MPPT DC Solar Hot Water

Contact Techluck for special situations or custom designs.

As an option, you could keep the upper grid powered element from coming on during the day using a simple electrical timer available at Home Depot or Lowes. This would help keep the upper element off and let the solar panels to do their thing in the daytime, saving even more on your power bill. Also solar hot water helps if you have high Time Of Use tiered power pricing.

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A little solar story

When I first started to want solar hot water I considered piping in a water type solar collector from outside. Then I watched videos and e-mailed a few people that did that and found a few problems.

First, if you don’t put in some sort of system to drain back the water you are going to have freeze problems and possible panel damage and leaks. Setting that up is not fun, you have problems with air in the system. It needs to be designed to totally drain or it will still have problems. And it still costs a lot and gets complicated. More stuff to worry about in the winter.

The other option is to drain it every time the temp drops. Well, if you do that, there goes free winter hot water and what if you forget? I like simple and automatic stuff I don’t have to mess with.

And then there’s the plumbing, all over the place, maybe a 2nd exchange / heat storage tank that will develop leaks later as any tank does. And a pump that wears out or gets clogged. It’s a maintenance nightmare and still a costly install.

So a system with solar electric PV is the only way to go. Wires are easy to run.

At first I tried to connect my solar panels direct to the element. But the mismatch without MPPT in the morning and afternoon is brutal, the panels are nowhere near their Max Power Point and you get little total daily heat that way unless you have the extra space and want to throw lots of panels at the problem and just say “oh well”.

Another choice would be to change the element. Have you ever seen the nut size on those things? What if I screw up the threads? Will it leak later? Do I really want to mess with a perfectly working expensive tank?

And without MPPT, you still have a mismatch in the morning and afternoon anyway, doesn’t really get that much better for all the hassle.

So I designed the Solar Hybrid Controller using MPPT and love it!! You will too!

It’s super simple to install with few components to go bad and just sits there quietly and works every day saving me money with no worries and little up front cost.

The idea is — how simple and hassle free can it be? And in the end does your upper element come on less for a total installed system cost of around $700?

That beats most of the other systems out there. All DIY, easy install with no plumbing nightmare, no soldering, no leaks and no worry of freezing. Almost anyone can wire up 2 wires.

Installing wires instead of pipes is much easier, and it gives me other options, like if the grid goes down during a bad emergency I can say heck with hot water and simply re-configure the panels for 24V by switching a couple of connections at the panels (or even inside depending on how I wire things) and have more power for my emergency back-up inverter and batteries.

Simple is better

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Other stuff

Your hot water heater is one of the biggest energy wasters in your house.

Go solar! A solar hot water heater is a good way to go. Little panels on the roof and away you go! Savings because the power is free from the sun!

You will be able to save a great deal by further investing in a timer for your water heater. Set the timer to turn the grid connected electric water heater element off during the day when solar is heating it. Then set it to come on again late at night so it can recover to a set point and be ready for the next solar day.

Another way to save with your water heater is by draining it on a regular basis. Unless you have soft water, it is important to drain a couple of gallons of water from the bottom of your water heater at least two times a year. This is because hard water deposits can collect on the bottom of your water-heating unit, surround the heating element and reduce efficiency.

Since the water from your water heater is used primarily for keeping yourself and your belongings clean, there is no need for you to use water that is heated to 150 degrees Fahrenheit or above. However, most elements on electric water heaters are preset to at least 150 degrees.

Not only is this dangerous, but it is also a waste of energy and money. We recommend you reset your electric water heater upper element to 125 degrees F. (keep the lower solar element turned up and store energy)

You may also want some batteries, a solar controller and solar panels for emergency power back up in case the grid goes out for things like lights, TVs and radios. You can also Grid Tie any excess energy that isn’t going to charge batteries. It’s fun and it’s priceless to see your power meter actually turn backwards!

The Solar Hybrid Hot Water Controller is Patent Pending.

Some TV people are calling Solar Panels a Solar Generator, watch out for the low power, over priced “as seen on TV” systems out there. Solar Panels are currently available for $1 a watt shipped to your door, look around!

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MPPT Solar Hybrid Hot Water Controller Load Tests

Also please read the FAQ in the link at the end of this article.

We have tested a number of different water heating elements in several configurations.

4500W 240V Water Heater Element is the “standard” and recommended element for USA tanks

Tested up to 1280W with the bigger box. Can work down to 500W, read more below for somewhat more efficient solutions at lower power levels.

3600W 240V Water Heater Element is another “standard” in many countries

It needs at least 900W minimum with the bigger box. Another common element is 3000W 240V and is way too high ohms to do you any good, you will need to change it out.

