# Have I got all of this figured out?

Posts: 13Registered Users
I'm trying to develop an off-grid system for a homestead that I'll be building over the next five years. I've never worked with solar panels before, so I'm still trying to understand how to make it all work. I think I'm finally at a point of comprehension, but I'd really like some experts to go over this with me.

My power usage will peak at 190w for 4-6 hours at night. I'll be running a satellite internet modem/router (~35w), LED LCD (~50w), small refrigerator (~65w), 2-4 LED lights (10-30w) and have a tablet plugged in to a USB outlet (10w). All of this will be 12v DC, with the USB outlet wired for 5v @ 2 amps (several outlets, actually, but this specific one will be wired to USB 3.0 spec and almost always have a tablet plugged in). If I understand the math, this means I'll be hitting a peak amperage of 95 over a six hour span, then dropping to ~33 over the next six hours, at which point the sun should be up and my battery charging as well as delivering enough current to keep that refrigerator supplied. If that is correct, then I think I should be planning for a ~128 amp draw over a 12 hour period, and doubling that to prevent cycling of the battery below 50%. So I should be planning for a battery with a minimum of ~260 amp hour rating. Correct?

If I've got all of that right, then I believe my next step is the panels. In order to put that ~128 amps back into the battery, I'd need panels which could deliver a cumulative 1536w throughout the entire day, or 384w per hour during peak insolation (10 a.m. to 2 p.m.). I would also want to account for losses and inefficiencies, multiplying the actual panel rating by 0.77, and, for my own peace of mind, also factor in the 20% efficiency loss over 25 years so I'd know whether I'd need to add another panel later down the road, or be pretty well set for the rest of my life (barring unforeseen circumstances, such as damage). So I'd take the panel wattage, multiply it by 0.77, then by 0.8 to get the total I could expect overall. If I picked up three 235w panels, the output I should expect from them would be, again after factoring for the 25 year drop in efficiency, (((235 * 3) * 0.77) * 0.8) = 434.28. That would deliver enough total amperage to recharge the battery during peak insolation, plus, I think, supply enough additional electricity for the refrigerator to operate in addition to the charge going to the battery. Correct?

Third step would be the controller. With three 235w 24v DC panels, at 77% efficiency in the first year, I'd be outputting slightly over 45 amps, so I'd need a controller capable of handling more than 45 amps, despite knowing that the output will drop over time. I'd also want a controller capable of stepping that 24v down to 12v. The Morningstar 60 amp MPPT controller appears to meet both criteria. Correct?

I also should use good, heavy wiring between the controller and battery, and keep the distance as short as possible, to reduce losses due to heat and poor transmission. Two to four gauge wire for that connection, and eight to ten gauge for the line running from the panels to the controller? And I should place a temp monitor directly on one of the battery terminals, to allow the charge controller to more accurately... well, control the charge going to the battery?

Do I need a battery charger, or does the charge controller handle that?

If I use 6v batteries, I'd want to get two, wired in series, and ensure that each delivered at least 225 amp hours, correct?

This will be a 12v DC system, no inverters, nothing using AC. Am I going to need anything in addition to the battery, panels, charge controller and proper wiring? Junction box, obviously, and fuses, but do you see anything that I'm overlooking? I'm totally new to this, and I'm going to be doing it all by myself, so I want to get it right the first time. If there's something I've misunderstood, point it out so I can learn and avoid making a critical mistake.

• Posts: 10,311Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?

welcome,
somehow your math seems a bit fuzzy to me and it does seem some of the loads you list may or may not be high enough.

also note that you may be confusing us a bit as amps and amp hours, plus the watts and watt hours (ah and wh respectively) should be used in there at some point. the reference to an hour is important to avoid confusion. here's an example, say you have a light bulb (incandescent type) at 100w. in 1 hour it is 100wh. a 50w bulb going for 2 hours is also 100wh. a load like a tv at 65w over a 6 hour period will yield 390wh. ah is similar in respect to that one hour time period. you must be certain of the load ratings and times and you don't want to shorten this to be conservative as the batteries have to supply that power and then some to the loads. it is similar for the pvs to charge the batteries as well. losses will appear such as resistive losses, charging losses, and even the losses for the inverter to be on in standby so you don't want to underestimate anything or you could over tax the system and ruin it quickly.

also note that many prefer to make it extra large to account for some underestimates and expansions, not to mention the possibilities of inclimate weather, seasonal solar lows, and other unforeseen circumstances.

let's take this a step at a time here and be certain of the loads and the times they will draw.
• Posts: 4,669Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
Luminara wrote: »
I'm trying to develop an off-grid system for a homestead that I'll be building over the next five years. I've never worked with solar panels before, so I'm still trying to understand how to make it all work. I think I'm finally at a point of comprehension, but I'd really like some experts to go over this with me.

Welcome, I'm no expert, but an experienced off grid person.
Luminara wrote: »
My power usage will peak at 190w for 4-6 hours at night. I'll be running a satellite internet modem/router (~35w), LED LCD (~50w), small refrigerator (~65w), 2-4 LED lights (10-30w) and have a tablet plugged in to a USB outlet (10w). All of this will be 12v DC, with the USB outlet wired for 5v @ 2 amps (several outlets, actually, but this specific one will be wired to USB 3.0 spec and almost always have a tablet plugged in). If I understand the math, this means I'll be hitting a peak amperage of 95 over a six hour span, then dropping to ~33 over the next six hours, at which point the sun should be up and my battery charging as well as delivering enough current to keep that refrigerator supplied. If that is correct, then I think I should be planning for a ~128 amp draw over a 12 hour period, and doubling that to prevent cycling of the battery below 50%. So I should be planning for a battery with a minimum of ~260 amp hour rating. Correct?

Kinda the right idea, but your loads should be calculated through out the day, your not going to turn off your fridge during the day, so it will be a load regaurdless of where the energy is coming from. About that fridge, most turn on and off on a thermostat, there are some 12V fridges that run all the time, 65 watts x 24 hours /12 volts = 130 amps (at 12V)...
...every thing starts with loads, so figure a 24hour day's worth of loads.

