Open Energy Monitor – Control and Monitor our Electricity Use

We had our solar panels installed nearly 4 years ago. We have had an electric car for a similar period. During that time I have been able to monitor our house electricity use, our solar generation and to charge the car. This has worked quite well but it is not really an integrated system. Moreover, it is a passive monitoring system and has no intelligence or control functionality. It allows us to monitor the current state (house kW, solar kW, exporting kW and history kW/kWh via the internet).

When we move into our new house (notice I said "when" not "if" – must be a good sign!) it will be a good opportunity to start again from scratch and to install a properly integrated system.

The current plan for the new system is:

Solar Panels

20101217-123300-20101217-123300-PAC-06695We are aiming for as many solar panels as we can sensibly fit on the roof and garage roof. Given that the main roof plane is north-facing and also that we will need to utilise at least 3 roof planes to get the kWp we are after it may mean using micro-inverters although this will only be determined once we are in and get a quote .For now though I am assuming we can have at least 4kWp generation capacity.

Electricity Storage System

Storage of surplus solar power has always been a bit of a Holy Grail but battery storage systems are now becoming commercially available. I want to be able to store at least 10kWh of power, enough to power the house needs for an entire evening. This will allow us to charge the storage system in the day from our surplus solar power and use it in the evening reducing our need to import and pay for electricity but also reducing our demand on the grid at what is the period of peak demand. As we are on the economy 7 electricity tariff a storage system will also allow us to charge the storage system over night during the period of cheap power and then to use that power in the daytime again meaning we buy less electricity at the expensive rate.

We will need to be mindful of a conflict there in that we also want to charge the car overnight or in the day using the cheaper electricity but if we could develop a smart management and control system to manage it so it might then be possible to always ensure that the storage system is topped up using either solar or cheap-rate grid power and to also always charge the car using that stored, cheaper electricity. The end result would be a greatly reduced demand on grid overall but especially during the expensive, peak times.

Integrated Control and Monitoring System

Having this tech is all very well but without a proper management, control and reporting system we are not likely to be getting the best from it. So we want a fully integrated control system allowing as much automation as possible ensuring that the car is charged using stored (cheap, low CO2) electricity, the storage system is kept charged using solar and cheap rate grid power and the house always uses the stored (cheap) electricity first before importing from the grid at the expensive day rate.

We will need to have all the metrics available online both as current and historic values with suitable graphs to aid understanding and help with tuning its performance.

So that is the objective. How close we can get to it is yet to be seen but we probably stand the best chance of success using the Open Energy Monitor System (OEMS). OEMS is an open-source solution to energy management and reporting using a combination of Raspberry Pi and Arduino boards. Being open-source and being based on those open systems allows the system to be tailored to almost any scenario. In all likelihood our system will not be one that many people before us has tried so we may well be involved in developing a lot of the system ourselves but it is worth the effort. We may even be able to eventually contribute to the open-source components.

Using OEMS I hope to develop a system to automatically (at least as much as is possible) control the system overall according to some basic rules. For example, control the charging of the car and the storage system to ensure that both are always kept as fully charged as is possible using only solar or cheap-rate electricity. There are some others already working on an OEMS extension to go part way towards this solution and I am hoping to hook up with them to develop it further and more towards my requirements. That is the good thing about open-source… we all contribute to the shared body of knowledge whilst developing solutions that fit our own personal needs.

I shall be posting further once I have more of a plan but for now this are the general objectives. If anyone has any comments or suggestions then please do get in touch, either by commenting below, or by email/Twitter etc.

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