Help designing a system

[Znate]

Hey everyone,

I've been lurking for a couple years. Finally ready to jump in and build an off grid system to power a house.

7 years ago my wife an I lived off grid with a small lead acid system.
4 Canadian solar 285w panels
Midnite charge controller
1000 watt pure sine samlex inverter
Used lead acid battery. 24volt. I think about 280 amp hour but they were near the end of their life.

We managed to run a fridge and small chest freezer in the summer when sun was strong. Come winter we'd unplug the fridge and use a cooler in a cold corner of the house.
We got by but could have used a bit more power to avoid running the genny so much, almost every other day from Oct-dec.
We lived with that system for 3 years. We've since moved and were on grid for the past 4 years.

We'll be moving off grid again. This time I'd like to use lithium batteries with dacian's bms.
I'm looking for advice on building a system. We have 3 kids now and our power use is way higher than it use to be.
I estimate we lived on 3 kWh/day when off grid before. When on grid we've been using 30. Electric water heater, dish washer, occasional use of a electric heater....
Obviously we'll have to cut our use down but my wife's not going to go back to life without a dishwasher and clothes dryer.

I like dacians idea to use a large solar array and do some opportunistic loads during to day to keep the battery bank smaller.
I also like the thought of using diversion for heat. I wish I could get a dmmpt because we're building a new house and could put wires in the slab. What's the best way of using the current system for house heating? I've read through the manuals but don't have enough electronics knowledge to figure it all out.
Can I put diodes in the cement floor to get efficient use of diversion?
Should I use wires in the slab for resistive heating? I guess that wouldn't be as efficient though?
Should I put water pipes through and use diversion to heat water that is then pumped through the slab?
Advice appreciated!

I feel I'll have too many questions in one post if I keep going so I'll leave it here for now.

Nate

[Dacian Todea]

Nate,

You can put wires in the slab and in a sunny day it may be close to 80% efficient just with simple diversion.

In average I use now around 4kWh/day (120kWh/month) but this excludes heating of course.

The dish washer uses energy mostly because it needs to heat the water and if used during the day it should not be much of a problem.

I recently got a small dishwasher (I think Toshiba may have came first with this but there are many brand producing almost the same one).

It only uses 5 liters of water and that was the main reason to chose this one as water is more of a problem than electricity. The washing takes one and a half hours and it will take water 3 times in equal amounts a bit over 1.5 liters each time for washing 45 minutes and two times for rinse and each time it will heat the water up to around 70C so fairly hot water and that is what takes most of the energy around 0.6kWh for one cycle but that is more than decent and not a problem at all.

It is also nice that it will not need a connection to water as it has an on board 5 liter storage (it will beep when full).

It was 599CAD including shipping on Amazon see some photos below.

[Bernd]

I can tell you, what i did, maybe that helps.

I´m building a house offgrid in germany, I plan to end up with 24V 1120Ah battery, i plan to not use dish washers or clothes dryers.

I bought 32x 280Ah EVE cells at sheila in china...

I have a water pump 30m deep for fresh water, which needs 800watt.

i currently only have 2kw inverter, but will update to maybe 5kw later. 

I have 5KW of solar, which could be updated easily depending on my loads or the SOC with the new battery.

I added a liquid gas tank (for the heating) it will give me much more flexibility compared to being 100% offgrid and eliminate the hot water topics out of my system.

For me this was the right step, i hope. 

I would expect you need at least 8kw for the load side. Maybe the same for the solar side.

concider enought solar for december to march!

[Bernd]

wow, thanks for this dish washer information!

This is a nice forum and very helpful.

Thanks for sharing all information here

[Znate]

Dacian,
Thanks for the info on the dish washer. I feel it may be a bit small for a family but I'll take another look.

When you put your heat wires in your house were they in the slab itself or did you put them in the mortar under tiles? How much insulation did you use below slab? Is there a post somewhere with more info about what you did. It's been a while since reading about your install and I forget where I found that info.