1500W 120V Water Heater Element (Home Depot) using 400W of “48V” configured 12V series connected solar panels, meaning 84V open circuit max. and also up to 750W (3 x 250W in series and bigger box)

MPPT worked perfectly with the standard Solar Hybrid Hot Water Controller as shipped. Total daily power output to the water is only a little more efficient (mornings) than a standard 4500W 240V element but may not be worth the drain and change out of the element for 750W input.

Note that 1500W elements are found on some smaller size tanks that use 120V. This was mostly a low power test at 400W for people who want to run a small tank, like maybe 20 gallons. The 750W test (with bigger box) shows that you might get a little more power in the mornings etc.. on a bigger more normal tank, and the heat-sink temps are still within limits.

WARNING – DO NOT GO ANY HIGHER WATTAGE WITH THIS ELEMENT !!

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2000W 120V Water Heater Element (Home Depot) using 500W (2 x 250W and Eaton box only)

MPPT worked perfectly with the standard Solar Hybrid Hot Water Controller as shipped. Total daily power output to the water is a little more efficient (mornings) than a standard 240V 4500W element but may not be worth the drain and change out of the element. Note that 2000W elements are found on some smaller size tanks that use 120V.

This was mostly a low power situation at 500W for 1 person who does not use much hot water. Working on a 50 gallon tank for months (still going).

500W is great with this element for low very conservative use in a more off grid situation, like using a generator or grid with a MANUAL, HAND PLUG IN (2 socket setup, one solar side) for more than a few bad solar days, connected to the normal top connection on the tank so the upper element comes on first, both elements changed out.

This element will also work on a small tank, like 10 gallons, with only one 250W panel. Although not very efficient, tests showed a 16F rise in 7 hours on a well insulated tank. Why 7 hours? The single panel got shaded at 3PM for this test. For a off grid cabin with low use this may work for you.

WARNING – DO NOT GO ANY HIGHER WATTAGE THAN ABOUT 500W WITH THIS ELEMENT!! This means DO NOT TRY IT ON 750W – The controller gets too hot! DO NOT GO THERE EVEN WITH A BIGGER BOX! You don’t need to do this at 750W anyway so DON’T DO IT! You want to smell smoke?

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200W 12V Immersion Heater for RV or a 200W 12V Car Heater using 200W of “24V” solar panels, meaning 42V open circuit max

This was just an experiment but the fan did run at about the same speed as normal. These heaters are sold to defrost windshields on cars where the defroster isn’t working and plug into a car cigarette lighter socket. MPPT worked perfectly with the standard Solar Hybrid Hot Water Controller as shipped.

Due to the lower voltages, a really good larger heat would be needed, like a 1/16 thick or better metal plate backing the Eaton box (box flattened in back) to increase heat sink area when using a 12V element, there is a heat issue and more wattage input will over temp the unit!

This was only for testing. Please do not do this with the standard controller. If this is truly your application for the SHHWC, please contact us and we may be able to build you a custom unit for this special application.

If you use your imagination and a little creativity in special situations you could maybe use a space heater (like the car heater above) or other resistive element device (with only a heating element, no motors) to heat things, like maybe heating a horse water trough or barrel to keep it from icing over in the winter.

It doesn’t have to be water that you are heating. Please contact us and we may be able to build you a custom unit for special applications. Please contact us before doing crazy things, you don’t want a dead controller and we don’t want to have to fix it.

Remember that all of the above tests were not done for a extended period. Meaning it’s up to you to monitor heat sink temps when increasing wattage or doing experiments like the above ones.

The best tested setup including customer feedback is the recommended 4500W 240V standard water heater element and a “48V” set of panels (minimum setup + grid backup), or 750W (3 panels in series + grid backup) with a bigger box for more heat sink area. Do not exceed the Solar Hybrid Specs!

Please read the FAQ.

Always use a thermostat on any element! A professional installer or electrician should be used for any install.

http://techluck.com/faq.php

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POSITIVES

• Very simple design, stick to instructions and can last a lifetime or more

• Easily replace any components that may fail by any electronics technician

• 100% off grid function, requires NO POWER to run device

• Simple flashing LED when working

• Compact with minimal wiring, 2 wires in, 2 wires out

• Saves you lots of money in the long term

NEGATIVES

• One man operation means limited support and product could disappear for sale at any time

• Protected code to run the MPPT function (can easily be reverse engineered including PCB)

• VERY EXPENSIVE

• Does not reflect good value for money on initial purchase

• Money better invested in a quality heat pump system

• Does little when cloudy, and next to nothing with heavy cloud

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