rmorey
Platinum Member
If you install a battery bank, you need a "charge controller" "like a voltage regulator in a car", to cut the voltage to the bank when its charged.
Are you talking about a charger feeding a battery bank, then a inverter running off of that? Something like the diagram below?
View attachment 307868
I could see that working with a couple of caveats:
- You would have to have a mechanical interlock so that the battery bank inverter couldn't be turned on when the utility power is on
- You would have to have some way to shut the battery bank charger off when the panels or a generator are not running (perhaps a trigger on the battery bank inverter to turn on/off when it is putting out more than x amps)
- You might need an additional loadbank depending on how the solar panel inverters handle less than a full load
Aaron Z
It's always possible to find negatives if we look for them. But tasking a grid-tied system with something it is not designed to do is sort of silly in the big picture. 99% of the time, grid-tied systems do an excellent job of doing what they are designed to do: make power when the sun shines and reduce our dependency on non-renewable energy sources. If they become commonplace, they will also allow re-thinking some of the grid management and load growth challenges.
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If you have to have it, there are a couple of manufactures of hybrid grid-tied/off-grid systems with limited battery capacity. They are expensive, and I think you would still want to have generator. It is just a question of cost versus utility.
PV has its limitations aka negatives and they are not obvious.
In the class I am taking, I know far more than the other students, and watching them understand that 10,000 watts on the roof is not 10,000 watts at the outlets is interesting. They also are shocked that they won't be able to use the PV system in a power outage unless they install batteries. Microinverters are the way to go but wait, they or single point inverters, won't work with out grid power. "We don't get power all day but only for five hours?" is another moment of understanding.
These are limitations on PV. They are big limitations and these limitations ARE NOT known to the vast majority of people.
PV is talked about as a wonderful idea that everyone should use but the reality is that it has limitations, negatives to use your word, and most people don't realize this at all. This is not a exercise in finding the negatives, the limitations, but understanding them to make intelligent decisions.
EVERYONE in my class, with me being the exception, was surprised that they would not be able to use the PV panels in an outage without having to use batteries. I think microinverters are the way to go and if we install a PV system we will use them, but for us to have some limited backup power we will have to have batteries which means no microinverters thus a secondary set of panels, a single inverter, different wiring, and of course batteries. This drastically increases the cost and complexity which most people do not understand about PV.
One of the things I have learned in this class is that in NC it is not worth the cost and effort to net meter. I still wonder if that is true and I will be investigating to make sure the numberd have not changed but this was surprising information to me. If the expense and trouble of NC net metering is not worth it, this changes how much power we should put on the roof. If net metering is not going to pay off, then the size of our PV system would be based on what power we use during five hours of daytime. I don't think we use much power during the daytime. Instead of putting up 10K watts we would be looking at far less because we just don't use that much power in the week day except in the summer. For most of the year we would be producing power and giving it back to the power company for nothing.
For us to cut our power bill by a meaningful manner we have to balance the install watts with what we use during the day without NC net metering. This drastically reduces the number of watts on the roof and would force us to install a solar water heater to cut the power bill further. A solar water heat is just more complexity which I would rather avoid while almost certainly driving up costs.
Later,
Dan
You can also waste the excess in a resistance in example electric heater sized to sink total peak power. The heater would have to be controlled by a voltage regulator. If the voltage starts rising the regulator would add load until equilibrium between supply and demand is reached. That way you could use power from your PV when the grid goes down. Since the microinverters are grid commutated and have only +/- 0.5 Hz tolerance you would need source with steady frequency. In example inverter generator.