Build Hypothesis

[DodgyJammer]

Greetings everyone, I have been devouring information on solar and have now found myself at a point where I need some sage advice on a setup.

The situation, running a 1400W pump that only needs to be on during the day. So about 8-12 hours of use.

We get an average of about 6 hours of peak sun.

I was looking at a,
2000W continues power inverter,
100A charge controller,
1 of 200Ah 12V Deep Cycle AGM battery
1 of 500W-ish solar panel

My question is would the panel provide enough charging to the battery while the pump was in use? or would it be better to get 1500W of panels to keep up with charging the battery?

The battery is essentially acting as a buffer and not so much as storage.

Trying to keep the system as small as possible.

Thanks in advance

 

[pollenface]

For starting pump motors you should consider an inverter with a surge capacity 7x greater than the rated power of the pump to handle the current inrush, hypothetically that is 9,800w for 0.2 seconds. I would look for a 5kw inverter to be safe. That said I have a KR3000, a 3kw 24v unit which will run my 1400w karcher pressure cleaner. I have another 2000w unit which will not start the 1400w karcher.

You may not get 8-12hrs of good sun in a day so I would want to oversize the PV array accordingly. Hypothetically, 16.8kwh which is 19.76kwh at the battery (divide by 0.85 for efficiency loss). My rule of thumb is to realistically expect 4-hrs of good strong sunlight so 19.76/4 is 5kw of solar.

Alternatively, you can try smaller things first and build the system up until it meets your needs, I think it's common to underestimate things to begin with, I sure did.

 

[DodgyJammer]

Thanks for the reply. I'm using mains to start to pumps off, so the initial draw isn't a problem. I was just hoping to get away with running the load all day with the 500w panel charging the battery enough to keep the system going. But I rate I'd have to scale the array to 1500W to sustain the load draw.

 

[Jordi]

Thanks for the reply. I'm using mains to start to pumps off, so the initial draw isn't a problem. I was just hoping to get away with running the load all day with the 500w panel charging the battery enough to keep the system going. But I rate I'd have to scale the array to 1500W to sustain the load draw.

8h at 1400W (11,2 kWh) require more than 1400W. Say 4 good hours of sun (max. output) and 4 medium hours (60% output) in one day; this is 6,4KWh per KW of solar panels. So 11,2/6,4 = You need 1750W. And that is an optimistic sunny day, only 8h of pumping (no 12h) and without inverter loss. So my recommendation is 2000W of panels at least.

I have a 100W panel myself and I can see how the energy I get from it is significantly lower than my initial expectation. Partly because is not a high quality panel.

 

[MichaelK]

Thanks for the reply. I'm using mains to start to pumps off, so the initial draw isn't a problem. I was just hoping to get away with running the load all day with the 500w panel charging the battery enough to keep the system going. But I rate I'd have to scale the array to 1500W to sustain the load draw.

How is that supposed to work? Unless the inverter that powers the pump is linked to your main grid power, the two sources of power will be out of phase with each other. Physically connecting an inverter to a circuit that already has current will result in spectacular fireworks.

In reality though, you should reconsider this whole idea if you already have a grid connection. You will NOT save a penny powering your pump with an off-grid solar system. It's the single most expensive way to make electricity. Grid power is by far the very cheapest source of electricity, so you are making a mistake here if the goal is saving money.

However, if you have other goals, then the situation changes. Wanting water when the grid fails is a good justification. The very first thing you should get is a clamp meter that can measure "inrush current". I have a UniT 216C. As Pollenface mentions above, the inrush startup current is far higher than the running current. For my well-pump it happens to be 38A at 240VAC as compared to 9.5A running. That's about 4 fold.

There's no way that a system as you outlined above is going to work. Let's assume your pump has the same startup inrush as mine. You'll need a 1400W X 4fold power = 5600W of power. Since you won't want to red-line your inverter and you don't want to run it past 50-75% of capacity, then what you want is a 7000W- 8000W inverter.

In the real-world, what I've found is that you really need 2X the number of panels to run the load you want. So, for a 1400W load, have at least 2800W of panels. The 500W panel you mention is far below what's actually needed.

Next is your system voltage. Not likely to work at 12V. 5600W at startup would be pulling 467A out of your battery. That just ain't gonna work! I'd suggest a 24V system as a minimum, but 48V would be better. Even 200Ah at 48V is rather light. I started out with 400Ah at 48V, which started my well-pump each and every time.

So, taking your numbers from above, here is what you actually need to make it work....

7000W continuous power 48V inverter, (make sure it has at least a 5 second 200% surge capacity)
100A charge controller,
8 of 200Ah 12V Deep Cycle AGM batteries (4S2P)
6 of 500W-ish solar panels