Should I build one expandable system or multiple independent systems?

[CampLife]

Hello everyone!

Excited to get back into solar and looking forward to learning from this site! I'm new to the form and don't have much experience with solar. I built a small 12v solar setup about 4 years ago. It consisted of two 100ah lead batteries, a 100-watt foldable solar panel from Renogy (with a 30a Adventurer Charge Controller), fuse box, kill switch, and 750-watt inverter. I had the system operational for about 8 months but unfortunately, the batteries got messed up are no longer useable.

Over the next couple weeks, I'd like to build a new system but upgrade to lithium this time around. I'm hoping to reuse the wires (have some 2-ga, 10-awg and 14-awg), fuse box and kill switch I have from my first build. I'd also like to add a Dc-to-Dc charger and whatever else may be necessary. The inverter I currently have is modified sine wave so it may be a good idea to upgrade since I am going to be powering laptops, phones etc.

I plan on using this new system for 2-6 months. Then, after that initial 2-6 month period, I should have more space for solar panels and batteries. At that point, I'd like to expand on the system or create a second one. However, I'm not sure which is the best approach to take, expand or multiple systems?

Another concern for me, for the first 2-6 months I'm planning on having just the one, 100-watt foldable 12v panel for solar. However, after the first 2-6 month period, I'd like to add more solar panels and batteries and make the whole thing a 24v system.

Because of all that, I'm not sure if I should build a 12v system now and add a second 24v system later. Or build a 12v system now and add a second 12v system later (or add onto the existing 12v system). Or If I should build a 24v system now and add a second 24v system later (or add onto the existing 24v system).

If, for my current build I go 24v and buy a 24v battery, a 24v Dc-to-Dc and a 24v inverter, then that'd make my 12v foldable solar panel obsolete. I don't think I have the ability to use two solar panels currently (there's a slight chance I can get two panels currently but it'll not ideal). Is there any way I can get a 12v solar panel to charge a 24v battery? Do you think I could rely solely on a 24v Dc-to-Dc charger to charge the system?

I like the idea of having multiple systems in case something breaks down, you could swap out components from one system to another. However, if I buy components for a 12v system now, then add a second system at 24v in 6 months, I don't think I'll be able to swap those components around anyways, so that'll defeat the purpose of having multiple systems. Would it be beneficial for any other reason to have two systems of different voltages, one 12v and another 24v?

For the initial 2-6 month period, my energy needs are as follows (I may be doing the calculation wrong):
Working on my computer for up to 10 hours a day (an 85watt laptop, I believe) - 850 watts
A small Dometic 12v fridge (CoolFreeze cf-25, 35 watts) - 840 watts
A 120v slow cooker for 7 hours every two or three days (says 250 watts on plug, it's a 6-quart Hamilton Beach) - 1750 watts
Enough lights for about 75 square feet, powering smaller portable batteries/phone, other misc. - 1,000 watts (a guess)
If possible, it'd be awesome to run a 120v electric water distiller for 6 hours a day (says 530 watts on plug) - 3,180 watts

For a total of 2860 watts without the slow cooker or distiller, 4610 watts without the water distiller and 7,790 watts with both. Does that sound about right? I was thinking 12v, 400ah (or 24V, 200ah) would be suitable if I don't plan on using a water distiller and 12v, 800ah (or 24v, 400ah) if I do use the water distiller?

To charge the battery, if I go 12v, I'd like to use the 100-watt foldable solar panel that I have. Unfortunately, it's not permanently attached to the roof or battery, so it won't get sun all day long. I plan on having the solar panel connected for about 6-8 hours a day. I'd also like to charge the battery using a DC-to-DC charger
that way I can charge the battery while driving. I'll likely be driving for 5-6 hours a day. That way, if I get 8 hours of full sun (66.67 ah) and 5 hours charging from a 60a Dc-Dc charger (300ah) I would get a total of about 366ah of charging a day? Does that sound about right or is my math wrong? Or, if I go 24v, I saw the Buck-Boost DC-DC Converter 25a / 50a / 100a... if I got the 100a version, and drove for 6 hours that would be 600ah of charging a day? Seems like either option would give me enough power, however I'm not sure I'm determining the charging ability correctly so I may be way off.

