Using excess solar to heat house

[Aussie_Pete]

Hello all from a solar & battery newbie,

I'm currently getting a 5.2kwp solar PV system and linked 7.2kwh battery on my house in Scotland. I've been researching for about 6 months and the system is due to be installed this month.

I've been looking at what technologies are out there to exploit excess solar once the batteries are charged. I'm aware of heating water using an Eddi or I-boost, charging an EV using a zappi, but was wondering if anyone had considered installing an electric flow boiler (like the one linked below) on their existing central heating system, driven by excess solar to reduce cost of central heating? It seems to be a relatively new technology, but when integrated with solar could significantly reduce gas or oil use for central heating.

For clarity, I’d be considering installing in addition to the existing oil or gas boiler, so that when there’s excess solar this would heat central heating and when there’s not solar the gas or oil boiler would run heating

Slimjim Electric Flow Boiler | @electricheatingcompany

The SlimJim is traditionally installed in properties such as apartments, domestic dwellings, holiday homes & light commercial properties with limited space

www.electric-heatingcompany.co.uk

 

[sunshine]

For clarity, I’d be considering installing in addition to the existing oil or gas boiler, so that when there’s excess solar this would heat central heating and when there’s not solar the gas or oil boiler would run heating

The fundamentals of solar....more in summer, less in winter....go against any economic benefits to purchase special equipment for the winter excess. You will find that your panels won't be able to keep up with normal demands during cold periods.

 

[Aussie_Pete]

The fundamentals of solar....more in summer, less in winter....go against any economic benefits to purchase special equipment for the winter excess. You will find that your panels won't be able to keep up with normal demands during cold periods.

So when the sun shines it’s too warm for central heating?

Not sure I agree. I live in Scotland, have wall to wall sunshine today and I’ve still got my central heating on as it a little chilly. On a day like today I would expect good solar generation (my system will be 5.2kwp) with significant excess over my base load (about 0.2kwh) and I want to use that excess as much as possible. I will divert to an Eddi or I-boost to heat my HW tank and that might take 2 hours of excess (2 hours of 3kw immersion), and as my battery will only need topping up (I estimate overnight it will have dropped about 1kw or 2kw) I should have excess to play with

 

[Daddy Tanuki]

So when the sun shines it’s too warm for central heating?

Not sure I agree. I live in Scotland, have wall to wall sunshine today and I’ve still got my central heating on as it a little chilly. On a day like today I would expect good solar generation (my system will be 5.2kwp) with significant excess over my base load (about 0.2kwh) and I want to use that excess as much as possible. I will divert to an Eddi or I-boost to heat my HW tank and that might take 2 hours of excess (2 hours of 3kw immersion), and as my battery will only need topping up (I estimate overnight it will have dropped about 1kw or 2kw) I should have excess to play with

is your last name Hort?

even if you have clear skies the entire day the output is lower in the winter due to the suns position in regards to the horizon and the actual length of the solar day. not saying it would not work if you had a big enough solar array, but during the bleary months (nov-jan) your output will be significantly lower. might be better served using the excess to pre-heat water for the house.

I have 7.6kws at my cabin and probably made enough extra to heat water but not on a daily basis. Do you get snow where you are at? My panels were covered about 4 times this year during dec- feb, we are only at the cabin on the weekends so there were a couple of times where the panels were partially covered for 3-4 days and it took my battery pack down pretty low.

now in the summer I can run my A/C unit daily if desired and still keep the batteries fairly well charged, but winter months really sucks on the production side. That's why i have such a large array is for the winter months. summer is easy.

 

[timselectric]

No matter what the season, or weather. Each individual should know if they are producing excess power. And then, try to find a use for it.

 

[noenegdod]

I keep seeing threads about using excess solar production for heat. A panel is ~15-20% efficient correct? Would it not be far more productive to instead have a dedicated solar thermal panel instead? You could then even use a mini split, powered by your excess solar production to move the heat from the thermal panel into the conditioned space and see a 3 or 4:1 return on your excess solar production and increase the efficiency of the thermal panel.

 

[timselectric]

Mini-splits are a very efficient way to heat and cool a space.

 

[Sverige]

You can use a PV panel as a heater. Dacian Todea of Electrodacus fame arranges his PV panels via solid state switches with “diversion”, so when the battery needs charging the solid state switches (DSSR20 / DSSR50) send their current to the battery, but when battery is full, the diversion kicks in and the current can go to PV panels inside the home, which radiate heat.

I’m unsure what inclusion detail he‘s used to make a PV panel look acceptable in the home, but from an engineering perspective the idea is sound.

 

[timselectric]

Very interesting solution.

 

[Daddy Tanuki]

No matter what the season, or weather. Each individual should know if they are producing excess power. And then, try to find a use for it.

I have every intention of doing so, I started with 3600 watts to start and that allowed me to run A/C but after losing one set of agm's due to capacity walkdown over a couple of winters I swapped to LiFePo4's and added another 4Kw for this winter for a total of 7.6kw. My plan this summer is to add a 12KL hot water tank that I will heat over the summer with excess production and then pump that into the house for both hot water and to use as a minor heat source to keep the house above freezing all winter long. (yes i said 12KL or about 3200 gal) I have been crunching numbers left and right and have tried several different calculations from various sources. some versions of crunching says it will work, others say it will give me hot (80°C) water at the start and lukewarm by mid January. (still not bad)... It's a hobby building my retirement house so when I do retire to my cabin it is as low cost and comfortable as i can make it. Not to mention anything that reduces the amount of firewood needed is a good thing.

