A 6.6kW pole mount tracker solar array installed by Maine Solar Solutions.  Courtesy Photo.

George Harvey

Maine Solar Solutions (MSS) is just outside the town of Freeport, in the southern part of Maine and not far north of Portland. Sam Zuckerman, the owner of MSS, provided us with some insight on how to design and install grid-tied photovoltaic (PV) systems with battery backup.

Like many other solar installers, MSS can design and install a grid-tied solar system or an off-grid system. MSS can also install heat pumps, such as those made by Mitsubishi or Fujitsu. Most installers seem not to be interested in designing and installing grid-tied systems that have battery backup, but Zuckerman says while there are not large numbers of these installations, he has a fair amount of experience with them.

The approach MSS uses for system design begins with understanding, and this is particularly important for grid-tied systems with battery backup. MSS makes a point of understanding the particular needs of the customer. Based on what they find, the MSS team can provide the customer with a complete understanding of available options.

Many customers for grid-tied solar systems are surprised that household systems will not provide power during a grid outage unless special attention has been put on providing electric power in that situation. There is such a thing as an inverter that provides a little power without a battery system, but even if such an inverter is chosen, it usually cannot supply power that is constant enough to do much more than charge cell phones or laptop computers. To provide for most living situations, a battery backup system is needed.

The costs of grid-tied battery backup systems are not trivial, so it is really important that they be designed carefully. For a customer who is grid tied, the least expensive alternative to batteries may be some sort of generator. A generator is a stop-gap solution and has serious drawbacks, including making sure there is enough fuel, but if the grid is sufficiently reliable, and whatever outages that do come are short, a generator might do.

For situations where the outages might last, and where energy security is important, batteries should be considered. Their design needs to be wisely undertaken, however, to avoid unnecessary expense. Both systems that are too large and those that are too small can prove costly in their own ways. A well designed system is sized carefully, taking into account the owner’s own critical load, the minimum requirement to provide for that owner’s energy security.

Two neighbors, living side by side can have very different critical loads. For example, one house might be heated by wood and have its water gravity-fed from a spring. If the grid fails to supply power, the critical load may only be what is needed to run the refrigerator and a few lights. Its battery system can be quite small and function well.

Another house may have a large number of people living in it, a refrigerator and a freezer, a deep well drawing a lot of electricity to supply water, and a heating system that needs electric power to run. For such a house, both the battery system and the PVs that charge it have to be sufficient to meet those needs.

Design does not stop with identifying the parameters. The components need to be chosen so they are compatible with each other. Zuckerman used the example of LG lithium-ion batteries and SolarEdge inverters to explain this. They are designed in a way that makes putting them together in a system particularly easy.

Given the rapid decline in battery costs and the rise of smart grids, grid-tied systems with battery backup are becoming more common in parts of the world. We could easily see that happening here in the Northeast.

The Maine Solar Solutions web site is mainesolarsolutions.com.