Planning for post-net-metering: How do you design?
For the sake of this post, assume as a given that, at some point, the current net-metering arrangements ("I give you a kWh when I find convenient, you give me a kWh when I find convenient") are likely to change over the next decades. I'm not sure exactly how they are going to change, and it's likely to differ somewhat, but let's assume that they're going to change.
How do you design a system for that, if you're aiming for a 30-50 year lifespan (yes, I know by 50 years, production will be down, and I'll probably just add another string to make it up)?
My thoughts, currently, are that a moderately batteried DC coupled system (with generator) is probably the ideal. It allows you to ride through outages, it allows you to export to the grid when the battery is full, and if you're subject to altered rules, you can alter the system operation to deal with the new rate schedules.
I think we'll likely see either ratioed net metering (1.5:1 or something), or a switch to more of a commercial demand schedule (pay per peak kW drawn, plus energy costs) for residential solar to split out the costs of grid maintenance from the costs of energy (which, right now, are combined).
If one is on a ratioed net metering, not much changes except the power bill in the high power demand months (winter, for me, since I heat on electric - I really need to get a pellet stove). In that case, there's no real change from a pure grid tied system, except higher power bills. Meh.
However, if the change is to more of a demand charge based system, then something that can buffer peak loads, and likely self consume a lot of production, seems more useful - and I think this is probably the fairest system for continued grid operation, with a higher monthly base fee. Depending on the nature of the rate schedule, a DC coupled system with generator could either trim demand significantly from the grid (draw from the battery bank to keep grid demand down, using the generator for periods that the bank can't provide), or would allow for sustained off grid use if the costs of grid connection are simply too high.
Doing some research, it seems like the Outback ecosystem is the best for this right now - the Mate3 can tie the charge controllers and inverter(s) together in a seamless unit that talks and does the right thing, including calling for generator start if you have a proper generator (or lighting up a "Hey, uh, plz go start generator nao!" light).
Put a smaller (10-20kWh) battery bank in for now, and you can easily expand that in the future if needed to make better use of locally generated solar. A generator running on propane has a very high storability factor (you don't clog the carbs like you do with an infrequently used gas generator, or have the cold start issues of a diesel), and should be fairly low maintenance if used a few dozen hours a year. It does require having alternate heat solutions, which I don't have right now, but doing some sort of CHP setup with a generator would help a lot, if you don't want to pull from the grid as much.
Thoughts? I simply don't see net metering as a 30+ year thing for system design right now.
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