Published 11/14/2021: Revised 12/29/2021
The JSE VeryPowerfulWall
I wanted a way to store electricity when rates were low and use that energy during the on-peak period when rates were high.
I looked into getting a Tesla Powerwall. Unfortunately they were in super high demand. Also Tesla won't allow a regular home-owner buy and install it themself. It has to be a distributor and approved company do all the work. I got a quote. It was over $12,000 installed. Even after a federal rebate, the ROI for saving $25/month from my already low electric bill would be around 28 years. Ouch!!
Maybe some day I'll get one but not today.
In JSE fashion, by early January of 2021, using components available from eBay, I cobbled together my own version of a Tesla Power wall. Coming up with the most knock-off name possible, I call it the JohnSavesEnergy VeryPowerfulWall. At 1/10th the cost, it covers most of our on-peak energy usage using a few COTS (commercial off the shelf) plug-in inverters on smart switches and a 2.4 kWh battery pack made from some lithium packs used in electric scooters. The inverters run during the on-peak periods and the battery pack charges up during the off-peak periods.
Making some assumptions about how much on-peak rate ($0.32/kWh) electricity could be avoided, I estimated the VeryPowerfulWall would pay for itself in about 30 months. Details on ROI will be explained later.
I also installed three 315 watt solar panels in the backyard on a ground mount array. This is a zero-export system because RMP does not allow net metering while on Time of Use (TOU) plans. The solar energy provides energy first and the battery covers the shortfall. At least until the inverters max out. Any additional power required by the house is pulled directly from the gird.
The JohnSavesEnergy VeryPowerfulWall (up to 2700 watts AC output and 2.4 kWh of battery energy storage)
The VeryPowerfulWall has battery powered, grid tied inverters, each with zero-export capability. This means that not a single electron is back-fed onto the grid but is instead consumed inside my own home. To the power company, it just looks like my home is not drawing very much power at all while on-peak. The inverters (one for each leg) run on battery power and in this mode are limited to 900 watts each. Another inverter is fed from a ground mount solar array in the backyard. The solar array (made from three 315 watt solar panels) is 945 watts and can be adjusted manually in elevation seasonally.
Parts list and costs for the VeryPowerfulWall are listed below:
| Item | Description | Brand | Store | Cost | Count | Total |
|---|---|---|---|---|---|---|
| Inverter (for Battery) | 1200 Watt Inverter w/ Energy Meter | Soyo Source | eBay | $264 | 2 | $528 |
| Battery | 48 VDC 20 Ah Scooter Battery w/ charger | Generic | eBay | $215 | 1 | $215 |
| Battery | 36 VDC 20 Ah Scooter Battery w/ charger | Generic | eBay | $168 | 2 | $337 |
| Smart Switches | 120 VAC 15A Smart Switch | Gosund | Amazon | $7 | 4 | $28 |
| --------- | ||||||
| Total (Very-Powerful Wall) | $1108 |
Parts list and cost for the 945 watt solar array that I installed are below. They are not included in the ROI calculations for the VeryPowerfulWall because they provide energy during both on-peak and off-peak periods.
Even thought I am not allowed to net-meter on my present TOU plan, I installed this solar array (zero export) because frankly after living in a net-zero home for 10 years, it felt wrong not having anything collecting the energy that rains freely from the sky into my own backyard.
This solar array provides around 8% of our total energy needs. I subscribe to the BlueSky program through RMP so that in effect all our energy is in effect 100% solar powered.
| Item | Description | Brand | Store | Cost | Count | Total |
|---|---|---|---|---|---|---|
| Inverter (PV) | 1200 Watt Inverter w/ Energy Meter | Soyo Source | eBay | $264 | 1 | $264 |
| Solar Panel | 315 Watt Solar Panel | REC | KSL | $140 | 3 | $420 |
| Panel Racking | Metal C-channel and support structure | Home Depot | $250 | 1 | $250 | |
| Ground Mounts | Poles and Concrete pillars | Home Depot | $50 | 2 | $100 | |
| Miscellaneous Wire | 6 AWG and conduit | Home Depot | $120 | 1 | $120 | |
| --------- | ||||||
| Total (PV Array) | $1154 |
Each battery inverter is plugged into a smart plug programmed to switch on during the peak period. The solar PV inverter's smart switch is programmed to switch on whenever the sun is up. Each 120 volt outlet is wired to its own dedicated circuit breaker.
This makes the VeryPowerfulWall effectively just an appliance.
Each battery pack is made from two 36 VDC 20 Ah scooter battery packs and single 48 VDC 20 Ah scooter battery pack. These battery packs are wired in series for a total nominal voltage of 120 VDC. These packs are all made from 18650 cells with battery management systems (BMS) built in. Each battery pack is re-charged by its own dedicated 2 Amp battery charger.
The battery chargers are all on a power strip fed into a smart plug programmed to charge up the batteries while off-peak.
All together, the VeryPowerful Wall with PV can supply up to 2700 watts of AC power.
