Calefacción solar

It's quite frío in January, the solar heating needs to be reinstalled, and properly this time. Decided to not drill holes in the wall for pipes, but use open windows instead, and simply blow the hot air through the mosquito screens.

Bathroom 2 gets its own heater, as that one has the outlet opening at the back, while the bathroom has a hole in the wall there for a ventilator above the (ex) shower:

Well, who would have thought. This palm tree casts a shadow later in the afternoon. We'll need to cut off the dead leaves, which is long overdue anyway.

And so it happened, with the 4m extendable Wolf telescopic cutter. Not that this is a lot better, shadow wise. Even on a non cloudy day. Oh well.

Solar Heater B continued (continued) continued

The second solar heater (B) now is connected to the house too, using a nifty flexible hose. It yields a little cooler air than the first one, 49º versus 53º. Heater B has a bit smaller converter, 4 cm narrower, 96 cm versus 100 cm, so 4% less surface area.

Solar Heater B continued (continued)

Frame for the mosquito netting.

Two sides, the netting 2 cm apart.

17:30, sunny: 44º! (110ºF)

Two heaters now. Yes, those greay pipes will be hidden.

But, as you do, then there's rain.

Solar Heater Capacity

All very well, a solar heating, but what does it yield? 50° hot air is of course nice, but is it significant? A calculation.

The system has a fan that moves 70 m³/hr of air, in principle.

The heat capacity of air is 1,005 kJ / m³ it therefore costs 1005 J of energy to make one kg of air one degree warmer.

1 m³ air weighs 1,225 kg.

The outside temperature is about 15º, while 50º is output, a temperature increase of 35º.

If that happens during one hour, there is 70 m³ air 35º warmer.
That costs 70 m³ * 1,225 kg * 1005 J * 35 = 3016 kJ in one hour.

Watt = J/second, so the capacity is 3016 kJ / 3600 s = 834 Watt

The sun emits around 2.7 kW of energy per m² this thing has a surface area of 2.1 m ², and thus captures 2.1 * 2.7 = 5.67 kW energy.

This means that the yield is about 834 / 5670 * 100 = 15%, which is not very different from the efficiency of electrical solar panels (15 - 20%)!

Is the capacity significant? An electric radiator has a capacity of 800W (low) to 1400W (high), the kitchen has a volume of 140m³
I have materials for three solar heaters, so perhaps a few degrees? I hope that will make the difference. And it's free, that makes quite a difference.

You can view solar heaters as a "remote window". Normally the sun shines through windows, and heats up an interior. However, this house hardly has windows, so we'll use these "remote windows" instead.

You can wonder if the 70 m³ per hour air really is achieved is a good question. Perhaps next time.

Solar Heater B (continued)

 Saw - drill - file - glue - clamp

Solar Heater B

Yesterday started the second solar heater, as I have materials for three. This time I screw aluminium profile and wood in one go. That saves a lot of time drilling precise holes in the aluminium, afterwards. Now I drill holes in the aluminium profiles first, punch a hole in the (soft) wood, and glue and screw all in one go. And ready! (Well..)

The Hot box: 50º +

12:00, bright sunshine: more than 50º! Beyond the end of the scale of our thermometer, around the bend!

The Hot Box BROKEN! (solar heater) 3 // Calefaccion Solar ROTO! 3

The mosquito netting apparently pulls so hard on the frame that one bar broke. Repaired with a new extra bar, and some bolts.

Ok, this needs some improvement, it's just the test setup.

52ºC / 122ºF at the exit of the solar heater!

47ºC / 116ºF hot air into the interior.

The Hot Box (solar heater) 2 // Calefaccion Solar 2

Today, 10:200, full sun, outside air temperature 16ºC / 60ºF. Result: 50ºC / 120ºF. Fifty! Not bad. What? Fantastic!
I removed the thermometer at 50, as it's the end of the scale.

