diy solar

diy solar

Excess Sun Power

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Repro

Solar Enthusiast
Joined
Jan 28, 2020
Messages
338
Location
Southwestern PA
I am still relatively new to solar power, and I am now seeing the raw benefits of it. I finished my current system and brought it online at the end of Oct. last year. So all of the following information is winter months with short days. Now I tried to calculate everything to get system components to cover my needs without going overboard. I have 20kWh in batteries, and a little over 4K in panels and my SCC is a Victron 150/70. A typical nights use on the batteries was 35%-45%. That load was a forced air gas furnace, one sump pump, two full size fridges, wash machine, two outlets in the kitchen and the whole office to include the computers. I have a second smaller system with 10KwH in batteries, three 440W panels, and it powers a freezer, a sump pump, our bedroom, the garage, garage lighting and door opener, and outdoor security lighting and oulets. I usually uses 30%-35% of the batteries overnight.

My batteries are usually topped off and in float around 1PM. Even on overcast days, my batteries top off a few hours later. Now with longer days, no furnace running and more power being produced, I have a LOT of excess power not being used. One thing I am doing is plugging in a dehumidifier during the day after the batteries are full to use some of the power. At night I switch the dehumidifier back to grid power. It draws 700-900 watts when the compressor is on.

My question is, does anyone have any creative ideas on how to use the power, other than just plugging stuff in during the day? I calculate that approx, 8kWh or more per day are just not being used. I feel like it is a waste.
 
If you only ran the dehumitifier during the day, off of the solar, that would shift a bit more load to the solar. This is assuming it is acceptable to leave it off at night and then let it catch up during the day.
 
First off, thanks! I have tried on many occasions to leave the dehumidifier on all night. In the middle of winter the humidity levels are so low that we can shut it off. The problem is that in southwestern PA, our humidity is usually 80% plus, and it is not uncommon to have humidity levels higher for a long time. So our dehumidifier cycles a lot. I left it on again last night as we hit 85 degrees yesterday with 78% humidity and with rain moving in, humidity will get much worse. I woke up to my inverter running on pass-thru. I have a Victron Quattro 5000, and I have it set to maintain 50V and 30% reserve. It hit the 30% and switched to grid pass-thru. Once the sun came up, it switched back to solar. It was on grid pass-thru for a little over an hour. The dehumidifier was on for a little over 24 hours on solar power. The loads and the dehumidifier are just too much for my batteries every night.

It is the excess daytime sunlight that I am trying to creatively use. I though someone may have found a terrific way to use it. There are a lot of VERY smart people on this forum.
 
Last edited:
Repro said:
First off, thanks! I have tried on many occasions to leave the dehumidifier on all night. In the middle of winter the humidity levels are so low that we can shut it off. The problem is that in southwestern PA, our humidity is usually 80% plus, and it is not uncommon to have humidity levels higher for a long time. So our dehumidifier cycles a lot. I left it on again last night as we hit 85 degrees yesterday with 78% humidity and with rain moving in, humidity will get much worse. I woke up to my inverter running on pass-thru. I have a Victron Quattro 5000, and I have it set to maintain 50V and 30% reserve. It hit the 30% and switched to grid pass-thru. Once the sun came up, it switched back to solar. It was on grid pass-thru for a little over an hour. The dehumidifier was on for a little over 24 hours on solar power. The loads and the dehumidifier are just too much for my batteries every night.

It is the excess daytime sunlight that I am trying to creatively use. I though someone may have found a terrific way to use it. There are a lot of VERY smart people on this forum.
Click to expand...
What I meant was, "If you leave the dehumidifier off at night does the humidity in the house rise to an unacceptable level?" If not, let it catch back up during the day (when plenty of solar is available) and shift that night load to the day.
 
Repro said:
is the excess daytime sunlight that I am trying to creatively use. I though someone may have found a terrific way to use it. There are a lot of VERY smart people on this forum.
Click to expand...
Yup, there is.

But there’s not too much smarts needed for this: heat hot water supply with solar. Can be done with a timer or a voltage controller assembly that triggers a high-current switch to load the hot water heater.
 
12VoltInstalls said:
Yup, there is.

But there’s not too much smarts needed for this: heat hot water supply with solar. Can be done with a timer or a voltage controller assembly that triggers a high-current switch to load the hot water heater.
Click to expand...
I might add, if you have room for a second water heater, connect the first water heater to solar for a pre-heat tank. That way you can leave the normal tank as the usage tank with the normal controls. Be aware, the water heater thermostat is not made for DC and should not be used. External DC controls will need to be put in place if you want to heat directly from PV.
 
Repro said:
One thing I am doing is plugging in a dehumidifier during the day after the batteries are full to use some of the power.
Click to expand...
Seems you could use solar to run dehumidifier as soon as the sun comes up (sooner if battery had capacity left). No need to wait until batteries full.

Sorry if this was specifically mentioned, I skimmed thru a lot of this.
 
DThames said:
I might add, if you have room for a second water heater, connect the first water heater to solar for a pre-heat tank. That way you can leave the normal tank as the usage tank with the normal controls. Be aware, the water heater thermostat is not made for DC and should not be used. External DC controls will need to be put in place if you want to heat directly from PV.
Click to expand...
So the solar "dump" tank in series with the main tank (output of solar dump tank connected directly to the inlet of the main tank)?
HHmm.....
 