On battery storage, what are you going to do in those cloudy winter weeks? Normally we look to discharge no more than 20% then have some reserve for those cloudy days, and a plan for cloudy weeks, generator or reduce your usage, are you prepared to eat every thing your storing in your fridge?
Luminara wrote: »
If I've got all of that right, then I believe my next step is the panels. In order to put that ~128 amps back into the battery, I'd need panels which could deliver a cumulative 1536w(fridge alone is 1560watts) throughout the entire day, or 384w per hour during peak insolation (10 a.m. to 2 p.m.). I would also want to account for losses and inefficiencies, multiplying the actual panel rating by 0.77, and, for my own peace of mind, also factor in the 20% efficiency loss over 25 years so I'd know whether I'd need to add another panel later down the road, or be pretty well set for the rest of my life (barring unforeseen circumstances, such as damage). So I'd take the panel wattage, multiply it by 0.77, then by 0.8 to get the total I could expect overall. If I picked up three 235w panels, the output I should expect from them would be, again after factoring for the 25 year drop in efficiency, (((235 * 3) * 0.77) * 0.8) = 434.28. That would deliver enough total amperage to recharge the battery during peak insolation, plus, I think, supply enough additional electricity for the refrigerator to operate in addition to the charge going to the battery. Correct?

Solar Isolation is a pretty good next step, where are you located so we can look at how much sun you can expect in the short days of winter. Loads grow, pretty much a given. I once lived on an array of 220watts, now I'm at @2000watts at the cabin, primarily wanting a fridge and AC, and looking at 6000watts for a 900sqft tin can. Even if you don't want to AC your cabin, build it well insulated!
Luminara wrote: »
Third step would be the controller. With three 235w 24v DC panels, at 77% efficiency in the first year, I'd be outputting slightly over 45 amps, so I'd need a controller capable of handling more than 45 amps, despite knowing that the output will drop over time. I'd also want a controller capable of stepping that 24v down to 12v. The Morningstar 60 amp MPPT controller appears to meet both criteria. Correct?

Yes, you've got the right Idea, you seem computer savy so you might look into a Midnite classic 150 lite, it will give you room to expand if needed and close to the same price at \$500, all controls and monitoring are available via network cable.
Luminara wrote: »
I also should use good, heavy wiring between the controller and battery, and keep the distance as short as possible, to reduce losses due to heat and poor transmission. Two to four gauge wire for that connection, and eight to ten gauge for the line running from the panels to the controller? And I should place a temp monitor directly on one of the battery terminals, to allow the charge controller to more accurately... well, control the charge going to the battery?

Battery temperature sensor between the batteries, not on the terminal, but you've got the right idea
Luminara wrote: »
Do I need a battery charger, or does the charge controller handle that?

That is the job of the charge controller.
Luminara wrote: »
If I use 6v batteries, I'd want to get two, wired in series, and ensure that each delivered at least 225 amp hours, correct?

In that neighborhood some 215amps some as high as 410amps or more. in series voltage adds, strings in parallel amperage adds.
Luminara wrote: »
This will be a 12v DC system, no inverters, nothing using AC. Am I going to need anything in addition to the battery, panels, charge controller and proper wiring? Junction box, obviously, and fuses, but do you see anything that I'm overlooking? I'm totally new to this, and I'm going to be doing it all by myself, so I want to get it right the first time. If there's something I've misunderstood, point it out so I can learn and avoid making a critical mistake.

It's possible, low voltage drops quickly over wires, if your array, batteries and cabin are near it might work, but likely you'll want to have pretty heavy wiring to hold voltage. If your fridge uses 65 watts continously you could have a full size fridge running on AC for about the same total wattage, might even do a chest freezer conversion for less than the DC fridge.

So I hope this helps a little, I'd say add up all your usage, then tell us where in the world you are, if your willing to have a generator to aid in charging...

,,,then work on a system.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 4,669Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?

If your 5 years out from building a 'true' system, you might consider a small system while your building.

Will you be using AC tools? I framed up an 'A' frame with 18v Dewalt drill and saw. I used my small 220watt array and 2 golf cart batteries and a cheapy 200 watt inverter to charge the batteries for the tools while I worked. This also provided my lights and fan, computer, while I camped while working (actually built a 2 weekend 8x12 shed to camp and store tools)

When I was robbed they left the array and batteries!

This would give you a working knowledge of solar, as cheap as panels are right now, if the DMsolar 12v nominal panels are still available (search here and amazon) I'd bet you could set up a minimal system for @\$600 today panels(2-140watt delievered (@\$320), batteries(local Sam's club 2 golf cart @\$160), CC(@\$80 here) and inverter(Cheapy 200 watt Wally World or Auto [email protected]\$30). I checked and know most Dewalt battery chargers will work on MSW(cheap inverter) NOT ALL WILL! EVEN Dewalt's before 1998? won't.

Just a thought, figured you'd want some power tools for building, I've built 2 sheds and 2 larger buildings with battery power tools.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 13Registered Users
Re: Have I got all of this figured out?
niel wrote: »
welcome,
somehow your math seems a bit fuzzy to me and it does seem some of the loads you list may or may not be high enough.

also note that you may be confusing us a bit as amps and amp hours, plus the watts and watt hours (ah and wh respectively) should be used in there at some point. the reference to an hour is important to avoid confusion.

I can do that.

I'll be using 190 watts per hour for up to six hours per night. 190wh, 6 hour total usage. After that, my usage will drop to 65wh, just the refrigerator running for the rest of the night. I'm not terribly conversant with the calculations for electricity, but I do understand volts times amps equals watts. Working back from that algebraically, I'm extrapolating that watts divided by volts would equal amps. Thus, if I'm using 190wh, I should be consuming 15.83 amps per hour. At 15ah, my usage after six hours would total 95 amps. It would then drop to 5.42ah for the rest of the night, and unlikely change in the morning since I won't be using any powered devices until later in the evening, after I've finished tending my homestead.

To supply that, I'm looking at three 235w 24v panels, an appropriate controller and 255-300 ah of battery power. I understand that there's only a 4-6 hour period during which solar energy can be harvested at maximum efficiency, so I'm trying to design the system to fully recharge the battery or batteries within that time frame, while also supplying a small bit of additional power to compensate for the refrigerator's requirements.
you must be certain of the load ratings and times and you don't want to shorten this to be conservative as the batteries have to supply that power and then some to the loads.

I'm confident of the load and time frame. I'm designing this to supply electricity for a 12x12 dwelling. I'll have four 5-7.5w LED lights, and probably only have one or two on at any given time. An LED LCD will draw 45-50w, and only be used for watching movies at night while I'm preparing and eating dinner. The refrigerator will be a 12v DC cooler with a 65w draw, its only function will be to keep some goat's milk cool so it doesn't spoil before I can use it. A 35w satellite internet router/modem drawing 35w will be used at night for Netflix and some surfing, and not much else unless I have an emergency. And the tablet will draw no more than 10w, and almost certainly less than that overall because it will remain plugged in and only charging when it drops below 95%.

