DIY Solar Whole Home Solution Gen + Critical Services

[JReich2609]

Hi there -

I need some assistance in designing a system that must meet several requirements. This discussion is NOT about the number of solar panels, etc. I am focusing on the pre-wiring necessary during new home construction to tackle those steps later.

The house will have a 400 AMP service in the pump house location. From there, the service will split into (2) 200 AMP services that will go into two panels in the garage. To supply backup power for both the well system and the home - the current plan is to install a 400 AMP Generac transfer switch at that location. A propane generator will be installed down the road to supply that service.

In addition, this initial contact point seems like an excellent place to install an AC-coupled solar system. AC is being considered, as I have no interest in storing solar energy for later use.

We are obviously grid-tied, and our goal is to decrease our power bill and replace it when possible. However, we are not interested in long-term battery storage, which would likely make more sense with a DC-coupled system. There is an exception, though, that complicates things.

Several CRITICAL switches in the home cannot disrupt service during the time it takes for the power outage and the generator to kick on and provide service. For this discussion, let's assume I need to gap 5 minutes reliably. These critical services will include (2) 30 AMP breakers and (1) 20 AMP breakers. This will power critical technology, so the pulls on the 30 AMP breakers will always be decently significant.

This means I need an inverter in the system with an appropriately sized battery to cover the 100 AMP sub-panel with these switches inside it. Again, I am not too concerned with the size of the battery and things of that nature. The battery capacity can be expanded to meet the actual need of service.

So my questions:

1. What AC coupled system would be the best-recommended system to install for the house with appropriate sizing (48v system) to cover the home?
2. What system would best recommend providing a GAP to critical services when grid-tied power becomes unavailable? But before the generator can kick in to provide coverage?

Also, I welcome to any feedback or additional thoughts. This is a fact-finding exercise to gather input.

Thanks, all!

 

[BentleyJ]

If you don't anticipate installing any kind of back up system or batteries. The easiest way to install grid-tie solar is with microinverters that will feed directly into one or both of the 200A panels.

Regarding the critical loads, I would seriously consider a self contained computer/data center UPS rather than an inverter based solution. You will have to be a little more specific about the current draw of the critical loads. The statement above is a bit vague. "so the pulls on the 30 AMP breakers will always be decently significant." Are these 120V or 240V breakers? Will make a significant difference in the capacity of the UPS needed and also the price.

 

[JReich2609]

Thanks for the feedback!
I was looking at the SolarEdge PV Inverter (or something similar). I intended to tie it into the 400 AMP panel, but I could also tie it into the 200 AMP panel without too much hassle. Again, I am open to feedback.

It will be 30 AMP 240V that will be converted for rack use. I can do UPS systems per rack, and I have certainly done that before. I also need to provide UPS with additional network racks that will feed off the 20 AMP 120V, which can all have independent UPS systems. But given the need, I was looking for something a little more holistic.

 

[wpns]

If you need a 7.2KW-class computer UPS you might want to look at the EG4 ESS (18Kpv plus PowerPro batteries), as it may end up being less expensive. If you are seriously into 50+KW generator, etc, then DIY solar isn’t going to help with that. Not that you couldn’t, just that you shouldn’t have your first DIY project be at that scale.

 

[Lawrence_SoCal]

We are obviously grid-tied, and our goal is to decrease our power bill and replace it when possible. However, we are not interested in long-term battery storage, which would likely make more sense with a DC-coupled system. There is an exception, though, that complicates things.

I just had a rooftop solar install, and my system does NOT have a hybrid inverter, so no inexpensive way to power from battery in a grid-down situation. As you are looking for future-proofing, and NOT whole-house (or even sustained critical load) battery backup, I'd suggest considering wiring such that adding a hybrid inverter at some future point, becomes less 'involved'. And leave physical room for whole house battery backup. Personally, I suspect most future residential whole-house battery solutions are likely to be more like LFP in terms of run-away thermal risk (ie, not like Li-Ion), so with most batteries doing better in temperate controlled space, I'd consider where you place them (indoors) and also avoiding making wiring them up 'problematic'.

Wiring implications depends on whether you plan something like a SPAN panel(s) to manage whole house load while on generator, or is generator (and /small/ battery) only powering critical load subpanel?
And as I ponder, I'm guessing you actually will have a hybrid inverter (create own micro-grid when grid down), and auto start generator? If yes, with right hybrid inverter, easy peasy to add battery... as noted above, quite possibly cheaper to get configured for your use case than server type UPS.. I have an APCC SU RM UPS here in my office), especially that can handle that many Amps [eg. see Will's recent video on EG4 PowerPro indoor only wall-mount battery].

