So what is the bottom line? What does adding energy storage cost?
Adding energy storage capability requires the addition of a battery(ies) and charge controller, an auxiliary essential loads sub-panel, and a more sophisticated hybrid inverter, Depending upon the level of instantaneous power and long term storage capacity desired the additional cost is generally between 10 to $15,000. During the day a properly sized solar array will be able to both fully power your home and charge the battery bank. As the sun sets the hybrid inverter will draw power for the house from the storage bank instead of the grid. If the battery is drawn down during the evening to the programmed maximum discharge level (generally 50-80%) the inverter will revert to purchasing power from the grid until the next day's sunlight is strong enough to start the cycle all over again.
If there is a power outage the hybrid inverter will instantly disconnect from the grid and begin to draw power from the solar array and the battery to feed the essential loads sub-panel. The most important loads of your home or business will continue to be powered silently without interruption or the need for an emergency generator.
Previously under the Cost and Incentives tab we had priced a typical 24 module 7.2 kW roof mounted solar system at an upfront gross cost of $16,560. The gross cost of an equivalent hybrid installation with a 9.8 kWh LG battery would rise to approximately $28,800, and the net cost after incentives would be $17,660. This may be difficult to justify if you look only at the return on investment figures, but in every case you have also gained the security of knowing that you have instantly available backup power for your essential loads. Investing $12,000 into a hybrid solar/storage system will grant you benefits 365 days a year, whereas buying a premium quality whole house generator for about the same cost will only benefit you during those few days of a power outage.
For clients connected to one of the New Hampshire public utilities (Eversource, Liberty, Unitil) that currently net meter at a dollar for dollar basis there currently is no financial advantage in a self consumption cycle, the grid is serving as your battery without any additional cost to you. This however is likely to change very soon when the public utilities will be allowed to use discounted net metering. However if you have a solar system installed before the legislative rulings take effect, you will be able to lock into the present dollar for dollar net metering until 2040 (as proposed). This change will have a huge effect on the cost of solar energy, book an installation now!
The member owned New Hampshire Electrical Cooperative however already net meters at approximately a 25% crediting basis. When you consume a kWh in your home.. regardless of whether it came from your solar array, storage, or the Co-op.. you are consuming it on a 100 percent basis. But if you send that same kWh back into the NHEC grid, you are only credited 75 percent for it. Self consumption by way of a storage battery definitely makes financial sense for you because you gain the advantage of self consuming at 100% of it's value rather than sending it back into the grid at a discounted credit rate.
In the case of the average home example the amount of power self consumed would rise from 22% without energy storage to 62% with the addition of a 9.8 kW battery. As you may recall the 7.2 kilowatt array in the example was expected to generate 9,600 kWh annually.
Without storage only 22% would be consumed directly and the rest would be sent back into the grid during the day at the discounted credit rate and bought back in the evening hours at the full utility rate. The annual cost of the 25% net metering discount would be $262.08 (78% x 9,600 kWh x 25% net metering discount x 14 cent NHEC residential rate).
By adding a battery the amount of power coming from the solar array and being self consumed jumps to 62% and the net metering cost drops to $127.68, an annual savings of $134.40. The system owner has now gained both the security of power after a storm and a very real financial savings.
It should be noted that the Co-op has a very reasonable utility rate in comparison to the public utilites (currently 14 cents vs ~20). The savings would be far greater for the Eversource, Liberty, or Unitil customer.
The combination of a solar array, home energy storage, and a utility grid connection is referred to as a hybrid grid tied system. There are two primary reasons to consider adding energy storage to your solar array; self consumption and as a backup power supply.
The desire for backup power when the grid goes down is fairly self explanatory and many assume that a solar PV system will provide this security. This is not true, a simple solar system must sense grid power to function and if the grid goes down the solar array will also instantly shut down. This is the law and done to protect the linesmen working to repair your utility company's lines.