 

[sunshine]

Each individual should know if they are producing excess power. And then, try to find a use for it.

As long as that use is practical and economical viable.
There is also a difference between daily excess cycles and OP's seasonal cycle that is opposite to solar production.. Obviously there would be periods where the two cycles coincide, predominately the mid-seasons, but solar fundamentals are against home heating. For Scotland the average December daily sunshine is one hour!

 

[timselectric]

Who cares if it's practical or highly efficient. Not wasting free energy, is a good thing.

 

[Daddy Tanuki]

sometimes its not so much the cost as it is the journey to building something yourself. the pleasure one gets from building a system themselves can often times completely outweigh the cost or lack of cost effectiveness.

 

[Zwy]

Hello all from a solar & battery newbie,

I'm currently getting a 5.2kwp solar PV system and linked 7.2kwh battery on my house in Scotland. I've been researching for about 6 months and the system is due to be installed this month.

I've been looking at what technologies are out there to exploit excess solar once the batteries are charged. I'm aware of heating water using an Eddi or I-boost, charging an EV using a zappi, but was wondering if anyone had considered installing an electric flow boiler (like the one linked below) on their existing central heating system, driven by excess solar to reduce cost of central heating? It seems to be a relatively new technology, but when integrated with solar could significantly reduce gas or oil use for central heating.

For clarity, I’d be considering installing in addition to the existing oil or gas boiler, so that when there’s excess solar this would heat central heating and when there’s not solar the gas or oil boiler would run heating

Slimjim Electric Flow Boiler | @electricheatingcompany

The SlimJim is traditionally installed in properties such as apartments, domestic dwellings, holiday homes & light commercial properties with limited space

www.electric-heatingcompany.co.uk

I like that boiler, if I decide to someday put solar on the shop, I'd get one and tie it into the radiant floor heat.

 

[noenegdod]

Who cares if it's practical or highly efficient. Not wasting free energy, is a good thing.

Is not getting more for free better? Dont get me wrong, doing a little to get a little for free is good too, especially if it is just going to waste anyway.

 

[schmism]

So when the sun shines it’s too warm for central heating?

Not sure I agree.

You clearly don't understand how solar irradiance changes during the year.

Solar Irradiance Calculator

www.solarelectricityhandbook.com

You didnt specifically say but I chose Glasgow as a "central" point for the sake of demonstration.
On a "perfect" winter day. Your only get to get 7% of the energy out of the PV array as you would in the summer at "your" location.

There is no such thing as "excess" PV power in the winter to heat something.

Perhaps if you lived in Sunny Spain or southwest US (Arizona) and the system was sized to run a MASSIVE AC unit in the summer, then you might have extra power in the winter.... but the cost to put such an oversize system in for you.... Who am I to tell you how to waste your money....

 

[Symbioquine]

There is no such thing as "excess" PV power in the winter to heat something.

This is just plain false in many cases.

For example, I'm in the PNW, US near bellingham (not quite 55 degrees north, but still a fairly northern latitude) and I have my system sized (roughly) for my loads in the winter such that I fairly rarely need to run the generator. 4KW panels, 14KW batteries, approx 2.5kWh base daily usage. In the trailing 30 days, I've dumped ~33kWh of excess energy into resistive heating because my batteries were full. Yes, there's plenty of days in December and January when the batteries would be empty without the generator, but there's also plenty of days in "Winter" like it is now when the batteries are full and there's extra to be had.

 

[timselectric]

This is just plain false in many cases.

For example, I'm in the PNW, US near bellingham (not quite 55 degrees north, but still a fairly northern latitude) and I have my system sized (roughly) for my loads in the winter such that I fairly rarely need to run the generator. 4KW panels, 14KW batteries, approx 2.5kWh base daily usage. In the trailing 30 days, I've dumped ~33kWh of excess energy into resistive heating because my batteries were full. Yes, there's plenty of days in December and January when the batteries would be empty without the generator, but there's also plenty of days in "Winter" like it is now when the batteries are full and there's extra to be had.

I just didn't see a point in responding anymore. My head isn't as hard as it used to be. I now try to avoid banging it against walls. lol

 

[hclarkx]

I think it's credible to do some analysis on winter heating potential to evaluate options before investing. PVWatts via the "NREL International" solar data base can provide hourly solar and ambient temperature data. Combining this with known or projected loads other than space heating would indicate the unused solar energy available for space heating (when and how much). The tool linked below might be a starting point. It does not currently cover heating but could. Or one could plot the hourly solar energy surplus alongside of the ambient temperature to get an idea of how much solar space heating might occur and when.

Battery and Solar Planning Tool Based on Representative Weather Data

I've assembled a spreadsheet to size my RV solar/battery system. I didn't find anything like it on the internet so did the DIY thing. I've been using it for six years, through three battery and solar upgrades. It is well tested. Currently the...

diysolarforum.com

 

[Aussie_Pete]

I keep seeing threads about using excess solar production for heat. A panel is ~15-20% efficient correct? Would it not be far more productive to instead have a dedicated solar thermal panel instead? You could then even use a mini split, powered by your excess solar production to move the heat from the thermal panel into the conditioned space and see a 3 or 4:1 return on your excess solar production and increase the efficiency of the thermal panel.

Yes and no. If you’ve got solar & you’ve got excess you want to find a way to use it.