense.

    For a small system every drop of power counts. To convert from dc to ac and back to dc, probably kills 50% of the energy, a situation at odds with the adage that RE implores load/demand side conservation.

    IMO - from a cost perspective it makes a LOT of sense to just stick with AC for everything. Think about ALL the additional costs with running 12v devices if you already have AC wiring in place (just a few off the top of my head):

    A. A large enough 24V(or 48v) to 12V converter to handle your 12v loads
    B. The additional wire runs for those loads, and needing a MUCH larger wire size due to line loss and larger amp draw of 12v vs 110v devices
    C. An additional DC breaker panel for all of those circuits (and DC breakers/panels are a lot more $ than AC ones)
    D. Your labor running all that additional wire (especially if you have to go inside existing walls)
    E. The added cost of 12v switches and fixtures (to handle the higher dc loads) vs 110v switches and fixtures

    I am sure there are other reasons people can think of. And I am not quite sure that you are losing 50% of your power. I know one of the experts here could work out the real math.

    Which makes me wonder if anyone has done a real comparison of the power requirements for 12v lighting vs 110v lighting from a lumens standard? I would be interested in knowing that.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    If you have extensive investment in ac light wire runs, fittings and lighting, then fine i agree, theres an inertia factor. But that wasnt what i was talking about.

    LED lighting has now well surpassed fluoro/CFL in efficiency. Better quaility LEDs produces 130 lumns per watt, cf CFL at about 70. But even cheap grades of LED produce 90. Color balance, and, frankly, safety is an issue in some of the cheaper grades though.

    DC,AC,DC. Maybe i was exagerating. DC-AC, 85% if inverter well loaded, if idling lets say 75%. AC-DC, 90%. So total efficiency 67%.

    The real damage IMO is the extra battery capacity required to support the inverter 24/7 tare loss. Batterys are expensive, and full of heavy metals, and, sadly, do not last long.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
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  • BB.BB. Super Moderators, Administrators Posts: 30,497 admin
    Re: Advice on small off grid system for mountain cabin

    Most non-filament lighting (CFL, LED, Florescent, Neon, etc.) needs some sort of ballast/voltage conversion/current control/etc... So once you leave Edison's light, there is really no "native voltage" (very big simplification/over generalization). Same for electronic loads--A computer may have 4 or more voltages generated internally to support the various power requirements.

    So, that really leaves wiring losses and conversion losses as the main variables. Obviously, low voltage/high current creates problems/expenses with the wiring (I2R losses--double the current, 4x the losses on the same wire).

    If we assume 3% wiring losses and 15% AC inverter losses--The AC inverters (or even DC-DC converters like 48 volt to 12 volt) are an added cost to the system. But between a 12 volt and 120 Volt system, you need ~100x as much copper (by weight/$$$ amount) to deal with the 10x higher currents to have the same wiring losses...

    Assuming wire runs are short and not too many circuits--You can probably do it with 12 volt wiring.

    However, as soon as you add more circuits and longer distances, the ~15% hit by the AC inverter vs the issues of low voltage DC wiring--The AC inverter (for me) is usually the better solution (more reliable, longer distances, higher power appliances--if needed).

    If most of your loads are 12 volt native loads--Then 12 volts makes more sense--But be sure that these are 12 volt loads that can run from 10.5 volts to 15+ volts DC.... Many 12 volt loads are optimized to operated from ~12.5 to 14.2 volts (automotive typical voltages)--And will not function well, or may even fail when operated on a full off grid DC power bus with the full voltage range (and temperature range) that your battery bank can experience.

    I much prefer to have a single AC inverter be the "only DC appliance" I have to worry about.

    So--Is a 15% larger solar array and battery bank plus the cost of an AC inverter (recommend TSW if possible) vs wiring 12 volt circuits (using Anderson connectors is a "standard" for HAM radio gear DC power). There is the issue that a low wattage load on an AC inverter can have much worse efficiency (i.e., a 6 watt AC load on a smaller inverter with 6 watt tare loading--Gives you 50% efficiency).

