Solar Powered Water Systems in Humanitarian Context III - Q&A

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This page documents the questions that were asked during the webinar: Solar Powered Water Systems in Humanitarian Context

Overview Questions

How best can you clean the panels when the pole mounts are high? What is the recommended height for the pole mounts for the solar panels?

The height depends on what you are trying to achieve, is it a flood-prone area? is it to discourage theft? of panels mounted on poles can be achieved by, for example, equipping the water operator with a ladder and a telescopic handle with a other places we have seen a holed pipe going along the top of the panels and having water flowed every now and then might be an option.

How long can the solar system battery serve or no need to have batter for tropical regions like Ethiopia?

Better to design your system so that batteries are no needed

Did you ever take a regeneration of power by using the downstream pressure just with the same pump? so that the pump would work as a generator turbine?

No, never.

How much its cost solar water project per watt?

Depends on a number of factors, the country where you are based, the quality of products used, the size of the system.

Which kind of solar inverter brand do you prefer?

More than brands we like to see at manufacturing certifications. The control equipment must meet EN 61800-1, EN 61800-3, EN 60204-1 or internationally recognised equivalent standards.

Would an inline chlorinator be an appropriate way of dosing the chemical in a solar set up

Yes, if the injection is proportional to the water flow

How to anticipate best the local conditions of irradiance (especially in emergencies)?

There are databases (NASA, EU, others) with historical data for long years that are used for that.

Which pumps are better suited for solar pumping? AC or Brushless DC pumps in terms of performance & costs?

If both options are possible, DC normally will have a longer lifespan, higher efficiencies and won't need DC/AC invertors, so will reducing the likelihood of problems since electronics is normally weaker than mechanics.

How can one design solar water pumping systems in a location without digging a well? Is there a way to determine if there is an aquifer underneath in a location without digging?

you will need to look for some hydrogeological data of the area, and have a look at nearby existing water points...normally that information exists already for many countries and areas

In this series, are we going to get any training on how to design solar water pumping systems to address the challenge of lack of technical knowledge?

There are already some options for can have a look at those at

Do the storage guidelines also apply to solar pumping for agricultural irrigation?

That will depend on the specific needs of the project and the capacity of the water, you will need to make the numbers for your specific project

When the pipe line breaks from the well to the tank.  Either by vandalism or water hammer, or age/light damage, etc. if the pump doesn't switch off it will cause cavitation of the aquifer and likely burn out the pump.

If the pipeline is broken, the water will flow out through the break...I'm not sure I understand what you mean

How do you keep chlorine dosing proportional to varying water flow from solar pumps with a by-pass connection (chlorine tablets, water driven dosing pumps)?

Normally through experience, your operators will end up knowing how much your valves have to be open or close to achieving the desired values, for different times of the day and weather conditions...of course, regular water chlorine monitoring is advised

Questions to Jared

What would you advise that the volume of storage tank be, is it 50% of daily demand or more?

Based on the literature review and personal design experience, I would recommend that a storage volume equal to 100% of the average daily demand be provided in the absence of a detailed hourly water balance analysis. A volume as low as 50% of the average daily demand may suffice but would need to be demonstrated with a detailed hourly water balance analysis.

Why chlorination but no modern and less dangerous technologies to purify water? Especially from boreholes with expected low turbidity? Chlorine is pretty dangerous stuff and the supply change is another hazard as well as special requirements to the equipment. Why not Ultra-Filtration or UV-C treatment?

In many (if not most) remote applications, it is advisable to use simple and robust technologies that are easy to operate and maintain. Tablet and flow-activated chlorinators provide this level of functionality for low-turbidity groundwater, where ultrafiltration (UF) and UV disinfection are more sophisticated treatment technologies with higher capital costs and much more significant operational costs and maintenance burdens. In particular, UF and UV are energy-intensive, which in this context would require large solar arrays or standby power facilities.

Chlorine disinfection produces a chlorine residual in the finished water which protects against biological contamination into the distribution system, where UF and UV do not.

Calcium hypochlorite in granular and tablet form is widely available and has a long shelf life. There are safety concerns with handling chlorine, but safety protocols exist and many organizations around the world use chlorine for water treatment safely and effectively. The key to a successful installation, as with any other technology, is the proper training of operators.

Could the presenter add some more notes specifically on how to calculate daily hourly demand when planning Storage Tank sizing?

There are general diurnal demand curves that have been proposed by various NGOs and government agencies, but a detailed survey of the community to be served is the best means of obtaining this information. Typical water usage and collection times (by family unit) can be used to construct a typical diurnal demand curve.