The Hot Box (solar heater) // Calefaccion Solar

This house is nice and cool in summer because of the thick stone walls. Alas, that means that also in winter the house is cool, even when sunny and 20º outside, which is not pleasant. The house hardly has any windows at the sun side, so there is no heat coming in. That can be helped, with a solar heater. There are various types, but in principle it's a (wooden) box with a transparent front, and a black contraption on the inside, the "absorber". Air passed through the absorber heats up, and is led into the house. The transparent front can be glass, or a plastic or polycarbonate material. The idea is to isolate the collector from the cold outside air, to prevent heat loss.

The black absorber can be various types. Some people make a pipe of soda cans, painted black. Others use a sheet of black metal. Air passed behind that sheet heats up. A very efficient type is constructed with two or more layers of mosquito netting. Pass air through and it heats up.

If you're curious have a look at: https://rimstar.org/renewnrg/solar_air_heater_types_diy_homemade.htm en http://stonehavenlife.com/comparing-solar-air-heater-designs-performance/, en http://www.builditsolar.com/Experimental/AirColTesting/Index.htm for various types and an efficiency comparison.

I have chosen the "Screen solar air heater (matrix)", with two layers black mosquito netting. As the transparent material I have asked for a sheet of Makrolon 3000 x 2100 x 6 mm to be sawn in three 1 meter wide sheets, so I can build three individual solar heaters of 2.1 x 1 meters. Makrolon is sheet material for transparent roofs. The box is made of thin triplex (4 mm) and 20 x 20 mm wooden bars and some aluminium profile. Used 3 x 10 mm screws and D3 wood glue. A small fan and a 4 Watt solar pan0el for moving the air through.

Today it's ready for it's first test, at 17:00, so near sunset. Outside temperature: 14º C (50º F). Hot air temperature: 38º C (100º F).

Setting sun, eh! Very curious how it'll be in the full sun tomorrow!

I have not insulated the box, nor sprayed it black. I have material for 3 solar heaters, so I will experiment with insulation and black paint with those.

The box is oiled with Tung wood oil inside and outside. (Inside only once.)

Solar panels, or not (hello, Enphase!?)

Now we have a swimming pool with a 1.2kW pump, running 8-9 hours a day, the decision to install solar panels has become more urgent. A big consumer like this costs 2€ a day, or about 800€ a year, while the sun is shining constantly. Alas, a private solar installation is not as easy a purchase as in The Netherlands. In the Netherlands you can feed back your surplus electricity to the grid, and you get paid for that too. In Spain the government decided to tax power generated by private solar panels. The lobby is strong, apparently. The idea is that you buy less electricity from the electricity companies, and thus you disadvantage other consumers. Of course it's just an obnoxious law, that "Europe" is protesting. But, the government here has been out of a majority for a very long time, and nothing much happened, and the law has not yet been changed.

What to do. We don't want to go "off the grid", and become totally independent. By day you use power form the panels and you charge the batteries. At night you use the stored power. But batteries are expensive, dangerous, end short lived (ten years). Remains "grid tied", where you use your own power first, and if your panels don't yield enough you use power from the grid.In the Netherlands that is all arranged, but here in Spain it isn't. There is another option: you do connect your solar panels system to the grid, but you don't feed back surplus power to the grid. That is called "zero grid feedback", or "self consumer". Zero feedback would be nice. No fuss with taxes, you are sort of independent, but you can still use power from the grid, if needed, like at night.

What/which system, and how big? Well, preferably more than 1.2kW for the swimming pool pump. But, do we keep on cooking with gas (bottles), or do we switch to electric? Atag refuses to market its products in Spain, see http://jansenendewaal.blogspot.com/2017/03/oven.html, so we could switch to electric cooking. A big electric "burner" is ca. 3kW, though that is not all day. And are we going for an electric car? As you can see we'd like to start small, ca. 1.5 - 2kW, and extend later.

