This seemingly simple question leads to a discussion that concludes, “Because it is a surprisingly complex problem with some devilish details”
Electricity is generally in the highest demand during summer weekdays when industrial needs combine with air conditioning loads. Therefore electrical generating companies are increasingly offering Electrical Time-of-Use (TOU) tariffs where the cost of purchasing electricity is higher during summer weekdays than summer nights. The difference in day and night pricing can be significant. This summer, California’s Pacific Gas and Electric (PG&E) raised its rates such that daytime electricity is nearly four times (4x) the cost of nighttime electricity.
One of the largest expenses in operating a water system is for electricity to pump water, especially during the summer. If electricity is 1/4 the cost at nighttime, why would anyone pump during the day?
Why You May Need to Pump During the Day
There are two reasons to pump during the day:
- You do not have sufficient storage capacity to pump only at night and then use that stored water during the day, or
- You do not have a control system capable of implementing electrical time-of-use.
If your water system does not employ a gravity tank, then you need pumps to run more or less continuously, so you really have no storage. If you have a gravity tank but don’t have sufficient storage capacity it means that you may need to pump during the daytime.
Whether you need to pump depends upon the amount of storage compared to usual water use during the periods of higher priced electricity.
Take a look at the figure of the typical TOU Layer Cake where there are two levels above the Off Peak rate level. You certainly want to avoid the Summer Peak Rate even if that means pumping during the Partial Peak times, immediately before and after the Peak rate period. This is not as simple as it sounds, however.
If you do have ample storage capacity, you simply pump after 9:30 PM and before 8:30 AM. That sounds simple and has led people to just put a time clock on their pump to prevent pumping during times. Unfortunately, the devil is in the details.
Recently, we talked about TOU with a seasoned water professional. He said, “We put a timer on the pump, but the tank ran dry!” He concluded that TOU does not work.
This brings us to reason number two above, as to why you would pump during the day when electricity is expensive, you do not have a control system capable of implementing electrical time-of-use.
The Things that Make TOU Complicated
As our seasoned water professional discovered, hooking up a time switch and simply locking out pumping from 8:30 AM until 9:30 PM can easily result in an out-of-water event because:
1. Your use on a particular day is unusually high;
2. You have an exceptional need such as fire support;
3. You have a leak;
4. The day is a holiday and use is very high;
5. At 8:30 AM, the tank is not very full since it was just beginning a pump cycle.
Hacking a Better Solution
Unfortunately, human nature being what it is, the usual response to the problems above is to add some band-aids, maybe a float switch and a few electrical relays.
For example, we could put another float in the tank and have it trip when the tank got too low, causing the electrical timer to be ignored. Problem solved? No, not so fast. Assuming that you could get this second float in the tank and hooked up and the system documented—which never, ever happens— then it will get the pump going and maybe prevent an out-of-water event, however it will likely cause you to pump during the period of most expensive electricity, which you really want to avoid: this system has no priority. This hack does not address the issue with the tank not being full at 8:30 AM or the holiday problem or even the fire support problem.
We have seen water systems with even more band-aids. A second timer, for example, that overrides the float at 7:00 AM and causes the pump to fill the tank. Unfortunately, you then run the risk of a tank overflow!
At XiO, our business is control systems for water operations. We come across a surprising number of hacked up water systems that are made up of good components but are not a system with integrity. These undocumented fixes often lead to systems with poor reliability. Out-of-water or tank overflow events are all too common. For this reason, TOU is usually viewed as a nice to have but not practical for small water systems.
What can we do?
A Fresh Look at the TOU Problem with a Better Control System
XiO’s entire focus is controls for small water. We looked at the TOU problem about four years ago and quickly realized that it is a surprisingly complex problem. However, it is an enticing problem to solve because at the end of the rainbow is the potential to save 25% on electricity costs.
In fact, one of XiO’s earliest small water customers has saved 25% per year on electricity with a combination of TOU and operating the best pump at the right time. Every year, they have reported a 25% savings.
Conclusions that are Difficult to Deny
1. Mechanical timers or even electrical timers are not up to the task for these reasons:
- Timers have to be set and then maintained. Mechanical timers stop when the power stops. Electrical timers with battery backup need battery replacement
- Timers don’t handle tariff changes. Utilities often use a different date for daylight savings adjustments which a timer cannot deal with
- Timers generally don’t handle weekends correctly. TOU tariffs are usually in effect on weekday non-holidays
- Timers simply don’t handle weekday holidays when water use and fire danger tends to be high
2. Deciding what to do if it becomes clear that the entire Peak/Partial-Peak cannot be avoided is tricky
- Not pumping from 8:30 AM until Noon can guarantee that you will have to pump during the most costly Peak period
A Complex XiO Solution is the Ultimate in Simplicity for the XiO Customer
XiO employs its Cloud SCADA® control system for small water systems. There are two parts to the control system, the part in the field that connects to the tanks and pumps, and the part in the Cloud, constantly monitoring the field units.
The XiO Cloud servers know:
- The time of day
- The day of the week
- The day of the year
- The holiday schedule
- The utility rate tariffs for that particular site
- The current storage level of all the tanks
- The historic water use
- The anticipated water use
- Which pump will be called upon to pump
- The pumping rate of this pump
With all this data, the XiO Cloud SCADA control system:
- Accurately predicts when pumping should begin in the morning such that the tanks are full at 8:30 AM.
- Constantly monitors tank levels to insure that a minimum reserve is always maintained
- Will pump during the morning or afternoon Partial Peak periods if required
- Will do everything to avoid pumping during the most expensive Peak tariff period
In addition, the XiO Cloud SCADA control system provides an authorized water operator access to a secure website where they can use their smartphone, tablet or computer to override TOU if—for example— they feel that they should fill their tanks because of some anticipated need.
Why Wouldn’t You Want to Save 25% on Your Water System Electrical Bill?
The answer, of course, is that everyone would like to save 25% on their pumping costs. And now, XiO has a solution to this surprisingly complex problem that is included at no additional cost with the remarkable XiO Cloud SCADA control system.