Is there a way to relate the need for water storage to the probability of a low irradiation event of a number of days? I mean, in the lowest irradiation month, taking the average irradiation implies accepting water shortage during a number of days, isn't it?

It will often prove overly conservative or cost-prohibitive to design for the minimum 2-week (4th percentile), minimum week (2nd percentile), or minimum day (0.3 percentile) condition.

Moreover, these low-irradiation conditions often coincide with the rainy season, when demand may be reduced as alternative sources of water are available, especially for non-potable uses.

Finally, typical monthly irradiance data is more widely available than TMY data that could be screened to identify the design conditions listed above. If this level of analysis is desired, the NREL SAM model (among other PV modeling software programs) could be used.

What is the software that he is using for water storage tank sizing?

Normally you can just use Excel to plot the data and have those graphs.

Questions to Brian

What kind of dataloggers they have used for the water tanks: Depth data loggers or Flowrate data loggers?

(Depth) Rugged Troll 100 (  The flowrate to tap stands was calculated from knowing the change in tank storage and the pump output/tank inflow (from pulse water meter connected to the Lorentz pump controller)

When the system was not interrupted by the operator, there was good performance wondering why it didn't indicate periods when the clouds are covered, and the irradiance is zero especially at night?

The issue was that the manual logbook that the operator kept did not capture in the same level of detail and accuracy all actions s/he took or the prevailing weather conditions.  The operator might be tempted to record that the pump was switched on at the start of shift, rather than acknowledge it was later because he was late to work for example.  The pump controller records Q and a whole host of other datasets including irradiation and when the pump stops and starts, and it was often only by studying these that we got an accurate understanding of what was happening.  [One factor that I didn’t talk about was the impact of the pressure switch in some storage tanks (where tank is distant from pump and a wired float switch is not practical).  When the tank is full the pressure switch should cause the pump to stop but because it wasn’t properly calibrated some pumps kept operating against a high head, but with low output.  The pump was running for 10 hours continuously but it wasn’t clear why the flow rate was so low during some peak sunlight conditions until we checked the pump scanner data and fully understood the configuration at the tank

What is the availability of spare parts in Cox Bazaar (or in Bangladesh as a whole) for PV pumping systems to keep running satisfactorily?

Spare parts for solar pumping systems are widely available and there is a well developed private sector able to design, implement and provide after-sales service and maintenance support. Bangladesh actually manufactures high-quality PVs (RahimaFrooz)

Where was the source of those percentage figures of power loss due to shading? some literature or as part of the study conducted in Cox.

I copied the image with percentage losses related to shading from a powerpoint presentation given by the Global Solar Water Initiative, 3 years ago - I don’t know their source.This short video is interesting in demonstrating the impact of shading.

Can the presenter shed some more light on his finding that "investment in generators was not justifiable" because there is this general understanding that back-up generators are there to "back" up solar power during rainy seasons OR to pump more water at night when solars are not operating?

The conclusion that they are not justified in Cox’s Bazar context was based on our observations that they were largely idle, and not being used as intended back-up, so essentially a wasted investment. The planning/design justification was that to guarantee 20 litres of potable water per person, 365 days in the year, back-up generators are required (and I would agree with the underlying logic).However the reality is different partly due to the context of Kutapalong where there are so many shallow wells/handpumps that people are happy to use.It echoes findings from webinar 1 (Adrian Honey – Lorentz) who indicated similar experience with generators elsewhere and that there are other ways to improve reliability (e.g. increase storage capacity and/or increase # of PVs to improve reliability in cloudy conditions. The generator manages risk – if you must have 100% reliability and solar can’t provide that a back-up power source is required, but then you also need to be testing, servicing and maintaining that equipment on a weekly basis.The risk of people not getting 20 litres of water from a tapstand in Kutapalong was low because if they didn’t, they would happy go to a handpump 50 metres away.

Is the pumping system in the camp also connected to the local grid, or is this an emergency supply? Or does the system rely solely on PV?

All solar systems are off grid, so solely PV, but some have the option to be connected to a diesel generator.

In Cox's Bazaar, to what extent were the safe yield / hydrogeological considerations factored into the design?

The WASH sector is closely monitoring groundwater levels and this is feeding into groundwater modelling looking at the long term impact of large scale abstraction.To date there has been a 5 metre drop in water levels since before the start of the crisis but it is predicted that the water level will stabilize, reach a new equilibrium in future years and is sustainable.I did question how organisations were estimating safe yields as it is very different to my experience elsewhere (which is based on a percentage of an extended constant rate test yield (e.g. 70%) assuming water level in borehole stabilises).In Bangladesh they were extrapolating safe yields at higher rates that the borehole had been pumped from short duration, limited stress test pumping, plotting discharge vs drawdown, calculating well efficiency.

