Large load question

[donb108]

New to the forum, thanks in advance for the help. I just went through hurricane Ida, which ripped one of my load center boxes off the brick wall, so I have electrical work in my future.

Planning to install a whole house generator and some solar. I just watched one of Will's video's on sizing; it looks like I would need a very large battery bank for my loads. So instead, I'm looking to do a hybrid of grid-connected (not sure that's the right terminology), whole house generator, and PV/battery/inverter.

The large loads are: 5 ton a/c condensing unit, 3 ton a/c condensing unit, two hot water heaters with two heating elements each (each element is 4kw, I think), blower motors in the two air handlers (1/2 hp or larger), and 1 kw microwave. The rest of the house is probably trivial; most lighting is LED, ceiling fans are fractional hp, and computers/tv's are under 500 watts each.

The idea would be to run the grid or generator when big loads are needed, but use the solar system for everything else. Is this direction-ally correct, or should I be re-thinking it? Would the batteries be really huge and expensive (over $2000), or did I miss something?

 

[noenegdod]

Do you not have natural gas in your area? Why do you have electric water heaters? Can you take that load out of the equation?

 

[FilterGuy]

You are thinking about this correctly. AC almost always creates a *huge* increase in system size.

It is really good that you are thinking about the loads/needs first. It is surprising how many people start buying and building without understanding what the energy needs are. I would encourage you to do an energy survey/audit to understand the total energy picture. It is a bit of work, but it will pay off in many ways,

The tool I use for this can be found here:

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...

diysolarforum.com

Going through this effort will give you a much clearer view of your energy usage. Not only will it help you size your system but it is likely to point out places where a little conservation would go a long way. It might even point out places where replacing appliances with higher-efficiency models might make sense.

A few notes about the spreadsheet:
* You will likely end up having to make some guesses.... that is not ideal, but it is better than nothing.
* The calculations for sizing the inverter assumes everything is turned on at once. This is fine for smaller systems but is probably larger than needed for your large system.
* Where possible, actually measure the appliance power usage. If you just use the wattage or current listed on the nameplate, it will be much larger than the actual. (Investing in a Kill-A-Watt is advisable.)
* You should do this for the whole house (including the large loads) and then start playing with taking loads out to see what it does to the system size.

 

[Bluedog225]

Others will be along with better answers than mine. Rethinking your approach may be in order. The loads you describe are large and best handed by grid power. A backup system with a small air conditioner is possible. And another way to heat water, like propane or natural gas.

 

[Rednecktek]

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.

1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the Uber-Sun-Hours calculator site to help figure out how much you'll have to work with. That will be a box in the Power Audit form.

2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that.

3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger. Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.

4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.

5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.

 

[donb108]

We live in LaPlace, La, pretty much ground-zero for Ida; yes, we have natural gas...kinda.

Sad but funny story, we lived in Ohio, our daughter lives here in La, so we moved here to be closer to grandchildren. We moved in June, both caught Covid in July, had Ida in August, and we've been rebuilding ever since. It'll probably be more funny than sad in a year or two.

We have natural gas at the house, but the water heaters in the attic don't have gas line taps. In June, we installed a gas line for the laundry room dryer and and added a tap for one of the water heaters at the same time. Switching to gas is a better idea, but not in the cards...yet.

I need to re-work the electric service asap. It's currently an outside mounted, two panel design with 20 slots each, 150 amps main breakers, and zero open slots. I hope to move panels inside, convert to a single panel with lots of spaces, and add whatever's needed to accommodate the generator and solar.

I'm guessing that I just need to add an automatic transfer switch for utility/generator, but maybe more homework is in order. I'll take a look at the energy audit spreadsheet.

 

[OffGridInTheCity]

Agree with comments above. Let me try to add a few cents to the discussion.

Planning to install a whole house generator and some solar. I just watched one of Will's video's on sizing; it looks like I would need a very large battery bank for my loads. So instead, I'm looking to do a hybrid of grid-connected (not sure that's the right terminology), whole house generator, and PV/battery/inverter.

Can you share more of your thinking on... Whole house generator vs solar? On the one hand, if you do a generator for emergency backup you may not need solar at all. On the other hand, if you're like me - I did solar as my primary focus and have a small generator as a backup for winter when solar is much smaller.

The large loads are: 5 ton a/c condensing unit, 3 ton a/c condensing unit, two hot water heaters with two heating elements each (each element is 4kw, I think), blower motors in the two air handlers (1/2 hp or larger), and 1 kw microwave. The rest of the house is probably trivial; most lighting is LED, ceiling fans are fractional hp, and computers/tv's are under 500 watts each.