    I will also add that I believe that AC power (even at the higher votlages) is safer regarding fire. Lower current flow, cheap/plentiful circuit breakers, GFI devices, and even Arc Fault, even transformer isolation if needed. (excluding actual hot to neutral/ground electrical shock).

    You have to send 10x the current to do the same job on 12 VDC (10x larger breakers, etc.).

    You do have less of a shock hazard (12 volts is pretty unlikely to shock somebody in normal operation.

    However, you are likely to weld your wedding ring to a 12 volt battery bus because of the very high available current. Not usually going to happen on a 120 VAC circuit.

    There is the ground loop issue too... DC radios/appliances frequently use the DC Chassis as the ground and return electrical connection. With modern 120 VAC appliances, the AC Hot/Neutral are isolated from earth ground--So, you don't have ground loop current issues.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    I don't know about down under but there is a dearth of DC fixtures and switches etc up here in Canada without going to an RV supplier and then paying a 'luxury tax' type of price as it obviously is not for your home... like AC products. for instance I used track lighting for our old cabin... ps I had to remove the AC to DC transformers, so lost what ever I paid for those. Tried GU 10's but had trouble getting replacement sockets, they still wanted $15 or so for the fixtures

    track, $15 to $20 per piece, fixtures $30 each, so for 3 fixtures I am paying $105 min per section of track and I had 4 = $420 plus in overhead before I turned on one light, then there were the LED s they still want $30 retail at the hardware store. Ebay? $1+ each plus shipping...

    so it also becomes an availability and an economic decision let alone the extra wiring needed to minimize line loss.

    It was OK in the old cabin as it was only 16 x 32 feet...

    So I can get AC
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
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  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Advice on small off grid system for mountain cabin

    My inverter is 96% efficient when loaded, 88% with my background loads. So DC->AC->DC conversion is not that bad. Certainly a fraction of loss that I would have if I decided to distribute 12V all around my property.

    12V would force me to 12V battery voltage, which would drop CC efficiency and forced me to deal with very high currents. Not to mention, I would have to buy 8 CCs instead of 2.

    If I wanted to disconnect batteries, I would have to seat in the dark. Right now, I just run a generator and all my loads are powered!

    If I had a brand new house to wire, I wouldn't even think of 12V.
  • SlappySlappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    Having both is good. Diversity
  • twinomadtwinomad Registered Users Posts: 6
    Re: Advice on small off grid system for mountain cabin

    Perhaps some of you are familiar with Marine electronics. My sailboat had everything 12VDC, from HAM radio to toilet flush, from fresh water to bilge water, night lights were all night and CD player never stopped. - and it did it all very well. Four 50 watt panels and a Airex wind generator. WE found everything we ever needed with 12VDC, from kettle for hot water to hand mixer. Lights of all sorts were the easiest to find, pumps and fans no problem. WE used deep cycle batteries group 27, note: no part of our house electrical was ever attached to the engine start system that was for safety reasons, so the sailboat had two completely independent systems.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    i think theres a circular argument in play here. "My lighting draws heaps of amps therefore i need fat wire, high voltage and ac fittings".
    Whereas lighting for our entire place draws a couple of amps at 24v.

    One of the problems with ac leds is that the driver is inherrantly bolted right on top of the heatsink. There goes any hope of decent life, the filter capacitors will die long before the emmitter array. I use a tiny 24V to 10ish dc-dc current limiting driver inside the cieling rose, and each fitting is about as bright as two 11 watts CFLs, but only draw 700mA at 20volts or so.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin
    NorthGuy wrote: »
    My inverter is 96% efficient when loaded, 88% with my background loads. So DC->AC->DC conversion is not that bad.

    Thats heartening to hear NG, i was previously under the impression that the average transformered inverter wasnt capable of those sort of numbers.
    Certainly a fraction of loss that I would have if I decided to distribute 12V all around my property.
    12V would force me to 12V battery voltage, which would drop CC efficiency and forced me to deal with very high currents. Not to mention, I would have to buy 8 CCs instead of 2.

    Nah, run battery voltage to the lights direct, then stack the LEDS in series til it takes up about 90% of the voltage, current limit the rest. In our case we run 24V throughout the house, then pairs of 3x3 emmitter arrays. Its a pretty elegent solution NG.

