diy solar

diy solar

Off grid new house build.

Am I dreaming?
It may all depend on resources in your area. If the hardware quote includes racking you are close to the number that I guessed at. I do not see a budget for inverters and some of those All In Ones include charge controllers so that $2,500 could go toward inverter{s} and charge controllers but is not enough for both or an All In One.
Another thought about solar panels if you are buying used, depending on charge controllers or inverters there may be an advantage to try and use all the same panels to make string sizing easier. Or phase the install based on the string sizes dictated by your charge controllers and the minimum size system you want to start with.
I've got other amounts for the inverters, I want the charge controllers separate so they charge the batteries directly.

Here are my rough numbers for now:


I'm building this house new from scratch so I've got every opportunity to run the wires at the rough in stage rather than trying to retrofit a house later. I hope that saves me some $$.
FLA - Today, some LiFePO4 cost less to purchase than lead-acid.
Also expected to last longer, unless battery bank is oversized for 3 days autonomy.

$2500 worth of charge controllers seems low for 37kW. Unless they are overpaneled to about 200% of rating, for more production on poor days.

$10,000 for 2x 5kW inverters is retail for Sunny Island (which I use), but there are still deals for about half that price.
What brand/model are you planning on?

10kW generator - maybe to entirely carry full load. Is that necessary, or could it be smaller with inverters charging and inverting to limit draw?
I want to stick with FLA. Reasons explained earlier in thread.

I would like Schneider inverters if I can afford them, I'm very familiar with repairing Trace and Xantrex so Schneider seems like the natural choice.

I could get away with a smaller Genny and I'll buy that used from Craigslist or Marketplace so I'll get what I can get. I'm mechanically inclined so I can often buy whatever I need in a non-functional state and then take it home and repair it. This saves me a ton of money and then I know it inside out so I can maintain it forever. I'd like 10kW just so that it will quickly and efficiently charge the batteries in the dark months. 5kW seems kind of small for a house (I have a 4kW genny on my travel trailer).
Since I use SMA, I would use 2x SI 6048US, 12kW to 24kW of earlier model Sunny Boy (5000US ... 8000US), balance of PV panels on Midnight charge controllers. Actually,, for off-grid, I would consider 3-phase 120/208Y.
If PV panels were of a couple orientations, 37kW of panels would peak around 24kW, so up to 100% could be AC coupled, but for all output to go to battery, half AC coupled and half DC coupled since 2x SI can charge about 12kW.

With some AC coupled, your loads would be powered PV direct, giving battery inverters a rest.

Schneider should be able to do the same thing, for models that support AC coupling.

4x SI

2x SI & Midnight Classic 250 (the 150V model would handle more watts)

SB (11kW model 240V only, not 208V)

What do you think of Kubota? There should be many near-new ones from DC Solar trailers.

Here's an older 6.5kW for $2000
Brand new 11kW for $7800

While 5kW generator would be small for a house, if inverter can add its power then it supplements surge load, so generator only supplies average load & charging while it runs. FLA battery's desired charge current (0.12C?) plus simultaneous loads may be what you want, for proper charging during overcast.
You are going to kick yourself in the future for going FLA, the newer lithium iron phosphate batteries are not your old lithium ion exploding batteries.
Seriously, very really seriously consider the best batteries that we can now get.
I am going to kick myself even more if I pay a premium price for lithium batteries and they only last ten years and the company is gone in the wind.

I can't afford Battle Born or Trojan in a lithium just now, still too expensive.

Are there other lithium battery manufacturers that actually own factories and have employees in America? I'll consider any manufacturer that has skin in the game in the form or hard assets within the USA, tangible assets that could be liquidated to pay out claims or lawsuits or bankruptcy creditors.

If the company structure consists of a management team and a marketing department within the United states and a supply chain from China then I consider that too risky. In the event of any problem the money all disappears and the company goes bankrupt and there is nothing left to pay out the customers or litigants. These companies are set up like this deliberately - it's not a fluke! Amazon is the perfect place for a company of this structure to operate. No retail footprint either.

I'm not saying that any of them are evil to begin with or out to screw their customers but they are set up to disappear without ill effect on the company directors. What if the Chinese factory has a defective run on batteries and those units only last say 8 years. No one will know right away but when the shit hits the fan the directors can decide to simply abandon that brand name. It may be a better decision since the brand is now tainted. The company has no real assets. The directors take all the money, shut the business down, leave the customers holding the bag and then they start over with a new office and a new brand name and they get the Chinese supply chain to change the stickers.

