Trigger heater to absorb solar electric power instead of exporting to grid.

[gschettl]

1st time Arduino user here and looking for help figuring out what components to buy and what software to install. Please assume I have no programming or electronics or hardware knowledge but I'm willing to learn.

Please see the attached flow chart I wrote for myself to help me understand how I MIGHT accomplish my goal of absorbing excess electricity generated by my rooftop solar panels. My power company cheats me out of paying a reasonable price for electricity I export to the grid so I'm wanting to use my solar power on-site.

It's winter here in Minnesota and I could consume my excess solar energy by firing one or two small heaters on different 120 Volt AC circuits, after detecting excess energy by sensing and comparing two different 240 VAC amperages.

Ideally if anyone enjoys helping by designing systems, plus a Bill Of Materials it would be greatly appreciated and I'll proceed to buying those components and figure out how to build a working system.

Thanks if you can help!

[Juraj]

I have this project GitHub - JAndrassy/Regulator: DIY Arduino consumption regulator build to use excess solar power for auxiliary 'summer' heating. The solar power data are retrieved over SunSpec Modbus TCP. IoT monitoring with Blynk and local Web server.

[PerryBebbington]

If this were my project I would approach it as follows:
I'd investigate what happens in terms of voltage and current output of the solar panels under different conditions such as in bright sunshine, low sunshine, no sunshine. High load, low load, no load. Supplying all the load, having some spare capacity, not having spare capacity.

I'd be looking for something in terms of the voltage or current that would give a good indication of when the panels have spare capacity I can feed into a heater.

Maybe I'd discover that's the wrong approach, maybe I'd find what I was looking for.

Then I'd have a heater on the DC side with PWM set up to absorb the excess output. I wouldn't have fixed output heaters like you are proposing. What, for example, will you do if there's 1000 Watts spare? with PWM you could dump it into a heater, with your set up you lose it.

Maybe PWM is not practical for some reason, in which case either phase control (not normally used for a heater) or burst mode on the AC side.

Please assume I have no programming or electronics or hardware knowledge but I'm willing to learn.

Which is a problem, this project is advanced. There is plenty of scope for starting fires or killing yourself. At the very least there is plenty of opportunity for killing the (expensive) inverter between the solar panels and the mains.

Please learn about electronics first and only think about this project when you understand the difficulties.

On a different point; during the summer when, I assume, the weather is warm and you have plenty of excess output from the panels do you need a heater? During the winter, when you need a heater do the panels produce enough spare output to be useful? As a rule of thumb a 1 meter square panel can produce about the same amount of heating as the sunshine through a 1 meter square window, probably less actually.

[Robin2]

Image from Original Post so we don't have to download it. See this Simple Image Posting Guide

...R

[Robin2]

If this system is actually connected to the grid then anything you do must NEVER create the possibility of power being exported when the electricity utility does not expect it - someone could be killed.

How does the existing system determine whether power is exported or used within the house?

Do you have access to a meter that can show minute by minute whether power is being exported or imported?

...R

[JCA34F]

I guess I don't understand the ins & outs of solar systems but why shorten the life of your panels by wasting power in a big resistor? I would be thinking of ways to partially shade the panels if they are generating more than you're using.

[JCA34F]

What would happen if you only used what you needed and let the panel voltage rise to their open circuit value? Would that damage the panels or the controller?

[Robin2]

JCA34F:
I guess I don't understand the ins & outs of solar systems but why shorten the life of your panels by wasting power in a big resistor?

I had assumed the OP wants to use the power to heat something where the heating value exceeds the price paid for exported power.

...R

[anon73444976]

Google "solar power diverter"

[JCA34F]

Understood, I was ass-ooming the OP wanted to dump the excess like dumping excess voltage from a regenerating motor into a load resistor. TNX for lesson.

[Robin2]

JCA34F:
Understood, I was ass-ooming the OP wanted to dump the excess like dumping excess voltage from a regenerating motor into a load resistor.

You could be correct - we must wait for an update from the OP.

