Best way to handle excess solar production

[1201]

I have a LG front loader with direct drive. Hot water tank is connected to the cold water inlet. I use COLD TAP WATER setting so no heaters come on in the machine. Normally cold water is used for all the dispenser fills. I have same machine at home and there is always a soap film left. In fact I have to clean the fill tube every couple years to remove mold buildup. At camp you could eat out of the soap dispenser. I leave the camp washer for seven months and there is no mold.

Ah smart! So it washes and does everything with hot water. Nice. One day when I have solar thermal I will do this.

 

[efficientPV]

Solar thermal would never work for me as there is no place that doesn't experience shade most of the day. I do have sun on my garage most of the morning and that is where I do my laundry. The whole system is four 260W panels, inverter for the washer, controller for the water heater, 40 gallon tank where I use the existing heating elements and the LG washer. There is no battery for the system which operates only off panel power. We only do laundry on sunny days in the morning as we use line dry. With just the two of us, we only need to wash clothes every two or three days. Still the neighbor thinks we are taking in laundry as we will do up to three loads before noon. 500-2,000WH is enough to recover and get the water really hot. The whole system described only cost $500 including the washer. And the panels also provide power to the house. The water heater only uses the excess of the excess after all other needs of the house are met. Diversion to hot water really works. Panel power is never wasted. There is far more excess than everyone imagines. It is beyond me that more people don't do this. In the picture the hot water controller is connected to he tank. There is a 3/4 inch pipe which serves as the expansion tank, not nearly enough as the pressure can get high. Topped off with a pressure gauge because I couldn't find a cap for the pipe.

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[740GLE]

ahh I see you got the Banks chip tune for the hot water heater ?

Also I like your lower disconnect

 

[OM617YOTA]

I've been thinking about getting the biggest 120v water heater I can find, and plumbing it in as a pre-heater for my existing water heater. Plug the 120v heater into the solar power system, leave the existing water heater alone and grid powered.

 

[efficientPV]

Perfectly fine to use just a light switch with this system. Both heaters run in parallel to get a low enough resistance. It used to have jumper cables to restore batteries. Switch was to limit charge current. The sticker covers a hole in cabinet.

I have two water heaters in series, you might call that a pre heater tank. Primary is only 2.5 gallons (also have used a 6 gallon) which quickly heats up with a few hundred WH . I'm generally against pre heat tanks, especially a large one. It doesn't make thermodynamic sense usually. It is just a major heat loss. A well designed system can usually provide enough power with solar. Everyone gets their head set on a particular idea and it is hard to change that. Typical tank needs 1.5KWH a day just to maintain temperature. Ideal water tanks are tall.

 

[lewisfla06m]

Where can I learn more about heating a hot water heater after the batteries are fully charged?

 

[efficientPV]

There are many strategies. Heating from a battery is often used because the system was already over designed. Heating from battery requires about 1KWH additional of battery more than is needed for other daily needs. This can leave you with a less than full battery at the end of the day. Many do supplemental heating where there is an additional heat source besides solar. I heat water only with excess power. That may leave some days with just warm water. Heating water is far more complex than charging a battery. My primary tank is just a few gallons that heats quickly with just a KWH in the morning. Battery voltage heating systems are high current and there can be considerable losses before the heating element.

These systems are popular because they are simple to understand. They use a voltage monitor and turn on when the voltage is high, indicating a full battery. Then turn off t a lower voltage. It would be preferable to turn on at a certain voltage and run a timer for say 5 minutes and then turn off. This would insure not too much battery capacity is used ad it will turn back on once that voltage is reached again. One issue is that the battery may never see a high enough voltage to fully equalize. It will work fine for a few years and a battery issue will just seem like bad luck.

I heat from panel voltage and that doesn't need additional charger, battery or inverter capacity. Battery charging is never messed with. Excess power just goes to the heating element standard in most tanks. This is more advanced water heating and it isn't off the shelf. Heating water isn't hard. Getting it at the time it is needed, even on the worst days efficiently is.

