Photovoltaic + heater. Power selection of panels and other components.

Hello,
For some time now, he has been focusing on heating hot water from the sun. I like the use of pv panels and a heater more. I believe that in many respects it is a better solution, and most importantly that it is more maintenance-free than water collectors. Only that at the moment it is a more expensive solution and hence my topic to dispel my doubts, pv or collector.

I would ask, preferably practitioners, to choose components for heating domestic hot water from pv. I would like to know what the smallest power of the panels I would have to install to heat a 100l level boiler, the heater would be in the middle, so theoretically half of it would be heated. Of course, what heater and driver for this (PWM or MPPT? Or maybe cascade switching?)

Some data in addition to the above:
- the panels would be mounted on the roof from the south (I do not know how many exactly, about 40 degrees I think)
- the length of the cables to the boiler room will be 10-12m
- from the calculations it turned out that to heat this 50l in an hour to 50 * it needs 2.3kw. I used the formula: E = Cw * m * (Tk-Tp).

In the attachment he adds the calculations from the page for my place of residence and 0.6kw panels. Anyway, he writes everything there.

I need hot water in this way mainly in the summer months, so from May to September it would be great to start with. If I like it, I would keep trying, because it's supposed to be addictive :D

I would like to achieve this at the lowest possible cost, so I am asking for the cheapest possible solution. Thanks in advance for your help.

This topic cannot be done cheaply and well.
You have to assume, not direct heating, first provide an energy storage - a power plant and 100% use of production from panels. Other combinations in the current framework and regulations are unfortunate and uneconomical.
The cheapest solution:
- a good company inverter, a stimulant, let's say SMA, Fronius 2-4 kW or new Chinese - cost 2000-3500 PLN
- depending on the inverter, at least 6 panels, expandable to about 18 panels - 6 pieces 260W - cost 3000 PLN - annual stimulant, 4200 PLN new - I'm talking about good panels

That is, the cost is about PLN 5,000 + about PLN 900 accessories - cables, structures, collection, etc. We connect to the power plant, we produce about 1500 kW annually and pick it up when it fits all year round, 80% taking into account that we do not use anything on a regular basis. Usually this ratio is 88%, so it will turn out that 1320 kW will be for free - return on investment. The more panels, the lower the installed cost of 1 kW and the faster payback. With an investment of 3 kW, the return on investment is approximately 6 years.

And only this is an optimal return, other things are just a waste of money - small inverter - no expansion - you need to buy another one, without legally connected to the power plant - energy losses - given for free or unused, poor sun - you choose energy from the power plant and pay or no warm water.

And probably so much in the subject.

Satisfied with the cheapest solution?

Everything's fine. Let me remind you that I set up this topic to dispel any doubts as to what type of solar hot water heating to choose, and I will not argue with anyone that I can heat the canister with 200w or 500w panels. At the moment, I am closer to the solution with a water collector, and as I still know little about pv, I wanted to make sure that I would not spit in the chin afterwards.

As for profitability. I care more about comfort here than about getting it back as soon as possible. I just want hot water during the summer months because I don't want to light the stove every day. Recently I have read a lot on forums etc. about pv water heating, there are a few such projects, but there are no details anywhere. anyway, the topic is still not very popular.

So you say that in my case it is impossible to do this: Used panels, heater, driver? As I look at it, with these three components I would fit in 2,000, maybe even 1,500, but I do not know how it would work. As I said, I am not interested in connecting to the mains, selling electricity, etc. I just want to heat the water in the summer months. If it is possible to put something together, I would ask for help in choosing the lumber, and if not, I take care of the collectors

