# Question about solar power?



## John and Cecil (Dec 22, 2019)

Hi, I was told by someone that to use solar power in your home in Portugal you had to pay for a permit or license or something. I assume that is only if you are connecting your solar array to the grid and not if it is an independent system? I do not have my home yet but I am hoping it will happen soon and I would like to start reducing my reliance on fossil fuels and the power companies. I am thinking hot water is a good place to start. In the USA it was not a problem, natural gas is cheap there and I used to pay less than $10 a month for my on demand natural gas hot water heater, but propane here is much more expensive and electricity costs about the same as propane too. If I get a pellet boiler for heat I could probably use that to make hot water during the winter since pellets generate 3 times more heat per euro than propane, diesel, and electricity, but that would not help on days when I do not need to heat the house.

I just thought of a possible way to get started without making a huge investment. I would like to get a few solar panels (maybe 3x 400w panels) and put them on the roof. I would hook them up to a charge modulator to convert them to household current. I would then plug that directly into an electric water heater with a decent size water tank. During the day the solar array should generate about 6kwh of electricity which would be stored not in expensive batteries but as hot water in a tank that I can use during the day. I would also hook up a tankless electric water heater (plugged into the grid) and directly after the water heater with tank outlet and program that to kick on only if the water temp is below a certain temperature (say 40C). Thus I would always have hot water but I would use much less power company electric to heat the water, and on sunny days I might not even use any power company electricity to heat the water. No batteries makes the system substantially cheaper, although perhaps I might need one small battery if the water heater cannot handle any fluctuations in the supplied power. I figure the electric bill savings would pay for all of the supplies in about 2 years. 

Has anyone tried anything like this? If the solar panels are not hooked up to the grid would a system like this be legal without acquiring a permit or license? Thanks!


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## Stevesolar (Dec 21, 2012)

Hi,
Why not use solar thermal panels instead!
They directly convert the energy from the sun into hot water!
Cheers
Steve


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## NickZ (Jun 26, 2009)

What Steve said. You're designing a Rube Goldberg setup

Most(maybe all?) solar hotwater setups have an electrical element to handle winter. 

Pellet boiler requires radiators and everything in between. Does your house need that? 

If you want pellet heat a simple air unit is likely half the purchase price and saves all the other work and parts.

You might want to compare the purchase and running costs of a heat pump instead. Modern heat pumps aren't just cheap to run but will also cool your house or dehumidify.


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## John and Cecil (Dec 22, 2019)

Stevesolar said:


> Hi,
> Why not use solar thermal panels instead!
> They directly convert the energy from the sun into hot water!
> Cheers
> Steve





NickZ said:


> What Steve said. You're designing a Rube Goldberg setup
> 
> Most(maybe all?) solar hotwater setups have an electrical element to handle winter.
> 
> ...


Hi, thanks for your reply. I do not have the house yet but the two that interest me so far either have radiators already installed or the pipe work is pre-installed. I know, I like the pellet stoves that heat the air. The other issue is one of the homes has a massive diesel boiler already installed and it is outside in another structure. The easiest solution is to remove the diesel boiler and tank and install a pellet burner in the same place. But if I can without too much difficulty close the 2 pipe loops for the radiators I could tie into them in the garage and install the pellet boiler in there and then vent it through the outside wall. I am going to need to wait until I actually have a house to worry about the heating system though.

I do not quite understand the solar hotwater systems. My neighbor here told me that their system was very expensive. Plus you must run waterlines up to the roof, wires are easier to deal with especially considering they do not built wood framed homes here which have wall cavities. 3 400w solar panels plus the modulator and wiring would probably cost 600 euros and save me at least 1500-2000kwh of company electricity purchases per year. If I needed a 6kwh li-ion battery to store that power it would cost a couple thousand dollars, this way I avoid that expense. That comes out to about 300-400 euros in electricity savings per year. Since an electric on demand water heater is fairly inexpensive (maybe 200 euros) and simple to install, and it is very efficient, *the system pays for itself in about 2 years*.

