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SerialLurker

People have done something similar with old radiators painted black.

QrizB

I remember an illustration from a 1970s self-sufficiency book where you feed a hosepipe through a string of glass bottles with their bottoms knocked out to make a solar collector for hot water.

The problem with all these direct-use systems is that in the summer they get too hot, while in the winter they freeze, while at the same time contaminating your water with eg. rubber or rust from the primary heat exchanger. Professional installations in the UK would normally use an indirect heating system where the solar collector is filled with a glycol mixture and is pumped to heat water held in a tank.

You can buy a rooftop system to DIY:
https://www.screwfix.com/c/heating-plumbing/solar-panels/cat14210003

ispookie666

Probably an old aquarium with two drilled holes, mdpe hoses and multiple loops and left in the garden? 

zeupater

Hi

This is an example of where an oversized PV array would benefit ... you could automatically divert excess energy to a cylinder or heat-bank and actually use little imported energy/fuel.

We have solar thermal based on evacuated tubes which provides almost all of our DHW and last paid to heat water in March of this year ... as it's been dull for a number of consecutive days the hot water temperature has just about fallen below MrsZ's shower threshold, so, unless it's a blazingly sunny day tomorrow, it'll probably need a top-up.

Now that PV panel prices have fallen considerably, unless you have roof (or other) space restrictions where the higher efficiency of solar thermal would benefit, then it's probably best to go for more PV & divert.  

If you're looking at a cheap DIY system for heating a hot-tub etc you'll find plenty of ideas based on coils of plastic tube in a glazed wooden box. I made a greenhouse heater from an old CH radiator and copper cylinder once, but not one of the coiled units, however, I do know someone a couple of miles away who has a built a number of them to heat a pool ...

HTH - Z  

chris_n

Lots of different ideas here
https://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

Alnat1

As you reveal more details about your lifestyle and the things you do to avoid using grid electricity, I see it as more hassle and expense. You still aren't off grid and it seems unlikely you will achieve that totally without further (to me quite drastic) impact on your day to day life. You are likely to still need some electricity from the grid for several months of the year.

You have already spent far more on equipment that my solar/battery install cost and because of  your complicated multi-inverter system, there's a lot more bits of kit that might need replacing in future.

My (March this year) install works all by itself, no complications of where and when I can plug something in. The only thing I really need to consider is if the battery needs filling overnight. The MSC allows me to claim SEG which so far has covered all my energy costs (gas and electricity) and should do until the end of the year with the credit it has built up over summer. I expect to pay for some energy Jan/Feb until the solar picks up again. 

I wish you luck with your dreams and ideals but really don't envy you. It's a hell of a lot of expense and complications just to avoid a smart meter.

zeupater

Hi

Consider the following ...

Your system is effectively an off-grid  ~2kWp of generation capacity with ~7kWh of various portable energy storage units giving you the option of using either grid sockets or ones attached to your 'generators' ... this total system cost you approx £7k ... (?)

The readily available kit for an off-grid system which would  provide a similar (but likely better) solution would look something like (inc VAT) ...  

• Inverter (5kW) ~£1600
  
• Batteries (10kWh) ~£3600
• Panels (5kWp) ~£2500
• DIY mounting materials allowance ~£500
• Delivery, cables, meters, breakers, accessories etc ~£1000

The above should be seen as 'top end' against your current setup and there's easily ways to shave ~£2k (or more!) off through limiting capabilities etc, but for something like a guide of £9200 you'd have an off-grid DIY system which could provide you with what you'd likely be looking for and would allow for future expansion & demand changes ... I think that you've mentioned your brother is an electrician, so the question is how much does he like you & how much alcohol (the normal inter-sibling currency) would be involved in accessing a day or two of his expertise ...

Note, expanding the system beyond the above wouldn't involve a linear cost increase ... you could expand the battery capacity or the number of panels without much effect on the other elements as long as it remains within the inverter capabilities ...  

Alternatively, the rough retail costs above are current (so inflated vs pre-pandemic) but still retail, so don't reflect the cost to installers. If you were to look down the professional installed grid connected route you wouldn't be paying VAT and the installer would be buying at a wholesale discount ... it'd probably be a little more expensive, but to what degree would be down to the installer margin aspirations in your area and your ability to negotiate ... have a look though the forum for current prices being quoted for fully installed systems and what users have paid for theirs ...  

I fully appreciate that you already have sunk costs in what you have to a degree which isn't too far away from the above, that may have been your choice, but it wouldn't have been mine ... if I needed a portable system to use in a portable way or simply a backup system to keep the freezer running in very rural area that's exactly the kind of kit I'd be looking for, but for a system to run my everyday life around I'd consider it a poor long-term investment due to it's poor scalability costs ... it's this that leaves you in the situation where you need to look into ways to supplement your DHW, where, with alternative choices, the solution could be much easier.   

Sorry to come across as being so negative as opposed to supportive, but it's simply the way that I (and probably many others) see it.

HTH - Z

gefnew

You could have a look through these and see if you could try one.
DIY Solar Water Heater: 10 Designs and How to Build Them (theearthproject.com)

chris_n

Just be careful with heating potable water, food grade silicone tubing can be used for that. If the hot water is going to be used anywhere you can create aerosols (showers etc) you need to consider Leigionella too. 
Don't get me wrong I'm not saying you can't do it, just that consideration is required. I did loose a friend to Legionaries disease 25 years ago so it does happen but in this instance it was ducted air conditioning in a hotel.