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Is the ESS or UES battery worth buying and how do they compare as energy storage solutions for todays homeowner?

Published on 12 Mar, 2018

Home energy storage has recently received a ton of press coverage as the backbone of a system designed to save home owners. Tesla released the first Powerwall back in 2015 and then released the Powerwall 2.0 a year later. Tesla’s Power wall 2 has been plagued with production delays. Having deposits, many customers have been waiting over a year for installation. This delay has paved the way for the LG RESU, Panasonic Pica and SunFusion Echo to gain market share

When it comes to the question of whether it is worth buying a battery storage system whether it is Tesla Powerwall 2, LG, Panasonic, Sonnen or SunFusion there are really three sub questions that need to be answered:

· Is the power it will store enough to make it economically viable;

· Is it the best value solar battery energy storage solution on the market in 2018; and

· Should I hold off buy given the rapid state of advances in this space.

Before I answer these questions and offer my opinion as to whether or not I would buy a battery, here’s the current state of play as of March 2018. I am mindful that things are changing so quickly in this space that new features may be added or removed, and prices may change by the time you read this.

What is the battery and how does it work?

A rechargeable home battery system that stores energy from solar or from the grid and makes it available on demand to meet the electrical needs of your house.

It is now an AC coupled energy storage solution which means it can take in AC electricity from either your standard grid connect solar inverter or the grid itself, convert it to DC electricity that can be stored in the battery and then, when this excess energy is needed, convert it back to AC electricity and use this energy to power your home or business.

The big difference is whether the battery contains its own battery inverter and battery management system. With the previous model, the DC coupled batteries you needed to also have a hybrid battery inverter. SunFusion’s Echo series AC coupled product line contains and onboard Outback or Schneider inverter included in the pricing.

The overall solution for many systems was two metal boxes, one (which looks like a very elegant giant iphone) contains the inverter and the Lithium-Ion battery and the Backup Gateway. The Backup Gateway provides energy management, metering and monitoring functions for the battery. It controls connection to the grid, safely disconnecting your home and starting backup operation during an outage. The Backup Gateway also includes communication functions. and receives updates for the system via a WiFi connection.

The Backup gateway is the part of the system that interfaces with your homes existing electrical supply and so for this reason the backup gateway is usually installed near your main electrical switchboard. Some manufacturers have created a single cabinet to contain the system as one simple solution.

What is the basic mode in which a battery operates?

They operate differently depending on what mode it is in.

Its most usual mode is self-powering your home. What this means is that whenever the solar system on the house is producing more energy than the electrical appliances in the house are using then the battery will grab that excess energy and store it in the battery until the battery is full. Whenever the electrical demands of the house are in excess of what is being produced at that instant by the solar panels then the battery will release the energy in the battery to power those electrical loads until such time as the battery is fully discharged.

This will mean that even during the day there can be times where the battery is charging and other times it is discharging. At night you will discharge if you house is using electricity. Once the battery has reached its programmed depth of discharge then it will stop supplementing your electrical needs and you seamlessly roll back to full grid power.

Will the battery provide back-up power when the grid fails?

Many readers may not be aware but when you have a normal grid connect solar system then when the utility grid fails it is a legal requirement that the grid connect inverter shut down the solar system to prevent feeding power back into the grid whilst a linesman is working on it.

When the Powerwall is installed it has an electronic disconnect that can disconnect your house loads, solar and battery from the grid and your house can then use either your solar or your stored energy in your battery to run the electrical needs of your house.

See how much you can save with a solar energy system

Do the math, your energy costs are calculated by the amount you use multiplied by the cost of energy. With several utilities moving to a TOU, time of use calculator, the time you use can be as important as the amount you use. Storage has become a hot topic simply because you can store your solar energy or grid energy when the price of energy is at its lowest and discharge into the home during PEAK priced times.

How much power can a battery supply in a black out and for how long?

The rate at which the battery will discharge power to meet loads is limited to a constant output of battery’s size. So, while operating in backup modes you cannot use electrical appliances with a combined draw of more than the amount of kWs the battery is designed to max discharge. Tesla’s Power Wall 2 is just over 20 amps on a 240V, SunFusion’s Echo 18 is up to 70 amps on a 240V

The length of time for which it can run these loads depends on how much energy was stored in the battery when the grid failed and how much power you use.

