Do I Need Batteries for My Solar Power System?

Battery storage can be a particularly confusing topic for homeowners who are interested in solar power. Knowing more about the variety of systems, and what goals they achieve, are two key factors in deciding what type of solar storage system is right for you. Solar power systems have four different storage options: 1) Self-Consumption, 2) Grid-Tie (no batteries), 3) Battery Backup, and 4) Off-Grid. The most common goals homeowners have are 1) Saving Money, 2) Having Emergency Electricity, and 3) Getting Power to a Remote Location.

1) I want to save money

The two storage systems relevant for homeowners whose primary goal is saving money are self-consumption, and grid-tie. Self-consumption systems are used in areas with time-of-use rates (different prices during different times of the day), and lower sell-back rates (different prices for buying versus selling electricity). These systems avoid low sell-back rates by using batteries that prevent back-feeding electricity into the grid.  The batteries also optimize consumption timing by consuming grid electricity when utility rates are low, and consuming battery electricity when utility rates are high. Virginia, and Maryland do not have time-of-use rates or separate sell-back rates, making self-consumption systems not particularly useful in these states.

Grid-tie systems do not use batteries. Instead, extra electricity that is produced feeds back into the grid, rolling the utility meter backwards. This takes advantage of state laws in DC, Maryland, and Virginia that require utility companies to pay customers the same amount for selling electricity as they charge for consuming it, thereby acting as a “free battery.” Grid-tie systems do not have separate systems for storing, and delivering power, so they do not provide power when the grid is down (which usually occurs less than one day each year – see below).

2) I want to have emergency electricity

According to data from the 2015 Eaton US Blackout Report, and the U.S. Census Bureau, the average home in DC, MD, or VA is without power for less than half a day each year [1] [2]. Most solar interactive batteries (like the Tesla Powerwall 2 or Enphase AC Home Battery) have a warranty for ten years, and may be expected to last as many as fifteen. The Powerwall 2 comes with a price tag of $7,000, costing about $933 for each day the backup battery is used (assuming one battery is all that is needed). Understandably, most people opt for candles. Nevertheless, people in need of power for medical purposes (like respirators or dialysis machines) cannot afford to go without electricity for any amount of time. In these instances, there are two primary options: backup storage systems, or generators.

Backup storage systems use batteries differently from self-consumption systems. Since self-consumption systems are constantly cycling, they may not have energy stored when the power goes down. On the other hand, batteries in backup storage systems do not cycle under normal conditions. They stay constantly charged waiting for the grid to go down. These systems are usually small, and are designed to power the essential equipment in the house for one day.

Generators are standalone sources for generating electricity, making them particularly useful for energy-use in remote locations, and emergency situations. Their primary advantages are 1) their low cost – with portable generators starting around $350, and 2) reliability – as they work without sunshine, or without having a stable connection to the grid. More sophisticated systems will power an entire home, and will automatically turn on when the grid goes down. Less expensive generators will need to be manually switched on, and are designed to only power essential equipment in the home.

3) I need power in a remote location

Those needing power in remote locations without a connection to the grid have two main options: generators (as discussed above), or an off-grid solar power system. Off-grid solar power systems are very straightforward; energy produced by the solar panels goes straight to a bank of batteries. These are usually AGM, or old-school lead acid batteries (due to cost advantages) that are combined to cycle together. These batteries are then hooked up to the home’s electrical infrastructure to power all necessary consumption.

What’s right for me?

 As you can see, several types of systems exist for various purposes. Understanding these differences, and the goals they achieve allows homeowners to find the best fit for them. Almost all homeowners in DC, Maryland, and Virginia go with grid-tie systems, or grid-tie systems with generators. If you are having trouble deciding which system is right for you, feel free to reach out to us at Nova Solar.

Barklie Estes,
Nova Solar

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