Saturday, 4 April 2015

Should I Divert Excess Power From My Solar Panels To Heat My Immersion Heater?

Whoever devised the solar PV tariff system in 2010 was obviously trying to make it as attractive as possible for householders.

1: Including the export tariff, they offered a 25 year index linked guaranteed rate of 44.85p for every kWh generated.

2: The electricity generated by the householder could be used for free.

3: Even if the householder used the electricity, they would still be paid the full feed in tariff rate.

Unsurprisingly, most householders try to make the maximum use of their "free electricity" by using energy hungry household appliances during daylight hours. The downside of this unfortunately requires you to be available during the day to switch appliances on and off.

It's very tempting to purchase a system which is linked into your PV panel output and once it detects that you're generating more power than your household is using, it automatically diverts it to heat your home or the water in your immersion heater.

Is this a cost efficient and viable solution? Well it depends on YOUR household.

Questions to ask yourself are these.

1: How many of you are there in the household? 

Families with children inevitably use more water and heat on a daily basis, but many people don't alter their energy settings as childre grow up and move away.

2: Do you bathe or shower?

Based on the average kWh costs, a 10 minute electric shower would cost between 8-11p. 

Heating an immersion tank from cold using the standard 3kWh element would take approximately 2 hours and based on a 15p kWh tariff would cost 90p-£1.

3: Do you heat your immersion tank with gas or electricity?

Electricity tariffs are currently 4 times more expensive than gas. I'm paying 15.5p for electricity and 3.7p for gas. 

I've kept a weekly log of my energy usage for the past 5 years. I can tell you which winters were the coldest and the effect on my gas usage during that period.

We are not an "average" household, I'm not sure that in reality there is such a thing. 

We use approximately 11,000 kWh of gas annually for our central heating, cooking and heating the immersion heater. During the summer months when we ONLY use gas for cooking and heating water our gas consumption falls to very small amounts, in June, July and August we used 225 kWh.

If you paste "convert pv to immersion heater" into Google and choose the Shopping option you're offered a range of devices that will automatically divert any excess electricity generated by your system.
They range in price from £170 to £350, however, unless you're a competent electrician you will need to factor in at least a further £100 for installation and materials. 

How long will it take to repay your initial investment? As I said initially it depends on your household and lifestyle. For my 2 adult household with minimal hot water usage it would take too long, but in a busy house with children the figures may start to make sense.

I'd be very interested to hear from anyone who has installed a device to divert excess generated electricity and has a payback period within 8-10 years. 

Unless you have a huge family and  VERY inefficient insulation and boiler I don't think it can be done, but I'm ready to be proved wrong!!!

Icarus Twitter: (@solaricarus)

1 comment:

  1. Hi,
    Thanks for this post. Soon I will need to replace my Combi boiler, and it had occured to me to go back to tanked hot water using a System boiler supported by PV generated electricity. You've given some thoughts. Thanks. John