I understand that the slow cooker and water distiller may be a lot for this solar system to handle. I'd like to do both with fire or propane, however that may not be practical for the first 2-6 months. So, I'm hoping it will work with electricity.

Is what I'm hoping to achieve possible or am I way off here? Any help planning my system is appreciated. Thanks!

 

[LordGarak]

Why are you running a water distiller? If your doing it for drinking water you may want to consider an RO water filter. Much more energy efficient.

Sounds like you are way short on panels. You generally want to have more than enough solar panels to run your loads all day on top of charging your batteries. Without the water distiller I'm thinking you need atleast 400W. I'd add another 500W to run the distiller. You only get so many hours of good charging a day.

If I was starting over I'd go right for a 48v system. The inverters/charge controllers are super cheap.

 

[CampLife]

I hear you about the lack of solar. The first 2-6 months the system will be in a vehicle, that's why I'm limited in space and solar. When I set up my full system, it'll be on a piece of land with a lot more space. When I have the land to build the system on, I intend to install 10- 100w panels and see how it goes from there. I just don't have the space at the moment. That's why I'm hoping I'll be able to rely on a Dc-Dc charger hooked up to the battery of my van to do the bulk of charging while driving, for the first 2-6 months. I saw a 100a 24v dc-dc charger... if I had a 24v system and drove for 6 hours and got 600ah that would solve all my problems. I get the feeling it doesn't work that way. I'm going to be researching that tonight so if anyone has any info on what to expect form dc-dc chargers that would be helpful.

I've heard the 48v systems were the most efficient and they seem like the best bang for the buck. Not sure I want to go that route because I heard 48v has a potential to be lethal while 12v and 24v do not. I'm still a newbie, so not trying to risk it, lol. Maybe once I'm more comfortable with it all, I'll go with a 48v system.

Yes, I have considered a RO filter and may get one for a backup. I may need to filter salt water from time to time so I like the idea of a distiller. It's not necessary at the moment but would be cool to have. I really like my slow cooker though... so easy to prepare meals and clean up. I'm trying to figure out how many amp hours I'll need, charging mainly off a dc-dc charger that is hooked up to a car battery and one 12v 100watt solar panel, to power at least a slow cooker for 7 hours, Dometic 12v fridge, 12v lights and up to 10 hours of laptop work.

 

[LydMekk]

My vote for a 48V system. Don't spend time and energy on lower voltages.
In a couple of years most of the market will be for 48 or higher ^^.
Think ahead.

 

[Ampster]

My vote for a 48V system. Don't spend time and energy on lower voltages.

That is my vote as well. There are a lot more choices in that segment.

 

[CampLife]

Hmmm... now I'm really considering a 48v.

Are there any Dc-Dc chargers that can charge a 48v battery off the battery of a van while driving? I've been searching for one but have only come across 12v or 24v versions.

If I got a 48v system, would I need at least 4- 12v solar panels to charge it via solar? Is there any chance that I can rig one 12v solar panel to charge a 48v battery?

I'm still concerned about the safety of a 48v system, what do I got to do to avoid a lethal shock with a 48v?

 

[Ampster]

If I got a 48v system, would I need at least 4- 12v solar panels to charge it via solar? Is there any chance that I can rig one 12v solar panel to charge a 48v battery?

12 V solar panels are expensive compared to two regular panels with a SCC that could charge a 48 volt battery. The only advantage is the smaller form factor of 12 or 24 V panels.

I'm still concerned about the safety of a 48v system, what do I got to do to avoid a lethal shock with a 48v?

There is really not much risk of lethal shock with 48 Volts unless you purposly put two 48 volt electrodes into your chest. Even between both arms with moist hands. there is enough resistance to prevent serious imjury. Wearing gloves wll reduce the risk significantly.

