Ben, Whether it makes sense depends on the total picture: - how much money can you save by shifting load to low cost hours versus - how much does the solution cost you?
To start with the latter - we know how much the battery costs and its warranty. We do not know what kind of inverter can be used with it, due to the skinny specs and then there is the issue of the (professional!) installation and permit(s) to satisfy building inspectors and others involved, incl your insurance (the safety aspect). Safe to say that the total system will be 2-3 times the cost of the battery, so probably somewhere between 8 and 10k for the 10kW pack and likely your cost goes up by about 5k for each additional 10kW pack you add, so the max would be some $50k for 90kWh installed and working as a system in your home. Now let's look at the income side. If you have no ToU like me, the result of load shifting is exactly zero. So, for me it makes sense to install solar to reduce the kWh overall, not to shift kWh from afternoon to night. My previous home did have a ToU meter after I reported to PG&E that I had an EV, they swapped out my meter for free and I was very eager to shift loads to the night so I would start saving money. I was very disappointed that even with only charging throughout the night (midnight to 7AM) and convincing my wife to only run the clothes dryer and bread maker during the night, we were still breaking even in overall costs compared to the situation before where we had a fixed kWh cost. What was the problem? Well, the night tariff was indeed lower than the old fixed one, but only be about 4 cents. The summer day tariff however was about 25 cents more expensive, so even though we used only a fraction of the power during the day, we were paying about the same overall. Not a very happy result, even though I like to make things good for utilities - they did not give me any benefit on my E-9 schedule rates. Now for the case with the PowerWall: Just for reference - I am taking numbers from the "EV" schedule as published here: http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_EV.pdf since that would be most appropriate for a ToU customer with an EV who is adding a PowerWall to shift load. Since the price of the old fixed tariff (the E-1 schedule, see http://www.pge.com/tariffs/tm2/pdf/ELEC_SCHEDS_E-1.pdf ) has risen to 16 cents (when I had E-9 the E-1 rate was still 10 cents) you can see that the differences with peak and off-peak versus the fixed rate are *still* in the same order: 6 cents cheaper off-peak and 26 cents more expensive on-peak: off-peak 0.10; winter peak 0.29; summer peak 0.43 Winter is Nov through April and Summer the other 6 months. Every day has a peak period so 365 days/year you can do load shifting. The average income for a kWh shifted (ignoring efficiency losses and different fixed fees between schedules) is 19 cents in winter, 33 cents in summer, so avg 26 cents/kWh Again, the most optimal case would be that you can shift the full 10kWh each day, which would yield $2.60 per day or $950 per year. In 10 years that would give you $9,500 which is about the money you invested in a 10kW system, 10 years earlier so this would give you a zero-percent investment with risks. Not good. For the 90kWh system that cost you $50k the situation is better *IF* you are able to shift 90kWh of energy around each and every day. Since in the weekends and holidays the peak hours are only 3-7PM, you have only 4 hours to dump the energy into the grid, so your 90kWh needs to be pumped at a rate of 90/4 = 22.5kW which is 94 Amps at 240V to empty the pack in time so this will require a dedicated 125A service just for your powerwalls. It might be feasible, I am not sure how much this could add to the cost if you need so much capacity added. Again, for me this is not feasible since my feed is limited to 100A at 240V so it would overload my main house feed. The income picture would look like 9 times the previous calculation (again, ignoring losses) so a little over $8.5k per year, $85k in 10 years. This at least looks to be positive, but the percentage is not that high, a little over 5%, but still with risks of tariff changes and maintenance cost to keep the equipment running for 10 years. Also, efficiency issues or legislation that limits the amount of power you can suck up and pump back, can throw a wrench into this business plan. It might work, but I still expect that the most likely chance of making good money is if you are dealing directly with the utility and get paid for the ability to stabilize the grid (load control) and not necessarily to breathe kWh on a daily basis. But time will tell... Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626 Skype: cor_van_de_water XoIP +31 87 784 1130 private: cvandewater.info www.proxim.com This email message (including any attachments) contains confidential and proprietary information of Proxim Wireless Corporation. If you received this message in error, please delete it and notify the sender. Any unauthorized use, disclosure, distribution, or copying of any part of this message is prohibited. -----Original Message----- From: Ben Goren [mailto:[email protected]] Sent: Monday, May 04, 2015 2:58 PM To: Cor van de Water; Electric Vehicle Discussion List Subject: Re: [EVDL] virtual power plant On May 4, 2015, at 1:07 PM, Cor van de Water via EV <[email protected]> wrote: > I mean 8 Amps at around 400V is not an EV power level, it is actually > rather underwhelming - I wonder why Tesla with a profile of high-power > application is releasing such a low power spec. A "nominal" 5.8A @ 400V is comparable to a 20A load on a 110V line, in line with a typical single home circuit. You can put up to nine of them in a single unit, with up to a 30kW combined peak load. That's pretty well in line with typical household circuitry and usage. They're selling them less as whole-home backup or off-grid batteries and more as arbitrage devices. Fill the batteries at off-peak hours, drain them during on-peak hours and only feed from the grid during on-peak when the batteries are empty. I've heard payback figures bandied about in the three-year range, making them the equivalent of a 25% annual return on investment -- simply phenomenal. If true, if you've got the capital to invest in them, you'd be an idiot to not buy them. ...if true.... b& _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
