Earning credits via grid-tied battery storage systems?

[RobbW]

For the discharge test, how about using one of these on the 12 volt battery while in READY? It'd provide a steady load and wouldn't be as wasteful as running a space heater for hours. I have one and use it with a couple of 12 volt panels as overcharge protection (you know, 'cause a real charge controller is too simple :lol: :roll: ).

http://www.ebay.com/itm/400-Watt-Power-Grid-Tie-Inverter-for-Solar-Panel-Wind-/130444131961

I am starting this new thread to discuss a thought I had after reading PV1's post in the "Batteries & Battery Management" forum..

With my next electric billing cycle, I will be switching to my utility's Residential Real-Time Pricing program, which bills your electricity usage by the hour at that hour's market rate. I am making this switch from the fixed-rate program I am currently on through an aggregate retail electricity supplier. The purpose of my switch is to save money on my electric bill by shifting high-load operations in my home to the overnight hours where the hourly market rates are significantly cheaper. My current fixed rate is roughly $0.08/kWh. The current overnight market rate is around $0.02/kWh or less. In fact, frequently the overnight market rate can go negative due to excess power generation. So, theoretically, it is possible for me to get paid to charge my Meepster, run my dishwasher, or dry my bedding/towels overnight! Winning!

Anyway, PV1's post brought up an interesting thought. Something I want to do in the future when I have a little extra cash is to install solar PVs on my house specifically to charge my Meepster. I want to someday make my car truly zero-emissions by powering it via the Sun! Since I am only able to charge my car at night, I will not be able to directly charge my car via solar. So, this system will need to be tied into the grid. I will generate power during the daylight hours feeding it into the grid and receiving a credit for the power generated at the then-current hourly market rate (which is often near $0.14/kWh). I will then charge my Meepster at night from the grid at the then-current hourly market rate (which is often $0.02/kWh or even sometimes negative!).

This got me thinking. Would it hypothetically be possible to use a battery system to charge and store power at night and use a grid-tie inverter such as the one PV1 linked to in his post (or one with a larger output) to feed the stored power back into the system during the day? In doing so, I could charge the battery system at night at $0.02/kWh and then feed it back into the grid during the day and earn a $.14/kWh credit. Am I missing something here? Would this not be a way of earning money (or at least significantly reducing my monthly electric bill) simply by selling my stored power back to my utility at a higher rate?

In preparing for future solar power installation, suppose I was willing to pony up the funds for a 10kW Tesla Powerwall now (estimated cost $3,500 plus installation) or any other battery power storage system. Between now and whenever I finally getting around to installing the solar PV system, could I theoretically charge the Powerwall overnight via my electric utility and then pump it back into the system during the day? A 10kW system would cost roughly $0.20 to charge overnight (10kW x $0.02/kWh). I could then earn a credit of $1.40 by pumping the stored energy back into the system during the peak demand periods during the day (10kW x $0.14/kWh credit). I could earn a net of $1.20 per day. That would be a $36 credit on my electric bill every month or $438 per year.

Okay, help me out. What am I missing here? Other than the fact that it would take 8+ years for this fancy scheme to fully recover the cost of the Tesla Powerwall battery system? But then, isn't that roughly the same amount of time for the ROI on a solar PV system? With a big enough battery storage system, I'd be able to guarantee myself a fixed rate of $0.02/kWh all day every day. According to my TED system, my average daily electric use is about 28kW. I could get 3 of the 10kW Tesla Powerwalls and be able to store up enough energy overnight to accommodate my entire day's worth of electric usage. Once I finally install my solar PV system, then I can store the free energy generated from the Sun during the day. Granted, my solar system will NOT generate enough power during the day for my daily electric usage. However, I think I should be able to make up any difference by topping off the battery storage system overnight when the electric rates are at their lowest, right?

 

[Aerowhatt]

Okay, help me out. What am I missing here? Other than the fact that it would take 8+ years for this fancy scheme to fully recover the cost of the Tesla Powerwall battery system? But then, isn't that roughly the same amount of time for the ROI on a solar PV system? With a big enough battery storage system, I'd be able to guarantee myself a fixed rate of $0.02/kWh all day every day. According to my TED system, my average daily electric use is about 28kW. I could get 3 of the 10kW Tesla Powerwalls and be able to store up enough energy overnight to accommodate my entire day's worth of electric usage. Once I finally install my solar PV system, then I can store the free energy generated from the Sun during the day. Granted, my solar system will NOT generate enough power during the day for my daily electric usage. However, I think I should be able to make up any difference by topping off the battery storage system overnight when the electric rates are at their lowest, right?

