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Solar Greenhouses shining at Murdoch University and now in Japan

Date

19 Apr 2022

Sections

Energy
Climate & Environment

HIGHLIGHTS

  • Stage 1 plant science trials at Murdoch University Greenhouse have been completed revealing some exciting power generation, thermal efficiency and plant science data and insights
  • ClearVue has made significant upgrades to the greenhouse systems in advance of its Stage 2 plant science trial, stemming from learnings of the Stage 1 plant science trial, confirming the readiness of ClearVue PV for commercial applications
  • Stage 2 plant science trial has now commenced with aim of finding the optimum balance between power generation, thermal efficiency, water savings and maximising plant growth across a wide range of species through adjustment to photosynthetically active radiation (or PAR) light
  • ClearVue continues to make positive progress installing its PV IGU glazing at the commercial greenhouse at Aqua Ignis resort in Japan

19 April 2022: Smart building materials company ClearVue Technologies Limited (ASX:CPV OTC:CVUEF) (ClearVue or the Company) is pleased to provide an update on the progress of its solar greenhouse trial at Murdoch University and the progress on the installation of a commercial solar greenhouse in Japan.

Greenhouse Energy Production & Thermal Performance – first 12 months

Energy production performance and energy efficiency of ClearVue’s PV glazing at Murdoch University Greenhouse has been measured continuously since the greenhouse officially opened on 19 April 2021.

The greenhouse comprises four glazed rooms and an enclosed, unglazed preparation room at the rear (south). The four rooms include one with normal glazing to create a scientific ‘control’ as a baseline from which to measure the performance of the ClearVue glazing against a traditional glazed greenhouse. 

The remaining three rooms of the greenhouse comprise three different versions of the ClearVue PV solar glazing technology. The second room uses the current commercially available ClearVue glazing product while the third and fourth rooms are variants of that product using different amounts of nano- and micro-particles to look at optimisation of power generation and impact on plant growth dynamics. 

This stage of the experiment which is being concluded at the greenhouse comprised three main elements:

  1. To measure the power generation performance, as an offset to the energy demands of the greenhouse itself;
  2. To assess the expected reduced energy load due to the thermal performance of the ClearVue product; and
  3. To consider the impact that the proprietary ClearVue interlayer technology has on plant growth within the greenhouse.

To conduct the energy efficiency and power performance trials, ClearVue’s own in-house technical team managed the data collection.

To conduct the plant science research, ClearVue engaged with Murdoch University’s Professor Chengdao Li, a world leading molecular geneticist, and his team including Dr Hao Luo under a collaborative research agreement.

Prof Li’s team looked at agronomic and physiological characteristics that were recorded from germination to harvest, to understand the plant response to the filtered light through ClearVue’s solar glazing panels.

In this context, certain plants need at least some ultraviolet (UV), whilst others perform better with little to none. Other plants need different levels of visible light transmission. The aim of the Stage 1 winter plant science trial (see below) was to commence investigation into finding the right balance for an optimum growing environment whilst maximising power generation and energy savings. 

As expected, different plants had different responses to the light passing through the solar glazing panels at different growth stages, where a significant amount of UV and infrared (IR) were removed by virtue of the operation of the solar glazing using those wavelengths for power generation.

For the purposes of the three elements of the experiment, the ClearVue greenhouse incorporates a range of sensors that record and present an array of data in real time providing the scientists with accurate information relating to conditions like temperature, humidity and the actual amount of light in all wavelengths that the plants were receiving.

This information was analysed to make automatic adjustments to lighting, heating, cooling, louvres, fans, blinds and reticulation systems, which in turn allowed scientists to maintain a constant microclimate to provide optimum growing conditions – a proportion of which is being powered by the energy generated by the ClearVue glass deployed on the greenhouse itself.

Trial Limitations

The four rooms of the greenhouse have been divided up with the use of insulated expanded polystyrene (or EPS) refrigeration type panelling and the two East and West ends of the greenhouse were blocked off with EPS to achieve (as close as possible) four consistent rooms for experimentation.

