Whole House Generator vs. Hybrid System

[Sunking]

You said that minimum battery capacity is 350AH... How did you come to that calculation? I have been looking for bank sizing guidelines for environments that are grid-tied and looking to minimize generator use during grid down. So far, most of what I have seen is for off-grid sizing. I don't plan to cycle the batteries too often or too deeply.

To start it is clearly printed in the specifications.

It has to do with both charge and discharge currents batteries can safely and operationally handle. This varies a bit between FLA and AGM batteries. For FLA batteries the maximum charge and discharge current they can handle is around C/8 where C = the battery rated Amp Capacity @ the 20 hour discharge rate, and the number 8 is 8 Hour Rate. So for example a 800 AH battery can should not be charged with more than 800 AH / 8 H = 100 amps.

On the charge side going above C/8 can cause over heating and excessive gassing. It can literally boil and roll the electrolyte right out of the cell spilling it. You cannot replace the acid. On the discharge side going above C/8 will cause excessive voltage sag which means the voltage goes too low and the loads like an Inverter will trip off line from under voltage...

AGM has much lower internal resistance and thus can handle higher charge and discharge rates of typically C/4. Some as high as C/2.

So where does the 350 AH minimum come from. The Inverters internal 115 amp charger. For FLA minimum is 8 x 115 = 944 Amp Hours. For AGM 4 x 115 = 460 AH. Now there are some AGM's out there that can handle a C/3 charge current or 3 hours x 115 amps = 345 AH.

Now look at the Discharge side. You have a 8 Kw Inverter with 95% efficiency meaning it demands up to 8000 watts / .9 = 8900 watts. At 48 volt battery is 8900 watts / 48 volts = 186 amps. That means you would need a minimum 8 hours x 186 amps = 1488 AH battery if you intend to pull the full 8000 watts from battery.

Yeah it sounds screwy and hoaky, but that is because they did IMO a poor job of matching things up. At 48 volts, 5000 watts is the max limit and 90 amps of battery to make all the pieces fit together. A 5000 watt panel generates 90 amps at 48 volt battery, requiring a 720 AH battery supplying a 5000 watt inverter backed up by a 10 KW genny.

Keep in mind the way you want to operates is like a hybrid auto. The batteries are only charged either by commercial power or genny. When the power fails the inverter uses battery power. If the outage is extended the generator comes on and recharges the batteries and carries the load while the batteries recharge. Once the batteries are fully recharged the generator shuts off. Cycle repeats until commercial power is restored. You generator has to supply the charger 5800 watts plus up to 8000 watts for power you are using. That comes up to a total of roughly 14 Kw. You load a genny no more than 80%, so a 16 Kw genny is required.

So ask yourself this. You still need a genny, a even larger genny, plus several thousands dollar of batteries you rarely use and have to replace every 5 to 7 years rather you use them or not. You are still going to be burning propane, just more of it during outages because you need a larger generator running at full capacity. Is that what your really want to do.

Or for a lot less money you get a conventional Grid Tied system, and keep your genny, or upgrade to a more efficient quieter unit and burn less fuel than a hybrid would use during a long outage.

Think all this out before you pull out the wallet. Once you pull the trigger you cannot get the bullet back and will have to live with your choice. Uncle Sam NoBama will not be around to bail you out.

Don't forget you can run a genny on a timer like 2 hours on/ 2 hours off. They even make controllers to only come on when needed like when you need heat, or twice a day to keep the fridges and freezes cold. No one says they have to run 24 x 7. That is what I did in TX and never broke a sweat in summer. I just kicked back and watched the neighbors suffer spending the whole day outside and having to cook on a charcoal grill every meal. Not for me.

FWIW I will not comment on DIY. I don't want my name associated with it.

[DanS26]

I live in Southern New Hampshire and averaged 6-9 days a year without power for the past four years. The longest single outage (13 days for an ice storm) was in 2009 before I moved to NH. We frequently have 3+ day outages. That is what happens when you live in a small rural town on the edge of of the utility's network. It is also a wonderful place to raise three small children and care for two elderly grandparents. We have no plans of moving any time soon.