...R

[Paul_KD7HB]

Two questions for the OP.

1. Does he actually own the solar power system or is it leased?

2. Did he sign a contract with the local power company to send excess power into their circuit?

Paul

[Robin2]

Paul_KD7HB:
2. Did he sign a contract with the local power company to send excess power into their circuit?

A relevant and interesting question. But it raises a further question "excess over what?".

...R

[Nick_Pyner]

I reckon

Paul_KD7HB:
2. Did he sign a contract with the local power company to send excess power into their circuit?

says it all, and if OP's system is capable and kosher to do what he wants, it is probably already doing it.

[Paul_B]

gschettl:
My power company cheats me out of paying a reasonable price for electricity I export to the grid

This is perfectly normal practice unless and until the government chooses to regulate the system honestly.

Using solar electricity for resistive heating makes no sense at all. You need a different system to heat your house using sunlight.

What you want to do is to get a battery. This way you use the electricity efficiently at night when it is valuable to you. For domestic installations, a battery is the only way of using the electricity effectively as you use it mostly at night.

For a business using most electricity in daytime such as for air conditioning (and incidentally, if you must use electricity for heating you need to have reverse-cycle air-conditioning), the battery is not so viable (except for your server computers ).

[gschettl]

Thanks for all your responses. Attaching a screen shot from my eGauge to help clarify. Unfortunately, eGauge doesn't supply any outputs I can use as triggers. It's a monitoring system only.

This screenshot was written before I knew the power company was paying me only $0.02/kWh for electricity exported to the grid. The area shaded in green where it says "power company pays us" is the area of interest. This is the power I'd prefer to use on site rather than export. It is generally 10-30 kW per day being exported.

The solar diverters tend to focus on heating water, which would be great, except I have a tankless water heater and don't want to mess with that system now.

I like the battery idea but it is far too complex for my level of knowledge.

My solar inverter is designed to shut down instantaneously if the grid goes down, but that doesn't come into play with what I'm trying to do here, (using energy, not creating it).

Excess power simply means I'm exporting to the grid, (undesireably).

The solar system and inverter are very expensive and I wouldn't dare mess with them playing with the DC power. If I do this project I want the worst case mistake to result in a thrown A/C breaker.

Thanks again for all the ideas & letting me know this is more complex that I realized.

[Nick_Pyner]

gschettl:
I have a tankless water heater and don't want to mess with that system now.

Perhaps you should, it sounds like an obvious and ideal solution. If you swallow hard, look at your shoes rather than at the complexity of batteries, and say it quickly, an electric storage heater is a sort of battery

[Robin2]

Image from Reply #15 so we don't have to download it. See this Simple Image Posting Guide

...R

[Robin2]

I don't think this is an easy problem to solve. I think you need sensors to measure {A} the current coming from the solar panels and {B} the current being used in the house. If A > B power will be exported. if A < B power will be imported. Note that this assumes the system always allows the solar panels to produce full power- I think that is true of a grid-connected system.

Locating a sensor to measure the solar output should be straightforward but the location of a sensor to measure the house load is not. The normal place where it all comes together is at the Utility's meter and that presents two problems {x} it may not be practical to install a current sensor at that point and {y} the house load at that point will be nett of the solar output.

Another significant problem is that the intensity of sunlight falling on the panels can vary very quickly - your graph illustrates that. It means that anything you measure is history whereas the decision to turn on the heater needs knowledge of what the solar output will be AFTER you have turned on the heater - in other words, a guess about the future. Do you want to run the risk that the heater draws power from the grid when a cloud obscures the sun?

While the marginal cost of solar energy is zero the cost of the system(s) to make use of it are not.

It may be worth considering whether a simple time-based system for operating the heater so it absorbs (say) 70% of the potential solar power would be economically attractive. That might be supplemented by a simple optical sensor (maybe a very small solar panel) that could independently detect if the sun's intensity was too low.

And an additional solar panel (just for the heater) might be cheaper than the system needed to measure and divert power from the existing panels.

...R