Anyone oversizing their system installation now for a future electric vehicle?

[Alchete]

I'm wondering if this is somewhat crazy or if it's worth thinking a few years ahead at install time...

My usage last year was approximately 5700kWh.

If I fill my south facing roof with panels, I can get ~7.8kW of panels, which would equate to a yearly output of 9000kWh. It' also brings the cost/watt down due to installation costs.

So, I'd potentially be running a surplus of ~3300kWh/year. But, I'd lock in the federal and state tax credits, and MA is an SREC state, so I'd start collecting SREC money for my electricity generation.

My plan is to get a Tesla Model III (or equivalent) in late 2017 or whenever it ships.

In MA, according to my research, there is no feed-in-tariff system to buy the electricity, but net metering credits never expire. So, I'd potentially be running a large surplus for ~2 years, until I get an electric vehicle, at which point I'd likely go negative and start drawing them down (depending on my yearly mileage).

Oversizing the system would also open up other options, such as converting other appliances to electric. In my case, I already have an electric stove, but I'm about to replace a 70 year old oil burner with a gas furnace & indirect hot water storage. However, having a surplus of electricity would allow me to potentially consider an electric hot water or even electric heating of some sort. I haven't researched electric heat yet and am guessing the efficiencies are horrendous, which would add up quickly in the Northeast over the winter.

So, for those who've installed recently or soon, are any of you oversizing your installation now for future plans (electric vehicle, etc.)?

[inetdog]

Depending on the rules of your particular POCO, you might have to go to great lengths to convince them of the sincerity of your intention to get an EV.
Many POCOs will not allow the system to be sized beyond about 10% over your historic utilization.

[silversaver]

Depending on the rules of your particular POCO, you might have to go to great lengths to convince them of the sincerity of your intention to get an EV.
Many POCOs will not allow the system to be sized beyond about 10% over your historic utilization.

+1 POCO will not allow you to oversizing your system unless you bring them a purchase of EV as additional documentation.

[Alchete]

+1 POCO will not allow you to oversizing your system unless you bring them a purchase of EV as additional documentation.

Interesting. The two installers I've talked to haven't mentioned it as a blocking issue, but I'll call my local power company on Monday and confirm.

[J.P.M.]

The concept of oversizing may need a bit of clarification.

If my current annual load is 5,700 kWh/yr., but I'm pretty sure that for whatever reason my usage will be, say, doubling to 11,400 kWh/yr. next year and staying that way, I'm not sure sizing a system to deliver, say, 9,000 kWh/yr. would qualify as oversizing.

On the other hand, if I oversize a system with not a strong likelihood of ever needing it, or my EV plans don't work out, etc. and I must find ways to chew up what becomes capacity that would otherwise be wasted, with those ways being excessively wasteful (by heating H2O w/ elec. resistance heat for example), and something I would not be doing except for the excess installed capacity, that's sort of the tail wagging the dog. I guess it sort of depends, in part, on how sure you are of the NEEDED load being there. Without the additional NEEDED and planned for load being there, the system would be oversized and cost Ineffective.

[Alchete]

The concept of oversizing may need a bit of clarification.

If my current annual load is 5,700 kWh/yr., but I'm pretty sure that for whatever reason my usage will be, say, doubling to 11,400 kWh/yr. next year and staying that way, I'm not sure sizing a system to deliver, say, 9,000 kWh/yr. would qualify as oversizing.

Oversizing, as I mentioned in my original post, is referring to installing more capacity than I'm using now, with the anticipation of my demands changing one, two, or three years down the road. It qualifies as "oversizing" in reference to my current usage, and, as you can see by the other responses, may be an issue for power companies.

Why is electric hot water "excessively wasteful" if electricity is plentiful? Completely leaving aside the CO2 argument, if I'm able to achieve breakeven in seven years, for example, by filling my entire roof with panels -- AND that also happens to generate MORE electricity than I'm currently using, then ANYTHING else I convert to electricity to fill my capacity will result in even further savings. In that case, it would actually be economically wasteful for me to use a different energy source for additional money solely because it would be more efficient at heating than electricity.

