Large DIY 48v off grid system to replace 2500 kWh/mo usage

[Dan3D]

Hello!!!

I am looking for any and all advice on a 48v solar / battery system for a house with 110 and 240v. I want to be fully off grid if possible. We heat with wood, have a well for water, and going solar is the next step toward a self sufficient country homestead and farm. I would like battery power for 3 to 5 days with minimal or no sun.

I’ve been watching DIY Solar channel for years and waiting for the right time to build my own system. Now is the time!!!

My property has several units on it. The main house and 3 additional tiny home / camper spots use between 2000 kWh and 2500 kWh per month total. We have not even began searching out how to lower our electricity usage yet but we will do that in the future. For now we want to get a system with room to grow so planning for 2000 kWh+ per month is the right move for us.

Simplicity is important to us, we want to build this system on our own. We have an electrician, a carpenter and a mechanic in the family that will help with our install.

An ideal build would be second hand parts, when appropriate to save money, and new equipment when that is the right call, but I do not want to build battery packs from hundreds of cells... purchasing prebuilt packs is best for us.

We have PLENTY of space for installs that take up a lot of room.

I was considering buying Rich Solar panels, I have no ideas yet on which battery systems to use (but I’m willing to get used gear to save cash), and I just recently found out about Growatt 48v 80amp charge controller / inverter. I believe those can be configured in series / parallel for 240v applications.

Please excuse how much of a newbie I am. Although I have watched Will Prowse YouTube channel for yearshave only just recently began researching for our system.

Budget: Depending on how off grid we can be, budget could be well over $20,000. If it’s possible to build it in a way that we can add on to it later, and spend less upfront (like fewer solar panels / batteries at first) we would like that.

We may buy a used Tesla after installing the system. We’re tired of ICE cars.

Suggestions for Panels, Batteries, Wiring and Equipment?

 

[snoobler]

Welcome to the forum.

2500kWh/month =

83kWh/day

You'd need that much battery power per day. You probably need to up your budget.

Use link #5 in my signature to find your available solar. If you can't find a nearby city, link #6 can use lat, long.

 

[snoobler]

Also, you need to account for inefficiencies. Assume a 15% conversion loss from battery to 120/240VAC, so you'll need

98kWh/day

Here's an example of my available solar in Mesa, AZ:




I selected my panels to have an optimal year-round tilt.

Using December as an example, since it's the lowest, to provide 98kWh/day of energy, I'd need:

98kWh/4.78h = 20.5kW of panels.

Buying used batteries is a great way to get very poor value. With used tires, you can take a look and see how much life is remaining in the tread. Not so with a battery. Definitely buy new batteries. Your best VALUE batteries may be flooded lead acid. Since your entire life is essentially daily maintenance, a weekly or monthly check of your batteries probably isn't a big deal. Properly maintained FLA can last a decade, and they're the lowest price option. AGM has about half the life for more money but no maintenance, and pre-assembled LFP is going to cost you big.

If you're looking at the MPPT solar/Growatt lines, make sure you purchase them from http://www.watts247.com as they're the authorized U.S. distributor. Anywhere else, and you may get no support. Note that most of those units are high frequency inverters with multiple cute little transformers that can't handle a significant surge like starting big electric motors or well pumps. Note that these are all cheap Chinese units with a limited history. You HOPE they last. There are bigger names with bigger price tags that have decades of reliable history that you EXPECT to last.

One big way to save on that kind of solar is with used:

Used SanTan 240W Solar Panel | SanTan Solar

store.santansolar.com

Hard to find cheaper panels, and with a very large order, their shipping would be tolerable.

You should immediately consider ways to conserve as you're budget is 1/3 to 1/2 of what you'll need.

 

[toms]

Work out your maximum overnight power use. That is 75% of your battery requirement. Use LiFePO4 cells.

Work out your solar input as described above, install enough panels so that on average your batteries get fully charged.

Install a generator the correct size to charge your batteries and use as required.

That will get you the most cost effective power system.

 

[Dan3D]

Awesome suggestions here so far. Thank you.

Does anybody on the forum have experience charging EVs from off grid solar?

I would love to know what equipment they are using to accomplish this.

I drive over 5000 miles a month for my company and removing gasoline from the equation will give me more room in my budget.

 

[Maast]

Regarding your battery bank size: an awful lot depends on where you live. If you're in a super-sunny area you can get by with just one days worth of battery power. If you live in a super-cloudy area (like me in the PNW) you'll need a full 3 days worth of energy usage in storage as your winter power input will be really variable and you'll find yourself tapping the grid or generator often.