I've been repairing electronics my whole life (I'm 59) and I've watched this pattern over and over. Customers at my door that bought something made offshore and the company is now gone and the warranty they were promised isn't worth the air it takes to fart. Costco is a big pusher of this stuff, off-brand TVs and equipment with limited or no support and a company that was only in business for a year or so. By the time a problem exists the company no longer exists. Caveat Emptor!

If I was 30 or 40 I'd build my own lithium bank to last 25+ years but at nearly 60 the ROI isn't there. The logical solution for a battery bank to last 15-20 years is a really good set of FLAs from a good, trusted brand like Rolls Surrette.
They aren't a premium, anymore.
Server rack batteries seem pretty economical. Just understand their surge current limit (designed for racks of computer servers, not inverters powering well pumps) and use a precharge system before connecting to inverters.

LiFePO4 battery manufacturers only exist in China, because no one here was interested in developing them. So patent owners gave an exclusive license (which has just now expired), and China ran with it. They are massively building out EV's there. The lesser performing batteries are good enough for our alternative energy systems and get used here.

The years you can get out of a lithium battery will be partly environment and charging, partly inherent in cell chemistry and partly quality.

I think AGM batteries cost $0.50/kWh of cycle life, FLA $0.25/kWh.
LiFePO4 server rack batteries appear to be $0.05/kWh, if they last 6000 cycles which is nightly for 16 years.
If that last 3 or 4 years with that sort of use, you will have broken even with FLA cost.

FLA forklift or Rolls Surette, you might get 20 years if sized for 3 days autonomy, mostly only discharged 15% at night.

LiFePO4, sized that large might age out before reaching cycle life. Cost could be $0.15/kWh. Sized for just one night's consumption you should achieve $0.05/kWh (and that only applies to power cycled through the battery.) Daytime you'd be using PV direct, or micro-cycling the battery (shorter life, I assume). Generator if overcast, unless massively over-paneled.

I do use AGM. 3 years ago, a fraction the cost of lithium I knew about, for a fraction the cycle life, ideal for backup. Today I'd look seriously at LiFePO4.
Hmmm. Maybe I had better take another look. If Hedges numbers are real without buying no name batteries off Amazon.

Any brand suggestions anyone?

Keep in mind I'll be using about 35kWh per day and I'll have a genny to run each day if needed.

I only plan on enough battery for one day.
I think if you stick to the two major players in the USA as in Signature Solar or Current Connected you will be fine for long-term support from them. Hedges sums up the pros and cons in the post above very nicely.
I bet you one server rack battery you will be happier with lithium ion phosphate than any lead version 10 years from now.
Communication between BMS and inverter is desirable, but not mandatory. It would let BMS tell inverter to slow down charge and hold where cell balancing can occur, without any cells hitting high voltage disconnect.

There are a couple different protocols, so good to select what works together.

I have Sunny Island, and there are higher priced batteries on the supported list (e.g. from BYD, about twice the price of server rack batteries.) REC is an expensive BMS some people use for DIY batteries. Current Connected says they have SOK server rack batteries working closed-loop with SI, but some issues with state of charge.

Open loop with SI, we say the battery is VRLA, possibly nominal voltage different from 48V (24 cells) so parameters match desired 16s LiFePO4 voltages.

Other inverters, other protocols. Research first and see what experiences others have had.
So if I bought two of the SOK server racks at 25kWh each I could run my house for a day and a half.

Price is $24700Cdn. 50kWh would be plenty of storage for my needs for a day or so.

Surrette will sell me 12 of their 371Ah batteries for $18312 configured in three strings of 4 I'll also get 48V, storage is about 45kWh

Going to have to think about this some more.

I'm not completely convinced SOK will still be around in ten years, I'm pretty sure Rolls Surrette will be.
Maybe Rolls Surrette tolerates similar depth of discharge; how many cycles in that case?

Another benefit of LiFePO4 is higher charge rate, about 0.4C, may make better use of generator or lots of PV. But that charge rate is only at comfortable temperatures. It must be reduced approaching freezing, stopped below zero C.

I figure fast charge is more important for EV; PV systems usually have all day to get it done.

