Frustration with utilities combined with declining costs of solar and energy storage has raised the possibility that customers will start divorcing from the grid. Cutting the cord and going “off-grid” has technically been possible for decades, but as costs fall, the idea is starting to gain some real traction. SolarCity, a solar power provider, plans to lease solar photovoltaic (PV) plus storage systems in Hawaii, where high power prices, abundant sunshine and frustration with the local utility has made grid divorce alluring.

While the thought of ending your relationship with a utility may be satisfying, it would undermine our capacity to reduce emissions and set back efforts to modernize the grid.

Battery storage clearly has an emerging and important role in our energy future, but using it to fully sever ties with utilities leaves many of the benefits of both storage and clean generation unrealized. Sure you may feel that you’re trapped in a one-sided relationship, that your concerns and needs are not being addressed, or that the utility does not reflect your values. But rather than cutting the cord, the solution is making structural changes to the grid that will move us toward a clean energy economy that benefits consumers.

Acadia Center examined the impact of adding battery storage (equivalent to Tesla’s Powerwall, a new battery system) and solar PV to homes in Connecticut, Hawaii, and Arizona to see what it would take to become independent from the grid. In all three states, going off-grid with a “right-sized” net-zero PV array (where a home’s demand for power approximately equals the energy it produces over a year) would be expensive. In New England, a very large number of batteries– 62 in Connecticut – would be needed to allow for year-round uninterrupted power off the grid. This is due to significantly lower winter PV production in the region and the resulting need for more batteries to store enough power to get a home through a long winter.

In sunnier and warmer climates with higher solar production in the winter, like Hawaii and Arizona, you would only need 40 and 42 batteries, respectively, to take a net zero home off-grid. But, average annual electric demand is higher in those states, so battery needs and cost would still be high when coupled with smaller solar PV arrays.

The least expensive path to an off-grid system is to oversize the solar PV array in order to reduce the number of batteries needed. (See chart and figure below.) Yet, while less costly, oversized solar arrays that are not connected to the grid essentially “waste” clean energy. In other words, once your demand is satisfied and the batteries are full, any excess energy that would otherwise be fed into the grid just dissipates. The Connecticut home with a 12.5 kW array may have reduced system costs, but it is now producing approximately 8,900 kWh per year more than it needs, and those kilowatt-hours are going unused. With a connection to the grid to use that otherwise wasted energy, the emissions reductions would be more than double what is achieved by only powering one home.

For a truly clean, efficient and affordable modern grid, customers should stay connected, and utilities should support that by avoiding discriminatory charges for solar customers and providing full and fair compensation for the unique value that rooftop solar generation provides to the grid. Cutting the cord will become less theoretical as solar plus storage systems continue to drop in price, but reducing overall emissions at the lowest cost and optimizing the function of the grid cannot be accomplished by going it alone. It may take a lot of counseling, but staying in a relationship with your utility is worth it in the long run.

System Size and Costs to be Grid Independent – Comparison of Net Zero & Optimally Sized (i.e. Lowest Cost) Systems in Connecticut, Hawaii, and Arizona

Annual electric consumption6,656 kWh (555 kWh/month)10,520 kWh (750 kWh/month)7,957 kWh (663 kWh/month)
Net zero PV system size5.50 kW6.75 kW4.75 kW
Net zero annual PV production6,850 kWh10,726 kWh8,216 kWh
Net zero PV system cost$19,250$23,625$16,625
# of 10 kWh Batteries needed to go off grid624042
Battery costs$217,000$140,000$147,000
Total net zero off-grid cost$236,250$163,625$163,625
Optimal system size12.5 kW10.0 kW6.5 kW
Batteries needed for optimal system size754
Optimal system cost$68,250$52,500$36,750
Optimal system  PV array potential annual production15,567 kWh15,890 kWh11,243 kWh
Lost PV production with off-grid array8,920 kWh5,400 kWh3,300 kWh

 Battery Needs by PV System Size and Total System Costs to be Grid Independent in ConnecticutBattery Needs By PV System Size



The Fine Print:  Our assessment used a blend of Department of Energy’s hourly electric consumption models to represent a new, high-efficiency single family home in each location.  The National Renewable Energy Laboratory’s PVWatts tool was used to simulate hourly electric generation in each of the homes for the various array sizes.  At net zero, the PV array size was set so that generation was approximately equivalent to consumption on an annual basis. The battery storage was modeled so that there was sufficient storage and production to meet hourly demand for every hour of the year. No safety margin was included, nor were considerations made for degradation of storage capacity or whether instantaneous demands (such as an air conditioning unit’s start-up requirements) could be met. Costs of $3.50 per watt for PV and $3,500 for each 10 KWh of battery storage were used for determining optimum configurations. Additional storage system integration costs were not included.