Can I Use A Solar Pump In My Garden?

If you’ve got a green thumb or just generally enjoy growing fruits and veggies, you know how expensive electricity can get for water pumping. Food crops need a lot of water, and the idea of an off-grid watering system can be enticing for multiple reasons. But are the savings in electricity worth the extra cost? What about quality issues? Let’s work through some of the questions folks may have about solar pumps when it comes to irrigation, as well as some case studies that explore how our technicians would work with each client calling in to come up with a solution unique to their watering goals.

Gardens cover a whole range of agricultural systems, but in general are a step below larger farming operations in terms of size. Water sources come from places as diverse as wells, creeks, ponds or even rain-harvesting systems, and output into a variety of sprinkler types, meaning that there is a larger variety of pump models that are applicable depending on the situation. Many of our gardening customers end up buying our smaller RPS 200 model, which handles between 2-5 GPM with ease (dependent on lift / PSI metrics). Other customers need larger pumps doing 20+ GPM, whereas professional farmers often buy 3 or 5 HP pumps from us that can handle 100’s of GPM. 

While it makes sense to buy a quality pump for larger farms, one of the common questions we get from hobbyists or smaller scale folk is if they’re better off just buying a smaller plastic solar pump from Amazon. Amazon solar pumps are incredibly cheap, and so are enticing to someone who’s looking to save money. However, these pumps aren’t meant to last longer than six months – or a year or two at the very longest. We have plenty of customers who after pumping through two or three amazon pumps finally buy from us, and wish they had just bought something higher quality at the beginning. For customers concerned about pricing, we offer refurbished models and financing to lessen any financial worries. Combine that with our stellar customer service and reviews, and we believe over the long haul you’d be saving money compared to buying something cheaper and lower quality. 

With all that being said, the easiest way to think through whether an RPS solar pump is a right pick for you is through some example pump sizings. The following case studies represent real problems we get all the time, maybe one of these is similar to yours!  

Example 1: Daryl is harvesting rainwater into a 250 gallon tank, outputting to 8 25’x3’ raised beds with drip irrigation. He has a total of 400’ of drip line, set at 0.5 GPM per 100’. What is his best option to save money, while getting at least 20 PSI to his garden beds?

From this example we know that Daryl’s primary goal is to stick to a budget. In cases like this, we will normally just stick with the previously mentioned RPS 200 pump (as opposed to our smallest transfer pump, the T400), since it is our cheapest model. Some folks in these situations would prefer a transfer pump over a submersible, but we’ve found that just placing the submersible pump within a storage tank works really well, as long as the pump is fully submerged in water. At 20PSI pumping, assuming no changes in lift between the rainwater harvester and drip lines, the RPS 200 will do about 4.5 GPM, which just means that you’d need to choke back the power on our universal controller to match the 2 GPM required for the watering system. 

While this is a bit of an oversize for the system, if Daryl ever wants to add raised beds or water a larger area, he wouldn’t be constrained by his water pump. We would just recommend adding a pressure switch and check valve to the system, as well as a timer that pairs with the RPS 200, so that Daryl doesn’t need to manually turn the pump on and off to water his garden. A pressure switch ensures that the pump never runs when any valves are closed, which would negatively affect the pump lifespan. 

Example 2: Richard is a huge fan of Curtis Stone and is planning a market garden in both his front and back yards, for a total of a half acre. He wants to pump out of a nearby creek on his property 80’ lower in elevation. He will plant ¼ acre as almonds and ¼ acre as mixed row crops. What sort of pump would be best for him?

We first need to start by calculating out water needs for Richard’s garden. If we follow a once every two days watering schedule for example, one day can be set aside for the almonds and one day can be set aside for the mixed row crops. In general, a ¼ acre of young trees at 50% cover needs about 1,000 gallons of water on a hot day, and almonds are particularly water thirsty, so if we’re watering every two days let’s assume 3,000 gallons pumped in one day. The mixed row crops will need a similar amount of water or a little less. While Richard hasn’t determined what sprinklers he wants to use, drip irrigation is going to generally be the most common setup used here. 

So the goal is to recommend a pump that in a six hour solar day (which is a conservative estimate for pumping time) can pump 3,000 gallons of water up 80’ into 20 PSI drip irrigation. That calculates to a total head of about 125’ at 8.5 GPM. Since there is a substantial amount of vertical lift to be overcome, we would again recommend a submersible pump, our RPS 800V. At 125’ this pump does 10 GPM, so again we’ve met our watering needs and allowed for some wiggle room in case there’s ever expansion. The pump will need to be floated in the creek, which customers often do with some floats attached to perforated PVC and tied down with safety rope. The submersible pump is then placed inside the perforated PVC. 

Example 3: Jennie has a 5 acre property, with a max elevation change of 75’. Her irrigation well has a 35 GPM capacity at a 50’ depth, and hits water at 20’. She has 2 acres of fruit trees, and ½ acre of mixed landscape plants all on drip tape. She’d like to run her irrigation with multiple valves, but needs some help figuring out what her best option is. What sort of pump would we recommend?

2.5 total acres are needing to be pumped, so at first thought let’s split that into 5 watering zones. Again, watering schedules are highly variable, but in order to minimize costs lets consider watering each zone every day for an hour. Fruit trees on a hot day will need about 2,000-2,500 gallons per day per ½ acre, and landscape plants will need significantly less than that. So if we assume that each zone needs a max of 2,500 gallons, we need a pump that can do about 40 GPM over 5 hours. That’s on the higher side, and outpaces Jennie’s well, so we should look for another option. In this scenario, there’s one zone that will need significantly less water, so there’s an opportunity to lower GPM requirements overall. We’d want to ask Jennie if it would be possible to match up the fruit trees with any nearby landscape plants, so that instead of five zones there are four. Each of those four zones could then be watered for 90 minutes instead of 60, with the landscape plants needing just a couple hundred gallons extra per zone. So let’s assume instead of 2,500 gallons for 1 hour we need 2,700 gallons for 90 minutes, which evens out to 30 GPM. Again, these are just estimates, but this is an example of how adjusting zones can lead to savings. 

At the end, we are looking for a 30 GPM pump that can do a max 95’ of lift + 20 PSI of pressure. The best option is our 25RPS15, a 1.5 HP pump that is within the pump curve for those values. This is a custom pump end option, it is equivalent in pricing to our PRO 1500M pump, but we’d get Jennie a slightly different pump end compared to the standard 1500M pump. We’d recommend a PRO timer for this install as well as a pressure assembly system, so that Jennie can program multiple watering schedules to further experiment or change up watering times throughout the year.  

Again, watering schedules are highly dependent on time of the year, type and age of what you’re irrigating. In general, we will always oversize just a little bit, since that leaves room for irrigation additions, and we’d much rather that than needing to upgrade the pump after a couple months of insufficient watering.

If you have any questions about our pump workmanship, how solar works, or if there are any government incentives for solar, please call us up at 888-637-4493 or email us at [email protected]. We love projects with multiple moving parts, so if that’s you, we’d be happy to chat through our systems. We hope to hear from you soon, but until then have a great day!