11/18/2023 0 Comments Inverter dc dc![]() On a 1,500V DC nominal system, this ‘wake up’ voltage may be around 500V DC. ![]() PV inverters typically require a minimum threshold DC bus voltage to operate. LOW VOLTAGE HARVESTING Make Money on the Edges With a DC coupled energy storage system, energy production can continue with energy being stored and available for discharge when curtailment ends. Curtailment is sometimes seen in areas of high solar penetration - such as California - when there is overall excess production on the grid. The same uptime capabilities apply when a large utility scale array is curtailed by the ISO or utility. When the PV inverter is offline the energy from the array can still flow to the batteries via the DC to DC converter ensuring energy can be harvested for later use. When storage is on the DC bus behind the PV inverter, the energy storage system can operate and maintain the DC bus voltage when the PV inverter is offline for scheduled or unplanned outages. CURTAILMENT & OUTAGE RECAPTURE Continuous Uptime and Revenue Generation In the simple example of Figure 2 where there is a 1MW AC inverter with a 1.4MW DC array, during the time of day with the array is producing greater than 1 MW DC - perhaps from 10am to 2pm - that excess energy can be used by the DC to DC converter to charge the batteries for discharge through the PV inverter later at a predetermined time when the either the PV output is low or when there is a peak demand on the grid for kWh production. Using a DC coupled storage configuration, the DC to DC converter charges the batteries directly from the DC bus with the excess energy that the PV inverter cannot use. It is not possible to move or shunt this power to an AC coupled battery system because doing so would force the PV inverter to exceed its rating to pass any excess PV energy onto the common AC bus. Note that this ability to capture clipped DC output is only possible using a DC coupled storage system.įigure 1: Example of annual lost production from clipped energyĬlipping is a phenomenon where the PV inverter has hit its peak AC output and therefore must drive the PV DC array voltage off of the maximum power point in order to effectively curtail the PV array. This stored energy can then be fed into the grid at the appropriate time. With storage attached to the array, the batteries can be charged with excess PV output when the PV inverter hits its peak rating and would otherwise begin clipping. Without energy storage these kWhs are lost and revenues stunted. Depending on your location and type of racking, the total clipped energy can be over 1,000,000 kWh per year. Using a simplified system for illustrative purposes, consider a 14MW DC PV array behind a total inverter capacity of 10MW AC. Given common inverter loading ratios of 1.25:1 up to 1.5:1 on utility-scale PV (PV DC rating : PV AC rating), there is opportunity for the recapture of clipped energy through the addition of energy storage. CLIPPING RECAPTURE Maximize Value of PV Generated Energy DC coupled energy storage allows project owners to access all six of these use cases, and, as compared with AC coupling, three use cases are only available with the DC coupled approach - clipping recapture, curtailment recapture and low voltage harvest. Six distinct solar plus storage use cases are discussed below. The addition of energy storage to an existing or new utility-scale PV installation allows system owners and operators the opportunity to capture additional revenues. The DC coupled solar plus storage approach leads to higher round trip efficiencies and lower cost of integration with existing PV arrays, while opening up new use cases not possible with traditional AC coupled energy storage.ĭC Coupled Solar Plus Storage Revenue Streams ![]() Here we will examine how a new cost-effective approach of coupling energy storage to existing PV arrays with a DC to DC converter can help maximize production and profits for new and existing utility scale installations. Traditional solar plus storage applications have involved the coupling of independent storage and PV inverters at an AC bus, or alternatively the use of multi-input hybrid inverters. ![]()
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