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ketchgould
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# Posted: 23 Sep 2022 12:01pm
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I am trying to design a solar system for a cabin I am building.
There seems to be a trend and possibly a real efficiency in building a 24 or 48 volt system instead of a 12 volt system.
Is the only benefit in a 48 volt system the lower amperage which means lower cost in wires and controllers?
Here is my scenario...I have 4, 12 volt lead acid batteries that are all 150 Amp hour reserve. If I want to build a 48 volt system wouldn't I need 4, 12 volt solar panels and then I would wire my batteries together creating 48 volts and then would only have 150 Amp hour reserve?
If I wired the system as a 12 volt system, wouldn't I only need one solar panel, or more if I needed it and then be able to use the 4 batteries together to have 600 amp hours in reserve?
My power demands are small for the next three years but will increase as my build continues. I want to buy an all in one solar charge controller for the 5000 watt load I anticipate someday, however the unit is generally voltage specific so I need to decide the system voltage now.
Thanks
Christian
Northern Wisconsin
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ICC
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# Posted: 23 Sep 2022 01:33pm
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Batteries and panels, etc..... (Should all be same voltage and amps or amp-hours when connected together)
Connected in Series, Add the Volts. The amps or amp-hours are NOT added. They stay the same.
Connected in Parallel, add the amps or amp-hours, but do NOT add the vilts. The volts remain the same.
The measure of how much energy you have is Volts x Amps = Watts or Volts x Amp-Hours = Watt-hours.
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ICC
Member
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# Posted: 23 Sep 2022 01:46pm - Edited by: ICC
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If building a system with a 24 volt or higher battery bank it would be best to buy higher voltage panels, IMO. My 13 year old cabin system is 24 bolts with 200 watt panels rated at 36 volts or so. But three in series because of the 200 ft distance between pv array and cabin. That reduces the wire size and cost. Use an MPPT charge controller.
Many of my aquaintences and friends who built 12 volt systems eventually changed to 24 volt systems. In general a 48 volt system is not needed unless one is getting into higher rates of use; more like a normal home than a part-time use cabin. My home is 48 volts.
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gcrank1
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# Posted: 23 Sep 2022 03:34pm - Edited by: gcrank1
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Ime' most people underestimate their off grid elec power use and overestimate the elec production of their 'proposed' solar system.
24v right off will be a huge advantage as to wire gauge over distance; copper cables Are Expensive and 12v requires bigger cables for a given distance than 24v to avoid line losses (ie, why generate elec power then not get as much as possible through the 'wires'?).
Those batteries you say have 150Ah 'reserve' do not sound like Deep Cycle lead acid, but 'starting batteries' (real deep cycle batteries dont have a 'reserve' rating). If not deep cycle you Will Not get that 150Ah's out of them, maybe a third of that.
And keep in mind that a lead acid battery needs to typically not be used deeper than the top 25-30% of charge.
So, 'if' those are what I expect they are, that 150 becomes at best 50, which if cycled to 50% depth of discharge (which will likely kill them within 2 years, maybe less).
LA bats will live the longest if only regularly cycled in the top 25-30%, and only occasionally to 50%.
If you need to use lead acid for now and have to buy new your best bang for the buck is Golf Cart batteries, which are Real deep cycle bats. They are 6v, so 2 of those in series makes a 12, another pair wired the same makes another 12 and you parallel wire those two pairs for a 24v bat-bank.
Note that the same caveat applies to all lead acid bats for depth of discharge, but the GC bats are made heavier duty to take some abuse.
Other thing about LA bats is they like to stay fully charged; Do Not let them sit in a discharged state for any length of time, they will self degrade and never fully recover.
Also, you need a min of '2 days autonomy', even better 3 days, that you can run off your battery bank if the weather is so bad you get no recharge sun to run the system. More bats than you think?
