Hi Jeff,

Must say I enjoy your website and value the information given.

I am trying to build an energy efficient house – too far away to get a grid connection. I am trying to find out what pump to buy for my system. Our appliances run on 240V – 50 hz

I have a 24V battery system with a whisper H100, 10 solar panels and 6 X 4V batteries and an inverter. I collect rain water (ok – in New Zealand) and it drains to a couple of tanks that are about 40 ft below the house level and 240 ft distant.

Our plumber has insisted to go with a mains pressure system so that we have good showers (no bath due to not sufficient rain for these) and so I have purchased the correct shower heads. Given that I cannot change this part of the system what sort of pump do I go with?

1. A DC pump with a reservoir so that once the pump is on it pumps up to a certain pressure – turns off and then only comes on again once a minimum pressure is detected? (Would I observe surging in the shower if this was the case?)

2. A DC pump with no reservoir that would come on every time a tap was turned on – in this household it would be 80 to 100 times a day?

3. If a DC pump is recommended could you indicate a model or give some indication as to what I should ask for? How should this be connected to the system? Direct to the batteries?

4. An AC pump + reservoir?

5. An AC pump with no reservoir?

Thanks for your time.

Regards

Louise Coats

Louise:

A standard well pump will kill your small solar power system and really small battery bank. Check out what I designed for another off grid family with limited solar due to mountains blocking most of the southern sky.

You should use a small 24 VDC solar Jack pump down in the lower cistern, which draws very little power since it pumps very slowly and is only filling a storage tank inside your house. This holding tank has a second 24 VDC pump but this one is a pressure pump and will pressurize your homes piping system just like a standard pumping system on the grid. Note that we have a sand filter on the line entering the holding tank, and an ultra-violet light filter and carbon filter on the pressurized line leaving the holding tank. This allowed drinking the water as it was tested as being free of all bacteria and other bad things even though the water source was a nearby river.

Good Luck,

Jeff Yago

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Hi Jeff,

Steve:

The short answer is yes, the long answer is this may be more trouble than its worth. Your state has had a net metering law since 1999, so it is legal for a homeowner in Montana to sell back to the utility. However, each state has allowed the local utility to set up specific requirements that must be met to ensure the safety of their service people and the quality of the power for the other customers.

Normally, in most states these requirements include filing a form with the local utility that describes the system, the installed hardware, indication that this equipment meets grid-interaction safety requirements (usually listed on nameplate), and the wiring into the electrical system was completed by a licensed electrician who also signs the form. Some states also add the requirement for an exterior dis-connect with a lever handle that can be locked-out by their service people. Again, these requirements vary from state to state, and you can contact your local utility for more information.

However, it does not matter that the source of the power that will be “back-fed” into the utility line is coming from a portable trailer, you will still need to meet most if not all of the states requirements just as if the solar system was mounted on the roof of your home. THey may omit the dis-conect at the meter since you or they could “un-plug” the trailer from the house, but I am betting this will be too complex a decision to make for the non-technical person you will most likely be dealing with and they will still insist on meeting all of their requirements.

Keep in mind that many inverters will meet the requirements for grid-interconnect and can easily be switched manually over to the “sell” mode. However, your trailer will most likely only have an “input” cable to allow charging the batteries from the house or a generator, so your trailer will need a second cable to connect its output to the house and this should NOT be a standard “male” plug with exposed pins since these exposed pins will be HOT at 120 or 240 VAC, depending on the model inverter you install.

If you want to stay “legal” but not go through all the hoops, why not just run a heavy extension chord from your solar trailer into your home and plug in a few appliances like a freezer or other load that closely matches the output of your trailer. This will remove this load from your utility bill, yet keep your trailer wiring from connecting into the other house wiring.

Hope this helps and good luck!

Jeff Yago

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