Concentration of CO2 in the Atmosphere

Battery System Helping Off-Grid Installations

Dual pole mounted solar arrays and a beautiful Central Vermont backdrop. The mini split heat pumps in this home keep this array hard at work.

George Harvey

Without doubt, there are still some among us who think of off-grid living, with solar electricity, in terms of very small and very primitive systems. Off-grid has been, and still can be, built of the simplest equipment imaginable, and some people prefer that way of living.

Surprisingly, however, an off-grid system may not only support a sophisticated lifestyle, but might even do it so well that we are unaware of any inconvenience, regardless of the demands we put on it. It is a situation that really is improving rapidly, because of great, new technology.

Chris Sparadeo, the off-grid division manager of Catamount Solar, recently gave us a run-down of how new, improved battery communication technology is opening new opportunities for off-grid living.

To explain this, let’s take a look at a concept associated with smart grids. Demand response is a tool that a utility and its customers can partner on to keep costs down for everyone, whether they participate in demand response or not.

The times when demand is highest and supply is lowest are predictably those when electricity is sold for the highest price on the market. As a separate issue, and not so obviously, a utility’s transmission costs are determined by the peak demand over a period of time. So, the costs associated with peak demand are reflected in all prices for electricity, regardless of when they occur. It doesn’t take a lot of thought to see that reducing the peak demand can reduce the cost of electricity.

One way to reduce peak demand is to defer certain kinds of electricity use until a time when demand is down. In order to do this seamlessly, there must be some communication between the utility and the participating households. The utility must be able to tell the household controller when demand is high, so the controller can decide what heavy loads to defer until later.

For example, charging an electric vehicle (EV), operating a clothes dryer, heating up a tank of water, and running a heat pump to keep the house warm are all operations that can be deferred to some extent. The amount and the circumstances of deferral are things that can be programmed by the consumer. If the system is properly set up, putting off electric use will possibly not be noticed at all. But it can reduce the electricity bill.

Now comes the truly interesting part for people who live off-grid. Demand response is no longer something that is set up to happen by the utility and the customer, acting together. The high-tech solution of today makes this possible, even to those who live off-grid, through something called smart load management.

A smart reader might ask what the point is. After all, there is no utility bill to save money on. That is true. But the system has another advantage. It gives the entire solar photovoltaic (PV) system new abilities to control the use of heavier loads, and in doing so makes the entire system more valuable.

The system’s Fortress Power 37 kWh battery bank and Sol-Ark inverter allows this southern Vermont home to make the most of the solar power it harnesses. (Courtesy photos: Catamount Solar)

The very simple solution to running an off-grid system is to charge the battery whenever possible and supply electricity to various loads as they call for it. But in a smart off-grid system, supplying electricity to the water heater is best done when the sun is shining, providing that the battery is charged. That takes some sophistication, however.

Chris Sparadeo gave us a good understanding of how this can work, using the example of actual equipment in operating systems for smart load management. These two systems have solar PV capacities of 9,600 watts. They use Sol-Ark 15K inverters and have paralleled Fortress Power eVault Max 18.5 kilowatt-hour battery systems.

These systems operate in closed loop. That means that the Sol-Ark inverter and the Fortress Power battery communicate directly with one another and allow the inverter to make important decisions about charging and discharging the battery. Because the inverter is operating with a very precise understanding of the battery’s state of charge, it can turn larger loads off and on via its dedicated smart loads circuit breaker.

When the inverter finds that the battery is fully charged while the solar PVs are still producing electricity, it does not throw the excess away. Instead, it will put that electricity into work that is useful. It can send electricity to the water heater, which can store energy as heat. It can send it to the EV, to charge that battery. It could use the excess electricity to run a heat pump or a de-humidifier, or any of a number of other high-demand pieces of equipment.

There are two important effects of this we might note. One is that the entire off-grid electric system is operating much more efficiently and precisely than it would without closed-loop communication. The second is that the system can operate heavier loads than had previously been possible due to smart load management technology. Advancements in off-grid system technology are allowing people to embrace the new age of electrification and help gain major energy independence in their homes.

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