I have a propane powered 12.5kW Generac (burning 1.6gph) installed by the previous owner that is 8+ years old. I plan to replace it with a Kohler when it is no longer repairable, but hopefully not for the next couple of years. I also have a manual 6.8kW gas generator as a backup. I have a 500gallon under ground propane tank that serves heat, cooking, DHW and the generator which powers the well water. My heating is ~650W of circulating pumps and a propane boiler. I previously moved all of my generator-backed loads onto a dedicated panel and feed that from the ATS in preparation for this solar project.

I am currently looking at my options for DIY solar installation. I am heavily leaning towards 8.5kW of SolarWorld (26 @ 315W) panels with an 8kW Outback Radian inverter, AGS and a 48v ~300A AGM battery bank for roughly $28k before rebates. Our monthly consumption is around 1400kW/h. That price includes equipment, assistance with racking and mounting, and me performing all electrical work (NH allows the homeowner to do this and I have a good background to do it safely). I am also considering adding a small (~40A) 120v battery charger that I could run off a quiet, fuel sipping, Honda EU2000i.

If I am going to do solar, I think it makes sense to have some battery capacity for the longer term outages. I don't like using my heating fuel to run a large generator 24/7 which is why I have the gas backup. However, I frequently travel for work and need something that can be automated. During the coldest months, we can go through 300+ gallons of propane in a month. Pick the wrong time of the month for a power outage, close roads stopping propane delivery and... At most times during an outage, our consumption can be low and the loud generator is still running. The wonderful feeling you get when it starts automatically goes away after the first day or so. Energy rates in NH have been going up and generation costs are predicted to go up as much as 30% over the next four years.

So that's my idea and a little bit of the situation. Any feedback is welcome before I write a check. Tell me I'm crazy, doing it wrong, using the wrong equipment, wrong supplier, etc. Or tell me I'm on the right track. Thanks in advance for any wisdom you can share.

Wow! 1400kwh per month. Forget the batteries. Build the biggest grid tied system you can afford. Downsize the genny to around 10kw....8kw preferable Buy a backup LP tank 1000 gal.... prefer two 1000 gal tanks.

Before you do this though, insulate the house and buy some LED's for crying out loud.

[SunEagle]

Wow! 1400kwh per month. Forget the batteries. Build the biggest grid tied system you can afford. Downsize the genny to around 10kw....8kw preferable Buy a backup LP tank 1000 gal.... prefer two 1000 gal tanks.

Before you do this though, insulate the house and buy some LED's for crying out loud.

1400 kWh/month is not really excessive depending on where you live. That is about what we use monthly which is down from almost 2200kWh/mth 5 years ago. That's when we installed the solar thermal water heater, added insulation, thermal barrier and replace 98% of the lighting with LED and CFL lamps.

But I agree with you. He should forget the batteries and concentrate on a large grid tie system with multiple gen sets and fuel sources.

[chuckb]

Wow! 1400kwh per month. Forget the batteries. Build the biggest grid tied system you can afford. Downsize the genny to around 10kw....8kw preferable Buy a backup LP tank 1000 gal.... prefer two 1000 gal tanks.

Before you do this though, insulate the house and buy some LED's for crying out loud.

I have regretted the 500g decision since it went in as part of the addition for my in-law's. I would be looking at close to $4k per 1000g tank installed. I upgraded the main house to spray foam insulation and the addition is all spray foamed. I have replaced almost all of the lights in the house with CFL or LED, but my in-laws removed the CFL/LED bulbs from the addition and went back to incadessant because they 'liked them better.' For the sake of a happy wife, happy life, I have let go of the issue and the fact that they leave their lights and plasma TV on all the time. I have been successful at getting them to replace some of the timer-based lights with LED, but not many.