    The advantage of having the dc converters on the end of the wire is that when they are off they are really off.

    Regards wire size, present day houses were and still are wired for a 100 year old lighting technology. Remember when lamps drew 100 watts a peice... when led lighting is putting out the same light as that but only drawing 15W, why do we need such heavy wire?

    In fact i would say that most of our wire is actually smaller than yours. The lighting branch lines are 'caravan' single insulated figure 8 half mil or so. 4 times less copper, 10 times less PVC, than the std 1mm2 double sheath required for ac lighting here. Theres obviously no need of an earth conductor, no electrocution risk, and reduced fire risk, (48 would start to creep up). Those lines do run into 6mm trunk lines, but thats because i could get it cheaper than i could 2.5mil. And my pet favorite, much less EMF noise. But note thata you do need to add output filtering to the dc limiter to reign in the square wave output.

    Those same dc-dc I limiters, would be harder to run on 48V though. LM2596 max is 45v i think.
    If I wanted to disconnect batteries, I would have to seat in the dark. Right now, I just run a generator and all my loads are powered!

    If I had a brand new house to wire, I wouldn't even think of 12V.

    Well you and i run different setups of course. Our place is more like a cabin than a house, 3kWh per day, pretty much by choice. While i would like to get round to finishing the hot water diversion, we dont want for much else. Our strategy wont be for everyone, but if i was (and we are about too) building a new house, all the lighting cabling will certainly all be DC.

    Apologies to OP for thread detour.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Advice on small off grid system for mountain cabin
    zoneblue wrote: »
    Regards wire size, present day houses were and still are wired for a 100 year old lighting technology. Remember when lamps drew 100 watts a peice... when led lighting is putting out the same light as that but only drawing 15W, why do we need such heavy wire?

    Heat losses in the wire are proportional to the square of current. To move the same power at 12V, you need 20 times more current than 240V, this is 400 times more losses.

    100W at 240V is 0.42A. 15W at 12V is 1.25A. Still 3 times more current and 9 times more losses through the same wire.
    Even 15W at 24V is 0.62A, still 1.5 times more current and 2.3 times more losses through the same wire. So, you do need a thicker wire. Otherwise, what you saved will be used to heat wires.

    In my particular case, I have heavier loads and long distances, so I simply couldn't do it with DC, but these considerations probably do not apply to the cabin.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Advice on small off grid system for mountain cabin
    zoneblue wrote: »
    Nah, run battery voltage to the lights direct, then stack the LEDS in series til it takes up about 90% of the voltage, current limit the rest. In our case we run 24V throughout the house, then pairs of 3x3 emmitter arrays. Its a pretty elegent solution NG.

    As battery voltage can vary, your should plan for the lowest voltage, say 22V. The current limiter will require some voltage drop, say 2V, so the combined forward drop of your LEDs should be no more than 20V. Which means that at normal operating voltages of 24V, the current limiter will have to drop 4V. During absorption at 29V, it will drop 9V. During equalizations at 32V, it'll be 12V. Therefore, the efficiency will be 83% for normal operations, 69% during absorption, or 62% during equalization. Assuming your LED array is 15W, the losses will be 3W during normal operation, 7W during absorption and 9W during equalization. This will require some serious heat-sinking to prevent damages during absorptions/equalizations.

    AC-based LED driver can expect relatively stable voltage and therefore can achieve better efficiency of 90+%.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    Nah NG, the chips in those current limiters are switch mode devices, not linear as you assume, more efficient than any ac inverter at any load.

    Seeing as we are being picky (and i was gona let you have this one but hey ;) ... if we follow your logic that a 15w led on the same sized wire as a 100W tungsten burns 2.30x more wire loss. 230% more than what? 230% times not much obviously. If we say that the wire in question is dropping 0.5% of load, then thats a grand total of, 15W * (1.15-0.5)/100, or an extra 0.0975W. Ok so we are comparing that to the total conversion loss using ac of 88% (inverter) * 95% (dc conversion) = 84%, which amounts over 15W to 2.46W, or to the 20,30,40W tare losses on a big inverter. I think we might be making a mountain outa a mole hill mate.

