Large or small packs ? Which do you prefer.

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Project

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I'm trying to decide which direction to go with my build. I will be 48v but I'm trying to decide if I should build large or small packs. I know many build 14s80p butIf I build small packs, 14s40p arrangement, I won't have a big storage drop if i have to take one out of service for maintenance or repair. On the other hand it add moreconnections and more possible points of failure. Decisions decisions..
 
Its all about what you have handy. Do you have many cells or not? How much do you need to keep your house running?

I build with n+1 in mind. Ie 1 hot spare. That said i build mine so i can take out 1 string at any time if needed without issues!
Its also about how you going to store them. Right now i have done 80p packs and i have done 14s11p packs :)
 
I have about 10,000 cells on hand. I like the thought of building large packs so that I'll have less mounts to build, less connections etc. I'm just thinking about 5 or 10 years after install. If I have an issue that may take a few weeks to resolve I will lose a good portion of my capacity with large packs. I don't know my storage needs yet because the house is still under construction but my goal is for 1700kwh per month or less.
 
How much do you want to spend on BMS or do you want to spend anything on bms?

With 10000 cells i would go for 4-5 strings. Not more.

4 packs would be around 175 cells per pack.
140 per pack if you go 5 strings.

If you go 5 strings you only drop 1/5th of the capacity for the time being. Thats how i would do it!
 
daromer said:
How much do you want to spend on BMS or do you want to spend anything on bms?

With 10000 cells i would go for 4-5 strings. Not more.

4 packs would be around 175 cells per pack.
140 per pack if you go 5 strings.

If you go 5 strings you only drop 1/5th of the capacity for the time being. Thats how i would do it!
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I don't want to spend any more on BMS than I have to but I want it to be safe and reliable. For what I'm saving on storage I can get a good BMS and still be a lot cheaper. My first thought was 6 strings with 160 per pack. I would need a few more cells but would have plenty of storage
 
Yes that's plenty of storage :D Im just a tiny bit jealous of all those cells :p

My BMS would be able to handle that. It would also have tunctionality that could disconect packs if needed. Though its not near done yet.
 
If you have that many cells just go ahead and build a spare pack, you can rotate your packs a few times a year to keep them all with the same approximate amount of usage.
 
Elmo said:
If you have that many cells just go ahead and build a spare pack, you can rotate your packs a few times a year to keep them all with the same approximate amount of usage.
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I'm still around 2000 cells short of my goal. It's a big house and thirsty for power. Staying below 1800kwa per month will be a challenge for this house.
 
kwa? kWh?

I use up to 1500kWh per month here.. Servers consume half of that... I have 11kw of solar but need to extend that to cover more of the dark time of the year (December, januari,februari)
 
daromer said:
kwa? kWh?

I use up to 1500kWh per month here.. Servers consume half of that... I have 11kw of solar but need to extend that to cover more of the dark time of the year (December, januari,februari)
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Are you off grid or grid tie? I want to eventually be off grid.
 
Grid-tie. Wont work with off-grid where i live.

December: 140kWh
Jan 120kWh
Feb 130kWh...

Not much to talk about. But i could most likely double those numbers up if i arrange them better for winter use. My setup is configured for producing most kWh during the summer hours. Then i easily do 1600+ /month :)

But i will rearrange some for next winter and add 20+ panels more.
 
I'm having to rethink this whole house build. I was originally going to rely mostly on solar but to be grid tie, the work has to be performed totally by a solar company approved by the power company including setting the poles for the panels. I wasn't allowed to touch it and after the $100,000 quote I was given, grid tie was out. Off grid became too expensive because of the battery storage cost and need for regular replacement until I stumble upon this which brings the price back down and hopefully less need for frequent battery replacement. I will have to make so big decisions with the house build soon if I'm going to be off grid. Starting with hot water supply, right now I have 6 electric instant on water heaters that are power hungry. The entire water supply system of the house will have to be completely changed and that's not easy to do in a log house.
 
Water heaters on the roof. Thats the way to go. I have water heated house here too but with fire.

Either you go that route and heat your house with boilers or you go water heaters or you combine the both. Dont heat water with solarelectric as first choice! That's just a big big waste. Only use excess energy for that.

You can also use solar-air heaters. They work damn good during the day but you need to complement with something else during the night unless you have storage for heated air.

http://diytechandrepairs.nu/utilize-excess-solar-energy-instead-of-wasting-it-diy/

This may be of some help (Dunno :) )

Nevertheless substainable energy is not cheap as of today. And unfortunately solar in many places is not good enough and neither is Wind...
 
I can change from electric to propane for water heating and only have to runna gas line to each water heater. Fireplace and heat pump will provide the heat. It's just a matter of changing a few things around to be more electrically efficient.
 
Yeap it is.

Look into solarwater heaters and solarair heaters. Sometimes you can get those 2nd hand almost for free. And with minor work it can be added up to existing systems.
 
I've looked into solar water heaters but they don't do very well where I'm building. It would be covered with snow from weeks to months at a time. I will already be cooking with propane so it's just a matter of adding a few gas lines from the manifold. My water heating should be under $150 per year using propane. I haven't seen much on solar air heating. Thanks for he tip.
 
AH ok :)

Solar air heaters are killers during day. Put them on the walls and you dont get any snow on them. And they will give you alot of heat during the day to cut down cost. Easy to build as well. Some glas, small solar panel to drive the fan, 1 or 2 computer fans and you are set.

When sun comes the fans start and get you heat to your house :) Plenty of people in sweden that adds those to their smaller off grid houses to add some more heat during the day.
 
This is a 7000sqft log house with 16" thick outside walls , in the shade with wrap around porches so a solar wall is out. It doesn't take much to heat and cool it once you start. Thermal mass takes over and you just move air around with ceiling fans. I have a southern facing mountain side about 150' from the house that is perfect for solar panels.
 
Project said:
I've looked into solar water heaters but they don't do very well where I'm building. It would be covered with snow from weeks to months at a time. I will already be cooking with propane so it's just a matter of adding a few gas lines from the manifold. My water heating should be under $150 per year using propane. I haven't seen much on solar air heating. Thanks for he tip.
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Reducing electrical load is always cheaper than additional batteries or PV panels.
Heating water is one of the most energy demanding part of powering a house.
So heating your water with anything but electricity will help significantly.

But unless propane is extremely cheap in your area, I dont see how you are going to do it for $150.
I spend about $300/yr on propane for an on-demand H20 heater and my stove.
Tiny house with much less usage than you.
1 person, 700 sq. ft. and average only 231 KwH/month or 7.7 kwh/day.
 
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