This page documents the questions that were asked during the webinar: Solar Powered Water Systems in Humanitarian Context - Making Sense of SPWS Expansion.
Questions to All
Which are the preferable solar water pumping systems that would eliminate the use of generators in the long run. We have challenges with solar systems in South Sudan refugee camps. Use of generators still takes about 60% of water pumping
when converting from diesel generator operation, the full details of the system (as being explained by Jeff) need to be known so that the right PV size can be designed to supply the required amount. Where solar cannot meet the requirements, a hybrid operation is then chosen
Regarding daily demand and solar, what sizing consideration do you do for consecutive cloudy days?
Usually, SWP sizing is based on the worst-case i.e. design is based on the season or days when you expect the least irradiation. So it should be ensured that the design is able to meet the demand when you have the least sunshine.
We realised one more factor important in design - slope and direction
In case you are referring to the tilt angle/orientation of the solar panels, then indeed you are right as the tilt angle and orientation impact the power output from the solar modules.
While there seems to be little or no support for using batteries in solar water pumping scheme could it not be feasible someday since the cost of battery storage is plummeting (as PVs did making PV water pumping much more feasible) would it not be possible to find batteries useful in some applications such as a situation where well capacity is weak and a longer pumping cycle would be needed to meet demand. This could be more efficient than opting for a solar-diesel hybrid system, no?
You are right. Battery technology is indeed evolving into batteries that have 15-20 years life as opposed to the current technology which has a short life (3-6 years) which has been the biggest deterrent for using batteries in SWP. However, the long-life batteries (lithium-ion etc) are very expensive prohibiting their wider use. Perhaps we will see this change in the coming years.
Questions to Jeff
I wonder how do you make solar systems like in Puerto Rico hurricane-resistant?
In a humanitarian context, how would you go about establishing the dynamic water level (where this information has not been established prior, but where there is anecdotal evidence of seasonal fluctuations and/or lowering groundwater levels?
AC vs DC motors, which one you recommend?
Pump and motor combinations that can take DC power input typically have a lower flow and head capacity than pump and motor combinations that can take AC power input. However, pump and motor combinations that can take DC power input are typically easier to install and operate than pump and motor combinations that take AC power input. My recommendation is to select the pump and motor that is needed for the project based on the desired flow and head parameters.
Is installing batteries to store solar power be an option in countries with lesser sunlight hours?
Yes. However, batteries present several challenges that must be anticipated and addressed before using them in a water system. Batteries have a high capital expense. They are difficult to install and operate. Different battery chemistries have different lifespans, and replacement costs must be anticipated and planned. Also, due to low use of batteries in rural water system installations, additional time and cost for addressing unanticipated problems must be planned. Water Mission does not currently use batteries for these reasons (except for installations where we are testing and monitoring closely).
Is there a policy or work done for balancing input vs discharge for developing countries? A policy to have a control of usage of water, limitation on usage of solar water pumps
Certain countries and regions limit the discharge from a borehole to a percentage of the tested yield. I am not aware of other policies that may be in place. However, every solar powered water system that is installed must follow the laws and regulations of all authorities with jurisdiction in the project area.
If funding was available for joint solar/water systems, how best can it be used? What would you say are the critical actions required for sustainable interventions?
There are several aspects to a full answer on this question, and space here limits a full answer. We recommend use of the resources available on thesolarhub.org website to address this question. Also, we very much encourage exploration of a solar powered water system as a preferred option for any water system.
Is there anybody who has experience with so called "sand dam" as water source? Are there any specific points to observe when planning and realizing a SPWS with this kind of water source?
Water Mission does not have experience in utilizing sand dams. However, if a sand dam has been constructed, then the water source could be accessed with a solar powered pumping system in a similar way that other surface water sources are utilized. Extra attention to seasonal fluctuations in the amount of water available would need to inform the capacity of the equipment selected. The Solar Powered Water System Design and Installation Guide (available at https://globalwatercenter.org/solar-guide-access/ ) does address using solar with surface water sources. (We would also strongly advise careful attention to the water quality in these type of projects.)
Can you talk about the use of solar panels for other purpose other than pumping?
The context of our experience is primarily limited to water. However, using solar power for other applications is a widespread practice, and there are many sources of information on the internet for most desired applications.
How you balance RSI rating with power supply by solar panels? I think the combined energy supplied by 72 solar panels will be greater than 15kw RSI.
You are correct. The 72 panel array is rated for just under 25kW. However, solar arrays must be sized for a capacity greater than that required by the inverter and pump motor for several factors. First, there is the variation of available irradiance throughout the year at the installation site. Then there are numerous sources of power loss in the solar array, including soiling on the panels, connections used, wiring, and others. It is common for the rated capacity of the solar array to be 1.6 to 2.5 times greater than the rating of the inverter or pump motor.