The impact of this on the overall experiment for all rooms is a loss of some light (in all wavelengths) entering the greenhouse – a normal commercial growing greenhouse (for example, the solar greenhouse under construction in Japan – see below) would have no such internal barriers to light entry and solar traversal across the greenhouse. 

This important limitation was understood at the outset of the trial and could only have been overcome by the construction of four separate adjacent greenhouses or by using clear room dividers made of polycarbonate or plain glass which would have been less reliable for data collection purposes and also allowed more natural light in that’s capable of reaching the plants, thereby generating less accurate measurement of the energy efficiency savings offered by the ClearVue product.

Additionally, it should be noted that the greenhouse is a research greenhouse and the rear (Southern side) of the greenhouse has an unglazed scientific preparation room running behind all four growing rooms, meaning there is no light is coming from that side – whereas in a regular commercial greenhouse this would not normally be the case and all sides of the structure would be glazed permitting maximum daylighting.

Another influence on accurate data collection was that louvre operation was impaired in all rooms during the course of the trial with three rooms staying closed and one room staying open. Repairs and maintenance have been completed on these in advance of the Stage 2 trials.

A focus of the trials is to measure the energy efficiency and power savings offered by the ClearVue glazing and the power generated from the glazing.  This focus has led to careful monitoring and control of the air-conditioning and fans in each of the greenhouse rooms leading to automated shut off of those systems where cooling or heating is not needed to maximise overall energy savings. This approach, although logical, ignores the importance of internal air circulation within a closed greenhouse environment. Air circulation is critical in a greenhouse for plant pollination where there are no natural insect pollinators.

Power Generation Results

Figures 1a and 1b (below) shows energy generation results of the greenhouse being 5.3MWh over a year of operation (mid-April 2021 to present).

The greenhouse is comprised of 153 total panels, almost all are 1115mm x 1228mm in size. There are 120 panels on the roof (North-facing, 20-degree tilt), 55 on the North vertical wall, and 25 panels in the West. There are 90 panels on the roof (North-facing, 20-degree tilt), 42 on the North vertical wall, and 21 panels on the West vertical wall.  Energy production performance at the greenhouse was collected through Enphase microinverters’ connected to the Internet accessible through an online user interface.

Figures 1a (above) and 1b (below): Energy Production as of 14/04/2022, with 3.7MWh produced from April 2021 until the end of 2021, and 1.6MWh produced so far in 2022.

Figure 2 (below) shows a comparison of energy generation at varying orientations. Each line on the chart represents the generation from an array of 12 windows (out of a total installation of 153) over a 5-day period. The observation is that the unique layout of internal PV cells within the ClearVue IGU gives an above-average performance at a vertical orientation compared to a regular PV panel.

Figure 2: Comparison of energy generation at varying orientations

Table 1 (below) shows a 21% decrease in performance at a vertical orientation. Normal roof-type solar panels typically display a decrease in the order of 30-35% generation[i] when placed vertically.  This observation is commercially significant for high-rise construction applications as well as greenhousing.

Table 1: Comparison of lifetime energy production of 12 panels (out of 153) at varying orientations.

Thermal Performance / Energy Efficiency

The ClearVue PV IGUs installed in the greenhouse also demonstrate a significant thermal advantage over the standard single-glazed panels in the control room. The specifications of the installed windows are as follows: U-Value: 1.4W/(m2.K), SHGC: 0.67, VT: 70%.

This specification is using a baseline configuration. The ClearVue IGU end-product for commercial construction applications is typically a customised product comprising different glazing types and the thermal performance is adjusted using additional coatings and fillings (such as argon or other noble gases) which can dramatically further increase the thermal performance. This exercise is conducted at the time of specification working with architects, façade engineers and sustainability engineers etc. These additional coatings and fillings have minimal impact on the ClearVue electricity generation performance.