[UkiwiS]

Why not just add panels if/when the need arises...in 2017

[DanS26]

Here in Indiana if your POCO is a non-public POCO then you have opportunity to negotiate an agreement to over produce.

My annual usage is ~12,000 kWh, but my solar system produces ~24,000 kWh. I get paid ~$.07 per kWh of excess production which approximates the wholesale price my POCO pays for power which includes transmission costs from Hoosier Energy. Hoosier Energy produces coal powered electricity at ~$.025 kwh but then they have transmission cost and over head which increased the cost to ~$.07 kWh as supplied to there REMC owners. My POCO settles up with me once a year so I do not lose any value of my over production.

Now Ladies and Gentlemen, Indiana coal is the dirtiest of the dirty.... very high in sulfur and especially mercury. In fact it is so dirty that some plants have to import "clean" coal from out west just to comply with the current air pollution rules. But remember SW Indiana sits on some of the largest and easiest to access coal beds in the world. Hundreds of years if not centuries of supply. As you can imagine we are having one of the fiercest fights in the nation to protect these special interests.

Now I'd rather use my excess power internally than sell it at wholesale even though my production cost is ~$.03 kWh. Yes, that is my true production cost...I built the system myself so I consider myself a low cost producer.

So here is what I have done over the past few years to absorb the over production. First I installed a Nyle water heater heat pump which I have on a timer so that it only runs in the daytime. Next I installed a Steffes electric heating system which is also only charged during daylight hours (works way better than my expectations). Plan to add a second Steffes system this fall. Next on the agenda is an EV.

But my real hope for the future is a cost effective energy storage system.

[J.P.M.]

Oversizing, as I mentioned in my original post, is referring to installing more capacity than I'm using now, with the anticipation of my demands changing one, two, or three years down the road. It qualifies as "oversizing" in reference to my current usage, and, as you can see by the other responses, may be an issue for power companies.

Why is electric hot water "excessively wasteful" if electricity is plentiful? Completely leaving aside the CO2 argument, if I'm able to achieve breakeven in seven years, for example, by filling my entire roof with panels -- AND that also happens to generate MORE electricity than I'm currently using, then ANYTHING else I convert to electricity to fill my capacity will result in even further savings. In that case, it would actually be economically wasteful for me to use a different energy source for additional money solely because it would be more efficient at heating than electricity.

Define oversizing as you wish.

The goal for the smart money is the most efficient use of resources, including financial resources - never perfect. In this case, if temporary oversizing of a system - in effect, building early to get incentives of limited availability - and temporarily using the excess electricity in relatively inefficient ways is unavoidable, while meeting a longer term but overall cost effective goal, that may well be seen as a better alternative. I'd suggest however, that the penalties, unavoidable or not, need to be accounted for in a thorough cost analysis.

As for the wasteful part of electric resistance water heating: In a thermodynamics sense, heating water with electricity using resistance heating is akin to cutting butter with a chain saw. Electricity is a very low entropy form of energy. That attribute of low entropy gives it a lot of diversity to perform many tasks that higher entropy forms of energy cannot perform. Try running the monitor you're looking at directly with coal or CH4. That diversity that electricity has comes at a price. It takes a lot of relatively high entropy coal or CH4 for example, to create electricity - bottom line roughly something like about 3 units or so of fossil fuel energy to create the equivalent 1 unit of electrical energy. That's also why electricity costs so much and why power plants are necessary, and also (parenthetically), why PV is only about 20% efficient as a conversion process, while solar thermal is close to or more than 2X as efficient at something approaching 40 % or so. About the only lower entropy source of energy than electricity is nuclear power and that's only after a lot of processing and concentrating. So, to a rough 1st approx., if you have 100 units of energy contained in, say, CH4, you can either burn the CH4 in a water heater in your basement/garage at about 70 % efficiency, or burn it in a power plant and produce something like 40 units of energy as electricity. Blow about 5 more units of electrical energy getting it to your house and use the remaining 35 units to heat the water with a resistance heating element. Where's the more efficient use of the CH4 - making low entropy electricity and then in a sense wasting the entropy decrease on a task better performed with the high(er) entropy fuel (the CH4) ? The more efficient use of resources way is to match the fuel to the task - in the example used here, heat the H2O with CH4 and use electricity for motive power to do work - as in turning a shaft and running a heat pump and in so doing get otherwise unavailable heat energy from the surroundings.