So far, with the VeryPowerfulWall doing its thing, 2021 numbers are looking very good.
| Month. | Off-Peak | On Peak | Total (kWh) | On/Off | Energy Cost | Avg Rate | Notes |
|---|---|---|---|---|---|---|---|
| 21-Jan | 1706 | 70 | 1776 | 4.10% | $78.43 | $0.044 | Added 2.4kWh energy storage device |
| 21-Feb | 1406 | 35 | 1441 | 2.49% | $56.50 | $0.039 | Rate channg 3.2¢ off-peak 32.5¢ on |
| 21-Mar | 1324 | 17 | 1341 | 1.28% | $48.03 | $0.036 | Johnny PC runs most of the time. |
| 21-Apr | 1185 | 36 | 1221 | 3.04% | $49.73 | $0.041 | Had to charge EV once while on Peak |
| 21-May | 1115 | 7 | 1122 | 0.63% | $38.07 | $0.034 | Driving more now |
| 21-Jun | 1593 | 9 | 1602 | 0.56% | $54.07 | $0.034 | |
| 21-Jul | 1763 | 8 | 1771 | 0.45% | $59.20 | $0.033 | |
| 21-Aug | 1326 | 26 | 1352 | 1.96% | $51.01 | $0.038 | Clothes Dryer used several times on peak |
| 21-Sep | 1525 | 13 | 1538 | 0.85% | $53.18 | $0.035 | |
| 21-Oct | 1447 | 28 | 1475 | 1.94% | $55.55 | $0.038 | Added more energy storage (4.8kWh) |
| 21-Nov | 1461 | 16 | 1477 | 1.10% | $52.10 | $0.035 | Added an additional battery inverter |
| 21-Dec | 1773 | 19 | 1792 | 1.07% | $63.09 | $0.035 | Driving EVs a lot more this month |
VeryPowerfulWall Cost Savings:
One year after installing the JohnSavesEnergy VeryPowerfulWall, look at the difference that having energy storage has made.
| Monthly Average | Energy (kWh) | % On Peak | Just Energy | Total Energy Bill | Avg Rate ($/kWh) | Note |
|---|---|---|---|---|---|---|
| 2020 | 1275 | 6.31% | $66.22 | $98.07 | $0.052 | No Energy Storage |
| 2021 | 1492 | 1.62% | $54.92 | $82.49 | $0.037 | With Energy Storage |
Even though our average monthly energy consumption went up, (mostly due to driving more, post COVID lockdown), our total electric bill went down. This also makes calculating the ROI trickier.
| Year | Total Energy | $0.037/kWh | $0.052/kWh | Savings |
|---|---|---|---|---|
| 2020 | 14,419 | $533.49 | $749.77 | n/a |
| 2021 | 17,624 | $652.09 | $916.45 | $264.36 |
After the 30% tax credit the VeryPowerfulWall new cost went from $1108 down to $776. My initial assumptions about the VeryPowerfulWall paying for itself in 30 months were not too far off.
Without the VeryPowerfulWall average energy rates would have remained at an effective 5.2 cents/kWh. With the VeryPowerfulWall the effective electric rate all year was only 3.7 cents/kWh.
Based on realized cost savings in 2021, the actual ROI of the VeryPowerfulWall is 35 months. Under 3 years is not bad at all.
Room Improvement:
Still, there were several days that the battery bank ran out before the on-peak period ended. In the winter time the sun sets around 5pm and more lights get turned on in the house sooner. With less solar energy available during the 3-8pm peak period, the battery has to provide more of its own energy. Somedays the battery bank even died a couple of hours before the on-peak period was over.
Remember how I had asked my wife and kids to avoid doing laundry and using the oven while on-peak? I'm not an evil dictator so this request was completely voluntary. As such, there were times when someone had a laundry emergency and needed to run the clothes dryer while on-peak.
Some days someone may have got a hankering for some pizza so they fired up the oven. Some days the dish-washer was full and needed to run so we could have clean dishes for dinner. Somedays they just forgot we were running on-peak.
There was at least a handful of times when an EV started charging up while on-peak. The 2012 and 2013 Nissan Leaf are not smart enough to manage scheduling two peak periods in a day. The morning winter peak from 8-10 am was the culprit.
After a year of limiting some activities to off-peak only and receiving feedback from my family, I have reconsidered a few of these energy consumption guidelines. For example, running the dish-washer when we are out of clean dishes is a luxury that I feel should not be infringed. It doesn't use that much energy. A 1200 watt heating element kicks on for about 20 minutes. Yeah that's kind of a big deal but after that it's pretty negligible.
Also our high efficiency washing machine doesn't really use that much energy either. The clothes drier does though.
Cooking something in the Insta-pot or on the stove top doesn't really use that much energy either, maybe a fraction of a kilo-watthour is all.
It would be nice if we could just do these things more regularly on-peak without negative consequence.
The large burner on the stove draws a lot of power and it would be nice if the VeryPowerfulWall could handle higher peak power draws too.
For these reasons in November 2021, I doubled the energy capacity of the battery in the VeryPowerfulWall from 2.4 kWh to 4.8 kWh.
I also added an additional inverter bringing total battery powered capacity to 2700 watts. Total battery + solar capacity is now 3600 watts.
The JohnSavesEnergy VeryPowerfulWall (up to 3600 watts AC output and 4.8 kWh of battery energy storage)
This peak power draw is still well below what the total pack is rated to deliver, but for now let's see how this new configuration pans out.
ROI of new VeryPowerfulWall
Adding an additional inverter and doubling the battery pack has driven up the price of the VeryPowerfulWall. Net cost is now $1346.
This brings the new ROI from 35 months up to 61 months.
Charging/discharging for 61 months x 21 days a month = 1281 cycles. I'm not sure what the capacity of the 18650 cells in the scooter batteries will be after that many cycles. My best guess is around 70% of their original capacity by that time. Still, 70% of 4.8kWh is 3.36 kWh, that's still larger than the original VeryPowerfulWall battery pack.
Happy Energy Storing Everyone!!