Electrical System

Input/ideas are welcome.

Our tiny home has been off grid for 20 years now. I've run through the entire gamut of battery banks, inverters, chargers, solar panels and generators. At this point it works as close to perfect I've been able to achieve. Wind, hydro and solar aren't viable in our situation in as we have old growth Oak trees that I am not going to cut down for solar or wind (I'd need a 100 foot tower for a turbine) and we're on a lake so no way to use hydro. Thus, I have a Ryobi inverter generator with bluetooth control in it's soundproofed shed and have the sound down to 25 db. Exhaust/heat control is using a 12 inch electric radiator fan mounted in the wall of the shed.

I started out with a couple of group 27 trolling motor batteries, moved up to 7 group 31 batteries, had a dubious adventure with surplus railroad deep cycle AGM batteries, really screwed up with some flooded "deep cycle" batteries that weren't and have finally have it (what I consider to be) right with 2 sets of Duracell Ultra SLIGC110 Group GC2 in series/parallel configuration for 430 amp hours and a 600 watt pure sine inverter wired with a power cutoff switch to disconnect it during the day. I also run my cellular amplifier from the bank 24/7 as well as my dual power fridge (runs on AC during the day and DC at night. Pretty cool fridge, will go down to -10 if needed, has an eco mode as well).

My auto mechanic set me up with battery connectors that have a twin pigtail on them that you put your tinned wires into and snug down the allen screw. A lot less wiring spaghetti.

I've been running the Duracells for 2 years now and could not be happier with them, their reserve capacity and charge times. My biggest issue is that I made the mistake of buying automatic chargers which on most days, don't think the bank is discharged enough to charge so I either have to make sure I leave a bunch of stuff on overnight to trigger them or just be frustrated. I've got a few old 6 amp manual chargers but those don't even come close to the charge rate needed of 40ish amps.

I've recently bought a new hydrometer that has temperature compensation built in and found that all my center cells aren't charging at the same rate as the outer cells. The outer cells were consistent at 1.240 - 1.250. The center cells were all 1.210. Obviously the bottleneck is the chargers. I've never liked automatic chargers so I set out to find a high amperage manual charger which apparently is now a unicorn.

I did find a wheeled cart type that will charge at 10, 20, 40 and 100 amps with a timer on it at Tractor Supply which oddly enough was on sale when I was looking. I should have bought this thing 15 years ago. It takes half the time to get the batteries to 1.250 and all three cells are now the same. I just have to set it at the 40 amp rate and set the timer in 60 minute increments, taking a hydrometer reading every hour until I know the correct charge time. Once my charge/rest/measure shenanigans are done, it should be a seamless operation. The charging now is pretty darn quick.

Hi Max,

This isn't what you're asking for, but when I heard the word "lake", are you allowed a floating dock? Or better yet, a floating swim platform that would be out there in the sun just begging for a few solar panels? There's a fellow in BC who's put in enough floating gardens to get some serious food out of it (too little sun and too many rocks on shore for a garden) and there's evidence that floating food gardens can actually improve water quality, so I'm just throwing the idea out there.

Jay Angler wrote:Hi Max,

This isn't what you're asking for, but when I heard the word "lake", are you allowed a floating dock? Or better yet, a floating swim platform that would be out there in the sun just begging for a few solar panels? There's a fellow in BC who's put in enough floating gardens to get some serious food out of it (too little sun and too many rocks on shore for a garden) and there's evidence that floating food gardens can actually improve water quality, so I'm just throwing the idea out there.

Our lake is private so there's no rules. There's enough watercraft out there that I'd never use it for growing veggies. However, I have actually thought about floating dock solar panels but the run would require cables thick as your arm. Likewise, I could put them on the embankment and get longer direct sun but we're still talking a 60 foot run.

I do have 55 gallon rain barrels and will have several 8 x 4 raised beds next year.

Max Cottrell wrote:

However, I have actually thought about floating dock solar panels but the run would require cables thick as your arm. Likewise, I could put them on the embankment and get longer direct sun but we're still talking a 60 foot run.

