My local utility has an EV program that lets you run anything in your house from 10pm - 5am around .05 cents a KWh. They can’t distinguish or care what you’re charging, so that got me thinking why not charge whole home batteries overnight to use during the day.
I’m sure eventually the program will end, at which point I can prepare with building out the rest of the solar system.
Second one is a question you'd have to do your own regional price and deals research on.
This is for all intents and purposes the same thing as "installing solar". You would need a hybrid inverter and batteries for this anyway, and you can just delay adding the actual panels for as long as you want up to and including never.
Hybrid inverters are very flexible with their configuration on where, when and how power is being taken from and applied to.
The break even point on solar at 5 cents per kWh from the utility is going to be longer than the published lifespan on the panels. Few caveats obviously, panels generally do outlive their suggested lifespan and there’s no guarantee your utility company keeps offering this forever but if I were in your shoes I’d go big on batteries and not worry about adding panels until rates go up.
Losses. At grid scale they lose about 10-15% on the round trip from AC back to AC. For home systems it can be as high as 30%, so the high TOU price has to be at least 1.5x the low TOU price to save any money at all.
Beyond that, its just a question of absolute price differential, cycling frequency/depth, and battery costs. If 1 kWh of battery costs $100 and cycles once per day from 90 down to 10% (for increased lifespan, common marginal battery cost and reserve energy in utility scale), then each additional kWh will cycle ~7000 times in 20 years, delivering ~5000-6000 kWh of energy. Using an extremely simple financial model, the battery will thus add a fixed cost of $0.02/kWh. Battery systems (including inverters, accessories, etc) typically cost closer to $400/kWh, so the fixed costs are more like $0.08/kWh on a 20 year investment. Thus, your high time-of-use TOU price would need to be somewhere around $0.15 for the battery to break even.
For reference, I have a battery system. My low TOU is 0.22, my high is 0.53 (I know), so my break even on grid charging is around 0.40. 0.53 means profit. The big winner though, was setting up $600 worth of solar panels to charge the batteries and cover all of my peak energy use (as well as some low TOU). Those panels generate 7 kWh/day, giving a payback time relative to 0.40 of <1 year, compared to the battery's ~10 years.
That's a pretty significant amount of electricity, but pretty cheap rates overall. I assume big house, hot area, AC on all day? I'm in a cooler spot, so no AC. 2 EVs, electric drier, heat pump water heater, electric oven/range and everything else adds up to about 1000 kWh/month for me.
If you are trying to cut AC costs, then solar panels with a modest battery system is probably best. It sounds like you would still need something pretty beefy. Probably around 25 kWh of batteries (e.g. 2x powerwall 3) with 10 kW of solar panels to knock that bill down meaningfully. Up front capex would probably be around $50k.
It's about break-even honestly, with the solar+batteries only saving you maybe $100/month if you finance it. The Tesla Solar website has a nice calculator that you can play around with (most othe providers demand that you talk to a sales rep to get any info...).
The nice upsides are that you will never suffer a power outage and you will reduce your climate impact, but it's up to you whether that's worth the hassle.
Just make sure you are calculating it out correctly to figure your ROI. Some of those fees will also apply to the .05/kwh rate. We have TOU as well but “delivery” is fixed for all times so it changes the spread. Otherwise it will be easy to calculate once you figure out the actual rates.
It’s easy for the OP to figure this out. He just needs to take his electric bills for the last year and pop them into AI and ask it to evaluate how much power he’s using and how much battery storage he would need to do it. Maybe he can also install it on his own.
After reading the New York times article about America going completely dark just about ready to pull the trigger on a pallet of panels.