But, the "inverters", the apparatuses that convert the direct current from the panels to 230V/50Hz alternating current are not that flexible. Most like a configuration within their capacity. Capacities range, for example, from 1700 W to 2140 W, while the next bigger version is 2500 to 3600 Watt. These inverters, that convert power from a series of solar panels, are called "string inverters".

There is another option: a mini-inverter, where each solar panel has it's own small inverter. Buy an extra panel, buy another mini-inverter. The manufacturer of these inverters is called Enphase: Enphase (https://enphase.com/). Good! Hm, no dealer in Spain. Yes in The Netherlands, France, Germany. Understandable, if Spain is making life for solar people difficult. But you can order your supplies by internet, and diy the installation, which is easy with Enphase.

Another advantage of micro-inverters is that they are long lived, about 25 years, versus 10 years for string inverters. And, a system built with separate inverters is very good with shaded panels. It will simply shut off panels that are shaded, and not the entire system.

Remains the choice for grid-tied, and yes or no zero-feedback. Before you know if this is possible with Enphase a lot of water has not run through the Rio Antas. Enphase themselves don't tell you much about zero feedback on their website. "Contact us" gives me no response (twice). My internet dealer says "I think it's possible". Ask on a forum, and one person says "yes it is possible", the other says "no you can't". Let's study this topic ourselves then.


Enphase has a number of series inverters that are basically compatible:

M215, 215W (4th generation)

M250, 250W (4th generation)

S280, 280W (5th generation)

IQ6 (60 cell panels, 230W) en IQ6+ (72 cell panels, 280W) (6th generation)

Modern solar panels yield 280-300W at the sunniest moment of the day.

Enphase does say something about zero-feedback: you need to apply a "zero feedback grid profile" using your Envoy. The Envoy is a small box that controls and monitors your collection of inverters, and delivers nice statistics and graphs via wifi. On Hawaii there are regions where you need to apply this zero feedback grid profile. But, you need a more recent series of inverter than is available in Europe: the S-series or the IQ. In Europe only the older M-series is available.

But, in Australia, where they have 230V/50Hz too, like us in Europe, there is the S270 (260 W)! But, that's Australia, and not here.


Strange people at Enphase.

And still no answer from Support.

Ticket : 00982541
Submitted : 6/24/2017
Subject : Solar panels system with Zero feedback to grid - Envoy-S standard or metered?

After some more studying you encounter a comparable manufacturer: SolarEdge, who also have sort of a micro inverter, and a scalable system. It's the same company IKEA uses for their solar panels systems. But, SolarEdge is from a country I prefer not to do business with. Yes, Israël.

Studying further you see the financial situation of Enphase is not that great. Not strange if your support department does not answer and you don't market your products in Europe.. Anyway, 25 years lifespan and guarantee does require a company that is still around after 25 years.

Next year (2018) they will market the 7th generation "international inverter" that will make everybody happy.

But what am I to do now? I would be perfectly happy with the M250 inverters, but then I need to be able to install a system here in Spain that is allowed to feedback the grid. No answer about that from ENDESA, who are not overflowing with information either. Their support department is the same as Enphase's, apparently: still no answers.

Sigh.

Ventilador 2

The garage is quite hot and stuffy; that's what you get without ventilation. High time to make a hole in the back wall, and fit a small solar ventilator.

The hole was made by Rafa, the handy man in the area. With a big hammer and chisel. Because these hollow blocks are easy to punch holes in, he said.

BENG! BENG! Well, not so easy after all. Especially as the block had been filled with concrete and an iron reinforcement bar. So, the hole (BENG! BENG! BENG! BENG! etc.) became slightly bigger than intended. But, with portland cement and mortero revoco blanco impermeable I can handle any damage.

The fan was wrapped in fly screen so no wasps, mosquitos, foxes, flies, dogs, wood lice, whales, etc, can get stuck in there.

Some foam tape for air tightness.

Outside nothing obvious can be seen.

El panèl solar. (4W, 17-24v, 230mA)