At least you've thought about the option. There are pros and cons to every location, and we all work within what our land supports. I know *all* about big trees blocking my light!

1kW Solar Panel Array $700 (this string would be 120V x 10A, you will need 3 or 4 solar panels)
10A Cable/Wire $40 (at 120V-DC the cable actually doesn't need to be thick for a 60ft run, no different from a regular 60ft 120V-AC extension cord)
100A Charge Controller $500 (it's very likely that you can continue using your current charge controller, battery bank, wires, inverter, etc)

S Bengi wrote:1kW Solar Panel Array $700 (this string would be 120V x 10A, you will need 3 or 4 solar panels)
10A Cable/Wire $40 (at 120V-DC the cable actually doesn't need to be thick for a 60ft run, no different from a regular 60ft 120V-AC extension cord)
100A Charge Controller $500 (it's very likely that you can continue using your current charge controller, battery bank, wires, inverter, etc)

Every few years I have another dubious look at solar. When I look at the cost versus time used and my age,, it doesn't add up to being worthwhile. Our tiny home is a part time residence - used for 80 days per year on average. In a SHTF it would obviously be more.  

Solar is really unfeasible on our property cost wise. The slope going to the lake gets 2 hours of sun. There are other areas that do have direct sun for some time. I'd actually need 12 panels to chase direct sun across the property in as there are 2 other areas that have direct sun for an hour each. The other big issue is the winters. We"re in a snow belt, usually seeing 160 + inches of snow so the panels would need to be taken down. I lost several panels when I did experiment with solar from snow load. Of course trees grow so the direct sun falls a bit each year.

Can you give me a quick overview.
How much energy do you use per day at the lakeside cabin?
What is your peak power usage?
How many hours of sunlight do you get per day if the solar panels were floating in the lake?
How far away would the floating panels be from the cabin/battery bank?
What price range would you consider to be affordable?
What was the total price of the system that you came up with in the past?
How could we remove the snow that accumulate on the floating panels? Do you use the cabin in the snow months?
Current Generator Wattage?
Current Generator Gas Usage per day/per week/month/etc


While I wait for your answer I am going to guess some numbers
Daily Energy Usage = 4KWH per day (1000W of solar panel x 4hours of sunlight for just $700)
Peak Power Usage = 4,000W (4000w inverter for $1000)
Hours of sunlight on lake = 4hrs+ esp between 10am and 2pm
Floating panel distance to battery bank/cabin = 100ft, (solar panels in series only carry 10A so very little power is lost over 100ft and at 120V for 1000W or 240V for 2000W, only thin solar wires are needed )
Affordable price range = $2,600
Past Price Estimate = $5,000
Winter Usage = NO (so the panel could be wheeled out and stored)
Winter Usage = YES (panel/snow could be washed off/submerged with the lake water every dusk and dawn)
Current Generator Wattage = 2500W for $1000
Current Generator Gas Usage = half a gallon per day or 5KWH of electricity for less than $2 or $150/80days

$2,600 = Solar Panel + Floating platform + 100ft/10A wire + Charge Controller + Inverter
$2,600 = $700(1000W)+$300 (IBC Tote+misc) + $100 MC4 wire + $500 MPPT 100A + $1000 inverter 4KW

I can give you an overview of the power usage. First, my previous and current design have all been done using a legacy version of HOMER, I believe V2.68. It's never done me wrong in all the years I've been using it.

My generator, a Ryobi inverter model, has a kill-a-watt built into the Bluetooth app. This is the 1800/2800 watt model sold at Home Depot. I might hit 50% capacity if I'm running the shop vac. Other than that, it just putters along close to idle. It uses 1 gallon over the 16-17 hours a day I use it. As I think I've mentioned, it lives in our wood storage shed and is soundproofed with 4 layers of acoustic tiles so it produces about 25 db of noise. Most people that stop by don't even realize it's running unless I point it out. Currently, it has just over 1500 hundred hours on it. It's a pretty amazing machine.

