Project profile: RayGen Power Plant Carwarp

Solar panel arrays at RayGen Power Plant Carwarp
Image: RayGen

RayGen recently celebrated the completed commissioning of its solar-plus-storage plant in Carwarp, Victoria, adding 4MW of solar and 2.8MW/50MWh of storage capacity to the West Murray grid. It is the world’s largest next-generation long-duration energy storage program, backed by some of the biggest names in energy.

The RayGen Power Plant Carwarp (RPPC) is powered by a receiver at the top of a tower that captures concentrated solar energy from a field of smart, rotational mirrors and stores the energy across two water reservoirs to create a ‘hot and cold’ solar-and-storage solution.

RayGen has an offtake agreement with AGL for the entirety of the plant’s production. RPPC is expected to save approximately 7,000 tonnes CO2e emissions per year and will provide enough renewable electricity to power approximately 1,700 average Victorian homes.

Related article: RayGen connects flagship Carwarp solar to grid

Integrated technologies

RayGen’s power plant integrates multiple technologies to supply large industrial customers and the electricity grid. RayGen’s system is flexibly configured and operated to meet the needs of customers and grid operators.

The RPPC is comprised of modular blocks of RayGen’s solar, integrated with RayGen’s centralised electrothermal energy storage hub. The facility has four 1MWe/2MWTh RayGen solar systems (for 4MW electrical with 8MW thermal total), a 2.8MW ORC turbine and a 2MW Chiller with Air Cooled Condenser. In addition, there are two pit thermal energy storage (PTES) water pits, each filled with 17,000m3 of Murray River water, and with enough thermal energy to power the ORC turbine at full discharge for over 17 hours (50MWh). The pits are fully covered and insulated to minimise heat loss and water loss.

The plant is limited by site-specific constraints to a grid connection of 3MW. All components have demonstrated operation at specification and nominal design capacity.

Hi-tech solar

RayGen’s hi-tech solar matches traditional solar photovoltaic panels (solar PV) on cost, land area, and output; enables heat capture and agrivoltaics; and transforms the solar supply chain.

Like solar PV, RayGen generates electricity using the photoelectric effect; like concentrated solar power (CSP), RayGen focuses sunlight using tracking mirrors; but unlike anything else, RayGen uses a field of mirrors to focus sunlight onto a central receiver of photovoltaic modules.

RayGen’s modules are almost 2,000 times more powerful than traditional solar panels—operating with almost 1,000 times the solar concentration, and using cells with almost twice the efficiency. The modules are actively cooled with water, to prevent overheating. One third of the sunlight is converted into electricity, and two-thirds into heat (hot water at 95°C). RayGen’s modules contain no polysilicon.

Thermal storage

Two water pits—each to a depth of 15–20m and the size of a farm dam—store energy thermally as hot and cold water. The cold water pit is ‘charged’ using low-cost electricity and a standard ammonia-cycle chiller. The hot water is sourced from RayGen’s hi-tech solar or a heat pump. The pits are covered and insulated, meaning minimal water and heat loss.
When electricity is required from storage, the temperature difference drives an organic Rankine cycle (ORC) turbine.

Ammonia, the working fluid in the turbine, is evaporated by the hot water to turn the turbine to generate electricity. The ammonia is then cooled and re-condensed by the cold water to go through the cycle again. The ammonia operates in a closed loop and no ammonia is consumed or lost in the process. The ORC turbine drives a synchronous generator, which in future projects can operate as a synchronous condenser when de-coupled from the turbine.

Next-generation LDES technologies include flow batteries, compressed or liquid air energy storage (CAES or LAES), non-lithium battery chemistries, electro-thermal energy storage (ETES) such as RayGen, but exclude traditional approaches for pumped hydro and CSP. AEMO classifies storage projects as short duration (less than four hours), medium duration (four to 12 hours), and deep (or long) duration (over twelve hours).

Aerial photo of RayGen Power Plant Carwarp with solar panels and energy storage
Image: RayGen

For this project, RayGen’s solar was targeted to utilise a cell with photovoltaic efficiency of 38.4% (DC, STC), capture heat (via water-cooling of solar modules) at a temperature of 95°C and operate with a nominal conversion efficiency of captured sunlight onto the receiver of approximately one-third into electricity and two-thirds to heat. RayGen’s storage was targeted to have an effective peak efficiency of the ORC engine of 12%, a Coefficient of Performance (CoP) of the industrial chiller of 6, with ambient temperature of 15°C; and an effective peak round-trip efficiency (RTE) of 70%. RayGen has now demonstrated operational results consistent with these targets.

There are two primary generator types within this facility: the asynchronous solar inverter and the synchronous ORC turbine. There are several different loads at the site, the most significant being the chiller. There are also secondary loads within the system, each of which contributes to the effective operation of the generators and major loads. All loads are included in the round-trip efficiency calculation.