So, with that in mind, your solar array needs to recharge the amp hours removed since the prev day and needs to do it asap and within about 3 hours (because that is about all the real solar charging hours you get in a day). Your guess as to 'how many panels' is likely far short.
To properly charge LA bats you have to be delivering much more than the nominal 12v to a 12v battery, same for a 24v bat-bank. This means that your array needs to be doing about a min of 30ish vdc to the MPPT charge controller. Why mppt? Because it will take that higher voltage and match it to the bat-bank in the most efficient balance of voltage and amps, and will do it sooner of a day than the less efficient, and cheap (ie, you get what you pay for) PWM controllers.
Thus, you choose the proper SCC based upon the array you have. Panels are relatively cheap today compared to 10 years ago (though with this inflation/devaluation of purchase power cost will be rising) so 'overpaneling' is a good choice.
This, imo, is where to start because it sets you up for the future and upgrades without having to basically start over new because the 12v system is inadequate. And IF you can sell any of it you will only get back a fraction of what you paid. By then the bat-bank will likely be dying or dead.
On the 'watts' part; amps x volts = watts.
At device that draws 48W on a 12v system will take out 4A per hour from the bat-bank.
Same device on a 24v system will take 2A/hr.
So you can see that the higher voltage will deplete the bat-bank at a slower rate.
Start thinking more in watts and watt hours than amps and amp hours.
Note: as of today 'storage', the bat-bank, is going to be some pretty big money. Even the min. 4 x 6vGC bats will cost you $450ish and up depending upon the quality. And imo you will need more. Even if you did your initial 'learners kit' build and used those bats you mentioned you best consider them sacrificial to the learning curve, you Will Kill Them. Then replace with the GC bats, or if you wont bet below freezing even LFP (dont charge them below freezing).
Btw, dont specifically buy expensive AGM bats in the LA category, they are overpriced for their performance.
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gcrank1
Member
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# Posted: 23 Sep 2022 04:00pm
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Were I you (and I have been  ) of building a cabin and planning.....
Build the cabin with the best solar exposure you can. Ground mounts are far easier to deal with as a practical matter than roof mounts. But either way, be close to good solar exposure and/or orient the roof so the array can be there.
Wire the place for 120v it as if a house. Use an adequate service panel for the size/ie, outlets and fixtures/future possible appliances.
Power the service box with a generator.
You may need to meet code and inspections, though?
With that done you will have all the power you want/need and can be really researching solar and 'working up to it'. It can always be added into the mix if you have done the above.
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ketchgould
Member
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# Posted: 23 Sep 2022 10:42pm
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The four batteries I have are 12 volt golf cart batteries.crown deep cycle lead acid. 125 AH rating. Don’t I end up with more amp hours in reserve at a lower voltage? If I create a 24 or 48 volt system wouldn’t the amp hour reserves be reduced by half or a quarter?
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ketchgould
Member
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# Posted: 23 Sep 2022 10:44pm
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Or does it balance out where the higher volts reduce the amount draw making the reserve capacity the same regardless?
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ICC
Member
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# Posted: 23 Sep 2022 11:13pm - Edited by: ICC
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With series connected batteries the volts get added. The amp-hour rating remains the same.
{All interconnected batteries should be same voltage and amp-hours. Unmatched combinations create various problems.}
Because the volts increase, the total energy, the watt-hours also increases.
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So two 12 volt batteries with a 125 AH rating, connected in series supply 24 volts and 125 AH capacity. 24 volts x 125 AH =
3000 watt-hours.
If those two batteries are connected in parallel they would supply 12 volts but at (2 x 125 =) 250 AH capacity. 12 volts x 250 AH = 3000 watt-hours. The same total energy.
The higher volts reduces the amperes drawn. If volts are doubled the amps are halved. That means smaller cables may be used. Or the cables can run a longer distance without excessive voltage drop.
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ketchgould
Member
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# Posted: 24 Sep 2022 10:31am
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Now I get it, thanks.