Should you check the well for sand content before investing in solar power.
This is correct. Sand content is undesirable for many reasons. Sand will cause problems for submersible pumps resulting in added maintenance or even premature failure of the pump. (Additionally, sand content presents a significant water quality concern.)
How long will it take to install the system and how much will it cost in the areas where water wells are deeper than 200M?
The full answer to this question is highly dependent on the location of the project, the daily water production desired of the system, the availability of the system equipment, and the experience of the solar powered water system designers and installers. There are solar powered pumping systems that can be used for boreholes deeper than 200m.
Can we have other water sources other than boreholes?
Yes. Other water sources have been used for solar powered water systems. The Solar Powered Water System Design and Installation Guide (available at https://globalwatercenter.org/solar-guide-access/ ) does address using solar with surface water sources.
Why did you choose Grundfos instead of Lorentz?
Water Mission has extensive experience with Grundfos. Therefore, it was an easy choice for us in the Puerto Rico installations. However, Lorentz also provides high quality, reliable equipment.
The big issue with retrofitting with solar, going from a constant and long pumping cycle with say diesel to a likely shorter and less consistent pumping cycle with solar as this could put more demand on the well, require a larger pump, require larger storage, etc. No?
Yes, but this is why we recommend a robust design approach, even to retrofitting, and a careful deliberation of the available options. Installation of a higher capacity pump would only be advisable if the water yield of the borehole (well) can support it, if the capital is available to purchase the larger pump and perform the installation, and if the infrastructure is present to support the higher water flow rate. If these items are not available, the second choice is to consider a hybrid powered system where the current pump would be powered by solar during the daylight hours and by diesel generator during the night hours. Appropriate disconnect (or change-over) switches would need to be installed and consistently operated.
With your experience in developing countries what is the importance / value of addressing demand side management (Water) prior to application of Solar PV system?
I assume that “demand side management” is referring to uses of the water other than for drinking water. The two most common uses in rural areas, other than drinking water, is water for livestock and for irrigation. If these water uses are to be provided by the solar powered water system, then these uses must be taken into account during the design of the system. This is one of the reasons that Water Mission stresses that the first step in the design is to identify the desired daily water production.
What is the cost for installation of remote controlling systems?
I assume that this question is meant to ask about remote monitoring systems. Remote controlling systems do exist, but we did not discuss these and do not have experience with them. Remote monitoring system costs vary widely. Water Mission’s use of remote monitoring systems that monitor water flow of a water system costs around $1,300 USD. Water Mission’s use of remote monitoring systems that monitor flow and ground water level of a system costs around $2,600 USD. However, it is also important to remember that there are ongoing data costs for every year that the monitoring is performed.
How high are the additional costs for groundwater monitoring devices?
Please see the answer to the previous question. In Water Mission’s experience, the additional equipment required to monitor groundwater in a system will cost approximately $1,300 USD at a minimum.
Your diagram showed separate sensors for water levels. Is that all that is needed for the long-term monitoring or what specific additional equipment is needed for the long-term monitoring you recommend? Also are there existing examples of where this monitoring is being done and by whom?
There are three essential components to any remote monitoring system. The first is the sensor that takes the desired readings, in this case this is a pressure sensor placed in the water column in a borehole that by pressure measures the water level. The second component is the device that transmits the data from the readings (also, this device may consist of one piece of equipment or multiple pieces of equipment). These devices will transmit the data from one sensor or multiple sensors. The third component is some means of reading the data. In a remote monitoring system this is typically computer software written to display the data in a way that makes it understandable to those that need it. These are the three essential components, but there is a fourth recommended component, which is some means of making the data actionable. Water Mission is happy to share its experience with remotely monitoring borehole water levels.
Questions to Rick
Sometimes after geological survey, wells later start drying Not because of the aquifer condition but because of weather changes, what could be done to address such issues.
Is there a limit of ground water table depth that makes solar system not effective? or very costly? and thus using the grid would be more cost effective?
With inverter technology nowadays, it is possible to solarize very large pumps (pump motor larger than 200kW, with Heads of around 500 meters) with made-for-purpose solar pumping inverters; we haven’t came across anything larger than that although we have seen in the past inverters for electricity production been adapted for large water pumping applications so possibly larger pumps with modified inverters could be solarized. Having said this, we haven’t made any cost analysis for those very large systems or compared them with grid or other pumping technologies as they are so rare to find in the contexts where we usually work.
Are there resources currently available in Africa for aquifer mapping, groundwater levels, and other parameters that can allow preliminary planning for a future system?
