Excess Sun Power

Heat pump water heaters unfortunately can't absorb that much excess power, about 500W. Adding that excess power using the existing heating element is a good idea. HPWH become less efficient the higher the temperature goes. Excess to resistive can raise the temps much higher for overnight loss. In winter, PG&E did an engineering study that said the actual COP dropped 44% based on natural gas heating. Resistance heating doesn't seem so bad considering that.

brum said:

One option that crossed my mind is to store the excess energy as hydrogen. But this was just a spike and I haven't researched many details. Some statements said that the conversion efficiency is ~80%. And we do aim for a clean future there is some chance that this will become mainstream.

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Small volume of course low-pressure or high-pressure tank.

An interesting concept for large volume long-term storage is hydrogenation. At least one company proposes this as a way to distribute hydrogen in fuel trucks, for a hydrogen economy.

Great news! I added two 6 gallon water heaters (ecosmart 120V) and they work great. Bad news, once they heat up the water to temp, they hardly use any power. So I still had excess power. Now that the days are even longer, I tested out our dehumidifier for an extended period of time and it works great. I have the dehumidifier on 24/7 for the past 8 days straight and I am now getting what I think is the best potential from my big system.

My smaller system makes 1400W/h in full sun and once the batteries are full, I had unused power there as well. One of my neighbors has an e-bike and an e-scooter, and now charges them during the day with my small system in my garage. We run the power through a Kill-A-Watt and will pay me for it. We tested it out, and it works perfectly. We haven't worked out how much he will pay yet, but once we get a handle on the amount he uses, we will work something out.

Thank you everyone for your input. I love the fact that we are getting the most out of our system now.

Yup, they don't take much to heat up. Less than a KW. This is the daily temperature cycle of my ECOsmart6.

efficientPV said:

Yup, they don't take much to heat up. Less than a KW. This is the daily temperature cycle of my ECOsmart6.
View attachment 94166

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These ecosmart's are great. Instant hot water, and REALLY hot. I installed a bypass valve so that I can switch to either the ecosmart's or the main hot water line. One of the ecosmart's was installed in the secondary bathroom, I bought a hose with shower head and attached it to the sink. The shower head has a on/off valve. I then showered with the 6 gallon's, and it lasted the whole shower. We have an RV that also has only a 6 gallon tank. If you shower like in the RV, it works with no problem. I am thinking of a way to run a line to my shower from the ecosmart with a bypass valve as well. That would be a big energy saver. It also forces you to save on water as well. So fast daytime showers will be heated by sun power.

I love this solar stuff!

DThames said:

We have a geothermal heat pump and a preheat hot water heater/tank. The elements of that preheat tank are not connected at all. We get waste heat in the summer and heat pump heat during the winter to preheat that tank. I have been thinking about dumping some of my solar emergency system's PV to that tank. We are grid tied with a main system and a separate secondary array just for emergency power. I have been doing some experiments with using it for resistance heating in the garage during the winter....just messing around with it.

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think of the solar as a "pre heater"- it pre heats the water before it goes into the main tank.

There are DC powered heating/cooling options as well.

I do want to warn anyone interested in the ecosmart 6 gallon water heaters. They are big and need lots of space, so if you are looking to install one, get the dimensions and measure. I had to heavily modify a big dual sink vanity to shoe horn it in. Now there is little to no useable storage space in the vanity. The other one is installed on the wall in our utility room and ran the plumbing along and behind the wall to the sink. I just installed two "T" fittings and ran hot water to the utility sink and wash machine as well as a back up. The wash machine really makes the solar work hard. We are getting lots of use from them now and this was definitely worth it.

Big, but it pays to have the extra insulation. I think that is how I got mine. Bought off craigslist for $75 because the guy never got around to installing it. Probably wouldn't fit under his sink.

efficientPV said:

Big, but it pays to have the extra insulation. I think that is how I got mine. Bought off craigslist for $75 because the guy never got around to installing it. Probably wouldn't fit under his sink.

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$75.......Great deal! That really payed off.

When I have excess solar, I lower the temp on the air conditioning.