I'll be alone, so there won't be anyone leaving the refrigerator open, or turning on every light and wandering off. I'll be outside almost all day, tending my animals and raised bed gardens, checking my fence line, working on projects like my root cellar, etc. 190wh will be the absolute maximum draw with everything turned on, and that would only occur if the tablet were charging and every light was turned on at the same time I had everything else running. In a 12x12 space, I won't need four lights, but I'm budgeting the system to account for them anyway.

I'm certainly willing to overbudget the batteries a bit more, kick them up to 275-300ah, but I have to cut it off there due to the expense of deep cycle batteries and shipping costs. I'm only making \$10.50/hr. and just paying for what I've tried to estimate I'm going to need is already sitting at \$1250. After shipping costs and including the expense of wiring, connectors, junction box, fuses and whatever else I might need, I'm expecting this to come in somewhere between \$1500 and \$1750. My budget for this is \$2000, so going hog wild with a huge battery bank isn't going to happen.
it is similar for the pvs to charge the batteries as well. losses will appear such as resistive losses, charging losses, and even the losses for the inverter to be on in standby so you don't want to underestimate anything or you could over tax the system and ruin it quickly.

also note that many prefer to make it extra large to account for some underestimates and expansions, not to mention the possibilities of inclimate weather, seasonal solar lows, and other unforeseen circumstances.

let's take this a step at a time here and be certain of the loads and the times they will draw.

I'm certain. 190wh max for 6 hours max at night, 65wh for the remaining 18h, part of which will be offset by incoming solar energy.
• Posts: 13Registered Users
Re: Have I got all of this figured out?
Photowhit wrote: »
Kinda the right idea, but your loads should be calculated through out the day, your not going to turn off your fridge during the day, so it will be a load regaurdless of where the energy is coming from. About that fridge, most turn on and off on a thermostat, there are some 12V fridges that run all the time, 65 watts x 24 hours /12 volts = 130 amps (at 12V)...
...every thing starts with loads, so figure a 24hour day's worth of loads.

I was expecting the incoming power during daylight hours to help reduce the load from the refrigerator. Even though I wouldn't be seeing full output from the panels outside of max insolation, I should be getting something, shouldn't I? Enough to keep the refrigerator running?
On battery storage, what are you going to do in those cloudy winter weeks? Normally we look to discharge no more than 20% then have some reserve for those cloudy days, and a plan for cloudy weeks, generator or reduce your usage, are you prepared to eat every thing your storing in your fridge?

I won't have much in it. It's just there for summer months, when I can't rely on my root cellar, and it's not even going to be used for much more than goat's milk/cheese/butter. What I can't can, cure, smoke, jerk, or just store in the root cellar, I'll probably sell or use for the goat. I'll only have four hens, so I won't have to worry about piles of eggs going bad. So I'll already be reducing my usage in winter, when I can unplug the refrigerator (actually a cooler that i'll mount vertically in a cabinet). If I have to do without movies or surfing for a few days, it won't bother me.
Solar Isolation is a pretty good next step, where are you located so we can look at how much sun you can expect in the short days of winter.

The homestead will be in Buckingham County, VA, 45 miles due east of Richmond, VA. 4 acre strip with a slope that climbs to the north. I'll locate the dwelling near the top of a hill about 1-1.5 acres up the slope and clear the garden area south of that, which will simultaneously open up perfect solar coverage for my panels due to the downward slope from where they'll be facing.
Loads grow, pretty much a given. I once lived on an array of 220watts, now I'm at @2000watts at the cabin, primarily wanting a fridge and AC, and looking at 6000watts for a 900sqft tin can. Even if you don't want to AC your cabin, build it well insulated!

I'm building it with three sides built into the hill, so I'll have, in addition to the thermal mass of the home itself, tons of earth adding directly to the thermal mass. It'll either be concrete slab floor and ceiling with cinder block walls (filled with concrete and rebar, of course), or slipform stone. Either way, it'll have enormous thermal mass and efficiency. The front will be entirely glass, probably sliding glass doors, to let in as much light as possible in the winter so the radiation from the floor will keep the place warm at night. To prevent that from happening in the summer, I'll use a combination of a 2' overhang to block some of the summer sun and drapes if it warms it up too much in the morning/evening.

I'm pretty confident in this design. As small as my home will be, it won't need much to keep it cool or warm, and it will be very resistant to sudden temperature swings.
Yes, you've got the right Idea, you seem computer savy so you might look into a Midnite classic 150 lite, it will give you room to expand if needed and close to the same price at \$500, all controls and monitoring are available via network cable.

I might do that. I won't have a regular computer when I move out there, just my tablet, but if it's got a web interface, I could access it via Wi-Fi. I'm really not expecting to need more room or power, though. I'm alone now, I'll be alone when I move out to my homestead, and my needs are very basic already. I live in a 10x13 bedroom. I only go out for work, groceries or banking. I have social anxiety disorder, so after 40 years, I've become very comfortable confining my life to a tiny space. That's half the reason I'm doing this, so I won't have to spend another 40 years living in fear. The other half of the reason is that if I stay where I am now, working the job I have, living where I do, I've got no future. I've got nothing to look forward to except a social security benefit which might not be there when I reach retirement age... and, frankly, nothing to make me get out of bed except knowing that I have to go to work. This is my retirement, and my solution to my mental illness.
Battery temperature sensor between the batteries, not on the terminal, but you've got the right idea

Touching either/both batteries, or just in the open air space between them?
That is the job of the charge controller.

Okay, good. One less thing to try to squeeze into the budget.
In that neighborhood some 215amps some as high as 410amps or more. in series voltage adds, strings in parallel amperage adds.

So... connecting two 6v batteries in series would give me the 12v I want for my home, but I'd need them both to be 255-300ah to ensure that I had the minimum of 255ah I need because the amperage wouldn't increase. I'll aim toward the 300ah side, but it'll depend on costs and where I am with the rest of the system. I'd rather have enough output from panels to ensure that my batteries will be charged in winter, or a controller which will keep them functioning well, than batteries that died early because they weren't hitting full charge every day or the controller fried them.
It's possible, low voltage drops quickly over wires, if your array, batteries and cabin are near it might work, but likely you'll want to have pretty heavy wiring to hold voltage.

