Self-consumption or grid independence

The primary goal for a renewable energy generated self-consumption system, is to optimize the use of solar and/or wind power. The major obstacle in such a system is that power generation times do not match with the actual times of power use. This results in a system being forced to import energy from the grid and export it when there is a surplus. In an optimized self-consumption system, surplus energy is stored locally, for local on demand use. Such energy storage is becoming an increasingly attractive proposition, especially with feed-in tariffs decreasing and grid supplies becoming less stable and more expensive.

Self-consumption versus off-grid systems

There are some major considerations which should be taken into account when comparing an off-grid system with a self-consumption system.

An off-grid system is a system that is not (or mostly not) connected to grid power and is used to supply the total energy needs of the complete energy system. Therefore it is sized to cope in a worst case scenario. This worst case scenario can occur when there is simultaneous usage of high loads which then requires a high power inverter for occasional use. The other worst case scenario is the lack of ability to generate energy in periods of overcast weather and/or wind outages. This results in substantial battery storage to overcome this, which, like the large inverter power situation mentioned above, is only used on occasion. In general it can therefore be stated that an off-grid system is oversized in both inverter power and storage capacity in order to deal with such situations.

For a self-consumption system this is different, as there is always a grid present. With Grid assist functionality the grid can be used seamlessly, whenever there is a high peak load, meaning the inverter can be sized according to the base load. The base load is the part of the total energy-need which generally comes from low powered equipment and these loads continue to draw energy almost constantly over the 24 hours of a day. Examples of this are heating pumps, chargers and the standby power of household equipment. In order to optimise PV usage and limit the import of energy this base-load is the most efficient part to target. Avoiding the import of the total energy need is possible but this would require a higher investment in the inverter, as it must then be able to cover for high loads. Most high loads are however peak loads and active over a limited period of time. So even though this requires a high energy supply, the time period is limited and the energy value within this peak load period is quite low - so the investment in a larger inverter is often not justified.

When considering battery capacity, a self-consumption system is able to work with a smaller battery capacity. The energy stored in such a system is limited to the surplus PV power as part of the generated PV power is directly used by the loads. In this case PV power is sized according to the base load and any surplus energy is used overnight.

The major considerations for installing a self-consumption system are often financially and/or morally driven. For both, the goal is to minimise the import of grid energy and to optimise the consumption of self-generated power. Modern inverter and battery monitoring technology helps to achieve this, by detecting how much energy to store and how and when to best use it.

Besides this there is another important factor to consider. This factor is the energy behavior of the end-user themselves. This can differ between households and it is heavily dependent on circumstances, which can change from day to day. This makes coding the software, to precisely achieve optimal use of energy, quite a challenge. If for example the washing machine is required on a particular day, the ideal day would be a sunny one just after the battery is (almost) full. Having said that direct power usage is preferable, which saves having to export energy to the grid or use battery power momentarily. In order to be able to make these kinds of energy use decisions, monitoring is crucial to fine tune and optimise energy use based on ever changing circumstances.

Monitoring systems are an essential feature for every self-consumption system. Tests have shown that users of self-consumption systems with monitoring score a much higher level of self-consumption than those systems which lack it.

Does it work?

A lot of people are surprised that being completely off-grid 'works'. The secret is that you have to manage your lifestyle ...and your energy use.

For example in the winter we turn the refrigerator off - because the whole world is a fridge, and we simply store food in an outdoor larder. If we want to run the washing machine, in the winter we check the weather forecast to see if it's going to be sunnier today or tomorrow, and then run it around midday. In the summer we could never use all the power available. And during a five-day blackout recently, we were unaffected.

Money no object or no other energy source available?

Managing your energy use, might sound like hard work - but it's actually easy to do, makes sense, and results in low to zero bills!

If money is no problem, we could simply oversize your system - more panels, and bigger battery storage - and the system would still pay for itself in time. We know people who have done that and it allows them to continue with their old habits - running loads at night when they come in from work, ground source heat pump, lots of electronic domestic devices - and never worrying about how much current they're drawing. They just install and forget - it's another approach and it works too!

Some projects done by us