Perhaps you're thinking generator = large stuff and solar = smaller stuff?

But what about all the time vs emergency. Are you thinking smaller stuff all the time and generator only for emergency?

The idea would be to run the grid or generator when big loads are needed, but use the solar system for everything else. Is this direction-ally correct, or should I be re-thinking it? Would the batteries be really huge and expensive (over $2000), or did I miss something?

Yes, all of this is way more than $2000

 

[BigGun]

Let me start by saying I feel for you -- Ida made that turn right before us in East Baton Rouge but I have friends and relatives through out that whole area

Are you just trying to have Backup power for storms or are you trying to use Solar to cut cost -- What you're describing your loads to be --you'd need a 27k - 30k water cooled generator

 

[FilterGuy]

I need to re-work the electric service asap. It's currently an outside mounted, two panel design with 20 slots each, 150 amps main breakers, and zero open slots. I hope to move panels inside, convert to a single panel with lots of spaces, and add whatever's needed to accommodate the generator and solar.

I'm guessing that I just need to add an automatic transfer switch for utility/generator, but maybe more homework is in order. I'll take a look at the energy audit spreadsheet.

There is a silver lining in this. When you redo the electric service, it is an opportunity to create one or more critical load panels. As an example, you might have one panel that holds the breakers for everything that needs to be driven by the generator and another panel that holds breakers for everything that goes onto the battery.

 

[donb108]

OK, that confirms it; do the energy audit.

Our original intention was to install a 20kw whole house standby generator, running on natural gas. But they have issues (cost to operate, oil changes, maintenance, etc.). So, I started looking at solar again; holy cow, prices have dropped and there's a lot more to pick from.

It looks like I can start small and build from there. Maybe get a 5kw all-in-one inverter/charger, a couple of 100-200 amp-hour batteries, and 1000 watts of PV panels. We don't plan to get caught like this again, so a generator is probably a given. That said, I would like to use it as little as possible. The large loads seem to force the issue.

If I have this right, the all-in-one units can be grid-tied and supplement/reduce energy coming from the grid. I'm assuming a transfer switch can switch back and forth between grid and generator and the all-in-one won't know the difference. The only catch is running the generator full time during a power outage.

 

[FilterGuy]

If I have this right, the all-in-one units can be grid-tied and supplement/reduce energy coming from the grid.

Correct

I'm assuming a transfer switch can switch back and forth between grid and generator and the all-in-one won't know the difference.

Correct.

OK, that confirms it; do the energy audit.

Yes.... and then play with different combinations. Figure out appliances that are not needed at all during a black-out. That will help keep the system size down. As an example, only put one water heater on the generator. Or maybe figure out how to get one water heater on natural gas and not power the other one at all during a blackout. That might mean you can't [comfortably] use some of the showers in the house, but it would still be liveable. Figure out what it would take to do everything... then figure out the absolute bare minimum... then pick your sweet spot in between.

 

[MarkSolar]

We already had a whole house backup generator for about 5 years when I installed solar. I considered batteries to provide the same functionality as our 22kW generator and the cost was just too high, the problem is you never know how long the grid will be down. So do you buy a days worth of battery backup or a week? So I'll continue running the generator as long as it lasts and maybe by the time it dies batteries will get cheap enough to consider. Given your large AC loads and the hot climate you're in, I'd say lean toward grid tied solar with a natural gas whole house backup generator. Are you able to sell your excess solar capacity back to the electric company?

 

[BigGun]

Around my house we usually only loose power 1-7 days --- Our house is Big -- 3500sq ft ---- I have a 10 kw generator that will run most of the household needs with one big 30k btu Ac (window unit on wheels) in the main area and 2 small 5k btu Ac --- during 14hrs of the daytime -- at night I have a small 4k generator to keep the Fridges going and the 2 small ACs in the bedrooms --both run on Propane ( I have 20 -5 gal tanks/easier to fill ) but will be on NG very soon

Wanting to play around with solar, I built a portable Solar Generator (no solar yet ) -- 2200 watt inverter with 350 AH Calb battery / 12v --During the night of Ida it ran one small AC and kept the main Fridge topped off -- about 7 hrs until morning when the storm was pretty much passed us-- I was able to easily charge the battery back up off generator power the next day -- If I had to I could get by with a small generator and my Inverter setup ---- My Wife Maybe Not

 

[donb108]

Are you just trying to have Backup power for storms or are you trying to use Solar to cut cost -- What you're describing your loads to be --you'd need a 27k - 30k water cooled generator

You're right, but jumping to a larger unit gets expensive fast. We certainly need backup power, but it would be nice to cut costs.