The panels will be 24v, so that will reduce the resistance some and make it easier to position them appropriately. The charge controller and batteries will both be right at the front of the dwelling, with the controller located no more than 2' from the batteries and both being as well protected from temperature fluctuations as I can make them. There won't be much distance for the current to travel to reach the batteries, and I'll minimize the travel distance inside the dwelling as much as possible. I'll also be running the wiring right through the concrete or slipform walls, inside flexible conduit buried in the walls during construction, so the thermal mass of the building and the earth surrounding it should help keep temps under control as well, thereby reducing resistance and losses. I hope.
If your fridge uses 65 watts continously you could have a full size fridge running on AC for about the same total wattage, might even do a chest freezer conversion for less than the DC fridge.

This actually was a chest cooler I was factoring for. I'm trying to avoid switching to AC for anything if I can help it, since it wastes electricity in the conversion and increases losses. If there's a chest cooler that I can use for less than 65w, I'd be thrilled to include it in the budget, as long as it wasn't exorbitantly expensive.

So I hope this helps a little, I'd say add up all your usage, then tell us where in the world you are, if your willing to have a generator to aid in charging...

,,,then work on a system.[/QUOTE]

No generator. I don't want to worry about storing fuel or making regular trips to buy fuel. Or dip into my savings account to pay for it.
• Posts: 13Registered Users
Re: Have I got all of this figured out?
Photowhit wrote: »
If your 5 years out from building a 'true' system, you might consider a small system while your building.

I won't be able to do that. I've allocated everything I'm making between now and January to pay for the property itself. Then I have to save up ~\$1000 for a garden tractor. Then ~\$3000 for the home I'm building. Then I'll be able to save up for the solar equipment, but it will take several months to save up the ~\$2000 I've budgeted for it. Even that's part of the plan, though. While I'm saving up for the solar equipment, I'll be working on building my home. Not much point having a complete solar package sitting there for 1-3 years, but no home to live in. If nothing else, it would eat away at the battery life unnecessarily.
Will you be using AC tools?

Probably not.

Probably regret it for a few years, but not much choice anyway. To afford to do this at all, I've got to spread it out over several years, so having access to faster methods of building wouldn't really matter. Doing the slabs for the floor and ceiling are going to be brutal, since I'll probably be mixing the cement by hand in a wheelbarrow, but hard work hasn't killed me yet. I might be using stone found on the property, if it's abundant enough, which would cut down significantly on the amount of cement I'll have to mix and make it look a lot nicer when I'm finished.
• Posts: 3,738Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
Luminara wrote: »
I'll be using 190 watts per hour for up to six hours per night. 190wh, 6 hour total usage. After that, my usage will drop to 65wh, just the refrigerator running for the rest of the night.

You MUST get watts and watthours figured out. "190 watts per hour" makes no sense. 190 watts for 6 hours is 1140 wattHours = 1.14 kwh.

Your fridge draws 65 watts when the compressor is running. You need to know how many hours it is running per day to figure out the watthours.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Posts: 4,669Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
vtmaps wrote: »
Your fridge draws 65 watts when the compressor is running. You need to know how many hours it is running per day to figure out the watthours.

I think he's using a thermoelectric cooler, I don't think they have a thermostat, no compressor, just on all the time...

I also think a full size fridge uses less electric, but perhaps not if you include the A/c conversion waste.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 4,669Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?

I've delt with anxiety issues as we all do, I once thought isolation would be a haven, I have a very 'social' job dealing with other peoples problems, but find I need some social interaction and plan my one trip to town each week to include playing in a pool league. I wish you the best in finding a level that works for you!

Back to 'A Cabin in the Woods', What are you doing for water? Sewer?, In the east there will be regulations on these and some person from the county is likely to come out asking questions. Building into a south facing hill side is Ideal! wish I could find some land, that I could afford that was situated that way! If you keep the building to 12x12 usually you can do things with out a building permit!

I would look into doing a chest freezer conversion. Even though it would mean doing some AC, they would use a lot less electric. Right now you have a 1.5Kw load running a somewhat tiny chest cooler! You can find standard size fridges that use less than that! If you search for "freezer conversion" you'll find people claiming under 1/2 Kw per day (search here and search google and add solar, don't know of a DC Freezer, but they might be out there, you have time to hunt!) You might well be able to run a standard, small effiecent fridge, on a small 12 volt system, but I thnk I'd shoot/think for 4 Golf cart batteries, series and parallel...

I lived in a small cabin, I built, 10x16 with a sleeping loft, and a seperate kitchen/bath building to keep the heat out, a composting toilet will help keep the cost of a septic system down, but will require some warming in the winter and ortganized finishing compost piles outside. I think most Eastern states want a grey water system as well, though perhaps you'll have a kindly inspector, a french drain for grey water might be OK. Water pumps can use a good bit of electric. (I was on a small water system that provided pressurised water to my door)

Good Luck! figure your loads in Watts per day and let us know. Be realistic about rainy day loads and storage, know that you'll have some finacial needs, taxes, vet, rural water?

FWIW- I have done my building and solar setup making less money than you do! I'm a burned out photojournalist, use to work for the Raleigh News and Observer around the corner. My big advantage is living on property I own and having no electric bill does free up money for other uses.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 3,121Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
Photowhit wrote: »
I think he's using a thermoelectric cooler, I don't think they have a thermostat, no compressor, just on all the time...

Yes, on all the time. The temperature they reach is determined by
1. the diminishing amount of cooling per watt as the difference between the hot and cold temperatures (delta-T) increases (either from the cold getting colder or the outside air getting hotter) and
2. The amount of heat leaking in through the insulation and from opening and closing which increases as delta-T increases. At some point the cooling just barely keeps up with the heat leaking in, and the inside temperature stops there.

The cooler you can keep the air outside the chest, the better off you are on both numbers.
SMA SB 3000, old BP panels.
• Posts: 13Registered Users
Re: Have I got all of this figured out?
Photowhit wrote: »
I think he's using a thermoelectric cooler, I don't think they have a thermostat, no compressor, just on all the time...

I also think a full size fridge uses less electric, but perhaps not if you include the A/c conversion waste.