Its very difficult and expensive to build a solar system that meets your needs 100% all year. You can save a LOT by building a 80% system and tapping the grid for the last 20%.

Bang-for-buck the best payoff is in energy usage reduction. The first thing to start spending money on is there.

If you drive that much, a 100% electric isnt going to meet your needs, the range is just too limited. A better option would be to a plug-in-hybrid with low cost/mile like the Hyndai IONIQ, Honda Clarity, Toyota RAV4. Of those the RAV has the biggest battery. Take a look at https://evadoption.com/ev-models/available-phevs/#current-phevs/?view_22_sort=field_5|asc
You can expect 40+MPG with a PHEV

 

[Dan3D]

I live in Cincinnati area. Full sun is available year round from my location so I can build the system to maximize on whatever Mother Nature sends my way.

If I did grid tie system instead of off grid, what electronics would be best for my needs? The Growatt looked interesting but if a product with a more proven track record is better then I want to get the right equipment. I’d rather up my budget than build it twice.

I know lead acid has a good value proposition, but I truly hate the chemistry. Can anyone ballpark figure a price for several large lithium ion packs from a reputable company vs a bunch of lead acid for similar available capacity?

If I was to purchase several dozen 240w used panels from a company like SanTan solar listed above, do they send the same panel for the entire order or do they mix and match similar spec panels from different manufacturers?

Thank you all again!

 

[snoobler]

You get about 1/2 the sun I do in Mesa, so you'd need 98000/2.5 = 39kW of panels

Assuming you meant Lithium-iron, no ion - for name-brand reputable LFP, you'll need upwards of $50K in batteries.

When I bought 36 panels from SanTan, I got 36 of the same brand and model, but that was the purchase I made with stickers intact. I paid a premium for that since they're still UL listed. You may need UL listing for your system. The 240W can't be used if UL is required. If you're subject to NEC code, probably can't use them.

 

[2009Bounder2020]

Awesome suggestions here so far. Thank you.

Does anybody on the forum have experience charging EVs from off grid solar?

I would love to know what equipment they are using to accomplish this.

I drive over 5000 miles a month for my company and removing gasoline from the equation will give me more room in my budget.

you need about a half an acre of solar panels to fast charge a tesla... its not even close to possible unless you have a huge budget.
better to charge the tesla off with a big generator.

 

[Maast]

View attachment 37981

You get about 1/2 the sun I do in Mesa, so you'd need 98000/2.5 = 39kW of panels

Assuming you meant Lithium-iron, no ion - for name-brand reputable LFP, you'll need upwards of $50K in batteries.

When I bought 36 panels from SanTan, I got 36 of the same brand and model, but that was the purchase I made with stickers intact. I paid a premium for that since they're still UL listed. You may need UL listing for your system. The 240W can't be used if UL is required. If you're subject to NEC code, probably can't use them.

Wow, thats even worse then here in western WA state, even in Jan we get 3.46kwh/m2/d I didnt think anybody in the lower 48 had worse solar figures than western WA but I guess Cincinnati does, where'd you get the data?

Edit: Solar Energy Local says Cincinnati gets 4.63kwhm2d

 

[snoobler]

Wow, thats even worse then here in western WA state, even in Jan we get 3.46kwh/m2/d I didnt think anybody in the lower 48 had worse solar figures than western WA but I guess Cincinnati does, where'd you get the data?

Link #5 in my sig.

 

[Maast]

Link #5 in my sig.

Interesting, that gives me 1.69kwh for my area. I can't seem to access the NREL right now to doublecheck it though.

Edit: NREL PVwatts gives a Jan data of 1.99 for panels tilted to my latitude (43 degrees) when tilted to 45 that goes up to 2.02, 50 gives a 2.07. thats with 12% losses included in the calculation.

 

[snoobler]

PVWatts just opened for me.

 

[toms]

Assuming you meant Lithium-iron, no ion - for name-brand reputable LFP, you'll need upwards of $50K in batteries.

That is why i recommended getting just enough batteries to cover maximum overnight useage.
The battery cost will likely be closer to 20k - and that 30k buys an awful lot of diesel.

Same for oversized PV. The cost of charge controllers is significant.

Over the total lifespan of an offgrid system, your per kwh cost will be less than half if you size your system as i suggested rather than going for zero generator runtime.