Maui Customer Self Supply (CSS)

Do I Need Batteries?

While you don’t actually “need” batteries, to participate in MECO’s “Customer Self Supply” program, it is a good idea in most cases. However, it can make some sense to forgo using batteries, if the cost outweighs the potential savings in the following situations:

• Home Office
• Commercial Property
• Occupants Are Retired
• The majority of your power usage is during the day, due to air conditioning, pool pumps and/or washer/dryers, etc.

In these cases, the inverters only provide enough energy to power the base loads during the day. However, by adding even a small battery in these situations, you can maximize your savings.

However, most people are not at home during the day. In those cases, and the vast majority of the time, it makes sense to have a larger battery, so that you can use all of the energy that was stored during the day, for use in the evenings, night and early mornings. Most of our customers have a payback period of 5-7 years, after taking into account the tax incentives. The tax incentives, combined with high sun hours and high electricity rates, make this program extremely financially beneficial.

Which Battery?

Currently, the two most widely used batteries for Self-Consumtion and backup purposes are the LG Chem RESU10H and the Tesla Powerwall 2 AC. We are certified to install both. In general, the Tesla Powerwall is a better value and a better choice for the majority of our customers. In a few cases, when the required system size is very small and the customer’s budget is limited, we may recommend the RESU10H. However, the installation price difference is fairly small and the Powerwall’s storage capacity is 30% larger. Plus, the features and level of integration that the Tesla Backup Gateway provides, are unparalleled.

Which Circuits Should I Backup?

You may also ask “Do I have to backup?”. No, you don’t, but the cost is minimal and is around $1,500 in most cases. This is a small cost for such a huge benefit.

We hear this a lot: “I want to backup my whole house”. If you have the capital and this is your dream, we can do this for you. However, in most cases, a single LG Chem RESU10 or Tesla Powerwall 2.0 can output 5kw, with short bursts of 7kw. One of those batteries can power these items at night:

• Refrigerator
• Freezer or 2nd Refrigerator
• Garage Door
• Some Lighting
• A Few Outlets
• A Small Microwave

However, because the Powerwall 2 is AC coupled, your system will have additional power available during the day. If you have a 6kw PV system, you will not only have the Powerwall’s built-in 5kw inverter, you will have the PV’s 6kw inverter as well, for a total of 11kw of available power, at mid-day. Besides, by giving more available power during the day, this architecture will also provide maximum self-consumption and savings.

In most cases, to back up an entire house, you will need at least 2 Tesla Powerwalls. Adding additional batteries will also maximize your energy savings. The added cost of 1-2 extra batteries and inverters is worth it for some people to have even more piece of mind, in the event of an extended power outage. A natural disaster, such as a hurricane, tsunami or earthquake could take the power out for many weeks, if not months. The 2006 Hawaii earthquake took the power down on the South side of Maui for three days and hurricane Iniki took out the power on much of Kauai for three months.