## What Size Battery Would You Need to Power Your House?

RegGuheert
Posts: 6332
Joined: Mon Mar 19, 2012 4:12 am
Delivery Date: 16 Mar 2012
Leaf Number: 5926
Location: Northern VA

### Re: What Size Battery Would You Need to Power Your House?

I finally managed to extract 5-minute production data from Enlighten for my solar array and convert it into one-hour data for the same hours that I retrieved from the power company. With this data, it is easy to calculate what my production, consumption and net consumption would be with various amounts of solar in place. I can also then calculate the impact of batteries on those results.

For this post, I will show the impact of simply adding photovoltaics with no batteries.

Assumptions:
- Net metering is NOT available (although with smaller arrays, most energy is self-consumed)
- Cost for photovoltaics is US\$2.00/kWp(DC)
- Photovoltaics last 25 years
- Cost per kWh will be for all photovoltaics added to the system (similar to what I did with the batteries)

Code: Select all

`-------------------------------------------------------------------------------------------|  Total  | Storage  | Storage |   Energy  |  Energy  |   Energy  | Net Energy | Cost per ||  Solar  | Capacity |  Power  |  Produced | Consumed | "Rescued" |  Consumed  |    kWh   || kWp(DC) |    kWh   |    kW   |     kWh   |    kWh   |     kWh   |     kWh    |  US\$/kWh ||---------|----------|---------|-----------|----------|-----------|------------|----------||     0   |       0  |     0   |       0   |  18,072  |     112    |  18,072   |   0.000  ||     1   |       0  |     0   |      17   |  16,654  |    1418    |  16,654   |   0.056  ||     2   |       0  |     0   |     132   |  15,353  |    2718    |  15,212   |   0.059  ||     3   |       0  |     0   |     524   |  14,319  |    3753    |  14,319   |   0.064  ||     4   |       0  |     0   |    1127   |  13,497  |    4575    |  12,360   |   0.070  ||     5   |       0  |     0   |    1858   |  12,803  |    5269    |  10,935   |   0.076  ||     6   |       0  |     0   |    2674   |  12,193  |    5878    |    9510   |   0.082  ||     7   |       0  |     0   |    3576   |  11,670  |    6402    |    8085   |   0.087  ||     8   |       0  |     0   |    4561   |  11,230  |    6842    |    6659   |   0.094  ||     9   |       0  |     0   |    5614   |  10,857  |    7215    |    5234   |   0.100  ||    10   |       0  |     0   |    6723   |  10,541  |    7531    |    3808   |   0.106  ||    11   |       0  |     0   |    7882   |  10,275  |    7797    |    2383   |   0.113  ||    12   |       0  |     0   |    9076   |  10,043  |    8029    |     957   |   0.120  ||    13   |       0  |     0   |  10,297   |    9838  |    8234    |    -468   |   0.126  ||    14   |       0  |     0   |  11,554   |    9670  |    8403    |   -1894   |   0.133  ||    15   |       0  |     0   |  12,827   |    9517  |    8555    |   -3319   |   0.140  ||    16   |       0  |     0   |  14,114   |    9379  |    8693    |   -4744   |   0.147  ||    17   |       0  |     0   |  15,417   |    9257  |    8815    |   -6170   |   0.154  ||    18   |       0  |     0   |  16,731   |    9145  |    8927    |   -7595   |   0.161  ||    19   |       0  |     0   |  18,053   |    9042  |    9030    |   -9021   |   0.168  ||    20   |       0  |     0   |  19,381   |    8945  |    9127    | -10,446   |   0.175  |-------------------------------------------------------------------------------------------`
There are a couple of interesting conclusions to be made from this result:
- Even without net metering, the first few kW of photovoltaics still make sense because nearly all of the production is directly self-consumed.
- OTOH, without net metering, the marginal costs of adding photovoltaics get very high very fast. The reason is that the production has little overlap with the consumption after a certain point. For instance, when I add that 13th kWp(DC) to my system to go from net consumer to net producer, I only reduce my actual consumption by 205 kWh/year! That means that spending \$2000 dollars on PV without net metering would cost me US\$0.39/kWh! If I had instead spent that \$2000 to purchase two Enphase AC Batteries, I would save 708 kWh/year, or 3.5X as much! And even though the life of the AC Batteries is likely shorter, the per-unit cost of the batteries would be lower at US\$0.28/kWh. (And I'm not convinced that the AC Batteries will not last as long, but I have no data on their calendar life.)

