12v solar package with AC backup charger for DC lighting system

[lumencache]

I would like to recommend a Solar (primary charger) package to my dealers with an AC backup charger that would only kick in if the battery does not reach a preset recharge level by the end of the day and solar charging is not expected until the next morning.  Basically, a charge optimizer using primarily free energy source unless reserves are projected to be too low to meet typical demand.

The application is a DC lighting system.  12V supply (10.25-28v is possible but 10.25-16v is better range).  The efficiency is very high and the controls help keep demand low.

I would like this to be bundled for mainstream homes so they have just a few PV panels to cover all their lights and other small DC loads. The battery can be large so they don't run out of juice regsrdless of the weather (week of heavy overcast or snow).  Small AC charger is the backup.  Not really concerned with selling excess PV as it's a small production.  Reliable and available power is critical.  It needs to be super reliable and not leave owners without power.

Average home size is 3000sf with full load of 600w.  NO AC except as backup supply charger.

Info on the DC lighting system at http://lumencache.com.  Resources tab shows example AC supply system design.

[mike90045]

Sadly, the fact is that if you have grid power, it's vastly cheaper than to be replacing batteries every 5-9 years.

[TomW]

Sadly, the fact is that if you have grid power, it's vastly cheaper than to be replacing batteries every 5-9 years.

A sad truth.

Certainly, in my experience,current  battery technology alone costs as much or possibly more than the power they store and provide.

But RE is certainly more fun that grid power.

Just from here.

Tom

[lumencache]

Sounds like the AC should be used at night to keep the battery from cycling daily and use relatively cheap lead-acid that will have a long life when not cycled.

[Westbranch]

If you are not going to cycle the battery, why have it....that will just kill it slowly, look up sulphation on this forum...  It 'looks like' LiFeYPO⁴ may be suitable but pricey and no long term track record, though the makers make bold claims...

[lumencache]

The benefits of battery + solar are well defined for sure with resilience and independence at the top of that list. Necessity in the case of off-grid.  Sounds like batteries are still the weak link but everyone here has them.  Question is how best to design a system given the options we have today so we can start getting those benefits.

I see a lot of 24v systems. Is that the ideal balance given available tech?

[Westbranch]

I see a lot of 24v systems. Is that the ideal balance given available tech?

The voltage generally depends on total load and peak loads to be placed on the system...  plus other non quantifiable issues, like a dislike/fear of a high DC voltage,  starting with the Voc of a 48Volt PV array... which can reach > 90Volts in very cold temperatures...

[TomW]

In my humble opinion, 24 volts is the minimum for anything but a very tiny system.

As Westbranch mentioned if you go above 48 volts nominal you run into some issues related to high voltage DC, both safety and code issues.

I started with 12 volts and regretted it as time went on but it was mostly a hobby system and low cost (spelled cheap Chinese) equipment was all 12 volt then.  When I upgraded I went to 24 volts and, again, as time has gone by, I wish I had gone 48 or even 96 volts. Higher voltage equipment is more common today and I have gone from hobby system to more mission critical use.

I am comfortable with electricity because I have worked with it for most of my life.

The question "What voltage should I use?" has an answer of "It depends.."

Just my opinion based on experience.

Tom

[lumencache]

I just learned about the Midnite HyperVOC feature to deal with cold PV.

Seems I need to refine the application definition further to include climate.

48v is planned for Gen2 product input.

[Westbranch]

48v is planned for Gen2 product input.

Yet still using 12 V lights?

Note: There are down conversion losses to deal with in that situation. 

Some use a small Charge Controller to keep a small 12V battery charged from the 24 or 48 Volt battery when they have a lot of 12V equipment to power...

[lumencache]

We rarely use 12v lights. Too inefficient.  The LED drivers boost to maintain the constant current through the LEDs so they usually operate in the 30-48v range with only 300mA through the Cat5.  Low current = low wire loss.  Plus there's no flicker or intensity changes like you have with constant voltage lights when the voltage fluctuates.