    BTW no batt here at 22V, so the 4-5v margin between emmitter and line works just fine.

    DC leds are very very cool.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
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  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Advice on small off grid system for mountain cabin
    zoneblue wrote: »
    ... if we follow your logic that a 15w led on the same sized wire as a 100W tungsten burns 2.30x more wire loss. 230% more than what?

    2.3 times more heat loss. Say, you sized your wire for a certain heat loss with your 15W/24V appliance. To achieve the same heat loss, one could use 2.3 times thinner wire with 100W/240V incandescent bulb. I said this because you complained that old (incandescent) method required thick wires. No, it actually required thinner wires.

    If we start comparing apples to apples, say 15W/240V LED light to 15W/24V LED light then difference in wire losses becomes dramatic. Let's say I would want to run a wire for 15W/24V LED light from my batteries to my house. This is 100 ft - 200 ft back and forth. Let's say I would use thin #22 wire (0.64 mm in diameter). Would give me 3.2 Ohm resistance. With 625mA current, this would drop me 2V. I would get 22V instead of 24V. Your current-limiting device would stop working every time the battery voltage drops below 24V, so my lights would go off without any apparent reason. I would have 1.3W losses (8%).

    Now look at the same wire with 240V. Now current is 63mA, which gives me 0.2V drop. I get 239.8V instead of 240V - unnoticeable. Heat losses are 13mW - unnoticeable. No troubles with lights going off.

    Then project all this to the whole house. I don't even mention coffemakes, pumps, motors etc.
    zoneblue wrote: »
    Ok so we are comparing that to the total conversion loss using ac of 88% (inverter) * 95% (dc conversion) = 84%, which amounts over 15W to 2.46W, or to the 20,30,40W tare losses on a big inverter. I think we might be making a mountain outa a mole hill mate.

    My inverter is sized to handle big loads, at which it gets 96% efficent. The inefficiency at lower loads is caused by 28W draw by such a big inverter. It draws 28W no matter what. If you don't count these 28W, the inverter is 98% efficient through most of the scale (except very heavy loads). If you want to support anything but lights, you would have to have an inverter anyway. Adding a light to the existing inverter only incurs an additional loss of 2% - fraction of the 8% wire loss that we incurred with DC lights.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Advice on small off grid system for mountain cabin

    I never said that there arent less wire losses, just that my wire for DC LEDS is smaller than std lighting wire. Hence the wire cost factor is not a biggie. In any event bigger wire, where i use it, for trunk lines, and for dc pumps, dc computer gear etc, doesnt have to be expensive double insulated mains rated stuff, you can generally find cheap single insulated wire, 13mm2 (beware that around here mil is short for mm2, confusing i know) for about half the cost of 2.5mm2 mains cable. In practice the voltage drop is negigible for our runs of more like 30ft.

    300ft of anything is gona cost something i suppose, but the length doesnt materially alter the premise, that we are talking, for lighting, about relatively small currents.

    NG, in my world 28W tare is 670Wh/d, or about 22% of my daily base load consumption, and enough to run an efficient full sized fridge. In accordance with the above line of thinking there is only one way to describe that... unacceptable. News around is the new SW series are even higher. Inverters makers need to address that.

    Anyway i enjoyed our conversation, NG.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Advice on small off grid system for mountain cabin
    zoneblue wrote: »
    NG, in my world 28W tare is 670Wh/d, or about 22% of my daily base load consumption, and enough to run an efficient full sized fridge. In accordance with the above line of thinking there is only one way to describe that... unacceptable. News around is the new SW series are even higher. Inverters makers need to address that.

    This loss depends on the size of the inverter. For me, it's about 5% of my daily consumption. For smaller consumption, you probably would have a smaller inverter with smaller loss.

    My peak loads are about 4kW. Theoretically, could be more, but never really happens. At 24V, this would be 167A. Cannot really move it 100 ft from the garage to the house, not to mention other outbuildings. Lights are a very small part of this, so I don't worry about lights.

    I understand that this could be different if lights were the majority of the loads. You certainly don't need an inverter if you only have two light bulbs and phone charger. But as the system grow, transmission losses pile up really quick.
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