I have a 57 kWh battery and a Chevy Bolt EUV with a 66 kWh battery.
Excess solar happens when both show they are "fully charged".

This actually rarely happens though. My usage is usually around 600W for the house. I easily use 9kW doing the laundry when the air conditioner turns on. I have an 11 kW EVSE for my car, but seldom use it higher than 4 kW.

Another option for "excess solar" is to feed it into the grid. Don't expect any kind of financial gain anymore doing this. The "balance" with my utility is -7.81. This is barely covering the minimum service connection fees.

jasonhc73 said:

When I have excess solar, I lower the temp on the air conditioning.

I have a 57 kWh battery and a Chevy Bolt EUV with a 66 kWh battery.
Excess solar happens when both show they are "fully charged".

This actually rarely happens though. My usage is usually around 600W for the house. I easily use 9kW doing the laundry when the air conditioner turns on. I have an 11 kW EVSE for my car, but seldom use it higher than 4 kW.

Another option for "excess solar" is to feed it into the grid. Don't expect any kind of financial gain anymore doing this. The "balance" with my utility is -7.81. This is barely covering the minimum service connection fees.

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Net metering varies from localities. I'm grandfathered for at least 10 years for a 1:1 swap.

jasonhc73 said:

When I have excess solar, I lower the temp on the air conditioning.

I have a 57 kWh battery and a Chevy Bolt EUV with a 66 kWh battery.
Excess solar happens when both show they are "fully charged".

This actually rarely happens though. My usage is usually around 600W for the house. I easily use 9kW doing the laundry when the air conditioner turns on. I have an 11 kW EVSE for my car, but seldom use it higher than 4 kW.

Another option for "excess solar" is to feed it into the grid. Don't expect any kind of financial gain anymore doing this. The "balance" with my utility is -7.81. This is barely covering the minimum service connection fees.

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Net Metering or Net Feedback is a can of worms I do not want to get in to. The additional costs, inspections and bureaucracy involved are not worth it. I would rather find creative ways to use the energy I am generating. The addition of the two 6 gallon water heaters were the perfect solution to maximizing the use of my daily power excess.

The really cool thing is that in winter when the days shorten, I can bypass the water heaters and save the power for more critical loads. Unfortunately I do not have 240V split phase inverters, battery and panel capacity to run my AC, that would be awesome. Thanks for your input!

You could get a window air conditioner or mini-split sized to the power your PV does generate.

Hedges said:

You could get a window air conditioner or mini-split sized to the power your PV does generate.

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Unfortunaltely I cannot use a window air unit. My windows all slide open sideways. I do not have double hung windows. I did look for a mini-split, but that would only cool one room, and I already have central air. So even if I have a mini split, I would still have to run the central to cool the house anyway, there would be no savings. Thanks anyway!

Repro said:

Unfortunaltely I cannot use a window air unit. My windows all slide open sideways. I do not have double hung windows. I did look for a mini-split, but that would only cool one room, and I already have central air. So even if I have a mini split, I would still have to run the central to cool the house anyway, there would be no savings. Thanks anyway!

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not exactly true. If you run the mini split to where the return air of your central air is, you reduce the return air temp which in turn, reduces the load.
I am not exactly sure how much effiicency you'd loose, but aint bad. The water heater is just the easiest of the bunch to do, but resistance water heating isn't as efficent as a heat pump water heater. There used to be a company called Glacier or something like that, that would make auxiliary add on heat pump water heating... but the company has since stopped making it.

The heating/cooling model of a structure is pretty straight forward, if you are heating/cooling a room separately than the main heating/cooling is only handling the rest of the house. That shows up in it running less time and compressor load. I use a couple of portable heat pumps that I only run during the day to either put heat into the house or remove it ( https://www.amazon.com/Cooper-Hunter-Conditioner-Including-Controller/dp/B098ZTKTRZ/ )

A related side project I'm working on is to convert a 2-ton window air conditioner to move heat from one 500 gallon IBC tote to another, one chilled for AC during the summer, another for pre-heating domestic hot water and also heating during the cold seasons. I want to set it up with a raspberry pi or PLC or something so that it can either dump excess heat or gather heat from an outdoor heat exchanger when needing to. It would basically just continually run when PV is at excess to charge up heat/cold storage.

