Engineering can become complex very quickly.  Fortunately, on a small scale, solar power is easy to understand and design, and is applicable for anyone with basic electrical knowledge or a willingness to learn.  Solar water pumping’s main components include a pump to move the water, solar panels to power the pump, and a controller/inverter to interact between the two.  For a smaller project, DC voltage from the solar panels power a DC pump with a basic DC-to-DC controller monitoring voltage and providing on/off switching capability.

On larger, community-scale projects, where more water pumping capacity is necessary, the main components are the same but the interactions are slightly different.  In these circumstances, a larger, three phase AC pump is powered by a large solar array, with a DC-to-AC inverter acting as the controller.  This controller has more functionality including DC-to-AC conversion, variable speed control, etc.  This leads to higher efficiencies in solar harvest – high voltage AC power which can be ran longer distances – and the utilization of high power AC pump which are readily available and lower cost. In both applications, the component count is minimal.  No batteries are needed, because the solar is running the pump directly and storage of excess water occurs in the distribution tank.

One of the most elegant aspects of solar water pumping is the simplicity of the operation of these systems.  When the sun is out, the pump is running.  In the morning, as the sun is coming up and solar resource is low, the pump starts slowly, only pumping a small amount of water.  As the sun rises and peaks around noon, the pump output increases, with maximum flow rates happening at noon.  Then, as the sun sets, the pump winds down, with extra water stored in the distribution tank above the community.  Designed properly, these systems can easily pump enough water for an entire community.

Control of day-to-day system operation is automatic, requiring only regular check-ins to ensure proper operation.  These check-ins include pump operations, spring flow, capitation tank water levels, and distribution tank levels.  The inverter regulates the solar power driving the pump.  The system can be manually switched off at the inverter if the distribution tank is full before the end of the solar day.  

In the retrofit, the grid power provides the peace-of-mind of having a back-up power source.  Switching between power sources is easily and manually done with a manual transfer switch.  A generator is also an option for back-up power.  Ultimately, the community has autonomous control and responsibility for operations.  They may also make the decision, in the future, to rely solely on solar for power and disconnect entirely from the utility grid, saving even more money month-to-month.  

Finally, safeguards such as over-current protection on the DC and AC side, surge protection for lightning or grid power surges, and dry-run switches to protect the pumps from damage are used.  This will design in protections to prevent possible future issues.

The majority of maintenance involved with these systems is cleaning and sanitation.  The communities with water systems currently have a regiment of emptying, cleaning, and refilling the tanks every three months.  An electrical maintenance checklist will be an easy addition to this regular maintenance schedule.  Simple maintenance tasks include: keeping the solar panels and balance of system components clean and clear of debris, keeping vegetation clear of the solar window and clearing trees if necessary, and checking electrical connections of the solar array and mechanical connections of the racking system.

A basic understanding of the inverter functions and operations will be important for the community.  Basic training on the operation and maintenance of the inverter and other balance of system components will be provided, along with troubleshooting for future.  A System Manual will also be assembled for each system.  This will include electrical schematics of the system, along with installation and operations manuals for the various system components. 

The water distribution system for the communities is based on gravity-fed supply lines from a large storage and distribution tank situated in the hillside above the community.  This is common throughout Central America, and this set-up will not change with the addition of solar power to the pumping side of the system.  By situating the distribution tank at a higher elevation than the homes in the community, gravity is used to create water pressure instead of pressure tanks or some other mechanical means.  The distribution tank also allows for water access 24 hours a day, or as long as the tank contains water.

The distribution component of the system is the same whether the water pumping is done with solar, utility, or generator power.  With projects that are already in place (Acrasame), the distribution system will not change.  In Motuse, the local municipal engineer has been brought in to design the distribution component of the projects, as they are proficient and experienced in these tasks.  This creates an opportunity to form partnerships for future collaborations, while allowing CoCoDA to focus on other aspects of the project where additional expertise is required.

Downstream from the distribution tank, where water enters the individual homes, water meters are installed.  Each home with water service has a water meter and an account with the community Water Board.  Water consumption is measured and monthly bills are tallied accordingly.  This creates an income stream for the communities for future maintenance (pump or controller replacement, tank rebuild, etc.).

Even though the cost of solar panels has come down significantly in the past decade, solar water pumping applications still have a higher upfront cost than other options.  However, in the long term, solar is generally less expensive.  This is because solar has zero ongoing fuel costs.  Sunshine is free!  Once the infrastructure is in place, the system can operate with minimal maintenance, and the associated costs, for many years.

In addition, utility power creates a dependence of the community on the utility company, as well as a monthly electric bill.  There is the potential of significant monthly savings by implementing a solar powered pumping system.  

Solar panels are generally warrantied for 25 years, with a service life of 30 years or more, so replacement is only necessary in the case of damage.  Capitation, pumping, and distribution tanks will have similar, multi-decade lifespans.  Therefore, long term plans and savings should be put in place to address this need in the future.  Pumps and controllers have shorter usable lifespans, generally 5-10 years.  Part of the income from the monthly bills, paid by individual households, is put into a savings account so that money is on hand to replace these components at the end of their usable life.