That had been my original intention, but doing more research, I'm finding that TECs aren't as efficient as I'd hoped, in regard to power usage. With the ambient temperature averaging 75 degrees inside the dwelling, it would work, but the current drawn would be heavier than I really want to deal with. None of them are designed for 24/7 usage over long periods of time, so I'd have to open it up and rewire it with heavier gauge wiring, install a thermostat and rheostat or monitor the temperature manually and cut power to it at regular intervals to keep everything from freezing... I think it'd end up being more hassle and expense in the long run. So as much as I want to experiment with a TEC refrigerator, and save money, I think the best long-term investment would be something with a Danfoss compressor.

That being the case, the power usage of a compressor-based unit is comparatively low, even when the compressor is running, and even a cheaper option like an EdgeStar would end up drawing half as much current as an always-on TEC... I really do not want to have to budget \$600-1000 for refrigeration, but I get the impression that it'd be the less expensive investment in the long run. Less risk of burning out batteries and wiring, not having to replace the unit in a few years and lower overall power consumption. And I can get a 12v DC model.

That said, I think I can estimate my power usage over a 24 hour period as... 50w LED LCD, 35w modem/router, 30w lighting, 10w tablet, 40w refrigeration with the compressor running. Refrigerator would be the only thing drawing power at all times, but without having it in place and monitored, I can't factor for how frequently it would be running the compressor, so I'll just factor for it at full draw over a 24 hour time frame.

((50 + 35 + 30 + 10) * 6) + (40 * 24) = 1710 watts used over a 24 hour period. 1.71kWh, 142Ah, have I got that correct now?

300Ah battery time, four 6v 225Ah batteries wired in series and parallel to provide a total 12v 450Ah, 60 amp MPPT charge controller, 2-4 gauge wiring for controller to battery. Three 235w 24v panels, factored at 100% efficiency for charge controller calculation, 59 amps, but also accounting for 80% degradation over time and 77% efficiency expectation after losses, three of these panels would provide sufficient power to recharge batteries. (((235 * 3) * 0.77) * 0.8 ) = 434 watts, 36 amps. 4 hours of maximum insolation at 434w, 36 amps, 1.736kWh, 145Ah.

Am I hitting the mark here?
• Posts: 13Registered Users
Re: Have I got all of this figured out?
Photowhit wrote: »
Back to 'A Cabin in the Woods', What are you doing for water?

There's a tiny creek on the property, or right at the edge. I might have to supplement it with a rain catch system, and I'm going to dig/auger a small, shallow well next to the creek, but I think it'll be enough for what I'll be using. My only real concern with the water supply is how to get it up to the cisterns. I don't know how to figure out what kind of pump I'll need. I know I want something with a discharge rate of 0.25 gpm, very low, just enough to keep the cisterns filled, and I know I'm putting the cisterns about 500' up the hill, and that I'm looking at about 50' of elevation increase. I've got a couple of years to figure out how to do the math to determine what type of pump I need, so I'm not in a hurry on that. Probably power it with a separate solar panel, only have it pumping during maximum insolation, since I won't be using much water (dishes, quick shower once a day, coffee... that's about it).
Sewer?, In the east there will be regulations on these and some person from the county is likely to come out asking questions.

Grey water from the shower and dishes will go into a separate cistern and be used for the garden. Composting toilet for my waste.

I'll use 275 gallon IBC totes for cold, hot and grey water. The cold water container will be located beyond the house, up the hill, to provide gravity feed pressure. Pump from the creek/well goes up to the cold water. Line from cold water splits off to the hot water container (which will be painted black and standing on a short (15-20') platform, catching sunlight for heat and providing gravity feed pressure for the house) and the house. Grey water will go into a container located downhill, near the garden, to be used for irrigation. Composted waste will go to a pile on the eastern edge of the property, away from the regular compost and garden, to prevent contamination issues.
I would look into doing a chest freezer conversion. Even though it would mean doing some AC, they would use a lot less electric. Right now you have a 1.5Kw load running a somewhat tiny chest cooler! You can find standard size fridges that use less than that! If you search for "freezer conversion" you'll find people claiming under 1/2 Kw per day (search here and search google and add solar, don't know of a DC Freezer, but they might be out there, you have time to hunt!) You might well be able to run a standard, small effiecent fridge, on a small 12 volt system, but I thnk I'd shoot/think for 4 Golf cart batteries, series and parallel...

I'm seeing what you're saying now. I might try a conversion, if it turns out to be less expensive than off-the-shelf DC refrigerators.
I lived in a small cabin, I built, 10x16 with a sleeping loft, and a seperate kitchen/bath building to keep the heat out, a composting toilet will help keep the cost of a septic system down, but will require some warming in the winter and ortganized finishing compost piles outside. I think most Eastern states want a grey water system as well, though perhaps you'll have a kindly inspector, a french drain for grey water might be OK. Water pumps can use a good bit of electric. (I was on a small water system that provided pressurised water to my door)

You've pretty much worked with the setup I'm trying to build. That makes me happy, because if it worked for someone else, it'll work for me. Some differences, like my dwelling being stone and concrete and built into the hill for additional thermal mass (hopefully alleviating the need for heating/cooling), and having to manage my own water source, but that's basically how I'm trying to make this work.

I hope my estimate above is right. I think it is now.
know that you'll have some finacial needs, taxes, vet, rural water?

I'm accounting for that. Five years from now, I'm planning to have \$35,000 in a savings account. Even with daily compounded interest, it'll reduce over time as I pay for things like satellite internet access, taxes and other incidentals, but it should be enough to last me for decades. If worse comes to worst, I can sell off excess produce, eggs and/or goat's milk for a pittance and still come out ahead, or put in a couple of weeks a year working for someone else. Financially, I've got this planned down to the penny, as long as I stay within or under the budget I've devised. That's why I'm so keen to get the solar equipment figured out, even though it's going to be upward of two years before I buy any of it. Knowing what I can expect to spend, I can figure out exactly when I can make certain purchases, when to do certain tasks, etc.
• Posts: 13Registered Users
Re: Have I got all of this figured out?

As there haven't been any responses in a week, I'm going to presume that I've got a usable solar setup outlined and use that for my budget planning. I'm sure there will be changes necessary, due to price fluctuations, new technologies introduced and other things in the next couple of years, but I have a target now. Thanks, folks! I'll be in and out over the next couple of years, watching for new information, new technologies and ways to improve my goals.
Re: Have I got all of this figured out?

And let us know what/how you are doing. Can help new users too.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 3,738Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?