Yes. There are many reports on geology and groundwater. The British Geological Survey has a map of the geology over the entire continent that is available through the Online Groundwater Atlas (https://www2.bgs.ac.uk/africagroundwateratlas/index.cfm). Regional reports can provide some information on the type of aquifers that are prevalent in the area of interest. Country-scale reports are more likely to provide the quantitative details on aquifer locations and properties that can be useful in planning. So literature reviews for the country of interest are beneficial. The Africa Groundwater Atlas also includes a literature archive with access to thousands of articles. Groundwater-level data are usually available on a country by country basis. Many countries have national networks of observation wells. The International Groundwater Resources Assessment Centre (IGRAC) recently published a report describing groundwater level monitoring networks for many countries (https://www.un-igrac.org/stories/national-groundwater-monitoring-programmes); it is a very useful report. IGRAC also has a Global Groundwater Monitoring Network (https://www.un-igrac.org/special-project/ggmn-global-groundwater-monitoring-network). The groundwater level hydrographs available from these sources can provide an idea about the dynamics of the aquifer systems and how it may be recharged during extreme events.
How would the quality of water decrease with a decline in ground water?
In many aquifers, water quality is not uniform. Typically, salinity (or total dissolved solids (TDS) concentration) increases with increasing depths. This is due largely to density effects; as TDS increases, so does the density of the water, and this water tends to sink to the bottom of the aquifer. So as pumping causes groundwater levels to decrease, the quality of the produced water often decreases because water is being withdrawn from deeper segments of the aquifer.
Also, aquifers located near oceans can be susceptible to saltwater intrusion. In these aquifers, freshwater lies above saltwater. As freshwater is removed, saltwater can move upward.
What are methods to manage aquifers with limited to no recharge, such as those in the Sahel?
The first steps for aquifer management in the Sahel region, and in any other region for that matter, is to collect data that can be used to assess the current state of groundwater conditions. The most important data are groundwater levels and groundwater pumping rates. Analysis of groundwater levels will indicate any increases or decreases in groundwater storage. If there are no prolonged periods of decreasing water levels, then it is safe to assume that the current water pumping rates are sustainable. However, if there are prolonged periods of decreasing levels, then actions can be taken to mitigate the problem. Pumping rates can be decreased (often times improvements in water-use efficiencies, particularly in regard to irrigation, can offset reductions in pump rates). It may also be possible to increase recharge rates by, for example, replacing native vegetation or use of Managed Aquifer Recharge (MAR) techniques. These are generalities. Each groundwater system is unique in its own way, and specific recommendations should be designed for each individual system.
How do you institutionalize groundwater monitoring to ensure that data are used, and the right conclusions are drawn for groundwater/water management? Which local institutions have the expertise/capability to develop water management plans based on monitoring results? Do you have a best practice/example?
This is an excellent question, but there is no easy answer. Developed and many developing countries have groundwater monitoring networks (https://www.un-igrac.org/stories/national-groundwater-monitoring-programmes). For many studies, data from these monitoring networks can be quite useful. But if there are only a small number of observation points in the network, the data may not be useful for local studies. Most countries have regulations governing groundwater use, but regulations are not always enforced. In some areas, groups of water users have come together voluntarily to support groundwater monitoring programs, with the realization that they all have a common interest in preserving their groundwater resources.
Solar Powered Groundwater (SPGW) Systems offer the possibility of affordable, remote collection of groundwater level and pumping rate data. The sensors and transmitters required for this data collection are embedded in these systems, and they are used to monitor and control system operation. Continued data collection after installation of a system comes with a relatively low cost. But this cost is offset by the savings realized by not having to make manual measurement of water levels. A single repository, such as an open access website, for the groundwater level and water quality data is highly desirable. The Global Water Center (https://globalwatercenter.org) is one place that could host this repository.
Groundwater management plans are generally developed by private groundwater specialists or consultants, in both developed and developing countries.
As an example, an organization of potato farmers in the Sandveld region of the Western Cape of South Africa have voluntarily come together and hired a private consultant to measure groundwater levels and determine several water quality parameters at about 50 observation wells on an annual basis. This is an arid to semi-arid region in which agriculture relies on irrigation from groundwater. The consultant prepares a report that contains all the data; if groundwater levels are declining in some areas recommendations may be presented on how pumping rates might be modified to avoid aquifer depletion. Decisions on adjustment of pumping rates are made by the individual farmers. This voluntary operation has been ongoing for almost two decades. Similar operations are common in developed countries.
Can you discuss the natural draining of the water levels by Karst and other means. That includes draining by earthquake etc.
