Hi All,

I've an interesting project to get stuck into and I'm currently looking at the most financially feasible solution. My background is a time served electrician plus 15 odd years in the design, manufacture and implementation of control systems so technically I can design and implement this system without issue. I have a local solar panel company willing to review, test and sign off on my implementation if necessary.

My plan is to have solar panels mounted to my garage roof which is facing south with a 15° pitch. I want to push down my current electric bill as much as is reasonable and need to strike a balance between 'Green energy' and cost savings. I was given a used set of 3kW Polycrystalline solar panels without mounting rails or inverter. I also have a Victron Multiplus II 3000VA power management unit.

What I would like to achieve is solar panel power stored in a battery system (approx 10-15kWh Lithium) for use as required as, like most people, our home is quiet through the day. I would configure the system for zero export / import and use the Multiplus to manage that. The multiplus will monitor consumption from the grid and use the energy in the batteries to balance that out to zero import or maximum output of unit. I am considering setting up an economy 7 tariff which if the batteries are below 50% at 1am will charge the batteries to 80% netting me half price electric when solar can't match my demand. Above 80% I would switch on a 1.5kW heating element to create domestic hot water.

As I already own some of the big ticket items I need to decide on the next options:
1) Use Victron MPPT chargers to take the solar energy to charge the batteries directly. The multiplus always draws from the batteries to reduce grid import.
2) Use a grid tied Solar panel inverter which will output when the solar panels are active. The Multiplus will take the excess energy not used by the dwelling and store in batteries.

My current consumption averages to 14kWh / day. My bill is approx £800 / year. My basic research into this estimates I could drive my bill down to approx £250 / year. As I can do all work by myself labour is minimal. Both options will cost approx. £4000 - £5000 to implement (mostly batteries and mounting rails). I'm located in sunny Northern Ireland so I'm a little pessimistic about my calculations. I know if I was purchasing all new equipment then at £8k+ it's not financially feasible.

My question is:- From people's experience is it realistic to expect these kind of savings from this system? If not what would be required to achieve the desired performance?

Any input or comments appreciated.

Jonathan

Could you reduce your base consumption at the same time to get an even better result?

We cut our gas and electricity usage more than in half, plus added PV and storage (on- and off- grid).

As a family of 4 our highest-ever (lockdown) electricity consumption was ~8kWh/d, more typical is 5kWh/d.

Bills for gas+electricity are under £600/y in total, mostly standing charges in fact, though more than covered by FiTs since we were in early.

Rgds

Damon

Lots of things for gas and electricity:
* We turn heating on in November (or December last year) and off at the end of March, which trims demand significantly.
* We don't run around in t-shirts in the heating season since keeping a body warm is much cheaper and more green than keeping the whole house very warm.
* We soft-zone the house with Radbot so rooms that are less occupied automatically fall back to a lower temperature when vacant.
* Target temperature during occupancy in most rooms last year (as set on Radbot) was 17C, and a bit warmer in the living room where most of the family spends much of its time.
* We use laptops (~10W to 30W when in use). Even without lockdown the adults are working from home most of the time.
* We have installed 2x single-room MHRVs to retain heat better.
* Quite a lot of IWI.

See more at my site, eg:
* https://www.earth.org.uk/saving-electricity.html
* https://www.earth.org.uk/superinsulating-our-living-room.html
* https://www.earth.org.uk/MHRV-mechanical-heat-recovery-ventilation.html

Rgds

Damon


PS: full disclosure I invented and sell Radbot, which I suppose is "scratching an itch" for our energy savings!

Also if they work based on light in the room would there not be a lag in heating the occupied rooms? Or would this be reduced as there is less load in unoccupied areas so possibly better heating response than normal? Thinking out loud here!

Posted By: quinnj3My wife is working from home now so PC is on for at least 8 hours a day at approx. ... My wife is always cold so it was a compromise to get the heating set as low as 21°C

Sitting around makes you feel cold - I'm rarely cold at home but if I'm working from home even I get cold.

Our fix is a 500W electric heater under the desk which keeps the office warm and the person at the desk very warm in the day meaning we can switch off the main heating - most of that is the solar PV for us.

We've also been experimenting with a 100W heated throw that sits at about 35C. Even if it's just over the office chair that also works pretty well.

Have you considered using the grid as your battery - I've attached the current outgoing octopus rates which many people are surprised by..

Personally if I was on oil I'd consider a heat pump before a battery, or at least use the battery to export 4pm to 7pm making you 15p/kWh.

About 10 years ago I worked in a large air conditioned office, one of those with externally managed temperature using a BMS (building management system). Every now and then some bloke would wander round in charge of the bms, and if he got complaints, would move the temp up or down a bit. It was frighteningly low humidity due to forced air ventilation with no control - the fan was just on or off. The secretary we had used to keep a 3kW bar heater under the desk to keep warm! I bought a 50W 12v chair cover, intended for a car, but worked fine on an office chair. It didn't completely stop her using the bar heater, but cut it back a bit.
Im glad to not work there now, I hated the low humidity all the time.