Reverse Inverter Charger

Re: Reverse Inverter Charger

You might be able to do it with some of the Grid Tie / Off Grid hybrids out there (like Outback and Xantrex XW). They certainly have generator controllers that are used to turn on the genset when the batteries are getting low... However, most (all?) seem to be based on battery bank voltage--not a very accurate way of determining state of charge.

However--if you are really aiming at 50% state of charge--then you would need something like a Xantrex Battery Monitor which has a programmable output (you can set it to change state at 50% state of charge and flip back at 90% state of charge).

Now--for the $64 question... Why?

Cycling batteries to power your home electronics when you have perfectly good A/C Grid power... At the very least, you are going to use some ~40% more electricity to do this. And because it switches from main to battery to main--you are not even getting 100% isolation from the main (power failure, voltage spikes). Batteries that need to be replaced every few years, more A/C to cool your home...

Everything is losses... You have the charger losses, the battery cycling losses, the inverter losses, etc... You have a very good chance of causing your electronics to reboot every time the system switches from AC to Inverter to AC...

Almost anything else you do will be more efficient. You could use grid power until it fails, then use battery (UPS). Or you can have the charger float the batteries and power the inverter (continuous conversion--used when bullet proof steady power is needed), etc...

Obviously, there are lots of used UPS's out there from old computer installations...

-Bill

Re: Reverse Inverter Charger

To be honest--you are pretty limited in what you can do regarding major Solar RE systems in an Apartment.

A year ago, I went through the basic costing of what if you had Time Of Use Billing... Very cheap power at night and over priced power during the day.

Priced a True Sine Inverter with transfer switch + good storage batteries (which need to be replaced every 5-10 years--system life of 10-20 years)...

If the power were "free"--just the price of batteries and equipment was something like $0.45 per kWhr just to time shift the power.

Not including the fact that end to end efficiency is down in the 55-60% range (80% Charger * 80% Battery Eff * 85% Inverter Eff = 54%) -- would almost double your "night time power" requirement for daytime usage.

You can play with the numbers--use a MSW (Modified Square Wave Inverter--dirt cheap), use AGM batteries (>90% efficient, but 2x as expensive), etc... But you will still have the basic issue that it is not cost effective.

Typically, your better bet is energy star appliances and appropriate equipment (newer fridge, use laptop instead of desktop computer, CFL lamps, reflective films on windows--cut heat gain--if issue, turn off unused equipment/wall warts, etc.).

The best place to start with electrical conservation is a Kill-A-Watt meter for $30 or less:

Kill-A-Watt AC Power Monitor Meter
P4400 Cumulative Killowatt-Hour Monitor

For our home (natural gas stove, hot water, drier) we can get down to 200-250 kWhrs per month (before solar Grid Tied electricity)...

200 kWhrs per month / (30 days * 24 hours per day) = 0.278kW or 278 Watts 24 hours per day 7 days a week average power usage...

Depends on your needs (some people here need 24x7 Linux servers and A/C--others do not) and what is in your control (apartment limits the major appliance/Air-Conditioning changes you can make).

-Bill