Take what you want of the above. Scrap the rest.

[bcroe]

Oversizing, as I mentioned in my original post, is referring to installing more capacity than I'm using now, with the anticipation of my demands changing one, two, or three years down the road. It qualifies as "oversizing" in reference to my current usage, and, as you can see by the other responses, may be an issue for power companies.

Why is electric hot water "excessively wasteful" if electricity is plentiful? Completely leaving aside the CO2 argument, if I'm able to achieve breakeven in seven years, for example, by filling my entire roof with panels -- AND that also happens to generate MORE electricity than I'm currently using, then ANYTHING else I convert to electricity to fill my capacity will result in even further savings. In that case, it would actually be economically wasteful for me to use a different energy source for additional money solely because it would be more efficient at heating than electricity.

No oversizing issues here in the Wild West. I wonder if you have calculated how many KWH
it would take you to convert to electric heat? My estimate is 27 KWH resistance heat replaces
about 1 gallon of propane. So 27,000 KWH will replace 1000 gallons of propane.

So propane here becomes more expensive than electric resistance heat approaching $3 a gallon.
We have seen it cleverly manipulated to over $5 a gallon just when you need it the most. If you
install a high tech heat pump, your electric energy may be multiplied by 2 to 4, making electric
heat pretty competitive with propane. Natural gas may be a lot less $, but I rejected that when
I learned the connect fee had risen 1000% to some $336 a year and could rise more.

There are also heat pump water heaters, generally affecting the air in your basement. Don't
forget that clouds in your area could reduce the efficiency of your system far below the same
equipment in the sunny SW desert. Bruce Roe

[SolarFamilyGuy]

I'm wondering if this is somewhat crazy or if it's worth thinking a few years ahead at install time...

My usage last year was approximately 5700kWh.

If I fill my south facing roof with panels, I can get ~7.8kW of panels, which would equate to a yearly output of 9000kWh. It' also brings the cost/watt down due to installation costs.

So, I'd potentially be running a surplus of ~3300kWh/year. But, I'd lock in the federal and state tax credits, and MA is an SREC state, so I'd start collecting SREC money for my electricity generation.

My plan is to get a Tesla Model III (or equivalent) in late 2017 or whenever it ships.

In MA, according to my research, there is no feed-in-tariff system to buy the electricity, but net metering credits never expire. So, I'd potentially be running a large surplus for ~2 years, until I get an electric vehicle, at which point I'd likely go negative and start drawing them down (depending on my yearly mileage).

Oversizing the system would also open up other options, such as converting other appliances to electric. In my case, I already have an electric stove, but I'm about to replace a 70 year old oil burner with a gas furnace & indirect hot water storage. However, having a surplus of electricity would allow me to potentially consider an electric hot water or even electric heating of some sort. I haven't researched electric heat yet and am guessing the efficiencies are horrendous, which would add up quickly in the Northeast over the winter.

So, for those who've installed recently or soon, are any of you oversizing your installation now for future plans (electric vehicle, etc.)?

Sounds like you live is a state which the PUD and state government are in bed together. If you can, go 100% off grid if you can. You already are spending this much money on a 7kw system, spend a little extra money and go 100% off grid with battery backup. This way you are not reliant on grid power or lack of political leadership.

[sensij]

Sounds like you live is a state which the PUD and state government are in bed together. If you can, go 100% off grid if you can. You already are spending this much money on a 7kw system, spend a little extra money and go 100% off grid with battery backup. This way you are not reliant on grid power or lack of political leadership.

100% off-grid is much more than "a little extra money".

[sensij]

Why is electric hot water "excessively wasteful" if electricity is plentiful? Completely leaving aside the CO2 argument, if I'm able to achieve breakeven in seven years, for example, by filling my entire roof with panels -- AND that also happens to generate MORE electricity than I'm currently using, then ANYTHING else I convert to electricity to fill my capacity will result in even further savings. In that case, it would actually be economically wasteful for me to use a different energy source for additional money solely because it would be more efficient at heating than electricity.

While it is true that once the array is installed, the cost is sunk, when you are calculating payback it is a good practice to look at the cost of what you are replacing.