Is there an easy way to heat water efficiently? I plan to have pipes through the slab for a compost heater. If the pipes are already there maybe I should use them for both solar diversion and compost. Perhaps even wood boiler if needed.

Bernd,
That's a lot of battery! I was hoping I might be able to get by with 8 of those cells, maybe that's just wishful thinking though.

What's the best way to power 220v loads? I'm thinking of the clothes dryer. I'm not familiar with what inverters are available and work well with electrodacus. Should I be looking for a 220v inverter or is there other ways?
I think the dryer is the only load at 220v so I'm tempted to look at propane dryers or running a genny when the dryer is needed. If I can get it set up to run solar without spending thousands above what I'll need already then solar is the way to go.

Nate

[Bernd]

I have a gliandel 2kw inverter to go up to 220V.

I have always up and running the inverter, a Fritzbox 6890 LTE, KNX system, raspberry pi with iobroker, rock64 with deconz stick for some sensors, ptz camera with power of ethernet and this all consumes an average of 30-35 watts.

This is my base zero setup which needs to be always up and running. 

The inverter is able to run a senseo coffee cup machine with 1500W, which helps me to enjoy the day. 

Currently I have 8 cells with 150Ah. This gives me 4 days with fog, snow, rain or heacy clouds more a less, just to power the base zero loads. any coffee or light reduces these times.

And we are not living there.... It is just a quick visit maybe an hour every few days.

During summer, it might be okay, but it needs 4-5KW of solar to keep the battery full during the winter....

The more you consume on cloudy days or have snow, the larger the battery you will need.

Where are you living?

[Dacian Todea]

Nate,

It is the smallest dishwasher you can find but it also the most water and energy efficient one and that was what I was interested in.  We are just a family of two and for us it works (I only got this about 3 weeks ago).

The other more common counter-top dishwashers like those from Danby are about 50% larger but take 12 liters of water for a cycle that is more than 2x compared to this one I have that uses 5 liters. The amount of energy will also be proportionally higher but that is less relevant for me than water use.

Most info about the house build was on google+ but that no longer exists.  There is a short video that shows how the house was build and you should be able to see the details on the foundation  https://www.youtube.com/watch?v=Y3g4gmRvgko but there amount of insulation under the slab varies and for more details you can download the house pdf project from here http://greensask.com/

There are 10cm of expanded polystyrene under the thicker parts of the slab on grade but under the slab there are another 15cm so a total of 25cm in most places. 

I will not waste my time with compost heater. Depending on your climate it may not even work at all. Wood will also be much more expensive than solar heating even if you only have wires directly connected to panels so 80% efficiency in a sunny day.

I do not know what dryer you have and what power will that require.

There are many inverters that can work with SBMS if you only want inverter and not also charger.

 

[Znate]

Bernd,
I'm in ontario, Canada.

Where did you get your batteries? I saw in another post/thread? That you paid a little over $100 per cell. I was looking at these,
https://www.aliexpress.com/item/1005001967463422.html?spm=a2g0o.cart.0.0.26953c00LpHo5U&mp=1
But they're going to be closer to 200 per cell.
Where should I be ordering my cells from?

Dacian,
I'm already using compost heat in my house now and for my specific situation it make sense. I have a couple cows for milk so I have their soiled bedding that I compost for the garden. Now I'm capturing the heat for the cost of running a circulation pump. It's my first winter with it set up but I've been capturing from 5000 to 8000 btu/h. I'm going to redesign the compost pile to reduce labour and I expect the change should also produce more btus.
I'm hoping compost will be my primary heat source with solar diversion as supplemental. Wood will only be used when/if needed.

I have limited data so I'll check out your YouTube vids when in town next.

Dryer says 5400 watts.
I have a 24v charger from my previous solar setup. It's an iota dls 27-40. If I purchase an inverter without charging can I use this or would it be best to get one combined unit?
Can I control 2 inverters? Wondering about using my samlex for normal house use and having a second larger inverter powering heavy loads.

