Smart Charging with Solar

[Grunk]

I'm curious, for people with solar on their roof where they charge (either at work or at home), do people have any tradeoffs between driving on solar vs. selling power back to the grid?

For example, if your utility has high prices during the day and will buy power from you during the day, maybe you want to sell electricity back to the grid during the day and charge your car overnight. Other utilities may pay a flat rate for solar power generated regardless of time, so driving on sunlight doesn't affect your bill. In California the utility may have too much solar around noon, so driving on sunlight can be both great for the environment and your pocket book, if your utility provides time-of-use rates with low periods during the day. However, the details may often be tied to your utility rate schedule.

There are apps that will help with issues like this, such as FlexCharging. That app will let you charge your car overnight, or if you have solar, charge at a different time.

What would you all prefer?

 

[1937highboy]

In my area of Texas i have Green Mountain energy. They pay me for every KWH i give them. I run my house and charge both my Tesla and Leaf and still have a credit of over $600 with them.

 

[Sharkbait]

I would purposely use more power than I need before selling it back to Edison, who would pay me pennies on the dollar for it and sell it to my next door neighbor for 30 cents kWh. If I could give it away to a poor family rather than use it, I would. I'm on NEM 1.0 (not TOU), and I always plugin whenever I return home, day or night, doesn't matter. Contemplating a 100D, which would require a full charge once a week for my driving habits. Currently use a SC about 20% of the time.

 

[BerTX]

Yeah, my utility screws me on solar, so any time I can charge while the sun is out, I come out ahead. It doesn't really save much, but like @Sharkbait says, anything to make the power company less able to gouge me for being green is worth it in my book. I voted "perfectly aligned" in the poll, as it seemed the best answer of those given, although I would never call it perfect in any way.

 

[Ampster]

It depends on my location. I am on NEM 1.0 at my primary home and charge overnight because that is the cheapest and almost free because it uses dollars credited at high rates during the day. Since that is my primary use i answered "saving money".
My second home has recently installed solar and will be on NEM 2.0. On that rate plan I think I am better off charging during the day because of the non bypassable charges.

 

[mblakele]

It depends on my location. I am on NEM 1.0 at my primary home and charge overnight because that is the cheapest and almost free because it uses dollars credited at high rates during the day. Since that is my primary use i answered "saving money".
My second home has recently installed solar and will be on NEM 2.0. On that rate plan I think I am better off charging during the day because of the non bypassable charges.

Can you share your math for NEM2 NBC?

I'm on PG&E, EV-A rate plan. The billing seems deliberately opaque. But as near as I can figure out, NEM2 NBC costs me about half a cent extra per kWh that I pull from the grid, regardless of my generation. That's a weak incentive to self-consume, because generation on-peak credits me with 32 cents/kWh in winter, and more in summer. Off-peak costs just under 13 cents/kWh. Looking at these numbers, the extra half-cent doesn't influence my behavior.

Should it? Am I missing something?

 

[mblakele]

I would purposely use more power than I need before selling it back to Edison, who would pay me pennies on the dollar for it and sell it to my next door neighbor for 30 cents kWh. If I could give it away to a poor family rather than use it, I would

Try telling yourself that your excess generation is going to CARE/FERA households.

CARE/FERA | Help With Your Bill | Your Home | Home - SCE

 

[SageBrush]

I am net metered, although any excess each year gains me 4 cents a kWh.

The PV I use to run my cars is PV not used to reduce coal use by my neighbors. So while I love the idea of running my cars on clean energy, I realize that it is a less than ideal use of the energy. And the loss is not just a kwh per kwh, since it would take way less than 100% substitution to force a coal plant closure.

Irony.

 

[Grunk]

I am net metered, although any excess each year gains me 4 cents a kWh.

The PV I use to run my cars is PV not used to reduce coal use by my neighbors. So while I love the idea of running my cars on clean energy, I realize that it is a less than ideal use of the energy. And the loss is not just a kwh per kwh, since it would take way less than 100% substitution to force a coal plant closure.

