What equipment for battery export?

[Matthewpk]

I'm doing a lot of reading and learning but I'm not sure what keywords to use to learn about my use case.

I have a grid tied system with no batteries today.
I'm not interested in complete grid independence.


However, my net metering isn't great. I get 15% on the exported power, and I significantly overproduce during the day, roughly 250% of daily use

This is a cabin that's usually unoccupied but has about 800w constant draw

So I'm interested in learning about how I might attach batteries to get me through the night. If the grid goes down I'm ok going down, and I'm ok exporting from batteries to grid. I'm imagining there's a way I can setup batteries to max discharge 1kw, which covers my constant usage.

When I try to search for equipment for such a setup I'm generally finding only systems with rapid switching so they go to battery if grid fails.

What should I look into? Thanks!

 

[Gold Country Russ]

Contact the utility and say you want to see if you qualify for the SGIP program. In PG&E land (N of LaLa land) that is a $200. per KWH rebate.

 

[DIYrich]

Post what equipment you have.

 

[Matthewpk]

Post what equipment you have.

I have timberline solar shingles and a delta M6-TL-US inverter.

It's not feasible for me to have a critical loads panel, but I can add a panel in the room where the inverter is, and where the batteries would go.

I'm open to buying new equipment

I don't want to attach anything at the grid connection. Currently my inverter is in a utility room far away from the main panel, back feeding it.

 

[Matthewpk]

Contact the utility and say you want to see if you qualify for the SGIP program. In PG&E land (N of LaLa land) that is a $200. per KWH rebate.

I'm in Big Bear lake, which is an independent grid and not subject to the common California NEM

 

[Hedges]

However, my net metering isn't great. I get 15% on the exported power, and I significantly overproduce during the day, roughly 250% of daily use

Possibly the most cost effective would be to overproduce, making 700% of daily use. Then that 15% credit is enough to cover the time when you're not producing.

PV panels are cheap. DIY GT PV might cost $1/W, and amortize to $0.025/kWh over 20 years. Making 7kWh for every 1 kWh you actually consume would be about $0.18/kWh, maybe or maybe not a savings over grid prices.

This is a cabin that's usually unoccupied but has about 800w constant draw

What draws the power? Can it be switched with a timer so it draws when PV is producing, coasts through the night?

So I'm interested in learning about how I might attach batteries to get me through the night. If the grid goes down I'm ok going down, and I'm ok exporting from batteries to grid. I'm imagining there's a way I can setup batteries to max discharge 1kw, which covers my constant usage.

When I try to search for equipment for such a setup I'm generally finding only systems with rapid switching so they go to battery if grid fails.

What should I look into? Thanks!

"Peak Shaving" is one approach. Battery charges attempting to zero export, discharges attempting to zero import, with current transformers at grid connection.

I picked up Sunny Boy Storage & LG RESU-10H plus Watt-node which by default configuration does that.
It would take two of the 9.8kWh batteries to cover your 20kWh/day consumption.

This particular equipment, at msrp, costs $0.50/kWh so not cost effective. Other brands of hybrid inverter plus battery may get down to $0.10/kWh (amortized over battery's 16 year cycle life, and ignoring time value of money.)


How much does it cost to simply buy power from the grid when PV doesn't cover it?
Have to compare cost of any battery + inverter equipment with that.

 

[DIYrich]

I have timberline solar shingles and a delta M6-TL-US inverter.

I'm open to buying new equipment

Does not look like the inverter is battery ready. Consider replacing the inverter with an eg4 18k or sol-ark 15k.

3000 or 6000xp may work. A little trickier to implement charging from ac pv.

3000 or 6000xp would easily work if you are willing to give up exporting, and buy enough battery (20kwh for 800 watt continous).

 

[Matthewpk]

Does not look like the inverter is battery ready. Consider replacing the inverter with an eg4 18k or sol-ark 15k.

3000 or 6000xp may work. A little trickier to implement charging from ac pv.

3000 or 6000xp would easily work if you are willing to give up exporting, and buy enough battery (20kwh for 800 watt continous).

Even with those devices I'm trying to find out how to learn about the use case.

Most content I find is about battery backup for grid outage. I'm looking to maintain grid connectivity but import zero most of the time.

 

[Hedges]

I think what you want is something like Powerwall - without backup.

https://www.tesla.com/support/energy/powerwall/learn/how-powerwall-works

Any of the hybrids that support CT targeting zero export should also do that. And easily provide a backup panel - if you have alarm or monitoring equipment, that could stay on during grid outages.

But you have to compare costs with your utility rates, may not provide any savings.
Products have been marketed and sold which cost more than they save. Some are still priced that way, but many are competitive for people with our higher California energy prices.

 

[DIYrich]

I think what you want is something like Powerwall

One powerwall is fine if all you need is 13kwh. If you need more battery, components start making more sense. Pay for inverter once, and add as much battery as you need.

 

[DIYrich]

Most content I find is about battery backup for grid outage. I'm looking to maintain grid connectivity but import zero most of the time.

Then you want to maximize self consumption. You can do that with an off grid system. 6000xp can store all the power in the battery, and then take from grid when battery runs down. Gives you grid backup, but you can't export to grid. For the cost difference between 6000xp and 18kpv, it can pay for a 15kwh powerpro.

For the cost of one powerwall you can get twice the capacity.

How many kW of solar do you have? Average daily production?

 

[Matthewpk]

Then you want to maximize self consumption. You can do that with an off grid system. 6000xp can store all the power in the battery, and then take from grid when battery runs down. Gives you grid backup, but you can't export to grid. For the cost difference between 6000xp and 18kpv, it can pay for a 15kwh powerpro.

