Solar dump load for small system?

[Marketermac]

I'm working on setting up a solar powered chicken coop. The system will only be used for lights and a small 12v pump. I was thinking that I might oversize it and use the excess production to run a dc water heating element, however the only controllers I have found that offer a dump load feature are mppt and very expensive. I'm looking at a small 2-300w system, spending hundreds on a controller just doesn't make sense to me.

The water heater is only to keep the water from freezing, I don't need to make hot water. Any ideas on an inexpensive way to accomplish this?

[solar pete]

Howdy Marketermac and welcome to Solar Panel Talk. As with anything off-grid its impossible to design a system until your daily load is calculated, in other words how many watts will the lights draw and for how many hours a day? Same for the pump, until we know that NO ONE can help you. Re the dump idea I think if your thinking a few hundred dollars for a controller dont make sence the dump idea makes even less sence to me, you need to do some reading in the off grid stickies section, good luck and keep reading, cheers.

[Marketermac]

Thanks for the quick reply Pete.

My system will use 400w @12v per 24 hour period, I planned on 2x 200ah 6v golf cart batteries for storage, but have no need of all the electricity 200w of panels would produce in northern Pennsylvania. My only motivation for excess energy production is to prevent water from freezing.

I suppose a simpler way to pose my question would be is there an inexpensive way to store excess energy production as hot water while making sure my batteries stay topped off?

[SunEagle]

Thanks for the quick reply Pete.

My system will use 400w @12v per 24 hour period, I planned on 2x 200ah 6v golf cart batteries for storage, but have no need of all the electricity 200w of panels would produce in northern Pennsylvania. My only motivation for excess energy production is to prevent water from freezing.

I suppose a simpler way to pose my question would be is there an inexpensive way to store excess energy production as hot water while making sure my batteries stay topped off?

I think you will find that 200 watt is not enough to keep a 12v 200Ah battery system charged let alone have enough left over to dump into a water tank.

You need about 20amp of charging which calculates to about 240 watts with an MPPT charge controller with no losses or about 400 watts with a PWM CC.

So what type of panels and charge controller do you have?

Also I presume you mean you will be using 400 "watt hours" in a 24 hour period and not 400 watt for the entire 24 hours. Your battery system is big enough for 400wh but not for 9600wh.

[Wy_White_Wolf]

Zantrex C35 charge controller can be used as a dump load controller.

WWW

[Marketermac]

Correct, 400 watt hours, not 400 per hour. This number has about 20% padding to account for my worst case. The pump utilizes 11w and during the winter I intended to use it continuously to help prevent freezing. The lights use 15w and would be run 4 hours per day during winter.

I do not have any equipment yet, I have only planned my purchase. Sounds like I'm missing something with the 200w panel sizing and charging my batteries, I assumed these panels would produce 600w + per day to make up for my usage and then some. Seems like I might need more panels.

[Marketermac]

Zantrex C35 charge controller can be used as a dump load controller.

WWW

That's more in my price range! Thank you for the excellent suggestion.

[SunEagle]

Correct, 400 watt hours, not 400 per hour. This number has about 20% padding to account for my worst case. The pump utilizes 11w and during the winter I intended to use it continuously to help prevent freezing. The lights use 15w and would be run 4 hours per day during winter.

I do not have any equipment yet, I have only planned my purchase. Sounds like I'm missing something with the 200w panel sizing and charging my batteries, I assumed these panels would produce 600w + per day to make up for my usage and then some. Seems like I might need more panels.

Unfortunately it is not just the amount of watt hours the panels can produce but the charging amps that get back into the batteries. That is usually managed by the type of charge controller you get.

For FLA type batteries the charging rates usually fall between C/8 and C/12 where C = the Ah of the battery system. C/10 is the sweet spot so for a 200Ah that comes to 20 amps. Too much and you will dry out the battery. Too little and they will sulfate the plates.

[Marketermac]

Unfortunately it is not just the amount of watt hours the panels can produce but the charging amps that get back into the batteries. That is usually managed by the type of charge controller you get.

For FLA type batteries the charging rates usually fall between C/8 and C/12 where C = the Ah of the battery system. C/10 is the sweet spot so for a 200Ah that comes to 20 amps. Too much and you will dry out the battery. Too little and they will sulfate the plates.

Thank you, you've been exceptionally helpful.

So if I move up to a 300w system, and move up to an mppt (Assuming one can be found in my budget that allows load diversion) I should be able to accomplish at least some water heating ability? I started this hoping to spend around $500, looks like it will be closer to $1000 when it's all said and done.