An 8.5kW system is about the largest I can do with the ideal roof space. To do more, I would need to use less ideal roof space and get into micro-inverters due to shading issues. Or, I would need to clear a few more very tall trees (with a neighbor's permission) and go for a ground mounted, auto-tracking system. Based on the feedback I have been getting, I may have to give those options another look. I don't plan to replace the genny until it dies, but I do have a second 6.8kW gas-based generator in case it does fail to start (happened twice so far) or if I want to give the automatic genny a break.

[chuckb]

FWIW I will not comment on DIY. I don't want my name associated with it.

Sunking-

Thank you for the valuable information. I need some time to go through your post a few more times to make sure I understand it, but work is getting in the way. I did get a professional quote of $39k to do a solar-only, grid tied 8.9kW SunPower/SunnyBoy system showing a 10 year payback which I think is way too much money for what I'd be getting.

I am trying to make the best informed decision I can and I appreciate your advice. I do plan to question the supplier who's been quoting/designing the system for me about the recommendations he's been making.

[Sunking]

I did get a professional quote of $39k to do a solar-only, grid tied 8.9kW SunPower/SunnyBoy system showing a 10 year payback which I think is way too much money for what I'd be getting.

That is a bit high? Does that include the fed and local incentives? For your area maybe in line.

I am trying to make the best informed decision I can and I appreciate your advice. I do plan to question the supplier who's been quoting/designing the system for me about the recommendations he's been making.

I am sure you know this, but keep in mind any salesman could care less about you and only has his interest covered. Solar salesman are pushing real hard right now trying to get all the work they can before December 2016 when the business model collapses, they cash out, and close shop. Trust me if I were a salesman, I would be doing whatever is necessary to sell you a hybrid system over a grid tied system.

[chuckb]

That is a bit high? Does that include the fed and local incentives? For your area maybe in line.


I am sure you know this, but keep in mind any salesman could care less about you and only has his interest covered. Solar salesman are pushing real hard right now trying to get all the work they can before December 2016 when the business model collapses, they cash out, and close shop. Trust me if I were a salesman, I would be doing whatever is necessary to sell you a hybrid system over a grid tied system.

All of the prices I have been quoting exclude any Federal and State rebates. The State rebate caps out at $3750. A friend of mine over the border in MA recently used this professional to put a 12kW system on his house, but MA has better incentives than NH. I am looking at $39k pre-incentives for a 8.9kW SunPower/SunnyBoy system or $28k for a Hybrid DIY system.

I am planning to source the batteries locally, so I don't think the supplier has a significant incentive to push Hybrid over Grid-Tied. However based on what I have been learning here, it doesn't seem like he is doing the appropriate due diligence on his recommendations. He initially said I would be fine with a 200Ah bank and I pushed it up to 300Ah after doing some back of the napkin calculations for 80% and 50% DoD usable watts. He also led me to believe that the solar panels would be used to charge the batteries in a grid-down situation and the generator would be used to supplement. This is different than the information you have provided... Another thing I need to verify and question the supplier about.

The batteries are only charged either by commercial power or genny. When the power fails the inverter uses battery power. If the outage is extended the generator comes on and recharges the batteries and carries the load while the batteries recharge. Once the batteries are fully recharged the generator shuts off. Cycle repeats until commercial power is restored.

The Duracell Marine Deep Cycle AGM batteries state the maximum charge current is 1/3 of their reserve capacity. The Group 31 battery has a reserve capacity of 200A giving me a maximum charge rate of ~65A. I will have 12 batteries in a 3x4 configuration to give me 48v with a maximum charge rate of 3 x ~65A which is more than the 115A of the Radian charger. Do have this right?

On the load side, my largest load is the well pump that pulls approximately 11A@240v and runs for about a minute to refill the pressure tank. Next would be the microwave at 10A@120v which only runs for a minute or two at a time. TV's, heating circulators, refrigeration, lighting, internet, etc would have longer run times but would be around 20A@120v. Most of the time, I'm looking at 2500-3000W with occasional spikes up to ~6000W. At night I'm looking at less than 1500W.

