Battery vs generator?

lasitter · October 2014

If all you need is xx hours of power in the event of a grid outage, would you rather have batteries and an inverter over a generator?

Generators have the advantage of not requiring sunlight, and being able to run as long as there's natural gas or until they mechanically fail.

If you have sunny skies, an array of batteries, and enough panels to charge them, you in theory have power indefinitely with no moving parts (mostly) and no fuel costs.

That sounds like a better outcome to me!

So help me with doing a spec on a system with a 15kw panel setup and a battery array spec that would carry a 1.5kw with occasional surge to 4kw (electric motors starting, etc.), in increments of 12 hours battery time.

I know it's another level of complexity, but I'm also considering a ground mounted tracker installation for the usual increases in output.

Finally: I'm assuming you have to have sufficient inverter capacity to satisfy whatever you want to put on the grid at any given time. Since (in Massachusetts) it doesn't matter what time of day you put power on the grid in terms of the value of your SRECs, and since inverters are not free, would it make sense to maximize your SRECs while minimizing your inverter cost by using special hardware / extra batteries to level out your power uploading (charging by day, uploading by night)?

Cariboocoot · October 2014

Re: Battery vs generator?

Generator has it all over solar for cost.

You're spec'ing a 15kW array? Try $15,000. Inverter capable of 4kW surge? $2,000 more. Battery bank to connect the two? Sixteen GC2's for $2,400. Now, how much generator and fuel can you buy for that? Far more power per dollar than solar can provide.

The batteries will go dead, used or not. The generator can be repaired/rebuilt; batteries can't. Keep fuel on hand and you have the power whenever; totally independent of sunshine.

When it comes to back-up power for the occasional outage nothing beats a generator for cost effectiveness. The only time when batteries would make sense is if you need a seamless, automatic switch over or if the noise of the generator would be a problem (inverter-gens are not very noisy).

Solar for short-term back-up is throwing away your money.

lasitter · November 2014

Re: Battery vs generator?

Cariboocoot wrote: »

Generator has it all over solar for cost.

If your only consideration is backup power at lowest possible cost, looking at your math, I'm no doubt you're right.

Cariboocoot wrote: »

Sixteen GC2's for $2,400.

How many hours of backup would you get from the output of these batteries? And you get the most bang for the buck going GEL vs wet?

I'm also looking at this also from the standpoint of "politically correct" power, as well as wanting to get in on the gold rush that SRECs appear to be. SREC-I is closed out, but the $285 per megawatt was utterly mouth watering.

http://www.solardelphia.com/pdf/What_is_an_SREC.pdf
These guys clearly have something to sell, but the idea of 10-13 credits (megawatts) from a 10kw array is pretty appealing.

This metric suggests 15-19.5 SRECs for a 15kw system. The auction payout of SREC-II has gone up to $277/per for the most recent reporting period. That could be $5,000 ROI per year beginning with the first year. The reduction to near zero for your energy costs is pretty appealing by itself without this bonanza, if you compare the near risk-free nature that this investment represents to your typical return on risk-free CDs, investing in solar is a complete no brainer.

This payout will go down over time as more people try to cash in, which for me is plenty of reason to sign up and start earning sooner.

Of course you have to do a lot of important things right when it comes to selecting and configuring the right components and having the system installed (I'm no DIY guy ...) and the batteries are just an option. You could always do the panels, buy the generator and forgo the batteries. The batteries just offer you redundancy and the potential of an instant transfer in the event of an outage.

15000w Complete DIY Solar Kit

The kit is under $22,000 delivered, after Federal tax incentive.

Which array do you like for $15,000, and is it before or after the tax credit?

Which inverters of good quality do you like?

Cariboocoot wrote: »

The batteries will go dead, used or not. The generator can be repaired/rebuilt; batteries can't. Keep fuel on hand and you have the power whenever; totally independent of sunshine.

I was also considering a generator for redundancy. The batteries are optional, as long as the kit indicated above can handle putting the max output of the system onto the grid.

I thought I had a 1.31 acre lot to work with, but I back up to a wetlands, and know I'll have to get permission to build anything ground mounted on the lot, which would have to be set back 100' from any wetlands -- not a problem you encounter so much in Arizona.

These panels are large, and I'm not sure how many I can actually fit on the lot given the setbacks.

Thanks in advance for addressing any of the specific questions I've posed.

BB. · November 2014

Re: Battery vs generator?

16 GC batteries * 6 volts * ~220 AH = 21,120 Watt*Hours of storage

21,120 WH * 1/2 days of storage * 0.505 max discharge = 5,280 WH = 5.3 kWH per day

5,280 WH per day * 1/5 hour discharge (charge during day/discharge during evening) = 1,056 Watt average load for 5 hour per night

That would be the nominal recommendation for an off grid home usage. If you use power during the day, you could use more power when the sun is up (solar panels both power loads and recharge battery bank).

Seems like a reasonable price for an Enphase based GT system (I am not in the business). Check on shipping costs (can be expensive), and you will (most likely) need the Enphase Envoy system to monitor the 60 micro inverters (also need full time Internet connection).