Peak load if I run the vacuum is 750 - 800 watts. Average continuous watts ranges between 250 and 350 watts depending on what I'm doing. At night I use around 20 watts total or around 12% of bank capacity overnight. When it's cold, even less than that because no fan. I could get by with using just the batteries and inverter during the day as well if I needed to since most of my lighting is solar based. Just have to move the panel for those around the yard all day.

Figures per 24 hour period

LED BULB X 3, 7 WATTS EACH
1 HOUR

USB CHARGER 15 WATTS
10 HOURS

NEW FRIDGE 50 WATTS 110 AC
10 HOURS

12 VOLT MANUAL CHARGER:
10A 220 WATTS
20A 450 WATTS, 1 HOUR TO FULL CHARGE ON AVERAGE
40A 610 WATTS

WATER PUMP 10 WATTS
AS NEEDED

NEW BIG FAN 47 WATTS
10 HOURS

RED FAN 36 WATTS
8 HOURS

Since some stuff is on/off for short periods, figure total wattage per day is around 1,000 watts.

Our tiny home is directly on the 45th parallel which makes solar panel positioning pretty easy. Getting into the sunlight portion of the discussion, our weather is forecast by the Gaylord, Michigan NWS office. I've toured the place a few times. It's like the bridge of the Enterprise, it's amazing. They're responsible for forecasting most miles of shoreline of any NWS office. They have the highest number of master degree meteorologists at any facility because many lives depend on what they do. Even so, because of the snow/rain belt that our property is on, they're correct about 60% of the time. In the summer when the heat and moisture are really kicking off lake Michigan, figure on 3 days out of 7 being overcast to some degree. And the thunderstorms are awesome if you like that sort of thing. Since we're on the Antrim Shale deposit we get a lot of lightning strikes especially on the gas well heads. We're also 7 miles from the gunnery range so we have ANG planes almost every day flying about.

Here's the dock situation at a glance.  A dock will cost about $1,500 because our shore is only 16 inches above the waterline and would need to be a raised version with steps. I would prefer one that can be removed in the winter which will add to the cost. I've lost a lot of docks in the winter there.

Distance from the tiny home is 75+ feet.

As far as removing the snow, the property is inaccessible in the winter so the system (s) would need to be removed in the fall.

Sunlight on the dock area is from sunrise to 10:30 - 11:00 am, maybe just after noon depending on the time of year (figure between beginning of April - mid May for most sunlight). The two secondary areas get sun 1 hour per day. Honestly in my opinion, not solar or turbine friendly.

Current Generator Production = 1gallon of gasoline = 114,000btu or 40KWH of heat = 13KWH of electricity @ 33% efficiency. Seeing as how you are only using 1KWH out of 1gallon of gasoline, that strike me as a very inefficient system. Even then it still use less fossil fuel per day than most folks, so its still a win.

Based on your appliances/devices, I see that you predict that you use only 1000W per day. Do you know what is the actual amount that you used. Can you pull up the numbers from the Kill-A-Watt log off the generator? That would give us the best reading. We could even get the total for the entire 80days say 88,000WH and then divide it by 80 days to get a daily usage of 1,100WH/day

Given that the sun stop hitting the lake where you could put the solar panel around 11AM, you get 1hrs of sunlight vs the 4hrs/day that is often used for solar calculation. So our solar production and price would have to be adjusted accordingly.

Energy Usage = Energy Production
1000WH per day = Solar Array x Hours of sunlight
1000WH = 1000W x 1hrs of sunlight.
I would still increase the Solar array to 3000W, so that 1day of sun captures enough energy for 3days of usage because of the frequent overcast/stormy skies.

$1800 Solar Array = 3000W (300V x 10A), this is 9 to 12 panels
$100 MC4 Wire = 100ft (300V and 10amp)
$500 Floating Dock
$500 MPPT Charge Controller (50V x 60A or 25V x 120A)
$1000 Inverter = 4000W
sub-total = $3,900

Cheap Dock

If you put the solar panels on the lake and the inverter and battery bank at that point you can run the AC from the inverter much further without the voltage drop of DC and using smaller wire.

