Today we are going to cover the 2 different types of battery systems that one has to choose from. Your application will determine the which one works best for you. We will highlight the differences and benefits of each. At the end we will make our recommendation AC Coupling is the most common method in the market currently so we will start there first.
An AC coupled solar + storage systems is the most common these days as it was Tesla who popularized it. There are multiple different brands available, but the Powerwall currently reigns. Why is an AC Coupled solution so popular? Because it can be added to any existing solar system. If you look at the graph above this section you will see a Hybrid (battery) inverter is used and coupled to both the AC output from an existing solar inverter and to the grid. This hybrid inverter is also DC coupled to the battery system. When installed correctly, this system can provide back up power, grid shaving, and load shifting even when the grid goes down.
If you follow the flow of electrons you will see how this system works. Solar modules produce DC electricity, next comes the Grid Tied inverter, converting the DC to AC, next the power flows through the critical load panel, into the hybrid battery inverter, and then the power gets rectified (turned back to DC) and then stored in the battery. The power is stored there until needed, and then converted again back into AC power to be used in the AC panels and then supply to the loads.
That is 3 conversions (DC to AC at inverter, back to DC again at hybrid inverter, then back to AC ) for every single electron. It is typical to have a 3% loss just in wire losses, and each conversion creates an additional 4% loss. So an AC coupled system, like the Tesla Powerwall, will provide about 15% losses in power for all power produced at the solar array.
The significant difference between the two battery options is that in an AC coupled system, 2 inverters are needed. The grid tied inverter, plus the hybrid (battery) inverter. This is a very effective means to create back up power and using solar energy if you already have a solar system installed. However there is a price you must pay for this kind of system. The additional inverter is an added cost, and lower efficiency than the DC coupled alternative.
Here is an example of a Tesla Powerwall AC Coupled to a SolarEdge inverter. The Powerwall houses a hybrid inverter inside the shell. This system will have approximately a 15% loss of energy from the solar array to the loads inside the home.
AC Coupled Micro-Inverter + Storage System
The above graph is for the Enphase IQ micro-inverted solar + storage solution. This is another AC coupled solution however it is a very intelligent and resilient solution. The graph is a simplified graph of the total picture, as it doesn’t show the multiple conversions of the DC power to AC and visa versa as stated earlier. While the total system energy efficiency losses mirrors that of other AC coupled systems like Tesla, this system provides the highest level of AC power resiliency due to have many smaller inverters throughout the solar and storage systems. With the best in class communications abilities and high resiliency, the Enphase IQ storage solution comes in as the highest cost solar + storage solution, and Rectify’s second favorite solar + storage solution.
**This system is not available as of April 2020, but will be very soon.
DC Coupled Solar + Storage Solution
Since solar power modules naturally produce DC power, and batteries naturally store DC power, a DC coupled solar + storage system naturally makes sense and is as you suspect, much more efficient. The DC from the solar array will directly charge the DC batteries, and do this can be done first before any conversion to AC power. So, the only losses seen are the line losses, or about a 3% loss. When energy is needed, only one conversion to AC power is needed, so DC coupled solar systems boost the highest energy efficiency with losses as low as 7%. So a DC coupled solar system provides all the same benefits as the AC coupled systems, but with a lower cost out the gate, and higher efficiency. Look below for some 2020 product data available as a side by side comparison.
Side by side comparision:
LG Chem DC Coupled vs AC coupled Powerwall vs Generac PWR Cell DC Coupled
*Notice: Powerwall is not not including the losses of the Grid Tie inverter 5-7% typical
For those who are on the market for new solar + storage system, here at Rectify, we recommend 2 options. An AC coupled Enphase IQ Engage system for this highest level of redundancy of AC power this will come at the highest cost, or a DC coupled solution due to highest efficiency, lowest cost of entry, lowest life-cycle costs, and maximize Future proofing potential.
If someone is seeking to add storage to their existing solar system and have at least 10 years of warranty left on their inverter warranty, then an AC coupled battery system like the Tesla Powerwall, is the way to go. Unless you are willing to complete a full swap out of inverter materials, it is actually the only option for you.
The battery system qualifies for the 26% federal tax credit as long as it is charged 50% of the time by solar. Applying the reduction in price as a result of the tax credit, and the installation price is comparable to that of many back up generators. We sell, install, and maintain those as well. If you are a California resident, SGIP rebates also apply to you. Utility rates, a lack of net metering, and/ or time of use rates can also help offset the additional costs in some markets, however…
One thing is Very Clear.. We are currently in a time of Disruption.
Our social life is disrupted. The Economy is disrupted. Emotions are disrupted. Are you prepared or worried about the next disruptor? How about the next storm that could wipe out power to your home, or neighborhood?
During these uncertain times, if you lose power, where are you going to go?.. Many of us have very little choices, many have no place to go. Everyone is socially distancing, and most places are closed.
Grocery stores are even closing at 8:30pm, so all your food you had been stand in line for, 6ft away from each other, and putting yourself at risk, just became that much more valuable. If another big storm comes through and whips out everyone’s power for a few days, then those empty shelves you saw are gonna happen all over again. Suddenly, the ability to power your fridge and freezer and other essential items, just got more important.
We are clearly in a time of Disruption. However, the Sun, cannot be disrupted.
Are you uncomfortable with the current level of disruption, chaos, and feelings of uncertainty? Do you see that solar + battery storage or a back up generator as possible path to alleviate those those feelings and negative thoughts?
If so, then we want to invite you pick up the phone and call us, or click on the button below to start the conversation to build a plan to help provide you with ability to access to that next level security, to mitigate the chaos, and uncertainty you are seeking.
Your current and potential future interruptions are at stake and can be prevented. Click below to start the conversation, or call us now, at 855-573-2843.
Rectify has chosen Generac as its preferred product for customers who knowingly want to add solar + storage into their home. This is due to the facts highlighted in the above sections for DC Coupling. The Generac system benefits include; offering highest round trip efficiency for DC coupling the solar system to the storage system, American made, solar pv string size can begin as little as 2 modules (unlike any other string inverter on the market), the battery system provides simple modular ability to add additional battery capacity, and the ability to add a Generac generator for extended outtages is in the roadmap. For those reasons plus reasons covered in the next section, we believe the Generac system provides the greatest ability to Future Proof your home compared to all other products currently on the market.
Rectify was Indiana’s first Pika Certified Installer (Generac acquired Pika in May 2019), and one of the first certified installers in California as well.
Rectify is featured on the Pika Energy (Generac) website with a story on how Rectify helped empower a customer through an uncertain time when a utility tried to tell the customer that they couldn’t have solar installed.
Click here to read that story.