Figure 3 (below) shows mean temperatures across each room during initial testing before the HVAC system was switched on in early April 2021. The chart shows temperatures within the ClearVue rooms were 2˚C warmer overnight, heating more slowly in the morning and cooling more slowly in the evening and overnight. This thermal advantage can lead to significant energy savings.

Figure 3: Room temperatures with HVAC system disengaged, 19/04/2021

Figure 4 (below) shows the cumulative energy consumption in each room over the lifetime of the greenhouse. The increased insulation of the ClearVue panels has led to a direct decrease in electricity use within the greenhouse grow rooms. This chart does not include generation, which is subtracted from electricity use on a building level. It should be noted that the control room has an additional HVAC unit to help with the thermal load, however this is only switched on when necessary, according to the control algorithm to avoid damaging the plants.

Figure 4: Cumulative electricity consumption since 18 April 2021 (kWh)

Conclusion on Power Performance and Energy/Thermal Efficiency

In summary, power generation data from each of the three rooms of the greenhouse using the ClearVue PV glazing performed better than was predicted for various periods of the year, and overall.

As previously reported:

  • advanced temperature control in the range of +/-2˚C was also achieved over multiple days (not all days) within greenhouse growing rooms where the ClearVue PV glazing was used. Data collected demonstrated that those growing rooms used approximately half the HVAC energy compared to the scientific control room, using ordinary glazing.
  • the microclimate control algorithms used in operation of the greenhouse are continually being refined and improved, so that a combination of significant energy savings and tight temperature/humidity control can be maintained over different seasons.  This aspect of the greenhouse operation has been further developed for the Stage 2 plant science trials and has been an important aspect in the greenhouse upgrades (detailed below).

The Murdoch University solar greenhouse demonstrates the readiness of ClearVue PV for commercial applications. The ClearVue PV product installed within the structure of the building has provided both electricity generation and thermal benefits, demonstrating direct savings for the customer. The product functions well when coupled with conventional PV inverter systems and wiring and demonstrates good electricity generation when installed at angles typically expected of window units. 

Plant Science Trials - Stage 1 (Winter season)

Plant science trials were conducted by Murdoch University’s Professor Chengdao Li and Dr Hao Luo during the period June 2021 through November 2021 with collation of data being conducted during December 2021 to February 2022. Final report preparation was completed during January through April 2022.

The plant science trials looked at, amongst other things, whether ClearVue’s solar PV glazing is suitable for use in protected cropping agriculture or greenhousing by evaluating the development, growth and yield of 10 crops, including leaf vegetables, fruit vegetables, grain crops, oil crops and legumes including wheat, barley, strawberry, lettuce, tomato, dwarf bean, chickpea, lupin, spinach and canola.

Light quantity and quality

Photosynthetically active radiation (or PAR) (mW/cm2) and photosynthetic photon flux density (PPFD) (µmol/m2/s) were compared among different glasshouse rooms (see Figure 5). The light intensity in conventional glasshouse room (glasshouse 898 – being a polycarbonate covered greenhouse adjacent to the ClearVue greenhouse at Murdoch) was reduced to 80% and the normal glasshouse room (control room ) was reduced to 77% for PAR and 82% for PPFD compared with the outdoors, whilst the ClearVue PV glazed solar rooms received around 55% sunlight. The light intensity in solar rooms was approximately 70% of the normal rooms.  A proportion of this reduction can be attributed to the trial limitations (referred to above).

The comparison of light quality between the different rooms is shown in Figure 6 (below). The light quantity and quality were both identical in the three solar PV glazed rooms. The spectra patterns were similar between the normal control room and solar rooms from 400 to 800nm, but the overall intensity was reduced. In the solar PV glazed rooms, the blue light intensity was 64% of the normal room, green light 72% of the normal room, red light 70% of the normal room, and far-red light 70% of the normal room.

The major light spectra difference was identified in UV light from 350 to 400nm. Compared with outdoors, the conventional polycarbonate glasshouse room received 82% of UV light, while in glass control room 14% of the UV light was present and in the solar rooms only 3% of UV remained, which was expected[i].