If the battery was fully charged when the power failed, and your house uses approximately 2kWh per hour then it could run your house for almost 7 hours with the Power Wall 2 and 9 hours with the Echo 18 or up to 18 hours on a 360 Amp hour discharge.

To provide for greater longevity of power supply for critical appliances in a black out some consumers who buy back up systems and only wire the system to backup specific loads, such as their refrigerator such that these important appliances will last longer if the grid is down for a long time. If a backup system was only running a refrigerator and some lights it could possibly last for days.

How much energy can a battery store?

Currently home storage sizing ranges from small .7 kWhs to 36 kWhs or larger. Smaller systems considered back up or ESS (energy storage systems) to UES (uninterrupted energy systems provide a range of solutions. The smaller back-up systems provide power to 3-7 circuits. UES systems can manage the home’s entire energy needs. Given the average California home uses around 29kWh per day, a 14 kWh system can be quite a reasonable amount of storage to deal with a lot of the night time electricity use of a typical house. Should you prefer to be able to power the entire home an 18 or 27 kWh storage solution makes more sense.

What is the warranty on a storage system?

Tesla and LG like most companies offer a 10-year warranty with the understanding that these systems will be used daily to store and then discharge power regularly and a degradation factor. SunFusion Echo’s come with a 25-year full replacement warranty.

While the systems were originally designed to be used with solar panels, most can be used independently if you wanted a backup storage unit that feeds off the grid.

So now we have worked out that storage is a valuable next step, would I buy one?

The problem that all solar batteries and energy storage solutions have is that there is net metering in over 30 states in the US.

So for those that live in states with net metering there was little point storing your own power in a physical device when net metering gave you the same economic result without an investment in a physical product and without having the worry about the degradation in performance over time of a solar battery solution. With the continuing rise of time of use electricity rates this has change the situation. In California, new peak rates in Edison territory topping $.49 peak 4-10pm and SDG&E at $.63 peak from 4-9pm, storage is a great way to short the market.

All public utility commissions are looking at ways to smooth out electricity use and reduce use at the peak times. It is the few moments of extreme peak use per year that can necessitate billions of dollars being spent on upgrading the grid infrastructure.

By making power at peak times of use more expensive, and power use in times of low grid use cheaper, we hope to move use away from the peak times and avoid capital expenditure on grid infrastructure. This is a change from the traditional tiered rate electricity plan which took no notice of what time of day you used power just how much total power you used over a month.

California has mandated the adoption of time of use rates for residential customers of investor owned utilities in that state by 2019Bottom of Form

Will time of use power shifting put batteries into the GOTTA have column?

One of the great things about the batteries and charge controlers is that it uses a series of electronic relays and switches that can be controlled by software.

This firmware can updated over the internet to both fix any bugs and also provide for new functions. One such new function that should be upgraded this year in firmware is a power shifting function.

This will allow you to ensure that the battery is full charged by the end of off peak times when electricity is cheap so that the energy stored can be released during peak timing.

This will substantially change the economics of adopting a battery system. If we take the biggest of the investor owned utilities in California as an example, PG&E, their peak time of use power rate on their E-TOU B plan is 20 cents higher than their off peak rate. However, the difference in peak and off peak rates in winter is smaller

Does the SGIP (self generation incentive program) and time of use electricity rates in California make buying a battery a no brainer?

So storage is a great solution and relatively affordable and time of use power shifting will add to the return it gives you to an extent, but economically it is still a line ball decision.

The thing about solar batteries and other energy storage is that the biggest economic benefit of its adoption is to the grid itself rather than the owner of the battery. Putting even a small amount of storage on a grid can avoid the need to upgrade that grid. In recognition of value of this the California PUC has authorized funding for a Self-Generation Incentive Program that pays at rate beginning at $400 per kWh and reducing through a series of steps to $300 per kWh.

There is a reserved SGIP budget for each investor owned utility controlled by the PUC.

Given the 18kWh energy storage capability of the Sunfusion this is a rebate of $7,200 on step 3 of the SGIP program for a solution and up to over $, in Federal tax rebates.

This would mean the storage solution costing less $10.000 including installation with a 25 year bumper to bumper warranty. This warranty reminds me of SunPower’s panel warranty. At this price I think people in California are crazy not to buy. Top of Form

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Author: Andrew Sendy

As chairman of Solar Investments Inc and chairman of the largest solar panel installation company in South Australia, Andy is passionate about solar power. With his unique working background he writes on the residential solar industry in America from a unique perspective.

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