A chest freezer converted to a fridge will be extremely efficient and much less expensive than a danfoss based fridge. The only fly in the ointment is that the converted AC freezer will have a startup surge that may necessitate a larger (more expensive) inverter than you might otherwise need.

Forum member 'Waynefromnscanada' has convinced a few freezers to run on a 300 watt inverter, but he is unusually clever. He has described his modifications somewhere in this forum.

I think your system design numbers look good. I would try to avoid the parallel golf cart battery bank. Try a single pair of L16 batteries.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Posts: 13Registered Users
Re: Have I got all of this figured out?
vtmaps wrote: »
A chest freezer converted to a fridge will be extremely efficient and much less expensive than a danfoss based fridge. The only fly in the ointment is that the converted AC freezer will have a startup surge that may necessitate a larger (more expensive) inverter than you might otherwise need.

Forum member 'Waynefromnscanada' has convinced a few freezers to run on a 300 watt inverter, but he is unusually clever. He has described his modifications somewhere in this forum.

I'm really keen to avoid any inverters, if at all humanly possible. The less complex this whole thing is, the better I'll be able to manage and support it myself, and tossing an inverter and AC into the mix adds another layer of complexity. I also want to maintain the lowest level of loss, squeeze every Joule of power out of this design as I can, and every switch from AC to DC or vice versa equates to loss. More loss means more drain from the batteries to compensate, which consequently means reduced battery life or redesigning the system around a larger battery bank, either of which results in an increase in expense. I might save \$300-400 by using a converted freezer, but the combination of immediate and future related expenses would negate that savings. At some point, maybe 5 years, maybe 25 years, the cost of replacement batteries would match anything I'd saved by using AC for refrigeration, and from that point onward, I'm just spending extra money to cover the need for AC. Sticking with a strictly DC system will give me better control over costs in the long run.
I think your system design numbers look good. I would try to avoid the parallel golf cart battery bank. Try a single pair of L16 batteries.

--vtMaps

The L16 series are comparatively expensive. I know, you get what you pay for, but the higher I push the budget for this, the longer it's going to take to implement it, and I'm already looking at 2+ years before I can make it happen.

I can run 4 of these, http://www.solar-electric.com/cr225am6vode.html , resulting in 450AH 12v for \$500 plus shipping (or finding them locally, if i can).
The cost for L16 batteries with a comparable AH rating, http://www.solar-electric.com/trl16vo435ah.html , would be approximately \$680 plus shipping (or, again, finding a pair locally). 36% increase to expense, and I lose 15AH.

Lifespan would, obviously, also be a deciding factor, and may tip the balance in favor of a pair of L16 if it turns out that the Crown batteries have much shorter lifespans, but without knowing that, I'm strongly leaning toward the Crowns. Longer term, if both have comparable lifespans under identical conditions, I'd be saving much more money when I have to replace them. Shorter term, if the lifespan of the Crowns is only 2/3 as long as L16's, the comparative costs level out over time, so I'm still not losing anything by using the Crowns. I'd have to see some indication that L16's have 1.5x, minimum, more longevity than Crowns to justify the expense of a pair of L16's over a quad Crown setup.

Shipping would also make a significant difference. It may be that shipping four Crowns will be ridiculously expensive, to such a degree that a pair of L16's would be comparable or cheaper after shipping, in which case I'd re-assess the situation. Whether I can get either of these batteries, or something comparable, locally would also be important, but unless there's a drastic reduction in cost buying locally (or from another online retailer), I'm probably going to order through NAWS, if for no reason other than because of this forum and all of the free education I'm getting out of it. I'm not doing any searches or comparisons right now, though, since it's going to be a couple of years before I'm ready to buy and all of this is academic at the moment. My goals are to have a basic understanding of what I'm doing by the time I'm ready to do it, a general design laid out so I don't make the mistake of buying a bunch of stuff I don't need, or stuff I haven't figured out how to work with and end up having it sit around for months while I educate myself appropriately, and a cost outline to work with so I don't under-budget for this.
• Posts: 13Registered Users
Re: Have I got all of this figured out?

My next step has been to try to understand and figure out the wiring I'll need for this.

Beginning with the panels, if I connect them serially, I'm sending 72-111v ~10a to the charge controller. The leads coming out of the panel are #6, and since I'd be running high voltage, low amperage, #6 would be sufficient, but at close to 0.5% loss. Loss at this voltage might be negligible, I'm not sure, so I might want to run #4 to reduce it a bit more. Serial should also reduce the number of "extras" (fuses and cut-off switches, for instance) to one apiece on that end, and should be less expensive than buying enough #2/0 to wire each up panel in parallel. All good things, but as I understand it, if your panels are serially wired, anything which affects one panel could affect them all. A bad cell, any shade, a wire fault, essentially anything which reduces a single panel's output can cause loss across the entire array, depending on where the problem occurs.

Connecting them to bus bars in parallel, to which the charge controller would be connected, would require use of #2/0 wire, and buying more than twice as much, plus the expense of the bus bars. 24v and ~10 amps from each panel, I'd end up with a 0.048 voltage drop on my farthest panel using #2/0, 0.032 on the middle panel and 0.016 on the panel closest to the charge controller. I could probably do well enough with #2, but I'd be concerned about both loss and safety (burning up my solar equipment would be a bad thing). The bus bars from the panels would be no more than 2' away from the charge controller, so the wiring to the charge controller could work with #2 and see a voltage drop of only 0.04, but considering the amperage running through them, I wouldn't be comfortable with anything less than #2/0, and since I'd have that gauge at hand anyway, it makes sense to plan for that if I wire them in parallel.

Is there a convincing reason to go one way or the other, serial or parallel? I don't think the losses would be significant enough to warrant a decision either way, so I suppose it comes down to an argument of cost efficiency (serial) versus ease of troubleshooting (parallel). Going serial, I'd save money on wiring and extras, but if anything did go wrong, I'd essentially have to tear the whole thing apart to isolate the issue. Parallel, I'd need more wiring, bus bars, more things like fuses and cut-off switches, but it'd be a lot easier to figure out where a problem was coming from. Given the cost of #2/0, I may have no choice but to connect them serially, just to keep costs manageable.

From the charge controller onward is a bit long to lay out, so I made a very crude diagram. Be gentle, it's my first time.

