Korishan said:
You would want a Hybrid Inverter. It charges from the grid and/or solar. You can usually adjust the preferences for each. And if you loads are higher than what the battery/solar can supply, it'll auto pull from the grid the remaining power needed.
You never pull 100% from the battery unless there is no charging happening at all, or you are pulling more than what solar and battery can supply (so at night, you always pull 100% if not grid connected)
Longevity of cells (the battery is full assembly) varies depending on how much current you pull from them on a regular basis and what the voltage range you run at is. You can get 1000's of cycles if you only use the cells between 3.2V - 4.1V. But going from 2.9V - 4.2V you drop down to only 100's of cycles.
Please the read the FAQ, it is located on the main page. Since you are new to this, there are probably a lot of questions that are already answered there.
Deleted your other thread as it was a duplicate and this one is in the right location.
Thanks, Korishan. I'll look at hybrid inverters. Are there any brand names that jump out at you?
Based on your response, my gut tells me that to reduce my demand charge, I would need to have some piece of electrical gear between the meter and the battery that would not limit energy in the direction of the utility (this would be the solar energy left over after charging the battery to 100% that would then be net metered for later use), but that would limit the amps coming from the grid (this would be the grid energy that would be used to charge the battery when no solar--but this is also the energy that I would have banked via net metering, while also being the energy that I need to limit coming back into the system due to the demand charge). Does anyone know what this type of electrical gear might be called? It seems like for me that this is the key piece of gear.
On the longevity of the cells, how would one design a system to maintain voltage between 3.2-4.1V rather than 2.9-4.2V? Sorry if this is a blatant newbie question, but I'm trying to get my head wrapped around this...
Thanks a ton for your time, Korishan. I really appreciate it.
Sean said:
87kWh a day is rather a lot - do you have lots of either roof or ground space available for panels, and do you have permission to install them,as you'll need a fair number in order to put a dent in that daily usage.
Yep; solar system size is currently planned as 19.6 kW-DC. We have plenty of space here. I own an energy company so I can install them at cost.
Korishan said:
Agreed, 87kWh is a lot! That's almost 3x what I use. Altho I only run the A/C down to 74F, and only at night. During the day it's set at 78F. I only don't use electric range. My electric water heater only runs twice a day for 2 hours each.
aventeren: What are your loads? Is there a possible way of lowering your load requirements?
I touched on a bit more of my data in an earlier post, but basically the house was set up with electric heating, which we actually REALLY liked prior to Northwestern Energy changing the net metering rules to include a demand charge. We could convert a portion of the heat to natural gas, but then we aren't doing our part for our 2 kids on the climate side--so we're exploring different ways to skin this cat rather than just burn more natural gas and buy lesselectricity.
We might be able to time shift our energy use around bit, but what we are finding out about this house is that the VAST majority of the electric bill is from the electric heat.
OffGridInTheCity said:
Reposting on this thread per request (forgive me if its wrong one
).
AIMS Pure Sine Wave Inverters allow for grid charging of batteries and transfer switch to run off the batteries. The AIMS has an adjustment to set the amps of charging from max to min. There are many factors here and I'm not pushing AIMS, just pointing out that a charge/transfer-switch/inverter unit might be a way to go. You can still have a MPPT controller to charge batteries from PV array at same time the AIMS does.
Right on, thanks. I'll look into this. Being able to set the amps of charging from a max to min is exactly what I'm looking for--so long as I would be able to effectively limit the grid charging while not limiting the solar charging. That's the technical question I am trying to solve. Grid charging comes with a demand charge, so I'm trying to limit the grid energy coming back to the system--while having no limitation on the solar energy side (both solar energy charging the battery and solar energy flowing into the grid).
billvon said:
aventeren said:
So I guess here are my questions:
1. Do grid charge controllers exist that would allow us to essentially trickle charge the battery in a manually adjustable fashion that would allow us to minimize our demand charge?
2. Are there any issues with pulling primarily from the battery 100% of the time? Longevity, degradation, practicality, safety, etc
3. If I was to use Jehus 18650 Lithium Ion battery-based powerwall (likely in a 48V configuration), what is the likely life of these batteries? The batteries are where the cost will be. How long will they likely last in the sort of operational configuration?