I expressed my opinion, and as for the costs, these 1.5-2 thousand is like investing in a bicycle, but a stationary one, you are pedaling but you are standing still. Now another thing, this type of heating is usually based on 12 or 24 V, i.e. on average later for use with standard inverters. In addition, you need to divide the installation into several low-power heaters depending on the number of panels, take into account, for example, by adopting a 250w 12v panel, you are able to power the heater max 200W and only in ideal conditions, noon full sun - a little clouds and it gets 100W in the morning and in the evening 50W. It follows that the heater will only heat up to 2-3 hours in great conditions, the rest of the time is energy wasted. Example: a 250W panel on an inverter will generate about 1.5 kW a day in summer and will be forced into the network, a solution with a heater only, max 400-600W. These differences are blurred at higher powers, but let's say, with a power of 3 kW from the panels, you will probably heat a 100-liter tank in 1.5-2 hours and what the rest of the time ... energy to the basket or forced heating of the second tank, plus losses heat, etc. Remember that energy in the network is not only heating water, it is air conditioning, heat pump, energy for the refrigerator, washing machine and TV, that is, everything that needs energy - the rest of solutions aimed at a single solution is a hobby.

Now let's assume, let's say 2 500 W heaters, you will need about 1300-1400 W on the panels, and this is even in specific stimulants, 6-7 panels, say 300 PLN each, so you already have 2000,000, 12 or 24 V heaters and a driver. In my opinion, the effects are bad, no return, but as a hobby it can and will be, but like any hobby it is too expensive to produce results. I think solar panels in this case will be a better alternative.

I don't think I can help any more, and for the opponents of my thinking, this is only my opinion and my thoughts.

I know that you advise me well what would be the best, and believe that if I had at least 5,000 for this purpose. I would certainly do that. Most of what you are explaining to me here I have already read several times.
If I were to assume pv now, it would only be in the variant that I am asking about and if you can, help me calculate what powers for such a solution would be needed. Because at this point I am not interested only in heating the water, when it is cloudy, it will heat up with a boiler which is why I probably have solar panels, although I consider pv to be a better solution.

Erbit wrote:

Calculator in hand and calculate. You will have the specifics.

If only I know how I have never been an eagle in mathematics and physics. On the other hand, calculations and practice do not always coincide and hence my questions here.

Only 2-3 weeks ago it was possible to buy stimulants from Germany 1kw for a little over a thousand zlotys. Now, when I look at it, it's at least 1500. Spring is coming and prices have probably jumped up.

Since you have loose 2,000 and you want panels, buy and connect so that you have about 230V at the operating point and a heater with exactly the same power as the panels.

In my opinion, 1.5kWp and a regulator holding the operating point would provide hot water.

PS
Estimate roughly based on my construction. Warm is a relative term, and even the angle of the panels has a significant impact on efficiency.

Erbit wrote:

I would ignore energy losses (e.g. on insulation) in the calculation - they will not have a significant impact on the needs assessment.

Sure, because the boiler is a perfect thermos ...

Either cheaply or conveniently. There is no compromise on this subject.

If you want to be comfortable, you need power, and the power from PV comes from the number of panels - so it will not come out cheap, even with stimulants, because you just need a lot of them, so that they quickly heat the water on those less sunny days and be comfortable with everyday use warm water.
Since you have a small canister, you need to have a lot of power, because you can not heat up water in a larger, standing canister.

In that case, dispelled doubts, I am forced to put on solar panels at this point. I will return to photovoltaics when I have a larger budget and maybe they will become even a little more.

Thanks for your help, gentlemen, "he helped".

If you had room for a vertical canister, it would not be such a problem, because you do not need that much heat (but regularly), and in a vertical one it would be slowly accumulating and waiting. The horizontal is very good for the oven. It can be reconciled with solar panels, but as you have already seen in the collector thread, the collector needs to be oversized. It can also be done with one factory solar panel, but you still need a bit of space for the mini buffer, but the driver will not be standard anymore, but rather specialized.

The matter is quite obvious with PV panels. On the roof you have to put (to my eye) 1.5kW in the panels and add circulation in the tank, so that the heat is in the whole, and not only in the upper half - if it shone, stronger, longer.

It will not be on the plot, only at home.

idepopizze wrote:

This can also be done with one factory solar panel, but you still need a little space for the mini buffer

Right now I am wondering whether to make solar (how to do it or from heaters or copper?) Or buy a ready one. How does the factory surface compare to a handmade one, carefully made of course?

Mini buffer, i.e. how many liters?

