An Innovative Solar Pump Applicable in Water Distribution Networks ^†

Abstract

The analysis of GHG emissions for different sectors shows that one of the main contributions, responsible for 25%, is electricity and heat production. An important aspect of electricity use concerns motor pumps, which are used for both urban water supply and agricultural water systems. Generally, the highest consumption corresponds to summer, when the maximum solar radiation makes the use of solar water pumps possible. However, the total conversion of energy by conventional solar pumps is about 10% of the solar energy. This low efficiency has limited the choice of solar water pumps to areas without alternative power sources. Moreover, the final efficiency will further decrease due to that of other parts of the system, so, in order to achieve higher efficiency and sustainability, a novel method for solar water pumps must be developed. The new solar pump that we propose will take advantage of the efficiency of solar concentration dishes to absorb solar radiation, which is about 80–90%, will pump water using water vapor pressure, and will not need an electrical motor. It will offer several benefits besides high efficiency in pumping water, like the number of mechanical parts required and their maintenance costs, making its application easy and removing the limitations of typical systems.

1. Introduction

The motor pumps used for both urban water supply and agricultural water systems represent a major consumer of electricity [1]. The highest consumption corresponds to summer, when the maximum solar radiation makes the use of solar water pumps possible [2]. Solar water pumps are mostly used for irrigation purposes during the summer when both solar radiation and water demand are at their highest level. In photovoltaic (PV)-based irrigation systems, the electrical energy generated by PV panels drives an electric motor. This motor, in turn, provides the necessary power to operate an electric pump. These systems can be further improved by combining them with a charge regulator, which depends on the pump type (AC/DC) [3]. In direct-coupled photovoltaic water pumping systems, a tank is usually installed to eliminate the need for battery storage. The system’s water discharge can be used directly for irrigation purposes or directed to a water storage tank. In this case, the potential energy of the stored water can be utilized for drip irrigation, which represents a sustainable and efficient solution [4,5,6].

As previous studies have determined, the use of solar PVs is becoming more common each day. However, the efficiency of solar panels is usually less than 20%, which means that a small fraction of the solar radiation in the limited roof area is being used for producing electricity. The total efficiency could be even lower due to the efficiency of inverters, and module production could decrease with rising temperatures [7]. In addition, the efficiency of solar water pumping systems depends on several factors; the photovoltaic module and the water pump are the most important ones. The solar panels’ efficiency in using solar radiation is usually less than 20%, although it must be kept in mind that this performance may depend on factors such as the temperature, an increase in which would lead to an efficiency decrease [7]. Additionally, the efficiency of centrifugal pumps with DC/AC motors is 35–70% and decreases over the pump’s lifecycle [8]. The efficiency is higher (about 70%) in the positive displacement pumps and diaphragm (usual for liquids with higher viscosity), and finally, the efficiency of solar PV-based water pumping is about 39% [9], but these numbers are just for the pump and not the total efficacity of the system. Therefore, not only do solar PVs limit the use of solar radiation, but the pumps are also losing a high portion of that, meaning a combined conversion of energy of about 10% of the solar energy.

Many studies have delineated the benefits of solar pumps. However, as explained, the low efficiency generally limits the choice of solar pumps to areas with no alternative power sources. Moreover, the final efficiency will further decrease due to other parts of the system, so, to achieve higher efficiency and sustainability, and considering these limitations, the development of novel methods for solar pumps seems necessary. Therefore, this study aims to propose a new solar water pumping system with several benefits, mainly, a high efficiency in pumping water, using more solar radiation, and decreasing the mechanical parts required; these benefits all make the system’s application easy and overcome the mentioned limits of conventional systems.

2. Materials and Methods

The research analysis diagram is shown in Figure 1. As can be seen, the conventional solar pump system was evaluated as the first stage, and for the second stage, we tried to improve it by proposing a novel system.

The Problems that the Proposed System Aims to Solve

• The low efficiency of the conventional solar pump system, such as photovoltaic panels (using under 25% of solar radiation);
• The low efficiency of existing solar pumps that is by a water motor pump (under 60%) joining with solar PV panels (using under 25% of solar radiation);
• The lack of availability of a system to power water pumps directly from a solar concentration dish (using 90% of solar radiation);
• Conventional solar pumps’ life cycles are limited based on the solar PV panels and electrical motors.

3. Results and Discussion

A Novel Solar Pump System

As shown in Figure 2, the newly invented system can pump liquids such as water from water networks, wells, rivers, lakes, and other sources and send them to the desired location, like reservoirs or buildings, via piston pressure. The new solar pump will use the solar parabolic dish, and the efficiency in absorbing solar radiation as a heat source is 80–90%, unlike solar panels, which have an efficiency of 15–25%. The system will work in two cycles. The first cycle will involve heating with solar radiation, and the second cycle will occur during the loss of the absorbed solar radiation. In the first cycle, the system will send the water, via the pressure of a piston from the tank near the resource, to the desired location, and the tanker will be empty. In the second cycle, the system will pump the water from the network (well, river, lake, etc.) to the tanker under negative pressure, and the tank will be refilled. In this regard, the system will use nearly all of the absorbed solar radiation both by achieving heat and by losing heat. Moreover, the new system can pump water directly based on pressure and does not need a motor pump. The water vapor pressure can regulate the required water heat. The water vapor pressure at 120 °C in H₂O is about 20.26 m, and at 140 °C, it is equal to 36.87 mH₂O. This means that at a temperature of 120 °C, the pressure would be enough to send water in the tanker to an upper level of about 20 m, corresponding to 36 m at 140 °C. Of course, one must consider the heat losses in the pipeline and system. The studies showed that the average temperature of water vapor formed by using an absorber at the focal point of a concentrator satellite dish with a mirror with a diameter of more than 2 m could be more than 300 °C, depending on the water volume [10].

4. Conclusions

This study proposes a novel system for solar water pumps, to solve the problems with conventional solar pump systems that we have mentioned. The proposed system uses a solar concentration dish of which the efficiency in absorbing solar radiation as a heat source is 80–90%, instead of using solar panels with an efficiency of 15–25%. Therefore, the new system has several benefits, mainly, high efficiency in pumping water, using more solar radiation, and reducing the need for mechanical parts, making the system’s application easy and overcoming the limits mentioned for conventional systems. In addition, high-efficiency solar water pumps can minimize the use of fossil fuels and reduce the total electric consumption in water distribution systems for cities and farming. In conclusion, the new system is a perfect choice for a water distribution system and can be installed in any location with low pressure and even without access to the grid.

4.1. Suggestions for Future Studies

Simulations of the proposed system with CFD software like ANSYS and Transys are suggested for future works investigating short-term and long-term performance. Moreover, laboratory and field test analyses of the novel solar system are recommended as future studies.

4.2. Patents

This manuscript’s concept was submitted as a patent in Italy, Ministero dello sviluppo economico, with application number 102019000023145.