SparkyJJO said:
So the solar "dump" tank in series with the main tank (output of solar dump tank connected directly to the inlet of the main tank)?
HHmm.....
Click to expand...
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.
 
Is there any power you presently consume from other sources? Gas/oil/firewood for heating? Gasoline in a car?
Offsetting that consumption is a possibility. Otherwise, the question is how you can burn off surplus power.

In winter, your solar might produce only 2 hours effective, so 8 kWh/day instead of 24kW or so produced. That will be the more important issue to address.

To get value from surplus power, some people "mine" bitcoin.
Dry foods? Put in decorative lighting? A garden water fountain or recirculating stream?
Provide power to neighbors?

My concern is shifting nighttime loads to daytime, because my battery is much smaller than one day's production. So I might disable refrigeration at sundown, let it coast and catch up in the morning. But you don't have that problem.

Now that PV costs about $0.50/W not $5/W like a couple decades ago, you produce power for $0.025/kWh.
It is reasonable to over-build PV and discard surplus. Cheaper than storing it in batteries and other options to creatively utilize it.
Similarly, power plants have to be oversized for peak demand, which means capital is idle the rest of the time. (Now with so much PV installed by utility customers, peaker plants aren't getting the utilization they once were.)
 
yep, have an extra inline waterheater, which is controlled by an esp breaker.
once batts reach 90% full, and load doesnt exceed the incomming solar ,my home assistant switches the heating element on, therefor (pre) heating the water going to the primairy heater.

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houseofancients said:
yep, have an extra inline waterheater, which is controlled by an esp breaker.
once batts reach 90% full, and load doesnt exceed the incomming solar ,my home assistant switches the heating element on, therefor (pre) heating the water going to the primairy heater.

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Click to expand...
You are switching DC with this breaker?
 
I switch my HVAC to solar power from city power during the day with a big relay. The relay is controlled with my victron programmable smaller relay. This way my HVAC only uses my solar array during the day automatically and I dont need a timer.
 
Does the relay switch two poles (DPDT)?
I had a Dayton 30A 2-pole relay twist (or arc) such that it cross-connected. Burned a contact and tripped a breaker.
I think a reliable, safe transfer switch is more than just a double-throw relay. e.g. could be two separate relays with interlocking controls.
 
WOW! I told you there were a lot of really smart people here. I have noted the water heating (from inline to pre-heat), food drying has always interested me. My only concern with food drying is the high initial cost. I am doing more research, more tips and suggestions are highly welcome!

DThames said:
What I meant was, "If you leave the dehumidifier off at night does the humidity in the house rise to an unacceptable level?" If not, let it catch back up during the day (when plenty of solar is available) and shift that night load to the day.
Click to expand...
Sorry for the misunderstanding. I am currently doing that, by connecting the dehumidifier to my smaller system when the batteries are at 95%. That is when my Victron Phoenix 3000 is set to go into absorption. I have an alarm set to inform me when 95% is reached. I then plug in the dehumidifier to the Phoenix. That keeps my smaller system busy until the sun goes down. Then I plug it into the grid at night. I usually connect the dehumidifier to the Quattro, but since the days are longer, it is a perfect match for the Phoenix.
 
MisterSandals said:
Seems you could use solar to run dehumidifier as soon as the sun comes up (sooner if battery had capacity left). No need to wait until batteries full.

Sorry if this was specifically mentioned, I skimmed thru a lot of this.
Click to expand...
I was doing that, but I have to be selective on the days I would do that. Some days the cloud cover won't let me catch up, that is why I wait until the batteries are close to full to ensure I have full banks at night.
 
I think I have found a very good use for my excess power. All of your ideas have lead me to research a water heater we used when I lived in Germany. Mini Tank water heaters that use 120V from an outlet. These are actually very energy efficient and provide enough hot water for most uses, and I mean really hot water. By installing two of these at a low cost, my system will actually be able to handle these day and night. Since we are in bed, no hot water being used, very low power usage. During the day, we have excess power to heat water. I can run the hot water through my kitchen sink sprayer so as not to bypass the main hot water tank. I can add an additional sprayer to my utility sink easily, and I can simply bypass the main hot water in our guest toilet. So even three of these would be feasible. I am going to do some research on the American market models. Found one an Amazon:


Still open to suggestions. Keep em coming and thanks!
 
Repro said:
I think I have found a very good use for my excess power. All of your ideas have lead me to research a water heater we used when I lived in Germany. Mini Tank water heaters that use 120V from an outlet. These are actually very energy efficient and provide enough hot water for most uses, and I mean really hot water. By installing two of these at a low cost, my system will actually be able to handle these day and night. Since we are in bed, no hot water being used, very low power usage. During the day, we have excess power to heat water. I can run the hot water through my kitchen sink sprayer so as not to bypass the main hot water tank. I can add an additional sprayer to my utility sink easily, and I can simply bypass the main hot water in our guest toilet. So even three of these would be feasible. I am going to do some research on the American market models. Found one an Amazon:


Still open to suggestions. Keep em coming and thanks!
Click to expand...
sounds like a plan :)

as my main 500l watertank is indirectly heated by my heatpump, with an extra top element to assist, i opted for an additional 200l , 2 element, tank inline.
the starting thought was to just preheat, but during the summer months the water gets hot enough to a point where the heatpump barely or not at all runs
 
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