 

[LordGarak]

Hmmm... now I'm really considering a 48v.

Are there any Dc-Dc chargers that can charge a 48v battery off the battery of a van while driving? I've been searching for one but have only come across 12v or 24v versions.

If I got a 48v system, would I need at least 4- 12v solar panels to charge it via solar? Is there any chance that I can rig one 12v solar panel to charge a 48v battery?

I'm still concerned about the safety of a 48v system, what do I got to do to avoid a lethal shock with a 48v?

Charging from the van may be quite limited. The typical alternator only provides like 100A when the engine is running at like highway speeds. Some of that current needs to go to powering the vehicle accessories and charging the starting battery. So say you get 75A@12v and drive on the highway 2 hours everyday, that is only 1.8kWh/day. That is pretty optimistic and before you account for any losses. You might be better served by a dedicated generator that you run for your larger loads and charging the battery. Then you can get away with a smaller battery bank and solar array. I'd suggest something like a 2000watt Honda.

If you are driving everyday then a second alternator may be a practical option. With a quick search, they do make 48v alternators and they can provide like 2900w or even 4800w. They might even produce decent power at idle depending on the engine and pulley ratios. That is if there is even room under the hood of your van. They are a specialty item, so they may cost more than a dedicated generator and also be less efficient on fuel. (Edit: Just found a price, ~$3000 for the 48v alternator before you even think about installation, not cheap)

"24v" panels are typically like 60v open circuit. The 12v panels are only like 18v open circuit. You could wire a few of the 12v panels in series. But they are typically 2 to 3 times the price of larger panels per watt.

The open circuit voltage is important as that determines the maximum voltage the charge controller needs to handle. The inexpensive($650) 48v charge controllers/inverter combo units can handle up to like 500v. In your case you would never fit enough panels to get that high. But you may need to watch for the minimum voltage required. Those inexpensive units can also serve as a battery charger when powered from a generator or the grid.

When I built my 12v system. I nearly spent $1000 on a solar charge controller and another $1000 on an inverter/charger. I'm maxed out at 1200watts of panels because the open circuit voltage limits of the charge controller. The 48v unit for $650 replaces both and can handle a whole lot more panels. There are cheaper units on the market than the ones I went with, but with limited capabilities. Being able to charge from the generator at atleast 80A was a requirement and it was expensive/hard to find that feature at 12v. My system isn't van based, so I could go with a lot more panels. I am running "24v" panels. The MPPT charge controllers switch the panel voltages down to the battery charging voltages.

We have 12v water pump, 12/24v fridge and 12v lighting. So switching to 48v at this point isn't easy/cheap. DC-DC converters large enough to handle the startup surge of the water pump isn't easy to find nor cheap.

I'm considering running two systems in parallel. Keep the 12v system as is (except for a new lithium battery) and building a larger 48v system for 120v. We are finding we are having to run the generator daily in the winter with the short days. So a larger solar array would produce more power with the few good hours of sun light we have. The fuel saving will pay for the system over a few years.

That said, I don't think we could get through the winter without running the generator atleast some of the time. In the summer we are fully charged by like 11am and then have all the power we can use until the sun leaves the panels. But in the winter we rarely hit fully charged even on the nicest of days. We can also have a week straight of grey skies and snow where the solar system generates next to nothing.

 

[50ShadesOfDirt]

Either 24v or 48v are good choices for your system, as opposed to a 12v system. We run our entire house on a 24v system, as a few others on this site do. You can spend some time at various websites comparing the component costs of either voltage. I find the two impacts from either are cable sizes and battery-bank configurations, plus the cost differences between a 24v or 48v component.

An all-in-one (AIO) will simplify things greatly, and would lend itself well to the scheme of two like systems where you can swap parts around. One in your van (or otherwise mobile like a "hand-truck" scenario), and later, one for the homestead. I like having backups (portable generator) and spares (another AIO on the shelf) anyway, as you don't want to be on the road, or back at home right before some big event or holiday, and a part breaking down throws everything off.