[Bernd]

I follow Andrew at the off-grid-garage on youtube and he ordered EVE 280Ah cells also at aliexpress. the seller is Shenzhen Basen Technology Co., Ltd. and the contact is Sheila Chou.

I´ve ordered beginning of january and it takes 45-50 WORKING DAYS to receive the cells. by train.....

this could mean 10 weeks or 2,5 months or in my case end of march :-)

[Dacian Todea]

Nate,

5000BTU/h is about 1500W. Is that continues ? how do you calculate that ? You should now the flow (volume of liquid over time) and temperature delta. Also is that 24h/day or is not continuously used.

Also how much energy is the pump using ? How long is that pipe and what sort of work it requires ?

The 5400W dryer will be quite significant load and probably a lot of the energy will just be wasted by trowing it outside.  If you do not have access to grid I do not think you will need a charger just inverter.

Most inverters are in the 2000 to 5000W range so you will need at least 2 or 3 parallel inverters to deal with that sort of large loads.

[Znate]

Dacian,
I did the calculations like you said, temp delta and flow rate. It's continouslly running. The pump draws 40 watts so I feel it's a good return for electricity used.
The compost pile is a 5 meter diameter and was 2m tall when first built, it's since composted/settled to around 1.5m. It's a mixture of cow manure, soiled hay and wood shavings. It has 200m of of 25mm poly water pipe coiled in layers throughout.
I dumped the material in with a front end loader on a tractor but had to spread it by hand and coil pipe. Then add another layer with the tractor and so on.
It will need to be disassembled by hand to avoid ruining the pipe. That's the part I feel will be too laborious. I plan to build a cage with the pipe coiled around it and suspend it high enough off the ground for the tractor the scoop the compost out from below the cage. I'll continuously add material to the top. As it composts it will pass over the pipes and the finished compost can be emptied out below with the tractor eliminating the need to build and dismantle a pile every year.
I'm considering the possibility of having a water storage tank inside the house high enough to allow the heat to thermalsiphon into the house. It would then only need the pump to circulate warm water through the floors when the house needs heat, reducing the time the pump is running thus saving electricity. The biggest drawback is having to support the weight of the water and the potential for damage if it leaks.
Anyone interested in compost heat should check out "the compost-powered water heater" by Gaelan Brown.

I'm looking at victron for my inverter, I'm a bit confused about the difference of the multiplus and the Quattro. Is the Quattro better for a situation where there is another power source (genny) or if you're using it as a ups?

[Dacian Todea]

Nate,

I did not looked in to compost heating so not an expert but I did some quick read here is one of the links https://smallfarms.cornell.edu/2012/10/compost-power/  and this http://compost.css.cornell.edu/physics.html

Seems like there is a lot of work for not that much energy in my opinion.

Is that compost pile insulated in any way ? if not then most of the energy will be lost to the environment if it will even work (guess not if it will be as cold as at my location).

if that is a round (cylindrical) shaped compost that means you have around 30m3 and with around 600kg/m3 that will be 18 tone so fairly significant amount.

The loss on that 200m 25mm pipe is equivalent with lifting the water at 3.5 to 4m and the flow will be very dependent of how optimized your pump is for this application.

But say is fairly well optimized then I expect around 1000liters/h so to get 1500W you will only need to have 1.4 Celsius delta between the input and output inlet.

I will be curious about your exact numbers.

  

[Ken R]

Have you looked into a propane dryer?  The advantage of a electric dryer is you can vent it inside thus saving the heat; dealing with the moisture can be a problem tho.

I will have a DMPPT450 for sale in the spring, an NIB SBMS120 available now and another available maybe in the fall.  The build of my home got delayed and I will be switching to the SBMS0+DSSR20 scheme. 

The county will not accept the solar electric heating as the primary heat source so I will be building a hydronic system and switching over to solar electric as things pan out.  I will be going with wires in the slab and building my own controller to switch them in and out using DSSR20s.  Will look at using using solar electric for water heating also.  The whole thing is not really cost effective but I consider it my retirement hobby.  It also fits with my belt and suspenders mind set.  This is about an hour west of Edmonton.

Ken