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NorthRick
Member
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# Posted: 24 Sep 2022 11:08am
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Quoting: ketchgould The four batteries I have are 12 volt golf cart batteries.crown deep cycle lead acid. 125 AH rating. Don’t I end up with more amp hours in reserve at a lower voltage? If I create a 24 or 48 volt system wouldn’t the amp hour reserves be reduced by half or a quarter?
To be more direct on what ICC said, convert everything to watts and watt-hrs and now you'll be doing an apples to apples comparison.
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ketchgould
Member
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# Posted: 24 Sep 2022 01:20pm
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Some of the inverters output AC at 230 volts. Is this for other countries than the US?
They seem to cost less money.
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Nobadays
Member
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# Posted: 24 Sep 2022 01:56pm
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Quoting: ketchgould Some of the inverters output AC at 230 volts. Is this for other countries than the US?
Mainly the All-in-One units....and yes and no. They put out single phase 230vac. If you need 240vac (US standard) you would need two of these units as in the US we use 2 phase (split phase) 240vac.
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ICC
Member
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# Posted: 24 Sep 2022 02:10pm
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That is useless in the US or Canada. It is also very likely putting out 50 Hz current.
For a simple small to medium system you need 120 VAC and 60 Hz.
Depending on what devices you want to operate you may need pure sine wave. Microwave, many items with motors....
Ya know when looking for solar system advice more information about the use and all that is better than little or no information.
And to NorthRick's comment.... Volts and Amps are important but, to me and many others, Watts and Watt-hours make thinking of what is required easier.
I reccomend that diysolar site. Take some time to learn about solar and batteries. "Haste makes waste" was a fave saying of my Dad.
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Steve_S
Member
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# Posted: 24 Sep 2022 04:26pm
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https://www.mobile-solarpower.com/all-in-one-122448v-packages.html
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gcrank1
Member
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# Posted: 24 Sep 2022 08:55pm
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Steve, do I understand correctly that those units can have a gen attached in place of the grid connection and still have the auto-transfer switch function properly?
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Steve_S
Member
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# Posted: 25 Sep 2022 08:37am - Edited by: Steve_S
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@gcrank1, Yes I believe so but it appears from posts made by some of the membership that a clean inverter generator works fine but not a rough construction type.
Personally, I would go with the Growatt product line rather than MPP "IF" I was to go with an AIO. The HF Models for virtually all AIO's (Except Victron) also have a fairly hefty standby power usage, the LF models are much more frugal on stand-by power.
NB: If I had deep enough pockets and building a system "today" I would go Victron all the way. They were not available in Canada when I built my system back in the day.
Now Will just did a review - teardown of a new EG4 6000EX All-in-one: 6000W LF 120/240V Inverter, 7500W PV Input, 120A AC Charger
https://youtu.be/NJIAS5hYg4s
It is only $1300 USD from
https://signaturesolar.com/eg4-6k-off-grid-inverter-6000ex-48hv/
Still has a high stand-by power usage.
A Little bit of "Hindsight" Experience to share for those considering a New Solar Setup. I built my system around a 120VAC plan with no 240V appliances or devices and due to cost (everything for 240V was a hell of a lot more bucks back in the day).
IF I was building a system TODAY, then I would do a Split Phase 240V. I would wire 240 for a stove space (even induction stove/ovens need 240), one for a dryer receptacle and one for outside (EV Charging).
When I ran my underground conduit from the Powerhouse to the house I did however put in 8/3 (40A@240V)& 6/3 (60A@240V) NMWU Wiring to accommodate 240VAC in the future. To properly accommodate 100A @ 240V I should have used "0 AWG or 00 AWG for 145A".
Depending on WHERE you are Nation/Province/State rules vary a lot. In Ontario Canada the Minimum 240VAC Amperage for any home is 100A and virtually no Insurance Company will insure a home with less than 100A service. Legacy systems with 60A service have a hard time getting insured and new builds with less than 100A service do not pass inspection.
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