One more time on this DPDT switch

goingtoghana

I am still trying to understand why I cannot use the same panels to charge the batteries and when they are full, divert the power to the house.

I am attaching a diagram of what I "think" makes sense.

- since I will have a combiner box with breakers, why can I not a) turn the breakers off b) switch the power to either the charge controller or an inverter tied into the panel c) turnn the breaker back on.

Thanks

BB.

Re: One more time on this DPDT switch

What kind of inverter are you looking at to take power from the solar array to the "house panel"?

Is the house panel a utility connected panel or completely off grid?

You can buy and install Grid Tied Inverters, and you can even put a DPDT switch in the array to switch between battery charger and a GT inverter... However, I am not sure there is a ~2kW 96 Volt nominal input inverter made at this time (there may be some plug-in/ebay type GT inverters--But I would doubt they have UL/NRTL Listing--which is required for building permits/utility approvals/insurance requirements).

And, if you are looking for Off Grid inverters that connect to solar panels--They pretty much need the backup energy of a battery bank, or you need a solar array many times larger to support starting loads (a 120 watt refrigerator may need 1kW or more to start). Also, any time a bird flew by, a cloud went over, the direct panel connected off grid inverter will drop its output to zero until there is adequate energy again to start and sustain the loads.

Most AC Appliances are not really designed for intermittent AC loads (a laptop computer with battery pack would be a good candidate).

And, if you already have the battery bank and off grid (even hybrid) inverter--Why not use the system as is--At most, you are losing around 5% of the energy due to the loses of the MPPT charge controller--Hardly worth going through the trouble of trying to make an off grid/battery less meet your needs.

-Bill

Cariboocoot

Re: One more time on this DPDT switch

Do you know of a grid-tie inverter that runs on 66 Volts? I don't.

There are people who have done this "the other way around"; utilizing the central GT array to charge a battery bank for an off-grid inverter in the event of a power outage. One way is to use the very expensive XW 600V 80A MPPT controller which can take the 400 or so Volts from a GT array and charge a 24 or 48 Volt battery bank. Another way is to reconfigure the array to a lower Voltage to power a conventional MPPT controller.

But at 66 Volts the array is not going to power any GT inverter I know of.

goingtoghana

Re: One more time on this DPDT switch

What already exists is a bank of batteries that are charged by A/C charges when the power is up. When power is down, the have a switch on the house panel to switch from grid power to the batteries.

The panels are being installed to help the batteries last longer during the day during blackouts. (it's africa)

When they panels are not charging the batteries and the grid is up, I would like to divert the panel power to the house panel to supplement what is coming from the grid.

I can change the panel configuration to 8 parallel strings to bring the voltage down if necessary for a grid-tie inverter. If this is doable, any suggestions on the type of grid tie inverter? 220V in africa.

Thanks

Cariboocoot

Re: One more time on this DPDT switch

goingtoghana wrote: »

What already exists is a bank of batteries that are charged by A/C charges when the power is up. When power is down, the have a switch on the house panel to switch from grid power to the batteries.

The panels are being installed to help the batteries last longer during the day during blackouts. (it's africa)

When they panels are not charging the batteries and the grid is up, I would like to divert the panel power to the house panel to supplement what is coming from the grid.

I can change the panel configuration to 8 parallel strings to bring the voltage down if necessary for a grid-tie inverter. If this is doable, any suggestions on the type of grid tie inverter? 220V in africa.

Thanks

No, you'd need to change the panel configuration to series to put the Voltage up to power most GT inverters.

Since you plan on getting a different inverter for GT, the most sensible plan is to replace the one that's there with a hybrid type GT inverter. That will automatically supply power to loads when the grid goes down, charge the batteries from the grid if it is available and solar is not, and supply power to loads/grid from solar whenever possible.

Some examples:
Outback http://www.solar-electric.com/ourags8wain.html
SMA http://www.solar-electric.com/suis5050waba.html (120VAC - needs 2 or transformer to supply 240
Xantrex http://www.solar-electric.com/nexaxwseinan.html

There are others. Your line frequency there is 60 not 50, right?

cruiser guy

Re: One more time on this DPDT switch

We are in Sierra Leone and we have a solar system with an inverter than can take a grid feed and power the house and/or charge the batteries. In our case we are completely off grid but I will plug the inverter into the generator on the "Grid" connections when needed to get the batteries charged back up in the rainy season. I think it gives a 13 amp charge current, not lots but if you run a small generator for the day you get something out of it. We bought the inverter locally and it is made by Su-Kam in India. You likely have these available in Ghana as well. Ours is a 1400 watt 24vDC model but they have larger ones and smaller ones available. It will automatically change over, no switches or anything that you might not be home to operate. Take your solar panels and feed them into the battery bank as well and all is fine. I doubt the inverter will take from the battery bank first once the batteries are fully charged which I think is what you're trying to do to cut down on utility costs.

We've had this for over a year and no complaints so far.