diy solar

diy solar

SMA Sunny Boy capabilities

I'd like to know too.

Sunny Boy has no way of knowing power to/from grid.

Sunny Island knows what flows it to grid (or at least to other household loads), but has no way to regulate Sunny Boy power output while frequency is set by grid. It does have RS-485 to older models, but no such control functions over it that I know about.

Sunny Boy can have a Speedwire connection. An external device can command over that. SMA has some such products, working with 3rd party watt meter and the internet. Don't know if it works without internet.
 
I looked at the recommended battery for a sunny boy with storage. Looks like I'm looking for a sunny island instead.
The battery cost for the sunny boy storage was a shock.

I'm trying to make sense of ac coupled vs dc coupled inverters with a goal of minimal investment in batteries, just enough to carry the critical loads for a few rainy days . If needed, I'll have a small gas generator as well, but haven't bought one yet.

What is the advantage of dc coupling vs ac coupling ? Is there a thread that covers pros and cons?
 
There is a power loss roughly proportional to how large a voltage conversion takes place.
Boosting 12VDC to 120Vrms has more loss than 48VDC to 120Vrms, which has more than dropping from 200VDC to 120Vrms.

You can look at efficiency numbers (often a single value) and curves of efficiency vs. power and DC voltage (which a few manufacturers publish) to see how DC coupled PV --> battery --> AC should perform compared to AC coupled PV --> AC (and a portion going AC --> battery --> AC)


With minimal battery, pay attention to maximum charge rate of battery. For lithium, that is lower as temperature approaches freezing.

For DC coupled, you either need battery large enough to accept 100% of PV, or an SCC (or AIO) that is aware of battery charge current and reduces power output accordingly. While producing more power when needed for inverter.

With AC coupling (or a hybrid with high voltage DC bus like SolArk), bidirectional battery inverter only draws the amount of power needed for battery charging. Power is harvested from PV as needed for AC loads including battery charger (SolArk usually pulls power from HV DC rail for battery charging, but can also pull from AC.)

Smaller DC coupled systems are simple. The limitation of battery charge current can be accomplished with extra equipment, for some brands (e.g. Victron, Midnight.)

AC coupling lets PV sources be distributed across AC distribution grid, e.g. on outbuildings. Typically more expensive than DC coupled, but competitive for large PV array and large AC capacity during the day.

Both can be used for large battery systems, and DC coupled will be more efficient at battery charging.

I hear AC coupling with high-frequency battery inverters doesn't work as well; they are limited in ability to switch direction of current flow. This would include Skybox, SolArk, others.
With low-frequency transformer type battery inverters, supposedly they don't have that issue. SMA is the brand I use, and I think they invented AC coupling and GT PV inverters.

For Sunny Island and Sunny Boy, recommended minimum battery size is 100 Ah (at 48V) per Sunny Island and 100 Ah per 1kW of GT PV. Maximum GT PV is 2x the size of battery inverters (most other brands say 1x).

I have GT PV 0.5x battery inverter size (due to export limits while grid tied; will increase towards 2x if net metering goes away.)
My battery is the recommended minimum size for Sunny Island battery inverter, but 1/3 recommended size for GT PV.
It works well, charging battery as sun comes up and powering A/C and other loads directly from PV.
Most of the time, it is on-grid with GT PV backfeeding for net metering.


Gas generator - some newer inverters have so much trouble with the AC from a generator that it is recommended you use it with a separate battery charger.
Older low-frequency transformer type inverter/chargers usually accept wider voltage/frequency range of generators, and have always been used with them.
 
OTOH, I could just use the 110v 2kw secure power outlet on a sunny boy and a charger to charge a pair of deep cycle batteries (24v 200 ah total, 100 ah usable ) during our 3 or 4 hours of peak sun, and yet another inverter to run the critical loads panel from the batteries. Around and around I go, losing power with each step... :ROFLMAO:
 
For the SI, I think you need a 48v setup. Generally 4x12v batteries at least. You can go to 46v but that is a different subject. But 100AH is gone in no time. Used/new forklift battery?

