Inverter/Solar backup

[RJ]

I originally started this discussion  http://www.microcogen.info/index.php?topic=3573.0 as a alternator question and it morphed into this so I thought I would restart it here:

Looking to build a battery backup system for the house during power outages. Basically to run items during the night to avoid running the generator for long periods.

I'm certainly new at this so for those of you that have knowledge please chime in.

I'm looking to run average 300w for 6 hours for a total of 1800 w/h

So 4 golf cart batteries in series for 24v@225ah should suffice and keep me within 50% discharge.

Debating on wether to install solar right off or wait. Leaning towards initially.

System components I'm considering buying:

Intverter: Cotek ST2500-124 https://www.invertersupply.com/media/data/ST2500.pdf  Originally planned to buy the 1500/ 2000w 24v version but this line is being discontinued and can purchase the 2500w version for a significant discount @ $600
             This inverter has a built in 30a transfer switch. I can supply electricity from either the grid or from my generator in the event of a power failure and when turned off with automatically switch to battery backup. Manual is here:
              https://www.invertersupply.com/media/data/ST%20SERIES_Manual.pdf

Batteries: 4 interstate 6v 225ah GC2 batteries ~ $350

Solar Charge controller: TS-MPPT-60 Probably overkill but can be re-purposed into a larger system down the road if desired plus I can also use this as a charge controller from a currently owned 48v 1000w power supply. $600

Panels at a total loss as to what is best looks like with one controller and 24v was looking at 4 of these https://www.ebay.com/itm/4PCS-S-ENERGY-300W-MONO-BLACK-FRAME-SOLAR-PANELS/253190891576?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 at about $1200 to my door.

My battery bank should be charged at around a C/8 from what I have read for FLA. 225/8= 30 amps I figured 4 panels would give me fudge factor and setting two due south and perhaps one SE and the SW. Just a thought...

Total cost ~ $ 2750 plus $250 for odds and ends... ~3k

I'm certainly not doing this for an economical standpoint. More as a learning/hobby standpoint. From a simple dollar cents perspective it's certainly not a wise investment.

Have several generators but am looking at a small Champion 2800/3100 inverter generator as the primary companion to this system. Already purchased.

Later down the road if my wife and I decide to get a camper we can adapt parts of this system into that. Sort of dual purpose.

-RJ

[Fordguy64]

There are much better deals out there for solar panels..

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F272901963548

Probably 300$ for shipping.


Other than that your general plan sounds good

[mobile_bob]

if it were me i would be looking to use what is known as the "50-80" charge regime

this will give you about the best in efficiency over the long haul, it works like this

you need 1800w/hrs? if so

divide by 3 and then multiply the result by 10
this will give you the total installed battery capacity needed to use the regime

so basically 1800 divided by 3=600.... 600 x 10 = 6000 w/hrs of battery capacity

for 12volts (as an example, you likely will want to use at least 24 volts and maybe even 48volt system)

6000 divided by 12 = 500amp/hrs

this allows you to use the batteries from 50% state of charge up to 80% state of charge,  this is the range where
the batteries can accept a higher charge rate and the highest transfer efficiency.

then every week to 10days do a top off, from 80% to 100% state of charge, which will take many, many hours
(comparatively speaking) at progressively lower charging efficiency... best done with solar panels in my opinion.

over the life of the batteries, assuming lead acid deep cycle batteries, this regime has been proven to be the most efficient
and will get you the most amp/hrs out of your batteries over the long haul, which of course equates to the lowest cost per kw/hr.

trying to use the batteries down to 50% and then recharge to 100% daily will be really hard to do, and over time harder on the batteries, uses more water, and results in higher cost per kw/hr, and shorter lifespan.

it has been many years since i was involved in this sort of question, and i think from memory i am correct in my assertion, at least as it relates to common deep cycle lead acid batteries and their charging.

went back and reread your post, and have a couple more thoughts that might be more appropriate to your needs?

if you are only using this for intermittent use, by that i mean maybe once a month or so for an overnight outage?

you might consider using agm (absorbed glass mat) batteries, use them down to 50% or so, and then recharge with your genset, or if there is enough time between outage, use the panels to charge them back up....agm's are more tolerant of high discharge rates, sitting longer between recharges, although a bit more of a stickler of charging rates so as not to cause them to vent and dry out...

it really depends i suppose on many more factors that you can answer

1. how often do you see then need to be on battery power?
2. can you use the genset to do bulk charging?
3. can you use solar to top off and equalize the batteries?
4. are you offgrid, or are you grid connected?
5. if ongrid, is this a system to handle the prescribed loading if the mains go down?
6. if ongrid, how often and how long are you out of power?
7. if offgrid, are you using a generator to supply most of your needs?
8. if offgrid and on generator power, is this a means to limit runtime?
9. probably a bunch more questions...

the deal is this, there are so many answers to this question, some better than others, some much worse than others, and some much better...

the more information you can provide the better a system that can be designed.

perhaps you have answered these and other questions in the other postings, if so, please accept my apologies
i find i am very far behind reading here, and often times miss lots of information.

fwiw
bob g

[RJ]

went back and reread your post, and have a couple more thoughts that might be more appropriate to your needs?

if you are only using this for intermittent use, by that i mean maybe once a month or so for an overnight outage?

you might consider using agm (absorbed glass mat) batteries, use them down to 50% or so, and then recharge with your genset, or if there is enough time between outage, use the panels to charge them back up....agm's are more tolerant of high discharge rates, sitting longer between recharges, although a bit more of a stickler of charging rates so as not to cause them to vent and dry out...  

