I've been watching videos and reading about off grid systems for a few years, and am about ready to take the plunge and build a smallish DIY system to power a few circuits with utility backup. There are a few things I'm not clear about, though, and could use some suggestions from the community. Context: I'm in the US, in Phoenix AZ.
I want to build a hybrid system that can use power from PV cells, battery, or the grid, based on a number of programmable parameters. This seems like it is more complicated or expensive than it needs to be, so I hope I'm missing something. For example, when I ask the design folks at different solar shops, they steer me toward an inverter that costs about 50% more and can only supply about half as much power (for example, Schneider Conext XW PRO 6.8kW Hybrid Inverter, which is $3495, vs a Growatt all in one 12kW that is $1800). I'd like to hear what solutions others would recommend.
Big picture, I'd like to build a system that can serve as both an emergency backup generator and shave my 'demand charge' and peak power usage.
Details:
The total load the system needs to be able to power is 8kW, including 240V (the AC) and 120V (the fridge and a set of lights).
1. During a power outage, I want to be able to power my AC and fridge/freezer at some level during the day (keep the food from going bad, keep the house below 90F). This is one of the reasons that I want an off grid solution, vs. grid tied.
2. When there is grid power, optimize my energy bill as much as possible on a relatively small battery bank (say 10 or 15 kWh). Here, we have a variable energy price based on time of day, and a demand charge that makes up about 50% of the total bill by dollar amount. The demand charge is based on the largest single hour usage between 4pm and 7pm during a billing period. This means I'm looking for the capability to program, for example, the following pattern:
* Prioritize charging the battery bank from PV panels so that they're fully charged at 4pm, without exceeding some C rate that I set.
* Use any excess power from the PV panels to power loads until 4pm
* from 4pm on, prioritize running the loads from PV panels, followed by battery bank (ideally, switching to grid at a different SOC for each hour, though I can imagine I might need to build some sort of Raspberry Pi DIY solution for this level of control )
* at any point when neither battery or PV can provide enough power for the loads, switch over to grid power
Is there a solution that does this without breaking the bank on a very fancy inverter? I'm open to suggestions that I change my approach entirely, other than deciding to sell power back to the utility. That seems unreliable in our current political environment, as utilities keep changing the deal and I'm not going to make a major financial decision based on parameters that are likely to change.
Demand charge characteristics are also likely to change, but in any circumstance, the ability to program switching should allow me to adjust.
I want to build a hybrid system that can use power from PV cells, battery, or the grid, based on a number of programmable parameters. This seems like it is more complicated or expensive than it needs to be, so I hope I'm missing something. For example, when I ask the design folks at different solar shops, they steer me toward an inverter that costs about 50% more and can only supply about half as much power (for example, Schneider Conext XW PRO 6.8kW Hybrid Inverter, which is $3495, vs a Growatt all in one 12kW that is $1800). I'd like to hear what solutions others would recommend.
Big picture, I'd like to build a system that can serve as both an emergency backup generator and shave my 'demand charge' and peak power usage.
Details:
The total load the system needs to be able to power is 8kW, including 240V (the AC) and 120V (the fridge and a set of lights).
1. During a power outage, I want to be able to power my AC and fridge/freezer at some level during the day (keep the food from going bad, keep the house below 90F). This is one of the reasons that I want an off grid solution, vs. grid tied.
2. When there is grid power, optimize my energy bill as much as possible on a relatively small battery bank (say 10 or 15 kWh). Here, we have a variable energy price based on time of day, and a demand charge that makes up about 50% of the total bill by dollar amount. The demand charge is based on the largest single hour usage between 4pm and 7pm during a billing period. This means I'm looking for the capability to program, for example, the following pattern:
* Prioritize charging the battery bank from PV panels so that they're fully charged at 4pm, without exceeding some C rate that I set.
* Use any excess power from the PV panels to power loads until 4pm
* from 4pm on, prioritize running the loads from PV panels, followed by battery bank (ideally, switching to grid at a different SOC for each hour, though I can imagine I might need to build some sort of Raspberry Pi DIY solution for this level of control )
* at any point when neither battery or PV can provide enough power for the loads, switch over to grid power
Is there a solution that does this without breaking the bank on a very fancy inverter? I'm open to suggestions that I change my approach entirely, other than deciding to sell power back to the utility. That seems unreliable in our current political environment, as utilities keep changing the deal and I'm not going to make a major financial decision based on parameters that are likely to change.
Demand charge characteristics are also likely to change, but in any circumstance, the ability to program switching should allow me to adjust.
