New install design

[taxesarewaytoohigh]

We are planning an off grid 32 x 42 shed in Wisconsin with an attached part-time passive solar living space (on cement slab) of 615 sq. ft., and have been trying to determine what is the best off-grid solar system for our situation.


We have calculated our power needs to be 7kwh during the day in the summer with a 12000 BTU mini-split for air. In the winter we believe we will need 2.6 kwh per day, not including any heating. We haven’t figured out the heating yet. We love everything about wood heat and have been heating with it for decades… but old age is making it a little less attractive… (well, okay, a lot less attractive.) We are considering in-slab radiant or propane direct vent units or possibly a mini-split. But primarily while still capable of chucking in wood we’ll likely keep chucking in wood.



We don’t plan to live in this house all year so, it will likely be vacant for the harshest part of winter which is generally December, January, and February. The plumbing is designed so that it can be drained in the winter when not in use. However, we can envision several scenarios where this might be used as a full-time, year-round house, and want to plan for that possibility.



I have limited experience with solar but have installed solar on a couple of truck campers so I’m not completely lost, close maybe.



Renogy has a roughly $6500 package (current deal) that is a 2.5 Kwh system with panels and 8-200 AH AGM batteries. This includes a 48V 3500 watt inverter charger and some installation items. This, out of the chute, looks like a reasonable system to this beginner.



My questions:

Is the Renogy system worth looking at?

Does this package have enough horse power to meet the need?



Are AGM batteries the best option based on price for part time use?

Do they need to be stored in heated envelope? Unless building codes say otherwise, we are planning to place the batteries in an insulated room inside of the shed that is open to the apartment; some heat may get in there if the door is open but no heat is planned specifically for the “storage room”. Is that a reasonable set-up?



My understanding is that lithium batteries can be stored in a sub-zero environment as long as they aren’t being charged or discharged. Is this a good idea? I understand that there are definite advantages to lithium, but we have concerns about fire hazards. Perhaps the batteries should be in a separate shed regardless of the type?



I have been reading some of the threads on batteries and finding that I don’t know what a lot of the acronyms mean. Is there any place on the forum that serves as a glossary or cross-reference? For instance, what is an EG4?



Comments are welcome.

 

[svetz]

Welcome to the forums!

We have calculated our power needs to be 7kwh during the day in the summer...In the winter we believe we will need 2.6 kwh per day...[looking at] 2.5 Kwh system with panels Assuming you run the AC May through August, you can expect an insolation of around 5.25, so 7/5.25 = 1.3 kW array minimum. 2.5 kWh is therefore plenty! In November you'd need 2.6 kWh and at an insolation of 2.7, a 1.3 kW array would provide 3.51 kWh. So, building for summer gives you plenty for winter. and 8-200 AH AGM batteries. This includes a 48V 3500 watt inverter charger and some installation items.

From solarElectricity, for Madison Wisconsin, panels at 62° to optimize for summer: (Madison was randomly picked, visit the linked website or use SAM for your actual location)​

See the Battery FAQ, and here's a Video that compares battery technologies.

8x200 AH batteries is 12x200x8=19,200 wh. But, discharging below 50% can seriously degrade them, so that's more like 10 kWh. How quickly you discharge them also affects how much power they have and there round trip efficiency isn't as good as lithium. AGMs don't have as many cycles, can't be as deeply discharged without degradation, and are expensive in terms of $/cycle.

How much battery do you need? If you go up on weekends, you'll need a max of two day reserve (although I doubt you'd do a weekend trip if it was going to be raining the whole time). If you're spending the whole summer, 3 days reserve isn't unreasonable. But, if you're consuming 7 kWh per day, for a 3 day reserve you'd need 21 kWh.

Option: If you drive an electric car with a 90 kWh battery, your car can easily be your battery and you can probably charge it up on the way out or in if needed. 3 days power would be 21 kWh in your worst-case scenario, so if the aforementioned EV had 300 miles range, 3 days of powering the place would be ~70 miles of range. (Heck, with this setup you could ignore the solar aspect all together ; -).


Will just tested a $132 100 Ah LFP battery. 8 would set you back a grand.

...Renogy has a roughly $6500 package ...Is the Renogy system worth looking at?