Im sure I will have more questions as I continue to plod along here, but Id like to start with getting some feedback on the above questions to help me build a foundation.
Thanks to all for your time and thought and experience and willingness to pitch in and help out. I REALLY appreciate it.
Here is some more info:
Average Monthly kWh use: 2,655 kWh/mo
Average Daily kWh use: 87.3 kWh/24-hr day
Average Daily Wh use: 87,287.7 Wh/24-hr day
Average Daily Ah use: 727.4/24-hr day
I'll post up what I'm thinking on system size after I've done some high level calcs.
1) No, charge controllers don't work like that. They charge the battery until it's full then taper charge. They don't care about demand charge (nor should they.)
2) Sure, you can pull 100% from the battery - just shut down the AC input and the solar charge controller. But why on earth would you do that?
3) Using a standard 18650 you'll get about 500 cycles. That's about a year and a half at full depth cycling.
Here's what you probably want to do:
1) Get a bighybrid inverter like a Radian. Add storage (48V) and a solar charge controller.
2) Set the inverter to"mini grid" mode - this will use AC from the utility only when needed to charge the battery.
Be aware that you are looking at something like $100K for this system. (You are going to need something like 20kw of solar, and battery backed solar runs about $4-5/watt without batteries.) Also be aware that if you are building the pack yourself you are going to need around 25,000 cells.
Thanks; so when you say that the 18650 cells have a life of 500 cycles, where did you get that number--and how did you determine that it would be 1-1.5 yrs of full depth cycling? What's your high level math there? Having to replace 25,000 18650 cells every 1-1.5 yrs obviously is a deal killer.
I'll look into the hybrid inverters--and I'll check out the Radians. Thanks
I have the solar piece covered. I'm just looking to better understand the battery side at this point. I'm first trying to understand the design elements--which will then inform cost and payback.
OffGridInTheCity said:
aventeren said:
Here is some more info:
Average Monthly kWh use: 2,655 kWh/mo
Average Daily kWh use: 87.3 kWh/24-hr day
Average Daily Wh use: 87,287.7 Wh/24-hr day
Average Daily Ah use: 727.4/24-hr day
I'll post up what I'm thinking on system size after I've done some high level calcs.
I have an operating system that produces 10,000 kwh / year off-grid. That's 833/mon which is *1/3 of your goal*.
To produce 10,000kwh/year I have
- 24 panels that total6,885kwh
- 2 x Midnite Solar Charge Controllers
- 40kwh 18650 Battery Bank (5,340 cells)
- AIMS 12,000 watt Inverter - e.g. 240v@50amps
- Several automatic transfer switches and a couple of APC UPSs to feed it all into the house
Cost - USTax Credit brings the bill to $26K. My electricity is .12 = $1,200 savings/year = 22yr ROI and that doesn't include replacing equipment/batteries over 22yrs.
SO - I agree that with previous post that you're talking over $100K outlay.
Its important to note that the size your talking about - e.g. 72panels + 36,000watt Inverter + x, y, z - is quite large in todays home solar. You might have non-technical issues such as neighbors / city that object to 72panels. Bottom line - its a significant undertaking to do the scale and quite serious level of power you listand you might do well to get some professional consultations.
Great info, thanks.
ajw22 said:
Are you sure it'll apply to you?
"NorthWestern spokeswoman Jo Dee Black said the new charge would ensure net-metering customers pay their fair share of service costs. Customers with solar panels already in place would be exempted."
https://www.apnews.com/f5e7fbca9e0c4bd1b4cc6b0236655585
Your 87kWh daily use is rather high. A review of what's using power _AND WHEN_ will be crucial to plan a battery system.
Shifting your loads (eg. hot water system) to run only when you have solar power will significantly reduce the required battery size.
And most conservation measures will likely be much cheaper than a battery system.
From my experience, replacing small electric space/oil heaters with heat pump systems made a huge difference.
Converting night time lighting to LED had the biggest bang for bucks&effort.
Yeah, I've been involved with the rate case.
Given that we use electric heat in the winter--and electric heat is where the vast majority of our electrical use is--I don't think we'll be able to time shift that energy use. We could convert it to natural gas, but we have 2 kids that we are trying to do good by.