Actually some companies are doing just that to cut electrical costs using Teslas 100KWh commercial battery modules. For them it is more about cutting their day usage and using night time priced power much as you suggest. Distributed storage makes a lot of sense in a lot of situations but from a financial standpoint in most regions it doesn't make that much sense for a residence. These commercial users use so much power they don't have the real-estate to make all of their own. You would be money ahead to just take the money that would go for the powerwall etc. and put into a larger grid tied solar system. With battery systems power is more expensive. Your powerwall would be worn out soon after it was paid for so not much gain there. Having extended grid down back up battery power does make sense and is cost effective (more expensive electricity or none is an easy choice). But maybe I've just been taking the "fear the walking dead" show too seriously

A large grid tied system does have you driving on renewable energy. Sure your neighbors directly use your solar power since you charge at night. But the power you provided offsets the power you used at night and then some. So it certainly would be fair to say that your solar charged your car even at night. That fossil fuel would have been used to power your neighbors if your solar hadn't right?

Aerowhatt

 

[Don]

If you had a 10 Kw Tesla power pack, you could indeed charge it at 2 cents and then sell it back at 14 cents and make a relative *fortune!* :lol:

Accounting for charging and inverter losses, you wouldn't actually be earning 12 cents per Kwh doing this, but lets say you were making a dime for each Kw (even a dime is VERY optimistic, IMO . . . . I think your losses would be greater than 20%) and you could do one charge/discharge cycle per day. Ten cents times ten Kw means a buck a day, best case scenario or $365 per year. After ten years, you'd be getting close to paying off the power pack, though you'd need another couple grand worth of equipment to tie it all together. Lets say the break even time would actually be 15 years which is probably about right

*If* the battery pack was still in good shape after 15 years, you could begin to make a little money, but you would then have about 5500 charge/discharge cycles on your battery pack and my guess is . . . . it would have pretty much given up the ghost a few years back

Generating PV power has become fairly economical over the past 15 or 20 years - Storing power on a small scale is still very hard and very expensive to do

It won't surprise me at all if you come back here after a year on your new power plan and report that you were actually saving a little money by paying the standard 8 cents vs your new plan where you get nearly free power overnight, but you pay 14 cents during the day. I think you're going to find you still use more power during the day than you do overnight. We pay 11 cents and with our A/C load during the day, I *know* I'd be losing money if I paid an extra 50% during the day and got free power overnight. Good luck and we'll see how it works out for you

Don

 

[BarryP]

For the discharge test, how about using one of these on the 12 volt battery while in READY? It'd provide a steady load and wouldn't be as wasteful as running a space heater for hours. I have one and use it with a couple of 12 volt panels as overcharge protection (you know, 'cause a real charge controller is too simple :lol: :roll: ).

http://www.ebay.com/itm/400-Watt-Power-Grid-Tie-Inverter-for-Solar-Panel-Wind-/130444131961

...Okay, help me out. What am I missing here? Other than the fact that it would take 8+ years for this fancy scheme to fully recover the cost of the Tesla Powerwall battery system? But then, isn't that roughly the same amount of time for the ROI on a solar PV system? With a big enough battery storage system, I'd be able to guarantee myself a fixed rate of $0.02/kWh all day every day. According to my TED system, my average daily electric use is about 28kW. I could get 3 of the 10kW Tesla Powerwalls and be able to store up enough energy overnight to accommodate my entire day's worth of electric usage. Once I finally install my solar PV system, then I can store the free energy generated from the Sun during the day. Granted, my solar system will NOT generate enough power during the day for my daily electric usage. However, I think I should be able to make up any difference by topping off the battery storage system overnight when the electric rates are at their lowest, right?

So this Tesla Powerwall puts out 350-450VDC @ 2kW. Where are you going to find a 120VAC inverter for that, and how much? Tesla recommends the Fronius Symo Hybrid for a mere $4k.