The SBS batteries are expensive. You can get others, but warranty might not apply unless you use SMA approved batteries. 512v batteries are usually for UPS backup systems for telecom, etc. If a 51.2v server rack can be wired in series to get the 512v the SBS needs, then those might work. Most can't though. Still, that is 10 server rack batteries at say $1,500 each = $15,000 for 51kwh storage. All in all, SI's are still a good way to go.

Keep the fridge doors closed and they might last through the night til the sun comes up again. The secure power supply is nice that way - no batteries needed.

Not easy to decide what to to. At some point you realize that being your own power company is not so easy.
1 SI for 120v = $3,000
2 SI for 240V = $6,000 +/-
Battery =min $1500, sky is the limit
Battery for over night power for a few days, probably 15-20kwh min = 4 server batteries = $6,000 SB can run stuff during the day so you only need the batteries for night time use. If you are super careful and only power fridge and a few lights at night, 5kwh might do it. Still, that is probably $10,000 right there.
 
Last edited:
OTOH, I could just use the 110v 2kw secure power outlet on a sunny boy and a charger to charge a pair of deep cycle batteries (24v 200 ah total, 100 ah usable ) during our 3 or 4 hours of peak sun, and yet another inverter to run the critical loads panel from the batteries. Around and around I go, losing power with each step... :ROFLMAO:

Manually enabled each day when sun comes up.

Just hand over $10,000 and be done with it!

 
Just hand over $10,000 and be done with it!

That is probably it.
Although I heard that you can plug into the F150 Lightning battery pack and use that as backup power. Not sure if you want to use a $70K battery for that though. Or go caveman - salt the meat, no A/C, no running water, candles, etc.
 
OTOH, I could just use the 110v 2kw secure power outlet on a sunny boy and a charger to charge a pair of deep cycle batteries (24v 200 ah total, 100 ah usable ) during our 3 or 4 hours of peak sun, and yet another inverter to run the critical loads panel from the batteries. Around and around I go, losing power with each step... :ROFLMAO:
One thing I immediately noticed that will really help is the ability to output high voltage stuff (210 .like the well pump, water heater, induction cooktop, even a clothes dryer on the critical needs box.
If I don't try to run them at the same time, but they can be wired correctly to a High Voltage Critical Loads Box. CN box goe on the west side of house with the arrays inverters batteries, etc.
This is all beginning to make some sense.
I intend to run 110v and lower for lights, modems, USB devices, etc throughout the house. (Must rewire the whole house anyway.,this is background.)
The only high voltage (220 ) needed ever on the east side are luxury circuits for us like the HVAC and a hot tub , clothes washer and dryer ,and all run directly from the main box.

While the whole kitchen will go to the CNbox, and all the lower voltage led lights throughout the house goes there too. As well as outlet from the array or battery or the grid all goes to CN box.
 
That is probably it.
Although I heard that you can plug into the F150 Lightning battery pack and use that as backup power. Not sure if you want to use a $70K battery for that though. Or go caveman - salt the meat, no A/C, no running water, candles, etc.
Indeed. My cave man days are long past. I still smoke the meat, but I do it in an electric smoker sitting on a patio with an electric fan and a cold beer from an electric refrigerator ...
 
'Manually enabled each day when sun comes up. 'Sure . While outside to feed the chickens anyway ....
And I haven't mentioned "rebate hell "... when you must replace every appliance in your home with whatever energy star version you can get at the same time as a government tax loophole to qualify ... scams will abound.
 
For the SI, I think you need a 48v setup. Generally 4x12v batteries at least. You can go to 46v but that is a different subject. But 100AH is gone in no time. Used/new forklift battery?

The SBS batteries are expensive. You can get others, but warranty might not apply unless you use SMA approved batteries. 512v batteries are usually for UPS backup systems for telecom, etc. If a 51.2v server rack can be wired in series to get the 512v the SBS needs, then those might work. Most can't though. Still, that is 10 server rack batteries at say $1,500 each = $15,000 for 51kwh storage. All in all, SI's are still a good way to go.

