For informational purposes, we’ll break this section down into two sub-sections.

The first type we will discuss is the grid tied system which uses the available solar power, then switches to the grid for support. This is a typical type of solar system where the utility does not allow intertie’s for “sell back”.

The second type is for use as a “sell back” system, but with frequent power outages or brownouts, allows the client to have an almost seamless switchover to battery power when the grid is down.

  1. Grid tied with battery system support (non sell-back)
    On islands or in states or countries where the local utility does not allow for a “sell back” arrangement, these systems are common and very useful for businesses or homes that need close to continuous power. We install the solar system so that it charges the battery bank. We also install the utility grid to the inverter in the system. Programming the system correctly ensures that the home uses the power the solar system makes first, then switches over to the local utility automatically until the solar system again charges the battery to pre-programmed parameters. This allows for maximizing your solar power, greater longevity of the batteries due to decreased discharge cycles, and almost seamless electricity within the system. I say almost because there can be a tenth of a second of so automatic transfer between the two sources of electricity (solar and grid).

When we are designing these systems we talk with the customer about how much battery capacity they might need as well as what percentage of their power they might like to make from solar.

  1. Grid tied with batteries (sell-back)
    Many people like the idea of “selling back” power but also want the independence that batteries provide. Generators are expensive, noisy and require regular maintenance. A battery based, grid tied solar electric system provides all the options and benefits these customers require. The downside for many people is that batteries are expensive and require maintenance.

In a battery based, grid tied system with a utility intertie (sell back) agreement with the local power company, your batteries will be kept at a preprogrammed level (float voltage)and any residual power being made by your soar panels not being used by the home in the moment will be sent back to the utility grid. A bi-directional meter measures that outgoing power and the utility puts that power in a power “bank account” for you. Each month the utility subtracts what you put back onto the grid from the total household usage. You get to use your power “credit” toward your bill. If you made more than what you used the power stays in your power “bank account” until it is needed. The current utility agreement allows the utility to keep the power for themselves if you have not used it one year from the month you made it. This is why proper design is important. We only want you to make the power you will use, not oversize the system and allow the utility to keep your excess power.

Grid tie system with batteries in Bahamas

Grid TieGrid Tie with BatteriesOff Grid
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Penobscot Solar Design
615 Back Ridge Road • Penobscot, Maine USA 04476
(207) 326-0779 • info@penobscotsolar.com

NABCEP Certified Solar Installer