When operating in the power market the owners of the electric boilers use software systems of their BRP or SCADA provider to place bids in the day-ahead market and intraday market
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and for balancing power – due to market design especially primary and manual reserves.
The BRP receives spot market results from the power exchange Nordpool and sends signals to the CHP plants and electric boilers via the software. Regarding balancing power, the system is the same, only the signals come from the TSOs. Most CHP stations have a Programmable Logic Controller (PLC) box installed receiving signals from BRP software and connecting the SCADA system of the CHP stations, thus automating the process. When the electric boiler is ready for activation of primary reserves, it receives signals from a ”frequency sensor box” placed on the grid. This frequency sensor box measures the frequency on
the grid and sends a signal to the electric boiler to start consuming electricity (negligible amounts, but enough to assist with frequency control) when frequency on the grid is increasing above a certain limit.
6.3 Operation of electric boiler on a CHP unit with a heat storage tank
If a heat storage tank exists on the CHP plant the plant should optimize it operation to minimize or avoid producing heat when the NHPC is high and instead produce more heat when it is low. The highest NHPC is seen around the interception of the red and the green line in figure 60. The plant should avoid or minimize producing heat when electricity prices are in this ”middle range”.
Instead, the plant should produce more (excess) heat when electricity prices are outside of the middle electricity price range and store the excess heat production in the heat storage tank. A heat storage tank does not impact the lines in the NHPC diagram, but the possibility to store heat allows for decreasing/increasing power/heat production during high/low NHPC periods and thus reducing the average NHPC. Having a heat storage tank thus implies:
• Minimize/avoid producing heat when NHCP is high
• Increase heat production to fill the heat storage tank when NHCP is low
• The heat storage tank can absorb some deviations from the planned heat production
» Relevant for heat production associated with the delivery of ancillary services – as results from the ancillary auction are not yet known when day-ahead market bids are submitted
» Relevant for errors in prognoses of for instance heat consumption
Optimizing the production on a CHP plant with electric boiler and heat storage tank and often also other production/consumption sources (e.g. heat-only boiler) is a complex planning task as it is not a trivial task to make prognoses of heat demand, electricity prices and free capacity of the heat storage tank. However, it is a task that Danish CHP plants undertake every day using planning tools offered by a variety of different providers. Some planning tools are integrated into BRP software while others are integrated within SCADA systems.
See an example of utilizing the heat storage tank at Skagen Varmeværk in section 6.7. This example also illustrates some of the information available in the SCADA system.
Part II Europe
1676.4 Issues regarding ownership of heat producing units by different stakeholders
Operation of an electric boiler becomes a complex task especially with the existence of a heat storage tank and several other heat production sources in the system, but the task can be undertaken with support from prognoses and planning systems. Moreover, when the electric boiler and CHP plant delivers balancing services the production plans have to be adjusted quickly as the activations of balancing services is not known before the hour of operation. Therefore, it is important that the production plan for all units – except maybe for certain baseload units such as solar heat and heat pumps – can be changed without any notice to reduce the total NHCP as much as possible. If the different heat production units are owned by different legal entities the contract between the different legal entities in the district heating system must be very flexible and allow for continuous optimization reducing the NCHP. This is, however, easier said than done, and the Danish experience is that the best and most frictionless optimization can be achieved when the flexible heat production units are owned and operated by the same legal entity. If other legal entities own heat producing units it is easiest to handle if they own inflexible baseload units such as industrial excess heat with heat pumps or heat exchangers.
6.5 History of Danish electric boilers and their participation in different markets
The Danish electric boiler market first began taking off when there was an expectation that the further installation of wind power would lead to a lot of hours with very low electricity prices. The market got a boost after Nordpool in 2009 changed the regulation and allowed negative day-ahead prices instead of having a price floor at zero.
The market for primary reserves was from 2009 to 2012 driving the market for investment in electric boilers. Before the change in regulation in 2009 for participation in the primary market, the Danish TSOs had already informed market actors about the plans to open the market. From 2009 the operators of the electric boilers were allowed to make block bids of 4 hours duration with asymmetric products (i.e. operators were allowed to just offer just regulation and not forced by regulation to offer a capability of both up- and down-regulation). This change in regulation opened up the market for electrical boilers and implied that electric boilers of almost all sizes could participate in this market. As shown in figure 5 both the number and the installed capacity increased slowly in 2006-2009, but then the installed capacity doubled in three years during 2010-2012.
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Figure 61: New electric boilers and accumulated installed capacity. Source: Danish Energy Agency and Danish District Heating Association.