This is why environmentally we are better off charging at off-peak times. If we can lower a utility's peak capacity needs throughout an entire year by spreading out charging overnight every night, then we can make it easier for them to shut down coal plants. However, utilities have different peak capacity needs based on season and time of day. So while Nevada may have a peak in the afternoon, in other areas like California or the Pacific Northwest it's in the evening.

I've spent years fighting to shut down a coal plant (and we're about 3/4ths of the way there). However if someone spends $30K on solar and $100K on an electric car, I'm not going to tell anyone they shouldn't be able to maximize the financial value of their investment. For you, it sounds like your utility's net metering plan means it doesn't matter when you use the electricity financially (though obviously it matters environmentally). For others, there might be a large financial difference for whether they use or resell solar based on time of day, and by shifting charging to the night they can reduce carbon emissions too.

With an appropriate app, I think we can make it easy to do the right thing environmentally, ensure you can still drive when you need to, and also reduce costs. It just requires understanding every utility in the US, their rate schedules, controlling when EV's charge, and understanding driver preferences (ie, where they charge, whether they have solar at home, etc).

 

[SageBrush]

This is why environmentally we are better off charging at off-peak times. If we can lower a utility's peak capacity needs throughout an entire year by spreading out charging overnight every night, then we can make it easier for them to shut down coal plants.

I think in general you have it backwards, although I cannot speak to the specifics of your local generator(s).

As for an app, there is too much variation between locales to generalize. As one example from my state of Colorado: we have excess generation of wind power at night* that is curtailed. You might guess that night time charging would then be optimal, but no. The wind generators are not owned by the utilities, but the coal plants are, so the utilities run the coal plants preferentially. Shifting EV charging to the night time improves the bottom line of the coal plants.

It gets complicated, and is very locale dependent. Not only because of the differing generation assets, ownerships, capacities, and local climate, but of course politics.

*"Excess" comes with a big asterisk. Here it means "less demand than our coal plants can supply."

 

[Grunk]

Fascinating, and disturbing. You'd think that Colorado could implement some kind of environmentally preferred dispatch, or the wind plants could say they have a marginal cost of 0, so utilities are best off taking power from them. But I see how that depends highly on the local structure of the market, and how much choice utilities have when trading power.

My understanding is that power dispatch in the Pacific Northwest is more of a normal market, with dams and wind farms advertising a near 0 marginal cost for power. There's a market clearing price set often by the cost to dispatch natural gas plants, and then everyone selling power gets that price.

But I get your point that optimizing for non-dispatchible energy resources like wind or solar could just as easily optimize costs for other non-dispatchible power, like coal or nuclear, in a very open market. And electricity market design could vary widely by state, or at least by region.

 

[Rockster]

My solar just came online last week, so I'm trying to determine what's best. My electric company doesn't pay for net excess production, per se, but they use my excess production to offset my consumption within the same billing cycle.

My rate is $0.10/kWh, no matter the time or the day, so at least that's not variable.

 

[dgpcolorado]

I try to charge during the day to use my solar, and that of my neighbors, directly. I don't have TOU, so there is no cost difference to when I charge, however midday is one of the off-peak times here, so it should help the power co-op. Peak load times for our area are mornings and evenings. AC is not used here except for a few commercial buildings, so no afternoon power load as happens in hot climates.

My power co-op lets me accumulate solar credits as long as I want, up to a maximum of 10,000 kWh, so I don't have to reconcile the excess at the wholesale rate. It is pretty much the ideal net metering situation and came about because the co-op is very renewable friendly, to reflect the views of the membership. I haven't paid more than the basic monthly service charge — currently $20 — since 2012 and am carrying a credit balance of 1103 kWh.

My solar array is just 2170 watts and I adjust the pitch of the panels eight times a year to maximize production — they are currently at 35º. I've been driving on sunpower since 2011.

 

[Don TLR]

I get charged the same no matter the time of day and figure I'll use my own power when I get home and the sun is still out.