I want to integrate it with hydronic systems from https://www.mbtek.com/ or https://www.chiltrix.com/

The ideal model is to have an insulated (swimming) pool with a heat pump that either heats or cools running off solar during the day, and then either remove or pump heat into the pool for HVAC/DHW. A decent sized pool would experience an unnoticeable temperature swing between day/night cycles.

One could do this with off the shelf liquid/liquid heat pumps (ground sourced hydronic heat pump).

What I should do initially is make a simple preheat loop in a home built thermal storage tank, and just put a heating element in there.

during winter or just cold, i use my solar to power a small space heater -- 350 watts. i checked one months electric bill and i saved
about $20...but the calculations are definitely not accurate.

I have my system pretty much at full use now. The addition of the two water heaters was what I needed. We have experimented with them and they are simply amazing. When the batteries are full, we start washing clothes, run the dishwasher... The system handles it well powering them almost totally with daylight sun power. I will admit that when both water heaters are running at the same time, they do draw some battery power as well, but they heat up very fast and the batteries top off again quickly. My brother-in-law helped me run PEX lines with a bypass from one of the water heaters to our small secondary bathroom for showering as well. It works great. We also installed a shower head with a button to turn the water on/off while showering like in our RV. Six gallons of hot water is more than enough for showering, and they heat up so fast, you never feel a drop of cold water.

Living in southwestern Pennsylvania has its disadvantages of being gray most of the time. We average 160 sunny days per year, and our solar works great. Even through the winter with short dark days, our inverter switched to grid two different times between 5 AM and 6 AM. When the sun came up, the solar charged the batteries and I have a set point of 53V to switch back from grid.

All in all, I am happy wih the two water heaters, they are saving us money, our gas bill will drop as our water heater is being used much less, and my system is using almost everything it has now. My Victron 150/70 Solar Charge Contoller gets so warm I could use it for heating as well.

notarichman said:

during winter or just cold, i use my solar to power a small space heater -- 350 watts. i checked one months electric bill and i saved
about $20...but the calculations are definitely not accurate.

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My house is still basically a rigid tent. So running the portable heat pump all day during the winter on solar paid for itself in the cost of gas.

I need to just pick up a large electric water heater and put it in series before my gas heater.

Hedges said:

Small volume of course low-pressure or high-pressure tank.

An interesting concept for large volume long-term storage is hydrogenation. At least one company proposes this as a way to distribute hydrogen in fuel trucks, for a hydrogen economy.

Hydrogenation - Wikipedia

en.wikipedia.org

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H20 Splitting by ionization

Cracking water into hydrogen with battery power and then burning it in a (less than 100% efficient) internal combustion engine isn't likely boost vehicle range as much as, say, removing fan belt and powering electrical accessories from the battery.

I never thought of drying food, that's an interesting idea!

Cooling, dehumidification, and heating DHW seem to be the most common energy dumps. Mining BTC can require faily significant initial capital expenditures, not to mention a learning curve to get there.

Repro said:

I have my system pretty much at full use now. The addition of the two water heaters was what I needed.

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I still don't understand why you didn't just preheat the DHW (using excess solar) inline before your main DHW heater. This would've been much easier, cheaper, cleaner, used less space in your living area, etc. Not to mention you have less heat loss through a larger single tank than you do through two smaller tanks (in your living area no less). But if nothing else, you did gain nearly instant hot water.

Wet1 said:

I still don't understand why you didn't just preheat the DHW (using excess solar) inline before your main DHW heater. This would've been much easier, cheaper, cleaner, used less space in your living area, etc. Not to mention you have less heat loss through a larger single tank than you do through two smaller tanks (in your living area no less). But if nothing else, you did gain nearly instant hot water.

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If they are anything like me, they probably scored used electric water heaters, and took whatever sizes they could get.