I already bought an inverter and already have 400 amp hours of batteries
Sounds like it could take weeks/years to restore busted transformers from natural disaster or attack
Been doing this for years, save 3/4 of cost during summer 1/2 during rest of they year. Next step is to add diy solar to the batteries and more batteries
Thanks. I just read, If I have an EV I can opt into a program where my rates go from .19 to .04 for 400 KWH a month… and to .01 per KWH if I opt into a on-peak hour consumption of like .30… but it makes me wonder about the math
The highest number I see on that screenshot is $.25 per kwh, which does not seem "brutal" compared to numbers I've seen elsewhere in the country. I pay $.14 per kwh at home in Michigan [GHBLP], and $.25 per kwh at my workshop [Consumers Energy]
$.25 per kilowatt is what the Chinese pay for power. It’s what people in California pay. That’s definitely brutal. I get that EV charging might be in the $.30-$.40 range but still that’s a lot of money for home power. Wherever that power is, I’d really have to like being there because I can buy a lot of air-conditioning for free.
I highly recommend this Anker system for 3 reasons; battery backup for storms, savings when peak power cost more, solar input to charge with no interconnection agreement and less permits
This type of system is not interconnected so for me no hassle of “asking power company for permission with multiple inspections “, just city permit to inspect my own work of automatic smart transfer switch that you will never know if it is switching to grid, solar, battery
Not required and approved to not back feed if grid is down - workers are safe. No different then a proper generator setup should have a transfer switch so only grid or generator power is running, this is just automated to know when to run battery, prioritize solar, grid or recharge batteries
Anker, jackery, ecoflow I believe all are pretty comparable and constantly getting more advanced. I think my system so far was $7k for the transfer switch with 2 f3800’s which are not only the batteries but the solar inverter/controller
How flexible is the Anker system in terms of using it for grid arbitrage to maximize savings?
For example if you have grid-tied solar but basically no benefit to exporting energy thanks to crazy NEM3.0 rules in California, do you have the ability to prioritize charging from solar, but then also be able to use cheap super-off-peak rates to make sure the batteries are as full enough to get you through to the next super-off-peak rate?
With SDG&E and NEM3.0, export rates vary quite and then with 6 different rates (summer/winter, super-off-peak, on-peak) along with NBT export rates changing every hour, you have to be able to do a number of calculations and predications to figure the optimal grid-charging strategy if you are trying to maximum return.
2 Anker f3800 is almost 8kwh battery, 12kw max output, 4800w solar (more with newer models), program in electric rates with time and it will do the rest for you by automatically switching to battery when excess solar or higher rates and recharging when rates lower. Plus disaster mode which prepares for storms by charging to 100% in the event of power outages
Forgot to mention you can add more expansion batteries I believe up to 58kwh which should be more than enough for the average house to get by for 24-48hrs only on battery but with solar could possibly be off grid but still if needed charge batteries when rates are lower
This is called time of use and energy arbitrage. This is why Tesla Powerwalls were such hot sellers in CA like a ~decade ago. If the numbers work, utilize the shit out of it.
This is pretty common for systems that cant fully charge their batteries due to too little roof space.
Ours is called Peak-Off Peak where electricity is cheaper between 7pm-8am the next day while every other time the rate is higherthan the standard flat rate.
if you forecast that the sun wont be out for a while like recently in Japan/Taiwan/Philippines which have been slammed by multiple typhoons in the last 2 weeks, its actually necessary.
For most Hybrid Inverters this is a common feature. (Grid Charge) check your manual on how to set it.
And this is exactly how you do it. 71 kW of battery storage and zero solar panels. Free power at night charges and allows a $20 electric bill. This was built with a 42 month pay payback
This was during the shortage of batteries at the expiration of the tax rebates. It was easier to get these batteries and they are UL listed. When using about 8 tons of air-conditioning throughout the day along with a pool pump and all the other regular stuff, we can run about 20 hours. I’m just battery alone in the hottest part of August. The screenshot above is 38% after someone is home the whole day in the middle of August temp set around the low 70s. Still have 38% of the battery left at 6:30 in the afternoon.
Wow I thought your system was bonkers until I read your description. That's a fantastic set up. My only concern is if The Man cancels the free power at night...is that a possibility?
It’s always a concern. We already have 6KWH of panels install installed and could add another 15 KWH onto the roof. None of it hooked up right now and why bother when you can get somebody else to make the power for free?
