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Wow, even at $5,320 (after rebates and tax credit) that's a great price! If the Panasonic lithium cells in the PowerWalls last anywhere near as long as the ones in Tesla cars, they seem to be surprisingly robust. Unlike the ones in my laptop and iPhone!
For comparison, when spec'ing a commercial UPS system from APC for example:
A unit's load capacity is generally spec'ed by it's Volt-Amp capacity -- For example, 20,000 VA = 240V * 83 Amps assuming a power factor of 1, and no reactive loads (aka motors). Often times the actual kW rating (depending on the MFG) will be a lot less as they play games with the power factor.
Generally you would for 60-80% (or less) to provide for growth and to prevent overload alarms during operation. If the UPS cannot handle the instantaneous load (of all your equipment turning on for example) it will drop the load,
Based on your actual load (for example my house runs about 1kW nominal, 6kW with AC running, and 8-9kW peak with AC, Microwave, Keurig, etc. From your observed loads you can estimate the maximal carrying and inrush currents that are needed to support these loads for comparison to the output specs of the UPS system. Generally there is a diversity calculation to estimate and allow for the fact that the UPS is generally not sized for 100% of the output wiring capacity. But in a home, the AC is the primary concern. Mine, for example, (older 4 ton) draws ~30amps @ 240 continuously, and has an inrush of 60-80 amps.
From there, once you have identified the kVA of the UPS, you can then scale the Amp-hours of the batteries to lengthen the kWh of the solution. Most UPS vendors have a modelling tool for this (see link above) where you supply the average continuous load in Watts, and based on the number of strings of batteries, it will tell you the run time.
I haven't tried to get technical punchouts for the Tesla PowerWalls, but they should be readily available. But, unless the PowerWall DC to AC inverter can put out 100amps or more at 240, I would seriously consider moving the circuit breaker for the HVAC condenser into a non-UPS panel. Is this new construction? Or are you setting this up in your basement or garage? That's a lot of wall space in your diagram.
Do you have any consumption data for your home? I would start by metering it and looking at the current/power specs for your HVAC. For comparison purposes, with the HVAC, I'm running an average of ~55 kWh per day with peaks up to 76kWh. So, I'd have to drop the HVAC from the equation to get any meaningful runtime from a 37kWh pack.
I agree the solar PV array is rather small, but remember, this is not an off-grid solution. Realistically, the PV array would never be able to charge the battery packs if they were discharged by more than 15-20% or so.
-Jonathan
For comparison, when spec'ing a commercial UPS system from APC for example:
A unit's load capacity is generally spec'ed by it's Volt-Amp capacity -- For example, 20,000 VA = 240V * 83 Amps assuming a power factor of 1, and no reactive loads (aka motors). Often times the actual kW rating (depending on the MFG) will be a lot less as they play games with the power factor.
Generally you would for 60-80% (or less) to provide for growth and to prevent overload alarms during operation. If the UPS cannot handle the instantaneous load (of all your equipment turning on for example) it will drop the load,
Based on your actual load (for example my house runs about 1kW nominal, 6kW with AC running, and 8-9kW peak with AC, Microwave, Keurig, etc. From your observed loads you can estimate the maximal carrying and inrush currents that are needed to support these loads for comparison to the output specs of the UPS system. Generally there is a diversity calculation to estimate and allow for the fact that the UPS is generally not sized for 100% of the output wiring capacity. But in a home, the AC is the primary concern. Mine, for example, (older 4 ton) draws ~30amps @ 240 continuously, and has an inrush of 60-80 amps.
From there, once you have identified the kVA of the UPS, you can then scale the Amp-hours of the batteries to lengthen the kWh of the solution. Most UPS vendors have a modelling tool for this (see link above) where you supply the average continuous load in Watts, and based on the number of strings of batteries, it will tell you the run time.
I haven't tried to get technical punchouts for the Tesla PowerWalls, but they should be readily available. But, unless the PowerWall DC to AC inverter can put out 100amps or more at 240, I would seriously consider moving the circuit breaker for the HVAC condenser into a non-UPS panel. Is this new construction? Or are you setting this up in your basement or garage? That's a lot of wall space in your diagram.
Do you have any consumption data for your home? I would start by metering it and looking at the current/power specs for your HVAC. For comparison purposes, with the HVAC, I'm running an average of ~55 kWh per day with peaks up to 76kWh. So, I'd have to drop the HVAC from the equation to get any meaningful runtime from a 37kWh pack.
I agree the solar PV array is rather small, but remember, this is not an off-grid solution. Realistically, the PV array would never be able to charge the battery packs if they were discharged by more than 15-20% or so.
-Jonathan
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