I came up with this system idea because a house I am considering already has an electric water heater (the tank type) and it looks relatively new. I prefer on demand water heaters so they are not keeping the water warm while I sleep. I was considering tossing the tank style water heater but then I thought why not use solar power to run that existing water heater and then let that warm water be heated by the on demand water heater (if it is not hot enough) so I will purchase less electricity. I have been told those rooftop systems are very expensive, how many years does it take for a solar water heating system to pay for all the upfront costs? I do not use too much hot water, if it is on demand hot water without a tank then I probably use between 4- 6 kwh per day depending on the season. *If a solar water heating system takes only about 2-3 years to pay for itself then I am interested.*

Also I would like to get my foot in the door using solar panels. In the future I would like several vehicles that can share swappable batteries ( a small boat, a motorcycle, and maybe even a small car). Then I can run a large solar array on the roof to power the battery charger. During the day while one battery is charging I can be using the one that charged the previous day to ride the electric motorcycle. Then at night I would take the full charged battery off the charger and replace it with the drained one to charge the next day. Eventually I may even cut my ties to the grid and use the swappable batteries to supply power to the house as well.


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## Strontium (Sep 16, 2015)

Hi, Using things which are ready available in a configuration which is reasonably common here is a flat plate with integral tank solar hot water (depending on size maybe 1400 euro at your local DIY) then either a wall mounted gas water heater or the electric immersion heater in the storage tank on top of the panel. The panel pre-heats the water in the tank and if it's not up to temp the gas boiler (on demand) boost the flowing water temp up when a hot tap is opened. 
A more efficient variation is a panel made of vacuumed balckened glass pipes on a manifold with some controls and a separate tank + PV panel to run the electrics. If/when you get your place it's an idea to check what other people in the area use.


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## NickZ (Jun 26, 2009)

John and Cecil said:


> I do not use too much hot water, if it is on demand hot water without a tank then I probably use between 4- 6 kwh per day depending on the season.


2000 kw/h per year sounds like one of the old style heaters. There is an Ariston heat pump heater that if you believe the numbers claims a fifth of that. I still can't convince myself it's worth changing over from my old high energy one. But I admit here most years I only need it running during the winter. In a colder area the math might work better. 

The Ariston is on Amazon at between €500 and 600 depending on the tank size. 80 or 100.


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## John and Cecil (Dec 22, 2019)

NickZ said:


> 2000 kw/h per year sounds like one of the old style heaters.





Strontium said:


> -


Thank you for your responses. I have been looking around but there is very little solar power being used up here, at least that I can see. And I just made that 2000 number up, I am not sure of yearly numbers as I always used natural gas on demand systems and it was very inexpensive (less than $10 a month for hot water and stovetop gas). But my last rental in Portugal had a water heater set very hot and was using about 8kwh er day. I shut it off and experimented with it and I determined it took about 2kwh of electric to make enough hot water for a 10 minute shower (in winter). I figured I should triple that number to account for hot water for 2 people per day (6kwh), then I multiplied by 365 to get 2000kwh per year. 

The upfront costs on most of these water heating systems are still high. Solar panel prices are coming way down, so building a solar panel system makes a lot of sense. A 150 euro solar panel produces up to 700kwh of electric per year which means the panel pays for itself in only one year. The controller to convert the power to household current is not very costly either. The cost problem is the batteries used to store the power (probably around 400 euro per kwh of storage capacity). a 150 euro solar panel requires an 800 euro battery to store 1 days supply of power.

A workaround to the costly battery issue is to connect to the grid, but apparently in Portugal you need to pay for a license to hook a solar array up to the grid and then they pay you very little for any uploaded energy. So the best solution appears to be to use solar panels whenever possible without using a large storage battery. Heating water is one such way to take advantage of an inexpensive solar array. Charging electric vehicles is another way, perhaps running an air conditioner or dehumidifier during the day would be another (although that might require using at least a small battery to supply a steady flow of power). 