You have an interesting situation, would a simple second hand panel set up with a longer cable run work while you are not there and may keep the batteries in good order?

Ben House wrote:If you put the solar panels on the lake and the inverter and battery bank at that point you can run the AC from the inverter much further without the voltage drop of DC and using smaller wire.

AC power operate at 120V or 240V.
Most solar string are made up of solar panels are connected in series with the DC voltage at 300V or higher, with the current never going over 10A or so. The wires can actually be smaller than with a 120V or 240V AC circuit. The only time that thick wires are needed is for a short 4ft or less run between the battery and the inverter/charge controller.

They have stop running thick wires between the solar panel and the house/charger controller at least a decade ago.

60 feet is no problem if you bump the voltage. I have 4/0 triplex aluminum and I'm running over 500 feet. You could run similar, probably much smaller, for 60 feet. Run your panels at 48v or higher, my array is over 300v.

John C Daley wrote:You have an interesting situation, would a simple second hand panel set up with a longer cable run work while you are not there and may keep the batteries in good order?

These Duracells lose very nearly no charge when sitting for the few weeks when I'm not there.  I've been using a product since the early 2000s that helps prevent mossing and stops the sediment production. I've got one group 31 trolling battery from 2006 that still operates at 89% of it's original capacity. I should have used it in all of them but I was young, stupid and paycheck to paycheck. Now I keep a half dozen bottles of it.

Actually, some clarification is in order. The Battery bank, inverter and generator spend the winter at the condo so keeping them charged isn't a problem. The inverter circuit is removed from the bank when not in use by using a switch on the positive connection. The inverter is pure sine 600W inverter - there is no need to have one any larger.

S Bengi wrote:Current Generator Production = 1gallon of gasoline = 114,000btu or 40KWH of heat = 13KWH of electricity @ 33% efficiency. Seeing as how you are only using 1KWH out of 1gallon of gasoline, that strike me as a very inefficient system. Even then it still use less fossil fuel per day than most folks, so its still a win.

I'm not nitpicking here but just pointing out a comparison of my 33% efficiency to that of solar panels being 11-15% efficient doesn't seem that bad. I know that's not a good comparison just pointing out that some people will realize that and stop there.

Comparing the cost between the two systems, the cost of the generator was $650 and monthly run costs are around $40 when I run it for 12 hours a day. That said, the 600 watt inverter I use would let me run nearly everything I run during the day - I just choose not to discharge the batteries below 80% at night mostly because I limit the bank size for ease of transport.

The payoff between the two systems, especially when I consider my age and life expectancy don't really compare in my particular case. I've found that most people don't consider that when they design a system. If I were in my 40s, then it would make sense. At my age with my condition which is terminal, building a solar array (in my opinion) doesn't make sense. For future owners after my passing, I'd leave the setup up to them.

Why do you move the batteries?

John C Daley wrote:Why do you move the batteries?

The property is inaccessible in the winter so I take them back to the condo for the annual Michigan ice storm power failure festival. I've already moved half the bank back to the condo - the 215 AH at the tiny home is more than enough for overnight or even a couple of days. We ran the house for 5 days once on the full setup. I have a boatload of coolers and keep bags of ice in the deep freeze for those times. Old Gatorade, big soda bottles make great ice packs too. Now that I have the new fridge, while small, it uses 50 watts or less, the usefulness of the system being moved is even more handy.

I'm building a sound proofing box for the generator at the condo too since I have a lot of plywood and acoustic tiles laying around from the remodel of the tiny home.

The reason why the property can't be used in the winter is because it's hard as hell to get anyone willing to work in northern Michigan. Took a full year to find a handyman that's reliable. The guy that plows the snow lives across the lake and does the 2 track and our neighbors driveway but hasn't returned my calls since late August. But Amazon seems to be able to make deliveries.