Bring in the Solar Batteries

By Russell Lowes, Rincon Group Energy Subcommittee Chair, April 2, 2017

Have you ever wanted to get off the electricity grid? You might have a number of reasons to do so. What about saving money? The economic breakeven may be here sooner than you think. There’s an interesting and eye-opening thing you can do with energy usage and cost numbers (step 4, below) to make your own cost estimates.

Let’s say that you have decided there are four things you want to do at your house. One, you want to reduce your energy use. Two, you want to buy solar. Three, you want to buy a battery system to back up your solar when the sun is not shining. Four, you want to go off the electricity grid.

This is how the process of battery-backed solar might work in the near future. However, you can get started with step 1 & 2 right now, and later with steps 3 & 4.

1) Reducing Energy Consumption

  • Let’s say you use 575 kilowatt hours (kWhe) of energy per month, a typical usage rate in southern Arizona;
  • 200 kWhe is a typical reduction per month by using energy efficiency techniques like insulating shades for your windows, weatherization, insulation for your attic, or getting a an evaporative cooler “piggyback system” added to your air conditioning system.

This translates into:

  • Your usage has been 575 kWhe X 11¢/kWhe, a typical energy cost in So. AZ, which equals $63.25 plus basic service charge, and other charges per month, going down to:
  • Your new usage, with a 200 kWhe reduction, would be 375 X 11¢/kWhe, or $41.25/month + other base utility charges.
  • If you were to leave it at that and not do the next steps, you savings would be $22.00/month, $264/year, $5280/20 years.

2) Adding Solar to Your House

Now that you have reduced your energy consumption, when you add solar, you won’t have to buy as many panels. Instead of paying for maybe 5.6 kilowatts of capacity (the average used by the National Renewable Energy Lab, at, you now would buy around 3.9 kWe.

Your new solar panel array would deliver energy at about 7.0¢ per kilowatt-hour to your home, plus financing, so maybe 8.5¢.

Solar Prices Continuing to Fall

Solar Prices Continuing to Fall “NREL Report Shows U.S. Solar Photovoltaic Costs Continuing to Fall in 2016” September 28, 2016 *
Solar Prices Continuing to Fall “NREL Report Shows U.S. Solar Photovoltaic Costs Continuing to Fall in 2016” September 28, 2016 *

3) Adding Battery Backup to Your Rooftop Solar

Batteries are the big unknown in this process. Costs are falling quickly, and there is a goal by the industry to bring them down to 14¢/kWhe, when combined with solar. This is a bit more costly, when compared to the roughly 11¢ average cost of electricity by the utilities of southern Arizona. However, you only have to get a portion of your energy from batteries, and with lower solar costs here in the Southwest, the deal gets sweeter. For example, you can get 35% of your energy needs met with energy efficiency, from step 1 above, and 45% from solar, from step 2, and 20% from battery energy, from step 3, well that leads us to that point I opened with. . .

4) Going Off-Grid . . . “There’s an interesting and eye-opening thing you can do with energy usage and cost numbers.”

First, you have to boost the number of solar panels a bit to power the batteries, so your cost of solar would go up from 8.5¢ to roughly 10¢/solar kWhe, fully financed. Let’s project that future battery costs are 20¢/kWhe, fully financed.

Take a look at the following table and if you copy these values and formulas onto a spreadsheet (or ask me for a copy at, you can change the percentages in column D, and as long as the total equals 100% at the bottom of that column, all the figures will automatically and accurately update! Likewise, if you change any of the projected costs/kWhe in column E, the spreadsheet will auto-self-adjust. But, you math wizards out there already knew that!

This has been about the process of going off the grid, but there are reasons to stay on the grid. The main one is so you can share your electrons with others so they don’t have to use coal, gas or nuclear energy from the grid. However, if the utilities resist the solar revolution, we may not have much choice. If the utilities keep fighting solar rooftop and keep putting onerous charges on our bills, the best choice for you and your family, and for you and your business, might be to go off-grid.


*A side note about the above NREL chart: One interesting thing about the residential-size solar (rooftop solar) versus centralized utility scale is that with rooftop there is much less non-power-generation cost. With centralized solar there are new transmission requirements, more distribution costs, land acquisition costs, switch yard and substation and a myriad of other costs that are not required, as much, as with rooftop solar. Right now, rooftop solar is cheaper when you consider these non-generation costs. I believe that rooftop solar will widen the gap of cost benefit over large utility-scale centralized solar in coming years.