Yes this would be intermittent use. This system is really to be a learning curve for me. Batteries/Solar the entire nine yards I looked at AGM batteries briefly. They looked to range about 2x-3x the cost of flooded.

To be completely honest, I see these batteries if anything dying of old age rather then life cycles, which is why I wasn't overly concerned about the 50% SOC. Say given battery is good for 500 cycles at 50% SOC. This system is designed primarily for power outages to supplement my generator during an outage. Even if I needed it 75 times in one year that would be a lot IMO  that's still nearly 7 years.

Perhaps I'm thinking about it incorrectly?

it really depends i suppose on many more factors that you can answer

1. how often do you see then need to be on battery power?
2. can you use the genset to do bulk charging?
3. can you use solar to top off and equalize the batteries?
4. are you offgrid, or are you grid connected?
5. if ongrid, is this a system to handle the prescribed loading if the mains go down?
6. if ongrid, how often and how long are you out of power?
7. if offgrid, are you using a generator to supply most of your needs?
8. if offgrid and on generator power, is this a means to limit runtime?
9. probably a bunch more questions...

1. 10-15/year
2. Yes
3. That is certainly part of the plan.
4.connected
5. Yes, then some. It will run everything but the 240v appliances.
6. As always depends. in the year I've lived here, the outages have been anywhere from  6 hours to 2 days, although recently several years ago it was out for 1 week from an ice storm
7.Yes
8. Yes, primarily at night.
9. I'm sure and agree

perhaps you have answered these and other questions in the other postings, if so, please accept my apologies
i find i am very far behind reading here, and often times miss lots of information.

fwiw
bob g

No worries, and thank you for chiming in, I know you're a wealth of knowledge.

[RJ]

There are much better deals out there for solar panels..

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F272901963548

Probably 300$ for shipping.


Other than that your general plan sounds good

Thanks for the link. That's a pretty low voltage panel. I would think for a 24v system I would want something with a higher VMPP?

As I said I have very limited experience in solar.

[LowGear]

Not to digress too far but where do you live that you need power back-up more than a couple of times a year?  And for more than a couple of hours?

[RJ]

Not to digress too far but where do you live that you need power back-up more than a couple of times a year?  And for more than a couple of hours?

No worries.

Used to live in VT but I couldn't handle the political climate and the taxes there are brutal. I was paying nearly $6,000/year in property taxes for a $275,000 house!  I still own that house but now have a friend living there paying them. Hel has use of all my toys still there, including my 8kw diesel generator, backhoe etc. He just got out from a 5 day power outage. Outages there are common and often extended. It's a rural state of only 600k.

Now I live in the sunny SC in an area that is a transition zone. Little snow but cold(cool) nights and warm(er) days in the winter. It also means ice is not uncommon and when it does snow it shuts everything down including pwr that is often slow to be restored. Then I also get the occasional tropical storm. Irma came thought recently and we lost power for two days and many for longer, last year it was Mathew. A few years ago we had an ice storm and power was out for nearly one week.

So the potential uses are there, and it seems like a good opportunity to get my feet wet with solar and batteries.

[glort]

I think the question low gear was asking as I am wondering myself is how many TIMES a year would you loose power?

[RJ]

I think the question low gear was asking as I am wondering myself is how many TIMES a year would you loose power?

Gotchya. Having only been living here just over a year, so far 5 times, two were 24+ hours.

[Fordguy64]

I️ would get 6 panels and run 3 in series and the two series in parellel. That will get your voltage up since you are using an not charge controller. Although I'm not sure what the max  input voltage is on that charge controller but most are 150v in

[mike90045]

TS-MPPT-60 Probably overkill but can be re-purposed into a larger system down the road if desired plus I can also use this as a charge controller from a currently owned 48v 1000w power supply. $600

That is a very fine controller, I have 2 of them and a Midnight classic   Generally, wire your PV array to be 2x battery voltage to get the best performance from the controller, more voltage is fine till you reach the 150V limit, but more than 2x battery voltage, you get higher downconversion losses (more heat)

[LowGear]

And you're not going to grid tie? 

[RJ]

And you're not going to grid tie? 

I don't have any plan to at the moment. The major limiting factor is I'm currently renting.

That being said this coming summer we will hopefully be building our next home, although the regulatory hurdles make it unlikely.  The extent will probably be in the form of load shedding as to avoid all the interconnect hurdles.

[RJ]

TS-MPPT-60 Probably overkill but can be re-purposed into a larger system down the road if desired plus I can also use this as a charge controller from a currently owned 48v 1000w power supply. $600

That is a very fine controller, I have 2 of them and a Midnight classic   Generally, wire your PV array to be 2x battery voltage to get the best performance from the controller, more voltage is fine till you reach the 150V limit, but more than 2x battery voltage, you get higher downconversion losses (more heat)

Mike, any input on the Victor Energy MPPT controllers? Such as the SmartSolar MPPT 150/85 https://www.victronenergy.com/solar-charge-controllers/smartsolar-150-85-150-100

[mike90045]

...

Mike, any input on the Victor Energy MPPT controllers? Such as the SmartSolar MPPT 150/85 https://www.victronenergy.com/solar-charge-controllers/smartsolar-150-85-150-100

No experience with them