I know very well that a solar water heater is much more efficient than a solar panel running an electric heater, however that is not the issue at hand. The issue at hand is the costs and the time it takes to get a complete return on your investment. Solar panels are manufactured at such a high rate now that the prices are only a fraction of what they were a few years ago. I do not think that solar water heaters are anywhere near that cost effective. Solar panel energy is very cheap now with only a minimal upfront cost. For 1000 euros you can build a solar array that can generate 10kwh of electricity per day. That is enough power to have hot water for one person plus power an electric motorcycle like the zero fx for 100km of combined highway and city riding (or 150km city riding only). So every day for the life of the solar panel array you can ride a motorcycle for 100 kms plus have hot water for the day and with only 1000 euros upfront cost. If I were to get my electricity from the grid it would cost more than 700 euros a year.

My point is that if you can find a way to use solar panel power without investing in extra storage batteries then the system will pay for itself in about 18 months. I do not believe that any of the solar water heater systems can compete with this in terms of return on the initial investment.


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## John and Cecil (Dec 22, 2019)

Also a solar panel system is upgradable. In a few years battery prices may be much lower than today. Then you can buy a large battery for much less and toss a few more solar panels into your existing array and hook up the battery. Then you can call the electric company and shut off your service and never look back. Or the solar panels can be removed from the roof and used to power a small boat (a lightweight 14' aluminum rowboat can use just one 400w panel and a small power tool battery to power a 36lb thrust electric trolling motor for free propulsion during the day. 

I like that the panels are low cost and that they can be used for different situations. There was even a guy on a forum who was building a recumbent bike towing a trailer with a solar panel to power the pedal assist motor and he was going to try to ride around the world. It seems like a good way to get started using clean energy and start learning from experience and then building bigger and better systems.


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## NickZ (Jun 26, 2009)

I think the smallest solar hot water system I've seen is 150litres. Many are bigger. They're overkill for one person. During the summer likely over kill for even a small family.

I still think you're looking at this the wrong way. Instead of investing in becoming your own power plant think about reducing your use.

10 kw/h a day ends up at 300 a month. I have my apartment 100% electric. Stove top,oven,heating ,cooling and a very crappy efficient hotwater tank plus all the usual lighting,computer and appliances. I never come close to that level But everything excluding my hotwater tank is rated aaa+++

The problem with your plan is to make it really work you'll still likely want to make the effort to reduce your consumption. Start here.


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## John and Cecil (Dec 22, 2019)

NickZ said:


> I think the smallest solar hot water system I've seen is 150litres. Many are bigger. They're overkill for one person. During the summer likely over kill for even a small family.
> 
> I still think you're looking at this the wrong way. Instead of investing in becoming your own power plant think about reducing your use.
> 
> ...


Yes I understand about reducing consumption. Eventually it will be an on demand water heater and low flow shower heads. In my last house my water usage was 20 US gallons per day. I had all led lights and I was even considering led cobs. But my lifestyle is riding motorcycles, me and my dog want to rip around the canyons every sunny day but I do not want to burn gasoline (otherwise I would already have a SMW SM500R parked outside). In California we rode 12,000 - 15,000 miles a year. On our Dorsoduro we would need to have a new rear tire put on every 2 to 3 weeks, and we had 2 bikes at the time (we had a Yamaha MT-09 that we took on trips and to commute, the Dorsoduro was strictly for riding winding mountain roads on the very edge of our tires). When we stopped to rest the rear tire would smoke. The plan is to slowly build a bigger solar system in preparation for when we get an electric supermoto motorcycle. Something like the Zero Fxs with swappable batteries. Me and Cecil want to ride here, there roads are ridiculously insane here! We can ride 100 miles of these twisty mountain roads every single sunny day. That requires generating about 10kwh of power just for the motorcycle alone. So when we aren't using all that power for the motorcycle (and until batteries become affordable for storage) I am looking for ways to utilize solar power without the need for a battery. 

