Energy and PV System Monitoring

12/08/09

Local Power is very interested in energy and PV system monitoring solutions.  We believe that having good realtime information, rather than just quarterly bills, is crucial to changing our behaviour in using energy as well as ensuring our PV systems are working well.

The Queensland State Government is currently offering a wireless energy monitor (Centameter OWL) as part of their ClimateSmart Home service which includes an energy audit, up to 15 CFL light bulbs, a low flow shower head etc. and costs $50.  This monitor can tell you how much energy your whole house is using.  Click here to find out more.  In addition if you are in the Brisbane City Council area, the council will rebate this back to you.  Click here to find out more about this rebate.  We recommend this excellent initiative to everyone!

Below is some information we have collected about monitoring solutions which can monitor the energy of your whole home and/or PV system.  These are different from portable power meters (see also below) that can measure the electricity used on an individual appliance or power point, although these can be very useful also to do your own energy audit.

You can click on the name of the solution and get more information and in some cases purchase from other websites.  We welcome feedback on the information below.

Monitoring Solutions - Pros and Cons

There are some "pros and cons" between the two main types of energy monitoring currently available, i.e.

• Wireless monitoring using clip-on current transformers.  Wireless monitoring is generally much easier and cheaper to install (1 clip on sensor, or 3 if you have 3 phase power, installed by an electrician in your meterbox), and doesn't need cabling installed around your home.  However wireless monitor displays and their corresponding transmitters usually require several batteries to power them which require regular replacement.  These monitors are also less accurate than a regular electricity meter and will tend to overestimate the electricity use which you pay for.  This is because they are really only monitoring current and assuming the voltage is 240V and always in phase with the current, which they are not for reactive loads like motors. 
  
  Despite these shortcomings we think wireless meters like the Centameter are very useful due to their low cost, ease of installation and usefulness to people having realtime electricity use information which can help people make better decisions to conserve energy!
   
• Wired in (or cabled) monitoring using real electricity meters.  Wired in monitoring systems aren't always ideal either.  Unlike clip-on sensors which have more than enough capacity to measure the total usage for the typical home, more than one monitoring meter is required to measure consumption for a typical home, particularly for energy hungry appliances (e.g. one for lights and power points, one for electric oven and one for air conditioner).  Also they require network cabling between the meters and the monitoring box and internet connection.  These increase the installation cost and complexity, but the resulting system tends to be very accurate and not need battery changes, as the display is any computer or mobile phone with a web browser.
   

Monitoring of PV systems with the Feed-in Tariff

For PV system owners the Solar Bonus Scheme (FiT Feed-in Tariff) often confuses the clip on wireless sensors during daylight hours because the FiT in Queensland is of the import-export (nett) style of metering.  In this model of FiT energy flows are both directions to and from your meter.  The clip on wireless sensors can only detect the amount of power which is flowing but not it's direction, so if you are importing 300W (using more than you are generating at the time) or exporting 300W (generating more than you are using at the time) the display will read 300W and at no time in daylight hours will you easily know your energy usage. 

The ClimateSmart Home information booklet in explaining this says "Depending on how your PV system is wired to your electricity box, your monitor may not always give you an accurate reading during daylight hours.  However, during the evening your monitor should give you a better indication of the energy your appliances are consuming - helping you to control your energy consumption"

It is possible for an electrician to counteract this problem according to an experienced PV engineer by "All they have to do is clamp the sensor around _both_ the fat consumer main active from the grid _and_ the skinny active wire from the inverter. That way any current going from inverter to grid passes through the sensor twice in opposite directions and the magnetic fields cancel out."  Changing wiring in a meterbox should never be attempted by anyone except licensed electricians!


Living Level monitoring pilot
Local Power is currently trialing the Living Level wired in monitoring solution on several buildings with PV (2kW and 3kW). 

In the same week that the giants of the internet and computer industries announced the google power meter initiative and IBM is building the first national smart grid, Local Power is pleased to provide live PV and energy use monitoring graphs below in partnership with a local Queensland company.

Click on the graphs below to see live generation data
(green line is PV generation, black line is electricity consumption. 
NB On the sample day shown below the Brisbane temperature peaked at 34.9 degrees Celsius
at 1pm and it was a perfectly clear day as the smooth green generation graph shows.)

sample building with 2kW system (upgraded from 1.5kW system)

sample building with 3kW system (upgraded from 2kW system)

sample building with 3kW system

Portable power meters
There are now many types of portable power meters that can measure the electricity used on an individual appliance or power point.  Click here to see some that are available from the ATA.  Some are very sophisticated and can be connected to a PC and graph the power use of an appliance over time.  Click here to see some of the "Watts up?" meters.

Local Power is currently trialing the "Watts up? .Net" meter and will provide links to some interesting graphs shortly.