Archive for September, 2010
Whilst most businesses and employees here in WA will have been enjoying last Monday off for the Queens Birthday public holiday, for many of our commercial buildings it was business as usual. The building management system (BMS) that manages the air conditioning, turns on the lights or powers up the lifts, is often blissfully unaware that its a public holiday and the building is actually empty. Significant energy (and dollars) are wasted as a result.
I took a moment to look over some data from one or two of the Greensense View® dashboards of our clients, and sure enough it didn’t take long to find an example of a BMS hard at work when it should be taking the day off. The image below shows the energy profile for one of our clients for the current week. Remember that Monday 27 was a public holiday.
The facility in question is a fairly typical office building. In this chart, we are separating out electricity used by the air conditioning system (the green data series) from general power used by office lighting, pcs and so on. You can clearly see that on Monday the air con fired up a little after 7am, just as it normally would, and ran through until the end of the business day, even though the office was empty. When you consider there are around 10 public holidays in WA each year, the wasted energy for this building alone would total more than $1000 a year.
So whilst a correctly configured and maintained BMS can be vital in helping to run a building efficiently, an incorrectly configured system can be worse than none at all. Naturally, when a building is being run for us by a computer, we often stop questioning what exactly is going on and simply trust that the computer is doing the right thing. This example highlights that this is not always the case and there are often good opportunities available to reduce energy waste simply by ensuring the computers we use to run our buildings are doing the right thing.
Many people install solar PV systems at their home or work, but do not have an easy way to monitor its performance. Most solar inverters only have a very small display and these are often very difficult to use and identifying short term or long term trends is extremely difficult.
Our Greensense View® dashboard can be used to monitor green power solar generation by displaying power being generated in real-time, as well as long term trends, on simple, easy-to-understand charts. This is of immense value for engaging with people on many different levels, but better still is that behind the scenes we collect additional technical information that can be used to manage the performance of a solar installation and diagnose issues.
One of our customers has a 30kW solar PV system. They are using Greensense View® to monitor on-site energy generation and consumption of electricity from the grid. Their dashboard was clearly showing that the solar panels were not performing as expected, and were not producing electricity on some fine, sunny days when you’d normally expect energy production to be at its highest.
The chart below shows two consecutive sunny days. The first day shows a normal profile. The energy produced is a nice curve peaking in the middle of the day. On the next day, just before 9am the system stops producing energy, and stays off until almost 3pm, missing the best part of the day.
In fact we can quantify this loss exactly. On the first day, 160.5 kWh of energy were produced, and on the second day only 37.5 kWh were produced. On the second day additional electricity had to be purchased from the grid to make up the shortfall from the on-site generation. The additional cost for that one day of lost generation was approximately $42, based on Synergy R3 Tariff peak-time. If you extrapolate this out over a year, this behaviour could have a direct cost of over $15,000, dramatically increasing the payback time for the solar panels.
So you can see that it is important to measure and monitor these systems to ensure the return on investment is achieved as expected and that corporate emissions reductions expected from the installation of this equipment are actually being met.
We narrowed down the problem for them by analysing the data we had been collecting. The issue in this case was a voltage cut-out. To be connected to the grid, the grid owner, in this case Western Power, needs to approve the inverter and there are obviously criteria that need to be met in this process. One of these criteria is cut-out at a low or high voltage threshold. The inverters need to automatically shut down if the voltage goes above 254 V and can switch themselves back when it returns below this level.
The chart below shows generation on one of the three phases overlaid with the voltage for that phase. It can be clearly seen that when the voltage rises above 254 V the inverter stops supplying electricity.
High voltages can also be damaging for other equipment on site as well, so the potential loss from leaving this unresolved is significantly greater.
Without Greensense View® monitoring the system in real-time, these problems can go undetected for long periods of time. Identifying the problem is half the solution, so armed with the right information, the client can now take remedial action.