You can find the calculations in my topic about the boiler and 2 heaters. It's just that for the vertical boiler, the horizontal one should always take into account the whole, i.e. 100l. On a sunny day, from 1 kW you can get up to 8 kWh (10 hours of work in the sun), i.e. the water in the boiler will heat up by about 65 degrees. On cloudy days it will be max 1 kWh, i.e. water warmer by 8-9 degrees. And never work with 230V at a power point! This would require the use of very small heaters (max 800W) and after activating the thermostat, the voltage may increase to approx. 300 V (open circuit), which will burn out various light bulbs, etc., elements that will be powered from PV. It is better to choose the voltage so that the already existing heater emits the right power. Examples in my thread and the pattern are:

U * U = P * R

For example, a 1.8 W heater is 30 ohms, so 800 (solar radiation power on a clear day) * 30 = 24,000. Root with 24000 = 155V, so the panels should be selected so that the Umpp voltage is close to 155V. The power is the same as from the 800W heater powered by 230V, but the maximum voltage will not exceed 230V, so the bulbs in the boiler are safe ;)

ps Today my installation heated the boiler to over 40 degrees, and it was clear until around 2pm

I have 2kW off-grid installations for water heating, I will describe from my own practice how it works.
12 monocrystalline PWR-180Wp panels, 2160Wp in total
Connected in two rows, they give a voltage of 212V
MPP regulator with a power of 2500W, giving alternating current (rectangle)
The structure is made of 40x40mm H-shaped aluminum profiles.
The rest of the bolts, connectors, aluminum or stainless steel.
Strings protected with 10A MC4 diodes and 6A 10x38 fuses.
Cable for the 10mm2 regulator (I had one) 8.5m.
On the roof, cables from panels to 6mm2 boxes are UV resistant.
Protection, two-pole DC circuit breaker.
The structure is earthed with a separate conductor.
100L horizontal boiler.
Standard heater 3x1500W 230V, 3kW connected to the regulator, 1.5kW for a separate thermostat as additional heating from the network.
On the side of the DC panels I gave a voltmeter and an ammeter, the regulator at the AC output is equipped with a voltmeter.
Panels set to the south at an angle of 18 °, from the east and west sides of the tree, in the morning the shadow descends around 8.00 am and reappears around 4.00 pm, of course in summer.
The installation has been in operation for the third year, flawlessly. I bought used panels, I don't know which year they are from, half of them are older, the cables are 2008 and they have older type of connectors. The rest comes from a demonstration installation, according to the seller, the newer ones were not connected, you can actually see the differences, in the older ones the foil is yellowed, but the current is the same.
From March to September the hot water comes from the sun, except on very cloudy, rainy days, even then, in summer, hot water remains in the boiler all day, sometimes it rises by a few degrees. Generally in summer, on a sunny day in the late afternoon, the water reaches 85 ° C. In spring and autumn the temperature rises by about 40 ° C. In winter, with temperatures of a few degrees plus plus, we smoke at home in the afternoon, e.g. in December, when there were sunny days, the temperature would rise by about 30 ° C. He writes approximately here, every day is different, same as the water temperature in the boiler in the morning, it is rarely below 30 ° C, hot water is also used during the day.
I noticed that in summer, when it is hot 25-30 ° C with full sun, the panels heat the water slightly better than in bright clouds. They are definitely sensitive to high temperature, at 35 ° C I measured the temperature of the panel by applying a thermometer to the frame, it was 65 ° C, the silicon plate closed between the glass and the foil probably warmed up to a higher temperature. From what I read a small tilt angle (as for me ) makes better use of diffused light, this would be confirmed by practice.
The Vmpp voltage should be 212W, but at about 200V, the panels heat the best, the regulator corrects them from 185 to 205V.
At the beginning, the installation was connected as a cascade, the 250/500 / 1000W 230V heater was switched on manually, but it worked so-so, switching between the heaters resulted in large voltage spikes. That's why I bought a regulator, the installation started to heat much better. At the beginning I left the heater from the cascade, only connected in a series of 1750W, but with strong sunlight it could not cope. When it was cool to 20 ° C, the voltage reached 230V, which is well beyond Vmpp, now it is 3kW. With moderate or weak sunlight, it heats the same way, while in strong sunlight, when it is cooler at 200V, the intensity exceeds 11A, i.e. several-year-old panels give over 100%. Of course, the measurements are made with cheap instruments.
The situation with the maximum no-load voltage, Voc, is interesting, it is higher in the morning when it is cool, but the sun is lower than at noon, but then the panel will give the most current.
I wrote a little, maybe it will be useful to others.

