DIY Solar Diverter to battery cheap simple, mostly off the shelf

[Doug42]

Hello! just wanted to get some thoughts on a project.

Problem: Adding a battery to house, there is a pre existing solar array which for regulation reasons can not be touched, but i want to make use it to help charge the House battery (other solar will be added but that's not relevant to the problem)

Market solutions for this exist but involve a lot of money and isolating house from grid

Solution: for a DIY solar diverter to battery. There are tonnes of solar diverters out there but most only work with hot water or by simply turning on some device when power exporting reaches a threshold. Rubbish IMHO, I would like a continuous power redirection and to capture that in a Battery. I think I have thought about a relatively cheap and easy way to build a DIY diverter for charging a battery bank. Basic concept: Big adjustable power supply that takes a 0-5V current control input (they exist and are cheap), running in Constant Current mode, max voltage set to max safe voltage of battery, Max current controlled by an arduino. The arduino measures the power going into and out of house using either a bidirectional power meter (CT clamp combined with Voltage measurement https://youtu.be/DWELwaMy2CQ?si=hedasl-GTkJAplBq&t=181) or 2 CT clamps. one on solar output the other on house. Connect Power supply to house side of clamp. Then use a PID library running on the Arduino (I have used before, both simple and effective) to adjust the power supply current and put the setpoint for the current leaving the house to 0. This would allow a continuously adjustable solar diverter able to push power efficiently into battery. I would introduce a chunky 100A diode between supply and battery. BMS should prevent over voltage of battery in fault but a voltage thresholded relay might be a nice reassurance.

Example of DC power supply:
https://www.aliexpress.com/item/1005005622031474.html?spm=a2g0o.detail.0.0.64c4NrCZNrCZgN&gps-id=pcDetailTopMoreOtherSeller&scm=1007.40000.327270.0&scm_id=1007.40000.327270.0&scm-url=1007.40000.327270.0&pvid=761dbe07-d065-4b29-b06f-5d37bc8d40c6&_t=gps-idcDetailTopMoreOtherSeller,scm-url:1007.40000.327270.0,pvid:761dbe07-d065-4b29-b06f-5d37bc8d40c6,tpp_buckets:668%232846%238116%232002&pdp_npi=4%40dis%21CAD%21607.43%21425.2%21%21%213183.58%21%21%402103200516940245753271015e125c%2112000033778837354%21rec%21CA%21%21A

To Complete the setup I could connect my battery to my house's circuit with a zero feedback inverter like this one:
https://amzn.to/2SZzpbM

Nice Vid of how that inverter works:
https://www.youtube.com/watch?v=FZ0FwW2pRj8

This seems like a common problem and this solutions seems easy and cheap without many downsides to me so my main concern is why isnt this already a thing? am i missing some big problem? thoughts appreciated. Obviously there are some nuances i haven't gone into to keep the post short but the concept seems sound to me?

 

[sunshine_eggo]

So, you're basically trying to store surplus PV energy in the battery and then feed it back to house loads later with zero export.

Looks like it will work.

Still have no power when grid is down.

 

[SamDeleted]

SolaX X1-AC 3.6

The 1ph SolaX AC coupled Inverter- 3.68kW<br>

midsummerwholesale.co.uk

Don't they do these in the states ?

 

[Doug42]

So, you're basically trying to store surplus PV energy in the battery and then feed it back to house loads later with zero export.

Looks like it will work.

Still have no power when grid is down.

Thanks, yes exactly. It is good to hear from someone else, as a sanity check, that the principle is sound. yeah the no power in an outage is not ideal but power cuts are rare where I am and it would be easy enough to fit a transfer switch and a cheap 2-4KW standard inverter for those rare occasions. There might be a way I could wrangle the zero export inverter to play ball (disconnecting the grid tie solar of coarse) Not the ideal setup, but that is the cross I must bare for the retrofit and tariffs

 

[Doug42]

SolaX X1-AC 3.6

The 1ph SolaX AC coupled Inverter- 3.68kW<br>

midsummerwholesale.co.uk

Don't they do these in the states ?

Ahhhh thankyou. for some reason I failed to find such a device, that was reasonably priced. I will look further into that option as it would save hassle.

The only problem is it does want a high voltage battery, I was going to go for a 48V setup for convenience and safety

 

[SamDeleted]

Ahhhh thankyou. for some reason I failed to find such a device, that was reasonably priced. I will look further into that option as it would save hassle.

The only problem is it does want a high voltage battery, I was going to go for a 48V setup for convenience and safety

I'd have thought there'd be loads of stuff like that AC couple inverter , surely there is a big market for them ,

but they are not common as you might think!

 

[Al Del Sol]

Ahhhh thankyou. for some reason I failed to find such a device, that was reasonably priced. I will look further into that option as it would save hassle.

The only problem is it does want a high voltage battery, I was going to go for a 48V setup for convenience and safety

Your simple set up should work just fine.
How big of a 48v battery are you thinking of using?

I had a similar idea with a temp-solar "emergency power" for my home at one point.

48v battery in the basement (only about 10kw)
A couple of portable solar panels
A 48v solar charge controller and 120vAC to 48vDC charger.
3000kw inverter

The inverter and chargers would be wall mounted in the basement near the battery. Surge protected power strip plugged into the inverter and also on the wall along with a battery disconnect. 4 extension cords plugged into the power strip and neatly wounded on the wall as well.

I was going to cut out 4 access ports to some of the rooms above. Those access ports would have vent covers on them when not in use and would serve as extra ventilation between the main floor and upstairs.

The AC to DC charger would keep the battery charged with grid power. When power does go out, I would simply remove those vent covers and make my way down stairs, unwind the extension cords and run them through each of the access ports. 1 for the kitchen, 1 for the living room, 1 to the master bedroom, and 1 to the kids room.

Kitchen extension cord will be just for the fridge and a light
Living room cord is for lights tv/radio and charging of cell phones/tablets/laptops
bedroom cords are for lights and small tv in kids room as well as cell/phones/laptops

We also keep a portable single burner induction cooktop. It, along with our instant pot will allow us to cook food with relatively little power consumption.

A 10Kwh 48v battery should be enough to get you through a weekend of no grid power with ease. The portable solar panels will help recover some of the power in the day.

I did not go this way though as I ended building a portable power station instead. We have tested it and works great for a weekend of no power.
It's a smaller 24v 6kwh battery based system with 2kw inverter that all fits in a large toolbox with a handle and rollers. It stays in a closet for most of the time. In a power outage it rolls out and I can plug extension cords and usb chargers right to it. Only problem with it, is making sure it's stays charge. Aside from the test we have not had to use it.... yet
I check up on it once a month to check it's charge level. I can take it outside and top it off with the portable solar panels, or simply plug it to a 24v battery charger.

 

[nickskethisnikske]

I have such inverter (sun2000) bought from gwl, works very nicely, but keep it out high humidity air they are not designed for outside.

You can look for the 48V charger at those eltek flatpacks (1800-2000W), sometimes you find those pretty cheap. You can control them over canbus with an Arduino. And have PFC and are extremely efficiënt!