Seeking Advice: Low Voltage vs. High Voltage Batteries for Home Energy Storage

[Emily Y]

Hey everyone,

I'm currently planning a home energy storage system to complement my solar setup, and I'm torn between using low voltage batteries and high voltage batteries. I've done some research, but I'd love to hear from those who have hands-on experience or insights into the pros and cons of each option.

From what I gather, low voltage batteries fit lower electricity loads. On the other hand, high voltage batteries seem to offer higher efficiency, reduced losses during charging and discharging.

I'm particularly interested in hearing about your experiences with either type of battery. What factors did you consider when making your choice? How has your chosen voltage option performed in terms of reliability, maintenance?

Any advice, tips, or personal anecdotes would be greatly appreciated!

 

[green mountain boys]

Hey everyone,

I'm currently planning a home energy storage system to complement my solar setup, and I'm torn between using low voltage batteries and high voltage batteries. I've done some research, but I'd love to hear from those who have hands-on experience or insights into the pros and cons of each option.

From what I gather, low voltage batteries fit lower electricity loads. On the other hand, high voltage batteries seem to offer higher efficiency, reduced losses during charging and discharging.

I'm particularly interested in hearing about your experiences with either type of battery. What factors did you consider when making your choice? How has your chosen voltage option performed in terms of reliability, maintenance?

Any advice, tips, or personal anecdotes would be greatly appreciated!

What do you consider to be "high voltage"?

 

[Ampster]

I am using 35 kWhs of nominal 48 volt batteries and have plenty of capacity and power. I installed it myself and not sure one can do that with anything higher than 48 volts nominal.

 

[LakeHouse]

Yeah, as above: what is high voltage to you?
I also run 48V nominal and I think it was the right choice.
I see lots of people on the forum struggling with massive cabling for 12V systems that require hundreds of amps and I’m glad I’ve avoided that.

 

[Emily Y]

I am using 35 kWhs of nominal 48 volt batteries and have plenty of capacity and power. I installed it myself and not sure one can do that with anything higher than 48 volts nominal.

Thank you. Do you have EV need to charge at home?

 

[Brett V]

Once you venture in to the realm above 48 volt systems, you’re mostly leaving the DIY category behind. The equipment and the personnel qualified to work on it get expensive.

 

[Ampster]

Thank you. Do you have EV need to charge at home?

Yes, I have two EVs, an electric dryer, electric heater pump for heating and cooling. Soon, converting water heater to electric. The heat pumps will run off batteries. The dryer and EVs run off excess solar or low cost grid overnight.

 

[Emily Y]

What do you consider to be "high voltage"?

I searched a battery from Goodwe, their nominal voltage are 192 to 384 volts and cover 9.6 to 19.2KWh. So what are differences if I use a 48V battery for my 25kwh demand?

 

[Ampster]

....... So what are differences if I use a 48V battery for my 25kwh demand?

I think in terms of kWh capacity so there is no difference between a 19.2 kWh high voltage battery and a 19.2 kWh 48 volt battery.
A 192 volt battery would be 100 Ahrs to have a capacity of 19.2 kWhs
A 48 volt battery would be 400 Ahrs to have the same capacity.
In terms of other differences, it would be choice of inverter that would have to match battery choice. I am only familiar with 48 volt inverter choices.

 

[Solar Guppy]

All the high voltage batteries available only work with active BMS communications between the battery and inverter and its the protocol is proprietary though many inverters are using the Pylontech HV protocol. These HV systems are very safe as all are UL9540, much lower costs for balance of system parts, but they are higher cost on the $$/Watt metric.

If and or when more consumers are willing to pay for electrical backup for residences and those that do want more than a critical loads panel, the currents on 48V batteries becomes unmanageable with the need insanely large wiring, so from a technologist view I see HV being the dominate choice, but no one knows when this crossover may happen.

 

[stojo107]

I recently asked about High voltage (>48) vs 48v ESS to an engineer at SMA, see their response below. I found it helpful.

HV batteries are more efficient and require smaller conductors due to the higher voltage limits. Also, they are able to charge and discharge more rapidly than LV batteries, and can provide more instantaneous power. The overall concept for battery technology has matured, where historically PV/Battery systems used Lead Acid (2V, 6V, 12V) batteries with very low voltage but very high capacity (AmpHours). This inherently requires larger gauge conductors, intimate knowledge of how lead-acid behaves and is operated and limitations of that technology, such as bad practice to drop the SOC to very low states. This architecture functionally worked but has design limitations (50% usability of raw capacity) and operational characteristics (different charging behavior float, bulk, equalization, etc). There isn't discreet battery cell information, just average over the system, so this makes diagnosis and troubleshooting more of a challenge.

