Solar Thermal Water Heating Systems

Although we have solar PV (Photo voltaic) panels that generate electricity there are also solar thermal systems that produce hot water directly from the sun heating darkened tubes that can then be stored in a normal hot water cylinder.

These are some photos that I was asked to take recently to show the setup of a commercial solar thermal hot water system.



Solar thermal tubes located on roof showing supports



Solar thermal tubes located on roof



Solar thermal panels temperature output reading



Solar thermal hot water cylinder

Solar thermal panels circulator

Solar PV Panel Feed In Tariff Cut Again

The Dept of Energy and Climate Change has announced that the FIT scheme will be cut by 3.5% from July 1st, one month earlier than originally planned.

The price of solar panels is still a long way below the prices charged when the Feed in Tariff scheme was introduced in 2010 with a 4kWp installation coming in at under £6000 from Solar Essence. This compares to a price of £16000 to £20,000 back in 2010. Our 3kWp system cost just under £9k in 2011 so prices have fallen substantially since then too.



Solar PV Panel Feed In Tariff Cut Again

Why does Inverter Output differ from generation meter reading?

A common question about solar panels is why the reading that the generation meter shows is different to the reading shown by the solar inverter. The difference between the two readings can work either way, sometimes the inverter reads a higher generation figure, sometimes the generation meter can give the higher reading from the solar panels.

The reason is that the generation meter gives the correct number as it is calibrated and produced to a specific tolerance to meet the requirements of the MCS scheme in the UK and electricity companies. The value shown by the solar inverter is only an estimate and can be a few percent different to the solar generation meter.

As an example our generation meter yesterday passed the 4MWh milestone for generated solar electricity but our inverter is still only at 3952 kWh. The difference between the two readings is around 1.5% with the generation meter giving the higher reading.


Why does Inverter Output differ from generation meter reading?
Inverter reads 3958kWh



Why does Inverter Output differ from generation meter reading?
Generation meter reads 4006kWh

How does heat affect PV solar panels?

How does heat affect the output of PV Solar Panels?

In general PV solar panel efficiency is affected by increased temperatures so hot sunny days can actually generate less electricity which is the opposite to most people's expectations.



How does heat affect the output of PV Solar Panels?

Solar panels are tested at 25C and an efficiency factor worked out which is quoted as the "temperature coefficient of power in % per degree C". This shows the amount that the solar PV panels will reduce in efficiency for every degree that the panels are above 25C. Equally it will show the increase in efficiency when the solar panels are below 25C.

For our solar panels this temperature coefficient is -0.54 which means that for every degree over 25C the solar panels will generate 0.54% less electricity. If, for example, the temperature reached 35C then as this is 10C above 25C the efficiency would drop by 10 x 0.54 = 5.4%.

So on a cold sunny day at 25C you may achieve a maximum output from your solar PV array of 20kWh over the day, on a hot day at 35C you would only generate 20 x 95% = 19kWh of electricity.

The heat affect on solar panels has been very effectively shown during April 2013 when the weather has been relatively sunny but exceptionally cold for the time of year and the month has given two new records for daily output. The maximum electricity generated from our solar panels in 2012 was 20.3kWh yet this has already been exceeded on two days during April 2013.



Graph showing peak of solar pv generation on hot day compared to cold day

Solar Panels Generate 4 MWh of Electricity

With another good day of electricity generation from our solar panels we have now generated 4MW, that's 4000kW of electricity produced from the sun. Quite an impressive number in almost 18 months although it is only around 70% of what we use in a year.

In addition we have received the FIT amounts at 46p per kWh which is paying back the cost of the system.