[SunEagle]

Thank you, you've been exceptionally helpful.

So if I move up to a 300w system, and move up to an mppt (Assuming one can be found in my budget that allows load diversion) I should be able to accomplish at least some water heating ability? I started this hoping to spend around $500, looks like it will be closer to $1000 when it's all said and done.

Your estimate is close to what a system like that costs. I spent much more but I also bought the wrong wattage panels, a PWM CC and AGM batteries.

Focus on the primary job of running the pump and lights. Keeping the water from freezing may be accomplished with any extra power generated or maybe not. If the frozen water is your primary concern then your system needs to be bigger.

Just forget that going solar will be low cost because it will not. Most times it is cheaper to just run power from a home to a remote building then to build an "off grid" solar/battery system.

[Marketermac]

Your estimate is close to what a system like that costs. I spent much more but I also bought the wrong wattage panels, a PWM CC and AGM batteries.

Focus on the primary job of running the pump and lights. Keeping the water from freezing may be accomplished with any extra power generated or maybe not. If the frozen water is your primary concern then your system needs to be bigger.

Just forget that going solar will be low cost because it will not. Most times it is cheaper to just run power from a home to a remote building then to build an "off grid" solar/battery system.

I can always cart down boiling water and adding it to the system as needed if it's a continuous issue, I thought if it's a problem this winter I could expand the system to accommodate in the spring.

As for running power, the area is about 1/2 a mile from the closest power source. I haven't priced it out, but just running a line that far will be pricey. Add in we pay above average for power where I live ( .18/kWh) so I wanted to give solar a try on a small scale to get my feet wet before moving on to a system for my house.

[SunEagle]

I can always cart down boiling water and adding it to the system as needed if it's a continuous issue, I thought if it's a problem this winter I could expand the system to accommodate in the spring.

As for running power, the area is about 1/2 a mile from the closest power source. I haven't priced it out, but just running a line that far will be pricey. Add in we pay above average for power where I live ( .18/kWh) so I wanted to give solar a try on a small scale to get my feet wet before moving on to a system for my house.

I understand. As a comparison it costs around $1.25 to $1.50/kWh to generate power from a solar battery system and then if you are lucky you have to replace the batteries in 4 to 5 years which is about 50% of the over all cost. On top of that it is very hard to expand a system because while you might be able to add panels you have to start all over with new batteries and possible a new charge controller because you tried to save money in the beginning and purchase a limit CC which is now too small.

Building an off grid solar/battery system to meet all of your power needs becomes a downward spiral money pit that in the end the cost to run power even 1/2 mile starts to look cheap.

I am not trying to keep you from doing it. I just want you to understand it is not cheap and at best it may not perform the way you want. Like me I spent $2500 and have a system that gets me about 600 watt hours daily. I could have spent $1500 and gotten a system that get me 700 watt hours. Still a lot of money for a little power.

[jflorey2]

I'm working on setting up a solar powered chicken coop. The system will only be used for lights and a small 12v pump. I was thinking that I might oversize it and use the excess production to run a dc water heating element, however the only controllers I have found that offer a dump load feature are mppt and very expensive. I'm looking at a small 2-300w system, spending hundreds on a controller just doesn't make sense to me. The water heater is only to keep the water from freezing, I don't need to make hot water. Any ideas on an inexpensive way to accomplish this?

A Xantrex C35/C40 will do this. HOWEVER it is a mistake. In the winter, when sun-hours are limited, you'll almost never get any power from the dump load, and the water will freeze. In the summer, when you have all the solar you need, you'll boil the water.

[Marketermac]

A Xantrex C35/C40 will do this. HOWEVER it is a mistake. In the winter, when sun-hours are limited, you'll almost never get any power from the dump load, and the water will freeze. In the summer, when you have all the solar you need, you'll boil the water.

There will be about 400 gallons of water, boiling it didn't seem likely to me, but I appreciate it. After this discussion I'll be going with mppt and more panels I do believe. In the summer I would simply disconnect the heating element.

[jflorey2]

There will be about 400 gallons of water, boiling it didn't seem likely to me, but I appreciate it. After this discussion I'll be going with mppt and more panels I do believe. In the summer I would simply disconnect the heating element.

Then you will need two regulators - one diversion and one conventional MPPT regulator. They may not "play well" together, though, so beware. With a good MPPT (one that has an aux output, like the Kid) you could drive a relay that will turn your diversion load on.