I will take another look at the non-hybrid options, but I still like the concept of a Hybrid system if I can find a way for it to be practical. I will agree that it is looking less practical with a 300Ah bank as I continue learning. The goal is to burn less propane during an extended outage by not having to run the generator 24/7. If the bank can't charge from solar during the day then it won't be saving any propane.

[Sunking]

Chuck you do know you are going to need two 80 amp MPPT charge controllers to operate the system as BACKUP right? That will allow you to use solar panels to recharge the batteries during outages. Even if you do that still requires a Generator as there is no way around it. All this info is in the online manuals.

Back to battery size. The manual lumps all batteries into one category of C/5 maximum charge rate. At 8000 panel watts put you at 8000 watts / 48 volts = 166 amps. In other words a minimum 5 x 160 = 800 AH.

You need to know and choose which mode you want the system to operate. The majority of the modes will use only Renewable Energy sources until the batteries are discharged before it will ever use utility or generator. If you do that with Duracell Marine batteries expect to replace them every year. They are not designed for RE applications.

You need to download the Installation manual and start on page 12 to page 16. A good 5 year 48 volt 800 AH battery is going to cost you $7000, or a 2 year battery as you plan around $3500. You do not want parallel batteries. Do that and you cut cycle life in half.

Here is a little cost analysis for you. A 48 volt 800 AH battery if used daily can supply you with 8 Kwh per day. Assuming you pay 15-cennts per Kwh works out to about $1.20 per day. In 5 years will provide 1825 days x 8 Kwh = 14600 Kwh. With a $7000 battery / 14600 = 48-cents per Kwh. But that is if you use them every day. Used as backup 3 weeks out of a year you might get 7 years out of them. 150 days x 20 Kwh @ 50% DOD = 3000 Kwh used in 7 years. You just paid $7000 / 3000 Kwh = $2.33 per Kwh in battery cost plus LPG fuel cost.

You really need to think this out because once you pull the trigger, there is no going back. Well actually there is. Take your losses. But that will be a $40K lesson you will never forget.

One last point here. Right now I assume your utility service is likely a 100 or 150 amp service??? But with this Radian you are only going to have 33 amps available. Is that going to meet your peak demands?

[Living Large]

For the sake of a happy wife, happy life, I have let go of the issue and the fact that they leave their lights and plasma TV on all the time.

If the wife ain't happy, nobody is happy. That is what I hear, anyway, as a confirmed bachelor.

[chuckb]

Here is a little cost analysis for you. A 48 volt 800 AH battery if used daily can supply you with 8 Kwh per day. Assuming you pay 15-cennts per Kwh works out to about $1.20 per day. In 5 years will provide 1825 days x 8 Kwh = 14600 Kwh. With a $7000 battery / 14600 = 48-cents per Kwh. But that is if you use them every day. Used as backup 3 weeks out of a year you might get 7 years out of them. 150 days x 20 Kwh @ 50% DOD = 3000 Kwh used in 7 years. You just paid $7000 / 3000 Kwh = $2.33 per Kwh in battery cost plus LPG fuel cost.

Sunking-

The $28k Hybrid system includes two Midnite Classic 150 charge controllers. I currently have 200A service to the house, but the generator protected panel is currently limited to 50A, average usage is significantly lower based on point in time ammeter testing. I don't think 33A during an outage is bad... I typically am using less than 10A during an outage while running a generator that can provide 50A and consumes up to 2.1g/h at full load, 1.6g/h at half. I have no intention of going off-grid with 8.5kW of panels and 300Ah of batteries except when the grid is down, which unfortunately happens 3-4 times a year and can last up to 10 days at a time. I would like to minimize propane consumption for power during the outage, even with a higher kWh cost overall.

I have about 560 ft^2 of ideal roof space for panels before I get into significant shading issues or have to look at ground mounting, auto-tracking and tree clearing.