On top of that Tesla claims 92% efficiency. And then the inverter might get 90% efficiency.

I don’t see how this pays back unless you’re patient for 20 years (and that’s hoping the batteries last that long). But it does set you up for complete off-grid living. And if you don’t dump that power back into the grid but just use it as you need it, I see an extension of life from your system.

Just thinking out loud…
-Barry

 

[PV1]

That is something you have to be careful about. Depending on the utility's terms, you may not be able to keep this pricing plan if you get solar net-metering. You touched on multiple methods of energy storage/PV, so I'll try my best.

That plug and play inverter I linked to is not something I'd recommend, as a solar system that small hardly returns any energy (less than 1 kWh per day in the summer). However, with micro-hydro, which can produce 24/7 power, that inverter would pair well with a 350 watt turbine and produce a meaningful amount of energy.

Solar
On the solar front, getting a proper system professionally installed will offer the best ROI. By this, I mean solar panels along the lines of the SolarWorld 280 watt modules with Enphase Micro-inverters, installed by a solar installer. This way, everything is legitimate with the utility, plus you can take advantage of state and federal incentives, which is not a trivial sum of money. With solar, there are several different system setups.

1. Batteryless grid-tie - This is probably the most popular setup, as it offers the simplest installation and maintenance and quickest ROI. All energy produced gets used in realtime in the building, with any excess flowing back to the grid, generating kWh credits. When usage exceeds generation, power comes from the utility like normal, but is blended with the solar and the meter spins slower than it would without solar. The only downside is that if there is a grid outage, the inverter(s) shut down and the owner loses power.

2. Battery-based Grid-tie - The next step up in resilient power. Solar panels charge a battery bank, which then powers a bi-directional inverter. Grid power passes straight through the inverter, and the inverter injects the solar power into the stream, acting just like a batteryless system. When the grid goes down, the inverter switches to standalone mode and provides all power to the house, using live and stored solar power. A disconnect switch is opened automatically when the grid goes down to prevent backfeeding the lines.

3. Grid-assist - Basically the same as battery-based grid-tie, but with extra features. These systems can be used in areas where net-metering is not allowed, and the utility does not need to be notified prior to installation. No solar power is back-fed to the grid (enabled or disabled in software on most systems). Based on the operating mode, the building is primarily run from live and stored solar power, but some grid power can be used when solar production is low and the batteries are below a set threshold. This is essentially an off-grid system with the grid as a backup generator.

4. Off-grid - As the name implies, this is a standalone solar power system with a battery bank. All loads run from live and stored solar power, with either another RE source or a generator as backup.

Batteries
You mentioned using batteries to buy and sell electricity with the utility to minimize your bill. Depending on the utility, they may have a specific plan for consumer-generators with this setup. What may be easier and more efficient is to install a grid-assist system. This is where you run your house on battery power during the day, and charge those batteries at night using cheaper off-peak energy. With the right grid-assist system, adding solar down the road is a breeze.

i-MiEV
Now, about putting pure solar power in the i-MiEV. Since you want to do a bulk battery charge at night and use that power during the day for the house, a separate solar system would be needed for charging the i-MiEV on sunshine, unless you change your charging habits to use some daytime solar power, which you said is not a possibility. At that point, you could install a grid-assist system for the house with no solar, and a separate solar system dedicated to i-MiEV charging. But, if the utility is paying you to use power at night, then it may end up being cleaner to simply use grid power to charge the i-MiEV (and definitely cheaper). For a utility to pay consumers for using electricity, they must be faced with serious over-generation and having trouble throttling-down the power plants. In a sense, charging your i-MiEV at night is acting as battery-storage.

 

[RobbW]

Thank you all for your informative replies! I definitely see where my thinking needed some help understanding all the complexities.

PV1, your response was uber informative. My thinking was geared more to the grid-assist system you described. Possibly purchasing/installing the battery storage system now and then adding on the solar portion later. Although, investing in the solar portion first seems like it would be the smarter way to go. And then add on the battery storage system later if I decide to do so. It's just that the solar PV portion is the more expensive part of the puzzle.

In any event, the conversation is probably moot since neither option is financially doable in the near-future anyway. It's just something I enjoy talking about for now!