This faulty assumption was brought painfully to the forefront by Hurricane Sandy. Before that storm most solar arrays in the affected area did not have storage incorporated into their design and during the weeks of power outages that followed that monster storm, those arrays were shut down and virtually useless. Adding energy storage and a hybrid inverter to a solar array will allow it to continue to produce power for your home or business even when the grid is down !
The New Hampshire Electric Cooperative is a unique application when it comes to properly integrating solar pv power back into their grid. The NHEC is unlike Eversource, Liberty, Unitil, and the other public utilities because it is member owned and thus not subject to the regulations established by the NH Public Utilities Commission. There are both downfalls and some unique opportunities that need to be addressed when designing a solar system that will work to well with the Co-op's programs. The key lies in home energy storage (solar batteries).
Even though having back up power is a huge benefit for the owner of a hybrid solar system, it is not the only reason to consider adding energy storage capacity. The primary financial reasoning for energy storage lies in the ability to be able to retain the excess power generated by a solar array during the day to be used in your home during the evening hours. This is termed "Self Consumption" or "behind the meter" and has become the operative format in areas with reduced or even eliminated net meter crediting. Most of the new hybrid inverters can be programmed to first fully charge your battery during the day before sending any excess solar power back into the grid for credits. Those same inverters can also be programmed to not draw power from the grid in the evening until your battery has reached a preset depth of discharge (generally 50-80%). By carefully balancing the amount of solar production and the storage capability of a hybrid system, a balance can be acheived where most of the excess power generated during the day and stored in your battery will be consumed in your home during the evening hours.
Higher consumption commercial and industrial users can use storage very effectively through a third technique called "Peak Shaving". Some of the utilities set a business's rates according to the peak momentary usage incurred by the business within a given month. Often this peak usage is only needed for a short duration. By using a battery to reduce ("shave") the high peak, the entire months utility rate can be reduced. The savings generated through peak shaving can be considerable!
The New Hampshire Electric Co-op credits their "Above the Cap" net metering at a discounted rate of roughly 75 cents on the dollar. This certainly isn't as favorable for the consumer as the dollar for dollar ratio currently legislated upon the public utilities, but it is probably more fair overall. Utility companies must carry the cost of maintaining their grids and business infrastructure and should rightfully be re-compensated. There are two ways to accomodate the 25% discount on net metering credits; oversize the solar array enough to account for the discounted net meter crediting, or store the excess array power generated during the day in a battery and self consume it in during the evening. Oversizing the array is in most cases the least costly manner to reach a 100 % annual offset, but adding energy storage has multiple other potential advantages both for the consumer and the grid and is a very cost effective solution for the long run.
OK, so how about combining the two stored energy operating concepts; self consumption and TOU optimization? Unfortunately this isn"t presently allowed by the NHEC, you must choose to use either the net metering or time-of use program. However by electing the net metering option and installing a solar array with a hybrid inverter programmed to maximise self consumption, a consumer could maximize their savings. A properly sized solar array should be able to power the home during the day and charge the battery with any excess production. During the evening hours the battery would be drawn down first before purchasing any power from the grid, and then recharge for the early morning needs during the lower off peak night time hours.
A second method for profitably utilizing home energy storage is termed "Time Of Use optimization" and functions well when a utility company offers differing time of use rates. The NHEC currently does offer three different elective TOU programs. Their Peak Planner program features two rates that are determined by the time of consumption and would seem the most suitable for use with local energy storage. The TOU peak rate centers around the late afternoon and early evening hours (times vary seasonally) and is considerably higher than the regular non-program rates. There are far more hours however that are classified as Off Peak and the rate during those hours is considerably lower than the non-program rate. At the time that this was written the TOU rate was $0.28/kWh and the rate during off peak was $0.10/kWh. Bear in mind that these rates would need to be compared against the non-program regular residential rate of 14.7 cents/kWh. By installing a properly programmed home storage battery the consumer would be able to purchase their power during the off peak time of use hours, store them in the battery, and consume them during the more expensive peak hours. Can it be justified financially? That depends both upon the consumer's total consumption and usage patterns, if you can't avoid consuming a lot of power during the daytime peak hours, then the addition of energy storage, even sans solar array, may make sense.