Supplying reactive power to the grid operator
Besides active power, the electricity grid needs reactive power to keep the voltage at the right level. Grid operators buy it in. Anyone with a solar park, wind farm or battery with a modern inverter can often supply it, without affecting normal operations.
What is reactive power?
Electricity transported across a grid consists of two parts. Active power does the work: it turns motors and lights lamps. Reactive power does not, but it is needed to maintain voltage and magnetic fields. It is expressed in VAr, and at grid scale in kVAr or MVAr.
The ratio between the two is called the power factor, or cos phi. At cosphi=1 all capacity goes to active power. A grid that has to transport a lot of reactive power loses transport capacity that on paper it does have.
Grid operators must keep voltage within narrow limits and buy reactive power from parties that can supply it. TenneT does so through a periodic tender; regional operators offer it as a congestion product.
Can you supply reactive power?
Usually yes, if you have a solar park, wind farm or battery with a modern inverter. Whether it works in your case depends on four things.
The inverter type. The manufacturer’s P-Q curve determines how much reactive power the device can supply, and whether the manufacturer enables that function.
The connection. A direct connection to the substation is generally a hard requirement.
Supply at night. Supplying reactive power while the sun is not shining is technically possible, but must be demonstrated with a measurement over a continuous night cycle.
Measurability. Without reliable measurement there is no evidence, and without evidence no contract.
What does it earn?
Supplying reactive power costs hardly any fuel. It costs a little active power, because the inverter has to work harder, and that is the main cost. Against it stands a fee per MVArh.
Whether it pays depends on your installation, on the agreement with the grid operator and on the price of electricity at the moment of supply. We calculate that per connection, using your own measurement data, before a bid goes out. A yield promise without that calculation is worthless.
How we go about it
Qualify. Establish per connection whether it is technically possible: inverter type, substation, night supply.
Measure. Demonstrate what the installation actually delivers. We measure every second and keep everything.
Offer. Determine the volume you can supply with certainty, with margin for outages.
Supply and demonstrate. Control, measure, and make the delivery verifiable for settlement.
We do not do this in theory. We were the first in the Netherlands to run a closed distribution system at cosphi=1 while supplying MVAr to the grid operator.
Further reading
The page Cosphi=1 and MVAr delivery describes what that first entailed. The page Network analysers describes the measuring equipment used to establish reactive power. References lists the projects where this runs.
Would you like to know whether your installation is suitable? Get in touch; we will look at it without obligation.