C’mon Doorman, Throw Us A Bone!

Where we live, 75kW would be a 3-phase supply. There are off-the-shelf systems from DYE, Sunsync, Victron, etc. that you can get. A 50kW system would probably be sufficient? In a 3-ph setup, you're looking at ~75A input current from your genset. The DYE example can do 50A+50A into a battery of 160V upwards, limited by the 50kW input constraint.

In real life you'll probably not average 10kW every hour, but you'll want to cater for those 4 days in winter when solar doesn't work and the grid is down. So, just increase the batteries, most inverters can manage a few batteries. And 10kW*4days*24hrs= 960kwH, which is a lot, and will take a long time to charge! Personally, unless the generator is very far away, I'd settle for a 2-day battery life and walk over to start the genset more often and then run it for a shorter period (remote start/stop is sometimes tricky to retrofit cost-effectively on older machines).

It seems that high-voltage batteries are more efficient, but you'll have to check the data sheets carefully for low-temperature operations. The few people I know playing in this ~50kW space had installed 3x1-phase inverters and normal low-voltage (48V) batteries, but their use-case was very different to yours, so it is difficult to say. It also depends on your redundancy requirements and cost appetite...

Keep us posted as you move along, I'm really curious as to the route you end up taking. Our high fixed (connection) fees means that more and more people are looking at going completely off-grid electrically, and we want to see and learn from what others are doing.

I would like to believe the consumption could be held to about 10 kWh/day *. However, the wild cards here are refrigeration and (seasonally) the furnace blower motors.

In the USA, citizens seem quite happy to stick a plug into every available outlet in the house. Mrs. Doorman likes these decorative tabletop night light/scented wax warmer things; there are 3 in my house right now, each sporting a 15w incandescent bulb. 45 watts/hr, 24 hrs ≈ 1kWh a day right there. Add the other little parasite loads, prolly consume another kWh/day, perhaps two. Then add in parasite standby loads from televisions, computers, clothes and dishwashers, battery chargers, garage door operators, motion activated lights… Our society sucks a lot of power! Identify and remove these loads from the battery backup environment.

Footnote *: As noted in OP, a number of routine house chores should be deferred. As well, lock out/tag out all of those power hungry counter appliances - toaster over, microwave, rice cooker, coffee maker, waffle machine… all of them. Hands off until mains power is restored.

Yes, loading up the genset to 80-ish percent as a routine is one of the (not clearly defined) goals of this discussion. It seems extremely wasteful and ill-advised, from many perspectives, to operate a generator at 5%-10%.

I fear that the machine preventative maintenance has been severely neglected. I have requested a copy of (or at least a hands on review of) the PM log and companion fuel reports… the reluctance to provide this leads me to believe there are many blank pages. The genset may be nearly worthless.

If this is the case, the machine can be replaced with something more appropriately sized… unless discussion here with you guys advises the 75kW is about right.

I would sell the big generator and use the money to buy a smaller appropriately sized unit...keep it simple...I would build an underground house to save energy, or at least partially underground...

I agree bro. I did m homework and settled on the 11KW genset and the 10KW of batteries. I can run the electric dryer for a couple of loads with that and not have a problem. 75KW could run a machine shop!

Where are the batteries? Inside a bunker out of the cold I hope.

LiFePo Is good. Safe enough for a boat.

Charging system? 240 to ?.

Then, inverters. I think 10kw or 15 for marginal extra use would be fine. It's the charging system that seems to me to be the problem here. The draw can be limited to the inverters supply, but you want to charge up fast and pull down over days.

Fortunately LiFePo is pretty tolerant of partial charge and BMS devices are easy to obtain. My boats batteries can charge off a regular Pb battery charger or alternator with no problems. But what switch-gear and voltages and currents are going to go into this battery bank?

“Then, inverters. I think 10kw or 15 for marginal extra use would be fine. It's the charging system that seems to me to be the problem here. The draw can be limited to the inverters supply, but you want to charge up fast and pull down over days.”

Yes. This issue, exactly, is for me the largest fuzzy part. How to utilize the generator efficiently to charge up the batteries. It is quite possible to continue piling batteries, enough energy storage for +/- a week… but how to recharge that battery array in a short period of time?

If I want to fast charge my boat batteries, I have to connect them as a 48v series arraignment and charge them at with 50+v. That limits the current to their 50AH current rating (and the limits of the BMSs). In that config I can charge all four at once in one hour. But charging stops when the first battery is fully charged and it's BMS cuts power.

If I charge at 12V (14V actual) I connect them in parallel but then I need 200A at 12V to charge in one hour. I usually only have a 12A charger for that, so, it takes 8-12 hours to charge them back up.

My house batteries are connected through a battery "gateway" switch gear. It only switches between sources and loads, the loads being PGE or the house, and sources being PGE or the batteries or the solar . They charge and discharge at the same voltage/current configuration. They take from sun up till Noon to charge and will last two to 3 hrs draw after dark.

You need to switch between charging and drawing modes somehow. Or you need to charge one bank of batteries while you draw on the other. Either way you need switch-gear.

What is the geometry of the batteries? What are the generators output voltage(s) available? What is the maximum current the generator can deliver? Can you change the geometry of the batteries?

Is the generator loud? Could you run it all night and charge the batteries then use the batteries all day? What if you just run the generator until you have full batteries and then run on them for a few days and then do it again?

Battery array exists now only within this discussion; restated, there is no battery storage in the existing scheme. I would be able to set this up in any configuration.