 

[Aridom82]

There are many strategies. Heating from a battery is often used because the system was already over designed. Heating from battery requires about 1KWH additional of battery more than is needed for other daily needs. This can leave you with a less than full battery at the end of the day. Many do supplemental heating where there is an additional heat source besides solar. I heat water only with excess power. That may leave some days with just warm water. Heating water is far more complex than charging a battery. My primary tank is just a few gallons that heats quickly with just a KWH in the morning. Battery voltage heating systems are high current and there can be considerable losses before the heating element.

These systems are popular because they are simple to understand. They use a voltage monitor and turn on when the voltage is high, indicating a full battery. Then turn off t a lower voltage. It would be preferable to turn on at a certain voltage and run a timer for say 5 minutes and then turn off. This would insure not too much battery capacity is used ad it will turn back on once that voltage is reached again. One issue is that the battery may never see a high enough voltage to fully equalize. It will work fine for a few years and a battery issue will just seem like bad luck.

I heat from panel voltage and that doesn't need additional charger, battery or inverter capacity. Battery charging is never messed with. Excess power just goes to the heating element standard in most tanks. This is more advanced water heating and it isn't off the shelf. Heating water isn't hard. Getting it at the time it is needed, even on the worst days efficiently is.

I was thinking about this excess solar power usage issue today. I am going to put an arduino microcontroller (i do a lot of stuff with them) reading battery voltage, but most important the amps going in and out the battery bank.

Above a certain batery voltage, i just start dumping power into resistive loads (in my case infrared heating elements in my warehouse), but the arduino checks constantly and if it detects current being drawn from the battery bank (solar is not enough to cover the whole power demand) then it dimmers down the load until the current flowing from the battery goes back to 0. If it detects current going into the battery then it dimmers up the resistive load until the current goes to 0 again. In this way i keep lets say 90- 95 percent of battery full and use every watt of extra solar energy in a very simple way.

 

[nc73]

I turn on the well pump to fill the pond...

 

[pollenface]

I'd like to try one of those upper end Victron SCCs which have a Float status function (starting from 150/65). Using a tx cable and a solid state relay while in float you may be able to trigger opportune loads, like water heating

 

[efficientPV]

I was thinking about this excess solar power usage issue today. I am going to put an arduino microcontroller (i do a lot of stuff with them) reading battery voltage, but most important the amps going in and out the battery bank.

Above a certain batery voltage, i just start dumping power into resistive loads (in my case infrared heating elements in my warehouse), but the arduino checks constantly and if it detects current being drawn from the battery bank (solar is not enough to cover the whole power demand) then it dimmers down the load until the current flowing from the battery goes back to 0. If it detects current going into the battery then it dimmers up the resistive load until the current goes to 0 again. In this way i keep lets say 90- 95 percent of battery full and use every watt of extra solar energy in a very simple way.

If you can do arduino, you should look at panel voltage rising above power point voltage. Then dump power right from the panels. That is a very good indicator of excess power. Don't mess with charge cycles of the battery and high currents loss going to the heater element. With higher voltages, standard heating elements can be used. My first diverters were with a nano. Here is my first diverter and used that for a year till I built my power shed. That was just for program development and it shows how minimal component count is. Later incorporated the program into the existing refrigerator program and drove the opto isolator from 50 feet away. Just FET and capacitor bank at the water heater.

 

[Aridom82]

I meant reading the voltage and current flowing in/out the battery as an indicator, the power i will use is the AC power the inverters are generating. I have 5 (soon to be 6) strings of panels with different voltages going into 5 mmpt's. Diverting power directly from the panels is just too complicated.
Your setup looks a bit messy and maybe also dangerous, even for a temporary setup, get a 3d printer. Microcontroller knowledge + 3d printing is a very powerful combination.

