48 volts?

[Bigbad]

I have read in a couple of places that "48 volts" is the most effecient solar setup to have. I read the context - was not sure if they were talking about putting 4 x12 volt panels in series connect to a 48V DC to 120 AC inverter, or just connecting the panels in series to make 48v dc and distributing that through the house. In the latter case, small, local inverters would be used for each appliance, i.e. one for the fridge, one for a mixer, etc. Also, in the last choice, 12 and 24v dc appliances would be used whenever possible. I will be building a small house (600 sq ft) in a year or so, so there are no remodeling costs associated with either choice. Any help is appreciated. Please feel free to direct me to other posts on this topic, or websites that can explain it.

[organic farmer]

I would rather have had a 12vdc system. One of our off-grid neighbors' system is 12vdc and I love his setup. His entire house is wired for 12vdc, all of his home appliances are 12vdc.

However when we were ready to design our system, I had just replaced our well pump a few months before, and it is 240vac. We looked at 12vdc well pumps, and my wife got upset. Since we had just bought a new well pump, she did not want me buying another well pump so soon.

At that time, the only inverters that had 120/240vac output were all 48vdc inverters. So that is how we ended up using 48vdc.

[Bigbad]

Thank you! That is the kind of information I am looking for. 240v ac needs a 48v inverter. Next?

[organic farmer]

You are welcome.

[peakbagger]

Resistance through wires is based on amperage. As long as the insulation is rated for the voltage, the higher the voltage the lower the amps for the same power draw. Current flow causes line loss due to electrical resistance. A 48 volt system is going to be able to have smaller wires than a 12 volt system. Why not a 96 volts system?. Various agencies recognize anything under 50 volts to not be a shock hazard so they do not regulate them like higher voltages.120VAC has even lower resistance and even smaller wires. DC appliances used to be standard for off grid but they sell at a big premium. For most its better to buy an inverter and put in an AC system and use standard appliances, fixtures, wiring and wiring devices. Especially with the current cost of copper you want to use the lightest gauge you can get away with.

Off grid solar systems have an annoying tendency to grow, start with 12 volts and you will outgrow it soon.

[chrisski]

This is a good explanation:

https://www.solarpaneltalk.com/forum/off-grid-solar/off-grid-solar-panel-systems/5140-solar-off-grid-battery-design

[sidpost]

It sounds like you don't have a good basic understanding of what you are trying to do. For most people, the easiest is to use a 120V/240V inverter from your solar panels that feeds into your main breaker box. That definitely stops remodeling costs and reduces wiring complexity a lot!

If you are doing a new off-grid build, then buying Vdc appliances becomes more viable. My advice, don't overthink and over complicate this.

Pay attention to how much power you can store, after all, you don't want your fridge and lights going out early in the evening. Then consider your load (how many lights, fridge, etc.) that you need your inverter to support.

16x304Ahr LiFeP04 batteries will give you a nominal 48VDC source with enough power to run a cabin conservatively. Lead Acid batteries will die quickly if you over-discharge them and have a shorter cycle life with more maintenance required to keep them healthy (know what a hygrometer is?).

Then there is the paneling issue. Do you have enough panels to recharge your system in the Winter months?

[Mike90250]

.........

16x304Ahr LiFeP04 batteries will give you a nominal 48VDC source with enough power to run a cabin conservatively. Lead Acid batteries will die quickly if you over-discharge them and have a shorter cycle life with more maintenance required to keep them healthy (know what a hygrometer is?)........

Li batteries will be ruined in a few hours if you over discharge them, LeadAcid batteries have a known cycle life per depth of discharge. One under-voltage event can destroy Li batteries.

have you priced the 12, 24, 48VDC appliances ? Happy with whats out there for the price ? I think it's much more flexible to do conventional wiring and use energy star 120Vac appliances

[sidpost]

Yes, my household appliances are on 120VAC Inverters as appropriate. I am converting my stove to Natural Gas. The clothes dryer and water heater are low priorities and will likely get converted as they fail over time. I have a wood-burning stove coming as well for winter heat support, which of course I could use to cook with as well.

In terms of discharge rate, yes you need to be aware of surges and start-up loads. My inverter will throw a breaker if I do something STUPID! This is a fail-safe to keep from overdrawing current and they will cut-off when the Voltage level drops. I manage my systems but, I have fail-safes to throw a 'breaker' to protect system components in case I have a personal lapse for whatever reason.

If I don't have "shore power" from the Texas PUC (public utility company), like during SNOW-MEGEDDON", I can dry my blue jeans on a clothesline and it wouldn't be my first 'cold' shower.

Priorities to me are more basic for things like radios, lighting, refrigeration, plus luxuries like a window unit A/C and some Ice from my ice machine for a cold drink (hot ones can come from the wood-burning stove).

I won't go totally off-grid until I build my new house. Right now this farm house is a PROOF OF CONCEPT for me and, for things like Hydroponics, enclosed Fish Systems, and similar things. Remote surveillance will likely stay on 29DC marine batteries for the next few years as I wait for a better battery solution.