 

[Carsten]

RobbW,
A lot of people don't have the immediate cash/home equity.
There is the lease options (usually 20years) for PV as well. For some people it is interesting, but:
- 0% down lease will give you a rate that is guaranteed to go up quite a bit over time,
- partial pre-paid lease will give you a better rate with lower rate increases,
- full pre-paid lease will give you the best rate with no rate increase.
- all future fees, fixed costs are yours - see Arizona solar fee battle,...
- if your roof needs new shingles in thee next couple of years, they might roll the cost for just the side of the array into the lease.
- if you sell your house before the end of the lease you will have to find a buyer, that takes the lease over or you pay the outstanding lease amount. Beware of buyer's/seller's market.
Depending on the system, they will guarantee you a certain amount of electricity per month as an average over the year. You don't have to care, if it comes from your PV or not.
I personally don't like lease, but for some people it is an option.

The other option is Community Solar, that is up and coming in a couple of states. You buy yourself into a bigger solar system in your utility area and get the electricity as a virtual net-metering credit on your normal electric bill at home.
I find that an interesting alternative for people, who don't like the aesthetics of solar on their roof or have no sunny area on their roof/property.
Just some thoughts to give a direction.
Regards,

 

[Aerowhatt]

Thank you all for your informative replies! I definitely see where my thinking needed some help understanding all the complexities.

PV1, your response was uber informative. My thinking was geared more to the grid-assist system you described. Possibly purchasing/installing the battery storage system now and then adding on the solar portion later. Although, investing in the solar portion first seems like it would be the smarter way to go. And then add on the battery storage system later if I decide to do so. It's just that the solar PV portion is the more expensive part of the puzzle.

In any event, the conversation is probably moot since neither option is financially doable in the near-future anyway. It's just something I enjoy talking about for now!

The solar option doesn't have to cost a lot as others mentioned there are leasing programs etc. I prefer owning and by using micro inverters and some pre planning you could put it up in fractions.

An acquaintance of mine put his up one panel and inverter at a time over a five year period. He got utility approval and pulled permits for the entire planned size of the installation and then pieced it together over time. With micro inverters and working from his connection point he had immediate benefit as each panel was able to put power into the grid from the time they were installed. Actually he did pretty well on equipment costs watching for close outs, etc., and picking up odds and ends on at sale prices. He paid $900 for 10 enphase inverters (a case) as that model was eclipsed by the newer one.

Where there is enough will, there is always a way.

Aerowhatt

 

[Don]

Possibly purchasing/installing the battery storage system now and then adding on the solar portion later. Although, investing in the solar portion first seems like it would be the smarter way to go. And then add on the battery storage system later if I decide to do so.

If you can charge overnight for 2 cents per Kwh, why would you need a battery storage system at all? Put up your PV array (one piece at a time, as you can afford it) and sell the utility your excess power at their daytime rate and then buy back whatever you need overnight at their much cheaper night time rate. Your battery storage system is never going to be economically viable when you can buy and sell power for the rates you've quoted

Don

 

[PV1]

From the thread Some Texas Residents get power for free (http://myimiev.com/forum/viewtopic.php?f=28&t=2913):

Battery buffering the house is a topic that should be explored in detail. Here, we have APS. I can figure the batteries, but there doesn't seem to be any UPL approved hardware to complete the interface to the grid and control the flow of power (unless I am completely missing the boat). Any ideas?

The trick is to look for grid-assist or off-grid solar power systems. These are systems that mainly run your house on battery power with a separate solar charge controller bringing power in from a solar array. It wouldn't be hard to take a system and set it up to run from batteries during the day and then charge the batteries from the grid at night. The only thing is that you would need a battery bank large enough to handle your daytime loads. At that point, it may still be worth it to make it a battery-based solar system.

For an example, here is a system that can handle a 13 kW load, which should be more than enough for most any house. You then pair it with a battery bank. Depending on the programming and features, the system could be programmed to run on battery power during the day and do a battery charge at night when the excess pricing is in place. Even if a battery system doesn't have that capability, a timer and a pair of appropriately-sized contactors could connect and disconnect the grid based on the time of day.

http://www.wholesalesolar.com/1440089/four-star-solar/power-center/four-star-solar-ms4448pae-triple-magnum