Option 1: Professional installation: $39k pre-incentives
- 8.9kW of SunPower panels
- SunBoy Inverters
- Installation and service warranty for 10 years, plus manufacturer's warranties
- Use of my existing ATS and 12.5kW generator for the entire duration of an outage

Option 2: DIY Installation: $28k pre-incentives
- 8.5kW of SolarWorld panels & roof mounts
- 8k Radian Inverter AC1=Grid-Tied / AC2=Generator Modes
- Auto Generator Start
- 2 x Midnite Classic 150 Charge Controllers
- Manufacturer's warranties only
- 12 x Duracell Deep Cycle AGM Marine batteries ($1400 for enclosure & cables; $2200 for batteries, included in $28k)
- In addition, I would have ~$2200 + inflation to replace batteries every 5-7 years.
- Current generator at 12.5kW is undersized and need to be replaced with 16kW when it dies.

I know I am being a slow learner, but you think I'm throwing $3600 in the garbage by trying to do any batteries and wouldn't see any benefit of having them over just running the generator 24/7 during the outages? Should I be looking at other options? Is a larger battery bank required for my desired usage? Am I being unreasonable in the premise of my desired usage of minimizing propane usage during an extended outage by being able to utilize solar/battery with generator backup? Should I do Option 2 without batteries? Should I be more selective with my loads?

I am truly grateful for the time you have spent helping me. Please don't take this as a personal attack, I just learn best by going back and forth picking apart ideas.

[Living Large]

I am truly grateful for the time you have spent helping me. Please don't take this as a personal attack, I just learn best by going back and forth picking apart ideas.

You are right in Dereck's wheelhouse. He won't take this as a personal attack. He's a quick starter out of the gate sometimes, and runs over the pace horse's hooves - but he stays in the race.

[Sunking]

The $28k Hybrid system includes two Midnite Classic 150 charge controllers.

OK I missed that earlier, my bad. Those are fine controllers, but in this case it would probable be a good idea to consider the Outback controllers because they can communicate with the inverter.

This changes the battery picture greatly. Essentially what you will end up with is two solar panel systems of 4450 watts each with its own controller. Both systems feed a common battery. However you will have up to 8900 watts / 48 volts = 185 amps of charge current. Trust me Chuck you cannot hit a 200 AH lead acid battery with 185 amps of charge current. You are playing with fire, well bomb is more like it. Most likely occurrence is with AGM's the valves would operate to release pressure spewing acidic hydrogen and oxygen to keep the batteries from exploding. Either way the batteries are toast. What I am telling you here is you will destroy the batteries first or second time they are charge up. Just a matter of time. The only battery type that can take that high of a charge rate is NiCd and Lithium which is out of your league

I am truly grateful for the time you have spent helping me. Please don't take this as a personal attack, I just learn best by going back and forth picking apart ideas.

No problem you couldn't hurt my feelings with a baseball bat. I would just take it away from you and impale you with it. . That is how you learn, and you are going about it the right way. Don't be like the 90% of the idiots who come here after they buy stuff and discover it will not work looking for help. We can fix Ignorance, but we cannot fix Stupid.

[Mike90250]

First, you may as well plan on a dedicated outbuilding with a firewall in it, to separate the battery bank, from the electronics.
The electronics side will need cooling for the summer to dissipate heat.
The battery side will need insulation and ventilation for retaining heat in the winter (cold batteries loose capacity) and all battery areas need ventilation to dissipate hydrogen.

I would consider 200ah 6v golf cart batteries as cheap starter bank. Most folks destroy the first set of batteries dialing in the system settings, and forgetting to do something (add water, replace a blown fuse.....)
Even with 200ah batteries, you will need oo parallel at least 2 strings.
parallel wiring:

http://www.smartgauge.co.uk/batt_con.html

And a large standby system will occupy your time.

Don't forget all the monitoring goodies and programming gadgets needed to work with each brand of gear.