I am very eccentric, and so is Cecil.  My needs are probably somewhat unique.


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## John and Cecil (Dec 22, 2019)

I just read something interesting. They apparently make modules that will allow you to power your home with an electric vehicle. 

Perhaps it is possible to have 2 electric vehicles (example: 10kwh motorcycle and a 20kwh small car). Then a rooftop solar array with no battery storage is used to charge both vehicles. When you take the motorcycle for a drive the car stays connected to charge from the panels and to power the house. Later when you need the car the motorcycle is plugged in. Sometimes both vehicles will be plugged in to run the house and charge from the panels.

With enough inexpensive solar panels and a system as I described above it might be possible to get off the electric grid permanently without the need for a "dedicated" storage battery. Even if you get a lot of bad weather and the battery power is getting low you can always drive one of the ev's to the nearest charging station and fill up with electricity to use at home.


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## John and Cecil (Dec 22, 2019)

I have been researching this when I have some free time (which is not very often). First from what I have read you need a license and a contract with the power company to hook up a solar panel array to the grid. In the past it was easier and they would pay you very little for the electricity that you upload to the grid. But then the laws changed and they are required to pay you a lot for the uploaded energy because it is coming from green technology. From what I read the power companies do not wish to pay that much for the energy so they make it extremely difficult for you to get a signed contract. If this is the case then the only other option is to install a solar array that is not connected to the electrical grid.


I am rethinking some of my original ideas and taking some of the suggestions into account too. I now think the best system for me would be a very efficient house as Nick suggested. I would then need to design my solar array to power the house in the winter as the solar panels may only average 20-25% of optimal in winter here (it is cloudy and it rains a lot in winter). Then in the summer I would generate much more energy which I could use to ride the electric motorcycle and possibly power an air conditioning unit. It would be best if the motorcycle had swappable batteries and the house system could have just 1 small battery (maybe 1kwh) so power would not be uninterrupted when I swap the battery on the motorcycle with the one being charged and powering the house.

I do have some large power requirements in winter though. I like to watch movies and tv and play video games on a 130" movie screen, that alone would use about 1.5kw a day. If I am using an electric on demand water heater and low flow water nozzles my winter power needs might be around 10kwh per day total for the house. Perhaps I can reduce that by quite a bit by using a pellet boiler to heat the house and the hot water in winter, maybe I can get it down to 7.5kwh per day. 

My thinking is I will need to build a solar array capable of supplying at least 30kwh of electricity in optimal conditions so I can run the house in the winter. I believe I read that optimal conditions are 5 times the rated hourly output of a panel, so I would need a system with at least 15x 400w solar panels. If I build a system with 15 panels then I would generate about 7.5kwh per day in winter and a maximum of 30kwh on sunny summer days. But since I would be using the electric water heater in the summer my house would then require about 10kwh per day. If I assume I will average maybe 20kwh per day of power generation during the warmer half of the year then I will have an excess of about 10kwh per day. This means that I can ride an electric motorcycle or run air conditioning or dehumidifiers to use up that excess power (since I cannot sell it to the power company), or possibly charge a plug in hybrid car.

This is where my idea about the solar panel running an electric water heater comes into play. I am making all these numbers up from some online research and no firsthand experience. I have no idea how much power a panel will produce in summer and winter and on cloudy days until I actually buy one and start using it.  I also would like to buy a small lightweight aluminum rowboat and put a 400w solar panel on that connected to a small power tool battery and then plugged into a 36lb thrust electric trolling motor but I am not ready to do that yet (need a car to tow). But my main issue now appears to be the winter. The house must be self reliant in the winter because I will be getting much more power in the summer and I can then get the perfect motorcycle to use all that extra power.


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## John and Cecil (Dec 22, 2019)

NickZ said:


> Instead of investing in becoming your own power plant think about reducing your use.


I found this webpage this morning. 