Groundwater naturally drains to springs, wetlands, streams, and other surface water systems. Groundwater flow in karst regions (such as those composed of limestones and dolomites) usually occurs in large openings (such as caves) that have developed over long periodsof time through the process of dissolution. These openings can rapidly transmit large amounts of water. Large springs are a common feature in karst regions.
Human activities and natural events can alter patterns of groundwater drainage (discharge). Increased pumping of groundwater can lead to decreases in groundwater discharge. Increases or decreases in precipitation will likely be reflected in similar patterns of natural groundwater discharge. Rare events, such as earthquakes or volcanic activity, can have substantial impacts on natural discharge patterns, but these impacts are difficult to predict; there are very few data available for these events, and the impacts can vary in different areas.
Questions to Alberto
Using the LCCA is great for comparing between the generator, hybrid and solar systems. But how can you use it to calculate what potential user fees would be to cover costs for the system? Given that it uses present worth as its basis rather than looking at inflation, I know that this has caused some confusion when looking at what real-time costs will need to be paid.
Usually, the exact cost of equipment, maintenance and repair costs are lucking in developing country so how you exactly calculated LCC or you take the estimate.
We were able to find national based contractors supplying good quality solar equipment and pumps in every country we visited (including places like South Sudan or Somalia). We got the prices from these contractors and from the organizations working in the area (NGOs and the like); so the capital costs of equipment we used for the economic analysis were based in real prices of products in the country. For maintenance and repair, we based our calculation in conservative estimations provided by manufacturers (you can find those within the Cost analysis tool at https://thesolarhub.org/resources/cost-analysis-generator-vs-solar/
How do we integrate financing of Solar powered water systems especially to Sub- Saharan African Countries?
That is a good question with a difficult answer. We have come across different financing depending on context and other variables: basically either a donor provide full capital costs and users/owners of the system take care of O&M or the capital costs are offered to a subsidized costs to the users. When solar pumping is meant for productive activities (eg irrigation) farmers might have the option to pay after the harvest or in small monthly or quarterly payments. In some facilities, it exists the option of paying for water as a service (rather than paying for the solar equipment, with a private contractor paying and maintaining the equipment and collecting the fees). In theory and looking at the comparison in costs of a generator based water scheme vs solar, it would be many times wise that community of users save and pay for a solar system but in reality this is hard to find in low income countries.
What is the life time for solar pump system invertor?
It depends on the quality of the invertor. A good quality one design and manufactured for solar pumping applications (eg Grundfos, Lorentz, Franklin etc) might last 6 to 7 years if well maintained, according to manufacturers.
Yes, we will post them in www.thesolarweb.org
Did you consider the maintenance cost of systems knowing that in remote areas people do not have the skills? How do you manage that because it could help to increase the lifespan of systems and empower local communities especially youth?
There are different kind of maintenance that a solar water pumping system requires. The routine maintenance (eg cleaning the panels regularly and others) can be easily done by the users if briefly trained cause it needs little skills. Other more specialized maintenance (preventive and repairs) have to be done by specialized technicians as it requires skills that can not be provided with a short training to community members without proper and solid technical background. Having those technicians (normally based at capital level) have a cost that we did estimate and include in the cost analysis.
When it comes to the maintenance of a generator, we based our calculation in conservative estimations provided by manufacturers (you can find those within the Cost analysis tool at https://thesolarhub.org/resources/cost-analysis-generator-vs-solar/
You can find more on maintenance in chapter 11 or this book at https://thesolarhub.org/resources/solar-pumping-for-water-supply-harnessing-the-power-of-the-sun/
What the justification on the difference on the break even period for different countries? why is just 1 year in Uganda and 5.1 years in Iraq?
These analysis depend on the size of systems, the number of pumping hours and the like and not all systems analyzed in different countries were of the same size. You can find those details in our country visit reports at https://thesolarhub.org/category/case-study/
The case of Iraq (the largest breakdown of those shown in the webinar) is largely influenced by the fact that the price of diesel is one of the lowest in the world and grid access was present in some locations, a big difference with Uganda (expensive diesel and off grid areas).
Is drilling of borehole included in the calculation?
Economic analysis were made with the aim to compare technology costs (solar vs diesel) rather than having total costs. That’s why in order to simplify the analysis, we decided to eliminate all the costs that were common for both technologies. The cost of drilling a borehole will be the same, whether we install a generator or a solar system to power the pump, and therefore won’t have influence in the comparisons of both technologies. All the common costs (fencing of water point, salary of operator etc) were eliminated for the same reason.
Why did you choose a solar stand alone and not a hybrid system solar with grid?
I’m not sure to which case you are referring to. Most of our visits happened in off-grid areas, so a hybrid solar-grid configuration was simply not an option. In grid covered areas, you could certainly connect the grid in addition to solar to give more security to the system although this would increase the cost of the installation.