As to design, look to sites like these to help you with sizing:

1. at this calculator page, enter in each appliance's values (watts, hours/day you want to run it, etc.):
unboundsolar.com/solar-information/offgrid-calculator

2. using numbers from above, fiddle with various entries/components, and you'll see in real-time what your system component (inverter, mppt, panel) sizing is:
altestore.com/store/calculators/off_grid_calculator/

You can do what-if's all day long ...

Hope this helps ...

 

[CampLife]

I like the idea of going with 48v, however, I intend to use my vehicle to charge the batteries so I don't think 48v will work for me (I'm unable to find any 12v to 48v dc to dc chargers). Because of that, seems my only option is a 12v or 24v system at this time.

If I do end up building a 48v system in the future, it'll likely be independent form the system I'm building now. I'm thinking, when I have a piece of land and can install a large solar array, I'll create a 48v system at that time.

The system I'm building now will be in a smaller van with limited space for batteries and solar. There is a chance I may switch to a larger vehicle at some point in the future (step van, box truck, schoolie etc.) but I'm not sure about that. Regardless, I'm thinking this system will always be in some sort of vehicle with the need for a dc-to-dc charger and it won't likely be hooked up to any more than 1000watts of solar (there's a slight chance it may be hooked up to more than 1000watts in the future, say 1000watts to 2000watts max, but not exactly sure).

Here's what I'm thinking: If I can get about 600 watts of solar or 600watts of dc-to-dc power, that should be enough for my needs with this system.

To get that 600watts with a dc-to-dc charger I found a 60a 12v charger from Renogy that would be enough (would have to go with a 12v system to use it).

To get 600watts from solar... I won't have permanently attached solar for the time being, but I think I can keep 6 solar panels in the back of my van and bring 1 or all out when parked. Does anyone know if something like that would work? Was thinking they could all be wired up ready to go stored on some sort of rack. Then, depending on where I'm parked and how much space I have, I'll bring out 1 or all 6. Do you think I'd run into any issues trying to do something like that?

Using a 12v battery with a the 12v 60a Renogy dc-to-dc charger should work but I'm still looking for a way to use a 24v system. The problem is, I can't seem to find a suitable dc-to-dc charger that can charge from a 12v car battery to a 24v battery bank. I thought I found one here: https://www.victronenergy.com/dc-dc-converters/buck-boost-dc-dc-converter-25a-50a however, whenever I click on any of the links in the "where to buy", none of the companies actually have that product. I found this one: https://www.redarc.com.au/24v-20a-lifepo4-battery-charger-low-voltage however, that option is not available in the United Sates. They have a similar version in the United States here: https://www.redarcelectronics.com/us/24v-20a-in-vehicle-dc-battery-charger however, it does not charge lithium batteries. The only dc to dc for a 12v to 24v that can charge lithium is the Orion- Tr Smart 12/24-15A (360W) Non-isolated DC-DC Step Up Charger / Converter (ORI12236140), but since its only 15a that may not be enough amps for my needs. Does anyone know of a 12v to 24v dc to dc charger that has 20 or more amps? Thanks for the help!

 

[OffGridInTheCity]

48v + expandable around a good core. I'm at 5 years (14kw PV, 121kwh bat, 24,000w inverter, 220a charging) and every year have added panels, batteries, charge controllers, breakers, wiring to get to this point bit by bit. At this point my core bus/control-box is strained - e.g. whish I'd made it larger - my best advice is to leave room for expansion 2 or 3 times what you originally think you might need. Having system that expands (as apposed to multiple individual systems) let's me maintain core monitoring/control and expand bit by bit.

A key component of this is the 'central battery side bus' and breakers. It's amazing how many things I have (now) - e.g. shunts, charge controllers (and their breakers), chargers (and their breakers), test take off (to repair inverters), and monitor/control components that revolve around the main + and - battery bus.


Recently added an EG4 Chargerverter and had to create a new set of bus-bars off the the main bus box - to have room to hook in the EG4 Chargeverter.