My family and I built a new energy efficient home in Cincinnati, Ohio, which was completed in 2015. Prior to building I was very influenced by Passive Home strategies and Martin Holladay’s 2014 article in Green Building Advisor entitled “A Pretty Good House”. Suffice it to say I wanted to make the home as energy efficient as reasonably possible. Given southern Ohio’s climate, I focused on airtightness over insulation. I intentionally avoided Natural Gas so that the home would be set up to generate most or all of its own energy in the future. Once the house was done, I couldn’t help but start to think about the next step toward reducing our carbon footprint… the PV / Home Battery System.
Why the battery? Why not net-Zero? Simply put, solar alone will not be able to displace the use of coal / natural gas for electricity generation. Because electrical demand peaks in the late afternoon / early evening but solar production peaks at noon or 1pm, the time of day during which solar electricity is generated does not match the time of peak demand. A utility must be able to meet peak demand each day. If a home does not reduce its peak electrical demand then a utility will never be able to close a power plant (and 68% of our power is from coal here in Ohio). Also there is the issue of having too much solar flowing into the grid during sunny days in mild weather, which is not a problem in Ohio, but is already a problem in Hawaii and California (known as the “Duck Curve” problem). Finally, I just want to say that I make no claim that what we are doing makes financial sense – for now. But plenty of people spend more money than this on a foreign car. We spent it on a PV / Battery System. I wanted a home and PV / Battery System that does its part to reduce its carbon emissions and do it in a way that will be sustainable and beneficial to the grid. Ironically, despite a home battery’s benefit to the grid, because in Ohio we have unlimited net metering, the incentive is actually to let our meter run backward and NOT store the electricity in a battery.
Why now? Why not put up the PV panels now then wait on the battery? Initially this was my plan, but a few things lead me to take the plunge sooner than later. First I learned that as of today, the Federal Tax Incentive for residential solar will start phasing out as of 2019 and expire completely as of 2022. Next I learned that in order to take the full 30% credit on the cost of the battery, you cannot charge the battery from the grid for 5 years. Obviously it would be of benefit to the grid (and possibly of financial benefit too, once hourly pricing comes to Ohio) to do so, but the IRS has imposed a 5 year waiting period. Also the battery was 5% off for Earth Day – sometimes it just takes that last little push! Basically I wanted to get the battery in now to make sure I could take the full 30% Federal Tax Incentive and get the 5 years over with. I am hoping that by 2021 utilities will be interested in using behind the meter storage for ancillary services such as frequency regulation and peaking. Finally, I want a system that allows our home to avoid any electricity use at all from the grid during peak demand times.
Why the Aquion Battery? And why 24 of them? First I liked that the Aquion was actually available (sorry Powerwall). I liked its 100% depth of discharge. I liked that it does not require a cooling system, will not catch on fire, and contain no toxic chemicals. The batteries are certainly more expensive upfront, but when I compared the price per kWh over its lifespan (taking into account its reported cycle life) it looked pretty much on par with any other option. Also I didn’t care how heavy it was (it’s just sitting in the basement). I got the individual stacks so that I could move them with a dolly and get them into the house. The Aquion’s main downside appears to be that it has a relatively high level of internal resistance, meaning that the more amps you draw from the battery the less kWh it has to give. For example, if discharged at 2 amps per battery stack you get the full 2.6kWh. But if discharged at 10amps you only get 1.2kWh. I basically solved this by getting 24 of them. After all, it’s going to be pretty rare that our home is pulling over 48amps. But even if it happens, no big deal. The inverters can only handle 40 amps each, so we’re topped out at 80 amps anyway. Also having 24 of them means that the average depth of discharge (DOD) for any individual stack will be less, thereby extending their life. According to Aquion the expected cycle life is 3000 at 100% DOD, 6000 at 50% DOD and 10,000 at 30% DOD. A terrific discussion (including graphs) of Aquion’s S10 stacks can be found at: https://www.altestore.com/blog/2016/03/the-rise-of-aquion-batteries-clean-safe-energy-storage/
Why not off-grid? Two reasons – first because of the sun angle and some shading we will not be able to produce all the electricity we need during winter. Second, as mentioned above, a home battery that is grid connected can provide benefits to the grid such as frequency regulation or peaking. Working with the utility is something I look forward to once the 5 year waiting period is over. Perhaps in the future there will be behind-the-meter storage co-ops where homeowners band together to sell these ancillary services to utilities. I hope so anyway.
In summary, though very expensive, I am proud to have installed a system that will work toward reducing the collective carbon footprint of both my family and of region’s utilities as well. I dearly hope that the collective transformation our nation’s grid to renewable sources is coming soon, and I want our home to be a sustainable part of that transformation. I want to thank Dovetail Solar and Wind for working with me so closely, for making this system a reality!
Moothart Residence Basic Stats:
2700 sq ft new build 4 bedroom single family home in Cincinnati Ohio. SIP Construction, very airtight (ACH 0.7). Walls R32, Roof R40, Subslab EPS (not XPS!) foam R16. Windows Marvin Integrity (Fiberglass), Double Pane. Passive Solar Orientation. Main floor poured concrete floor for high Thermal Mass. ERV. Geothermal HVAC (3 ton). All LED Lighting. No Natural Gas. Large South facing white Standing Seam Metal roof. LEED Gold.
PV / Battery System Basic Stats:
24 Aquion Energy S30 2.6kWh 48V Battery Stacks
24 Canadian Solar 320 Polycrystalline PV Panels (7.68kWh System)
Tigo DC-DC Maximizer System
2 Outback Radian 48V 8kW Grid-Interactive Inverters
2 Outback Flexware 80 amp 150VDC Charge Controllers
Design and Installation by Dovetail Solar and Wind
Cost of Batteries: $29,993 (including tax / shipping)
Cost of remainder: $48,835 (including labor).
Minus Solarize City of Cincinnati Incentive of $2,000
Minus 30% Federal Incentive Tax Credit of $23,048
Net Total System Cost: $53,780
Update April 2017:
- We took the Federal Tax Credit - no problems there.
- It has taken a lot of work and back and forth to get the Outback system to do the peak shaving, but we finally have it working consistently and correctly.
- Due to shading + low sun angle we made only 10-15% of our total electricity need during the winter.
- Since late March the sun is high enough that there is no shading on our panels and we are producing 100% of our total electricity need at this time.
- We have not used any electricity at all from the grid for the last several days!