15 kWatt is a pretty large system. You will need to check with your utility on connection requirements. Also, you will probably need >= 300 Amp main panel (and utility drop) to accept that amount of power, unless they allow a "line side" tap from the utility.

Don't buy anything until you are sure you got all of your ducks lined up in a row.

-Bill

lasitter · November 2014

Re: Battery vs generator?

BB. :

Thanks. I have time to ask lots of questions because the approval process of doing anything near wetlands can be a lengthy one.

It probably won't be 15k simply because of the size of the panels used.

And: for $30,000, you get free shipping!

RandomJoe · November 2014

Re: Battery vs generator?

I suppose it would depend on just how long 'xx' hours is, and what your primary needs are.

If 'xx' is relatively short, and you primarily want to ensure seamless operation for a relatively small load, a battery bank and inverter with sub panel could be just the thing. Might not even need the solar part, just a grid-powered charger - basically an oversize UPS. It won't be "cost effective" but can be useful.

That's mostly how my system is used now, my "critical" circuits (mostly computers and such) are on my inverter's sub panel. Even when I'm using grid power I don't notice a failure. The inverter switches to battery so fast the lights don't even blink. (Used to notice the occasional tiniest flicker with CFL bulbs but now with LEDs nothing at all.) I only know about it because the microwave clock (not on the inverter) has reset!

I could, if needed, pare down some loads and run 24x7 off-grid but normally I have enough computers going that I'd be taking the bank down to 60% SOC every night in winter so I switch to grid at sunset and if the forecast is sunny to inverter when I get up (several hours before the sun hits the panels) to give the batteries something to do. Sometimes in summer I can leave it off-grid days at a time with the extra sun.

However I'm definitely not running the whole house off the system. A/C stays grid-tied, as does the microwave and electric stove. Heat & air blower unit is normally grid-only, but I have a gas furnace so could - in a pinch - plug it into an inverter-powered outlet if desired. Can't run the furnace on battery very long though, even though it's gas the blower and other electrical parts still draw 800W while running.

So I still have a generator. Honda EU2000i that doesn't get test-fired nearly enough because "out of sight out of mind". It'll handle the furnace (for heating) just fine, can charge the battery bank if necessary, and will run a very long time on a small amount of fuel so I don't have to keep a small gas station on hand.

One other reason I favored the solar system over a big generator: noise! A neighbor two houses down put one of those Generac whole-house units in. We had an ice storm where we were without power for several days and all we heard all day long was that godawful racket coming from his backyard! First, it's annoying - especially late at night, especially the cheaper (and much noisier) brands. Second, it advertises there's a generator there. My solar system is silent!

Edit: Once, for giggles, I calculated when my payback would be. If everything ran perfectly and nothing required replacement, I'd see financial payback in something like 57 YEARS! Of course I've since had to replace the battery bank so probably closer to 100 years...

Point being, this will never be a financially reasonable thing I'm doing, but it does have other advantages.

gww1 · November 2014

Re: Battery vs generator?

Edit: Once, for giggles, I calculated when my payback would be. If everything ran perfectly and nothing required replacement, I'd see financial payback in something like 57 YEARS! Of course I've since had to replace the battery bank so probably closer to 100 years... Point being, this will never be a financially reasonable thing I'm doing, but it does have other advantages.

My pay back guess was very simular.
gww

jcheil · November 2014

Re: Battery vs generator?

gww1 wrote: »

My pay back guess was very simular.
gww

I installed a real electric meter (because it was cheap and is a good conversation piece) on the output of my off-grid system and take readings every month (just for fun).
So far I average about $30-$40 worth of grid-power each month. So, payback time for $32k assuming nothing breaks and batteries never need replacing...76 years

stmar · November 2014

Re: Battery vs generator?

jcheil wrote: »

I installed a real electric meter (because it was cheap and is a good conversation piece) on the output of my off-grid system and take readings every month (just for fun).
So far I average about $30-$40 worth of grid-power each month. So, payback time for $32k assuming nothing breaks and batteries never need replacing...76 years

Alternative power = $$$$$$$$
Security knowing you have power when the grid is down = Priceless!!!!!!

jcheil · November 2014

Re: Battery vs generator?

stmar wrote: »

Alternative power = $$$$$$$$
Security knowing you have power when the grid is down = Priceless!!!!!!

Actually I 100% agree with you on that fact.
Not to mention I have no other choice IF I want power

It was funny, my 6 year old niece was here last week and during a thunderstorm she said "what do we do if the power goes out?". I laughed.
They are so used to the grid going down every time there is a storm in the "real world"

gww1 · November 2014

Re: Battery vs generator?

j
On the opposite side in the real world my inverter shorted in a storm and left me on the grid for power or I would have had none.

I now need the 2000 watts more panel and mini-split acs and I might get close to a system as impressive as yours.

You need it more then me and it is nice to see what you contend with so I sorta get to try before I buy, living through you experiances.
Cheers
gww

jcheil · November 2014

Re: Battery vs generator?

gww1 wrote: »

j
On the opposite side in the real world my inverter shorted in a storm and left me on the grid for power or I would have had none.