With high voltage lithium batteries, they are constructed in a similar fashion, with modular 'blocks', so each block has a contributing voltage that gets added up and similar capacities (Amp Hours) also add up. There is also a BMS (Battery Management System) which collects individual block data and can share information on the overall system, with fine tuned block data too (which is communicated to the inverter, taking out much of the battery algorithm control inverter has to do). With newer improved, lower cost components (in both battery cabinet and inverter) that can handle these higher voltage scenarios, it is now cost effective to use higher voltage batteries to achieve the same overall outcome for battery storage. With 100% usability, this makes for more energy dense systems (less footprint onsite for same capacity)

Generally higher voltage of contributing sources yields smaller conductors for installation, smaller fuses if any, and more energy dense overall system, With higher voltage, there is a higher conversion efficiency, and more granular data between 'blocks' to ensure 100% usability and long term reliable operation.

 

[stojo107]

It makes a lot of sense to me that the trend of ESS voltage increasing over time (12 -> 24 -> 48 -> ??) will continue. SMA's upcoming Sunny Boy smart energy hybrid inverter (just shipped this past week to SMA's distributors) only works with HV batteries (90v+ IIRC), which is really telling. But I'm kinda bummed, bc I really want to use that inverter but SMA said its currently only compatible with BYD HV battery systems, which are like $600/kWh, which is way more than some of the 48v ESS options out there (EG4/Goodwe/etc ~$300/kWh or less). Anyone know of any HV (>48) battery systems aside from the BYD ones? $600/kWh is too much!!

 

[koppted]

It makes a lot of sense to me that the trend of ESS voltage increasing over time (12 -> 24 -> 48 -> ??) will continue. SMA's upcoming Sunny Boy smart energy hybrid inverter (just shipped this past week to SMA's distributors) only works with HV batteries (90v+ IIRC), which is really telling. But I'm kinda bummed, bc I really want to use that inverter but SMA said its currently only compatible with BYD HV battery systems, which are like $600/kWh, which is way more than some of the 48v ESS options out there (EG4/Goodwe/etc ~$300/kWh or less). Anyone know of any HV (>48) battery systems aside from the BYD ones? $600/kWh is too much!!

The problem, as someone mentioned earlier, higher the voltage, the more you're leaving DIY territory, which a lot of us don't want to do. I can't tell you how many times I've touch the wiring live leads on my 48v system, because I really had nothing the worry about. Higher than 70vdc and you're entering deadly voltages in terms simple mistakes.

 

[Hedges]

For the earlier Sunny Boy Storage, several brands of batteries are listed. Expect more to be added for SBSE; it just came out now with one available battery.

Both SBS and SBSE have pretty wimpy surge when operating off-grid, like 20% above continuous rating. And not parallelable.

There are some other HV battery inverters as well, e.g. Solar Edge.

I may install SBSE for a relative, or maybe will use the just-discontinued Sunny Boy. Wanted to be able to add battery for the future.

Kind of ironic that the higher surge inverters use 48V batteries. I've been using Sunny Island, of course.
The HV battery AIO architecture makes sense for grid-tied systems; can process 200% PV, storing half in battery to export later.

 

[stojo107]

Thanks, should I think about the dangers of high voltage differently on the storage circuit vs generation circuit? I suppose if a DIYer is willing/planning to go well over 100v on panel strings, then they should also be willing to go >>48v on the storage side, assuming they follow the same precautions (dry hands, thick soled shoes, rubber gloves) as you do on the panel side?

Now I'm wondering if HV batteries will always come at a price premium because of more costs on safety testing / insulation / misc safety features?

 

[hwy17]

Thanks, should I think about the dangers of high voltage differently on the storage circuit vs generation circuit? I suppose if a DIYer is willing/planning to go well over 100v on panel strings, then they should also be willing to go >>48v on the storage side, assuming they follow the same precautions (dry hands, thick soled shoes, rubber gloves) as you do on the panel side?

Yes you should think about them differently.

A 300v battery is about 100x scarier than a 300v solar string because it can deliver 100x the amperage.

If 96v inverters arrived, I would be interested. But as long as we're not going there, I don't lament 48v. It's nice to work around skin touch safe equipment.

 

[Hedges]

A 480V or 600V PV string has touch-safe connectors.
Battery probably doesn't.

Either can deliver all the current that your body's resistance would allow to flow.
Both can pull an arc.
Battery can deliver enough to make a plasma explosion.

PV panels make power in the slightest light, and don't have a disconnect.
Battery always has power, but may (or may not) have a shut-off switch.

They're different, but each can be handled safely or can present a risk.
Knowledge, test equipment, safety gear, and working practices make the most difference.

 

[stojo107]

Thanks! I'm building some grid-tied systems for neighbors in San Francisco, and I'm finding these battery systems have much higher C rating than cost-optimal for small grid-tied applications. would love to have a C rated LiFePo4 system with C=0.25 so its cheaper and safer. For example, my ideal specs would probably be 8 kWh, 2kW, touch safe connectors, UL9540 compliant. Anything like this exist?!