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

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

Note: This page is still being developed!

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?....cleaning of panels mounted on poles can be achieved by, for example, equipping the water operator with a ladder and a telescopic handle with a cloth....in 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 training...you can have a look at those at www.thesolarhub.org

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

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.

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.

He 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.