I now need the 2000 watts more panel and mini-split acs and I might get close to a system as impressive as yours.

You need it more then me and it is nice to see what you contend with so I sorta get to try before I buy, living through you experiances.
Cheers
gww

Yeah that sucks when equipment fails, but that is also (in a way) why I got the dual inverter setup with the X240 transformer. If one of my inverters takes a crap, I can limp by on the other and still produce 240V. But yes, like you said, all at a cost $

oil pan 4 · November 2014

Re: Battery vs generator?

A solar power system is infinitely more complex and expensive than a regular generator.
Plus the batteries are not just going sit around and wait for you to use them. They will constantly be wasting away even with non use.
You could get a new $1200 generator from lowes and a $200 to $300 used generator off CL as a backup and have $14,000 to spend on gas. If your budget is $15,000, which seems reasonable. Then put together a spare parts bag for about $100 with a generator voltage regulator, spark plug, fuel filter, carb gaskets and so on will cover most breakdowns.
Then for a few hundred more dollars you could add some inverters and a battery or 2. Have generators for battery charging and to power large items and inverters and battery for small loads. That is what I did.

When things go bad and you need to trouble shoot and fix something what will be easier?
A rudimentary generator or solar power and battery system built upon advanced digital electronics that control high power solid state switching SCRs or IGBTs.
A generator in a shed is virtually impervious to most bad weather. A solar power system with exposed solar panels and wiring seems like a bad backup to a situation that will be caused by bad weather, lightning strikes, falling tree limbs, wind damage, hail ect.

I will take the generator.

gww1 · November 2014

Re: Battery vs generator?

Oilpan
I agree with you 100% however, just the generator does not sound nearly as (fun?), nor can you learn as much or make as many mistakes.
Cheers
gww

jcheil · November 2014

Re: Battery vs generator?

gww1 wrote: »

Oilpan
I agree with you 100% however, just the generator does not sound nearly as (fun?), nor can you learn as much or make as many mistakes.
Cheers
gww

I'd have to say if you wanted to have FUN, and see what it is like to spend a crap load of money, buy a boat instead

BB. · November 2014

Re: Battery vs generator?

"Boat" -- Noun: A hole in the water, surrounded by wood, into which money is poured.
"Genset" -- Noun: Device which turns $100 bills into noise and smoke.
"Solar Power" -- Noun: A shed whose roof, walls, and floors are covered in $100 bills.

-Bill :roll:

Blackcherry04 · November 2014

Re: Battery vs generator?

BB. wrote: »

"Boat" -- Noun: A hole in the water, surrounded by wood, into which money is poured.
"Genset" -- Noun: Devices which turns $100 bills into noise and smoke.
"Solar Power" -- Noun: A shed whose roof, walls, and floors are covered in $100 bills.

-Bill :roll:

Unfortunately, I have several of all three. Bigger isn't necessarily better either, just more expensive.

stmar · November 2014

Re: Battery vs generator?

Funny you should mention BOATs, I was thinking of buying a place in a warmer climate on the water and of course a boat would be involved. More elaborate than the canoe I now have, which has an "electric" battery powered motor. A friend once told me the definition of BOAT = Bust Out Another Thousand.

oil pan 4 · November 2014

Re: Battery vs generator?

gww1 wrote: »

Oilpan
I agree with you 100% however, just the generator does not sound nearly as (fun?), nor can you learn as much or make as many mistakes.
Cheers
gww

If you want a small solar project to mess have you seen the solar monolith post? If I remember right it was a small portable solar power supply that would be perfect for backing up lower powered loads.
Using solar for backup power just doesn't seem like a great idea.
At least with the solar monolith you can try it small scale first then scale it up.

jcheil wrote: »

I'd have to say if you wanted to have FUN, and see what it is like to spend a crap load of money, buy a boat instead

No, personal water craft. Usually cheaper, more fun and you can tow one with just about anything found driven on the road aside from the smart car.
Boat usually = truck too.

ZoNiE · November 2014

Re: Battery vs generator?

BB. wrote: »

"Boat" -- Noun: A hole in the water, surrounded by wood, into which money is poured.
"Genset" -- Noun: Devices which turns $100 bills into noise and smoke.
"Solar Power" -- Noun: A shed whose roof, walls, and floors are covered in $100 bills.

-Bill :roll:

Yep, that about covers it.:roll:

jcheil · November 2014

Re: Battery vs generator?

oil pan 4 wrote: »

Boat usually = truck too.

Or in my case:
Where I live Off Grid = REQUIRES 4x4 TRUCK

(but I wouldn't have it any other way)

AuricTech · November 2014

Re: Battery vs generator?

stmar wrote: »

Funny you should mention BOATs, I was thinking of buying a place in a warmer climate on the water and of course a boat would be involved. More elaborate than the canoe I now have, which has an "electric" battery powered motor. A friend once told me the definition of BOAT = Bust Out Another Thousand.

Back in May 2014, someone posted on this forum about this project, which uses a canoe with outriggers and a trolling motor as the basis for a trailer-mounted solar generator. It can provide power for the owner's RV, when he's not out on the water with it....

Battery vs generator?

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