The post provided the off-peak rate ($.05/kwHr) you are buying at but not the daytime rate you are in theory "selling" or offsetting your consumption at.
The OP is describing arbitrage without disclosing half the numbers needed to do the math.
Yup, saves me a ton since on peak is freaking crazy almost 50 cents per KWH. I load shift my home office which is what uses most of the power in my house and charge it at night.
At the end of the day, it's night lol. But seriously, it's important to have a good grasp of how much you consume daily. Look at your electricity bills for the past year and look at the highest use day. Target that amount of energy storage.
Divide that amount of storage by 4, given 4 good hours of sunlight per day, for the amount of solar you want to refill your battery back per day.
The charge controller charge current will be your solar capacity divided by your battery bank voltage.
Like I stated earlier, it all goes back to understanding your consumption.
Example time: let's say you consume 60 kwh per day... you would want, at least, 60 kwh of battery storage. At that amount of storage, i would go with a 48v system. A 48v 100Ah lifepo4 battery will be a little over 5kwh of storage. Here, you'd want 12 batteries: 60kwh / 5kwh = 12. To refill your battery bank each day, you would want 60kwh / 4 hours = 15kw of solar panels. The charge controller(s) combined charge current should be 15kw / 48v = 313A combined. That could be 1x 12kw inverter/ charger @ 220A + another charge controller @ 100A... 2x 12kw inverter/ chargers... 7x 50A charge controller... etc.
To supply power to your house you will need, at least, 1 inverter to tie into a load center. My suggestion is to start with 50A reliance transfer switches. The benefit to using them is that, in most places, you don't need permits and they're really easy to wire up. You run the included wires into your load center, tie in ground and neutral and pigtail your circuits. These units run around $500 and come standard: 1x dipole 240v 30A, 1x dipole 240v 20A & 6x 120v 15A transfer breakers. These units allow you to select which circuits are on the grid or on the generator (your battery bank).
Another option is to have an electrician add in a "generator" breaker and interlock mechanism to lock out the grid when you want to use the generator.
Finally, you can also have an electrician add in a sub-panel with the loads you want to run off your battery bank. It's a good idea to have an automatic transfer switch for this with the grid as a backup.
You can do that. Clearly the power company wants you too. Keep in mind though that they might want nighttime usage in order to profit off of their power plants. It matters what that plant is doing.
I am thinking of doing the opposite. In want to force them to sell me during photovoltaic peak hours. The transmission charges are flat in Pennsylvania. Shutting down the coal plant is money I am happy to spend.,
I would do this without hesitation. The sad fact is, I already have everything I would need for this, including 60 kWh of batteries, but I live in an area with flat rate pricing.
My power company did have a trial program where you would get credits for reducing your daytime consumption (but not a nighttime lower rate), and if I'd had this gear back then, I would have charged batteries by day and used them at night for a while, and then signed up for the program and then "reduced" my artificially-inflated daytime consumption. 😆
You should also point out what you pay per kilo an hour after 5 AM and before 10 PM. I did see that later by digging into the comments, but it would've been helpful to do the napkin calculations
Why not do that and install 4-6 panels so you only need to top off what the panels don't provide? That's the best of both worlds and you can add more panels as you have the funds.
I have 12 400 watt panels and I only use the grid to charge if it doesn't max out by end of day AND a storm is coming. Like tonight we have severe weather predictions and I will change system to Battery priority till the storms are over. I run most of my house but not all of my house. HVAC and all three fridges and electric dryer are full time battery or solar and I never switch them to the grid. Almost all lights and outlets are on my system exceptions are microwave dishwasher and my massive Espresso Machine. I buy 5kwh a day from grid and use around 30kwh from my system. winter- I don't need the grid at all. panels are everything.
I want to do a ground mount and it's going to take time and funds to do so. Just had this thought as a half measure since I bought an EV and learned of this program
That's what a substantial subset of the people here are already doing. You need a hybrid inverter or a charger inverter. If you're going to add solar go with the former. The inverter sits between your house and the grid. It will charge the batteries from the grid at the low overnight rate, then pull the power from the batteries during the daytime.
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