Grid Tie Question-

[dsnyderdsnyder]

I'm trying to maximize my home energy system and I'm wondering if something is possible-

Details-

I live in Phoenix, Arizona.

I have a 5000watt Grid Tied Solar energy system on my house right now.

My house is heated and cooled by a 15 seer heat pump.

I have what is called a load controller on the house that limits how many major appliances can be used.

I am on what the utility company calls a time/demand advantage rate. What this means is that I can use electricity from 9pm to 9am at a very cheap rate $.025 a Kilowatt and there is no demand charge.

From 9:00am to 9:00pm I pay about $.11 a kilowatt with a demand charge. To offset the demand charge, I have the grid tied solar and the load controller which won't let the major appliances turn on at the same time.

My problem is from roughly 6pm to 9pm, my solar system stops generating but the demand for electricity is obviously still there- especially in the summer where outside temps can stay around 90 degrees almost all night. From 6 to 9 I'm using high priced utility electricity and paying a demand premium.

What I'd like to be able to do...

I have a 6000watt diesel generator that I run off of biodiesel I get from a friend's restaurant.

I'd like to incorporate the diesel generator into the overall system so that power is used on a three priority basis. Household needs first come from the solar cells. When the demand exceeds what the cell produce, the generator kicks on and finally, if it goes beyond what the generator can produce, utility power feeds into the system. Can this be reasonably done?

Thanks!

Dave

[Allcanadian]

@dsnyderdsnyder

I'd like to incorporate the diesel generator into the overall system so that power is used on a three priority basis. Household needs first come from the solar cells. When the demand exceeds what the cell produce, the generator kicks on and finally, if it goes beyond what the generator can produce, utility power feeds into the system. Can this be reasonably done?

No, we can put men on the moon and probes on mars but what you are asking is impossible. Well maybe not impossible but difficult and expensive, the first problem is that your diesel generator is AC which means the frequency has to be synchronized with the 60Hz grid frequency before connecting it or bad things happen.

However depending on what type of grid tie inverter you have there may be a cheaper solution. The grid tie inverter usually has a DC input from the solar panels and this Direct Current is then converted to AC in the inverter which is already synchronized at 60 Hz with the grid. When you are not producing enough power from your solar panels then power is routed from the grid to your electrical panel or when your producing excess power it is routed from the solar panels through the inverter to the electrical panel and grid. If the grid fails then the grid tie inverter automatically disconnects from your electrical panel and the grid for safety reasons.

As such a cheap solution may be simply to use what you have, a grid tie inverter which already manages the power distribution safely for you. If you were to rectify the diesel generator AC output to DC with full wave rectifier's which are relatively cheap then you simply connect the rectified generator output to the input of the grid tie inverter however (big very important however)the diesel generator output voltage must be within the Min/Max input voltage of the grid tie inverter. As well there must be diodes to prevent a current flow from the generator to the solar panels. The diesel generator would start when the solar panel voltage reaches a preset low level and feed the grid tie inverter DC which it then converts to AC to feed your house or the grid.
You may have to cut back the speed regulator on the diesel so that the voltage is compatable with the grid tie inverter voltage input, just idle up the diesel slowly until it starts producing a high enough voltage to the grid tie inverter to carry the household AC demand.
In theory this should work,lol.

Regards
AC

[dsnyderdsnyder]

I was considering that as there is a DC output from the generator. -I'm not sure how much power the unit sends out the DC output. The manual does say it is only for charging batteries and not for running anything DC. Not sure why it would say that. Thanks for the suggestion.