Power Smart Pricing from Ameren

My electric utility company now has a real-time pricing program and I’ve enrolled. Instead of a paying a flat rate for electricity, my rate will vary by the hour depending upon demand at the time. I'll minimize my electricity use during peak demand times. Tasks like washing and drying clothes can be done late at night when rates are low.

My current electric bill is hard to understand, but from a recent one this is what I’ve been able to determine:

I am charged 0.072 per kwh of electricity of electricity I use.

With taxes, customer charge, distribution charge, and other miscellaneous charges and credits, I am actually paying 0.1016 per kwh.

Based on program information from the utility’s website, I’ll be paying as little as 0.015 per kwh when demand is low, or as much as 0.15 per kwh when demand is high. In addition to the rate information available to me over the Internet, I’ll be alerted when rates are expected to exceed 0.13 per kwh.

A new electric meter was installed on December 3rd, allowing my electricity use to be monitored by time-of-day.

To get the most from this program I’ll run as many daytime loads as possible off of my solar photovoltaic (PV) system. To the extent that my small system can keep up, I’ll run my refrigerator and chest freezer off of it. At night, when rates are low, I’ll run them off of grid-supplied power. Fortunately, the PV system operates most efficiently during the day because energy goes straight to the load, instead of being stored in and retrieved from batteries. As I add solar panels to my existing array, I’ll add electrical items to the daytime load when utility rates are highest.

Perhaps the easiest way to switch between the grid and solar is by way of a simple timer and relay as illustrated below:

The circuit above will work, but for safety and NEC code compliance a transfer switch should be used. The inverter can be switched on and off via a timer as shown below:

The transfer switch can be wired so that it selects the inverter when AC is present, and switches to grid-supplied power when necessary. The timer can be programmed to switch the inverter on during the day, and off at night.

With nightly electricity rates below 0.035 per kwh, I’ll have to reevaluate my Plug-In-Electric-Vehicle (PHEV) recharging strategy. It no longer seems practical to purchase extra solar panels for this. I’ll buy extra panels for the daytime loads instead.

I might also benefit from this plan by using the grid to charge batteries. I'll charge batteries at night when rates are low, and use the stored energy to power household loads during the day when rates are high. I suspect that the losses associated with storing and retrieving energy will be more than offset by the low nighttime electric rates.

As I gain experience, I suspect that I’ll discover other ways to get the most from this plan. I welcome suggestions and comments from others.

For more information about the plan I’ve signed up for, click here: http://www.powersmartpricing.org/

John