As for the advantages of on-grid, I absolutely agree and that will be the next stage. However, I'm going to leave 2-3kW off-grid for water heating anyway, and in order not to waste energy, you can connect the panels through a relay, which, after disconnecting the heating, will supply electricity to the inverter to a separate MPPT output. Nothing will be wasted and electricity will flow to the grid when it is needed most, in the afternoon.

My proposal for a 1kW installation with the possibility of expansion to 2.5kW in the amount of up to PLN 2,500. Prices taken from a well-known auction site.
195Wp monocrystalline panels at PLN 298 x 5 = PLN 1490.
MPPT regulator PLN 590
5 panels will give 975W at 186V, if you add one more 1170W and 226V
6mm2 cable, DC switch, the rest in the description above.
You can buy cheaper panels, e.g. amorphous ones, only they work with a higher voltage, they take up more space. You need more connectors, cable, profile, and that also costs money.

Erbit wrote:

How many people use these 100 liters?

4 people, although I would not compare it so much, because one of them takes a quick shower, the other takes a deep bath. Just like a dishwasher, it significantly reduces hot water consumption, and it is at home, although the dishes are still washed by hand.

We use the electricity from the panels not only to heat water.
The cable from the panels is connected to the "box", from which exits to; regulator, kitchen, garage, additional installation is made for about 200V DC.
Here I use the advantage of the regulator, which is maintaining the voltage at an appropriate level. I bought an old AEG 1200W cooker with a porcelain 3-range switch, it is used for cooking in sunny weather. The LED floodlights are great with direct current, one works up to 90V, I use it for work in the basement. Heaters in winter. These devices, thanks to the fact that they are connected `` before '' the regulator, receive a current not higher than 200V, and the energy that they do not consume, the regulator will use to heat water. The installation may be primitive, but it gives little savings and allows you to use all the energy from the panels. In summer, it is rare for the boiler to be heated to its maximum temperature.

Well, direct current with appropriate parameters can be widely used. I also have a separate DC network used for cooking, heating the house on sunny days, etc. However, after 2 years of work with a voltage of Umpp of approx. 200 V, I decided to switch to a lower one. Now the installation works on 120-150V, so there is no risk that the voltage will rise above 230V while burning everything that is connected. In the case of a network> 200 V, it is safe as long as the MPPT (or PWM) connected behind it monitors the voltage. When it is disconnected or falls down and the remaining elements are of low power, they may fly up in smoke. The only disadvantage of the reduced voltage solution is the need to use more power. For example, a stove with a nominal power of 2.5 kW works for me as 1-1.5 kW.

@ anaba255
It's nice to read a practice from PV.

As you can see, I probably assumed too optimistically that 1.5kW would be enough

@ philips89
Take a look at the last diagram:
https://www.elektroda.pl/rtvforum/topic482463-11640.html#16346871

Imagine your vertical garage instead of your horizontal.

Will you be able to put it together and organize a controller that simultaneously supports a pump in the solar system and a pump that is run periodically in this mini buffer with a heat selection coil?

Do you have a place for such a pot somewhere? It can be a plastic barrel, it will be cheap, but you need to insulate it anyway.

Because if you can, you can build. Personally, I would recommend a copper collector covered with black chrome, if it is not a self-made copper meander drawn with black paint (from the pistons or exhausts there). It is still a radiator, but in a drainback I do not see that it makes sense in the long run.

idepopizze wrote:

@ anaba255
It's nice to read a practice from PV.

As you can see, I probably assumed too optimistically that 1.5kW would be enough

IMHO, up to 100l can easily be enough. My colleague anaba255 has 0.5 kW more and the bulb heats up to 85 degrees. Probably the rate at which the heat escapes at this temperature is so great that even with 2 kW it is (almost) impossible to exceed 90 degrees. For my taste, take 1-2kW per 100l, i.e. 1.5 kW will be a beautiful compromise.