For the cost of one powerwall you can get twice the capacity.

How many kW of solar do you have? Average daily production?

The system has only been operating since February but average daily production 32kWh
Average daily usage 13kWh.
Average daily from grid 6.5 kWh


What feature name should I have tried to look up to learn that the 6000xp could do this? For example it's advertised as an off-grid inverter so I would have assume it could not be grid tied.

 

[Matthewpk]

I think what you want is something like Powerwall - without backup.

https://www.tesla.com/support/energy/powerwall/learn/how-powerwall-works

Any of the hybrids that support CT targeting zero export should also do that. And easily provide a backup panel - if you have alarm or monitoring equipment, that could stay on during grid outages.

But you have to compare costs with your utility rates, may not provide any savings.
Products have been marketed and sold which cost more than they save. Some are still priced that way, but many are competitive for people with our higher California energy prices.

In this context is "CT" an abbreviation for something?

 

[DIYrich]

The system has only been operating since February but average daily production 32kWh
Average daily usage 13kWh.
Average daily from grid 6.5 kWh


What feature name should I have tried to look up to learn that the 6000xp could do this? For example it's advertised as an off-grid inverter so I would have assume it could not be grid tied.

"Grid tied" means can export power to the grid. Almost all AIO can take power from the grid, just like they can take from a generator. The grid is a big generator.

 

[DIYrich]

In this context is "CT" an abbreviation for something?

A CT measures the power flow. If you put it on the line to the meter, the inverter can zero power movement across that point.

 

[Gold Country Russ]

What pulls .8KWH all night? Refrigerator, freezer, lights, heat traced pipes, water heater, or what? Our family use to have two cabins at Big Bear from 1940's to 1970's.

 

[jpwhit]

Just joined the forum, but have been doing solar and DIY battery storage for quite a while.

The GoodWe A-ES series inverter will do exactly what you want. If you can get away with 2 MPPTs then a GW5000A-ES will probably be enough. And I think it's a good deal at around $2600. If you have to have more MPPT inputs, then you'll need to move up the GW7000A-ES with 4 MPPT inputs. The GoodWe is a High Voltage battery hybrid inverter so the battery part is super-efficient and because it's high voltage you can put the batteries pretty much anywhere you want because the current to and from the batteries is quite low. The GoodWe A-ES series will also give you complete backup if you want it if you buy the optional auto-former which is only about $350.

In a nutshell, the way it works, in the default mode, is any PV power coming into the inverter will first go to satisfy any demand from your house, next any PV power above that will charge the batteries, then as the battery approaches 100%, any excess PV is fed back to grid.

When PV generation falls below the level of power the house is demanding, the inverter will draw from the batteries, when the batteries hit the cutoff state of charge you set, or if the demand from the house is more watts than the inverter can provide, it draws power from the grid. In your case, unless you have a lot days with very little sun, sounds like you'll almost never need any power from the grid.

I've been using the GoodWe GW9600A-ES inverters at my houses for well over a year now and have been extremely impressed. In my case, I built my battery storage system from surplus Tesla Model 3 and Y battery modules. I have 210kwh battery storage at my lake house and 120kwh at my main house. That's way more than you would need, but since I'm using surplus Tesla modules it only cost me about $50 per kwh. In my case, I have 2 Tesla cars and the solar and ESS system provide all my power for the houses and all my charging for my EVs.

In your case, I would think maybe as small as 15kwh or so would be all you'd need to avoid buying power from the grid on a day-to-day basis. More if you wanted go multiple days. In your case, I'd probably look at BYD High Voltage battery. This may not matter in your case being with an independent power company, but I remember seeing that GoodWe inverters are on the California approved lists.

 

[DIYrich]

The GoodWe is a High Voltage battery hybrid inverter so the battery part is super-efficient and because it's high voltage you can put the batteries pretty much anywhere you want because the current to and from the batteries is quite low. The GoodWe A-ES series will also give you complete backup if you want it if you buy the optional auto-former which is only about $350.

How much are the high voltage batteries? Where can you buy them?

 

[Hedges]

In this context is "CT" an abbreviation for something?

"Peak Shaving" is one approach. Battery charges attempting to zero export, discharges attempting to zero import, with current transformers at grid connection.

Oops, I knew I had said "Current Transformers" earlier, but turns out I didn't also say "CT" the time.

They snap around a wire, measure the AC current. Together with voltage it shows power flow, both watts and direction (import vs. export).

Because they work off magnetic field, you could run a wire from another circuit through them to measure sum or difference (e.g. if I also ran PV wire through it in the right direction, I could measure total consumption ignoring power from PV that landed on same breaker panel.)

In your case, battery or hybrid inverter with CT could charge battery to avoid export that gets the low 15% credit, then discharge to avoid import that costs you money.



I'm trying that out with this product, Sunny Boy Storage.
The energy meter I'm using does not wire in-line with power, rather has current transformer like shown above.
(SBS + LG RESU-10H battery does not make sense financially, but I got them at liquidation prices. You can buy inexpensive hybrids that make more sense.)

https://files.sma.de/downloads/SBSXX-US-DS-en-22.pdf

 

[Hedges]

One powerwall is fine if all you need is 13kwh. If you need more battery, components start making more sense. Pay for inverter once, and add as much battery as you need.

For 20 kWh of daily usage, 13 kWh should be just about right for the night. On grid, so OK if a little over or under.

How much are the high voltage batteries? Where can you buy them?

The HV batteries from BYD (used with SMA inverters) cost about 2x what 48V server rack or PowerPro batteries do.

I'd be interested in lower cost HV alternatives.
Or what DIY BMS works with the inverters.