Loud? My request to observe genset operate was declined… This is a 75kW diesel genset inside a dedicated powerhouse (I dunno, about 12’ by 20’), so I presume it is pretty loud. It would be my desire to run genset in daylight; noise seems to carry further at night when it is snowy and cold… I desire that very few of the area residents are aware that I am operating a generator. In fact, I would be pleased if nobody were to become aware it even exists.

Characteristics of existing genset are unknown. Property tour was conducted by a real estate broker, within a pretty small time window.

You mentioned back-up/emergency power supply.

are you talking about a alternative to a genset, or adding a battery array et al to the genset?

About the genset, there’s a difference between a Prime/Continuous Power vs. Standby/Backup Power genset. You mentioned stand by? Where it sounds like it’ll be used rather often.

Also I gather is one thing you need to avoid, is getting something because it appears ‘cheap’ and then expanding upon it to get what you need instead of buying what you actually need and can use.

Good points!

I am investigating several mini goals here. Installed today is a presumed intermittent use emergency genset, not intended for 24 hr weeks on end running, and a single 300 gal (estimated) fuel tank. There are no batteries in place today: power drops out, ATS changes over, genny starts up.

In the historically most likely event of occasional mains disruption of a few hours, I am looking at battery supply in lieu of the genny starting up. When mains returns, the inverter ATS returns to normal, recharges the battery bank from mains supply.

If the mains power loss is of the rare 3 or 4 day type (or the even more rare 8 days), I need to be able to charge up the battery bank. I desire a charge time of about 8 hours.

As the thread title should lead you to deduce, I don’t have very many informational bones to toss you guys. I don’t have a good power audit on the building, I have almost no good info about the genset. I am hoping critical system consumption is about 10kWh/day, but it’s prolly more like 20kWh a day with peak demand of about 5kW.

I’m with ya on the dollars. This is a terrible project to cheap out on; I’m seeing $25 to $50 thousand on gear/batteries, about the same for labor. Rule of thumb - double your WAG estimate and you might be about halfway to the end price.

Hi Doorman, there are a few points which are unclear or hazy to me.
1: it would appear this is a business property which you are thinking about converting to a private house

2: your assumption that it's a single phase 240vac is probably wrong, more like a 440vac three phase. (see table below.)

3: a 75 kW Gen would be for a house Overkill to say the least, not to mention fuel consumption / noise / modification costs etc.

4: There are combi Back-ups now on the market where the Gen, Invertor and Storage battery are all in a compact unit, might be worth looking at. or at least downgrade to around 15 - 20 kW Power. That should be enough for a large house.

5: As the building was intended for use as a Restaurant, it could be that the Gen is already hooked up the house..

6: From your comments, it would appear that you have not personally seen the property and depending on the Real Estate agent. As the seller seems to be holding back on info regarding the Gen, makes you wonder what else is being held back.

3 Phase Generator Size Guide

Good morning!

In an effort to clear away any fuzz, responses by the numbers:

1) Yes, refer to paragraph #3 in original post.

2) Okay

3) Yes

4) I’ll check this out… from your description, this sort of setup is prolly on the small side for my desired use.

5) Yes, it is

6) I have visited the site; the tour was very brief, the subject emergency power system is but one small part of the entire property. Another, more focused, tour is somewhere on the event horizon.

Re #4 in my list of questions and referring back to your original post, why would you want to have 4-5 days worth of Battery power before the gen kicks in ?
If you have a small battery capacity, say 1 day back-up, the Gen could kick in and start recharging the battery pack before it gets emptied, bit like a PHEV Hybrid car, runs on stored energy until the energy level falls to a preset point then the Engine kicks in and keeps the car running and recharging the battery at the same time.
Way far cheaper than investing a ton of money just to have 4-5 days worth of power available in batteries and you still need a Gen in case the power outage lasts more than 4-5 days.
Re the maintenance records of the existing Gen, most commercial Gens have a hourmeter fitted showing how long it ran for. My guess would be very low, especially if the Restaurant never went into business so basically no need to run the gen if the place was never opened.
It would help if you had the details of the Gen, then you could check out the market to see what value it would have on the used market. Having a new Inspection - Service would also increase its value. You might get enough to pay for a smaller 240v Gen more suited to your house size, without having to invest any money !
Have you calculated how much power your house would need, not counting charging batteries?
Have you taken into account if you would ever need 3 phase outside of using mains electricity ?
You could also put up a small wind turbine or two depending what sort of winds you would get there !
from your description the area gets a lot of snow, kills off the Solar but not the wind.

The 4-5 days is arbitrarily voiced here, an indefinite quantity. An auto start scheme has been considered, but I would prefer the genset not run at night. The option of auto start hasn’t been shelved, but is not a first choice option.

Turbine(s) and/or PV have been considered, and remain viable options. These are also not first choice options, rather I am concentrating on a more ‘Control your own destiny’ sort of path.

Hour meter shows 92 hours, engine is very clean. Coolant, air filter, and engine oil are all dirty. I believe (I am well known as being cynical) neglect is the uniform of the day in the genset maintenance department.

3 phase is present at the site, but I believe the only utilization is in the sawmill (yes, this property has an operational sawmill!). It won’t ever be necessary to run the mill is the mains are down.

As I said in OP, thanks to all here at CR4 for your interest and comments about this not-very-well defined project. I realize it is difficult to offer advice when there isn’t some sort of a goal that is visible.