This can simply be divided into "solar thermal" which produces heat and "solar PV" (photovoltaic) which produces electricity, the one to choose for your project will depend on what you are trying to achieve. There is also "passive solar" which is the energy from the sun that come in through the windows and heats the rooms, this is wonderful because its FREE of carbon implication and cost. All these energies are sustainable because as long as there is "weather" there will be energy.
Covering 5 square meters of the roof with solar thermal panels will produce about 2200kwhrs (SAP) of useful heat energy over an average year, enough to supply a reasonable proportion of an average home's annual hot water need. At current energy prices if you are "on gas grid" and this solar energy displaces gas it will be worth around £65/year, if you are "off gas grid" and on oil, LPG or electricity only, it will be worth between £75 & £125/year. Covering this area will be sufficient to supply the majority of the hot water requirements in spring, summer and autumn, covering more area would be superflous for hot water in these months, but the extra energy harvested in the autumn, spring and winter months could be used to contribute to space heating. In addition to this you could receive a Renewable Heat Incentive payment (RHI), for more information look at the Energy Saving Trust website.
Covering 5 square meters of roof will produce about 620kwhrs of electricity, some will be used in the home the rest can be exported to the grid. This will be worth approximately £93/year. Typically an average house uses about 3500kwhrs/year of electricity, this can be met by about 25m2 of solar PV. This size of system produces a peak output of around 4kw and will save about £325/year if all of it is used. Realistically not all of it will be used so you will receive an additional payment for the energy exported, this is currently "deemed" at 50% of what you generate. Look at the Energy Saving Trust website for a more geographical presentation.
With 5m2 of solar panels the simple illustration above shows that about 440kwhrs/m2 can be acheived with Solar Thermal, and about 124kwhrs/m2 with Solar PV, this is because of the different harvesting efficiencies of the two technologies. Ideally the roof should accomodate both types of solar generation giving you sustainable and local energy.
In addition to the energy saving provided by the technologies, currently both provide an additional payment for generating the energy. The additional thermal payment is called the Renewable Heat Incentive (RHI) and the electricity payment is called the Feed in Tariff (FiT), both are temporary and subject to change at any time, but once you are receiving the payment they will run for their contract term. The important point is the energy generated by the technology and the future expenditure saved. Producing your own solar energy future proofs the building against increasing energy costs, and additionally gives you a warm glow of satisfaction! For a business it will give predictability and therefore some financial security as far as energy is concerned.