In other words, at higher levels of production, net metering reduces the costs of photovoltaics to the point that they are more attractive than modern batteries, even though at some points batteries become both cheaper and better for the power grid (at least here).
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

GetOffYourGas
Posts: 1943
Joined: Tue Dec 20, 2011 6:56 pm
Delivery Date: 09 Mar 2012
Location: Syracuse, NY

### Re: What Size Battery Would You Need to Power Your House?

I'm loving the details of your math, Reg, but I'm starting to think I need a glossary to keep up with your terms.

Take "kWp(DC)". I thought this means rated DC power in kW of the panels. But then you said

RegGuheert wrote:- Cost for photovoltaics is US\$2.00/kWp(DC)

Photovoltaics are more like US\$2.00/Watt. So what do you mean by kWp(DC)? Or is this a typo?

Thanks!

P.S. I really wish I had this data for myself so that I can run some simulations of my own. I'd love to come up with a Matlab function or something to simulate adding more power and/or storage. Maybe even add in the dimension of TOU metering?
~Brian

EV Fleet:
2011 Torqeedo Travel 1003 electric outboard on a 22' sailboat
2012 Leaf SV (traded for Bolt)
2015 C-Max Energi (302A package)
2017 Bolt Premier

RegGuheert
Posts: 6332
Joined: Mon Mar 19, 2012 4:12 am
Delivery Date: 16 Mar 2012
Leaf Number: 5926
Location: Northern VA

### Re: What Size Battery Would You Need to Power Your House?

GetOffYourGas wrote:I'm loving the details of your math, Reg, but I'm starting to think I need a glossary to keep up with your terms.

Take "kWp(DC)". I thought this means rated DC power in kW of the panels. But then you said
RegGuheert wrote:- Cost for photovoltaics is US\$2.00/kWp(DC)

Photovoltaics are more like US\$2.00/Watt. So what do you mean by kWp(DC)? Or is this a typo?
Oops! Perhaps it was wishful thinking!
GetOffYourGas wrote:Thanks!
You're welcome! Thanks for checking my work! All the critical equations are in my spreadsheet now (on the 'Calculations' tab in Row 9). Now I'm trying to figure out how to present those numbers in a meaningful way.
GetOffYourGas wrote:P.S. I really wish I had this data for myself so that I can run some simulations of my own. I'd love to come up with a Matlab function or something to simulate adding more power and/or storage.
My spreadsheet is set up to take many more datasets from wherever I can get them. I need year-long, hourly data for home consumption, EV consumption and PV production.

I would like to be able to do nested parametric sweeps of PV and battery to produce a family of curves, but I'm not sure how to manage that in Google Sheets. If I could do that, I could produce tables like the ones in the posts above and perhaps even graphs. I can certainly duplicate stuff, but that will simply make a slow spreadsheet slower. Perhaps if I pull it out to Excel I can manage. (I'm currently consuming nearly 60,000 cells for the calculation of ONE condition including PV, EVs and batteries.)
GetOffYourGas wrote:Maybe even add in the dimension of TOU metering?
I'm willing to give simple TOU a shot at some point since that is certainly one potential application for grid-tied storage as the costs come down. But I have no data to work with. If anyone can come up with a dataset for a net-metering situation (one which is comprehensible) I might be able to put something together.

In case anyone else is still not clear: the current work is for no net metering and no TOU. I wonder if that case even exists anywhere. Does Hawaii have TOU? In any case, long term I feel it is important to work towards PV and storage being able to handle real year-round applications, even in colder climates.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280