The past few months have seen some huge developments in the field of renewable energy. These developments are almost certainly going to have an impact on the way we all use energy.

Until a few months ago, solar thermal hot water heating had been the most cost effective way for people to generate their own renewable energy - for every pound invested it has usually delivered the highest units of energy.

The controllers used in solar thermal systems come in many different shapes and sizes and offer a variety of different options. The most basic controllers just have a differential control - this activates the solar pump when the temperature at the sensor on the collector is at a higher temperature than the sensor on the storage tank.

I have a 7 year old Solartwin panel on my roof which I believe is performing poorly and is not metered. The company say that the harder water is likely to be too much for the panel and that it needs an indirect panel. Thus I feel I need to replace it. It is a landscape shape high on my roof, now surrounded by PV panels, so its replacement needs to fit the same space. Given the space constraint, what is the best panel/system to install? I cannot easily find outputs per square metre gross.

There are two ways of installing a solar thermal system with a combination boiler. In both cases you will need a new hot water cylinder. This can often be the biggest problem as in most cases where a combi-boiler is installed, there is no room for a cylinder

I am often asked whether a solar thermal system can be used for space heating as well as for hot water.

Technically, it can. However in most cases it is neither cost effective nor energy efficient to do so. The cost of upgrading the system to work with space heating as well as hot water can be expensive.

A vital part of a solar thermal system is storage. The sun is not always shining when you need your hot water!

On larger systems molten salt is sometimes used as the storage medium for the heat. Generally however, the heat is stored in water, especially if the purpose of the system is to provide hot water.

Evacuated tube collectors are the Formula One of the solar thermal world. They are more efficient than other types of collector as they are almost perfectly insulated, and heat cannot pass through a vacuum. As the tubes are cylindrical, they are always perpendicular to the sun reducing the amount of energy that is reflected before it hits the absorber. They are capable of achieving much higher temperatures than other solar collectors as the vacuum ensures that no heat is ever lost.

Have you ever wondered how much energy falls on your roof each year? Well probably not, but it is really quite interesting.

The average UK house with a south facing roof of 30m² will be exposed to around 30,000KwH of the sun’s radiation every year. When you compare that to the amount of energy that is used to heat the hot water for a 3-4 bed house (approximately 3,000-5,000KwH per annum) we have far more energy than we need.

Financial incentives for people generating electricity with photovoltaic solar panels (PV) are provided though the system of renewable obligations certificates, (commonly referred to as ROCs).

All electricity providers have to buy these certificates each year, in proportion to the amount of electricity they sell. This started at 3 per cent in 2003 and the intention is to increase it to 15.4 per cent by 2015. They can either generate their own renewable energy or buy certificates from other generators. If they fail to secure enough each year they must pay a fine.

Comparing costs of different renewable technologies and working out potential savings in cash and carbon has just got a whole lot easier. Encraft has developed a range of calculators that help you work out all the figures, so that you can see what's best for your house much more easily. Anyone can use them free of charge by clicking on the calculator link on the Encraft home page. You just have to register to get access.