 

[Kenny_]

Solar thermal would never work for me as there is no place that doesn't experience shade most of the day. I do have sun on my garage most of the morning and that is where I do my laundry. The whole system is four 260W panels, inverter for the washer, controller for the water heater, 40 gallon tank where I use the existing heating elements and the LG washer. There is no battery for the system which operates only off panel power. We only do laundry on sunny days in the morning as we use line dry. With just the two of us, we only need to wash clothes every two or three days. Still the neighbor thinks we are taking in laundry as we will do up to three loads before noon. 500-2,000WH is enough to recover and get the water really hot. The whole system described only cost $500 including the washer. And the panels also provide power to the house. The water heater only uses the excess of the excess after all other needs of the house are met. Diversion to hot water really works. Panel power is never wasted. There is far more excess than everyone imagines. It is beyond me that more people don't do this. In the picture the hot water controller is connected to he tank. There is a 3/4 inch pipe which serves as the expansion tank, not nearly enough as the pressure can get high. Topped off with a pressure gauge because I couldn't find a cap for the pipe.

View attachment 153979.

Love the elephant!

 

[Scph9002]

cheapest would be to dump excess energy into a large hot water tank for later use. Most economic (but upfront expensive) is to refuel hydrogen cells for winter season usage.

Dumbest is to sell it to the grid because:
When are you able to sell to the grid? When sun is shining
When is power cheap to buy(and sell)? When sun is shining

 

[Kenny_]

cheapest would be to dump excess energy into a large hot water tank for later use. Most economic (but upfront expensive) is to refuel hydrogen cells for winter season usage.

Dumbest is to sell it to the grid because:
When are you able to sell to the grid? When sun is shining
When is power cheap to buy(and sell)? When sun is shining

THIS!!!

 

[Aridom82]

cheapest would be to dump excess energy into a large hot water tank for later use. Most economic (but upfront expensive) is to refuel hydrogen cells for winter season usage.

Dumbest is to sell it to the grid because:
When are you able to sell to the grid? When sun is shining
When is power cheap to buy(and sell)? When sun is shining

I looked into all kinds of long term (from summer to winter) energy storage solutions but hydrogen is just too difficult. I was thinking some type of flow battery, like the iron redox battery could work better

 

[timselectric]

I'm planning a "sand battery" for this, in the future.
Store heat in summer, to be used in the winter.
It's a perfect option for me because the local sand mining company is one of my customers. So the largest part of the system is free (to me). If I can just find a steel pipe supplier that needs some electrical work, it will be a done deal. lol

 

[Aridom82]

I'm planning a "sand battery" for this, in the future.
Store heat in summer, to be used in the winter.
It's a perfect option for me because the local sand mining company is one of my customers. So the largest part of the system is free (to me). If I can just find a steel pipe supplier that needs some electrical work, it will be a done deal. lol

I looked at this too. The thing is that sand has a very low heat capacity compared to water, i believe is 20 percent when compared to water. So you need a very big amount of it. You can heat sand a lot more than water, but in the long term that heat is lost because there is no insulation that can keep that amount of heat at high temperature (with high temperature the thermal coefficient of insulators goes up a lot).
So unless you are heating a mountain of sand (very big volume at high temperature) keeping that heat in is very difficult, and that did it for me so i discarded this idea.

 

[timselectric]

I looked at this too. The thing is that sand has a very low heat capacity compared to water, i believe is 20 percent when compared to water. So you need a very big amount of it. You can heat sand a lot more than water, but in the long term that heat is lost because there is no insulation that can keep that amount of heat at high temperature (with high temperature the thermal coefficient of insulators goes up a lot).
So unless you are heating a mountain of sand (very big volume at high temperature) keeping that heat in is very difficult, and that did it for me so i discarded this idea.

The key is large sand quantity. The extra sand is the main insulator. Every time I think about mine, it gets larger. lol

 

[Aridom82]

Every time I think about mine, it gets larger. lol