Hybrid Electricity Generation

An innovative architecture for PV solar, wind, grid & generator on grid/off grid UPS functions energy & CO₂ emission saving

Cost of energy generation from renewable sources per kW and per kWh evolves towards real competitive grid parity when compared to traditional forms of generation, and this new scenario is changing the decision making criteria of new investments in electricity generation and infrastructure. The challenge of real distributed generation is breaking through—both in remote grid-less sites and populated grids in developed countries. The hybridizing of electricity generation is no longer a technological challenge, but an opportunity to feasibly choose the most cost-competitive investment and lowest possible kWh for each case. As part of its Sepec product range, Zigor has developed the technological family of products to provide the best solution: HIS/HIT inverters, plus a design and dimensioning simulation tool which delivers a high Return on Investment (RoI). (Index Terms: Investment Criteria for Energy Generation, Renewable Energy, Storage, Hybridisation of Energy, Availability, Energy Saving, Competitive kWh)

By Jose Luis Iribarren, Dr. Raquel Ferret

HIS/HIT

Figure 2 shows the major application opportunities derived from the hybridizing of power sources and the storage control facilitated by the HIS/HIT. The HIS/HIT operation is simply based in a flexible DC & AC/DC/AC converter capable of processing both DC and AC forms of energy. 

Figure 2. HIS/HIT architecture concept and applications (Source: Zigor)

It is also capable of continuously regulating the energy flows of the different inputs (generation) to the multiple outputs (consumer).

The simple idea of combining fuel-based and renewable sources in alternating or direct current forms is today very commonly done by integrating standard existing products available in the market. However, what Zigor introduces as an innovation is the possibility to continuously add energy to the demand or user from the available energy sources: grid, generator, solar, wind and battery, following a customizable or cost function defined to have the lowest possible cost of the demanded energy. Although the idea is simple, it requires a sophisticated energy conversion and control system: the new development from Zigor called HIS/HIT. The ability to manage and store energy offers a valuable function to increase the availability and provide what we refer to as UPS (Uninterruptible Power Supply) function. 

Figure 3. Load profile versus energy generation from the different sources (Source: Zigor)

The Figure 3 shows a typical energy demand pattern, identifying the source used to guarantee maximum availability at lowest cost.

The application load profile shown in Figure 3 corresponds to HIT application using both solar panels and a small wind turbine, which provide most of the energy during the day, a battery capable of compensating the peak demands until the diesel generator starts and a generator acting as a complementary generation only running when the renewable sources are not available. The battery plus the wind turbine produce the energy for the lowest consumption requirements during the night. 

Figure 4. A typical example using standard utility grid into AC1, an additional diesel generator connected to AC2, potentially connected to a Photovoltaic unit (PV) or mini wind installation ifthese resources and the investment is worth doing. (Source: Zigor)

Application Possibilities

Zigor has developed a series of new products, namely HIS and HIT for single phase and three phase applications respectively and a design methodology to easily find the best combination of resources for a specific electricity demand. Besides helping the customers to find the most adequate solution in terms of investment, additional ad-hoc topologies are possible to meet with the customer specification, which frequently has additional requirements to pure energy generation.

Hybrid Off-grid

Hybrid off-grid is the most common application of hybrid topologies normally designed to bring energy to remote sites where the grid does not exit. Typical examples are remote telecom or utility sites, small rural villages, water pumping, etc.

Many different combinations of input energy sources can be used with the HIS/HIT solution, which is very flexible and scalable to meet growing energy demand over time. A typical configuration will connect to the AC1 and AC2 inputs, one or two diesel generators combined with a solar panel and/or a small wind turbine.  

Hybrid On-grid and the UPS Function

Although nowadays in many cases government subsidies are still required for the development of this new form of generation, there are some interesting market niches where, because of other cost reasons or low levels of mains availability, some forms of hybridizing might be interesting.

The HIT has been especially designed for this application for small villages and small and medium industries where the power availability from the grid is low.

Figure 4 shows a typical example using standard utility grid into AC1, an additional diesel generator connected to AC2, potentially connected to a Photovoltaic unit (PV) or mini wind installation if these resources and the investment is worth doing.

The ability of the HIT to manage the energy irrespective of the utility or from the renewable source combined with a battery back-up (for unpredictable peak demands), also offers a valuable UPS function to critical load.

Notice that this configuration is also useful in places where obtaining higher levels of power from the utility is impossible due to limits of the infrastructure or impossibility to upgrade the existing lines because of environmental restrictions.

Fuel and CO₂ Saving

When combining renewable energy and battery power with either grid or diesel generated power important fuel reductions are, therefore, feasible. This is a valuable technique used in many remote telecom sites. The innovation introduced in the HIT is that the energy generated to the load could be continuously combined from the three traditional sources used in these applications. 

Figure 7. Telecom site off grid: Batt+PV+Genset: DC & AC back-up (Source: Zigor)

This advantage allows a lower cost design in battery and longer life expectation of these critical elements, especially in telecom sites, since they are used only for real back-up not for daily cycles that happen to be very expensive. Additionally the fuel consumption is reduced since the generator only contributes to the energy not generated by the renewable resources. This is different to other system designs where the generator will operate to provide the full load demand when the renewable source is not capable of fulfilling the total required load. Another potential use for energy saving is using the critical/non-critical load discriminator when the energy available is not enough to cope with the overall demands.

Managing Renewable Energy Sources

This function is probably the biggest challenge that the world is facing today—to let the renewable sources grow to compete with traditional forms of generation.

New control methods are changing the way the generation is handled. The HIT brings to the market an opportunity to manage these traditionally competing forms of energy and provide small and medium energy consumers with the possibility of hybridizing the utility service of proprietary generation.

Available Product Range and Application

In the Figures 5 and 6, the available product portfolio for HIS (single phase) and HIT (three phase) are presented. Additionally typical applications are summarized. 

Figure 9. Residential / home off grid: Gens and/or grid batt, PV, wind (Source: Zigor)

Sample Projects

Some real projects are presented summarizing the source of energy used and the application (See Figures 7, 8, and 9).

Jose Luis Iribarren is an electrical engineer who specialized in electricity at ETSII of San

Sebastian (Basque Country University, Spain) and now the R&D director at Zigor (www.zigor.com) since 1998. Formerly research and development activities chief for SAFT IBERICA, R&D chief of SAFT NIFE Iberica and responsible for Technological Strategy at SAFT INTERNATIONAL. Iribarren has participated in several national and international research projects and he holds several patents.

Raquel Ferret graduated in Chemistry in 1994 from the Basque Country University, Spain.

Ferret worked as a research assistant in the Chemical Engineering Department in the field

of catalyst and environmental issues where she completed a PhD in 2000. She then worked at TEKNIKER in the area of tribology, lubricants and fuels and moved onto surface chemistry research and life cycle assessment issues, participating and coordinating several national and international projects. In 2006 she joined ADIGEST as technological consultant and International projects coordinator and in 2008 she joined Zigor as Innovation Project Coordinator.