$1056 - 8x 100Ah LFP batteries
$ 800 - 6x 400W solar panels (Santan sale)
$ 650 - Renogy 48V 3500W Inverter

$6500 seems high to me, but I don't know what all is in the kit. For example, you'd still need mounting hardware for the panels and wiring.

My understanding is that lithium batteries can be stored in a sub-zero environment as long as they aren’t being charged or discharged. Is this a good idea? I understand that there are definite advantages to lithium,

Most LFP batteries will be ruined the first time they try to charge in subzero. However, most these days come with low-temperature cutoff (Will tests these in the batteries he reviews). The problem with them being cut-off is that you can't charge them. Some have heaters to get around. Cut-off might be sufficient for you since you don't plan to be there in the coldest months. But, a small conditioned space can keep you going, unlike AGMs, they don't lose the majority of their power when cold so the space just needs to be kept above zero (or whatever the brand of batteries calls for, some of the newer ones can go colder).

but we have concerns about fire hazards. Perhaps the batteries should be in a separate shed regardless of the type?

LFP are safe. Take that with a grain of salt, a screwdriver falling across the terminals could easily set fire to something else. It's other chemistries that you have to watch out for that have thermal run-away (e.g., NMC).

I have been reading some of the threads on batteries and finding that I don’t know what a lot of the acronyms mean. Is there any place on the forum ...

See Commonly used Forum Acronyms & Abbreviations

... what is an EG4?

EG4 Electronics is a company that primarily manufactures its products in China, with facilities in Guangdong and Jiangsu provinces. Their website says they have a system integration facility in Houston, Texas, where final assembly and quality control for North American markets take place to comply with U.S. regulatory standards.

Hope that helps!

 

[NC_hydro]

Just get an LFP that has built in heater that can charge if cold. Trophy is one I'm sure there are others. If budget is paramount then I would look at one of these for around $1k shipped: https://www.alibaba.com/product-detail/New-SRNE-ASF48100U200-H-Inverter-10kw_1600810731909.html 10kw, split phase should run everything you would need in a build like yours.

https://trophybattery.com/ a single 300Ah from these guys would give you 15kWh of capacity roughly. 10yr non pro-rated warranty, meaning if at year 9 the battery dies they give you a replacement vs 1/9th of the cost of the battery.

But if you have some wiggle room in your budget I'd lean towards a Victron System with two of these https://www.currentconnected.com/product/victron-48v-multiplus-2-5kva-120v-inverter-70a-charger/

And one of these 250/100 MPPT. https://www.currentconnected.com/product/victron-smartsolar-charge-controller-mppt-150v-250v-vecan/

If budget is most important for panels: https://watts247.com/product/insane-5kw-solar-panels-pallet-used/ 5kW of panels.
Also check Facebook Marketplace sometimes there are some good deals on panels there, all depends on your budget.

 

[svetz]

Heated batteries seem expensive compared to a diy Insulated/heated enclosure (or just buried below the frost line).

 

[NC_hydro]

Heated batteries seem expensive compared to a diy Insulated/heated enclosure (or just buried below the frost line).

Of course DIY will always be cheaper.

 

[taxesarewaytoohigh]

I appreciate all of the comments and advice… very informative! There’s a lot to learn.
After watching the video on batteries we feel that lithium is actually the better option for us.

We see after working with the PV watts program that we might not actually need the 2.5 kw system we were looking at from Renogy… a 2.0 kw system would probably be enough even for 2 – 3 days of autonomy.

We were thinking 12v because that’s what we’ve used in our RV’s, and it’s familiar, but we realize now that 48V makes more sense.

Since we are newbies at this stuff we would prefer to stick with higher quality providers rather than going with the cheapest things available. I’d feel more comfortable going with a kit from a single source that is reliable and has good customer service.

Can anyone recommend a supplier that fits that category?

Another thing that we’re wondering about is the fact that so many of the components we see seem to be internet connected for updates and communication. Our remote location is not only off-grid, but there’s not reliable internet. Is this a problem, or does it limit us to some specific brands?

Last question: Our building should be going up in early summer. Have tariffs already kicked in for the solar panels and batteries (I assume most components come from China), or does it make sense to buy what we need for our system ASAP?

Thanks for all the help. This forum is amazing!