You mentioned that the actual Q of the borehole was less than expected ( 128 me expected and the actual was 60 for some cases) .. what is the reason for this change?

Actual Q was often significantly less than design Q for a range of factors both supply and demand side including

i) demand doesn’t require pump to operate to full capacity

ii) shading

iii) Operational issues including inefficiencies due to operators error and limiting tapstand opening hours which forced people to take water from handpumps.

Is there any effect on the distance between the borehole and the location of the solar panels in terms of energy losses etc?

Yes, and to minimise this (and reduce cost of cabling) it is good to minimise the distance between solar array and pump.The international standard is to try to not exceed 3% voltage drop due to wiring but this may be exceeded if necessary for siting PV in a secure location or away from obstructions. See section 4.3 – Solar Pumping for water supply for more details.  

How does the GLOWSI solar manual arrive at a tank size of 1 to 3 times daily demand?

As said in the manual, that is a quick approximation when for some reason, you can not do a proper analysis of water pumped vs demand to size the tank...the data of 1 day comes from field assessments showing that the great majority of systems retrofitted from diesel to solar with tanks of less than 1 day of water demand volume faced overflow problems. The limit of 3 days is given with the risk of having too low chlorine concentrations for water stored for longer than that period of time.

How about opinions in regard to charging some money for received water?

Please see the webinar recording.

How was the number of taps/person determined in such a large camp? I imagine the population density and terrain makes things very difficult with queuing.

Please see the webinar recording.

You referenced 20 litres per person per day.... could you comment on whether sphere standards or other country standards are in mind?

20lpd is the UNHCR standard for refugee locations, which is normally the reference taken for those contexts...this can be increased depending on the context.

Could you please share the standard and references for minimum water consumption per day per for shelter and community? Page 105

Did enough information come out of the study to inform on things like optimal tank size, water demand etc. for use in other contexts?

No this wasn’t the primary aim of the study.In terms of tank size, I would agree with the first presenter (1 day storage capacity as rule of thumb is desirable) although in Kutapalong due to congestion this wasn’t always possible.In terms of water demand it perhaps would have been helpful to have undertaken more community consultation at the design stage to understand people’s habits.This might have confirmed that chlorinated tapstand water from the solar networks didn’t need to provide 100% of the water as people were happy to continue to using handpumps.I would always be cautious about applying information from one context to make assumptions about another context without first understanding the behaviour, needs and engaging/involving affected population and being informed by them.

Questions to Antonio

In the last picture, it seems like this is the South Sudan national standard design (I've seen similar from our WASH interventions ins SSD). The solar panels are laid flat, not tilted. What is the reason for this? I thought that it should be at a minimum be tilted 15 degrees?

The panels are effectively tilted at 25°, it is just a matter of the perspective of the photograph, which was taken from below. The tilt angle is always considered in the design and varies depending on the location of the installation, particularly on its latitude.

How realistic is it to have all required skills and capacities in-house (for INGO's)? I.e., geo-hydrologists, electrical engineering, contract managers etc. etc.... If not realistic (in my opinion) what do you recommend? How/where to find/contract this capacity? Esp. in humanitarian contexts (i.e., places like South Sudan).

The level of expertise in -house should be adequate to be able to recognize the gaps in knowledge and take action to address those. The latter can be actioned by reaching out to rosters and standby agencies for specialized personnel, through collaboration agreements with other NGOs, engaging with consultants and private sector consultancy firms.

I understand that the solar-powered pumping water supply infrastructure is recommended all over the world, but we have difficulty maintaining this infrastructure after the hand-over to the community or local authority... Investment is quite big and each material is very expensive, so if something happened to the materials, how can a community or local authority manage...?

There should be substantial work with the local authorities and communities to prevent that such situation happens in the first place. Equipping them with the structures to manage and protect the facilities and empowering ownership and accountability from within.

Rate of return on investment - when compared with fuel run generators, solar is always attractive. However, if there is a fairly reliable electricity source, the rate of return is not attractive. On the other hand, the use of solar power is more environmentally friendly. How we can make it easy to understand for decision-makers that using solar power even when electricity is available? This is especially for development setting

In principle, we should always explore and advocate for the use of clean energy in our interventions. Environmental responsibility should be an imperative driving our decision making. The return of investment when electricity connection is available may not be as attractive if compared with diesel generators in hard to reach areas, but it is still at reach and a determinant in decision making and should be considered in long-term sustainability analysis.