The charge controller wiring goes out and splits to two positive and two negative leads. Each positive lead is connected to a different battery, each negative lead is connected to a different battery, and the change controller itself is never connected to the same battery twice. The batteries themselves are connected serially to give 12v output, and no connections overlap with the charge controller's connections. This should, I think, and I stress that, I think, equalize the charge across all four batteries equally, thus ensuring that there's never a time when one battery will be de-sulfating or floating and another battery isn't.

Coming from the battery bank, I'm running parallel from the 12v battery pairs to bus bars, pulling from opposite leads from what I used to connect to the charge controller. That way, if I'm drawing current while the charge controller is working, I'm not taking it from the current going into the batteries and leaving them too short, potentially, to de-sulfate or float when they need to. Again, trying to equalize the current drawn through and from the batteries so no individual cell is being charged or drained more than any other. I think this promotes good current flow throughout the entire bank, which should help prolong the lifetime of all of the batteries.

I think. As I said, this is my first diagram, and I've never worked with anything like this before, so if I've got something crossed, it'd be nice to know now.

All of the wiring between the batteries, from the charge controller to the batteries, from the batteries to the bus bars and from the bus bars to the junction box will all be #2/0. I don't want to leave any chance for fires or high losses here.

Running from the junction box, I can use #8 for everything. The lights and USB outlets (probably just pick up some quality USB 3.0 car cigarette lighter adapters and wire them directly to a 12v line) will be easy, none of them will draw more than 10w, or 0.834a, over a maximum distance of 15' (one way), so a separate #8 line running to where each of those will be installed will be acceptable. The modem/router(35w, 2.92a) will be a few feet away from the junction box, so I can use #8 for that as well. The refrigerator (40w, 3.34a) will be up to 10' away from the junction box, so I'll need #6 or #4 for that, which just happens to match what I'll be using if I do a serial panel array, so that works out nicely. The last device, the LCD, is a bit of a stickler right now. I could just buy a standard 30" LED LCD, which uses 45w, and do a complex adaption to make it run off of 12v, but I'm banking on a direct USB-powered LCD at that size being available at some point in the next few years. http://www.itproportal.com/2011/06/03/asus-shows-24-inch-led-usb-powered-monitor/ , for example, uses 9w through a USB 3.0 connection and needs nothing else to provide power. No wall wart, no brick, no AC, just a now standard USB 3.0 port. It's not the 30" that I'm aiming for, but I'm pretty sure I'll be able to find something in the size I want by the time I'm ready to buy one. So for now, and taking into account the placement of the LCD in my floor plan (it will need less than 3' of wiring), I can plan for #8 right now and make revisions later if necessary.

I'll obviously need to add fuses, switches, cut-offs, breakers and other things to the outline, but I just wanted to lay out the wiring itself and see if I'm making any major mistakes, like cross-wiring the batteries and blowing them up in my face.
• Posts: 3,121Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
Luminara wrote: »
My next step has been to try to understand and figure out the wiring I'll need for this.
That way, if I'm drawing current while the charge controller is working, I'm not taking it from the current going into the batteries and leaving them too short, potentially, to de-sulfate or float when they need to. Again, trying to equalize the current drawn through and from the batteries so no individual cell is being charged or drained more than any other. I think this promotes good current flow throughout the entire bank, which should help prolong the lifetime of all of the batteries..

Unfortunately, the flow of current does not work quite that way. And even if the current flowed into the batteries and back out again instead of
"bypassing" the batteries, that would not count as full current going into the batteries.
You need to make sure that there is enough power coming from the panels to deliver simultaneously the current needed by the daytime load and the current needed to recharge the batteries.

But the biggest problem is that the way you have connected your bus bars, you will have zero volts between them. (They are connected to each other by the brown wire, and neither of them are connected either the + or the - end of the series string.
SMA SB 3000, old BP panels.
• Posts: 4,669Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?

Other than the inverter, an AC converted freezer should actually use less DC current from begining to end, there is a nice Blog like entry about a freezer conversion here. They end up liking the chest refridge, which was a concern of mine.

I started using mostly if not all 12 volt loads, I had lights, a fan, video tape player, and small TV all that work off 12 volt from a camper van I had setup on my original system. As I setup a camper for daily use I tried to stay 12 volt, but the added expense of heavy lines to avoid line loss and finding 12 volt versions of things got me to switch over to an 120 inverter. I think a search for 'capacitor start' will help you find the waynes system for running on a 300 watt inverter.

Stop by your library and read or order to read a copy of twelve by twelve it's abot a 60 year old lady physician, in North Carolina who lives in a 12x12 cabin. The 12x12 is to avoid having restrictions. It might address things you will face.

There is a thread currently on expected battery life with some pretty good numbers, know that the first set is normally a learning experience, they tend to get abused in assorted ways. I don't think NAWS will complain if I suggest sourcing batteries locally, people have had pretty good luck with the Sam's club and/or Costco, 6 volt golf cart batteries. Reguardless read and understand the Battery FAQs!
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 4,669Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?

Not a clue on your battery bank, basically, wire the bank so that it acts as one battery with equal resistance across each set if you have 2 strings, same length, same gauge, connectors between the batteries and between the batteries and the bus bars, then hook your charge controller to the battery, directly to the bus bars.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 3,738Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?

inetdog has pointed out some of the problems with your diagram. Try this:
.
.
--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Posts: 13Registered Users
Re: Have I got all of this figured out?
inetdog wrote: »
Unfortunately, the flow of current does not work quite that way. And even if the current flowed into the batteries and back out again instead of
"bypassing" the batteries, that would not count as full current going into the batteries.
You need to make sure that there is enough power coming from the panels to deliver simultaneously the current needed by the daytime load and the current needed to recharge the batteries.

I'm confident that it will. I've over-budgeted the wattage on almost every device, factored for excess usage beyond what I'm actually planning and even calculated for the refrigerator running 24/7, never shutting off, and the output from the panels is still higher than usage. I've also been using 25 year degradation projections for the solar array itself, not first year, and an assumed 77% output. My projections are much higher than my actual usage will be. I'll be able to cover the daytime usage without issue.
But the biggest problem is that the way you have connected your bus bars, you will have zero volts between them. (They are connected to each other by the brown wire, and neither of them are connected either the + or the - end of the series string.

That's something I never would've caught without help. Thank you.

Should I just hook up the batteries, junction box and charge controller to bus bars (one pos, one neg)?

Like that?
• Posts: 3,121Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
Luminara wrote: »
That's something I never would've caught without help. Thank you.

Should I just hook up the batteries, junction box and charge controller to bus bars (one pos, one neg)?

