Recommendations to support car charging & separate sub-panel in garage?

[chumbaz]

I have an EV with a ~150kwh battery and a PHEV with a ~20kwh battery and the normal use-case is charging 20-50% every couple days for the EV and every night for the PHEV. I'd love to figure out a way to have a solar system that could sustain both charging and possibly provide supplemental power to my garage.

The reason I'm asking is I'm currently building a separate garage and having a completely separate 200a sub-panel put in specifically to support solar and to extend power to the other end of the house to be able to support a patio project I'm doing later this summer. Ideally I would love to figure out a way to have the solar system tie either into the garage or to the main panel so that some portion of the house could be on battery OR a portion of the panel be dedicated for backup power (garage fridge/freezer) and also be able to charge the EV. I'd just much prefer the battery to live in the garage than in the basement with the main panel.

I'd love recommendations if it's smarter to have the solar feed into the main panel, or if it's worth while to feed it into the garage with the battery/inverter and run a feed back from the garage sub-panel back into the house, or some other solution I've not considered.

Also, what size battery bank (or specific all-in-one products) would you recommend to live in a garage but be tidy and professional? I live in the midwest in zone 5B so the garage is insulated but not heated, if that matters.

Thank you!

 

[chrisski]

I think the best you can do is sell electric back to the grid in the day, and hope for the best to reduce your bill at night.

I'd just much prefer the battery to live in the garage than in the basement with the main panel.

Code says only 80 kWh of battery for household use in the garage. You have 180 kWh of EV batteries to charge. Pretty difficult problem set.

For that battery, I’d want a 220 kWh battery bank for maths sake, but that is not practical.

My Tesla charger with a 60 amp circuit breaker can charge 48 amps at 11 kW. You 150 kWh battery charger I’m sure is more.

 

[time2roll]

Can you charge when the sun is up? That is a lot of power to store up and charge overnight.

 

[chumbaz]

Can you charge when the sun is up? That is a lot of power to store up and charge overnight.

Yes, it wouldn't be completely at night. I just wanted to plan for worst-case scenario.

 

[chumbaz]

Code says only 80 kWh of battery for household use in the garage. You have 180 kWh of EV batteries to charge. Pretty difficult problem set.

Ah, I had no idea there was a limit. Thank you!

 

[zanydroid]

This sounds rather expensive if you math out the utilization factor and size of array. If it was me I would do the math and fast fail the concept to move on.

You might only have the surplus in the summer, leaving the stationary battery only partly filled the rest of the year.

 

[chumbaz]

This sounds rather expensive if you math out the utilization factor and size of array. If it was me I would do the math and fast fail the concept to move on.

If the system is able to offset the cost of charging the vehicle, it'll easily pay for itself because my power company implemented a substantial rate hike once you go over a certain amount of KWH usage per month.

I don't care if the batteries supplement the house and that offsets the car, or the solar is able to charge the car. It's the same drop in KWH. I don't need it to just charge the car, I just want it to be able to support the load that a L2 car charger if at all possible.

You might only have the surplus in the summer, leaving the stationary battery only partly filled the rest of the year.

Isn't this any solar system? I don't understand if this is the way to think about it that any solar+battery system makes any sense.

 

[400bird]

Does your utility provider do net metering? Are you willing to go through the paperwork to sign up? Those two answers drastically change the equation.

Rough numbers:
150 kWh * 50% / every other day = 37kWh per day
20kWh per night.
Minimum of 57kWh of production, all it 70 to have some buffer and not run short of a single cloud passes over.

You can calculate your own, more precise numbers (Google NREL PVwatts)
Let's say you get 3.5 hours of sun in the winter.
57kWh/3.5h = 16.3 kW of panels.

This is the bare minimum and would take days to charge the larger EV.

If you want to fully charge in one sunny winter day you'd need more like +50kW of panels.

Then somewhere between 25-190 kWh of batteries depending on your desire to charge overnight.

The plan falls apart when you realize Ohio probably has clouds and storms for days are a time in the winter, right? Do you add more battery to make it through the storms?

 

[zanydroid]

Isn't this any solar system? I don't understand if this is the way to think about it that any solar+battery system makes any sense.

Good point. I think what I'm concerned about here is that you would make a 4x bigger mistake with a system sized to handle EVs.

my power company implemented a substantial rate hike once you go over a certain amount of KWH usage per month.

If you are thinking of shifting TOU then an arbitrarily sized battery will help in all seasons. If you are thinking of offsetting KWH usage with local solar either you have a massive system or you are limited in the number of months.

With cross-season net metering I'm not incentivized to buy any battery, and the seasonal imbalance doesn't matter because it is shifted into an annual bank. Without cross-season net metering, in the summer the battery can achieve the full expected payoff (IE, bypass the utility), but it can only do this in the winter for part of the load, while the majority of the load will not bypass utility.

Do the scenario modeling for each season.

What are the $ numbers here? For the different tiers, TOU, demand charges, everything.

What is the biggest solar you are willing to install?

Note on the storage side alone, if you are DIY installing a UL9540 ESS of 80 kWh you are looking at $17-20K+ after taxes creditds.

I just want it to be able to support the load that a L2 car charger if at all possible.

This can be defined in energy terms and in power terms. In power terms you don't need as big of a system.

Isn't this any solar system? I don't understand if this is the way to think about it that any solar+battery system makes any sense.

The ROI is very different as you cross various breakpoints in the way you size the system. It might be rather positive ROI in some portions of the sizing curve (which is multi-dimensional). But terrible (IE longer than system lifespan) in other parts.