Chest Freezer To Fridge Conversion-The Most Energy Efficient Fridge Ever | A Self Sufficient Life


Great advice on how to simply convert a chest freezer in to a fridge to save huge amounts on your electricity bill.




www.aselfsufficientlife.com





These folks live in Spain and to cut their energy consumption they modified a 260L capacity chest freezer into a refrigerator. They are claiming a daily consumption of 150-180w for an entire day in warm weather. I read a standard refrigerator consumes 1-2kwh per day, so this option can possibly reduce daily electricity consumption by 1kwh. When solar power is more readily available in the summer you can use a standard fridge and turn the temperature setting down on the chest fridge to use it as a chest freezer again during the summer.

I do not know what the prices are here in Portugal but LED cob lighting is another way to cut power consumption. They can be twice as efficient as standard LED light bulbs. The trick with the cobs is to use a more expensive higher power cob and then run it at very low voltages so the efficiency goes up. At standard voltage I seem to remember about 120-150 lumens per watt, but when running them way below their standard power the efficiency can jump to over 200 lumens per watt (especially in the.higher temp color spectrums like 6000k). But they require an led driver too, so they may be difficult to wire and install here in the land of interior walls with no cavities.


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## NickZ (Jun 26, 2009)

Right now I think the better fridges are claiming 160 or 170kw/h per year. My LG which is now approaching three years old claims just under 180kw/h a year.

None of these are extremely expensive if bought on sale.

A third of a kw/h a day is great but you're back to the question is it worth it when you can get off the shelf fridges which are 0.5kw/h


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## John and Cecil (Dec 22, 2019)

NickZ said:


> Right now I think the better fridges are claiming 160 or 170kw/h per year. My LG which is now approaching three years old claims just under 180kw/h a year.
> 
> None of these are extremely expensive if bought on sale.
> 
> A third of a kw/h a day is great but you're back to the question is it worth it when you can get off the shelf fridges which are 0.5kw/h


I am not seeing any of those. I went through several appliance websites and the most efficient full size refrigerators appear to require about 350kwh / year (or 1 kwh per day). What model fridge do you have that only requires 180kwh?

The modified chest refrigerator only uses 1/6th of a kwh per day which would still be 1/3 as much power as your fridge. Perhaps a standard fridge can be modified to be more efficient, like a custom insulated cabinet and/or a small wall built inside the front (or a big tall bin for veggies with a couple slider trays on top). This would stop at least some of the cold air from "falling out" whenever you open the door.

Actually I would think that a refrigerator could be made to be more efficient if it had drawers instead of doors. They would need some sort of mechanism that would allow cold air to circulate inside the drawers from the back when they are closed. This way when you open a drawer the cold air will sit inside the drawer until you close the drawer and not "fall out".

It would be a real pita but I guess an off grid fridge option could be to make ice during the day when the panels are running, then put the ice in the fridge at night when there is no power. This would be another way to utilize inexpensive solar panels in a way that does not require an expensive storage battery.


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## Strontium (Sep 16, 2015)

Hi,
My personal view is you are suffering under the common problem small Solar PV installations of not having real world data to base your designs on. Solar installations have variables such as type and size of panel, orientation, variable local sunshine over day/season and degradation over time etc which can only really be quantified by data logging an installation over time which, unfortunately, is not generally available. If you do set up a system then it would be useful (for me) to have a basic data logger to see real world information. 
Otherwise here's a link to a free upcoming UK Lecture on net-zero (tis at a place I worked on their solar array).






21 Apr 2021 - The path to net zero emissions in the UK | University of Surrey







www.surrey.ac.uk


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## John and Cecil (Dec 22, 2019)

Strontium said:


> Hi,
> My personal view is you are suffering under the common problem small Solar PV installations of not having real world data to base your designs on. Solar installations have variables such as type and size of panel, orientation, variable local sunshine over day/season and degradation over time etc which can only really be quantified by data logging an installation over time which, unfortunately, is not generally available. If you do set up a system then it would be useful (for me) to have a basic data logger to see real world information.
> Otherwise here's a link to a free upcoming UK Lecture on net-zero (tis at a place I worked on their solar array).
> 
> ...