These generators and loads can operate independently, or in combination. The gross import or export from the facility is limited by the 3MW grid connection. The four modes of operation (which can occur in certain combinations) for this integrated plant, reflective of power flows between subsystems and the grid:

  1. Export power to the grid from RayGen’s hi-tech solar (via inverter)
  2. Export power to the grid from RayGen’s thermal storage (via ORC turbine and generator)
  3. Charge RayGen’s thermal storage (via chiller) with electricity from RayGen’s solar (behind-the-meter)
  4. Import power from the grid to charge RayGen’s thermal storage (via chiller).

All four modes have now been demonstrated.

A challenging build

The RPPC faced numerous unexpected challenges. The most significant was COVID-19, which lengthened supply chains substantially. Delivery of certain components, and the construction itself, was complicated by flooding that forced a lot of lateral thinking and problem solving from the team.

“When we started on this journey, we had nothing but an idea and an Excel model. We put in a cold call to AGL and hoped for the best. Today we have the world’s largest long-duration energy storage program, backed by some of the biggest names in energy,”
RayGen CEO Richard Payne explains.

The project achieved multiple technical world-firsts. The project delivered the world’s: only wireless and self-powered heliostats in commercial operation; largest cold storage facility; and the highest and lowest temperature pit thermal energy storage (PTES). It is also Australia’s: largest renewable energy manufacturing facility; most operating heliostats; largest solar heat generation project; largest hot storage project; largest deployment of ORC turbines; and only deployment of PTES.

This means that RayGen’s Carwarp power plant achieves the world’s largest next-generation, long duration energy storage (LDES) project, the world’s highest efficiency solar photovoltaic project, and is contracted to one of Australia’s largest utilities, AGL Energy.

Construction begins at RayGen Power Plant Carwarp with bulldozed site
Image: RayGen

Choosing the location

Many traditional solar farms have been installed in the area around Carwarp. On a sunny day, there can be an over-supply to the grid leading to curtailments. In fact, the region is part of the so-called “rhombus of regret”, as many renewable energy projects have struggled to connect to the grid due to the mismatch between the energy supply and demand. This gave RayGen a great opportunity to showcase its credentials as it can act as a load and time-shift the energy surplus.

The site itself is a sheep paddock in a sunny location. These elevated off the ground mirrors are self-powered and move dynamically, avoiding fixed shading and increasing feed growth suitable for sheep grazing.

Project completion

Conception of the RPPC began four years ago, and on August 31, the project achieved the status of ‘commissioning complete’—the final project-related milestone with the Australian Renewable Energy Agency (ARENA). RayGen’s Carwarp project has been exporting electricity day and night, and has been charging our storage from our solar and from the grid. All component systems have demonstrated performance against specification. The offtake agreement with AGL will soon come into effect.

Running the ORC for the first time was an extremely gratifying moment for the RayGen team. “It’s easy to understand the theory, but seeing a 2.8MW turbine–enough to power 1,000 homes–generating electricity from just hot and cold water is unusual and satisfying!” RayGen CEO Richard Payne says.

Related article: RayGen gets $10 million federal funding injection

“Our approach transforms renewable energy supply chains. RayGen’s photovoltaic solar modules were manufactured by RayGen in Melbourne, Australia, and include no polysilicon. Self-powered and wireless mirrors were assembled onsite and bolted onto pile-driven posts—no concrete foundations, no field wiring, no ground preparation. The chiller and turbine were sourced off-the-shelf from established suppliers and installed by local HVAC contractors. Our storage medium is Murray River water. Our storage does not degrade with cycling or depth of discharge. We avoid rare earth materials such as lithium, cobalt, and nickel, and the system will produce near-zero e-waste.

“RayGen’s thermal storage is a critical storage capability for congested grids like the West Murray region, where the Carwarp project is connected. RayGen’s thermal storage can be charged with electricity from the grid or RayGen’s hi-tech solar and can store that charge for days, weeks or months with minimal losses. The thermal storage can discharge continuously at full capacity for 17 hours without requiring recharge and can recover when discharging more than 70% of the electricity stored during charging. RayGen’s thermal storage is enabled by RayGen’s hi-tech solar, which converts approx. one-third of sunlight into electricity, and approx. two-thirds of sunlight into by-product heat.

“The successful delivery of this project is a remarkable achievement by the RayGen team with the support of our partners, investors, suppliers and contractors, and is truly the culmination of many years of hard work, support and commitment from all of our staff and stakeholders.”


When the team was filling up the storage pits, the Murray River was in drought, which added cost and time to the fill. Once the pits had been filled, the region was in flood–to the extent that a crane could not reach the site as the Hume Highway had been washed away. Talk about exquisite timing!

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