The 5 ton a/c unit cools the living area and the 3 ton is for bedrooms. They usually don't run at the same time, so the generator people recommended 18-20 kw, just for the 5 ton unit.

Also looking at soft-start hardware for the condensing units, but not sure if it would help on the capacity question.

But what about all the time vs emergency. Are you thinking smaller stuff all the time and generator only for emergency?

Yes, normally use the grid/solar and switch to generator/solar during an emergency (power outage). Is there a better approach?

When you redo the electric service, it is an opportunity to create one or more critical load panels.

I've always wondered this; if the generator is large enough to handle the entire house, use a single panel. If not, isolate loads as you suggested. Or, use a single panel and create an automation program that manages loads and prevents overloading. Does Solar Assistant do any of that, or is it monitor-only?

 

[RCinFLA]

I have a system similar to what you are attempting. When you have grid available running the high loads from hybrid inverter on a regular basis is not practical. You already mentioned the hurricane tore you AC panel off side of house, likely PV panels will fair worse.

Tree branches did a job on my panels during last hurricane.

Here is what I have.

I have 8 kW hybrid inverter feeding auxilary panel with all 120vac house loads and transfer option for some 240vac loads like range and clothes drier.. The 8kW inverter runs all the time as UPS backup. It has about 70 watts of idle overhead consumption, not including any battery charging maintanance.

I also have 11 kW inverter solely for high power 240vac loads, including a 4 ton central A/C with softstart/cap boost Easystart unit.
All the 240vac loads are normally on grid with manual ability to transfer to inverter if needed. With grid power the 11 kW inverter is in shutdown so it does not draw idle current.

Both inverters have generator inputs with 15 kW generator.

For daily PV suppliment it is best to use a GT inverter to feed into main AC panel (with zero grid export) with ability to switch to AC coupling on hybrid inverter output during power outage. This allows you to normally keep your heavy 240vac loads on grid and still get the PV suppliment without the hassles of managing load levels on hybrid inverters.

For batteries, I have 48v 1000 AH's. This can give me one to two days of backup with some conservation. During hurricane power outage I run the 15kW generator twice a day for several hours in morning and evening to fully recharge batteries. I also have a small, quiet 3kW inverter-generator for 'trickle' charging to extend battery life between heavy gen recharging which allows me to run central A/C all day. At night I can run central A/C all night just on battery power so I can run silent at night.

Using big generator just to charge batteries gives me better fuel efficiency as I can load generator to sweet spot for maximum fuel efficiency. I usually give the hot water heater power from big generator when I run it for charging. This is effective even with inverter charge/discharge efficiency losses. It is not a lot of fun to find gas after a hurricane so you want to get best fuel efficiency possible. If I consume as if I have normal grid power during a full outage I consume about 8-10 gallons of fuel a day. 15kW gen at 12kW load gets about 7.4 kWH's/ gallon. 3kW inverter-gen at 2kW load gets about 6 kWH/gallon. There are some things like range and hot water heater that can be painlessly cut back on consumption during outage. You don't really need to run the oven for an hour to make a bake potato for dinner. Pre-prep'g meals, doing all laundry, etc. before storm helps a lot.

My original system has been installed for 24 years. Last time 8kW inverter was shut down was about 18 years ago when I added 11 kW inverter to the system. Never have any computer or DVR resets due to grid power glitch, only some computer resets occasionally compliments of Microsoft.

 

[FilterGuy]

I've always wondered this; if the generator is large enough to handle the entire house, use a single panel. If not, isolate loads as you suggested. Or, use a single panel and create an automation program that manages loads and prevents overloading. Does Solar Assistant do any of that, or is it monitor-only?

Do you mean the solar assistant that runs on Raspberry Pi? That is just a monitoring tool.

One of the new things on the market is the 'Smart Panels' that take the place of the breaker panel..... and add a whole bunch of power electronics. These allow you to use Sowtware to designate certain circuits that are critical loads and other circuits that are not. A start-up called SPAN has one and Leviton has one. There are probably others out there. (Search on Smart breaker boxes)

I have no direct experience with them. My concerns with them would be:
1) Reliability: With all that power control circuitry... how long will they last? If one of them fails....it might shut down your whole house!
2) Safety: With all that power control circuitry... is it a fire hazard?
3) Cost to repair: If something breaks, do you have to replace the whole dang thing? If you can swap components, what will the components cost?
4) Expense: They are $2K-$3K or more
5) Building code: Will a building inspector accept it?

The products have not been out long enough to get a good handle on #1 or #2. You would need to do a bit of research for #3-#5.

 

[donb108]

Tree branches did a job on my panels during last hurricane.

