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PV Pum

On a sunny plateau outside of Santa Fe, New Mexico, sits the home of Paul Benson and Stephanie Mattes. It's a modern and amenable home, a mile from the nearest power line. Built in 1995, it incorporates a state-of-the-art photovoltaic (PV) system to power their lights, tools and appliances. But there was one missing link. When their home was built, a solar pump for their 400 foot deep well was not available at an affordable price. A conventional 1.5 HP AC pump was installed, and connected to a 6.5 KW propane-burning generator.

Above: Windy Dankoff retrofits a PV-powered water pump eliminating the need for the propane generator.

Paul and Stephanie's power system had always produced a surplus of energy. It was a shame to run their generator to pump water, when their batteries are usually 90-100% charged. And besides, they need the most water during dry sunny weather when the most solar energy is available. All they needed was the right pump.

In 1996, the right pump became available. The SunRise™ Submersible Solar Pump can handle depths to 600 feet by pumping slowly on low power. It uses 1/3 to 1/2 the energy (Watt-hours per gallon pumped) of a standard AC pump. It takes power directly from a PV array, without battery or inverter losses. Stephanie and Paul are modest water users, so there was no need to expand the size of their power system. It now handles their water supply and still produces a surplus of energy. The installation took one day, and their total cost was less than that of the AC pump and generator!

If you don't understand some of our terminology, please refer to the glossary at the end of this article.

The Power System

Paul and Stephanie's power system is typical of the mid-sized remote home PV systems being installed today. It uses 8 Solec 70 watt modules wired in seriesparallel for a 24 volt, 560 watt nominal array, mounted on a Zomeworks passive solar tracker. Energy is stored in a battery bank of 1100 Ampere-hour capacity. 115 vac power is provided by a Trace 4000 watt inverter.

Before installing the SunRise pump, Paul and Stephanie used an average of 50 Ampere-hours per day, as recorded by their Tri-Metric Ampere-hour meter. Multiplied by 24 volts, that equals 1200 Watt-hours per day of average energy consumption. After inverter and battery losses, the system yields about 3800 Watt-hours per day (summer) and 2000 (winter). Clearly they have a surplus of energy, even in the winter months.

Stephanie & Paul's PV Water Pumping System

Float Switch in Tank

Manual Switch

Float Switch in Tank

House Only Sub-Array

Manual Switch e©

24 VDC from house

To SunRise Well Pump switched 24/48 VDC

To Charge Controller in house e©

24 VDC from house

House Only Sub-Array

The Water System

Paul and Stephanie are typical residential water users, with a clothes washer, two dogs, small garden, and a few trees. Typical summertime use runs around 150 gallons per day, dropping to 75 gallons per day in winter. To make their generator-pump system practical, they have a 1500 gallon storage tank, so they only had to run the generator once a week. Their tank holds about ten days of water supply, to carry them through prolonged cloudy weather with a good reserve. The tank is buried, level with the house. A 24 VDC Flowlight Booster Pump supplies water pressure to the house, just like in town.

The well is 400 feet deep, with a static water level at 165 feet. When drilled, it was tested and found to produce 18 gallons per minute. Figuring that the level will not draw down very far, we placed the SunRise pump at 250 feet. Since the SunRise pumps slowly and can tolerate running dry, there is no point in placing it all the way at the bottom of the well as is usually done with conventional AC pumps. At 250 feet, the SunRise produces 2.5 gallons per minute (drawing 230 watts). On an average solar day of six peak-hours, it will produce 900 gallons. This is eight times their average daily usage. So, the pump will only run about 1/8 of the solar day while using just 1/2 of their PV array. They won't even notice the reduction in home energy input.

48 Volts from a 24 Volt Array

The SunRise requires a 48 V solar array, and the DC voltage of their home power system is 24 V. We reconciled the difference easily. When power transfers

To SunRise Well Pump switched 24/48 VDC

To Charge Controller in house to the pump, it is reconfigured to 48 V within the pump controller. The transfer of solar power is triggered automatically by a float switch in the storage tank. When the tank level drops below full, power is transferred to the pump. When the tank is full, it is switched back to the home system without any human attention.

Why a 48 Volt Pump?

A 48 Volt standard was chosen by the SunRise pump manufacturer to accommodate the long lengths of wire required for deep well settings. The wire size requirement is drastically reduced by raising the system voltage. If the SunRise had been designed for 24 V, it would have required four times the wire size in order to maintain a low level of power loss! The electrical cable would cost much more, and the added weight of copper would make it impractical to install by hand.

More About the SunRise Pump

SunRise uses a unique "sealed piston" mechanism. It pumps more slowly than conventional centrifugal-impeller well pumps, but uses much less power. In typical full-time use, it will need minor parts replaced at 5-8 year intervals. Because the Stephanie and Paul will only pump 1/8 of the solar day, they will earn a lot of gray hair before they need to maintain their pump.

There are three models of SunRise pumps. They all use the same 1/3 HP motor, but have different piston stroke lengths to handle different ranges of vertical lift. Paul and Stephanie obtained the intermediate model 5226. They also got the electronic controller that is

A Typical Water System

Cable to Pump Controller

Pivot Weight Float Switch

Well Cap

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