I am sure it would have been obvious that there was a problem once you hooked it up and thought about it for awhile.
I would add the fuses, as shown by vtMaps in his sketch. And make sure that the sum of the lengths of wire (yellow + brown + purple) are the same for each of the two pairs of batteries.
Since they connect only to the bus bars, the relative length of the red and grey wires is unimportant, except that they should be as short as practical.
SMA SB 3000, old BP panels.
• Posts: 13Registered Users
Re: Have I got all of this figured out?
Photowhit wrote: »
Other than the inverter, an AC converted freezer should actually use less DC current from begining to end, there is a nice Blog like entry about a freezer conversion here. They end up liking the chest refridge, which was a concern of mine.

Clever. It makes sense, now that I see how it's done. Temperature-controlled digital power switch, just turns the current on and off as necessary. I expected a rheostat, drilling, rewiring, etc., but this is surprisingly simple.
I started using mostly if not all 12 volt loads, I had lights, a fan, video tape player, and small TV all that work off 12 volt from a camper van I had setup on my original system. As I setup a camper for daily use I tried to stay 12 volt, but the added expense of heavy lines to avoid line loss and finding 12 volt versions of things got me to switch over to an 120 inverter. I think a search for 'capacitor start' will help you find the waynes system for running on a 300 watt inverter.

I'm still not enthusiastic about the idea of putting an AC draw on my system, the added layer of complexity and additional device to monitor/repair/replace at some point, but it does look like the most efficient, feasible and cost-effective route. It would also, admittedly, save me the hassle of rewiring an LCD to accept a DC power source, or waiting for a low-wattage LED LCD to come to market. I could just pick up a good 30" monitor with an HDMI input, slap it on the wall and plug it into the inverter, done and done.

I'll put it on my reading list. Still working my way through Back to Basics, Basic Butchering of Livestock & Game, Edible Wild Plants (The Wild Food Adventure) and Mini Farming (Self Sufficiency on 1/4 Acre).
There is a thread currently on expected battery life with some pretty good numbers, know that the first set is normally a learning experience, they tend to get abused in assorted ways. I don't think NAWS will complain if I suggest sourcing batteries locally, people have had pretty good luck with the Sam's club and/or Costco, 6 volt golf cart batteries. Reguardless read and understand the Battery FAQs!

Good advice. I'd be a bit peeved if I spent \$500 plus shipping on batteries and did something to blow them up in a year.
• Posts: 13Registered Users
Re: Have I got all of this figured out?
vtmaps wrote: »
inetdog has pointed out some of the problems with your diagram. Try this:
.
.
--vtMaps

Connect the batteries to each other, then connect everything to one lead coming from the positive side and one lead coming from the negative? Would that properly equalize the charge across all of the batteries? There's so much talk about series versus parallel, and how important it is to properly wire for parallel if you are going to do it, but this isn't as complicated as I thought I had to make it. Did I just over-build in my diagram?
• Posts: 13Registered Users
Re: Have I got all of this figured out?
inetdog wrote: »
I am sure it would have been obvious that there was a problem once you hooked it up and thought about it for awhile.
I would add the fuses, as shown by vtMaps in his sketch. And make sure that the sum of the lengths of wire (yellow + brown + purple) are the same for each of the two pairs of batteries.
Since they connect only to the bus bars, the relative length of the red and grey wires is unimportant, except that they should be as short as practical.

The rest of my wiring sounds reasonable, then? I've got the gauges in the right range for the current and resistance in play? I used to have a truck that overheated the starter cable and killed the battery on a regular basis, which taught me how important it was to properly gauge for DC, so I'm trying to keep every wire as short as possible and ensure that none of them will be undersized for the current they'll be carrying. Also, the shorter I make the wiring, the less I have to spend on it. I have the benefit of having complete control of every aspect of this, since I'm building the dwelling myself and can decide exactly where everything will be located, how I'll lay out the wiring... I can even build the conduits and outlets directly into the walls, so I won't have to run a single inch that isn't necessary (i will give each wire a few inches of slack, of course).

Once I'm sure of the gauges, lengths, how I'll run things from the junction box (might be more cost effective to run a single #2-6 to a certain point, then split it off to individual lights, for example) and the amperage running through everything, I'll lay out some new diagrams of the whole thing, with fuses, cut-off switches, junction box wiring, everything. I'm taking this one step at a time, though, so I understand how and why everything works before I move on to the next piece.

Hm... I have to design a small enclosure to be attached to the dwelling, to house the batteries. Not air-tight, or hydrogen will build up, but something which will keep the batteries cool and dry. I'll have to add an extra bag or three of cement mix, maybe some cinder blocks... shouldn't make any difference in the housing budget.
• Posts: 3,121Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
Luminara wrote: »
The rest of my wiring sounds reasonable, then? I've got the gauges in the right range for the current and resistance in play?

I have not actually looked at that part of your proposal. You can get a good idea of voltage drops using this calculator.
SMA SB 3000, old BP panels.
• Posts: 3,738Solar Expert ✭✭✭✭
Re: Have I got all of this figured out?
Luminara wrote: »
Connect the batteries to each other, then connect everything to one lead coming from the positive side and one lead coming from the negative? Would that properly equalize the charge across all of the batteries? There's so much talk about series versus parallel, and how important it is to properly wire for parallel if you are going to do it, but this isn't as complicated as I thought I had to make it. Did I just over-build in my diagram?

Note that in my diagram the batteries are connected "on the diagonal". The 2 curved wires (on the right and left sides of the battery) must be matched to each other. The 2 wires that make the series connection must also be the matched to each other. Every other wire in my diagram may be any convenient length. This scheme will have the same resistance to each series string. The current to each battery string will pass through ONE of the curved wires and ONE of the series interconnect wires.

Your revamped diagram will work just as well. In your revamped diagram you must have TWO matched wires running from each bus bar to the battery box. The (slight) advantage of my system is that the bus bars can be near your electronics (rather than in the battery box) and you will only need ONE wire running from each bus bar to the battery box, and the wires from the bus bars to the battery box can be different lengths if convenient.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Posts: 205Solar Expert ✭✭✭
Re: Have I got all of this figured out?

Did anyone mention using a Propane refrigerator?
• Posts: 170Solar Expert ✭✭✭✭✭
Re: Have I got all of this figured out?

I would definitely hook everything to your bus bars, batteries, loads, and chargers. That's what they're there for.