I'm fortunate in that I'm on a non-curtailment circuit from PoCo. But stuff still happens on rare occasions. Having a whole house battery is absolutely in my future plans, and the electrician costs for main load center and related wiring likely to many thousands of dollars. In my case, made sense to wait to have such work done, as 45 yr old house, and future electric needs uncertain with potential move (in decades to come) if/when moving from some natural gas to electric appliances (which I presume will happen at some point, just don't know when)
My point, in new house construction, just as I'd wire shielded ethernet into every room (and then some. ex. think PoE security cameras including outdoors, etc), I'd also make sure adding a hybrid inverter and whole house batteries is a minimal effort activity. Really want to future proof stuff... make sure that networking stuff is in conduit so you can easily pull new/replacement as needed (for when 100gb/s fiber to desktop is standard ;^) ... no, I don't mean independent full-length conduit runs from every outlet to MDF location.. things like unfinished attics, and elsewhere, simply want to make sure you can replace current data networking cable with somethign newer/faster without ripping out walls. And no, WiFi is NEVER as fast and stable as wired Ethernet (though better in a rural environment), so no, I don't consider that a viable long-term alternative... but I digress

 

[wheisenburg]

In addition, this initial contact point seems like an excellent place to install an AC-coupled solar system. AC is being considered, as I have no interest in storing solar energy for later use.

I agree with you here. Your best option to meet your first stated goal of power bill energy offset is a AC grid tied system. In order to prevent undesirable and damaging interaction between your grid tied PV and your generator, your simplest and least expensive option is this:

1. Install a 400 amp disconnect on the grid connection as the first component of the system just after the meter. This will allow you to turn off the incoming power to the system so it can be worked on without requiring that the incoming service be disconnected.
2. Connect a fused disconnect between the grid disconnect and the ATS. This would provide the connection point for the grid tied PV.
3. At this point you would connect the disconnect to either Solar Edge type inverter or a combiner box that was hooked to micro inverters.

This avoids all the complications of trying to use Hybrid inverters like Sol Ark.

 

[wheisenburg]

Several CRITICAL switches in the home cannot disrupt service during the time it takes for the power outage and the generator to kick on and provide service. For this discussion, let's assume I need to gap 5 minutes reliably. These critical services will include (2) 30 AMP breakers and (1) 20 AMP breakers. This will power critical technology, so the pulls on the 30 AMP breakers will always be decently significant.

For your second stated goal what you need is an off grid (as opposed to hybrid inverter). Now an off grid inverter is not strictly required. It just needs to be possible to configure the inverter to not attempt to export power. As for sizing we have 60*240 + 20 * 120 = 16,800 watts max. So 16,800 / 50 = 336 amps of DC. This is the worst case based on your breaker sizes. Most of these 100 Amp Hour server rack batteries can deliver 100 amps continuous, so we need 4 such batteries. One more issue is that 240 volt breakers should always pull a balanced load from the inverter. If using a high frequency inverter you need to calculate 30 * 240 + 20 * 120 = 9600. Then 9600 * 2 = 19,200. The reason is that a high frequency inverter is really two 120 volt inverters tied together. So to actually get two 9600 watt inverters, you will need to buy inverters rated for 19,200 watts.

2 Schneider 6848 low frequency inverters should handle this load with no problems. Although they are only rated at 6800 watts each, that is their continuous rating. Two of these can surge to 24,000 watts for a full minute. Also, because of their low frequency design, they can handle unbalanced loads with no issues. Many competing inverters have trouble supplying their rated output even instantaneously.

Now one thing to consider is how sensitive is the equipment to glitches. In my house the transition from AC to backup does effect some equipment. My computers will always stay on, but sometimes my router will reboot. Probably it is an issue that the cheapy wall wart power supply cannot ride through the power drop. Best case the inverter needs some time to figure out that the power has dropped. Then it needs time to switch over to the inverter mode. The only way to completely eliminate this switching time is to basically have chargers and inverters back to back. If you lose power in that case the chargers will quit, but the inverters will continue to run uninterrupted. Some inverters may have a faster switching time. Alternatively, you could provide a true "UPS" for any equipment that is extremely sensitive.

In any case it is likely that the right quantity of any stackable inverters is going to work OK. Sol Ark or the large EG4 inverters would also be good options.

 

[wheisenburg]

Maybe I oversized things here. If you have a better idea of exactly how many watts are need, then you can scale the system down. You do need to make sure that you size the inverters for (1/2 of your 240 load + your 120 load) * 2 if you go with a high frequency inverter like Sol-Ark. The batteries can still be sized for total watts. Because you are talking about 5 minutes, the batteries need to be sized to provide enough amps. Amp Hours should not be an issue.