Let's say a 40 gal, 36000 BTU gas water heater has an energy factor of 0.62, and your gas costs $0.95 / therm. The cost to operate it would be estimated to be 365 * (0.4105 / 0.62) * 0.95 = $230.

An equivalent electric water heater might have an energy factor of 0.92, leading to the following estimated annual operating cost, with electricity cost of $0.15 / kWh: 365 * (12.03 / 0.92) * 0.15 = $716.

So, you can see, replacing an electric water heater with solar will have a much faster payback than replacing a gas heater with an electric one that is powered by solar. If you've penciled the electric replacement payback at 7 years, the gas replacement payback would be over 20 years. Again, if you've already installed the array and are looking for something to do with excess energy because the power company doesn't provide compensation for it, *maybe* it would make sense. Intentionally oversizing an array to do the same thing is foolish, in this example, unless you are convinced the environmental benefit is worth the higher price you are paying for your hot water.

The math for tankless heaters might be a bit different, but probably the conclusion would be the same, since the fundamental limitations that J.P.M. described are unavoidable. In CA, I think electric tankless systems will eventually be problematic, since they require high power for short periods of time. Solar is better at delivering low power for longer periods of time. As demand charges such as those rolling out in AZ make their way into CA, keeping instantaeous demand low may become a big part of how to keep the electric bill low too, even with solar installed.

(cost estimates were made using the same usage assumptions described here)

[J.P.M.]

While it is true that once the array is installed, the cost is sunk, when you are calculating payback it is a good practice to look at the cost of what you are replacing.

Let's say a 40 gal, 36000 BTU gas water heater has an energy factor of 0.62, and your gas costs $0.95 / therm. The cost to operate it would be estimated to be 365 * (0.4105 / 0.62) * 0.95 = $230.

An equivalent electric water heater might have an energy factor of 0.92, leading to the following estimated annual operating cost, with electricity cost of $0.15 / kWh: 365 * (12.03 / 0.92) * 0.15 = $716.

So, you can see, replacing an electric water heater with solar will have a much faster payback than replacing a gas heater with an electric one that is powered by solar. If you've penciled the electric replacement payback at 7 years, the gas replacement payback would be over 20 years. Again, if you've already installed the array and are looking for something to do with excess energy because the power company doesn't provide compensation for it, *maybe* it would make sense. Intentionally oversizing an array to do the same thing is foolish, in this example, unless you are convinced the environmental benefit is worth the higher price you are paying for your hot water.

The math for tankless heaters might be a bit different, but probably the conclusion would be the same, since the fundamental limitations that J.P.M. described are unavoidable. In CA, I think electric tankless systems will eventually be problematic, since they require high power for short periods of time. Solar is better at delivering low power for longer periods of time. As demand charges such as those rolling out in AZ make their way into CA, keeping instantaeous demand low may become a big part of how to keep the electric bill low too, even with solar installed.

(cost estimates were made using the same usage assumptions described here)

For those who plan on providing the power for electric resistance water heating with PV: Think again. Unless you change over from elec. resistance to a heat pump for H2O heating, you'll be better off with solar thermal for water heating than solar PV.

As for tankless ELECTRIC using resistance, sizing for, say, a 3 GPM demand with a 60 deg. F. rise will require something like a 26+ kW power draw. That's a pretty big amount. Possible, but not real practical. As for gas fired demand water heating, more practical, but sort of expensive and a bit complicated, meaning increased probability of service problems. For now, if CH4 service is available, the smart money is to stay w/a simple, proven, and reliable tank system, and insulate the crap out of the tank and the lines. The other less cost effective but still possible alt., at least in moderate climates, is a heat pump water heater w/ the power supplied by PV. That alt. is probably more cost effective than solar thermal at this time. Like everything else when comparing ways to save, conservation is almost always more cost effective than using more energy - particularly solar energy. Low flow shower heads and water saving appliances are the order of the day if money and cost effectiveness is important.

[samotlietuvis]

I am oversizing by ~ 15kwh per day - buying my wife a used Volt at the end of the year. That should get her 30 miles or so per day... Some day hopefully I will own Tesla or a Bolt. More panels will be added