Thank you, I will check out the lecture.  I also just got a book someone recommended, "Solar Electricity Handbook" by Boxwell that may be helpful.

The way I see it I have 3 major issues. The first one is the Portugal bureaucracy. Not being able to connect to the grid is a major problem, especially because of issue number 2. 

The second issue is current battery prices. I can buy a solar panel that can create up to 3kwh per day of electricity in optimal conditions for less than 200 euros. But a 3kwh battery able to store that energy will cost between 2000 and 3000 euros. The battery prices make the system not feasible.

The problem that you mentioned is a large part of issue number 3, which is designing a system to power a home in the winter during extended periods of cloudy and rainy conditions. The general consensus seems to be that winter power generation will be less than 30% of that of the summer. About the best description I found seems to state that power generation will be about 10-30% on cloudy days as it would on sunny days. I also read somewhere that if the sunlight is not bright enough to cast a shadow then it probably will not generate any electricity. 


So taking all this into account I must cut my winter electricity usage and design a system that will provide enough power throughout the winter and without a large "dedicated" battery. 

As for battery storage the only battery option that makes sense would be something like the Zero modular batteries that are used in the Zero FXS motorcycle. They are 3.6kwh batteries (102v (116v max) @ 32a) and the motorcycle can carry 2 batteries at once. I read that 48v batteries seem to be the best for home solar systems so perhaps these are not a good choice and I will need to find another motorcycle, but if I can mount Cecil's box to the back then this is our ideal motorcycle. The batteries are expensive at around $2800 each (probably more in Europe) but at least they will save a lot of spending on gasoline and break my dependence on the oil companies. I was thinking I could purchase the motorcycle with 3 batteries and use 1, 2, or 3 batteries at once to power the home and charge from the solar array. In the winter I would leave all 3 batteries connected to the home and at times disconnect one to use in the motorcycle. In the summer I would disconnect 2 batteries to use on the motorcycle at times and leave 1 connected to the house.

To cut winter home consumption I would try not to use the microwave or electric oven and cook only with the propane stovetop. Hot water would be from an on demand gas hot water heater and possibly a pellet boiler during the winter. Home heating would be from wood pellets. I can probably cut my electricity usage down to 3 kwh per day, and if a large storm arrives I can use half that much in an emergency. 

Summer usage does not matter as much since the panels will be supplying much more energy. I will have an electric water heater with a large tank, and 2 of the 500w solar panels from my system will have a switch that allows me to disconnect them from the house system and use them to directly power the water heater instead and the gas water heater will supplement this if the water is not warm enough. This gives me hot water in the summer and it gives me 2 extra solar panels to use with the array in the winter. I also want to build a small 4m aluminum rowboat with one 500w solar panel that will use an ebike battery and a 40-50lb thrust electric motor for propulsion. I will not use the boat much in the winter, but I can park it outside and connect that panel to the house array during the winter as well. That is a total of 3 extra 500w panels in winter, or a 33% more solar generating capacity. 

In summer I would like to generate an average of about 12kwh a day so I am probably looking at about 9x 500w panels. In summer would have a 9x 500w panel solar array connected to up to 3x 3.6kwh batteries in summer plus I would have a 2x 500w solar panel independent water heating system and a 1x 500w solar panel boat system. In winter I would then have 12x 500w solar panels to use in the array. 10% of optimal output would probably be enough to power the home in winter, and if the weather is better for a few days then I have the option of switching 2 panels back over to the water heater tank and also I can ride the electric motorcycle. 

I guess the issue comes down to days where you generate little or even no power. Solar panels are much cheaper than batteries, the price of reserve battery capacity for 24 hours is the same as an extra dozen 500w solar panels. Considering this the most cost effective option, and the one that will return your investment the fastest, would be to have your home connected to the grid and to use the grid power occasionally during storms and at night and use the solar array with just a very small 1kwh battery for storage. But because this situation is unique to Portugal nobody has figured out how to do it


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