Direct Connect

draines

Is there a way to have an appliance like an A/C connected direclty to an inverter - directly to the grid - where the A/C will run only when there is sufficient power? Or something like a dehumidifier...where there isn't a specific time of need in the house?

My main question is can the appliance pull through an inverter directly from the grid without batteries? If so, would you still run a calc with only the ~85% efficiency?

Thanks-
Dan

BB.

Re: Direct Connect

Are you looking at a GT Inverter system? No batteries, no backup AC power (in general). Cheapest and most efficient.

The 85% efficiency I use is "typical" for the DC to AC conversion efficiency. If you add solar panel deratings (marketing vs real life numbers), then a GT Solar System will be closer to 77% efficiency (higher altitude/colder weather/clean arrays can be a bit better).

If you have grid power and a utility that has a good Net Metering power plan, GT Solar is usually the best bang for the buck. You could always setup a controller that monitors GT inverter output and/or solar output to prevent A/C from drawing "too much" energy during peak billing (if you have a time of use plan).

If this is an off grid system--You could certainly setup so that the AC would only run under certain conditions--You would have to set up so that the A/C does not "chatter" on decision points (i.e., AC load > than DC from panels, AC is turned off, now battery is net charging--So controller turns AC on again, etc.).

You do have sort of an issue with off grid systems. You cannot easily tell if the charge controller is capable of more output current or not by monitoring battery bus voltage (is it late in the day and the maximum controller current also the float current that is it presently outputting?).

One way around it would be to take a small solar panel (even a single cell photo diode) and put a shunt on it. The current through the shunt is basically the amount of sunlight available. You could program the AC to only run with (for example) >50% of available sun shining on the monitoring panel.

-Bill

draines

Re: Direct Connect

I was not thinking that it would be GT system, just PV+Inverter+dehumidifier. Just trying to wrap my head around how it would work? Say the need was ~50amps and 600w to start/run the dehumidifier, which would be quite an expensive system just to power a dehumidifier, when the power was right. Just trying to better understand some of the aspects of using energy (non-GT) when everything else is off? An energy dump of sorts.

Cariboocoot

Re: Direct Connect

draines wrote: »

I was not thinking that it would be GT system, just PV+Inverter+dehumidifier. Just trying to wrap my head around how it would work? Say the need was ~50amps and 600w to start/run the dehumidifier, which would be quite an expensive system just to power a dehumidifier, when the power was right. Just trying to better understand some of the aspects of using energy (non-GT) when everything else is off? An energy dump of sorts.

This can't be done.
The only type of inverter that works without batteries is a grid-tie unit, and that needs the grid to run.

If you want to offset the power demand of a certain device during sunlight hours a GTI can be rigged to come on only when that device demands power, but frankly it would be a huge waste of money.

If you want to use an off-grid inverter with batteries you may as well design it to be able to run the device as-needed. Frankly that too would be a huge waste of money compared to powering off the grid.

TucsonAZ

Re: Direct Connect

You would have to at the very least add a battery and a charge controller, that is, if you needed to run something for say 1 hour per day and when wasn't the issue. You would need to give more info though, such as why, is this just to see if you can, is it because your power goes out often? It wouldn't make practical sense but you could do that, even with a cheap battery during peak hours for sunlight and provided you weren't trying to run a 3,000 watt inverter.