Keep the fridge doors closed and they might last through the night til the sun comes up again. The secure power supply is nice that way - no batteries needed.

Not easy to decide what to to. At some point you realize that being your own power company is not so easy.
1 SI for 120v = $3,000
2 SI for 240V = $6,000 +/-
Battery =min $1500, sky is the limit
Battery for over night power for a few days, probably 15-20kwh min = 4 server batteries = $6,000 SB can run stuff during the day so you only need the batteries for night time use. If you are super careful and only power fridge and a few lights at night, 5kwh might do it. Still, that is probably $10,000 right there.
Wow. I am glad to see a real world answer. And like it or not, a real world solution is going to include a few thousand more dollars for a diesel generator that puts out the whole rated power of the CN box.
 
Yup. Got that also. 20kw diesel with 300 gallons of fuel (purchased at $2.19/gal) (worth millions now.) We started out with a small 5k inverter that we ran off of our 48V forklift (2 birds with 1 stone). That ran fridge and lights fine for a few hrs, but not a good long term multi day solution. Inverter would not run a water pump, so no water. Upgraded to 2 SI 6048 and a new fork lift battery (double duty again - use in fork when the old 17year old battery gives it up plus an extra now). That is fine for a few weeks w/o power, but also not great for long term (running A/C 24/7), so we got 2 more SI so we have "true" 100A service (56A x 2 at 240V). FLAmps from the A/C is over 100A, 2x SI will do it, but not great for long term either. The good thing about the SI/SB option is that you will hardly ever need the generator. SB can power house during the day light hours and SI takes power from the battery to power smaller loads at night. So you really only need enough batteries to make it through the night. Course it also depends on where you are and how much sun you get. Here in Ca, solar can run all the big loads during the day, then at night you only need enugh for fridge, lights, etc. Run dryer, water pumps, etc. all during the day when the solar is available. It is sort of a big change from when peak/off peak rates meant it was best to run big loads at night. Now peak/off peak is also mostly the same and makes no sense to run anything at night anymore. With more EVs around, using them for a few day of back up is not a bad idea.
 
Excellent. We have a stable grid and cheap ish electricity and cloudy skies in Pennsylvania, We also have a good grid buy back program with the the local power supplier and my old system still saved me some money. But nice weather, stable cheap electricity, and cheap diesel can all vanish virtually overnight.
 
There are many kinds of GOOD batteries today, and some very slick electronics to keep them charged up. This is an example from a company I'd never heard of ... EG4.

Signature Solar

Signature Solar provides solar components and full kits for off-grid, grid-tie and custom diy solar systems. Providing Solar 101 and hands on experience within the solar industry. Quality inverters, bifacial solar panels, complete solar kits, solar batteries. Holding best in class brands such as...
signaturesolar.com
signaturesolar.com

Maybe 2 or 3 grand in batteries and ALL electronics from some such company, and twice that much in panels and mounts seems like it buys a lot of resilience , even if it won't run the whole house.
 
:ROFLMAO:

May I suggest you do read the related threads on this forum?
Start to finish, including the ones with > 1000 posts?

:)
 
Not saying they don't have satisfied customers. Some have posted here.
But there have been some very vocal ones ...
 
SS started carrying Schneider recently.



Alt E Store is another retailer well known to people here.



SanTan is a liquidator, also well known to forum members.



Be sure get an inverter that meets your needs, and in the case of lithium, a battery that works well with it (may mean communications compatibility)
 
Appreciate the leads to retailers that have been around awhile. I remember talking to someone about a well pump at alt e a decade or more ago . I will probably overbuy on an inverter and battery.

TBH, at my age I am not looking at payback as much as prepaying for energy while it's still affordable and as insurance that power will be still available if the cheap and stable grid suddenly isn't there for weeks, months, or a whole season.
 
Back
Top