I've been toying around with this idea and I'm not sure if it's feasible. I live in an area where the power company has recently adjusted rates to make grid-tied net metering rooftop solar uneconomical (SRP in central Arizona)
Rather than go traditional grid tied with net metering, I have been thinking about, for example, running my electric water heaters (yes I have 2, and not by choice, we don't have natural gas service, and I've looked at solar thermal. PV makes more sense.) from solar directly from a sub panel, and storing the excess power in a battery instead of sending it back to the grid. The long term plan would be to migrate additional circuits to the solar/battery sub panel over time, and monitor the system adding panels and batteries to get to an optimum system.
I'd like to be able to use the grid as a backup in case with an auto transfer switch if the batteries run low. Ideally this transfer would be limited to some pre-defined spread, so that the power transfers to grid once the battery is below 20% but won't transfer back to battery until the battery reached 30% (example numbers, actual levels TBD).
To further complicate things I would want to have load shedding to prevent both water heaters from coming on at the same time, prioritizing the bathrooms over the kitchen/utility, potentially adding the heat pump (8kw) to that at some point.
Ideally this setup would use panels with micro inverters to allow for easier expansion. Otherwise I'd need to get a significantly oversized inverter for traditional DC strings to allow for expansion.
WiFi / Ethernet monitoring of all the major components is desired.
I'm having a hard time figuring out if there is off the shelf equipment that could be used for this or if it's even feasible. I would install the panels myself but have an electrician wire everything up.
I doubt the power company would like this, but since I'm not going to be sending power to their grid I don't think they have any say so.
- I have an old 200 amp panel that will be replaced.
- It's assumed that I would need to move loads to a sub panel.
- The power company isn't going to try to intervene.
- Since the water heaters are 3,500 watts, I'd want to size the initial system to maybe 2kw, since the duty cycle on them is maybe 15%, and they are on timers (off from 9PM to 7AM)
So my specific questions are:
- is this even possible or is it completely daft?
- has anyone done this or heard of someone that has?
- if it's doable, is there off the shelf equipment that would support it?
- I'm not familiar with transfer switches, how is sensitive equipment affected? All my computer equipment is on decent sine wave UPS' but what about the TV, refrigerator, etc (I've had to replace the logic board in my fridge after a power surge.)?
- I've no idea how to size the battery.
I'm sure there are lots of details that I'm overlooking.