And most of my shingles ended up in the yard. On the up-side, I got a new roof, compliments of the insurance company.

Here is what I have.

I have questions, but it'll take some time to absorb this; I'll get back to you.

Do you mean the solar assistant that runs on Raspberry Pi? That is just a monitoring tool.

Yes, RP4. I looked at some home automation sites and didn't find much (anything) on energy management; it was all about turning things on/off, automatically and remotely, during normal operation. There must be someone doing it, I'm just not finding it.

I have no direct experience with them. My concerns with them would be:

Right on each point. I'm retired now, but in my professional life, did lots of work in controls. The breaker companies are very cautious about any changes, or anything new. We should be too.

 

[OffGridInTheCity]

But what about all the time vs emergency. Are you thinking smaller stuff all the time and generator only for emergency?

Yes, normally use the grid/solar and switch to generator/solar during an emergency (power outage). Is there a better approach?

Not better - just different. My goal was/is to have a functioning home without grid - this includes the big stuff like whole house heat-pump, cooktop, oven, dryer, hot water etc right from the beginning. For example - replace gas hot water with heat-pump hot water.

But that doesn't mean I'm against grid while it's available - I just wanted produce enough power to achieve 70% of what I currently use and from that, I'd have a chance of continuing to run my home if the grid went down. For example, I can let the hot tub go and serialize cooktop, oven, and dryer use in an emergency. So I started off planning to run 'the big stuff' and achieved this for 8 months of the year - but it takes significant PV, inverter, and battery. And even with all that - the winter 4 months are still an ongoing effort.

If you were thinking this way as well, (which is why I asked) I could offer some hands-on advice but since you're thinking more as an emergency situation - the advice you're getting is fine.

 

[Quattrohead]

Don you must have a big house, that is a lot of AC !!!! Any of them old enough they might need replacing soon ???? Ideal time to get an inverter type system. Can you insulate the home better ?
I am also an EM engineer and have been looking at methods of load control. I am sure with some current sensors and PLC/Amazon/ebay contraptions we can make some fun stuff. For example, I was thinking of monitoring the current of the electric stove, and when any load is drawn, turn off the contractor feeding the clothes dryer. It will need a time delay to stop it cycling with the burners until you are finished cooking.
I am lucky (I think) to be building a new home with ICF and a low energy/off grid plan from day 1.

 

[donb108]

When you have grid available running the high loads from hybrid inverter on a regular basis is not practical.

Still learning the terminology. Hybrid means Grid-tied-inverter plus battery, synchronized to the utility? Grid-tied is just the inverter, synchronized to the utility? Which part is not practical, solar panels or hybrid...or did I miss the point altogether?

Tree branches did a job on my panels during last hurricane.

Did insurance cover any of it?

The 8kW inverter runs all the time as UPS backup.

It sounds like this inverter normally powers the house; the house always has power, and is effectively backed up by battery. I was confused by the UPS backup part, did I get it right?

I also have 11 kW inverter solely for high power 240vac loads, including a 4 ton central A/C with softstart/cap boost Easystart unit.

During and outage, could you run the large loads directly from the generator? Are you doing the inverter/battery/generator-recharge combination purely for efficiency?

Both inverters have generator inputs with 15 kW generator.

Does this generator run on gasoline or NG? I agree, foraging for gasoline is terrible.

The night before the hurricane, my neighbor sold me a brand new, in the box, 5kw generator. That night, 15 minutes after I started it, it got swamped by flood water (water got into the fuel tank). Bought another generator the next day at Home Depot.

Not better - just different. My goal was/is to have a functioning home without grid

I think we're both aiming at the same goal, but coming from different perspectives. We don't ever want to go through something like this again, so standby power is a pretty big deal. She's convinced that a generator is a must and solar is a nice-to-have. At the end of the day, we'll have both, but will start with the generator designed-in.

Don you must have a big house, that is a lot of AC !!!!

Yep, 3500 sq ft. We weren't looking for a big house, but properties were going onto the market and put under contract so quickly that we had to move fast. My wife happened to be here when this one went up for sale. She looked at it in the morning and we bought it that afternoon. Pretty much sight-unseen for me.

Any of them old enough they might need replacing soon ?

Probably the original units from 2004, but both are scroll machines and work fine. I hate to replace them if I don't have to.

Can you insulate the home better?

Insulation is actually pretty good; R-15 in the walls and R-30 in the ceilings/attic. Attic ventilation is terrible, so will be re-working the soffit vents to correct that.

I am also an EM engineer and have been looking at methods of load control.

Same here, but I have to get some of the basics in place first; I really need to get that load center panel corrected right away. That said, I just ordered an RP4 to experiment with.