So I want a DIY battery backup solution for my home but don’t know where to start

[Southpaw]

Hi everyone,

I was talking with my local utility worker today about how my wife and I were considering adding a battery backup to our home. We moved into this house back in June and it had solar previously installed (a 10.695 kWh system from SunPower consisting of 31 panels on the rear roof of our home).

I’ve been trying to get quotes for battery solutions from various companies, all of them seem outrageously expensive to the point that they don’t make sense. So I was intrigued when this utility worker mentioned he built his own batteries and I should look into it myself. Well, a couple of glasses of wine and a few hours later and here I am…

Now, I’ve been reading through the Beginner threads and FAQs, but I don’t see the kind of answer I need before I even consider this DIY option: Can I use a DIY battery with a pre-existing solar array from SunPower? This probably is a simple and obvious question, but I honestly don’t know a DIY battery would play nice with my system. Everything I’ve seen so far in the Beginner threads and FAQs seems to imply this solution is for those who sourced/installed their own panels?

Sorry for the naivete, I’m truly interested in making a DIY system work. I’m excited by the prospect of this project because I know my father-in-law would love to work on this with me and this could honestly save me a lot of money to get me the solution I’m looking for - at least that’s what I’m hoping…

 

[Bud Martin]

Try to DIY battery pack to interface with your existing system will require lots of research about the existing system, the local regulation involve, I do not think it will be for the beginner.
So your system uses SunPower panels, but how about the control system, who is the maker? Can you get details about your system? It may be Enphase which it works with SunPower to supply the whole system. You need to find out more about what you have first.

 

[400bird]

Lots of research is par for the course when going down this road, diy home battery and all.

Most grid tie solar inverters (that's what you have) can be made to work with varying success.

First step: identify you inverter by model and part number. As mentioned, you might have micro inverters, mounted one at each panel. SunPower is the vendor that bolted the stuff to the house, not the manufacturer of the parts.

Second step: energy budget and figure out how much load you want to have backed up (battery inverter size) storage capacity (how long you want the back up to last in an outage)

Third step: are you comfortable and familiar working with 240 volts AC and 48 volts DC?
Hmm, maybe that should have been step one...

 

[Rednecktek]

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.

1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the Uber-Sun-Hours calculator site to help figure out how much you'll have to work with. That will be a box in the Power Audit form.

2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that.

3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger. Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.

4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.

5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.

 

[wattmatters]

I was talking with my local utility worker today about how my wife and I were considering adding a battery backup to our home.

Before we get to energy audits and system scoping, I think we need to start with the above statement and clarify what exactly it is you think you need. Because the following statements don't quite gel with it:

I’ve been trying to get quotes for battery solutions from various companies, all of them seem outrageously expensive to the point that they don’t make sense.

Can I use a DIY battery with a pre-existing solar array from SunPower? This probably is a simple and obvious question, but I honestly don’t know a DIY battery would play nice with my system. Everything I’ve seen so far in the Beginner threads and FAQs seems to imply this solution is for those who sourced/installed their own panels?

Grid tied battery solutions cover a whole slew of functionality/outcomes. Providing backup is but one of them.

So my first question is to clarify exactly what you want a battery for? What is it you are trying to achieve?

The answer to this makes a big difference to the solution path you can/might choose.

If it really is just for grid outage backup, then that represents quite a different (and often simpler) challenge than designing a grid tied battery system fully integrated with your existing solar PV and which can operate isolated from the grid if/when required. For instance, you can build a battery backup system which does not provide many (or any) of the features/functions of a grid tied battery system. It can be an off-grid system. Indeed the right solution for you may not involve a battery at all.

 

[Acho_303]

Check you electric bills kwh, the average apartment is 20to30, then use a online calculator to go from kwh to watts to ah... then you know how many cells you need