Well, you can be right about these heat losses in the horizontal one, I ignored it in general estimates, because I was guided by the parameters of the horizontal insulation, and in the vertical ones it is not so bad with the losses. Besides, when the boiler is on fire, you cannot see them, because the boiler room is also heated.
On the other hand, loading the canister with high temperatures also does not make much sense, because at a temperature higher than 60 degrees, limescale begins to build up.

So what if the owner will be happy when he gets to 90 as well as the other side of the coin is shortening the life of the pot with a stone.

These 1.5kWp panels according to estimates anaba255 would cost about PLN 2400

idepopizze wrote:

You can put it together and organize the driver

There will be no major problem with putting it together and making it. The driver is also probably not a problem, if it is not very expensive, of course.

I'm just a bit skeptical about this solution for two reasons:
- two pumps, which is twice as much energy consumed
- and will such a solution not be less efficient due to the fact that the collector will heat the water in the buffer, and the latter only the boiler? Because I understand that the coil in the buffer heats the DHW directly?

At 70%, I am determined to buy a ready-made collector, because the prices start from PLN 700, and it will certainly be more efficient. Of course, if only one panel was enough. Because if I had to buy two, it would be more profitable to do.

Coming back to connecting the solar panel to the mantle. Would such a single purchase of 2m2 be enough for the 100l? Can it be calculated somehow? As I wrote somewhere, it will be a temporary solution, because after the renovation of the heating and boiler room, I do it as it should with the vertical baniak. So I don't know if there is any point in doing this with a small buffer, unless it actually has more advantages than disadvantages.

@ philips89
If you plan to renovate the installation, why do you play with these makeshift works?
Give it a rest for now, and then you will do it godly with two collectors connected to a vertical canister. If you have some time and resources, do it yourself in copper 2 collectors. You will really get more benefits from it and then more comfort.

Read because it's a solution for you:
https://www.elektroda.pl/rtvforum/topic3112753.html

Except that he immediately suggests a stainless vessel.

idepopizze wrote:

If you plan to renovate the installation, why do you play with these makeshift works?

Because this renovation will be at the earliest in two, maybe even three years, and I would like warm solar water this year. I had already tried on a year ago, but finally summer was over and I put it off until spring.

Would the diagram you recommended to me be in the drainback system? I just read about it and it's a cool solution. Before that, I didn't know exactly what it was about.

idepopizze wrote:

Read because it's a solution for you:
https://www.elektroda.pl/rtvforum/topic3112753.html

I will read, maybe I will find something interesting.

Another question about the self-made. Would aluminum tape, such in rolls, be suitable for an absorber?

philips89 wrote:

Would the diagram you recommended to me be in the drainback system?

This is drainback

philips89 wrote:

Would aluminum tape, such in rolls, be suitable for an absorber?

Do you have any methods of joining copper with aluminum?
And I don't know how to stick to ammeline paint

I have a factory one, because I did not want to mess with the glass, and they are standing in front of the house.


Take count what is profitable for you.
An additional pump (the second one), this small insulated buffer with a coil, will go to the ejection, an additional controller will also not be useful anymore. In addition, fittings for connection, i.e. valves, etc., will go to waste. You spend a little and then you throw it away anyway. Besides, you have no guarantee that it will start immediately and it will heat up like you want.

idepopizze wrote:

And you have some methods of joining copper with aluminum

I thought to carve, for example, grooves in polystyrene and stick the whole thing with such a tape. Then the pipes would fit into these grooves and you would not have to solder. But I'm not sure if such a tape will last, or rather the glue under it.
I have a small burner from a supermarket for soldering, noi migomat, but I don't think it will be useful in this case.

Boy, you're raving. What styrofoam?
You leave an empty drainback in the sun and have a hitch of 90 degrees. And what will be left of the polystyrene after such heating?

Take the time to read how to do it correctly, watch a few videos like:
https://www.youtube.com/watch?v=tOpoupq7DRI

There is really no shortage of reading material