Yet another, it is OK to not fully charge. So unlike FLA, you can cycle in the middle if that's what production and loads want to do. FLA, I think you want to bulk charge with generator earlier in the day, let PV do absorption.

Are you able to keep the batteries warm?

For FLA, 3 strings of 4 (12V) batteries? Do you prefer that over one string of 4V or 2V?

In 10 years, likely lithium will be of a new chemistry.
Have to wonder how much lead-acid will remain. Some people think most of the remaining brands will have been sold to holding companies, and quality will be lost. What's Rolls Surrette's primary market?
So if I bought two of the SOK server racks at 25kWh each I could run my house for a day and a half.

Price is $24700Cdn. 50kWh would be plenty of storage for my needs for a day or so.

Surrette will sell me 12 of their 371Ah batteries for $18312 configured in three strings of 4 I'll also get 48V, storage is about 45kWh

Going to have to think about this some more.

I'm not completely convinced SOK will still be around in ten years, I'm pretty sure Rolls Surrette will be.
You can get a 30kWh rack from Signature Solar for $8943 USD, which I think comes out to about $11950 Canadian. So for about the same money as the SOK you could get 60kWh in the Lifepower4. If you don't really need that much nothing says you couldn't do a rack and a half. Also they run sales pretty often. I think I got my last 30kWh rack from SS for something less than $9k including shipping.
With my ~half year experience on solar/batteries and actually running a working set for only three months now I'm hardly in a position to educate anyone on the matter, I can only speak about my observations. I designed and executed my setup DIY without any previous experience on solar and tried to keep everything on budget, thus there were some difficult times. Luckily I found this forum and got help when needed.

I have an old 30kWh 48V FLA forklift battery which I got free and then purchased ultra cheap 3x5kWh Lifepo wall batteries (new) to see if they are any good. Both have about the same usable amount of power (~15kWh, as LFP can be used 2-98% without problems), but to charge them up from "empty" is ~20kWh(FLA) vs. ~16kWh(LFP). That extra 4kWh is heat/vaporized water. In winter that's not a problem, but in summer I use mini-split to keep my "solar corner" around 17C (63F). I also need to add 1L distilled water every two to four days depending how hard FLA has been used. I have a distilled water generator, so it's practically free, but needs my attention unlike LFP. I bet FLA numbers would be somewhat better if the battery was new and not 18 years old like it is. My additional 60kWh LFPs have already arrived but haven't got time to install those yet. That's why I need to push my batteries ATM, and that's one shortcoming of FLA as you shouldn't charge it more than 0,2C. At days like today when sun is only occasionally available there's no time to charge FLA full as you always should. LFP doesn't mind about charging state and with enough solar power (like I have) they were full before 10am. One last problem with FLA is acidic smell which in my case is not that important as my "solar corner" is located in unused old horse stable.

As I'm cheap I'm going to use my FLA, maybe even buy another one if I find something close to free. Otherwise I would not even think of using anything but LFPs at the moment. You can go with tier1 product if you like, but as I'm on-grid I have the luxury to go with the cheapest ones I can get my hands on. So far every battery has been as promised, maybe top balancing needed somewhere in the near future. With my price point that's more than acceptable.

For panels in snowy conditions you should consider bifacials and vertical installation. I think I have already demonstrated how superior this kind of setup can be in winter time and how little it is actually hurting due to wrong tilt angle in summer. While one would think that bifacials have to be way expensive, they were one of the cheapest offers we got from China, around 0,3e/W delivered.
Are catalytic recombining caps available for those forklift batteries?
I think that's what makes for "maintenance free" FLA like some automotive starting batteries, also AGM a.k.a. VRLA.

And then there is automatic watering, I think a hand pump with float valves. Just push to dispense correct amount.
Are catalytic recombining caps available for those forklift batteries?
I think that's what makes for "maintenance free" FLA like some automotive starting batteries, also AGM a.k.a. VRLA.

And then there is automatic watering, I think a hand pump with float valves. Just push to dispense correct amount.
I haven't been able to find any useful information about my FLA using google. This Exide battery seems to be built before Internet era.

I have automatic watering with float valves. No pump, just pouring some water down the tube and it stops taking it in when floats close. Without it I wouldn't even think of using FLA. It usually takes less than a minute to fill.

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